Chapter 3 Biological Foundations of Behaviour

7/27/2019 Chapter 3 Biological Foundations of Behaviour

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Chapter 3 Biological Foundations of Behaviour

The Neural Bases of Behaviour

Termed as our 3 pound universe To understand how the brain controls our experiences we must first know how its individual

cells function and how they communicate with one another

Neurons

Basic building blocks of the nervous systemo Linked together in circuits,

At birth, the brain contains 100 billion neurons Each neuron has 3 main parts:

o A cell body (aka soma) Contains biochemical structures needed to keep the neuron alive Nucleus carries the genetic information that determines how the cell develops

and functions

o Dendrites Emerging from the cell body are branchlike fibres called dendrites Specialized receiving units like antennas collect messages from neighbouring

neurons and send them on to the cell body

There the incoming information is combined and processed The many branches of dendrites can receive input from 1000 or more

neighbouring neurons

The surface of the cell body also has receptor areas that can be directlystimulated by other neurons

o Axon Extending from one side of the cell body is a single axon which conducts

electrical impulses away from the cell body to other neurons, muscles, glands

Branches out at its end to form a number of axon terminals Each axon may connect with dendritic branches from numerous neurons

allowing for a single neuron to pass messages to 50000 other neurons

b/c the structure of the dendrities and axons, it allows for interconnections inthe brain

neurons vary in sizes and shapes sculpted by nature to receive process and send messages Neurons are supported in their functions by glial cells

o Surround neurons and hold them in placeo Make nutrient chemicals that neurons needo From the myelin sheath around some axons and absorbs toxins and waste materials that

might damage neurons


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o During prenatal development, new neurons are being formed through cell division, glialcells send out long fibres that guide newly divided neurons to their targeted place in the

brain

o Outnumber neurons 10-1o Protects brain from toxins

Foreign substances can pass from the circulation into the different organs of thebody but cannot pass from the blood into the brain because of a specialized

barrier called the blood brain barrier prevents many substances including toxins

from entering the brain

walls of the blood vessels within the brain contain smaller gaps than elsewherein the body and they are also covered by a specialized type of glial cell

together the smaller gaps and glial cells keep many foreign substancesfrom gainin g access to the brain

o modulates the communication among neuronsElectrical Activity of Neurons

Neurons do 2 important thingso Generate electricity that creates nerve impulseso Release chemicals that allow them to communicate with other neurons and with

muscles and glands

How nerve impulses occuro Nerve activation

At rest, the neuron has an electrical resting potential due to the distribution ofpositively and negatively charged chemicals(ions) inside and outside the neuron

When stimulated, a flow of ions in and out through the cell membrane reversesthe electrical charge of the resting potential, producing an action potential or

nerve impulse

The original distribution of ions is restored and the neuron is again at resto In detail...o Like other cells, neurons are surrounded by body fluids and separated from this liquid

environment by a protective membrane

o This cell membrane is like a selective sieve, allowing certain substances to pass throughion channels into the cell while refusing or limiting passage to other substances

o Ion channel is literally a passageway or channel in the membrane that can open to allowions to pass through

o The chemical environment inside the neuron differs from its external environment insignificant ways, and the process whereby a nerve impulse is created involves the

exchange of electrically changed atoms called ions

o In salty fluid outside the neuron are positively charged sodium ions and negativelycharged chloride ions


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o Inside the neuron are large negatively charged protein molecules and positively chargedpotassium ions

o The high concentration of sodium ions in the fluid outside the cell together with thenegatively charged protein ions inside results in an uneven distribution of positive and

negative ions that makes the interior of the cell negative compared to the outside

o This internal difference of around 70 millivolts is called the neurons resting potentialo At rest it is called the state of polarization

The Action Potential

Alan Hodgkin and Andrew Huxley found that if they stimulated the neurons axon with a mildelectrical stimulus, the interior voltage differential shifted suddenly from -70millivots to +40

millivolts

These scientists forced a action potentialo Sudden reversal in the neurons membrane voltage during which the membrane voltage

momentarily moves from -70 to +40 millvoltso The shift from negative to positive voltage is called depolarization

The scientists found that the key mechanism is the action of sodium and potassium ion channelsin the cell membrane

In a resting state, the neurons sodium and potassium channels are closed and theconcentration of sodium ions is 10x higher outside the neuron than inside it

