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Neurology > Neurophysiology > Flashcards

Neurophysiology Flashcards

1
Q

What part of the neuron generates the action potential?

A

Axon hillock

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2
Q

Describe the generation of an action potential.

A
  1. Resting membrane potential = -70mV
  2. Passively depolarises until it reaches ‘threshold’ = -60mV
  3. Na and K channels open
  4. Sodium flows into cell first causing upstroke and then Na channel closes
  5. K channel still open, K flows out repolarising the neuron
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3
Q

Why is the neuron ‘leaky’ for current?

What does the body do to overcome this?

A

Neuron membrane has a low resistance

Envelop neuron in myelin sheath

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4
Q

What cell produces myelin?

A

Oligodendrocytes in CNS

Schwann cells in PNS

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5
Q

Describe the flow of the action potential through a normal neuron.

A

Saltatory conduction

Action potential jumps from rode of ranvier to node of ranvier

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6
Q

Describe neurotransmission.

A
  1. Precursor synthesised to neurotransmitter and stored in vesicles.
  2. Action potential depolarises cell which opens Ca channels causing Ca influx
  3. Ca influx releases neurotransmitter by exocytosis
  4. Neurotransmitter in synaptic cleft acts on post-synaptic receptor
  5. Neurotransmitter inactivated, recycled into presynaptic neuron or diffuses away
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7
Q

What features of the pre and post synaptic neuron aid neurotransmission?

A

Active zone: terminal ends of presynaptic neuron have high concentration of neurotransmiter vesicles

Post-synaptic density: post-synaptic neuron have high concentration of receptors

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8
Q

What is the excitatory neurotransmitter?

How does it cause excitation?

A

Glutamate

Activates post-synaptic cation receptors which depolarise the cell and contribute to the action potential

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9
Q

What is the inhibitory neurotransmitter?

How does it cause inhibiton?

A

GABA

Activates post-synaptic anion receptors which polarise the cell and inhibit the action potential

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10
Q

What do EPSP and IPSP stand for and what are they?

A

EPSP = excitatory post synaptic potential = positive change in membrane potential (depolarise) caused by influx of cations (Na)

IPSP = inhibitory post synaptic potential = negative change in membrane potential caused by influx of anions (Cl)/efflux of cation (K)

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11
Q

Describe the two processes used by the cell body to integrate the inputs.

Which of these is more important?

A

Spatial summation: number of inputs determines output

Temporal summation: frequency of inputs determines output

Both are used together and are of equal importance

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12
Q

Polarisation of the neuron membrane generates an action potential.

T/F?

A

False

Depolarisation of the action potential by influx of Na generates an action potential

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13
Q

Depolarisation of the neuron membrane generates an action potential.

T/F?

A

True

Depolarisation of the action potential by influx of Na generates an action potential

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14
Q

Which of these would be inhibitory and which would be excitatory?

  1. Sodium channel agonist
  2. Sodium channel antagonist
  3. Potassium channel agonist
  4. Potassium channel antagonist
A
  1. Excitatory
  2. Inhibitory
  3. Inhibitory
  4. Excitatory

Sodium channels cause influx of sodium which depolarises the cell and contributes to the action potential

Potassium channels cause efflux of potassium which polarises the cell and inhibits the action potential

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15
Q

What are the two main classes of neurotransmitter receptor?

What are their main differences?

A

Ionotropic (receptor part of channel it controls, aka ligand gated ion channels)

Metabotropic (receptor distinct from channel it controls, aka G-protein coupled receptor)

Ionotropic receptors are faster and generally excitatory by generating action potentials

Metabotropic receptors are slower and generally inhibitory and moduate neuronal activity

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16
Q

What are the two classes of glutamate receptor?

What are their main differences?

A

non-NMDA: simple Na/K transfer, fast transmission

NMDA: Na/K/Ca and other ion transfer, slower

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17
Q

What neurotransmitter receptor is the most important in neurotoxicity?

Why?

A

NMDA

It allows Ca influx. Ca influx contributes to neurotoxicity

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18
Q

What are the two classes of GABA receptor?

