neurons Flashcards
what are neurons?
- nerve cells
- in nervous system
- specialised for communication
- connect with each other and with other excitable cells
- many different types
- structure is related to function
what are the parts of a neuron?
- dendrites
- cell body
- axon
- axon terminals
where do input signals enter the neuron?
dendrites
where do output signals leave the neuron?
the axon terminals
name different types of neuron?
- Purkinje cell (cerebellum)
- Spinal interneuron
- Sensory neuron (dorsal root)
- Pyramidal cell (cerebral cortex)
- Motor neuron (spinal cord)
- Bipolar cell (retina)
what is a membrane potential?
potential difference across the cell membrane
with membrane potential, is the inside or outside of the cell more negative?
inside
what is the range of the membrane potential?
20-90mV
what is a word to describe the membrane in regard to membrane potential?
polarised
what determines the resting membrane potential?
- diffusion of K+ from cell interior through K+ channels
- the sodium potassium pump also contributes by moving unequal amounts of Na & K (3 Na+ out / 2 K+ in)
what could alter the membrane potential?
applying an electric current (stimulus)
what could alter the membrane potential?
applying an electric current (stimulus)
what does hyperpolarisation do to the membrane potential?
moves it away from 0
what does depolarisation do to the membrane potential?
moves it closer to 0
what happens if membrane potential overshoots 0?
the polarisation is reversed
what is an action potential?
occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize- it is an all or none event
describe the sequence of an action potential
- AP is all or none, amplitude is independent of stimulus
At ‘threshold’: - voltage-gated Na+ channels open
- Na+ diffuse in depolarisation
‘Peak’ - Na+ channels close
- voltage-gated K+ channels open
- K+ diffuse out repolarisation
Resting membrane potential
how does local anaesthetic work?
stops nerve conduction by blocking Na+ channel
how does local anaesthetic work?
stops nerve conduction by blocking Na+ channel
what is the refractory period?
- After an AP is initiated, the neuron cannot generate another AP until the first one has ended
- This period of inexcitability is called the refractory period
- It is due to the inactivation of voltage-gated sodium channels
- Action potentials cannot add together; they are all-or-none events
how is an action potential propagated?
- An AP in one section of axon depolarises adjacent ‘resting’ parts of the axon
- The AP is regenerated further along the axon
- Action potentials travel along the axon as waves of depolarisation
action potentials travel along the length of the axon, but why does it not travel back along the axon?
the refractory period
what increases when the diameter of the axon increases?
the speed of the action potential propagation
describe giant axons
- Their speed of AP propagation is too slow to enable the fast postural reflexes present in vertebrates
- Vertebrates evolved a means of increases AP conduction speed, whilst decreasing axon diameter
what is myelination in relation to action protection?
- Wrapping a layer of myelin round an axon greatly increases the AP conduction speed
- Maximum speed of conduction = 120m.s-1
what does myelination do?
- Myelin is a fatty layer
- Formed by wrapping the membranes of ‘glial’ cells round the axon
- This in effect ‘insulates’ the axon, and improves conduction
what are nodes of ranvier?
- The myelin sheath is interrupted at intervals by ‘nodes of Ranvier’
- Here, the axon membrane is exposed to the ECF, and ion flow can occur
what is saltatory conduction?
the way an electrical impulse (action potential) skips from node to node down the full length of an axon