But when a neuron is stimulated sufficiently, nearby sodium channels open up Attracted by the negative protein ions inside, positively charged sodium ions flood into the axon

creating depolarization

In a reflex action to restore the resting potential, the cell closes its sodium channels andpositively charged potassium ions flow out through their channels restoring the negative restingpotential

Eventually the excess sodium ions flow out of the neuron and the escaped potassium ions arerecovered

Figure 3.2 page 72 Once an action potential occurs at any point on the membrane, its effects spread to adjacent

sodium channels and the action potential flows down the length of the axon to the axon

terminals

Immediately after an impulse passes a point along the axon, however, there is a recovery periodas K+ ions flow out of the interior

During this absolute refractory period, the membrane is not excitable and cannot generateanother action potential

This places an upper limit on the rate at which nerve impulses can occur In humans it is about 300 impulses / second


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Its all or nothing

All or nothing lawo Action potentials occur at a uniform and maximum intensity or they do not occur at allo The negative potential inside the axon has to be changed from -70 to -50 (the action

potential threshold) by the arrival of sodium ions into the axon before the actionpotential will be triggered

o Changes in the negative resting potential that do not reach the -50 millivolts actionpotential threshold are called graded potentials

o Under certain circumstances, graded potentials caused by several neurons can add up totrigger an action potential in the postsynaptic neuron

For a neuron to function properly, sodium and potassium ions must enter and leave themembrane at the right rate

Myelin Sheath

Many axons that transmit information throughout the brain and spinal cord are covered by atube like myelin sheath

Fattish, whitish insulation layer derived from glial cells during development The myelin sheath is interrupted at regular intervals by the nodes of Ranvier where myelin is

either extremely thin or absent

Nodes make myelin sheath look like sausages placed end to end In unmyelinated axons, the action potential travels down the axon length like a burning fuse In myelinated axons electrical conduction can skip from node to node, and these great leaps

from one gap to another account for high conduction speeds of more than 300 km /hour

Most commonly found in the nervous systems of higher animals-in many nerve fibres, themyelin sheath is not completely formed after birth

Damage to myelin coating is apparent in people suffering from MSwhen immune systemattacks myelin sheath which disrupts timing of nerve impulses which ultimately end in paralysis

How neurons communicate: Synaptic Transmission

Nervous system is like a communications network and its action requires the transmission ofnerve impulses from one neuron to another

Famous scientists Santiago Ramon y Cajal and Charles Sherrington claimed that neurons wereindividual cells that did not make actual physical contact with each other but communicated at

an synapse, a functional connection between a neuron and its target

This was controversial until Otto Loewi showed that neurons released chemicals and thesechemicals carried the message from one neuron to the next cell in the circuit

o Called neurotransmission Synaptic cleft

o Tiny gap between the axon terminal of one neuron and the dendrite of the next neuron


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Neurotransmitters

Chemical substances that carry messages across the synapse to either excite other neurons orinhibit their firing

Process of chemical communication involves 5 stepso Synthesis

Chemical molecules are formed inside the neurono Storage

Then the molecules are stored in chambers called synaptic vesicles within theaxon terminals

o Release When an action potential comes down the axon, these vesicles move to the

surface of the axon terminal and the molecules are released into the fluid-filled

space between the axon of the sending (presynaptic) neuron and the membrane

of the receiving (postsynaptic) neuron

o Binding The molecules cross synaptic space and bindattach themselves to receptor

siteslarge protein molecules embedded in the receiving neurons cell

membrane

The receptor siteslook like lily pads have a specially shaped surface that fits aspecific transmitter molecule

o DeactivationExcitation, Inhibition, Deactivation

The binding of a transmitter molecule to the receptor site procures a chemical reaction that canhave 1 or 2 effects on the postsynaptic neuron

o It can have the reaction depolarize (excite) the postsynaptic cell membrane bystimulating the inflow of sodium or other positively charged ions

Neurotransmitters that create depolarization are called excitatory transmitters This stimulation alone or in combination with activity at other excitatory

synapses on the dendrites or the cell body may exceed the action potential

threshold and cause the post synaptic neuron to fire an action potential

o The chemical reaction created by the docking of a neurotransmitter at its receptor sitewill hyperpolarize the postsynaptic membrane by stimulating ion channels that allow

positively charged potassium ions to flow out of the neuron or negatively charge irons

such as chloride to flow in the neuron

This makes the membrane potential even more negative ( eg. Changing it from -70 to -72 millivolts)

Hyperpolarization makes it more difficult for excitatory transmitters at otherreceptor sites to depolarize the neuron to its action potential threshold of -55

millivolts

Transmitters that create hyperpolarization are inhibitory in their function


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A neurontransmitter can have an excitatory effect or inhibitory influence onneurons

