Fqah 0113 - Nervous System Intro

8/3/2019 Fqah 0113 - Nervous System Intro

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BIOLOGY SEM 2 2009/10

FQAH 0113

PHYSIOLOGYOR ORGANISM

MJ, NHH, MHM

FQAH 0114

GENETIC &DNA

TECHNOLOGY

AMM, KH, KAR


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NERVOUS & HORMONAL COMMUNICATION

The Organization of Nervous SystemNeuroneNeuroglia

Properties of Nerve ImpulsesResting PotentialAction Potential

SynapseStructure of Synapse


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Synaptic Transmission

Mechanism of Drug ActionNeuromuscular Junction

Skeletal MuscleStructure of The Skeletal MuscleSliding Filament Theory

Central Nervous SystemBrain

Spinal Cord


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Peripheral Nervous SystemSomatic & Autonomic Nervous System

Sympathetic & ParasympatheticNervous SystemVertebrate Reflex Arch

ReceptorEye - Structure & Function of The

Eye- Structure of The Retina Rod& Cone

- Structure of Rod & Cone- Photoreception in Rod & Cone


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Ear - Structure and Function of the ear

- Coclear- Hearing Physiology- Vestibular Apparatus- Semicircular Canal

HormoneTypes of Endocrine Glands &

Hormones Produced

Mechanism of Hormone Action


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REFERENCES1. Biology For STPM. Volume 1. Kamaludin et

al. Thomson Learning. 2005

2. Biology for Matriculation. Semester 1. 2ndEdition Updated. Lee Soon Ching et al.Oxford Fajar. 2009


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NERVOUS COMMUNICATION

The nervous system - centre for body control andcommunication network

3 functions of the nervous system:

Detect any changes (stimuli) that occur inside andoutside the body

Define the changes Respond to the defined changes


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Terms and Definition

Stimulus any change in the external or internalenvironment which provokes a response

Receptor specialized cells that detect a stimulus

Neuron cells which transmit nerve impulses

Effector organ that respond to the stimuli and

bring about a response


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Receptorspecializedcells thatdetect a

stimulus

Stimulusany change in

the external orinternal

environment whichprovokes a

response

CNSDefine

changesEffector

organ thatresponds to thestimuli and

brings about aresponse


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+ +

maintain a stable internal environment

of the body

Nervous

systemEnzyme

systemEndocrine

system


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The organization of the nervous system consists of2 types of cells

1. Neuron

- basic functional unit of nervous system- able to generate and transmit nerve impulses

2. Neuroglia

- supporting cells


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Neuron (Nerve cell)

Divided into 3 parts:

1. Cell body2. Dendrites

3.Axons


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1. Cell body @ sentron @ soma

Carries out maintenance activity, i.e.,synthesizes materials required by neurons Possesses organelles such as nucleus,

mitochondria, ribosomes, golgi apparatus,

endoplasmic reticulum, etc. Cytoplasm contains Nissls granules rich inRNA (for protein synthesis)

Various shapes, e.g., sphere or pyramid


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2. Dendrites Short extensions from the cell body Carry impulse towards the cell body

3. Axons Long extensions which carry impulses away from

the cell body Terminal end branches with swollen endings

known as the synaptic knob

Possess cytoplasm axoplasm surrounded by

axomembrane


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Mylenated

axon

Dendrites

Cell body


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Structure of a neuron


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Neuroglia Cell

Provides structural support

and metabolism forneuron

E.g., Schwann cells formmyelin sheath surroundingthe axon


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Myelin sheath

- between 2 nodes of Ranvier

- increase the speed of impulse transmission

Nodes of Ranvier

small uncovered parts of a myelinated axonbetween the myelin sheaths


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3 Types of neurons according to function:

1. Sensory neuron (afferent neuron) Long dendrites and short axons Carries impulses from receptor to CNS

2. Interneuron (in CNS) Connects the sensory neuron to the motor

neuron

3. Motor neuron (efferent neuron) Short dendrites and long axons Receive nerve impulses from interneuron and

transmit to effector, e.g., muscles and glands


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Types of neuron according to function


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3 Types of Neuron According to Structure

Depends on the number of extensions leavingthe cell body

1. Unipolar

Possesses a single extension from the cell body

Characteristic of invertebrate nervous systems

and sensory neurons


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2. Bipolar

Possesses 2 extensions: dendrites and axons,e.g., neuron in the retina

3. Multi-polar Possesses a few extensions from the cell body,

generally in mammalian nervous systems, e.g.,

pyramid cells, Purkinje cells and motor neuron


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Impulse Transmission

1. Along theaxon - as an

electricalsignal

Ii2. Acrossthe synapse

as achemical

signal


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Impulse transmission along the

axon

1. Resting Potential

2. Action Potential (depolarization andrepolarization)


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1. Resting Potential

The potential difference which exists across theaxon membrane when the neuron is not

conducting an impulse or is at rest

It is caused by the unequal distribution ofcharged ions inside and outside the neuron

membrane (inside more negatively chargedrelative to the outside) axon is polarized

No stimulation axon at rest axon is polarized


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Axon is polarized when it is in resting potential

Inner membranevely charged[Na+] low, [K+] high

Presence of anion: Cl-

Negatively charged protein and organic phosphate

Outer membrane +vely charged[Na+] high, [K+] low, Cl- also present

These differences will cause electrical potential differenceacross membrane - resting potential ( 70mV)


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Distribution of ions across the axomembrane

Lipid

bilayer


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How The Resting Potential Is Maintained

3 types of ions play significant roles to determinethe resting potential

Sodium (Na+) Potassium (K+) Large negatively-charged organic

molecules (amino acids and proteins)

Involve 2 mechanisms: K+/Na+ pump

Non-voltage gated K+/Na+ channel


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Voltage gated

Na+

/K+

channel

Non-Voltage gated

Na+

/K+

channel

Na+/K+ pump

Na+

The different concentrations of these types of ions


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The different concentrations of these types of ionsare maintained by an interplay of several factors:

1. Diffusion

2. Electrical attractions and repulsions

3. Active transport across the cell membrane4. Selective permeability of the axon membrane to

these three ions.


