Nerves, Hormones, and Homeostasis

Nerves, Hormones, and Homeostasis

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The Nervous System Links Sensation to Response

Structure and Function of the Nervous SystemNeurons (Nerve Cells) – Basic Unit of the nervous system• Neurons are specialized to carry electrical

signals

Nervous system has two subsystems:

1. Central Nervous System (CNS)• The body’s main information Processing

center

Nervous system has two subsystems:

2. Peripheral Nervous System (PNS)• Outside the CNS• PNS delivers information to the CNS and carries

messages from the CNS to other organs

Nerve – Consist of one or more bundles of neuron fibers surrounded by connective tissue

Two Categories of Peripheral Nerve

1. Spinal Nerve – 31 pairs (left and right) emerge from the spinal cord. They are mixed nerves, some sensory and some motor

2. Cranial Nerves – 12 pairs of these emerge from an area of the brain known as the brainstem.

• I.e. The optic nerve – that take visual info. from the retina to the brain.

Stimulation & Interpretation

There are many types of nerve receptors• When touched:

– That touch or pressure stimulates an action potential

– This information reaches the spinal cord– Sensory neurons stretch from receptors to the

spinal cord

Stimulation & Interpretation– Once the action potential reaches the spinal cord, it

is routed in the CNS to the appropriate area for interpretation

• Touch, pain, pressure, etc.

Relay Neurons – neurons that carry impulses within the spinal cord and brain

Stimulation & InterpretationResponse

• Interpretation is made by the appropriate area of the brain

• Reaction to a stimulus• Deciding to move:

– The brain’s relay neurons pass the action to spinal nerve pairs

– Action potential is now on a pathway of motor neurons (neurons taking an impulse to a muscle)

• Spinal nerve contains both sensory and motor neurons

Stimulation & InterpretationResponse

Motor End Plate – the junction which a neuron sends a chemical to muscle tissue which results in a contraction

– Action potential reaches the motor end plate causing the muscle contraction initiating a response

Effector – muscle that contracts because of the message to contract

3 Main Functions of the PNS and the CNS working together:1. Sensory InputStimulus – (plural, stimuli) information received from the environment by a receptor and elicits a response• Information received by the PNS• Examples: colors, change in

temperature, being touchedSensory Neurons – neurons that carry

information about stimuli, to the CNS.

Main Functions of the PNS and the CNS

Sensory InputSensory Receptors – highly specialized cells that receive stimuli.


2. Integration• CNS interprets the information

– Neurons are located entirely within the CNS

Interneuron – neurons in the CNS, integrates sensory input


3. Motor OutputMotor Neurons - neurons that carry signals away from CNS• Like moving an arm / Throwing a ball


Reflex – a rapid, automatic (unconscious) response without thinkingReflex Arc – the nervous system pathway that regulates a reflex

Reflex :

1. Receptors detect / receive stimulus• Pain receptors receive the stimulus of excess

heat, pressure, or chemicals produced by injured tissues

2. Sensory neurons in the PNS convey this information to the CNS (spinal cord)

• The axon of the sensory neuron enters the spinal cord in the dorsal root and sends a chemical message across synapse to a relay neuron

Reflex• Relay neuron is located in the grey matter of the

spinal cord– White matter occurs wherever conduction of

impulses is the major event– Grey matter occurs wherever integration of impulses

may occur

3. CNS (spinal cord) transmit signals to both motor neurons and interneuron

• Relay neuron synapse with a motor neuron in the grey matter and transfers the impulse is transferred chemically across the synapse

Reflex 4. The motor neuron is located in the ventral root of

the spinal cord5. The motor neuron Is located in the ventral root of

the spinal cord6. It carries the impulse to an effector

Structure of Spinal Cord & components of the reflex arc

Effects of Natural Selection• Animal behavior can change in response to

their environment• The behaviors can be so extreme that a new

species is formed• Variations in behavior can occur in population

in the same way variations can occur in appearance – Variations in behavior can be selected by the

environment

Effects of Natural Selection• Genetically programmed behavior can have

variations that can work better than another in a changing environment – Causing that organism to survive and reproduce

• Read page 339 - 340 about European Blackcaps & Sockeye Salmon

Neurons Conduct Nerve ImpulsesStructure of a Neuron

Cell Body – Contains neuron’s nucleus and most organellesDendrites – Receive signals and carry them towards the neuron’s cell bodyAxon – Carries electrical impulses away from the cell body and toward other cells.• Some axons can be very long, like from spinal

cord to the toes.