Every neuron is constantly bombarded with excitatory and inhibitory neurontransmitters fromother neurons and the interplay of these influences determines whether the cell fires an action

potential

Even when receiving excitatory stimulus from several neurons at the same time, the action of aninhibitory transmitter from one presynaptic neuron may prevent the postsynaptic neuron from

reaching the action potential threshold

Inhibition allows tunes of neural activity and prevents an uncoordinated discharge of thenervous system eg. Seizure when large numbers of neurons fire off action potential in a runaway

fashion

Once a neurontransmitter molecule binds to its receptor, it continues to activate or inhibit theneuron until it is shut off/ deactivated

This occurs in 2 major wayso Deactivated by other chemicals located in the synaptic space that break them down into

their chemical components

o The deactivation mechanism is reuptake The transmitter molecules are reabsorbed into the presynaptic axon terminal When the receptor molecule is vacant, the post synaptic neuron returns to its

former resting state awaiting the next chemical stimulation

Specialized Transmitter Systems

The brain has systems that are uniquely sensitive to certain messages Because various systems in the brain recognize only certain chemical messages, they are

protected from cross- talk from other systems Each substance has a specific excitatory/inhibitory effect on certain neurons Two widespread neurotransmitters are simple amino acids, glutamate, glutamic acid, and

gamma-aminobutyric acidGABA

Glutamate and GABA are found throughout the central nervous system and therefore have arole in mediating all behaviours

Glutamate is excitatoryo Important role in learning and memoryo Improving memory cannot be as simple as enhancing glutamate activity since it has a

power excitatory effect

o Over activation of glutamate will induce seizure within the braincerebral cortexo GABA is an inhibitory neurotransmitter

Important for motor control and the control of anxiety Alcohol makes the brain more sensitive to GABA

Acetylcholine(ACh)o Involved in memory and muscle activityo Underproduction is thought to be important factor in Alzheimers disease


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o Excitatory transmitter at the synapses where neurons activate muscle cellso Drugs that block can prevent muscle activation eg. Botulismserious type of food

poisoning

Botulinum bacteria blocks the release of ACh from the axon terminal resulting ina potentially fatal paralysis of the muscles including the respiratory system

o The opposite is bite of black widow spider The venom produces a lot of ACh, resulting in violent muscle contractions

Dopamineo Mediates motivation, reward, feelings of pleasure, voluntary motor control and control

of thought processes

o Helps us understand diseases Parkinsons one group of dopamine producing neurons degenerate and die

As dopamine is lost in the affected brain areas, there is a accompanyingloss of voluntary motor control

o Anti psychotic drugs-attach to dopamine receptors and block dopamine from having itseffects

Effective in treating symptoms of schizophrenia For depression

o Depression involves abnormal sensitivity to serotonin, a neurotransmitter thatinfluences mood, eating, sleep, and sexual behaviour

o Antidepressant drugs increase serotonin activityo Prozac blocks the reuptake of serotonin from the synaptic space allowing serotonin

molecules to remain active and exert their mood-altering effects on depressed patients

o Other antidepressant drugs work by inhibiting the activity of enzymes in the synapticspace that deactivates serotonin by breaking it down into simpler chemicals-this

prolongs serotonin activity at the synapse

Endorphinso Reduce pain and increase feelings of well-beingo Bind to the same receptors as the ones activated by opiate drugs such as morphine

which produce similar psychological effects

o The ability of people to continue to function despite pain Neuromodulators

o These substances circulate through the brain and either increase/decrease thesensitivity of millions of neurons in their specific transmitters

oImportant in eating, sleep, stress

The Nervous system

Master control center 3 major types of neurons carry out the systems input, output, and integration functions


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o Sensory neurons Carry input messages from the sense organs to the spinal cord and brain

o Motor neurons Transmit output impulses from the brain and spinal cord to the bodys muscles

and organs

o Interneurons link the input and output functions outnumber sensory and motor neurons, perform connective/associative

functions within the nervous system eg. Recognizing a tune by linking the

sensory input from the song with the memory of that song stored in the brain

allow for complex higher mental functions, emotions, and behaviouralcapabilities

o broken down into several interrelated subsystems-2 major divisions Central nervous system

consisting of all the neurons in the brain and spinal cord Peripheral nervous system

Composed of all the neurons that connect the central nervous systemwith the muscles, glands, and sensory receptors

