Chapter 4.docx

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14 Apr 2012

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Chapter 4 : Biology of Behaviour
Brain and components
- 10-100 billion nerve cells in our brain along with helper cells.
- Flourens emphasized different parts are responsible for different functions
- Donald Hebb considered nerve cells are organized into larger units (modules) which are
connected to other
Structure of the nervous system
- Brain has three major functions
1) controlling behaviour
2)processing and retaining information we receive from the environment
3) regulating the body’s physiological needs
- Central Nervous system (brain and spinal cord)
- Spinal cord: long thing collection of nerve cells attached to base of brain and running down
spinal column
- Nerves: bundles of fibres that transmit information in and out of the central nervous system
from organs
- Peripheral nervous system: the cranial and spinal nerves that are attached to the brain and
spinal cord
- Cranial nerves: bundle of nerve fibres attached to the base of the brain from face and head
- Spinal nerve: bundle of nerve fibres attached to spinal cord and carries messages to muscles
and glands
Three major parts:
1) brainstem: includes medulla, pons, midbrain
2) cerebral hemispheres: largest part of brain, covered by cerebral cortex
3) cerebellum: attached to the back of the brain stem, controls and coordinates movements
- Vertebrae: column of hollow bones encase the spinal cord and constitute the vertebral column
- Meninges: the tgree layered set of membranes that enclose the brain and spinal cord
- The brain floats in a clear liquid called cerebrospinal fluid
- Blood-brain barrier: barrier between blood and brain produced by cells in brains capillaries
prevents toxic
- Cerebral cortex: outer layer of the cerebral hemispheres of the brain 3mm thick, Grey matter:
portions of CNS that are abundant in cell bodies of neurons rather than axons.
- White matter: portion abundant in axons, colour derives from myelin sheaths on axons
- Fissure: large grooves and gyrus: the little bumps
Celles of nervous system
- Neurons/nerve cells: bring sensory information to the brain, store memories, control activity of
the muscles
- Glia: a cell of the central nervous system that provides support for neurons and supplies them
with some essential chemicals. They work as immune system, help neuron stay in place
- Dendrites: tree like growths attached to body of nerve cell teceive message from other neurons
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- Denritic spines: a small bud-like protuberance on the surface of a neuron’s dendrite
- Soma: cell body is the largest part of neuron
- Axon: a long thing part of a neuron attached to the soma divides into a few branches in the
terminal end
- Terminal buttons: located at the ends of the twigs that branch off from their ends
- Neurotransmitter: chemical secreted by terminal end, secreted whenever action potential is
sent down
- Myelin sheath: protein and fat like substance around axon increasing the speed and insulating
- Multiple sclerosis: affects the myelin causing neurological symptoms
Action Potential
- Brief electrochemical event that is carried by an axon from the soma of the neuron to its
terminal buttons, causes release of transmitter substance. Basically reversal of electrical charge
- At resting potential = -70 milivolts
- Ion: positively or negatively charged particles. Produced when many substances dissolve in
- Ion channels: can open or close
- Ion transporters: work like pumps using energy resources of the cell to transport particular ions
into or out of axon
- Negative inside, positive outside.
- Some ion channels open causing sodium ions to enter, and changes the electrochemical charge.
This causes other channels to open and creates a wave of action potential. Charge is restored by
potassium ions out of the axon.
- Ion transporters try to get the normal balance of ions again
- All-or-none law: once an action potential is triggered in an axon, it is propagated without getting
- Sensory neurons: neurons that receive information from sensory organs such as eyes tell other
- Motor neurons: a neuron whose terminal buttons form sunapses with muslce fibres tell it to
- Synapse: junction between the terminal button of one neuron and membrane of muscle fibre,
gland or neuron
- This is how neurons communicate with each other
- Presynaptic neuron: the one that sends the message
- Postsynaptic neuron: receives the message
- Muscle contractions depend on the rate of axon being fired
- Exitatory synapse: excited the post synaptic neuron by transmitting chemicals that have
molecules that attach to postsynaptic membrane and activates it. Receptor molecules are either
excitatory or inhibitory: suppresses it
- Excitatory: permit sodium to enter neuron and inhibitory allows potassium to leave cell
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- Synaptic cleft: fluid filled space b/w pre and postsynaptic membranes; terminal button releases
transmitter here
- Neurotransmitter receptor: special protein molecule located in the membrane of postsynaptic
- Reuptake: process by which a terminal button retrieves the molecules of transmitter substance
that it has just released, terminates the effect of the transmitter on the receptor of the
postsynaptic neuron.
Drugs and Behaviour
- Sap, fruit, leaves bark plants release chemicals mainly to kill insects but also benefits human
- How can they affect the neurons? Stimulate or inhibit neurotransmitters, mimick, or interefere
with reuptake, or block these effects.
- 1) stimulating or inhibiting the release of neurotransmitter
- They can either release it continuously or inhibit it’s release
- 2) stimulating or blocking post synaptic receptors
- They may mimic in a way that it stimulates the receptors when they fit in the right positions, or
they might simply block the neurotransmitter from getting to the receptor and inhibiting it as a
- 3) inhibiting reuptake
- Basically doesnt allow the neurotransmitter to get back to where it was released from so in this
case it keeps stimulating the post-synaptic membrane
Neurotransmitters, their actions, drugs that affect them
- In the brain there are two main transmitters: glutamate that has excitatory effects and GABA
that has inhibitory effects. Other transmitters have modulating effects (wakefullness, vigilance,
facilitate learning)
- Excitatory transmitter in the spinal cord and brain.
- NMDA receptor plays a critical role in the effects of environmental stimulation on the
developing brain
- NMDA is deactivated by alcohol which accounts for when drinkers dont have any memory of
what they did
- Most drugs that depress behaviour, causes relaxation, sedation, or loss of consciousness act on
GABA receptor
- Barbiturates: drug causes sedation and effects the GABA receptor increasing its sensitivity to
- Ethyl alcohol is the common ingredient in alcohol that makes it addictive
- Anti anxiety dugs: a tranquilizaer which reduces anxiety working on GABA receptor
- Benzodiazepine: a class of drug having anxiolytic effects
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