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During the resting potential, Na+/K+ pump activelytransports Na+ and K+ across the membraneagainst their concentration gradients

The presence of more non-voltage gated K+

channels compared to those for Na+ more K+diffuse out than Na+ diffuse in. Always some Na+

leaking in and this is reduced by the Na+/K+ pump

3 Na+ are transported to the outside membrane for

every 2 K+ brought into the cytoplasm of the axon. These processes always more K+ inside

so the resting potential is maintained almost

entirely by this K+

difference.


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Presence of anions, e.g., proteins in the cellwhich are too large to diffuse out

The Na+/K+ voltage gated channels are bothclosed

The net result outer membrane is +vecompared to inner membrane

Resting potential is established


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2. Action Potential

An action potential is the change in the potentialdifference across an axon membrane whichoccurs during the passage of a nerve impulse

Nerve impulse- an information that passes along the axon,changes the potential difference across the

membrane and generate an action potential- only can be transmitted as a series of electricalsignals when the stimuli > threshold intensity (> -50 mV).


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The action potential has 3 phases (2 - 3 msec)

1. Depolarization2. Repolarization3. Hyperpolarization


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1. Depolarization (1 msec)

Stimulus reaches a resting neuron, somevoltage-gated Na channels open

Na+ diffuse into the axon

The inside of the neuron becomes more positiverelative to the outside

The axon membrane is depolarized


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More gates open more Na+ diffuse into theaxon further depolarization

When the membrane potential difference reachesa threshold value, many more gates openrapid diffusion of Na+ sudden increase in the

membrane potential difference (+35 mV)

The action potential stimulates other Nachannels down the axon to open, thus causing

the impulse to travel down the axon

Ii2


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Ii2

2. Repolarization

Reversal in polarity to +35 mV voltage-gatedNa channels close

Voltage-gated K channels open K+ diffuse out

of the axon

The outside of the neuron becomes more positiverelative to the inside

The axon membrane is repolarized

Action potential alters from +35 to -70 mV


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3. Hyperpolarization

Voltage-gated K channels are slow to closeexcess K+ leave the axon

Inner membrane becomes moreve thevoltage falls slightly below -70 mVhyperpolarization

Within a few msec, voltage-gated K channelsclose

Resting potential (-70 mV) is re-established


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Factors Affecting Impulse Transmission

1. Diameter of the axon

- the larger the axon diameter the faster thespeed of impulse transmission

- the smaller the diameter, the greater theresistance created by the axoplasm lower

the speed of impulse transmission


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2. Myelinated neurone- an action potential can only be generated atnodes of Ranvier because Na+ and K+ are able

to move across the membrane

Hence, action potential jumps from 1 node

of Ranvier to another along the axonincreases the speed of impulse transmission


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Propagation of nerve impulse


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Propagation of Nerve Impulse


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Propagation of Nerve Impulse

Information is transmitted along a neuron as anerve impulse which consists of a series of actionpotentials

When a neuron is stimulated, Na+ flow into theneuron depolarization of the inner membrane

action potential is generated

This part of the membrane is more positiverelative to the adjacent part (still at restingpotential)


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The difference in potential between the active andresting membrane parts creates a localizedelectric current (LEC)

LEC stimulates the adjacent part (2nd part) of themembrane

Na+ flow in, depolarize and generate a secondaction potential


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After the action potential, the first part of themembrane is repolarizing as K+ flow out

This process is repeated

Impulse is propagated as a series ofrepolarization and depolarization along the axon


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COMMERCIAL

BREAK


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Refractory Period

Period after an action potential has passed, i.e.,period when axon is not able to transmit a newimpulse (5 10 msec)

1. Absolute refractory period

the axon membrane is unable to respond toanother stimulus

action potential is not generated 1 msec


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2. Relative refractory period

Resting potential is gradually restored by the Na+/K+ pump

5 msec

All or Nothing Law

All action potentials are of the same amplitude, i.e., afterthreshold is reached, the size of the action potentialproduced remains constant and is independent of theintensity of the stimulus


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Synapse

Connection site between

1. neuron-neuron2. neuron-muscle


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Synaptic knob (at the end ofaxons) contain mitochondriaand synaptic vesicles

Synaptic vesicles containneurotransmitter important inimpulse transmission

Neurotransmitter- small chemicals found inthe synaptic vesicle

- helps to transmit an

impulse across the synapse

small gap

between theconnection -synaptic cleft(20 nm)


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Neuron that carriesimpulse to synapsepresynaptic neuroncovered by presynaptic

membrane.

Neuron that carriesimpulse away from

synapse - postsynapticneuron covered bypostsynaptic membrane.


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M

Synapticvesicle

Synaptic cleft

Membrane

receptor

Presynapticmembrane

Postsynapticmembrane


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Impulse transmission across the synapse

Mechanism of Impulse Transmission Across A


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pS

Impulse that reach synaptic knob stimulatesopening of Ca channels

Ca2+ (in the interstitial fluid) enter the knob

Stimulate binding of vesicles and presynapticmembrane

Vesicles release neurotransmitter into synapticcleft (each synaptic vesicle contains 10 thousandmolecules of neurotransmitter)


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Neurotransmitter binds with receptor onpostsynaptic membrane

Change configuration of protein on postsynapticmembrane

Na channels open

Na+ enter and depolarize postsynaptic membraneexcitatory postsynaptic potential (EPSP)


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If EPSP reaches the threshold level, actionpotential is generated and transmitted to the 2nd

neuron/muscle

*If acetycholine stays in the receptor sites, Nachannels remain open - continually producing

action potentials


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Mechanism of impulse transmissionacross the synapse


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COMMERCIAL

BREAK


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To prevent continuous production of actionpotential remove the neurotransmitter (nt)i. Direct uptake of nt

e.g., noradrenaline is transported back into the

synaptic knob and inactivated by the enzymemonoamine oxidase

ii. Enzymes are released to degrade nt

e.g., enzyme acetylcholinesterase splits

acetylcholine into acetyl coenzyme A and choline

taken up by the presynaptic neurone

combined to reform acetylcholine


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Two main neurotransmitters used in the vertebratenervous system are1.Acetylcholine

Neurons releasing acetylcholine are called

cholinergic neurons. Found in most synapses

2.Nonadrenalin (norepinephrine)Neurone releasing nonadrenalin are called

adrenergic neurons. Found specificallyin the synapses of the sympathetic nervoussystem


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Both nt can be inhibitory or excitatory, dependingon the type of receptor

Other neurotransmitters:

Dopamine, serotonin (brain), glutamate, etc.