What are their main differences?

A

GABA-A: controls ionotropic Cl channel

GABA-B: controls metabotropic K channel

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19
Q

Where is the neurotransmitter glycine found?

Is it inhibitory or excitatory?

A

Found in interneurons in spinal cord

Inhibitory (inhibits antagonist muscle contraction during flexion)

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20
Q

What is graded potential?

A

Changes in membrane potential which vary in size (not all or none as with action potentials), they are the summation of the impulses coming in through the dendrites

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21
Q

Where are the soma of upper and lower motor neurons and where do they synapse?

What is the basic function of these neurons?

A

Upper motor neuron: soma in brain and extend to ventral horn where they synapse

Lower motor neuron: soma in ventral horn and extend to muscles

Lower motor neuron contracts the muscles and upper motor neuron modulates contraction

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22
Q

What are the two types of motor neuron?

What are their functions?

A

aMN - contract extrafusal muscle fibres and generate force

yMN - contract the intrafusal muscle fibres in the muscle spindle in parallel with aMN which prevents them going slack as the extrafusal muscle fibres shorten

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23
Q

Where in the ventral horn would you find a neuron which supplies an

  • axial muscle
  • flexor muscle
  • extensor muscle
  • distal muscle?
A

Axial: medial
Distal: lateral

Extensor: ventral (posterior)
Flexor: dorsal (anterior)

24
Q

What is a motor unit?

A

aMN + muscle it innervates

25
Q

Where would you find a motor unit which innervates few muscle fibres?

Where would you find a motor unit which innervates many fibres?

What is the significance of this?

A

Few: extraocular eye muscle

Many: antigravity/leg muscles

The fewer muscle fibres a motor unit innervates, the more precise the movement is, but the movement is weak (extraocular eye muscles)

The more muscle fibres a single motor unit innervates strengthens the movement but it doesn’t allow fine movement (leg muscles)

26
Q

What are the 3 types of muscle fibre?

What are their main differences?

A

Type I

  • energy from oxidative phosphorylation
  • appear dark due to myoglobin
  • slow contraction
  • fatigue resistant (good for marathons)

Type IIa

  • energy from oxidative phosphorylation
  • appear red
  • fast contraction
  • fatigue resistant (not as much as T1)

Tupe IIb

  • energy from glycolysis
  • appear pale as poorly vascularised
  • fast contraction
  • faitgue easily (but good for sprinting)
27
Q

What is the muscle spindle?

A

Sensory organ contained in the muscle which sense stretch of the muscle through its intrafusal muscle fibres

28
Q

Describe the myotatic reflex.

A

Stretch of intrafusal fibres in muscle spindle

Sensed by sensory afferents in muscle spindle which activate an aMN in the spinal cord

aMN contracts the muscle preventing further stretch

29
Q

What is the Golgi tendon organ?

A

Sensory structure at muscle-tendon junction which assesses muscle tension

30
Q

Pain is produced when a sensory neuron is overloaded by a strong stimulus.

T/F?

A

False

Pain is produced when a strong and potentially damaging stimulus is strong enough to activate high threshold units (HTU)

It is not produced by increased low threshold unit (LTU) activity

31
Q

What are the 4 main types of sensory neuron?

Describe their functions and how myelinated they are.

A

Aa - proprioception - lots of myelin/very fast conduction

Aß - mechanoreceptor - some myelination/fast conduction

Aδ - temperature and acute pain (e.g. stab) - little myelination/moderate conduction

C - slow pain (e.g. ache) - unmyelinated

32
Q

What is the receptive field?

A

Area over which one neuron can sense a stimulus

33
Q

Where on the body might you find neurons with large/small receptive fields?

A

Small: areas with lots of sensory neurons (e.g. finger)

Large: areas with few sensoty neurons (e.g. back)

34
Q

Name 3 low threshold mechanoreceptors and their function.

A

Merkel cell: mechanoreceptor

Meissner corpsucle: vibration

Pacinian corpsucle: pressure

35
Q

What sensory nerve fibres are nociceptors?