Peripheral Nervous System

Contains neural structures that lie outside the brain and spinal cord Helps carry out the input and output functions that are necessary for us to sense what is going

on inside and outside our bodies and to respond with our muscles and glands

2 major divisionso Somatic nervous systemo Autonomic nervous system

Somatic Nervous system

Consists of the sensory neurons that are specialized to transmit messages from the eyes, ears,other sensory/motor receptors, to send messages from the brain and spinal cord to the muscles

that control our voluntary movements

The axons of sensory neurons group together like many strands of rope to form sensory nerves,and motor neurons axons combine to form motor nerves

Inside the brain and spinal cord, nerves are called tracts Allows to read page...

Autonomic Nervous system

Bodys internal environmentcontrols the glands and ht smooth involuntary muscles that formthe heart, the blood vessels , and the lining of the stomach and intestines

Related to involuntary functions such as


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o Respirationo Circulationo Digestiono Motivationo Emotional behaviouro Stress responses

Two divisionso Sympathetic nervous system

Arousal function-tends to act as a total unit Eg. When youre in a stressful situation, the sympathetic nervous system

simultaneously speeds your heart so it can pump more blood to your muscles,

dilates your pupils so more light can enter the eye and improve your vision,

slows down your digestive system so that blood can be transferred to the

muscles, increases your rate of respiration so your body gets more oxygen and

mobilizes your body to confront the stressoraka flight or fight response

o Parasympathetic nervous system Slows down body processes and maintains/returns you to a state of rest Slows down heart rate

o Often affects the same organ/gland in opposing wayso These two divisions work together to maintain equilibrium in our internal organs and

maintain homeostasis

o Sexual function requires coordinated sequence of sympathetic and parasympatheticactivities

Central nervous system

The brain and spinal cordSpinal Cord

Most nerves enter and leave through the spinal cord Adult 40-45 cm long 2.5 cm diameter Spinal cord neurons protected by vertebraethe bones of the spine Central portion resembles H/butterfly

o Consists of grey coloured neuron cell bodies and their interconnectionso Surrounding the grey matter are white coloured myelinated axons that connect various

levels of the spinal cord with each other and with the higher centres of the brain

The back side of the spinal cord along its length are sensory nerves Motor nerves exit the spinal cords front side Spinal reflexes

o Simple stimulus response sequenceso Triggered at the level of the spinal cord without any involvement of the brain


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o Eg. Touch hot thing, sensory receptors in the skin trigger nerve impulses in sensorynerves that flash into spinal cord and synapse inside with interneurons

o Interneurons excite motor neurons that send impulses to your hand so that it pulls awayfrom the hot objectthis spinal cord and no brain is faster and helps prevent tissue

damage

The Brain

1.4 kilograms of protein, fat, fluid Most active energy consumer of all body organs-use 20% oxygen during resting state Brain never rests; rate of energy metabolism relatively constant day/night

o Dreaming makes you use more energy!Unlocking the secrets of the brain

Neuropsychological tests

Psychologists have developed these tests too measure verbal and non verbal behaviours that are known to be affected by particular

types of brain damage

used in clinical evaluations of people who may have suffered brain damage figure 3.9

Destruction and stimulation techniques

experimental studies are another useful method to study the brain researchers produce brain damage under controlled conditions in which specific nervous tissue

is destroyed with electricity, cold/heat, chemicals

They also can surgically remove some portion of the brain and study the consequences Also stimulate neuronsusually produce opposite effects

o a specific region in the brain can be stimulated by a mild electric current/chemicals thatexcite neurons

o electrodes can be permanently implanted so that the region of interest is stimulatedrepeatedly

o chemical stimulation studies a tiny tube is inserted into the brain so the chemical can goto the desired place

Wilder Penfield, pioneered brain surgery when he stimulated specific points of cortex with amild electrical current to map out the functions of the cerebral cortex on an awake patient

Electrical Recording

b/c electrodes record brain activity as well as stimulate it, we can listen to the electricalconversations occurring in the brain

measured by inserting small electrodes into particular areas/neurons of the brain


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scientists can tune in to crowd noise by placing larger electrodes on the scalp to measure theactivity of large groups of neurons with the electrencehalogram(EEG)

specific EEG patterns correspond to certain states of consciousness eg wakefulness and sleep detects abnormal electrical patterns that signal presence of brain disorders researchers use this to find change in the EEG record that accompany specific psychological

events like the presentation of a sensory stimulus-event related potentials (ERP)

