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Chapter 4: Biology and Behaviour
xBrain contains btw 10billion and 100billion nerve cells and as many helper cells (take care of
important support and housekeeping functions)
xThere are many types of nerve cells (shape, size, chemicals they produce)
xPierre Flourens emphasized that different parts of the nervous system were responsible for
xDonald Hebb considered how individual nerve cells are organized into larger units; proposed
principles of organization by which these units were organized, suggested they could
generate memory, thought, decision making.
xNerve cells of the brain are organized in modules: clusters of nerve cells that communicate
xParticular modules have particular functions
Central nervous system: The brain and spinal cord
Spinal cord: A long, thing collection of nerve cells attached to the base of the brain and
running the length of the spinal column. Controls simple reflexes
Nerve: A bundle of nerve fibres that transmit info btw the central nervous system and the
body's sense organs, muscles, and glands.
Peripheral nervous system: The cranial and spinal nerves; that part of the nervous system
peripheral to the brain and spinal cord. Consists of the nerves that connect the CNS with
the sense organs, muscles, glands.
xThe human brain has 3 major parts: The brain stem, the cerebellum and the cerebral
Brain stem: The "stem" of the brain, including the medulla, pons and mid-brain. One of the
most primitive regions of the brain. Primarily controls physiological functions and automatic
Cerebral hemispheres: The largest part of the brain; covered by the cerebral cortex and
containing parts of the brain that evolved most recently.
Cerebellum: A pair of hemispheres resembling the cerebral hemispheres but much smaller
and lying beneath and in back of them; controls posture and movement (coordination),
especially rapid ones.
Vertebrae: One of the bones that encase/protect the spinal cord and constitute the
Meninges: The 3-layered set of membranes that enclose the brain and spinal cord
Cerebrospinal fluid: The liquid in which the brain and spinal cord float; provides a shock
absorbent cushion. Fills the space btw the 2 meninges.
Cerebral cortex: The outer layer of the cerebral hemispheres of the brain; approx 3mm
thick. Memories are stored, plans are formulated/executed.
Grey matter: The portions of the central nervous system that are abundant in cell bodies of
neurons rather than axons. The colour appears grey relative to white matter
White matter: The portion of the central nervous system that are abundant in axons rather
than cell bodies of neurons. The colour derives from the presence of the axons' myelin
xBulges on the brain called gyri (singular gyrus); large grooves called fissures
xFissures and gyri expand the amount of surface area of the cortex and increase the number
of nerve cells it can contain
xSense organs detect change in the environment and send signals through the nerves to the
xBrain sends signals to muscles (causing behaviour) and glands (producing adjustments in
internal physiological processes)
Spinal nerves: A bundle of nerve fibres attached to the spinal cord; conveys sensory info
from the body and carries the message to the muscles and glands. Serves all the body
below the neck
Cranial nerve: A bundle of nerve fibres attached to the base of the brain; convey sensory
info from the face and head and carried messages to muscles and glands.
Neuron: A nerve cell; consists of a cell body with dendrites and an axon whose branches end
in terminal buttons that synapse with muscle fibres, gland cells, or other neurons.
Glial cell: A cell of the central nervous system that gives support for neurons and supplies
them with some essential chemicals.
Soma: A cell body; the largest part of the neuron. Contains mechanisms that control
metabolism and maintenance of cell. Receives messages from other neurons.
Dendrites: A treelike part of a neuron in which other neurons form synapses. Transmit info
Axon: A long, thin part of the neuron attached to the soma; divides into a few or many
branches, ending in terminal buttons. Carries message away from soma. These messages
called action potentials, consist of brief changes in the electrical charge of the axon.
Dendrite spine: A small bud-like protuberance on the surface of a neuron's dendrite.
Appear on neurons of the brain.
Terminal button: The rounded swelling at the end of the axon; releases transmitter
substance. Connect to dendrites, dendrite spine, soma and the axon of another neuron.
Transmitter substance: A chemical released by the terminal buttons that causes the
postsynaptic neuron to be excited or inhibited. Aka Neurotransmitters
Myelin sheath: The insulating material that encases most large axons. Increases speed of
action potential and prevents the scrambling of messages.
xMyelin: part protein, part fat--produced by special cells, the glial cells, that individually wrap
themselves around segments of the axon.
xMultiple sclerosis: immune system attacks its own body. Hard and damages tissue of brain
and spinal cord. Attacks protein of myelin sheath. Suffer from sensory/motor impairments.
xMembrane of axon is electrically charged. When resting- charged at -70millivolts with
respect to the outside
Action potential: A brief electrochemical event that is carried by an axon from the soma of
the neuron to its terminal buttons; causes the release of a transmitter substance.
xElectrical charge of an axon occurs because of unequal distribution of + and - charged
particles from inside the axon and in the fluid surrounding it
Ions: A positively or negatively charged particle; produced when many substances dissolve
Ion channel: A special protein molecule located in the membrane of a cell; controls the
entry or exit of particular ions.
Ion transporters: A special protein molecule located in the membrane of a cell; actively
transports ions into or out of the cell using the energy resources of the cell.
xOutside of membrane is positively charged and vice-versa
xWhen an axon is resting, its ion channels are closed-ions cannot move in or out
xOpening of channels permits positively charged sodium ions to enter (reverses membrane
potential at that place). This reversal causes nearby channels to open, which produces
xAs soon as the charge reverses, the ion channels close and another set of channels open for