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Phase 1 Medicine (JA) > Neuro physiology > Flashcards

Neuro physiology Flashcards

1
Q

What is the distribution is the distribution of K+, Na+, Cl-, Ca2+ on the inside and outside of a neuron?

A 
Ki = 140mmol/l, Ko = 4mmol/l
Nai = 14mmol/l, Nao = 142mmol/l
Cli = 8mmol/l, Clo = 107mmol/l
Cai = 0.1mmol/l, Cao = 2.5mmol/l
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2
Q

Name the 4 main phases of the initiation of an action potential.

A

1) Liminal stimulus - stimulus-associated Na+ channels causes Na+ channels to open, and approach the threshold potential of around -60mV
2) Threshold - reaching threshold opens voltage-gated Na+ channels causing membrane depolarisation
3) Repolarisation - reaching +30mV inactivates voltage-gated Na+ channels, and causes voltage-gated K+ channels to open and K+ efflux
4) Hyperpolarisation - Voltage-gated K+ channels are slow to close causing hyperpolarisation of the membrane

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3
Q

What is the absolute refractory period?

A

Occurs between phase 2 and 3 of the action potential. Voltage-gated Na+ channels are inactivated due to depolarisation, and no stimulus can open them again. Prevents the action potential going backwards.

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4
Q

What is the relative refractory period?

A

Occurs at stage 4, or hyperpolarisation. When the cell is hyperpolarised, voltage gated K+ and Na+ channels are closed, but could open again with a big enough stimulus. Stimulus would need to be bigger because membrane is hyperpolarised.

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5
Q

What is resting membrane and threshold potential of a neurone?

A

-70mv and -55mv, respectively

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6
Q

What is saltatory conduction?

A

Propagation of an action potential down a myelinated neuron axon. Nodes of ranvier boosts the action potential.

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7
Q

How fast is the transmission of an action potential down an axon which is myelinated?

A

100m/sec

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8
Q

What is summation?

A

Individual stimuli are all subthreshold, and individually cannot cause an action potential. All together, they can take the membrane potential over threshold and generate and action potential.

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9
Q

Name two types of summation.

A

1) Spatial

2) Temporal

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10
Q

Name two types of synapse.

A

1) electrical (fast)

2) Chemical (neurotransmitters)

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11
Q

Explain synaptic transmission.

A

1) Action potential reaches terminal bulb of the presynaptic neuron
2) Causes voltage gated Ca2+ channels to open and flow down the gradient (2.5 > 0.1)
3) Ca2+ bind to receptors on the vesicles
4) Causes vesicles to bind to membrane and release contents into the synaptic cleft

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12
Q

What is excitatory post synaptic potential?

A

When the summation of all the potentials from all the neurones brings the membrane potential over the threshold to propogate the action potential in the post synaptic neuron.

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13
Q

What is inhibitory post synaptic potential?

A

A stimulus which causes the post synaptic neuron to hyperpolarise, mean that the membrane potential moves away from the threshold potential (-55mv). Therefore no action potential is generated in the post synaptic neuron.

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14
Q

What is pre-synaptic inhibition?

A

When a neurotransmitter prevents the terminal bud from secreting it’s contents into the cleft. E.g. GABA.

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15
Q

Where do the vesicles originate that are found at the presynaptic terminal?

A

The neuron soma (body) - they are secreted down the axon

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16
Q

Where is acetylcholine formed?

A

Within the presynaptic terminal (bulb). Choline + Acetyl CoA = Acetylcholine (via acetyl choline transferase)

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17
Q

How does increase Ca2+ stimulate vesicles to be released into the cleft of a neuromuscular junction?

A

1) Synaptobrevin and synaptotaxin found on vesicle membrane
2) SNAP25 and syntaxin found on bulb membrane
3) Ca2+ causes them to entangle and release Ach into the cleft of the neuromuscular junction

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18
Q

What type of receptor does acetylcholine bind to on the post junctional folds of the neuromuscular junction, and what is the effect?

A

Nicotininic ligand gated ion channels (pentimer). Two Ach molecules bind causing them to open and allow Na+ to enter the muscle cell.

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19
Q

What is end plate potential?

A

The summation of potentials from Ach on Nicotinic type I receptors that brings the membrane potential toward the threshold (-55 mv).

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20
Q

What are the invaginations of the sarcolemma on the post synaptic muscle fibre called?

A

Transverse tubules (T-tubules)

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21
Q

What is the triad?

A

Sarcoplasmic reticulum on either side of a T-tubule

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22
Q

Which two receptors react to depolarisation of the T-tubule?

A

1) Dihydropyridine receptor
2) Ryanodine receptor type 1 (plugs the sacroplasmic reticulum) (depolarisation causes the ryanodine receptor to unplug and release Ca2+ from the SR)

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23
Q

Draw a sarcomere and label the bands.

A

Z lines lateral boarders of the sarcomere
M line in the middle
H band = ends of actin filaments distance
A band = Length of the myosin
I band = ends of the myosin filaments

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24
Q

Describe the proteins associated with the actin filament, and what happens when Ca2+ is available.