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Functions of Synapse

1. Transmits information between neurons2. Transmits nerve impulses in one direction

because nt are only released by the presynaptic

neuron3. Filters out low-level stimuli of limited importance4. Protects the effectors from damage by

overstimulation, i.e., by action potentials

continually being generated

D


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Drugs

Chemical substances that cause changes in thenatural chemical environment and functioning ofthe body

Can be ingested, injected, inhaled or put into thebody in some other ways

Used in medicine to help prevent, diagnose andtreat diseasse or injuries


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Psychoactive drugs (PAD) interfere with thenervous system and cause changes inthe mental state and behaviour

Overdose of PAD over dependence(addiction) of the drug

Affect the nervous system by altering themechanism of synaptic transmission

Examples:


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i. Cocaine blocks re-uptake of nt e.g. dopamineii. Curare binds to receptors on the postsynaptic

membraneiii. Organophosphate insecticides & nerves gasesblock acetylcholinesterase that degrades the ntthus allowing acetylcholine to remain active for

longer periods.

Mechanism of Drug Action


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Drugs are categorized asi. excitatory psychoactive drugs (amplify synaptic

transmission)

ii. inhibitory psychoactive drugs (decreasesynaptic transmission)

i. Excitatory psychoactive drugs work in variousways:


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ways: (a) Mimic a natural neurotransmitter, fitting into

the same receptors e.g. nicotine mimics

acetylcholine.

(b) Interfere with the normal enzyme breakdown ofa neurotransmitter.

The drug (a)/neurotransmitter (b) stays in thereceptors & continues to stimulate thepostsynaptic membrane

- causes continuous stimulation & contraction ofmuscles E.g. Organophosphate insecticides.


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ii. Inhibitory psychoactive drugs work in variousways:

(a) They prevent the release of a neurotransmitterE.g. Botulinum is a poisonous toxin produced bythe bacterium Clostridium.

It will stop respiration muscles contraction &resulted in impossible breathing


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(b) They block the action of a neurotransmitter at

the receptors on the postsynaptic membrane.E.g. Curare is a natural poison.It blocks the action of acetylcholine atneuromuscular junctions

stop muscle contraction.


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Skeletal Muscle Structure


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Sk l t l M l St t


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Skeletal Muscle Structure Skeletal muscle is made up of hundreds of muscle

fibres.

Each muscle fibre- surrounded by connective tissue endomysium.

- long, cylindrical in shape & arranged parallel toeach other- consists hundreds of myofibrils- cytoplasm sarcoplasm

- contain many mitochondria

M fib il


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Myofibrils- thin threads that arranged parallel to one another.

- made up of alternating light & dark bands due tooverlapping strands of contractile protein (myosin& actin).- each contractile unit sarcomere

Sarcomere(myofibril basic unit)i. e. region between one

Z line & another Z line


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M fib il i f


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Myofibrils consist of: Thick filament are composed of protein - myosin

- long tail- globular head site for ATPase enzyme.

Thin filament are composed of protein - actin -

helical backbone consist of 2 strand.- contain 2 other proteins(tropomyosin & troponin).

Sarcoplasm of muscle fibre consists of


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Sarcoplasm of muscle fibre consists ofi. longitudinal interconnected tubules between the

myofibrils - sarcoplasmic reticulum.

ii. Transverse tubules which are invaginations ofsarcolemma membrane T tubules.

Ends of sarcoplasmic reticulum form vesiclesterminal cisternae - involved in the intake &release of Ca2+.


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Under light microscope - muscle fibres show a

pattern of alternating light & dark bands.

Thick filament

Thin filament


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COMMERCIAL

BREAK

Structure of Neuromuscular Junction &


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The NMJ a synapsebetween a motorneurone & skeletalmuscle fibres

Impulse Transmission


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Each muscle fibre has a region motor end plate

where the axon of the motor neurone divides

& forms fine branchesending in synapticknobs.

The NMJ includes themotor end plate & thesynaptic knob.

On stimulation the synaptic knob release Ach


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On stimulation, the synaptic knob release Achwhich binds to the receptors on the sarcolemma.

This increases the permeability of the sarcolemmato Na+.

This depolarises the postsynaptic muscle fibre &triggers an AP.

The AP passes along the sarcolemma through the

T tubules system, deep down into the miofibril &results in muscle contraction.

How impulse is transmitted across the synapse

and causes muscle contraction


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and causes muscle contraction

The Sliding Filament Theory


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The Sliding Filament Theorysuggested by Huxley & Hanson

1. Muscle at rest Outside of muscle membrane +ve charge. Inside of muscle membrane -ve charge.

2. Muscle stimulation Nerve impulse (action potential) travels along a

motor neurone & reaches the neuromuscularjunction.

Acetylcholine (Ach) is released into the synaptic


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Acetylcholine (Ach) is released into the synapticcleft, diffuses to the sarcolemma & bind with

receptor on the sarcolemma.

When action potential (AP) reaches it thresholdvalue, an AP is created in the muscle fibre.

Ach in the cleft is then hydrolyzed & the productsare reabsorbed into the motor neurone.


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AP travels along the sarcolemma, spreads into the

T tubules & stimulates the release of Ca2+ fromthe cisternae terminal at sarcoplasmic reticulum.

Ca2+ diffuse out to the sarcoplasm.

3. Actomyosin-Cross bridges formation


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3. Actomyosin Cross bridges formation Ca2+ bind to troponin & alter its shape.

Tropomyosin strand moved to the sides &exposed the binding sites.

A molecule of ATP bindsto myosin head.

ATPase is activated.

ATP ADP + Pi+ ENERGY

The energy is transferred to myosin head &


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The energy is transferred to myosin head &changes the myosin from low energy

configuration high energy configuration.

