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MD4001 > Neurophysiology Revision > Flashcards

Neurophysiology Revision Flashcards

1
Q

Describe the pathway of information through excitable cells.

A

1) Information arrives at the cell body via dendrites (and cell bodies) where it is assimilated and processed
2) Processed information is then digitized into APs which are transmitted along the axon
3) At the end of the axon the information is passed to the target (muscle or neurons) at boutons

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2
Q

Identify factors which affect speed of conduction in nerve cells.

A

For unmyelinated nerve fibers, large diameter = faster conduction
Myelinated small diameter fibers conduct faster than large unmyelinated ones.

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3
Q

Are there more myelinated or unmyelinated nerve fibers ?

A

Myelinated

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4
Q

State normal conduction velocity in nerve cells.

A

Normal conduction velocity= 50-60 meters/second

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5
Q

What type of nerve fibers conducts fastest ? What is the conduction velocity in those nerve fibers ?

A

Alpha motor-neurons (largest neurons in spinal cord, myelinated)
120 m/s

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6
Q

Clinically, what does the following mean: slowing of conduction (increased latency) ?

A

Loss of myelin in a nerve (Na channels spread all the way along nerve rather than concentrated at the nodes of Ranvier, so no longer so efficient )

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7
Q

Clinically, what does the following mean: decrease in amplitude of signal ?

A

Conduction block

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8
Q

How many neurons are there in the brain ? How many synapses are there in the CNS ?

A

100 billion neurons in the brain

1000 trillion synapses in the CNS

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9
Q

Define resting membrane potential.

A

“The difference in potential across the membrane of a cell when it is at rest, i.e., fully repolarized”

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10
Q

What is the resting membrane potential of nerve cells ?

A

-60 to -70 mV

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11
Q

Why is the resting membrane potential of nerve cells negative ?

A

Due to active transport of Sodium out of the cell and Potassium into the cell in the 3 out:2 in ratio

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12
Q

State the intra and extracellular concentrations of Sodium in nerve cells.

A

EXTRA: 150 mM
INTRA: 15 mM

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13
Q

State the intra and extracellular concentrations of Potassium in nerve cells.

A

EXTRA: 5 mM
INTRA: 140 mM

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14
Q

Describe the changes in channel opening/closing that occur with an AP.

A
  1. At resting potential Na+ channels are closed - the activation gate is closed
  2. Depolarization opens the activation gate and Na+ flows into the cell along it’s electrochemical gradient (membrane potential becomes positive)
  3. A delayed component of voltage dependent activation is the blocking of the channel by the inactivation gate (after about 0.5ms)
  4. Repolarization of the cell (Sodium channels close and K+ channels open) re-sets the two gates to their equilibrium positions (membrane potential returns to negative)
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15
Q

Define refractory period, and explain why it happens.

A

Absolute refractory period: the cell cannot be stimulated to its threshold potential– All voltage gated Na channels closed

Relative refractory period: a stronger stimulus than normal could induce an action potential– some voltage gated Na ready but more voltage gated K channels are open than usual– cell still hyperpolarised

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16
Q

Draw the AP of a nerve cell.

A

Refer to slide 9 of lecture “Neurophysiology Revision”

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17
Q

What is the main function of myelin ? How does it do this ?

A

Reduces size + maintains speed

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18
Q

How is myelin produced ?

A

Schwann cells provide myelination in the peripheral nervous system (one Schwann cell will make one internode only)
Oligodendrocytes provide myelination in the CNS (one Oligodendrocyte cell builds a number of internodes)

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19
Q

Draw the main components of a neuron.

A

Refer to slide 2 of lecture “Neurophysiology Revision”

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20
Q

Draw the main components of an axon.

A

Refer to slide 11 of lecture “Neurophysiology Revision”

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21
Q

Which type of axon does saltatory conduction happen in ? How so ?

A

In myelinated axons

The local currents can extend further as the normal current leakage is curtailed by the myelin sheath (which form internodes) wrapping around axon plasma membrane.
In this way the conduction of the nerve impulse flows rapidly along the inside of the axon to the node, where it slows and ionic depolarisation (AP) takes place (Na channels are concentrated in the nodes of Ranvier). Note only a few ions are needed to do this so there is energy saving

And then the fast conduction along the inside of the axon resumes afresh

Note then that the action potential only exists at the node of Ranvier

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22
Q

Draw the synapse between two neurons, and describe its main features.

A

Refer to slide 13 in lecture ‘“Neurophysiology Revision”

  • The synaptic cleft is the gap, the presynaptic cell is before the gap and the postsynaptic cell is after the gap
  • The terminal of the presynaptic cell forms a swelling called a bouton
  • Most nerve cells communicate through neurotransmitter release by release of vesicles (containing the NS) in synaptic cleft
  • Receptors for the NS in the post-synapse
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23
Q

State the size of the synaptic cleft.

A

20nm in size (20 x 10-9 m)

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24
Q

Describe the main pre-synaptic events.