A

Actin active site heads are bound to nebulin. Actin heads are covered by tropomyosin. Troponin connects to tropomyosin. When Ca2+ binds to c-site of troponin, it pulls away the tropomyosin and reveals the actin heads.

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25
Q

What is the sliding filament theory?

A

Myosin heads dragging the actin filaments and shortening the H zone.

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26
Q

Name the phases of the sliding filament theory. (when ca2+ is bound to troponin)

A

1) ATP attached to myosin head - detached from actin
2) ATP hydorlysed into ADP+Pi, causes myosin heads to cock back, and bind to actin head behind
3) Pi is lost from myosin head, causing a power stroke
4) ATP replaces ADP on the myosin head to detach from the actin head

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27
Q

What do antibodies attack in patients with myasthenia gravis?

A

Nicotinic type 1 receptors (acetylcholine can no longer bind and cause influx of Na+ to propagate the action potential at the NMJ. Weak musculature.

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28
Q

Which autoimmune condition causes antibodies to attack voltage-gated Ca2+ channels on the pre-synaptic bulb, preventing the release of acetylcholine into the cleft?

A

Lambert-Eaton syndrome

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29
Q

How does succinylcholine cause a depolarising blockade, and where would this drug be used clinically?

A

Succinylcholine is an agonist for nicotinic type receptors on the post synaptic NMJ. It will cause prolonged activation. This leads to the premature inactivation of Na+ channels and loss of the end plate potential. Can no longer propagate action potential to the muscle, causing relaxation.

Used to open the airways when trying to intubate a patient.

30
Q

What do curare-derivative drugs inhibit?

A

Nicotinic type I receptors, where Ach normally binds, preventing the propagation of end plate potential. Causes paralysis and can be used in general anaethesia and to avoid the gag reflex during intubation

31
Q

How does organophosphate poisoning affect the NMJ?

A

Binds with acetylcholinesterases and renders them inactive. Causes Ach to build up in the cleft and promotes prolonged end plate potential.

32
Q

Explain 3 ways in which a neurone ensures that an action potential propagates in one direction.

A

1) Very few Na+ channels at the axon hillock
2) Absolute refractory period of Na+ channels
3) Action potentials only begin at the initial segment

33
Q

How does benzodiazipine modulate the synapse?

A

Enhances the effect of GABA and pre synpatic inhibition. Acts as a sedative, anxiolytic, and muscle relaxant.

34
Q

How does atropine modulate the synapse?

A

competitive antagonist of muscarinic acetylcholine receptors. Antagonises the rest and digest system. Causes increased heart rate.

35
Q

How do SSRIs work?

A

Selective serotonin reuptake inhibitors. Work by preventing the reuptake of serotonin in the synaptic cleft via serotonin transporters (SERT)

36
Q

How does strychnine work?

A

Strychnine is a poison that works by being an antagonist for Ach and glycine receptors.

37
Q

How does acidosis and alkalosis affect synaptic transmission?

A

Decrease pH, increased H+, increased in ionised calcium, decreased neuronal action, depressed nervous system activity (opposite for alkalosis)

38
Q

What are tonic and phasic receptors?

A

Tonic - will continuously fire as long as a stimulus is applied (think about isometric muscle contraction.

Phasic - Only fires when the stimulus strength changes, but will not be continuous e.g. skin pacinian corpuscles

39
Q

What is the labelled line principle?

A

Each type of sensation (pain, touch, smell, sight) is known as a modality of sensation. The specificity of nerve fibres for transmitting a single type of modality is called the labelled line principle.

40
Q

What is hole called at which the brain stem protrudes to form the beginning of the spinal cord?

A

Foramen magnum

41
Q

Which vertebrae make up the spinal cord?

A

C1 - L2

42
Q

What are the components of the central and peripheral nervous system?

A

CNS - Brain and spinal cord

PNS - Sensory and motor neurones

43
Q

How many spinal nerves are there and how are they arranged?

A 
31 pairs in total.
Cervical (8) (has one that runs above C1)
Thoracic (12)
Lumbar (5)
Sacral (5)
Coccygeal (1)
44
Q

What is the conus medularis?

A

Where the spinal cord at L2.

45
Q

What are the cauda equina?

A

All the spinal nerves below L2 to coccygeal spinal nerve.

46
Q

How do the white and grey matter get their appearance?

A

White matter - myelinated axons

Grey matter - Cell bodies and dendrites (which are not myelinated

47
Q

Draw a diagram of the transverse section of the spinal cord between T1 and L2.

