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The Nervous System - Coggle Diagram
The Nervous System
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Action Potential
The temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse.
All-or-nothing
A principle that states that all stimuli above a certain threshold value will generate the same size action potential, regardless of the strength of the stimulus.
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Cell Body
The region of the neurone that contains the organelles, notably the nucleus and the rough endoplasmic reticulum.
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Cholinesterase
An enzyme responsible for the hydrolysis of acetylcholine in the postsynaptic neurone.
Dendrites
Short, branched extensions of the cell body that receive nerve impulses from other neurones.
Depolarisation
A sudden, temporary change in the membrane potential of a neurone in response to the transmission of a nerve impulse. The inside of the axon is less negative than the outside and the potential difference reaches approximately +40 millivolts (mV).
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Effector
An organ, tissue or cell that produces a response to a stimulus.
Grey Matter
The darker tissue of the CNS which lies centrally and consists of relay and motor neurone cell bodies.
Hyperpolarisation
A decrease in the membrane potential of an axon (due to the opening of K+ channels), so that it is even more negative than the resting potential.
Meninges
Three membranes that cover the brain and spinal chord: the pia mater, arachnoid mater, and dura mater.
Motor Neurone
A neurone that carries nerve impulses from the CNS to the effectors via the ventral root.
Myelin Sheath
An electrically insulating layer consisting of the membranes of Schwann cells. It increases the speed of nerve impulses.
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Nerve Net
The simplest form of nervous system found in Cnidarians. It consists of interconnected nerve cells with short extensions allowing a response to a limited number of stimuli.
Neurotransmitters
Chemicals that are used for communication between neurones and their target cells, Neurotransmitters are stored in synaptic vesicles in the presynaptic neurone and released into the synaptic cleft.
Nodes of Ranvier
Gaps between adjacent Schwann cells in the myelin sheath at which action potentials can occur.
Oscilloscope Trace
A trace showing the change in electrical potential across the membrane of an axon at each stage of an action potential.
Organophosphates
Chemical substances that act as cholinesterase inhibitors, preventing the hydrolysis of acetylcholine in the postsynaptic neurone and resulting in continuous stimulation of the neurone. They can be used as insecticides.
Peripheral Nervous System (PNS)
Pairs of nerves that originate from the CNS and carry nerve impulses into and out of the CNS.
Postsynaptic Neurone
The neurone after the synapse which contains specific receptor proteins on its membrane, complementary to the neurotransmitter.
Presynaptic Neurone
The neurone before the synapse which releases neurotransmitters from synaptic vesicles into the synaptic cleft.
Psychoactive Drugs
Excitatory drugs (e.g. amphetamine) that stimulate the release of neurotransmitters such as adrenaline.
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Reflex
A rapid, automatic response to a sensory stimulus by the body. It serves as a protective mechanism.
Reflex Arc
The pathway of neurones involved in a reflex action:
Stimulus --> receptor --> sensory neurone --> relay neurone --> motor neurone --> effector --> response
Refractory Period
The time period after an action potential during which further action potentials are prevented. This ensures that action potentials can only be propagated in one direction.
Relay Neurone
A neurone located in the spinal cord that links the sensory neurone to the motor neurone.
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Saltatory Propagation
The process by which a nerve impulse is propagated along a myelinated neurone. Depolarisation occurs at the nodes of Ranvier and action potentials jump from node to node, speeding up transmission.
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Sensory Neurone
A neurone that carries nerve impulses from the receptors to the CNS via the dorsal root.
Sodium-Potassium Pump
A carrier protein found in the plasma membrane of an axon. It actively transports three sodium ions (Na+) out of the axon for every two potassium ions (K+) that pumps into the axon.
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Synaptic Cleft
A small gap between neurones across which a nerve impulse is transmitted via neurotransmitters.
Synaptic End Bulbs
The end of an axon that is bulbous shaped and contains synaptic vesicles filled with neurotransmitters.
Synaptic Vesicles
Secretory vesicles located in the presynaptic neurone that store neurotransmitters. Upon fusion with the presynaptic membrane, their contents are released into the synaptic cleft.
White Matter
The lighter tissue of the CNS which surrounds grey matter and consists of myelinated axons.