Chapter 15 Flashcards
benefits of a myelinated neuron
the axon is myelinated so sodium and potassium can only move across at the Nodes of Ranvier
what’s the conduction in myelinated neurons called
saltatory conduction
effect of temperature on speed of transmission
higher temp speeds up the rate of transmission
effect of axon diameter on the speed of trasnmission
the wider the axon the faster the rate of transmission
Resting potential
the neurone is not transmitting an impulse so the cell remains polarise and the electrochemical gradient is maintained by the active transport of sodium ions (out) and potassium ions (in) and the relative membrane permeability favouring the outwards movement
resting potential difference
-70mV
Generation and transmission of an action potential
A stimulus that exceeds threshold will cause depolarisation of the neurone and stimulate an action potential. Depolarisation occurs when the distribution of the charge reverses as more sodium ions flow into the axon via facilitated diffusion due to more sodium voltage-gated channels opening. As more sodium channels open more sodium channels can open due to the depolarisation creating positive feedback. The membrane permeability for sodium then decreases causing sodium to stop diffusing into the axon. Simultaneously the membrane permeability for potassium increases causing more potassium to diffuse out of the axon, returning the potential difference back to resting. During repolarisation there is a temporary overshoot where too much potassium can diffuse out which then levels off back to the resting potential.
Refractory Period
neurone is unresponsive due to the membrane being temporarily impermeable to sodium and potassium
Stages at a cholinergic synapse
an AP arrives at the end of the presynaptic axon (synaptic knob) causing an influx of calcium ions. This stimulates the release of acetylcholine from vesicles. ACh diffuses across the synaptic cleft and binds with complementary receptors on the post synaptic membrane. This triggers a rapid influx of sodium ions, depolarising the cell. If the threshold is reached, an action potential in the post synaptic membrane will be stimulated. Acetylcholinesterase then hydrolyses the ACh so it can be reabsorbed and re used
Spatial Summation
action potentials from different presynaptic neurones reach the threshold causing an action potential
Temporal summation
occurs when several action potentials arrive in quick succession, reaching threshold and triggering an action potential
Synapses at neuromuscular junctions
ACh attaches to receptors on the muscle fibre membrane, if the threshold is reached the muscle fibre will depolarise triggering an action potential. The AP moves along the muscle membrane and T-tubules allow the transmission of the action potential into the muscle cells causing the muscle to contract
Myoglobin definition
respiratory protein found in slow-twitch muscle fibres that has a high affinity for O2
colour of slow-twitch fibres
darker due to more myoglobin
colour of fast-twitch fibres
lighter due to less myoglobin
