A2 OCR Biology Key Terms and Definitions Nerves

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Central Nervous System
The brain and the spinal cord.
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Peripheral Nervous System
All of the nervous system apart from the brain and spinal cord, made up of nerves (containing axons and dendrons of neurones).
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Neurone
A nerve cell, specialised for the rapid transmission of electrical impulses called action potentials.
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Action Potential
A fleeting reversal of the resting potential, generally to about +40mV inside, which sweeps along an axon.
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Motor Neurone
A neurone that transmits action potentials from the central nervous system to an effector.
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Dendrites
Short cytoplasmic processes that transmit action potentials from other neurones to a motor neurone.
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Axon
A long cytoplasmic process that transmits action potentials away from the cell body of a neurone.
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Transmitter Substance
A chemical that is released by a presynaptic neurone and diffuses across the synaptic cleft to slot into receptors on the postsynaptic neurone.
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Sensory Neurone
A neurone that transmits action potentials from a receptor to the central nervous system.
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Dendron
A long cytoplasmic process that transmits action potentials towards the cell body of a neurone.
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Intermediate Neurones (or Relay Neurones)
A neurone in the central nervous system that transmits nerve impulses between a sensory neurone and a motor neurone.
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Schwann Cells
A cell that wraps itself around an axon producing a multiple layer of membranes, called myelin.
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Myelin Sheath
An insulating layer around an axon or dendron.
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Myelin
A mixture of proteins and phospholipids forming a whitish insulating sheath around many nerve fibres, which increases the speed at which impulses are conducted.
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Node of Ranvier
A gap in the myelin sheath.
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Reflex Arc
The path travelled by an action potential from a receptor to an effector to bring about a reflex action.
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Reflex Action
A fast, stereotyped response to a stimulus, not involving conscious thought.
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Spinal Reflex Arc
Reflex arc in which the nerve impulses are carried into and out of the spinal cord (without involving the brain).
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Effector
An organ that carries out an action in response to a stimulus, such as a muscle that contracts or a gland that secretes a substance.
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Perineurium
Protective connective tissue surrounding neurones.
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Resting Potentials
The potential difference, usually about -70mV inside, across the plasma membrane of a neurone while it is not transmitting an action potential.
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Voltage-Gated Channel
An ion channel in a plasma membrane that responds to a change in voltage (potential difference) across the membrane by opening or closing.
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Electrochemical Gradient
A stiuation in which the concentration and charge on one side of a membrane differs from that on the other.
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Depolarisation
The loss or reversal of the resting potential.
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Repolarisation
The recovery of the resting potential following depolarisation.
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Refractory Period
The time immediately following an action potential when an axon cannot transmit another action potential, because of the time needed to restore the resting potential.
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Saltatory Conduction
Conduction of an action potential along a myelinated neurone by 'jumping' from one node of Ranvier to the next.
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Synapse
An area where a nerve impulse can be passed from one neurone to another, or from a neurone to an effector.
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Synaptic Cleft
The tiny gap between two neurones, or between a neurone and an effector, at a synapse.
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Noradrenaline and Acetylcholine (ACh)
Transmitter substances.
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Dopamine and Glutamate
Transmitter substances that are found in the brain.
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Neuromuscular Junction
A synapse between a motor neurone and a muscle fibre.
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Acetylcholinesterase
An enzyme that breaks down (hydrolyses) acetylcholine to acetate and choline.
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Nicotine
A substance found in cigarette smoke, whose molecules have a similar shape to part of the acetylcholine molecule, and that can slot into acetylcholine receptors on postsynaptic membranes.
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Card 2

Front

All of the nervous system apart from the brain and spinal cord, made up of nerves (containing axons and dendrons of neurones).

Back

Peripheral Nervous System

Card 3

Front

A nerve cell, specialised for the rapid transmission of electrical impulses called action potentials.

Back

Preview of the back of card 3

Card 4

Front

A fleeting reversal of the resting potential, generally to about +40mV inside, which sweeps along an axon.

Back

Preview of the back of card 4

Card 5

Front

A neurone that transmits action potentials from the central nervous system to an effector.

Back

Preview of the back of card 5
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