Brain Imaging

CT scans( Computerized axial tomography)o Developed 1970so Use x ray technology to study brain structureso Highly focused beam of x-rays takes pictures of narrow slices of the brain

Computer analyzes the x rayed slices and creates pictures of the brains interiorfrom many different angles

Helps pinpoint where injuries or deterioration have occurred and this helps usknow the relationship between brain damage and psychological functioning PET scans(positron emission tomography)

o Measure brain activity including metabolism, blood flow, neurotransmitter activityo Based on glucose is the major nutrient of neuronso When neurons are active, they consume more glucoseo When preparing for scan, a harmless form of radioactive glucose is put in bloodstream

and travels to brain where it circulates in blood supply

o Energy emitted by the radioactive substance is measured by PET scan and a computeruses readings to get a color picture of the brain

o How active a neuron is depends on the amount of radioactive glucose that accumulatesin themwhere the glucose is concentrated

MRI(Magnetic resonance imaging)o Combines CT and PET scans and used to study brain structure and activityo Creates images based on how atoms in living tissue respond to magnetic pulses

delivered by the device

o More clear than CT scano Researcher places part of the body to be studied in hollow core of long magnetic

cylinder and exposes the atoms in the subjects body to a uniform magnetic field

o The field is altered and when the field is shut off the magnetic energy absorbed by theatoms in the tissue emits a small electrical voltage

o Picked up by detectors and relayed to a computer for analysiso Shows images in color and tells which chemicals are active in the tissueo fMRI can produce pictures of blood flow less than a second apart unlike conventional

MRI which is several minutes apart

The Hierarchical Brain: Structures and Behavioural Functions


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The Hindbrain

As spinal cord enters brain, it enlarges to form the structures that compose the stalklike brainstem

Attached to this stem is the other major portion of the hindbrain, the cerebellumThe Brain stem: Life support systems

Medulla is the first structure after leaving the spinal cordo 3.8cm long medulla has an important role in vital body functions such as heart rate and

respiration

o The medulla allows these functions to happen automaticallyo Damage to the medulla results in death or the need to be maintained on life support

systems

o High alcohol intake causes suppression of medulla activity=deatho Two-way fare for sensory and motor nerve tracts coming up from the spinal cord and

descending from the brain

o Most tracts cross over within medulla so the left side receives sensory input and exertsmotor control over the right side of the body

o Right side of the brain serves the left side of the bodyo -cross over is unsolved mystery

Ponsmeaning bridge in latino Lies above medullao Bridge carrying nerve impulses between higher and lower levels of the nervous systemo Clusters of neurons that help regulate sleep and involved in dreamingo contains motor neurons that control the muscles and glands of the face and necko like medulla, pons helps control vital functions, especially respiration

The Cerebellum: Motor Coordination Centre

look like a miniature brain attached to the rear of the brain stem directly above the pons wrinkled cortex is mainly grey cell bodies cerebellum concerns primarily with muscular movement coordination(timing and coordination)

but also plays a role in learning and memory

regulates complex changing movements that require very good timing-cats have goodcerebellum

alcohol easily disrupts the motor functions that the cerebellum controls intoxicated people cannot walk in a straight line or touch their nose with their index finger physical damage to the cerebellum results in

o severe motor disturbances characterized by jerky, uncoordinated movements,o the inability to perform habitual movements like walking

a tumor in this area of the brain will cause impairment in walking in a straight line, wideseparation in legs when walking and after a few days be unable to walk without assistance


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The Midbrain

Above the hindbrain is the midbraino Contains clusters of sensory and motor neuronso Sensory and motor fibre tracts that connect higher and lower portions of the nervous

system The sensory portion of the midbrain contains important relay centres for the visual and auditory

systems

Nerve impulses from the eyes and ears are organized and sent to forebrain structures involvedin visual and auditory perception

Contains motor neurons that controls eye movements-movement out of the corner of my eye-midbrain activity causes eyes to swing toward the source of movement

The Reticular Formation: The brains gatekeeper

Within the midbrain is a finger shaped structure that extends from the hindbrain up into thelower portions of the forebrain

Because of its resemblance to a net-reticulum, the reticular formation acts as a kind of sentryalerting higher centres of the brain that messages are coming and then either blocking those

messages or allowing them to go forward

The reticular formation has an ascending part, which sends input to higher regions of the brainto alert it and a descending portion through which higher brain centres can either admit or block

out sensory input

Has a central role in consciousness, sleep, and attentiono Therefore attracted a great deal of interest for psychologists

