Ch 48 Ap Bio

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absolute refractory period

Back 1

period after Na+ channels close and they cannot be opened again until resting potential has been reestablished; about 0.25 to 1.0 milliseconds

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acetylcholine

Back 2

neurotransmitter; found in brain and neuromuscular junctures

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action potential

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a self propagating nerve impulse

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axon

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an extension of a neuron which carries information away from the neuron; usually only one of these per neuron

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brain

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ganglia in the head

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cell body; soma

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part of a neuron which contains the nucleus and most of the organelles

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dendrite

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an extension from a neuron which receives information from other cells or from the environment; many may be present

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depolarization

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when the charge difference across a neuron membrane is less than -70 millivolts

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dopamine

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neurotransmitter; small group of neurons for muscular activity; lack of this causes Parkinson's disease

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effectors

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organs that carry out responses

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electrically gated

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ion channels which open and close when electrically stimulated

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endorphins

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neurotransmitter known as the brains natural morphine

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excitatory

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an increase in the likelihood that a nerve will fire an impulse ; caused by depolarization

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glutamate

Back 14

neurotransmitter; an amino acid; excitatory transmitter; found at more brain synapses than any other

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hyperpolarization

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condition produced by K+ ions leaving the inside of a neuron which produces a greater charge difference than -70 millivolts; it is less likely for an impulse to be created

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inhibitory synapse

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tend to dampen or tune multiple signals in the brain; sharpens the brain to certain stimuli and dulls it to others

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interneurons

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nerve cells that relay messages between neurons

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local potential

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when a neurons cell body or dendrite receives a stimulus opening Na+ channels and allowing them into the cell which lessens the charge difference across the membrane

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medulla

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most obvious part of the hindbrain in a fish

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microglia

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scavenger cells of dying neurons and other debris in the central nervous system

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mininges

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three layers of membranes which protect the brain and spinal cord

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myelin sheath

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a fatty layer around the axons of some neurons; formed by glial cells; acts as an insulator

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nerve impulse

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electrical signal which travels down an axon

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neuroglia (glial cells)

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cells which support neurons and convey food and other molecules to them; about ten times more of these than neurons in the human body, oligo- ones produce myelin

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neuromuscular junctions

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synapses between neurons and skeletal muscle cells

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neurotransmitter

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a molecule which can cause a chemically gated channel to open and create a local potential

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nitric oxide

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neurotransmitter; a gas; aids learning and memory; causes erection of penis by relaxing muscles in blood vessel walls

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nodes of Ranvier

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gaps in the myelin sheath

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norepinephrine

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neurotransmitter; functions during stress;

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nuclei

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located in the medulla; ganglion like clusters of neurons within the central nervous system

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parasympathetic system

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one of two divisions of the autonomic nervous system; slows things down, conserving energy

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posterior colliculi

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analyze and relay information coming from the ear via the auditory nerve

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postsynaptic membrane

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the membrane of the cell which is receiving the impulse after it crosses the synaptic cleft

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presynaptic membrane

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membrane of an axon at its terminal end just before a synapse

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receptors

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part of the nervous system found in the sense organs that perceive stimuli

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recognition memory

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any memory that can be recalled by a conscious effort

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reflex arcs

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responsible for extremely rapid responses such as an eye blink and a knee jerk

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repolarization

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the falling phase of a nerve impulse when the K+ ions rush out of the neuron and the inside of the cell regains its negative charge

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resting potential

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in a resting neuron the difference of charge across the membrane is about -70 millivolts; the inside being negatively charged with respect to the outside

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saltatory conduction

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rapid conduction of action potential along myelinated axons

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Schwann cells

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glial cells which form myelin in the peripheral nervous system

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serotonin

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neurotransmitter; produced in brain stem; sensory perception, regulation of body temperature, sleep etc

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spinal nerves

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in humans, 31 pairs of these nerves connect the spinal cord to various parts of the body

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stimuli

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changes in the body's internal or external environment, such as blood chemistry, sound, or light

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synapse

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a junction where an axon terminal lies close to the next cell in line

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threshold

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the level of depolarization which must be reached before an impulse is generated by a neuron