Structure of a Neuron

Myelin Sheath – Axons are insulated by a thick coat of material; they resemble a chain of oblong beads.Nodes – Areas between the myelin sheath

(beads) that are un-insulated.• Signals will jump from node to node

nodes

A Neuron at Rest

To better understand how a neuron works, first you need to

understand a neuron at rest

Resting PotentialNon-myelinated Neurone – an axom that does not contain a myelinated sheath • Myelinated sheath speeds up the action

potential Resting Potential – The state of being where a neuron is ready to send an action potential• This area of the neuron is said to be polarized

Resting Potential– Key is the plasma membrane:

• Separates ions inside and outside the cell (ions electrically charged atoms / molecules)

• Because opposite charges attract, separating them is a form of potential energy

Resting Potential

Voltage – the “pressure” created when holding opposite charges apart.• Measured in units called volts

– A resting neuron has voltage of -70 mV• The (-) indicates that the inside of the nerve cell is

negative in charge compared to the outside.

Resting Potential

Resting Potential – the voltage across the plasma membrane of a resting neuron.• Potential = potential energy

Ion Channels• The ions we are talking about in this Resting Potential

are Na⁺ (sodium ions) outside• K⁺ (potassium ions) are more concentrated inside• Specific proteins in the membrane act like channels for

each ion• So….. Na⁺ goes in cell; K⁺ goes out

– There are more K⁺ channels than Na⁺• So K⁺ goes out faster than Na⁺ goes in

• This “unbalance” causes the outside of cell to be more (+) than inside

• In addition there are negatively charged ions inside the cell

Ion Channels

Ion Pumps

Sodium Potassium Pump• A protein on the membrane (of

neuron) that pumps ions across the membrane– Requires ATP– The resting potential creates a

resting neuron that is ready to fire / transmit a nerve signal

How a Nerve Signal Travels

• All cells, not just neurons, have voltages across their membrane– Only muscles and nerve cells can

use this energy

Triggering the Nerve Signal

Depolarization – if a neuron is stimulated, the voltage across the membrane changes at the point of stimulation.• Charge difference decreases across the

membrane decreases. – Stimulation causes Na⁺ diffuses into the cell.


• Normally there is more Na⁺ outside the cell membrane– inflow of Na⁺ ions (⁺ charge)

depolarizes the membrane


Threshold – the point when stimulus is strong enough to depolarize the membrane to a certain level.• Usually – 50mV• Additional Na⁺ channels open

– Then there is a “rush” of Na⁺ into the cell– Causes greater depolarization


Action Potential – This is a stronger depolarization and the start of the nerve signal.

Transmitting the Nerve Signal

• The 1st action Potential; causes Na⁺ gates to open nearby, causing more action potential; and so on….– Like tipping over the first domino in a chain– Self – propagating part of action potential; once you

start an impulse at the dendrite end, that action potential will self propagate itself to the far axon end of the cell

Transmitting the Nerve Signal• After a nerve signal passes a region of the

neuron the resting potential is restored– The return to resting potential is caused by opening

K⁺ gates– During action potential; concentration differences

of Na⁺ and K⁺ ionsRepolarization – the active transport is required to pump the two ions to their resting potential positions

• This happens very quickly

Action Potential

The Speed of Transmission

• 5 meters per second – along neurons membrane• Faster Even: because of myelin sheath

The Speed of Transmission• Action potential “jumps” from nodes to nodes

– Makes nerve impulse faster• Neurons with myelin sheath transmits signals at

150 meters per second• From Spinal Cord to Toes in 7 milliseconds

Measuring Stimulus Strength

• Action Potential = nerve signals; are all or none events• All nerve signals are equal• A stimulus becomes more intense when the

frequency and the number of action potential increase

Measuring Stimulus Strength• The brain “reads” the number of action

potentials to determine signal strengthRefractory Period – the time it takes for any one neuron to send an action potential so it can send another

Crossing SynapsesSynapse – the space between nerve cells, transmitting information / communicating• The first neuron is called presynaptic neuron• The second neuron is called postsynaptic

neuron• Synapses can be chemical or electrical

Crossing Synapses• There are different patterns in presynaptic and

postsynaptic communications– Can be one to one communication– Can be one presynaptic to many postsynaptic– Can be many presynaptic to one postsynaptic

Action Potential

Crossing Synapses

• A sensory pathway is unidirectional only because they are lined up so that the terminal end of the axon of the first neuron adjoins the dendrites of the next neuron.