The ascending reticular formation rouses higher centres in the brain, preparing them to receiveinput from our sense organs

Without reticular stimulation of higher brain regions, sensory messages do not register inconscious awareness, even though the nerve impulses my reach the appropriate higher areas of

the brainas if the brain is not awake to notice them

Some painkillers work by deactivating neurons of the ascending reticular formation, producing astate of unconsciousness in which the sensory impulses that are usually experienced as pain

would not register

Also affects sleep, wakefulness, and attentiondamage to this area of brain can causepermanent coma

Attentiono Active process in which only meaningful sensory inputs get through to our

consciousness and other inputs have to be toned down or blocked out

o Other stimulation is toned down/blocked outo Descending reticular formation is key for this process

Serves as a kind of gate through which inputs are admitted and other inputs areblocked out by signals coming down from higher brain centres


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The forebrain

Difference between my brain and other animals is the size and complexity of myforebrain/cerebellum

Consists of two large cerebral hemispheres-left and right side hat wrap around the brain stemthe way you might wrap your hands around the bowl of a spoon

Outer portion has thin covering/cortexThe Thalamus: The brains sensory switchboard

Located above the midbrain Resembles two small footballsone in each hemisphere Important sensory relay stationswitchboard that organizes inputs from sense organs and

routes them to the appropriate areas of the brain

Visual, auditory, body senses-balance and equilibrium all have major relay stations in thethalamus

o Nerve tracts from the sensory receptors are sent to specific areas of the thalamuso There they synapse with neurons that send the messages on their way to the higher

brain regions that create our perceptions

Disrupted thalamic functioning can make victims very confusedschizophrenic peopleBasal Ganglia: Movement

Surrounding and enveloping the thalamus is a group of 5 distinct structures collectively knownas the basal ganglia

Important for voluntary motor control Unlike how the cerebellum controls reflexive, automatic, and rapid movements, the basal

ganglia is important for deliberate and voluntary control of movement, especially initiating

voluntary movements

Parkinsons diseaseo The neurons that supply dopamine to the basal ganglia degenerate and dieo B/c dopamine is lost from the basal ganglia, it functions improperly, and the ability to

perform voluntary movement is lost

o Initially signs are small tremors of the hands and head but becomes shaking and jerkymovements and jerky movements occur only when there is assistance involveda push

o When no dopamine is present =complete paralysisHypothalamus: Biological Drives

Under the thalamus are tiny groups of neuron cell bodies that lie at the base of the brain, abovethe roof of the mouth

Important in controlling basic biological drives like sexual behaviour, temperature regulation,eating, drinking, aggression and expressiving emotion


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Important connections with endocrine systembodys collection of hormone producing glandso Through connection with pituitary glandmaster gland that controls other glands in the

system) the hypothalamus directly controls many hormonal secretions that regulate

sexual development and behaviour, metabolism, and reactions to stress

The Limbic System: Memory and goal-directed behaviour

Go up brain =limbic system ; set of structures deep within cerebral hemispheres Shaped like wishbone are important with the hypothalamus Helps coordinate behaviours needed to satisfy motivational and emotional urges that arise in

the hypothalamus

Involved in memory Organize instinctive activities in lower animals such as mating, attacking, feeding, fleeing from

danger

If this system was injured, I would be unable to carry out organized sequences of actions tosatisfy my needs

Two key structureso Hippocampus

Involved in forming and retrieving memories damage can result in severe memory impairment for recent events and an

inability to transfer information from short term memory to long term memory

o Amygdala Organizes emotional response patterns, especially aggression and fear Electrical stimulation can cause fear or aggression Key part of a larger control system for anger and fear that also involves other

brain regions Can produce emotional responses without the higher centres of the brain

knowing that we are emotionally aroused

May show evidence that we have unconscious emotional responses James olds and Peter Milner studied effects of electrical stimulation of the reticular formation in

rats

o Accidentally an electrode was implanted in the hypothalamusclaimed they found thepleasure center of the brain

o Hypothalamus brain area for motivation and reward

Hypothalamus

Electrical stimulation of the hypothalamuso activates neurons within that brain region ando activates axons that are going from neuron cell bodies in the midbrain to a limbic

structure called the nucleus accumbens


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o It is the activation of axons going to the nucleus accumbens that is important for rewardand motivation

Roy wise shown the reward value of electrical stimulation can be amplified or diminished bydrugs that enhance or block dopamine actions within the nucleus accumbens