Myosin heads attach to the actin binding sites -actomyosin-cross bridges.

4 Slides


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4. Slides ADP & Pi are released.

Myosin head returns to it low-energyconfiguration.

It bends & propels the actin towards the centre ofsarcomere.

Actin & myosin filaments slides between each

other.

5 Breakdown of the Actomyosin-Cross bridges


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5. Breakdown of the Actomyosin-Cross bridges A new ATP molecule binds to each myosin head.

Each myosin head detaches from the actin &returns to it low energy configuration.

Troponin reverts to its original shape &tropomyosin block the binding site on the actinfilaments.

Myosin heads are ready to bind to the nextbinding site on the actin filaments.


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6. Repolarization

After contraction, Ca2+ is actively absorbed backinto the terminal cysterna.

Muscle relaxed.


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COMMERCIAL

BREAK

Nervous System Communication network and centre of body


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ycontrol.

Found in all vertebrates and non-vertebratesorganisms.

The nervous system can be divided into 2:

1. Central Nervous System (CNS)(CNS)BrainSpinal cord


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2. Peripheral nervous

system (PNS)

The nerves originatein the brain & spinal

cord & spreadthroughout the body

Somatic nervesAutonomic nerves

Central Nervous System


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Central Nervous SystemBrain

The most complex structure. Surrounded by meninges membrane.

Encased in bony skull. Made up of

i. grey matter & form the cerebral cortex,the folded outer layer of the cerebrum.ii. white matter & found on the inside of thebrain.


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There are cavities ventricles Ventricles

i. continuous with the centralcanal of spinal cordii. richly supplied with

blood capillariesiii. fill with cerebrospinalfluid (CSF)


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Functions of the CSF

i. source of nutrition & respiratory gases for theneural tissue.

ii. removal of waste products.

iii. intracerebral transport of neuropeptides &hormones.

iv. protective function a shock absorber.

The functions of the brain:


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i. Receiving sensory information

from both inside & outsidethe body.

ii. Processing & coordinating

the response to thisinformation.

iii. Initiating voluntary activities

such as locomotion.iv. Reasoning, learning &

memory.


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Parts of the brain


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The 5 lobes of the cerebrumi F t l l b


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i. Frontal lobeMental processes & motor regulation

towards body partsii. Parietal lobe

Information on stimulus are integratediii. Temporal lobe

Language and hearingiv. Occipital lobeVision

v. Insular lobe

Smell

Spinal Cord


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p

Extends from the

brainstem to the lowerback.

Enclosed & protected

by the vertebrae whichform the vertebralcolumn

Pairs of spinal nerves


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p- originate in the spinal cord & extend to parts of

the body below the head.

- consist ofi. ascending tracts i.e. sensory neurone

carrying impulses towards the spinal cord.ii. descending tracts i.e. motor neuronecarrying impulses away from the spinal cord.


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When viewed in section, the spinal cord

i f


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consists of2 areas:

i. the central grey mattercontaining the cellbodies of interneurone

& motor neurone.

ii. the outer white mattercontaining myelinated

axons.

iii. in the centre of the grey matter -central canal which contains CSF.

Possess 33 vertebrae i.e.


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cervical at the neck (7)thoracic at the thorax (12)

lumbar at the abdomen (5)sacrum (5) &coccygeal (4)

Produces 31 pairs of spinalnerves i.e.cervical nerves (8)thoracic nerves (12)lumbar nerves (5)

sacral nerves (5) &coccygeal nerves (1)


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Peripheral Nervous System (PNS)


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PNS connecting the brain & spinal cord to the

receptor, muscles & glands.

43 pairs of nerves- 12 pairs connected to the brain cranial

nerves- 31 pairs connected to the spinal cordspinal nerves

Divided into


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- somatic nervous system control activities that

are usually voluntaryE.g. contraction of leg muscles for walking

- autonomic nervous system (ANS) control

activities which are normally involuntaryE.g. heart rate, breathing rate & sweating

ANS has 2 division sympathetic &parasympathetic.


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Sympathetic nerves have an excitatory effect &parasympathetic tends to inhibit or decrease bodyactivity.

Differences between somatic & autonomic nervoussystem Table 1

Differences between sympathetic &

parasympathetic nervous system Table 2

NERVOUS SYSTEM


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Cranial Nerves Spinal Nerves

BRAIN SPINAL CORD

AutonomicNervous System

Somatic NervousSystem

Sympathetic NSParasympathetic NS

Afferent Nerve Fibres(Sensory neuron)

Efferent Nerve Fibres(Motor neuron)


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Reflex Action


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A reflex action - a rapid automatic response to astimulus which is involuntary i.e. not underconscious control.

Reflex actions produce a fast response which is

important to prevent body damage.

E.g. Human knee jerk & withdrawal of hand awayfrom fire.

Reflex Arc Structure A reflex arc - specific pathway taken by the nerve

i l i fl ti


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impulses in a reflex action.

Involves a series of structures including receptor,neurones & effector.

Receptors- sensory cells that scattered in the skin or specialsensory organ eyes - received stimuli.- convert energy associated with a stimulus to an

electrical signal i.e. nerve impulse.


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Example 1: Irritation on the skin Involves 3 neurones

& 2 s n ses


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& 2 synapses.

The receptors on theskin receivedstimulation.

The receptor

generates an impulse. Impulse spinal cord. The impulse passes through interneurone in the

grey matter flexor muscles

contraction of arm occurs.

sensory neurone

motor neurone


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Example 2: The Human Knee Jerk Reflex Involves 2 neurones & 1 synapse.


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The knee tendon is given a light tap with a rubberhammer.

Stretches the

muscle attachedto the tendonabove the patella.


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The muscle spindle detects the stretching &

generates impulse spinal cord

effector

straighten the leg

sensory neurone

motor neurone

Receptor A structure which detects a particular type of

stimulus


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stimulus.

Receptor is sensory cells which are branchesof dendrites or free nerve ends of sensoryneurone.

The sensory cell may be single (receptor cell),scattered uniformly or a group of receptorcells (sense organ) e.g. mammals eyes and

ears.