Crossing Synapses

Electrical Synapse – the action potential at the end of axon directly causes an electrical change in receiving cell• Common in the heart and digestive organs

– Steady impulses are needed• Rhythmic muscle contractions

Crossing Synapses

Chemical Synapse – nerve impulse must be transmitted across a tiny space.

Crossing Synapses

Synaptic Cleft – space between knoblike tips and dendrite. • In chemical synapse the electrical signal is

converted to a chemical signal.Terminal Buttons – located at the at the far end of axons are swollen areas• Area contains vesicles containing neurotransmitters

Crossing SynapsesNeurotransmitters – Nitrogen-containing organic compounds, used to transmit signals across the synaptic cleft.

When action potential reaches the knob:• Calcium ions diffuse into the terminal buttons• Vesicles are released into synaptic cleft by

fusing with plasma membrane• NT diffuses across the synaptic gap

Crossing Synapses• Receptor proteins on the postsynaptic neuron’s

membrane accept the neurotransmitter– The result is a new impulse / opening of ion

channels and sodium ions diffusing in through this channel (action potential)

– Neuron is depolarized and action potential begins to move down the postsynaptic neuron

Crossing Synapses - Neurotransmitters

• After neurotransmitter triggers the new signal, the neurotransmitter is broken down by enzymes or reabsorbed into the sending neuron– Thousands of signals are sent and received

simultaneously from different synapses– Reabsorbing prevents impulses from being

generated continuously in the receiving neuron.

Effects of Neurotransmitters• Some neurotransmitters are excitatory and

stimulate the next neuron to forward the message.– This is done by increasing the permeability of the

postsynaptic membrane to positive ions• Some neurotransmitters are inhibitory they

cause positive ions to move ions to move out of the postsynaptic cell– This chemically depresses the postsynaptic cell and

makes it harder to excite

Effects of NeurotransmittersThe sum of excitatory & inhibitory messages

received by the postsynaptic neuron determines whether or not a message is carried forward by

the postsynaptic neuron.1. The impulse which moves down the presynaptic

neuron is called action potential2. As the action potential reaches the axon bulb, Ca ions

rush into the end of the neuron3. This causes vesicles containing neurotransmitters to

fuse with presynaptic membrane

Effects of Neurotransmitters

4. As the vesicles fuse with the presynaptic membrane, they release the neurotransmitters into the synaptic cleft.

5. The neurotransmitter binds to specific receptors on the postsynaptic membrane. The receptors are like gates which let ions enter or leave when the neurotransmitter binds to them.

Effects of Neurotransmitters

Types of NeurotransmittersExcitatory Neurotransmitter

Acetylcholine – Triggers action potential• Excitatory neurotransmitters increase the permeability

of the postsynaptic membrane to positive ions • This causes positive Na ions which are in the synaptic

cleft to diffuse into the postsynaptic neuron

Types of NeurotransmittersInhibitory Neurotransmitters

GABA - Gamma-Aminobutyric Acid• These neurotransmitters inhibit action

potential• An inhibitory neurotransmitter causes

hyperpolarization of the neuron making it more difficult for action potential to occur– Movement of chloride ions into the neuron makes

it more negative on the inside of the neuron

Types of Neurotransmitters

Serotonin and Dopamine(in the brain)

• Trigger sleep, mood, attention, and learning– Low levels can lead to depression

• Prozac – (drug Fluoxetine) blocks the removal of serotonin from the synaptic cleft.

The PNS Carries Information to and from the CNS 28.3

Sensory Division• Contains 2 sets of sensory neurons

– 1 brings information about the outside environment

• From eyes, ears, skin, and other external sense organs

– 1 brings information from within the body• Temperature, heart rate, and activity level in the blood

• Both provide the brain with sensations of pain.

From PNS to CNS

From PNS to CNSMotor Division• Carry CNS’s response messages to muscle cells and

gland cells• Motor Neurons are made of two systems:1. Somatic Nervous System

– Carry signals from the CNS to skeletal muscles• Made of voluntary actions

From PNS to CNS

2. Autonomic Nervous System• Carries signals to organs

– Mostly involuntary• Neurons in this system are separated into two

divisions:1. Sympathetic Division– Increases the general level of activity in the body

and makes more energy available – Prepares body for intense activities that consume

energy

From PNS to CNS

Sympathetic Division

From PNS to CNS - Sympathetic Division

“Fight or Flight Response”Happens under extreme levels of physical or

emotional stress• Certain sympathetic division neurons stimulate

organs directly– Other neurons work indirectly signaling certain

glands to secrete hormones

From PNS to CNS - Sympathetic DivisionFight or Flight

Results:• Increase Heart Rate• Liver releases Glucose• Airway in lungs relax (breath easier) Slows down digestive system