Also linked with the rewarding and motivating effects of abusive drugs by stimulating therelease of dopamine in the nucleus accumbens of the limbic system

Alain Graton found that naturally occurring rewards like food and sex cues/behaviour leads tothe release of dopamine from axon terminals in the nucleus accumbens

o Therefore not only do abusive drugs/preferred foods activate the nucleus acumens butcues that reliably predict this has a similar effect

The Cerebral Cortex: Crown of the Brain

2/3 cm thick sheet of greyunmyelinated cells forming the outermost layer of the brain-crowing achievement of brain evolution

Cortex constitutes 80% of brain tissue Essential for human quality of living b/c the cortex is wrinkled, a great amount of cortical tissue is compressed into a relatively small

space inside the skull

75% cortexs total surface area lies within its fissures/canyonlike foldso Three of these fissures are important

One large fissure runs up the front and along the top of the brain, dividing it intoright and left hemispheres

Another major fissure within each hemisphere divides the cerebrum into frontand rear halves

Third fissure runs from front to rear along the side of the brain These landmarks allowed neurologists to divide each hemisphere into four lobes

Frontal Parietal Occipital Temporal

Speech and skeletal motor functions are in the frontal lobe The area governing body sensations is located in the parietal lobe immediately behind the

central fissure which separates the frontal and parietal lobes

Visual area is in the occipital lobe at the back of the brain Messages from the auditory system are sent to a region in the top of the temporal lobe Large areas not associated with sensory or motor functions -3/4 of cortex is called association

cortex

The Motor Cortex

Controls muscles involved in voluntary body movements


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Lies at the rear of the frontal lobe adjacent to the central fissure Each hemisphere governs movement on the opposite side of the body Specific body areas are represented in different parts o the motor cortex and the amount of

cortex devoted to each area depends on the complexity of the movements carried by the body

part

Torso less cortical tissue than fingerSensory cortex

Specific areas of the cortex receive input from our sensory receptors Other than taste and smell, at least one specific area in the cortex corresponds to a sense Somatic sensory cortex

o Receives sensory input that gives rise to our sensations of heat, touch, cold, and oursense of balance and body movement

o Lies in the parietal lobeo Organized in an upside down fashion, feet being represented near the top of the braino The regions sensory sensitivity corresponds to the amount of cortical tissueo Mainly fingers, lips, tongue

Notice that the organization of the sensory cortex is such that the body structures it serves lieside by side with those in the motor cortex, an arrangement that enhances sensory motor

interactions in the same body area

Hearing and sight in auditory area which lies on the surface of the temporal lobe at the side ofeach hemisphere

o Each ear sends messages to the auditory areas of both hemispheres to the loss of onetemporal lobe has little effect on hearing

The representation of the face in the somatosensory cortex may be upside down with the chintowards the top

Speech Comprehension and production

Two areas are responsible for understanding and production of speecho Wernickes area

In temporal lobe involved with language comprehension Carl Wernicke 1874 discovered damage to this cortical region left patients

unable to understand written/spoken speech

o Brocas area Frontal lobe Necessary for normal speec production Use grammar and finding the correct word Paul Broca found that damage to this frontal area left patients with the ability to

understand but not express themselves in words or sentences


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Association Cortex

found within all lobes of the cerebral cortex involved in the highest level of mental functions including perception, language and thought silent areas electrically stimulating them does not create sensory/motor responses Damages can result in loss of functions such as speech, understanding, thinking, and problem

solving

Known as evolutions missing link-75% of cerebral cortex and is responsible for our superiorcognitive abilities

Importance shown in people who suffer from agnosiain ability to identify familiar objectso Oliver Sacksfound associative neurons responsible for linking two types of information

Info sent to visual cortex to info stored in other areas concerning the nature ofthe object

The frontal Lobe: The Human Difference]

Consists of a lot more in our brain than in animals Responsible for self awareness, planning, initiative, responsibilitymysterious least understood

part of the brain

Phineas Gage 1848o A spike went and damaged his brain he psychologically came out as a different person

Damage in the frontal lobe acuses a loss in the ability to plan and carry out a sequence ofactions and judge the order in which a series of events has occurred