Usually can be foundi i t d t t h f t l


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i. integumen detect changes of externalenvironment.

ii. in the body detect internal changes e.g. [CO2] inblood & level of muscle contraction.

Able to convert stimuli electrical impulses innerve cell & transmitted through sensory neuroneto the brain or spinal cord.

5 main categories of receptor depending on the

t f th ti l


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nature of the stimulusi.Chemoreceptors - detect chemical stimuli when

we taste or smell a particular substanceii. Photoreceptors - detect light raysiii. Thermoreceptors - detect changes in

temperatureiv. Mechanoreceptors -detect pressure, movements& vibrations

v. Electroreceptors - detect electrical fields mainly in

fish

Types of Sensory Receptor1. Mechanoreceptors sense physical deformation caused by stimuli


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sense physical deformation caused by stimulisuch as pressure, touch, stretch, motion &sound.

Bending or stretching of mechanoreceptors

plasma membrane increases the membranespermeability to Na+ which results indepolarization of sensory neurone & generationof action potential


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2 Chemoreceptors


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2. Chemoreceptors

Include both general receptors that transmitinformation about the solute conc of a solution &specific receptors that respond to individualkinds of molecules.

Chemoreceptor in malesilkworm are highly sensitive

t f l h

E.g. Male silkworm moth


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- The stimulus molecule

binds to a specific siteon the membrane ofreceptor cell,

- initiates changes in

membrane permeability,- depolarizes the

receptor cell &

- generate an actionpotential able todetect

to female sex pheromone

3. Electroreceptor


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E.g. Some fishes generate electric currents & use

electroreceptors to locate prey that disturb thosecurrents.

3. Electromagnetic Receptors Detect various forms of electromagnetic energy,


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Detect various forms of electromagnetic energy,such as visible light, electricity & magnetism.

E.g. Snakes have verysensitive infraredreceptors to detect bodyheat of prey against a

colder background Two receptors (eye & infraredreceptor) in rattlesnake &

other pit vipers

4. Thermoreceptors Respond to heat or cold help regulate body


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Respond to heat or cold, help regulate bodytemperature by signaling both surface & body

core temperature.

For heat/warmth receptors, the rate of impulses

discharge from these receptors increases as thetemperature rises.

For cold receptors, the rate of impulses discharge

from these receptors increases as thetemperature falls.

On receiving a stimulus, Na+ move into thet ll d l i & f t

How Receptor Cells Work


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If GP reaches threshold level, action potential isgenerated in the nerve fibre & transmit to the

brain for response.

Schematic diagrams show the development of a generator

potential & generation of action potential when a receptorcell is stimulated

receptor cells, depolarize & form generator

potential

How Receptor Cells Work On receiving a stimulus the sensitive part of the


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On receiving a stimulus, the sensitive part of thereceptor cell develops a local non-conductedpositive charge generator potential.

GP is caused by depolarization of the membrane

surrounding the receptor cells, due to themovement of Na+ ions into the receptor cells.

On receiving a stimulus, Na+ move into the

receptor cells, depolarize & form generatorpotential

Tongue Taste Receptor*Taste or gustation is detected by taste

t it t d i i illi j ti


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receptor situated in microvilli projecting

from sensory cells sunk into goblet-shapeorgans taste buds.

4 taste sensation sweet (as elicited byglucose & other simple sugars), sour (acid),salty (NaCl & other salts) & bitter (planttoxins, including alkaloids).

The production of a generator potential

depends upon substances (fluids) eitherpenetrating the receptor membrane orattaching to specific receptor sites.


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Nose Olfactor Receptor*


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Nose Olfactory Receptor*

Olfactory receptors detect water soluble orvolatile substances.

Axon lead into one of two olfactory bulbs &synapse with a group of cell that sort out thecomponents of given scent.

olfactory tract

Scent information cerebrum


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The Eye* Human eye is a complex organ containing


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Human eye is a complex organ containingphotoreceptors.

It is able to- control the amount of light that enters the eye.- refract light rays in order to focus them.- transduce light energy into action potential.

Involved eyeball, optic nerves & brain

Structure & Function of The Eye

(Figure 15)


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Retina Innermost layer of the eye


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Innermost layer of the eye.

2 types of photoreceptor cells sensitive tolights i.e. rods and cones.

Rods & cones transduce light energy nerveimpulse

Both possess the same basic structure &function. 120 million rods & 6 million cones.

Differences between rods & cones (Table 3)


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Cone cell

Rod cell

Sensitivity - ability to detect low light levels.

- able to see in condition of low light


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able to see in condition of low lightintensity.- rods are more sensitive than cones.

Acuity - the degree of detail which can be seen.

- ability to distinguish between 2 pointswhich are close together.- cones have better visual acuity thanrods.


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Synaptic network : manyrods to one bipolar neurone

high sensitivity

Single connection : onecone to one bipolar

neurone high acuity

Structure of Rod & Cone Cellsi. Outer segment


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g- Light-sensitive region containing

photosensitive pigments.- Region where light energy generatorpotential.- Rod contains up to 1000 membrane line

vesicles & rhodopsin is embedded in it.- Cone is made up of infoldings of theouter membrane to form vesicles & iodopsin

is embedded in it.

ii. Inner segment- Active metabolic region.


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- Contains many mitochondria to provide the

energy toresynthesize the photosensitive pigments& process vision.

- Contains nucleus & ribosomes to synthesizeproteins for

the production of membranous vesicle& photosensitive pigment.

iii. Synaptic region

- Photoreceptor cell form synapse with


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p y pbipolar neurone which synapse with ganglion

cell (neurone of optic nerve).

- Bipolar neurone connect one cone to oneganglion cell to provide high visual acuity.

- Bipolar neurone connect a number of rods toone ganglion cell (synaptic network) to

provide high sensitivity.


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Rods & cones (synapse) bipolar cells(synapse) ganglion cells axons fromganglion grouped together optic nerve inthe brain.


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Focusing Light Onto Retina Lights from the object will pass through the eye


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Lights from the object will pass through the eye

lenses that focus the light to the retina.

Image formation on the retina requires 4processes:i. Refraction of light light rays are refractedwhen passes through medium that differ indensity with air i.e. cornea, acqueous humour,

lense & vitreus humour.