A

1) SNARE proteins in the vesicle and the cell membrane bind
2) These then form helical structure which brings the two membrane close
3) Entering Calcium binds to Synaptotagmnin
4) Calcium bound Synaptotagmnin catalyses membrane fusion

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25
Q

Briefly explain how to Botulinum toxin affects muscles.

A

Botulin toxin interferes with SNARE proteins. This happens peripherally (between motor neurons and muscles), thereby causing paralysis.

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26
Q

Identify a therapeutic use of Botulinum toxin.

A

Torticolis is neck spasm, can be reduced with controlled amount of Botulinum toxin

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27
Q

What happens to the neurotransmitters in the synapse after binding to the receptors on the post-synapse ?

A

Neurotransmitters are always inactivated, either by diffusion, re-uptake (into pre-synaptic neuron) or enzymal inactivation

28
Q

Identify the main kinds of post-synaptic receptors.

A
  • Ionotropic (directly gate ion flow)

- Metabotropic (indirectly gate ion flow or activate oth er pathways)

29
Q

Are post-synaptic receptors excitatory or inhibitory ?

A

Can be both, depending on the ions they let into/out of the cell

30
Q

What is the major excitatory neurotransmitter ? inhibitory ?

A

Glutamate (excitatory)

Glycine (inhibitory)

31
Q

Can one receptor be associated with more than one NS ? Can one NS be associated with more than one receptor ?

A

Receptors are associated with only one neurotransmitter,

but one NT can activate multiple receptor types

32
Q

Describe the main post-synaptic events.

A

Following NS release, and receptor binding, ion channels open, conductance change causes current flow, post-synaptic potential changes, post-synaptic cells are excited or inhibited –> Summation determines whether an AP occurs (only when the post-synaptic membrane potential reaches a certain treshold can you develop AP, i.e. two EPSPs summed together are more likely to cause an AP than one EPSP by itself or one EPSP with an IPSP membrane potential)

33
Q

How do sensory receptors work (wrt APs) ?

A
  • Each receptor type has a modality and feeds information about modality to the CNS
  • Most receptors code the duration and magnitude of external signals using a generator potential
  • This means stronger external signals result in a higher frequency of APs in the axon
34
Q

Explain what is meant by slowly and rapidly adapting generator potential.

A

Sensory receptors can adapt to a stimulus with time, and not all receptors adapt in the same way:

  • “Slowly adapting- continue to discharge during a stimulus (send information about ongoing stimulation)
  • Rapidly adapting- respond only when the stimulus starts and sometimes when a stimulus ends (send information related to changing stimuli)”
35
Q

Draw a slowly adapting and rapidly adapting generator potential.

A

Refer to slide 22 of lecture on “Neurophysiology Revision”

36
Q

What is the purpose of stretch reflexes ? How are they mediated ?

A

Stretch reflexes enable muscle to oppose external forces that tend to elongate them. They are mediated by sense organs within muscles known as
muscle spindles.

37
Q

Draw, and identify the main components of reflex networks.

A

Refer to slide 24 in lecture on “Neurophysiology Revision”

  • Homonymous, synergist, and antagonist muscles
  • Alpha motoneurone (to the homonymous, synergist, and antagonist muscles)
  • Inhibitory interneurone (to the alpha motoneurone supplying the antagonist muscle)
  • 1a afferent (from homonymous muscle, to the alpha motorneurones suppling homonymous and synergist muscles, and to the inhibitory interneurone)
38
Q

What are muscle spindles ?

A

Peripheral nerve endings of afferent fibres wrapped around modified muscle fibres (ie intrafusal fibres).. Function as stretch receptors.

39
Q

What are the main components of muscle spindle fibers ?

A
  • Contractile (Gamma MN efferents from spinal cord connect here) and elastic portion
  • Less Elastic/contractile sensory portion (group IA (primary) sensory afferents to spinal cord connect here)
  • Group II (secondary) sensory afferents to spinal cord connect between those two regions.
40
Q

How do muscle spindles work ?

A
  • Muscle spindles stimulate reflexively a muscle contraction to prevent overstretching and muscle fiber damage.
  • While stretching the muscle spindle (e.g. flexing your biceps causes load which stretches spindle ?), an impulse is immediately sent to the spinal cord through group IA and II sensory afferents, then into alpha motor neurones, and a response to contract the muscle is received, for protecting it from being pulled forcefully or beyond a normal range (as stretch spindle, the APs increase).
41
Q

Explain the effect of muscle length on spindle sensory output.

A

IA:

  • Muscle stretches, increase in rate of firing as stretching takes place
  • When steady at fixed longer length, new rate of firing that is quicker from shorter length but not as quick as dynamic change

II:

  • Slow rate of firing at shorter length
  • Rate increases up to a rapid rate at longer length (and stays like that)
42
Q

Draw the main components of the Neuromuscular junction.

A

Refer to slide 28 in lecture on “Neurophysiology Revision”

43
Q

What NS is usually present in the neuromuscular junction ? What kind of receptors does it bind to ?

A

ACh

Binds to nicotinic receptors

44
Q

How is the ACh released at the neuromuscular junction removed ?

A

Through AChesterase

45
Q

Identify a pathology resulting from abnormality of the ACh receptor at the neuromuscular junction.

