Topic 3: APs, synapses and neurotransmitters Flashcards
Nerve impulse: ‘resting’
When a neuron is not firing; its cell membrane is polarized.
Describe what a polarized membrane is
It has an electrical gradient (difference) between the outside of the cell membrane and the inside. The outside contains more sodium (Na+ ions).
A neuron remains resting/polarized until…?
there is a stimulus.
What happens when a stimulus reaches the neuron’s threshold?
- Sodium ion channels on the resting neuron’s membrane open suddenly and
- Allow the Na+ that was on the outside to go rushing into the cell.
Def: complete depolarization
When a threshold is reached, complete depolarization of the axon results because the neuron continues to open Na+ channels all the way long the cell membrane of the axon.
Complete depolarization/wave of depolarization- AKA (2)
Nerve impulse; action potential (AP)
Def: refractory period
The time when the neuron is busy returning everything to the normal polarized (resting) state; usually doesn’t respond to incoming stimuli.
Def: saltatory conduction
APs jump from Node of Ranvier to Node of Ranvier.
What does the speed of conduction depend on (regarding saltatory conduction)? (2)
- Axon diameter and
2. If it is myelinated
Why is saltatory conduction important? (2)
- Increases nn conduction velocity without having to dramatically increase axon diameter (ie not be huge)
- S.C. requires much less energy than continuous conduction bc the sodium ion pumps only need to operate at the nodes of Ranvier and not along the whole axon. (ie more energy efficient)
Demyelinating pathologies/in relation to saltatory conduction?
Often accompanied by debilitating fatigue because cell transmission is more slow and less energy efficient. Eg- MS.
NN impulse propagation in myelinated vs non-myelinated fibers/difference?
In unmyelinated: the impulse is propagated as a continuous wave of depolarization, spreading along the axon.
In Myelinated: The impulse ‘jumps’ from node to node (faster and more energy efficient [saltatory conduction])
Synapse- list the components (3) and define
Consists of:
- presynaptic neuron
- snaptic cleft
- post-synaptic neuron
Synapse = where an AP is transmitted from one neuron to another neuron.
Where can synapses occur? (2)
- Btwn neurons and mms
2. Btwn neurons and glands
Def: neurotransmitter and its fxn
A chemical released by a presyaptic neuron.
It diffuses across the synaptic cleft to stimulate or inhibit the postsynaptic neuron.