Makes more blood available for heart, brain, muscles

From PNS to CNS

2. Parasympathetic Division• Calms the body• Returns the body to regular maintenance

functions– Decrease heart rate and glucose release– Stimulates digestive system to breakdown food

again• Most organs receive both sympathetic and

parasympathetic signals and adjust to maintain homeostasis

Sympathetic vs. Parasympathetic

Sensory Receptors Link the Environment to the Nervous System 28.5

Sensation & Perception• Sensory receptors detect stimuli

– Light– Sounds– Skin Temperatures

• Then send information to CNS

Sensory Receptors

• Receptors are found in high concentration in your nose, eyes, ears, mouth, and skin.

Sensation – an awareness of sensory stimuli• As your brain integrates information you

become aware of stimuliPerception – meaningful interpretations of sensory data.

Types of Sensory Receptors

• Five categories of sensory receptors that collect information from the external and internal environment.

I. Pain Receptors• All parts of your body have pain receptors except

your brain• Pain is sensed by free nerve endings

– Dendrites– It is not a “pain receptor” cell

• Pain indicates your tissues are in danger


II. Thermoreceptors• Found in the skin and some internal organs

– Detect heat and cold• Like pain receptors they are free nerve endings

– Not a separate cell.• These receptors “report” to the hypothalamus

– Hypothalamus acts like the body’s thermostat.– Using thermoreceptors from the whole body the

hypothalamus keeps the body temperature between a certain range.

Types of Sensory ReceptorsIII. Mechanoreceptors• Sense touch, pressure, stretch, and motion• In each mechanoreceptors a change to the shape of its

membrane alters permeability to ions– Change can generate an action potential

• In our arteries, pressure receptors can detect a change in blood pressure

• In our lungs, stretch receptors respond to the degree of lung inflation

• We can tell the position of our arms and legs by the use of proprioceptors found in muscle fibers, tendons, and joints

– Help maintain posture and balance

Types of Sensory ReceptorsIV. Chemoreceptors• Located in your nose and taste buds; all

sensitive to certain chemical stimuli• Also gives information about internal body

environment– pH – changes in pH can adjust breathing rate– Some pain receptors respond to chemicals

released by damaged tissue


V. Photoreceptors• Found in your eyes• Receptive to various wavelengths of light


IV. Chemoreceptors• Located in your nose and taste

buds; all sensitive to certain stimuli

V. Photoreceptors• Found in your eyes• Receptive to various

wavelengths of light

Structure & Function of the Human Eye

Part Function

Iris Regulates the size of the pupil

Pupil Admits light

Retina Contains receptors for vision

Aqueous humour Transmits light rays & supports eyeball

Vitreous humour Transmits light rays & supports eyeball

Rods Allow black and white vision in dim light

Cones Allow color vision in bright light

Fovea Area of densely packed cone cells; vision is most acute

Lens Focuses light rays

Sclera Protects and supports eyeball

Cornea Focusing begins here

Choroid Absorbs stray light

Conjunctiva Covers the sclera & cornea & keeps eye moist

Optic nerve Transmits impulses to the brain

Eye lid Protects the eye

Vision

Sclera – outer white surface, made of connective tissueCornea – a transparent area on the sclera where light enters• Helps focus the light to the back of• the eye ball• A thin membrane that secretes• mucus keeps the cornea and sclera• most and debris free.

Vision

Iris – just beneath the sclera, (pigmented) contains blood vessels that nourish the eye.Pupil – Dark opening in the center of the iris• Muscles in the iris control how much light

reaches the interior of the eye.

Vision

Lens – disc shaped, after pupil; muscles attached to ligaments pull on lens, changing its shape as you look at distant objectsRetina – inner surface of the eye, where lens focuses images• Vision begins when light enters the eye & is focused on the photoreceptor cells of the retina

Structure of the Retina

Vision

Photoreceptor Cells are rods & cones • Both rods & cones synapses with their own

bipolar neurons– Each bipolar neuron synapses with a ganglion cell

• Are cells in retina carry impulses from a rod / cone to ganglion

• Called bipolar because each has 2 process extending from the cell body

– Axons of ganglion cells make up the optic nerve

VisionCones:• 3 types of cones: responds to 3 colors of light

– Blue, Red, and green• Color Blindness is a result of deficiency or malfunction

of one or more types of cones

Rods – another photoreceptor • Does not distinguish colors• Very sensitive to light• Allow sight in dim light; but only in shades of

grey.

