Psyc100: Biology of Behaviour (Chap. 4) Terms and Definitions
Central nervous system: The brain and spinal cord.
Spinal cord: A long, thin collection of nerve cells attached to the base of the brain and running
the length of the spinal column.
Nerve: A bunch of fibres that transmits information between the central nervous system and
the body’s sense organs, muscles, and glands.
Peripheral nervous system: The cranial and spinal nerves; the part of the nervous system
peripheral to the brain and spinal cord.
Cranial nerve: A bundle of nerve fibres attached to the base of the brain; conveys sensory
information from the face and head and carries messages to muscles and glands.
Spinal nerve: A bundle of nerve fibres attached to the spinal cord; conveys sensory information
from the body and carries messages to muscles and glands.
Brain stem: The ‘stem’ of the brain, including the medulla, pons, and midbrain.
Cerebral hemisphere: The largest part of the brain; covered by the cerebral cortex and
containing most recently evolved parts of the brain.
Cerebellum: A pair of hemispheres resembling the cerebral hemisphere but much smaller and
lying beneath and in back of them; controls posture and movements, especially rapid ones.
Vertebra: One of the bones that encase the spinal cord and constitute the vertebral column.
Meninges: The three-layered set of membranes that enclose the brain and spinal cord.
Cerebrospinal fluid (CSF): The liquid in which the brain and spinal cord floats; provides a shock
Blood-brain barrier: A barrier between the blood and the brain produced by the cells in the
walls of the brain’s capillaries; prevents some substances from passing the blood into the brain.
Cerebral cortex: The outer layer of the cerebral hemispheres of the brain, approximately 3mm
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 portions of the central nervous system that are abundant in axons rather
than the cell bodies of neurons. The colour derives from the presence of the axons’ myelin
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 provides support for neurons and supplies
them with some essential chemicals.
Dendrite: A tree-like part of a neuron on which other neurons form synapses.
Dendrite spine: A small bud-like protuberance on the surface of a neuron’s dendrite.
Soma: A cell body; the largest part of a neuron.
Axon: A long, thin part of a neuron attached to the somas; divides into few or many branches
ending in terminal buttons.
Terminal button: The rounded swelling at the end of the axon of a neuron; releases a
Neurotransmitter: A chemical released by the terminal buttons that causes the postsynaptic
neuron to be excited or inhibited.
Myelin sheath: The insulating material that encases most large axons.
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 neurotransmitter.
Ion: A positively or negatively charged particle; produced when many substances dissolve in
Ion channel: A special protein molecule located in the membrane of a cell; controls the entry or
exit of particular ions.
Ion transporter: A special protein molecule located in the membrane of a cell; actively
transports ions in and out of the cell.
All-or-none law: The principle that once an action potential is triggered in an axon, it is
propagated – without getting smaller – to the end of the axon.
Sensory neuron: A neuron that detects changes in the external or internal environment and
sends information about these changes to the central nervous system. Motor neuron: A neuron whose terminal buttons form synapses with muscle fibres; when an
action potential travels down its axon, the associated muscle fibres twitch.
Synapse: The junction between the terminal button of one neuron and the membrane of a
muscle fibre, a gland, or another neuron.
Presynaptic neuron: A neuron whose terminal buttons form synapses with and excites or
inhibits another neuron.
Postsynaptic neuron: A neuron with which the terminal buttons of another neuron form
synapses and that is excited or inhibited by that neuron.
Synaptic cleft: A fluid-filled space between the presynaptic and postsynaptic membranes; the
terminal button releases a neurotransmitter into this space.
Neurotransmitter receptor: A special protein molecule located in the membrane of the
postsynaptic neuron that responds to molecules of the neurotransmitter.
Reuptake: The process by which a terminal button retrieves the molecules of a
neurotransmitter that it has just relaxed; terminates the effect of the neurotransmitter on the
receptors of the postsynaptic cell.
Glutamate: The most important excitatory neurotransmitter in the brain and spinal cord.
GABA: “gamma-amino butyric acid”; the most important inhibitory neurotransmitter of the
brain and spinal cord.
Barbiturate: A drug that causes sedation; one of the several derivatives of barbituric acid.
Anti-anxiety drug: A ‘tranquilizer’ which reduces anxiety.
Benzodiazepine: A class of drugs having anxiolytic (‘tranquilizing’) effects.
Acetylcholine (ACh): A neurotransmitter found in the brain, spinal cord, and parts of the
peripheral nervous system; responsible for muscle contraction.
Botulinum toxin: A drug that prevents the release of acetylcholine by terminal buttons.
Black widow spider venom: A drug that stimulates the release of acetylcholine by terminal
Neostigmine: A drug that enhances the effects of acetylcholine by blocking the enzyme that
destroys it. Nicotine: A drug that binds with and stimulates acetylcholine receptors, mimicking the effects
of this neurotransmitter.
Curare: A drug that binds with and blocks acetylcholine receptors, preventing the
neurotransmitter from exerting its effects.
Monoamine: A category of neurotransmitters that includes dopamine, norepinephrine, and
Dopamine (DA): A monoamine neurotransmitter involved in control of brain mechanisms of
movement and reinforcement.
Parkinson’s disease: A neurological disorder characterized by tremors, rigidity of the limbs,
poor balance, and difficulty in initiating movements; caused by the degeneration of a system of
Norepinephrine (NE): A monoamine neurotransmitter involved in alertness and vigilance and
control of REM sleep.
Serotonin: A monoamine neurotransmitter involved in the regulation of mood; in the control of
eating, sleep, and arousal as well as in the regulation of pain.
LSD: “Lysergic acid diethylamide”; a hallucinogenic drug that blocks a category of serotonin