A

Include the following:

  • Posterior/dorsal median sulcus
  • Posterior/dorsal grey horn
  • Anterior/Ventral grey horn
  • Lateral grey horn (only between T1-L2)
  • Posterior dorsal finiculus
  • Lateral finiculus
  • Anterior/ventral finiculus
  • Anterior median fissure
48
Q

Draw a diagram including the following structures: Posterior/dorsal root, anterior ventral root, spinal nerve, dorsal rami, ventral rami

A
  • Posterior/dorsal root comes from the posterior/dorsal grey horn
  • Anterior/ventral root comes from the anterior/ventral grey horn
  • Dorsal and ventral roots come together to form the spinal nerve
  • From the spinal nerve comes the dorsal rami and ventral rami
49
Q

With regards to the anatomy, explain the route of a sensory afferent fibre and motor efferent fibre through the spina cord.

A

1) Sensory afferent will travel through the dorsal rami, and also through the ventral rami
2) Travel through the spinal nerve via the dorsal root ganglion through the dorsal root toward the posterior/dorsal grey horn
3) Stimulates motor neurones in the anterior/ventral grey horn, through the ventral root
4) Motor neurones will meet sensory neurones in the spinal nerve and will exit via the dorsal or ventral rami

50
Q

Name 2 spinal cord sensory pathways.

A

1) Dorsal-medial lemniscal pathway

2) Spinothalamic

51
Q

What types sensory information does the dorsal medial lemniscal pathway respond to?

A

1) Fine & discriminitive touch (2-point touch)
2) Pressure & stretch in the skin
3) Vibrations
4) Proprioception

52
Q

What sensory structures in the skin muscle and tendons begin sending information to the dorsal medial lemniscal pathway?

A

1) Meissner’s corpuscles
2) Merkel discs
3) Parinian corpuscles
4) Peritrichial nerve endings (hairs)
5) Ruffini corpuscles
6) Muscle spindles (type 1A fibres)
7) Golgi tendon organs (type 1B fibres)

53
Q

What are the fastest and slowest types of nerve fibres?

A 
In order:
Aalpha (120 m/s)
Abeta 
Adelta
B
C (30 m/s)
54
Q

At what points do primary neurons of the dorsal medial lemniscal pathway enter the spinal cord?

A

Lumbar (below T6) > Faciculus gracilis
Cervical (above T6) > Faciculus cuneatis
Enter the ventral grey horn via the dorsal root and dorsal root ganglion.

55
Q

What do the faciculis gracilis and cuneatis travel to in the dorsal medial lemniscal pathway?

A

To the medulla, and the nucleus gracilis and cuneatis, respectively. (Ipsilaterally)

56
Q

In the dorsal medial lemniscal pathway, where does the pathway go following medulla?

A

The left and right medial lemniscus travel contralaterally toward the thalamus (ventroposterior lateral nucleus), then to the somatosensory cortex

57
Q

Which sensations stimulate the spinothalamic ascending tract?

A

1) Crude touch
2) Pain
3) Temperature

58
Q

At what level do sensory neurones decussate in the anterior lateral spinothalmic tract?

A

Within the spinal cord

59
Q

Which sensory nerves decussate in the spinal cord to the anterior white column from the dorsal grey horn?

A

Crude touch & pressure

60
Q

Which sensory nerves decussate in the spinal cord to the lateral white column from the dorsal grey horn?

A

Pain

61
Q

Where do sensory neurones of the spinothalmic tract terminate?

A

1) 15% in the Thalamus at the ventral posterior lateral nucleus
2) 85% at the reticular formation in the brainstem

62
Q

Where do sensory neurones go following the ventral posterior lateral nucleus in the thalamus?

A

The somatosensory area in the parietal lobe

63
Q

Name 2 descending motor pathways that begin in the motor cortex.

A

These are corticospinal tracts

1) Lateral corticospinal tract
2) Anterior corticospinal tract

64
Q

Where is the primary motor cortex found?

A

Within the precentral gyrus of the frontal lobe

65
Q

Which four areas help to control the motor movement via the descending fibres?

A

1) Primary motor cortex
2) Pre motor cortex
3) Supplemental motor area
4) Primary somatosensory cortex

66
Q

Which layer of the primary motor cortex can the pyramidal cells and the cells of Betz be found?

A

5th layer

67
Q

Explain the journey of the motor neurones from primary motor cortex to the medulla of brain stem (known as the corticobulbar tract).

A

1) Pre motor cortex sends a command to move
2) Pyramidal cells and cells of betz in 5ht layer send out axons
3) axons move through midbrain
4) Axons move into the pons. Within the pons, there are pontine nuclei which send information to the contralateral cerebellum (to fine tune movement)
5) Axons continue to medulla, where 80% of axons decussate to the contralateral side (20% stay ipsilateral)

68
Q

In the lateral corticospinal tract, where do the axons synapse in the spinal cord?

A

With motor neurones in the anterior grey horn on the ipsilateral side

69
Q

What type of movements is the lateral corticospinal tract associated with?

A

Skeletal movements in the distal limb. Fine movements of the fingers for example.

70
Q

In the anterior corticospinal tract, where do the axons synapse in the spinal cord?

A

Synapse with motor neurones in the anterior ventral grey horn on the contralateral side.

Phase 1 Medicine (JA) (8 decks)

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