What sort of pain do they cause?

A

Aδ - acute pain (stab, prick)

C - slow pain (ache, throbbing)

36
Q

Where in the spinal cord does

  • pain enter
  • touch enter
  • proprioception enter?
A

Pain: anterior dorsal horn

Touch: posterior dorsal horn

Proprioception: ventral horn

37
Q

What information does the dorsal column medial lemniscus (DCML) transmit?

A

Fine touch and conscious proprioception

38
Q

What information does the spinothalamic tract transmit?

A

Pain, temperature, pressure

39
Q

Describe the path of an action potential through the dorsal column medial lemniscus (DCML).

A

First order neuron: skin > medulla

Second order neuron: medulla (crosses midline) > thalamus

Third order neuron: thalamus > somatosensory cortex

40
Q

Describe the path of an action potential through the spinothalamic tract.

A

First order neuron: skin > dorsal horn

Second order neuron: dorsal horn (crosses midline) > thalamus

Third order neuron: thalamus > somatosensory cortex

41
Q

What tract have the fasciculus cuneatus and fasciculus gracilis?

What are these?

Where are they in relation to each other?

A

Dorsal column medial lemniscus (DCML)

Fasciculus cuneatus: carries sensory information from upper limb through DCML (lateral to gracilis)

Fasciculus gracilis: carries sensory information from lower limb through DCML (medial to cuneatus)

42
Q

Describe the path of an action potential through the trigeminal system.

A

First order neuron: skin > trigeminal ganglion

Second order neuron: trigeminal ganglion (thourgh trigeminal lemniscus) to thalamus

Third order neuron: thalamus to somatosensory cortex

43
Q

Where on the trigeminal ganglion do pain/temperature and touch synapse?

A

pain/temperature: spinal nucleus

touch: sensory nucleus

44
Q

What happens to the region of the somatosensory cortex supplying an amputated arm?

A

It is utilised by other sensory inputs (remapping)

45
Q

What happens to sensory information after it is delivered to somatosensory cortex?

A

Integrated in the posterior parietal cortex

46
Q

What helps integrate synergistic flexion and extension?

A

Interneurons

(e.g. extension of arm stretches flexor muscles which would induce the myotatic reflex. interneurons inhibit the myotatic reflex of flexor muscles during extension)

47
Q

What is the flexor reflex?

What occurs in the other limb when this occurs?

A

Noxious stimuli causes flexion and inhibition of extension by excitatory interneurons (flexor reflex)

Contralteral limb is extended and flexion is inhibited to aid posture (crossed extensor reflex)

48
Q

What information does the corticospinal transmit?

A

Fine motor movement

49
Q

Describe the path of an action potential through the corticospinal tract.

A

UMN: motor cortex (cross midline at decussation of the pyramids) > anterior horn

LMN: anterior horn > muscle

50
Q

Name the pyramidal tracts.

What are their functions?

A

Corticospinal: conduct impulses to the spinal cord

Corticobulbar: conduct motor impulses to the cranial nerves

51
Q

Name the lateral descending tracts.

What are their general function?

A

Corticospinal tract
Rubrospinal tract

Cause movement

52
Q

Name the ventromedial descending tracts.

What are their general function?

A

Reticulospinal tract
Vestibulospinal tract
Tectospinal tract

Modulatory, control movement

53
Q

Function of reticulospinal tract.

A

Enhances antigravity muscles and posture

54
Q

Function of rubrospinal tract.

A

Help control limb flexor muscles

Soma in red nucleus

55
Q

Function of vestibulospinal tract.

A

Inputs from vestibular labyrinth and cerebellum

Controls posture and head movements

56
Q

Function of tectospinal tract.

A

Has inputs from retina

Influence neck/upper tunk muscles in response to visual stimulus

57
Q

Which sensory fibre has both afferent and efferent functions?

What is its efferent function?

A

Some C fibres

Release proinflammatory mediatiors (substance P, CGRP) with pain

Neurology (11 decks)

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