A

Myasthenia Gravis (autoimmune attack of ACh neuromuscular receptors by antibodies)

46
Q

Describe treatment for myasthenia gravis.

A

Anti-AChesterase (blocks AChesterase, which increases ACh at the neuromuscular junction)

47
Q

Define nerve conduction studies.

A

”
-Noninvasive method for assessing a nerve’s ability to carry an impulse (can help to identify causes of neurological abnormality, e.g. if demyelinating or axonal neuropathy or both)
-Quantifies a) latency periods and b) conduction velocities
-Larger peripheral motor and sensory nerves are electrically stimulated at various intervals along a motor nerve
“

48
Q

Identify possible abnormalities in a nerve conduction study, and the clinical meaning of each.

A

Reduced amplitude = less axons (which means reduced size of compound AP)
Slowed conduction velocity = less myelin

49
Q

Define SNAP and CMAP in the context of nerve conduction studies.

A

SNAP: The electrical impulse that carries information along a sensory neuron.
CMAP: a group of almost simultaneous action potentials from several muscle fibers in the same area usually evoked by stimulation of the supplying motor nerve and are recorded as one multipeaked summated action potential

50
Q

Draw a typical graph obtained from nerve conduction studies, showing its main components.

A

Refer to slide 30 of lecture on “Neurophysiology Revision”

51
Q

Draw a typical graph obtained from nerve conduction studies, showing its main components.

A

Refer to slide 30 of lecture on “Neurophysiology Revision”

Components which should be identified are:

  • amplitude
  • latency
  • duration
52
Q

What are the main general causes of neuropathies ?

A

Loss of nerve cells themselves (axonal neuropathy) or loss of myelin (demyelinating neuropathy) or combination of both

53
Q

Graph and explain the nerve conduction study graphs which result from axonal, and demyelinating neuropathies.

A

Refer to slide 31 in lexture on “Neurophysiology Revision”

  • Axonal (loss of amplitude)
  • Demyelinating (increased latency)
54
Q

Identify common nerve and neuromuscular junction problems.

A
  • Carpal Tunnel Syndrome
  • Myasthenia Gravis
  • Chennelopathies (e.g. Cystic Fibrosis)
55
Q

State the main clinical features of Carpal Tunnel Syndrome.

A
  • Compression of median nerve, by carpal ligament
  • Signs/symptoms: numbness or pain of area of hand innervated by median nerve (lateral aspect of the palm, lateral three and a half fingers on the anterior (palmar) surface of the hand)
56
Q

State the epidemiology of Carpal Tunnel Syndrome.

A

Especially occurs in people who use hands a lot (e.g. computer workers)

57
Q

Describe treatment for Carpal Tunnel Syndrome.

A

Surgically cutting through Carpal Ligament (under local anesthetic)

58
Q

Describe the typical presentation of Myasthenia Gravis.

A

Ocular myasthenia (in middle age, droopiness of eyelids which increases as day goes on)

59
Q

Distinguish between normal response and the response of a Myasthenia Gravis patient to repetitive nerve stimulation, in graphical form.

A

Refer to slide 34 in lecture “Neurophysiology Revision”

60
Q

State the following dermatomes:

  • Umbilicus
  • Nipples
  • Knee
  • Knee reflex
  • Ankle reflex
  • Biceps reflex
  • Triceps reflex
  • Sole
  • Big toe
  • Middle finger
A 
Umbilicus (T10)
Nipples (T4) 
Knee (L3)
Knee reflex (L3-L4)
Ankle reflex (S1)
Biceps reflex (C5-C6)
Triceps reflex (C7)
Sole (S1)
Big toe (L5)
Middle finger (C7)
61
Q

State what dermatomes C5, 6, 8 and T1 innervate.

A

C6- On the dorsal surface of the proximal phalanx of the thumb.
C5- On the lateral (radial) side of the antecubital fossa, just proximally to the elbow.
C8- On the dorsal surface of the proximal phalanx of the little finger.
T1 - On the medial (ulnar) side of the antecubital fossa, just proximally to the medial epicondyle of the humerus.

62
Q

Identify the main nerves which arise from the brachial plexus. Also state the origin of each, and what each nerve innervates.

A
  • Axillary nerve (from C5-6): deltoid
  • Musculocutaneous nerve (from C5 to C7): elbow flexion (biceps)
  • Radial nerve (from C5 to T1): elbow extension (triceps) + dorsiflexion of wrist
  • Median nerve (from C5 to T1): thenar eminence
  • Ulnar nerve (from C8-T1): interossei
63
Q

What are the main divisions of the brachial plexus ?

A

“The brachial plexus is divided into five roots, three trunks, six divisions (three anterior and three posterior), three cords, and five branches.”

64
Q

Identify examples of compression syndromes.

A
  • Carpal Tunnel Syndrome

- Ulnar nerve compression at elbow

65
Q

What is the main problem with the complex number of proteins involved in neuromuscular transmission ?

A

Complex number of proteins involved in neuromuscular transmission, increasing number of genetic abnormalities, all rare

MD4001 (74 decks)

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