Accomodation the elastic lense changes its

shape to focus objects onto the retina


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shape to focus objects onto the retina

depending on the distance of the observedobject.E.g. The light from a near object can beclearly seen if the muscles of cilliary bodycontracts, suspensory ligaments relaxed,lense becomes convex.

iii.Constriction of iris

- Light will fall on the retina


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Light will fall on the retina.

- Protects the eye from sudden lightexposure or brightness.

iv. Focus- movement of both eyes so that both willfocus to the same object.


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Photoreception in A Rod Cell Rods sensitive to low light intensity.


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Light detection depends on pigment rhodopsin.

Rhodopsin consists of a protein, opsin joined withretinal (retinene).

When rhodopsin absorbs light the retinalchanges its shape & no longer attach to the opsin

bleaching depolarization of rod membrane.

A generator potential is created.

If the generator potential reach a threshold level,an action potential is generatedoptic nerve

Optic center


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p g

Resynthesis of Rhodopsin

Rhodopsin must be resynthesized from the opsin& retinal.

Requires energy from ATP provided bymitochondria.

Optic center

in the brain


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Photoreception in Cones Cones high light intensity color receptor.


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Photosensitive pigment iodopsin. Iodopsin

- exists in three different forms & types.- less easily broken down & takes longer to beresynthesized

- can be resynthesized in the light enable to seein light conditions.

Photoreception is similar to rods.

Dark Adaptation An experience when we enter a dimly lit room


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from bright light.

At first nothing can be seen, but gradually webegin to make out our surroundings.

Vision becomes possible when the photosensitivepigment, previously broken down by the brightlight, has been resynthesized.

Bright environment Dark environment- Cones are responsivebecause bright light isneeded to breakdown

-Cones are unresponsivebecause dim light unable tob kd i d i f


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needed to breakdown

iodopsin for light/day vision- Rods are unresponsivebecause bright lightbreakdown all rhodopsinmolecules.

breakdown iodopsin for

dark/night vision-Rods are responsivebecause dim light breaksdown rhodopsin molecules

for dark/night vision

Bright environment Darkenvironment- Cones are responsive

because bright light isneeded to breakdown

-At the beginning (a few sec),unable to see the

di b

enter


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needed to breakdown

iodopsin for light/day vision- Rods are unresponsivebecause bright lightbreakdown all rhodopsinmolecules.

surroundings because

during this time, bleachedrhodopsin is resynthesized(to form rhodopsin)- After a few sec, rhodopsin

become fully responsive- dim light breakdownrhodopsin GP AP

Cones day vision Rods night vision


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y g(light vision) (dark vision)

Questions:1. During day time & doing work in dark room?

2. During night time & doing tutorial in study room?

Trichromatic Theory (Color Vision Theory) There are 3 types of iodopsin located in 3 different

t f & iti t 3 l ht


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types of cones & sensitive to 3 wavelenghts.

Each type responds to one of blue, green & redlight.

Color vision dependson the primary colorsmixture i.e blue, green

& red in various ratios.

EarFunction - hearing cochlea.

- body balance - vestibular apparatus &i i l l


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semicircular canal.

Structure of The Ear*


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Cochlea Divided longitudinally into 3 parallel canals:

i. The vestibular canal connecting with


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oval window.

ii. The middle canal consist of corti organ.

ii. The tympanic canal connecting with roundwindow.

These canals are separated by:i. Reissners membrane between the

vestibular & middle canals.

ii. Basilar membrane between the middle& tympanic canals.

Filled with fluid

Endolymph in the middle canal.


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Perilymph in the vestibular & tympaniccanal.

Into the middle canal, projects a tectorial

membrane run parallel with the basilarmembrane.


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Receptor cells - lies between these 2 membranes

their bases rooted in the basilar membranet d t fib j i t dit


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connected to nerve fibre join to auditory nerve.

The other end is the sensory hairs which justreach the tectorial membrane.

Hearing Physiology Sound waves (compression & decompression of

air) amplified & directed by pina into the ear canaltympanic membrane vibrates


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tympanic membrane vibrates. Vibration detected by ossicle bone which will

increase & transfer the vibration to the ovalwindow.

Movement of stapes forward & backward oval window moves in the same direction

displacement of perilymph fluid in the vestibular

canal movement of Reissner membrane


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movement of Reissner membrane

displaces fluid in the middle canal moves the basilar membrane sensory hairs of the receptor cell repeatedly

brush tectorial membrane.

Impulse is generated in the receptor cell& transmitted to the auditory nerves & auditory

centre in the brain.


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Two structures involved in equilibrium:

i. Semicircular canal

ii. Vestibular apparatus

i. Semicircular Canal Arranged in 3 spartial planes.

Detect changes in the rate of rotation or angular


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Detect changes in the rate of rotation or angular

movement of the head i.e. up, down & sides.

Ampulla (cristae ampularis)- a structure at the end of

each canal - contains receptorcells with hairs.

- The hairs are embedded indome-shaped gelatinous cap cupula.

When head position changes, cupula will bedeflected to opposite direction of head movement.

Endolymph fluid exert pressure to the cupula


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Endolymph fluid exert pressure to the cupula

which detected by sensory hair.

Impulse is generated in thereceptor cells transmittedto the aference nerve fibre the brain to be defined &ready for action.

ii. Vestibular Apparatus

Semicircular canal are


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Semicircular canal are

connected to 2 cavities- the utricle & saccule.

Detect changes in head

position relative to gravity.

Macula a structure can be found in the


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Macula - a structure can be found in the

utricle & saccule.

- consist of receptor hair cellsembedded in jellylike substance whichcontains calcium carbonate crystalotholite.

A change in head position relative to gravity t f th lit d t t d b th


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movement of otholite detected by the sensoryhairs.

Impulse is generated in the receptor cells

transmitted to the aference nerve fibre the brain to be defined and ready for action.


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Nervous System Diseases & Disorders Schizophrenia

hallucinations delusions blunted emotions &


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- hallucinations, delusions, blunted emotions &

other symptoms.

