Impulses and NMJ Flashcards by Anjaly Joseph

What is the resting potential of a neuron?

-70mV

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Describe the stages of the generation of an AP (5)

Polarised (Na+ / K+ ATPase pump and K+ movement out)
Depolarised (influx of Na+ and +ve feedback)
Repolarised (efflux of K+)
Hyperpolarised (continued efflux of K+)
Reestablishing the resting potential (K+ channels close and Na+ / K+ pump)

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Generation of AP: what happens at a membrane potential of +30mV? (2)

Voltage-gated Na+ channels CLOSE

Voltage-gated K+ channels OPEN

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Define absolute refractory period

Period whereby a 2nd AP cannot be produced

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Define relative refractory period

Period whereby a 2nd AP is only produced if the stimulus is greater than usual

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What are the purposes of the refractory periods? (3)

Produce discrete/ separate signals
Propagate signals in one direction
Limit the number of APs

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How can you increase conduction speed along a neuron? (2)

Increase its diameter

- Insulate axon (myelination)

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What is saltatory conduction?

When APs jump from one node of Ranvier to the next along a myelinated neuron

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What is the conduction velocity in a small-diameter unmyelinated fibre?

0.5m/s

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What is the conduction velocity in a large-diameter myelinated fibre?

100m/s

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What is an excitatory synapse?

Membrane potential of PSN brought closer to threshold

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What is an inhibitory synapse?

Membrane of PSN driven further from threshold / stabilised at resting potential

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What happens in an EPSP?

Depolarisation

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What happens in an IPSP?

Hyperpolarisation - through entry of Cl- or leaving of K+

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What are the two ways to integrate synaptic input?

Temporal summation (from same presynaptic cell at different times)
Spatial summation (inputs occur at different locations on postsynaptic neuron)

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Define pain

Unpleasant sensory & emotional experience usually caused by tissue damage

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What is acute pain?

Pain < 12 weeks

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What is chronic pain?

Pain > 12 weeks

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Define nociceptive pain

Activation of nociceptors caused by damage to non-neuronal tissue

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Define neuropathic pain

Caused by primary lesion/ dysfunction of nerves, brain or spinal cord

What is hyperalgesia?

When bradykinin and prostaglandin E2 reduce the nocioceptor AP threshold –> more sensitive to stimuli

What are C fibres?

Nociceptor fibres that respond to thermal, mechanical and chemical stimuli.

What type of pain do C fibres carry?

Slow pain: diffuse, dull, aching, burning

What are A-delta fibres?

Nociceptor fibres that respond to mechanical stimuli over a certain threshold.

What type of pain do A-delta fibres carry?

Fast pain: well localised, sharp, stinging, pricking

What is substance P?

Peptide neurotransmitter that remains bound to receptors for longer so transmit long-lasting pain

What modulates pain?

Periaqueductal grey - opioid receptors activated under extreme stress, inhibiting substance P --> reduced pain sensation

Define analgesia

Selective suppression of sensation. | Consciousness isn't lost.

Define anaesthesia

Uniform suppression of all sensation. | Consciousness sometimes lost.

What is a motor unit?

An AMN and all the skeletal muscle fibres it innervates

Where on the spinal cord are AMNs controlling distal muscles located?

Laterally

Where on the spinal cord are AMNs controlling proximal muscles located?

Medially

What is a muscle spindle?

Consists of intrafusal fibres and stretch receptors

What do muscle spindles detect?

Muscle stretch | Speed of stretch

What parts of the muscle spindle are contractile?

The two ends of the muscle spindle (central portion is non-contractile)

What do gamma motor neurons innervate?

The two ends of the intrafusal fibres

What innervates the middle 1/3 of the muscle spindle?

Type 1a afferent sensory fibres

What innervates the superior and inferior 1/3 of the muscle spindle?

Type 2 afferent sensory fibres

What does activating gamma motor neurons do?

Increases muscle sensitivity to stretch

What does alpha-gamma coactivation achieve?

Keeps central region of the muscle spindle taut during muscle contraction so info about muscle length is continously available

What do Golgi tendon organs detect?

Muscle tension

Where are Golgi tendon organs found?

In junction of skeletal muscle and tendon

What do Golgi tendon organs do?

Afferent impulses from golgi tendon organ result in inhibition of AMNs in the same muscle

Which posses slower afferent fibres, muscle spindle or Golgi tendon organ?

Golgi tendon organ

What is a monosynaptic reflex arc?

Direct connection between sensory and motor neurons w/out interneurons

What is a polysynaptic reflex arc?

Have one/more interneurons between sensory and motor neurons

Define reciprocal innervation

Activation of AMNs to one muscle whilst simultaneously inhibiting AMNs to its antagonistic muscle

What is the withdrawal reflex?

Painful stimuli: - activates flexor muscles - inhibits extensor muscles Allows the affected leg to move away from stimulus

What is the crossed extensor reflex?

Painful stimuli causes on the contralateral leg: - activates extensor muscles - inhibits flexor muscles Allows contralateral leg to support body's weight