Vision

• Each eye’s retina is lined with 130 million photoreceptor cells.– Detects light as it moves and sends signals to the

brain via optic nerve

Three Most Common Visual Problems

• All three problems are related to eye shape– Creates an issue with focusing

1. Nearsighted2. Farsighted3. Astigmatism

Processing Visual Stimuli• Light rays pass through the pupil and are

focused by the cornea, lens and the humours.• The image is focused on the retina upside

down and reversed from left to right.

Processing Visual Stimuli• Once photoreceptors are stimulated, they

send impulses to the bipolar neurons and the ganglion cells.

• The axons from the ganglion cells travel to the visual area of the cerebral cortex of the brain.

Processing Visual Stimuli• The brain must correct the position of the image

so that it is right side up.• It must also coordinate the images coming from

the left and right eye• There are many things about vision that are still

not understood

Processing Visual StimuliEdge Enhancement

• Scientist studying vision have used optical illusions as powerful windows into the neurology of vision– Studies using illusions began 1865

Hermann Grid Illusion• Read 345 “Edge Enhancements”

Processing Visual StimuliContralateral Processing

Optic Chiasma – The area where information from the right and left half of each visual field converge here and pass to the opposite part of the brain. The information usually ends up in the visual cortex of the brain• Since each visual area only receives half the information

from each field areas they must share information in order to get complete image


• Remember the image received by the cortex is inverted and reversed.

• The brain must correct the image in order to correctly perceive what is in the whole visual field

• Other stimuli like color, form, and motion are parceled out to other visual association areas of the brain

• Cerebral cortex rebuild all the parts into a visual image


• A patient with a brain lesion (injury) presents an abnormal perception of any object

• For example:– I f we see a bucket in any shape or form we know it

is a bucket– Right side lesion looking at a bucket from above do

note recognize the bucket – Left side region can describe the function of a

bucket but cannot name of it.


It takes both sides of the brain working together

to have a correct “vision” which is able to recognize an object and understand what

it is.

See page 346

Hearing and Balance

Hearing and Balance

Hearing• The ear is made of Outer, Middle, and Inner ear.

Outer Ear• Flap-like structure “ear”Auditory Canal – Tunnel-like opening• Outer ear collects sound waves and channels

them to the eardrum– Vibration of air molecules

Hearing and Balance

Outer EarEardrum – a sheet of tissue that separates the outer ear from the inner ear.

– AKA – Tympanic Membrane• Sound waves causes eardrum to vibrate

Hearing and BalanceMiddle Ear• Eardrum passes vibrations on to three small bones

– Together they magnify the sound up to 20 times

1. Hammer / Malleus2. Anvil / Incus3. Stirrup Stapes – strikes oval window causing it to

vibrate / this vibration is passed to fluid in the cochlea

Oval Window – a membrane covered hole

Hearing and Balance

Inner EarAuditory Tube – (Also called Eustachian Tube)• Conducts air between middle ear and the back of the

throat.– Keeps pressure equal pressure on both sides of the

eardrum

Hearing and Balance – Auditory Tube

• Tube enables your ear to move air in out to equalize pressure– Popping your ears on a plane ride

• Without this your ears would bulge inward and outward– Distorting your hearing

Hearing and Balance

• The inner ear consists of fluid-filled channels in the skull

• Sound waves move this fluid

Hearing and Balance• Cochlea – a long coiled tube shaped like a snail shell• Fluid in cochlea moves in waves causing hair-like

projections along the membrane of the cochlea to move– Movement of the hair-like structures (receptors)

initiate action potential in nerves that go to the brain.– Chemical message passes the synapse to the sensory

neuron of the auditory nerve• The louder the sound the stronger the vibration• More action potential; the louder the interpretation

Hearing and Balance

• Sound is processed in the auditory area of the cerebral cortex

Hearing and Balance - Chochlea

Very loud sounds can damage hair cells, causing hearing loss

Balance

• In addition to the chochlea; inner ear has 5 fluid filled structures that help maintain balance.– The 3 semicircular canals are lined by hair cells

• Hair cells detect the position of the head

Psychoactive Drugs Alter Brain Function

Cholinergic versus Adrenergic SynapsesCholinergic Synapses - synapses using acetylcholine• Nicotine stimulates transmission in cholinergic

synapses• This is why it has a calming effect on the body and

personality / without it agitation!!

