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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 ¶sympathetic.
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Sympathetic nerves have an excitatory effect ¶sympathetic 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 &