Depression- manic (high-mood) & depressive (low-mood)

phases.- major depression patients have a persistentlow mood.

Alzheimers diseasen ge rel ted de enti in hich ne rofibrill r


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an age-related dementia in which neurofibrillarytangles & senile plagues form in the brain.

Parkinsons disease

- a degenerative disorders of central nervoussystem that often impairs the sufferers motorskills & speech.

Hormonal Communication Helps in controlling the internal environment.

Assist body in facing critical condition such as


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Assist body in facing critical condition such as

during infection, stress, famine, etc.

Function ini. body growth and development.

ii. reproduction including gamete formation,fertilization, nutrition & delivery process.

Hormoneschemical substances secreted by endocrine


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chemical substances secreted by endocrine

glands (glands without ducts) directly intoextracellular fluid to the blood circulation & sentto whole body reaction.

required in minute quantities.

The Endocrine System Coordinate slower but longer-acting responses to

stimuli such as stress dehydration & low blood


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stimuli such as stress, dehydration & low blood

glucose levels.

Regulate long-term developmental processes byinforming different parts of the body such as how

fast to grow or when to develop thecharacteristics that distinguish male from femaleetc.

The Nervous SystemConveys high speed electrical signals along


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Conveys high-speed electrical signals along

specialized cells called neurons.

These rapid messages control the body

movement in response to sudden environmentalchanges- E.g. pull away hand from hot pan

Similarities between Endocrine System andNervous System

Provide communication in the organism body


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Provide communication in the organism body.

E.g. ES - [Glucose] in blood pancreasNS - Reflex action receptor & effector

Involve transmission of messages generated by astimulus and resulting a reaction.

Target organ of hormones are similar to nerveeffector.

E.g. ES uterus, mammary glands

NS muscles & glands

(Table 4)


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Overlap Between Endocrine & Nervous Regulation

The endocrine & nervous system often functiontogether in maintaining homeostasis


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together in maintaining homeostasis,

development & reproduction.

Endocrine glands secrete hormones & specializedsecretory cells (neurosecretory cells) derived

from nervous tissue secrete neurohormones.

E.g. Adrenaline- as a neurotransmitter is released by nervousstimulation in response to physical or mentalstress.


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stress.

- functions in the body as the so-called fight-or-flight

- as a hormonewhen [G] metabolisme ofglycogen (in the liver) and tricylglycerines (fattissue) [G]

Hormonal Control Pathways3 major types - endocrine,- neurohormone- neuroendocrine


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Relationship Between the Hypothalamus &Pituitary Gland

Hypothalamus contains different sets of


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yp

neurosecretory cells. Some produce direct-acting hormones that are

stored in & released from the posterior pituitary.

Other hypothalamic cells produceinhibiting/stimulating hormones that aretransported to the anterior pituitary gland.

These hormones control the release of otherhormones from nonpituitary glands.

Pituitary Hormones1. Posterior Pituitary Hormones Secretes direct acting hormones which act

directly on nonendocrine tissues.


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y

E.g. i. Oxytocin induces uterine contractions &milk ejection.

ii. Antidiuretic hormone (ADH) enhanceswater reabsorption in the kidneys.

2. Anterior Pituitary Hormones Secretes inhibiting/stimulating hormones which

inhibit/stimulate other glands to secrete/inhibit


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g

other hormones.

The inhibiting/stimulating hormones arei. Thyroid-Stimulating Hormone (TSH)

ii. Follicle-Stimulating Hormone (FSH)iii. Luteinizing Hormone (LH)iv. Melanocyte-Stimulating Hormone (MSH)

v. Prolactinvi Adrenocorticotropic Hormone (ACTH)


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vi. Adrenocorticotropic Hormone (ACTH)

vii. Growth Hormone (GH)

Each acts on its target endocrine tissue to

stimulate release of hormone(s) with directmetabolic or developmental effects.


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Nonpituitary Hormones1. Thyroid Hormones Thyroid gland2. Parathyroid Hormone (PTH) & Calcitonin


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2. Parathyroid Hormone (PTH) & Calcitonin

Parathyroid gland3. Insulin & Glucagon Pancreas (pancreatic islets)4. Adrenal Hormones Adrenal cortex & adrenal

medulla

5. Gonadol Sex Hormones Testes & ovary 6. Melatonin Pineal gland7. Thymopoietin Thymus gland


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Vertebrate endocrine glands and theirhormones (Refer to pg..Figure..Table ..)

Nonpituitary Hormones1. Thyroid Hormones

The thyroid gland produces iodine-containing


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hormones (T3 & T4) that stimulate metabolism &influence development & maturation.

2. Parathyroid Hormone (PTH) & Calcitonin

Secreted by the thyroid, stimulates Ca2+


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deposition in bones & excretion by kidneysblood Ca2+ levels

PTH secreted by the parathyroid glands has the

opposite effects on bones & kidney blood Ca2+levels

3. Insulin & Glucagon Secreted by the pancreas (pancreatic islets).


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Insulin (from cells) reduces blood glucose levels promotes the cellular uptake of glucose,glycogen formation in the liver, proteinsynthesis & fat storage.

Glucagon (from cells) increases blood glucoselevels - promotes glycogen breakdown in the

liver, fat breakdown & conversion of protein toglucose.

4. Adrenal Hormones Neurosecretory cells in the adrenal medulla

release epinephrine & norepinephrine in


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response to stress-activated impulses from thenervous system.

The adrenal cortex releases

i. cortisol influence glucose metabolisme & theimmune system.

ii. aldosterone affect salt & water balance.

iii. sex hormones small amount

5. Gonadol Sex Hormones Produce most of the bodys sex hormone.

i. estrogen stimulate the development &


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maintenance of the

reproductive system.ii. testosterone stimulate the development &

maintenance of the reproductive system.

6. Melatonin Secreted by the pineal gland. Affects skin pigmentation.

The Mechanism Controlling The Release ofHormones by Glands Presence of a specific metabolite in the blood.

E.g. Excess glucose in the blood release of


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insulin from pancreas lower the blood glucoselevel.

Presence of another hormone in the blood.

E.g. Many of the hormones released from theanterior pituitary gland are stimulating hormones release of other hormones from other glands inthe body.