Psychoactive Drugs Alter Brain FunctionAdrenaline Synapses – synapses using noradrenaline• Cocaine and amphetamines stimulate adrenergic

synapses• Both can cause increased alertness, energy, and

euphoria

Psychoactive Drugs Alter Brain Function

Effects of Drugs on the Brain• Drugs can alter your mood or your emotional

state.• Excitatory drugs (nicotine, cocaine,

amphetamine) increase nerve transmission• Inhibitory drugs (benzodiazepines, alcohol, and

tetrahydrocannabinol (THC)) decrease the likelihood of nerve transmission

Effects of Drugs on the Brain• Drugs act at the synapses of the brain by different

mechanisms to determine your emotional state.• Ways drugs change synaptic transmission:

– Block receptors for a neurotransmitter (drugs structure similar to neurotransmitter)

– Block release of neurotransmitter from the presynaptic membrane

– Enhance release of a neurotransmitter– Enhance neurotransmitter by mimicking a neurotransmitter

• Same chemical structure, same effect, but are not broken down

• Block removal of a neurotransmitter from the synapse & prolonging the effect of the neurotransmitter.

Effects of Drugs on the Brain

Excitatory Drugs & How They Act• Nicotine in tobacco products is a stimulate that

mimics acetylcholine• Acts on the cholinergic synapses of the body

and the brain to cause a calming effect• Enzyme (acetylcholinesterase) cannot

breakdown the nicotine molecule which binds to the same receptors


Excitatory Drugs & How They Act• Postsynaptic neuron releases a molecule called

Dopamine.– Dopamine gives you a feeling of pleasure– Has affect on the “reward pathway” of the brain

• Cocaine stimulates transmission at adrenergic synapses and causes alertness and euphoria.– Also releases Dopamine– Cocaine blocks removal of dopamine

• Both nicotine and cocaine act the same way, BOTH LEAD TO ADDITCTION


Excitatory Drugs & How They ActAmphetamine

• Stimulates transmission at adrenergic synapses• Causes increase activity levels, decrease

appetite and general sense of well-being• Drug acts by passing directly into the nerve

cells which carry dopamine (euphoria) and noradrenaline (alertness & high energy)

• Interferes with the breakdown of neurotransmitters

Effects of Drugs on the BrainInhibitory Drugs

• Benzodiazepine reduces anxiety and can also be used to reduce epileptic seizures

• Benzodiazepine increases the binding of GABA – GABA – gamma aminobutyric acid– This causes the postsynaptic neuron to become even

more hyperpolarized– Stops nerve transmission


Alcohol• Acts similar to benzodiazepine• Decreases the activity of glutamate an excitatory neurotransmitter• Alcohol also helps to increase the release of

dopamine– Process not well understood

• Stops the activity of the enzyme which break down dopamine in the synaptic cleft


Marijuana Tetrahydrocannabinol (THC)• Mimics the neurotransmitter anandamide

– THC binds to the same receptor (AKA cannabinoid receptor)

• THC causes postsynaptic neuron to be hyperpolarized• Disrupts short-term memory• Anandamide may be involved in eliminating information

from memory

THC

• THC acts on cannabinoid receptors• Receptors affect several mental and physical

activities:– Learning– Coordination– Problem solving– Short-term memory

THC

• Since THC mimics anandamide it inhibits the neurons that anandamine inhibits– Body probably does not break down THC in the

synapse– Stays longer

• High concentrations of cannabinoid receptors are found in areas of the brain

THC

• Hippocampus is important for short term memory

• Cerebellum and basal ganglia coordination

Causes of AddictionAddiction – a chemical dependency on drugs where the drug has “rewired” the brain and has become an essential biochemical in the body• The body often develops a tolerance and needs

more and more of the drug to produce the same results

Causes of Addiction• People who smoke crave the dopamine spike• Since the role of most commonly abused drugs

is to stimulate the “reward pathway” located in the brain, withdrawal of the drug produces symptoms which are the opposite of euphoria

Causes of Addiction• Symptoms:

– Anxiety– Depression– Craving– With alcohol addiction can

be fatal (seizures & delirium tremens)

Causes of Addiction• Continued addiction can be more harmful

– Inhaled drugs can damage lungs– Sharing needles; spread HIV, hepatitis B & C– Kidney disease

Causes of Addiction

Genetic Predisposition• Evidence in studying identical twins show that

there is a 50% greater chance of second twin to be an addict when the first twin is addicted

• Other studies show that people that have a genetically determined deficiency of dopamine are predisposed to addiction

Causes of AddictionSocial Factors

• Family addiction• Parenting skills• Mental skills of family and or child• Peer group• Cheap drugs = more addiction• Drugs introduced in a cultureDesensitization – when dopamine receptors are

constantly stimulated. Over-stimulation decreases the number of receptors & the remaining receptors become less sensitive to dopamine.