Also involved in emotional experienceo People with normal brains there is increased activity in the frontal cortex when these

people are experiencing feelings of happiness, sadness etc A region in the frontal lobe called pre-frontal cortex is more attentively studied

o Located behind the forehead performs executive functions Goal setting, judgement, strategic planning and impulse control, allow

behaviour in a adaptive fashion

o Damage/disorder to this area causes people to be oblivious to the future consequencesof their actions and seem to be only aware of the immediate consequences

o Also dysfunction leads to violent murderers to plead not guilty because they are insaneo During 1940-1950s a lot of emotional behaviour disturbed people had prefrontal

lobotomieshad bad side effects of no goal setting therefore not used anymore and

drugs are used instead

Hemispheric Lateralization: The left and right brains

The left and right cerebral hemispheres are connected by a broad white band of myelinatednerve fibres

Corpus callosum is a neural bridge that acts as a major communication link between the twohemispheres and allows them to function as a single unit


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Lateralization refers to the relatively greater localization of a function in one hemisphere or theother

o Patients who suffered various types of brain damages showed that the left side of thebrain is for verbal abilities and speech as well as math and logic

When Brocas or Wernickes speech areas are damaged, aphasiapartial or total loss of theability to communicate

o Eg. Meaning of words, communicating or both When right hemisphere is damaged, person cannot perform perceiving spatial relations well

o Recognizing faces or forget a well travelled route or mistaking wife for hato Mental imagery, musical and artistic abilities, and ability to perceive and understand

spatial relationships are for right side of brain

EEG studies have shown that the right hemisphere is more active when negative emotions likesadness anger are experienced and positive emotions are accompanied by greater left

hemisphere activation

The split brain : Two minds in one body?

Paitents who suffer from a form of epilepsy in which a seizure beings as an uncontrolledelectrical discharge of neurons on one side of the brain spreads to the other hemisphere

Cutting nerve fibers of the corpus callosum, they could prevent the seizure from spreading toother hemispheres

Some of the fibres of the optic nerve from each eye cross over at the optic chiasm and travel tothe opposite brain hemisphere

Fibres transmit messages from the right side of the visual field project to the left hemisphere;fibres from the visual fields left half project of the right hemisphere

When the corpus callosum is cut, visual input to one hemisphere can be restricted by projectingthe stimulus to either the right side of the visual field or left side

o When words were send to right side of visual field so info sent to left hemisphere,subjects describe verbally what they saw and could write what they saw with right hand

but if words were flashed to left side of visual field and sent to right hemisphere then

they cannot describe what they saw

o Look at page 100 for hand experimentswitch hands then could name what it iso Psychologists have suggested that we call the conscious self resides in the left

hemisphere because it is based on our ability to verbalize about the past and present

Important to know that the brain is working together-integrated system so although there issome localization right brain teaching would not show drastic results

Hemispheric lateralization of language

Evolutionary significance that our genetically closest relative has larger left hemisphere those who use both areas of the brain for language have larger corpus callosum left hemisphere also used for sign languagedoes not need to be verbal


20/20

studies show right hemisphere does not lack language ability because both hemispheres areinvolved in speaking reading and listening

study shows men greater left hemisphere activation while women show activity in bothPlasticity in the Brain

Neural plasticityo Ability of neurons to change in structure and function

2 aspectso Effects of early experience on brain development

Fetal alcohol syndrome-exposure to high levels of alcohol disrupts braindevelopment and produces lifelong mental and behaviour damage

Stimulating early environment had larger neurons and more dendrite branchesand greater concentrations of acetylcholinerat pup study

MRI shows string musicians who do elaborate movements on the strings withtheir left hands had larger right hemisphere somatosensory areaearlier =morecortical change

Chronic alcoholism inhibits production of new neural connections in thehippocampus impairing memory, learning, and other cognitive functions

Cultural factors affect brain developmentchinese pictoral characters process inright hemisphere we might expect less left hemisphere lateralization of

language among speaker of Chinese than English who are alphabet

Brain goes through own personal evolutiono Recovery from brain damage

Natural reorganization-allows neurons to take over functions of those that died Brain damage suffered early in life is less devasting than as an adult

Greater availability of synapses may help to explain why children can recoverfrom brain damage more quickly than adults

Synaptic pruning Cell death is in every neuron and therefore adults have less synapses than

children

Elizabeth Gould first evidence of neurogensis tracked newly devloepd neuronsfrom birthplace in subcortical tissue

They migrated upward along myelinated nerve tracts into the association areasof the cerebral cortex where they sprouted axons and extended them toward

existing neuronsnew neurons responsible for higher order mental functionslike complex learning and memory-primate study

Chapter 3 Biological Foundations of Behaviour

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Transcript of Chapter 3 Biological Foundations of Behaviour