Stimulation by neurons from the autonomicnervous system.


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e ous syste

E.g. Adrenaline & noradrenaline are released fromthe cells of the adrenal medulla by the arrival ofnerves impulses in situations of anxiety, stress &danger.


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Two Main Categories of Hormones1. Steroid Hormone Characteristics of Steroid hormone:

i. Produced by endocrine gland originated from


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the mesoderm.

ii. Small size molecules, lipid & fat soluble & ableto pass through cell membrane.

E.g. testosterone, estrogen & aldosterone.

iii. Involved in long term mechanism of bodyphysiology.

Mechanism of Steroid Hormone Action Diffuse through the phospholipid layer of the

plasma membrane of target cells.

Enters the cytoplasm & binds to a specific


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Enters the cytoplasm & binds to a specificreceptor protein forming activated hormone-receptor protein complex (HRPC).

HRPC passes through the nuclear pore & enters

nucleus.

Binds to specific site on DNA activation ofspecific gene(s) which transcribes mRNA

The mRNA moves into cytoplasm & ribosomalsubunits get attached to it.

Translation occurs polypeptides chains are


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synthesized.

Polypeptides chains then fold to form specificproteins or enzymes required for the

physiological response to steroid hormone.

E.g. Estrogen - stimulates the repair andthickening of the endometrium


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2. Non-Steroid Hormone (Peptide/Amino Hormones) Produced by endocrine gland originated from the

ectoderm.


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Involved in short term mechanism of bodyphysiology.

Large size molecules & not able to pass through

cell membrane.

E.g. Insulin, antidiuresis & tyrotrophic hormone.

Mechanism of Non-Steroid Hormone Action* 2 messaging system

extracell - the specific hormone.intracell - cAMP from phosphorylation process


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act upon the information from thehormone.

Hormone molecule reaches the target cell.

Binds to a specific receptor protein on the outersurface of the plasma membraneconformational change in the receptorincrease the affinity to bind with G (guaninenucleotide) protein (binding protein).

G protein is activated stimulate the enzymeadenylyl cyclase convert ATP into cAMP.

cAMP as second messenger initiates a complex


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enzyme reaction chain (enzyme cascade reaction-ECR) which triggers responses of target cell.E.g. permeability change of cell membrane,increased production of glucose, etc.

*ECR process where the action of 1 enzymeactivates another enzymatic reaction whichresults in many product molecules.It brings about a rapid and amplified response tothe hormone.

E.g. Adrenaline activates the enzyme kinase.Through the enzyme cascade effect, glycogen


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phopsphorylase is activated & convert glycogento glucose.

ii. Vasopressin H activates enzymes that change

the permeability of the cell membrane forreabsorption of water in kidney tubule cells.


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G protein is activated stimulate the enzyme

adenylyl cyclase convert ATP into cAMP.


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cAMP as second messenger which initiates acomplex enzyme reaction chain (cascade effect).

activates protein kinase enzyme activatesphosphorylase kinase enzyme activates

glycogen phosphorylase enzyme catalysesthe breakdown of glycogen glucosephosphate oxidised to release E


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Steroid Hormone Action Non-Steroid Hormone

Action


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That is all for this topic

TAKE CARE & GOOD LUCK


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DISCUSSION QUESTIONS

1. How impulse is transmitted along the axonand across the synapse.


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y p

2. Explain how the skeletal muscles contract.

3. Distinguish between rod and cone cells.

4. Discuss the structure of the rod cell.

5. Cochlea involved in the hearing process.Explain the hearing physiology.

6. There are two types of hormone. Discuss


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ypthe characteristics of the hormones and themechanisme of the hormone action.


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Photoreception in A Rod Cell* Rods sensitive to low light intensity. Light detection depends on pigment rhodopsin. Rhodopsin consists of a protein, opsin joined


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with retinal (retinene).

When rhodopsin absorbs light the retinal tochange its shape & no longer attach to the opsin

bleaching.

The chemical breakdown of the rhodopsinchanges the permeability of the rod plasmamembrane to Na+.

The rod membrane become less permeable to


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Na+ - less can diffuse in. Na+ pumps continue topump Na+ out causes the inside of the rodbecomes > -ve.

The alteration in the potential difference generator potential involves ahyperpolarization.

If the generator potential reach a threshold

level, it causes an action potential.

nerve impulse optic nerve optic center inthe brain.


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Types of Endocrine Glands & HormonesProduced1. Pituitary Glands 2 lobes


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i. anterior 6 hormones Gonadotrophin hormone FSH, LH & prolactin Adrenotrophic hormone control adrenal glands Tyrotrophic hormone control secretion of

thyroxin hormone

Somatotrophic hormone control growth. Diabetogenic hormone control insulin action. Melanocyte stimulating hormone control

i f ki i


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secretion of skin pigment.

ii. posterior 3 hormones

Vasopresin hormone muscle contraction. Oxytocine hormone uterus muscle contraction. Antidiuresis hormone (ADH) changes in kidney

collecting ducts permeability.

2. Metabolic Hormones Secreting Glands Important in controlling metabolic enzyme

activity.


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Secreted by:-Tyroid gland tyroxine hormone.Parathyroid gland parathyroid hormone

(control composition of Ca+ & PO4- ions inblood).

Adrenal i. Cortex adrenal 3 hormone

(cortisol, aldosteron & androgen).ii. Medulla adrenal adrenalin


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hormone.

Pancreas (Langerhans tissue cells)

i. cells insulin hormone (glucose glycogen).ii. cells glucagons hormone(glycogen glucose).

3. Gonad Glands Gonad = testes

testosterone promote development of testes &2 sexual character.


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Gonad = ovaryE2 - promote development of ovaries & 2

sexual character.- control menstrual cycle & pregnancy.

Pg - control menstrual cycle & pregnancy.

4. Digestive Glands Produce hormones that controls secretion of

digestive enzymes. E.g. i. pyloric part of the stomach gastrin

h i l


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hormone secretion HCl.ii. intestine secretin hormone secretionof pancreatic juice.

5. Thymus Glands Production of stimulating hormones &

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Fqah 0113 - Nervous System Intro