• Need more for same results

HomeostasisThe bodies ability to stay within certain

physiological variables• Variables Include:

– Blood pH– Carbon Dioxide Concentrations– Blood Glucose Concentration– Body Temperature– Water Balance within Tissue

HomeostasisNegative Feedback Mechanism

• The physiological changes that bring a value back closer to a set point

• Negative feedback works like a thermostat:– The temperature is set (say 76°)– If the temp. goes above or below that number the

thermostat turns on the AC unit (or heater) to bring the temperature back to the set mark.

Homeostasis

• The nervous system along with the endocrine system work cooperatively to ensure homeostasis

• Many homeostatic mechanism initiated by your nervous system are under the control of your autonomic nervous system

Homeostasis• The endocrine system consists of numerous

glands that produce hormones– Each hormone is transported by the bloodstream

and affects only specific cell types

Homeostasis – Body Temperature• The Biological Thermostat is located in the

Hypothalamus • As Temperature rises thermoreceptors in your

skin sends a signal to the hypothalamus– Hypothalamus activates cooling mechanisms

• Cooling mechanisms include sweat produced by sweat glands

• Arterioles in the skin dilate this fills capillaries with blood

• This helps radiate the heat out of the body cooling off blood (red cheeks)

Homeostasis – Body Temperature• In cold temperatures:

– The signal from the thermoreceptors send signal to the hypothalamus

– This initiates a response that causes vasoconstriction of arterioles so blood is diverted to deeper organs • Less loss of heat through radiation

– Hypothalamus also directs skeletal muscle to shiver• Muscle contraction increase body temperature

Homeostasis – Blood GlucoseBlood Glucose level is the concentration of

glucose dissolved in blood plasma.• Cells need glucose for cell respiration• Cells are constantly reducing the amount of

glucose in the blood

Homeostasis – Blood Glucose

• Foods with carbohydrates are broken down to glucose.

• Glucose is absorbed in the villi of the small intestine into the blood stream.

• So when we eat we will increase our blood glucose levels (if we eat carbos)

• Cells use glucose, blood glucose is reduced– We eat this starts again

Homeostasis – Blood Glucose• Blood glucose must be maintained close to the

body’s set point • A negative feedback mechanism ensures this

Homeostasis – Blood Glucose• From the intestinal villi, the glucose is routed

through the venous system to the Hepatic Portal Vein

Hepatic Portal Vein – takes blood to the liver


Blood Glucose in Hepatic Portal Vein• Blood Glucose concentrations in hepatic portal

vein varies depends on the time of our last meal• The hepatic portal vein is the only blood vessel

that blood glucose varies greatly• Blood vessels receive blood after it has been

acted on by liver


Blood Glucose Above set pointΒ (beta) cells – found in the pancreas and produce a hormone named insulin• Insulin is secreted and absorbed into the blood• Insulin cause cells to open protein channels on

their cell membranes• These channels allow glucose to diffuse into the

cell by a process known as facilitated diffusion



• Insulin also stimulates the Hepatocytes to take in glucose (a monsaccharide) and convert it to glycogen (a polysaccharide)

• Glycogen is then stored as granules in the cytoplasm of the hepatocytes– Also takes place in the muscles

Both Processes Lower Glucose Concentration!

Homeostasis – Blood GlucoseBlood Glucose Below set point

• Blood glucose goes down when someone does not eat for many hours or exercises too hard for a long time.

• Body needs to use stored glycogen in liver and muscles

• Α (alpha) cells of the pancreas begin to produce and secrete the hormone glucagon.

Homeostasis – Blood Glucose• Glucagon stimulates the hydrolysis of the

granules of glycogen stored in hepatocytes and muscle cells– This process produces the monosaccharide glucose– This produces a short supply of blood glucose

Negative Feedback Control of Blood Glucose Levels

DiabetesHyperglycaemea – high blood sugar

Two Types of Diabetes:1. Type I – caused when β cells of the pancrease

do not produce enough insulin2. Type II – caused by body cell receptors that do

not respond properly to insulin • People with type II have cells that do not take

in glucose, so glucose remains in blood

DiabetesType I Diabetes

• An autoimmune disease • Immune system attacks β cells of the pancreas

so little or no insulin is produced• Type I diabetes usually develops in children or

young adults

DiabetesType II Diabetes

• The result of the body cells no longer responding to insulin– AKA Insulin Resistance

• Initially, the pancreas produces the normal amount of insulin but, that decreases over time

• Most common for 90% of diabetics• Associated with genetic code, history, obesity,

lack of exercise, advance age, and certain ethnic groups

Uncontrolled DiabetesEffects

• Damage to the retina leading to blindness• Kidney Failure• Nerve Damage• Increase Risk of Cardiovascular Disease• Poor Wound Healing

Innate & Learned Behavior

Ethologist – a person who studies the behavior of animals in their natural environment

Innate Behavior• Develop independently of environmental context

A spider spins a web for the first time

Innate Behavior

• They are controlled by genes and inherited by parents– A bird song– Sucking behavior in humans (mammals)

• Behaviors aid in survival• Can be performed in a certain order

– See figure 11.11 on page 349

Learned Behavior

• The process of gaining new knowledge or skills or modifying existing knowledge skills

• Not genetically programmed / can result from experience– How to read– Ride a bike

• Learning can be explained by a change in performance that we are sure is stored in the nervous system as memory

Taxis• In simple invertebrates there are two basic

kinds of movement: Taxis & KinesisTaxis – a directed response to a stimulus• If an animal goes towards the stimulus we say

it is a positive stimulus • If an animals moves away from a stimulus we

say it is a negative stimulus

TaxisTaxis are identified by the type of stimuli they are

responding to:• Chemotaxis – the response to chemicals in the environment

– Moving towards food or other chemicals• Phototaxis – the response to light• Gravitaxis – the response to gravity• Rheotaxis – a response to water current• Thigmotaxis – a response to touch

Kinesis• Movement in response to a non-directional stimulus

– Like humidity• Organisms will move according to the intensity of the

stimulus• Since there is no direction of the stimulus there is no

direction in the movement– It will be rapid if uncomfortable or slow if

comfortable Orthokinesis – when an organism moves slowly or rapidly to response to the stimulus but it does not move towards the stimulus

KinesisKlinokinesis – when an organism turns slowly or rapidly in response to the stimulus but it does not move towards the stimulus

Review: Example on page 352 - 355

Learning Improves the Chance of Survival

Imprinting – the process by which young animals become attached to their mother within a day of so after hatching or birth• This improves the chance of survival

Learning Improves the Chance of SurvivalHording – when animals store food when it is

plentiful• Animals will return to their storage when food

is low

Learning Improves the Chance of SurvivalBirdsong• If a young male sparrow hears an adult song

within its first 100 days of life it will sing a full adult song the next year

• Song attracts a mate• Deters rival males

Learning Improves the Chance of Survival

Mimicry a type of false learning• Some animals are tricked into false learning

Pavlov & Conditioning• Classical conditioning can be used to modify a

reflex response.Unconditional Stimulus – the act the initiates a response (UCS)Unconditional Response – the response to UCS (UCR)Neutral Stimulus – eliciting the UCR with a neutral stimulus plus the stimulus (a sound etc)

Pavlov & Conditioning

Condition Stimulus – responding to the neutral stimulus without the act that initiates the response (CR)• Review experiments designed by Ivan Pavlov

Page 358• Heinemann.co.uk/hotlinks

– Express code: 4273P– Web link: 11.9

Learning of Birdsong• Male birds sing to attract a mate and deter

other males• Generally females do not sing• Birds hatch with an inherited crude template

– This crude song is species specific• Memorization Phase – bird is silent but listening to the song of his species from adults

– The hatchling is modifying the inherited template

Learning of Birdsong• As the bird listens he attempts to match the

template to full adult song– It is a type of memorization– Memorization phase is over in about 100 days

• Sensitive Phase – the first 100 days– If the bird does not hear the adult song within this

time period he will not modify his inherited template

Learning of Birdsong• Motor Phase – this is the second phase, where the bird practices the song that he has heard• He begins to hear himself sing and begins to

shape his song to match what he heard as an adult

• Crude template is an Innate Learning and learning the adult song is Learned Behavior

Documents

Nerves, Hormones, and Homeostasis