IC2&3: Neurophysiology

Question 1

Compare the threshold MP to the resting MP

Answer 1

The threshold membrane potential is more positive than the basal/resting membrane potential

Question 2

Explain the processes in depolarising stimulus

Answer 2

AP begins when a graded potential (depolarising potential) reaching the trigger zone (-40mV) depolarises the membrane, which is generated by the opening of the ligand-gated channels by the excitatory neurotransmitter released at the NMJ

Question 3

Explain depolarisation

Answer 3

As the cell depolarises, voltage-gated Na+ channels are activated, making the membrane much more permeable to Na+ (The Na+ is more concentrated outside of the cell).

Rapid Na+ entry into the cell through voltage-gated sodium channels depolarises the cell, peaking at 50mV

Question 4

How does hypokalemia affect the body in general

Answer 4

hypokalemia affects the resting MP and impairs the ability to generate AP at the NMJ, leading to muscle weakness and paralysis

Question 5

What is the neuromuscular joint (NMJ)?

Answer 5

NMJ is the synapse between the axon terminal of a motorneuron with the motor end plate

highly excitable region of muscle fibre plasma responsible for initiation of action potentials across the muscle’s surface, ultimately causing the muscle to contract

Question 6

Explain how the application of intense heat (above 43 ºC) to the skin is perceived (3)

Answer 6

The application of heat leads to sensory transduction by nociceptors (free nerve endings)

involves the depolarisation of the receptor membrane from the receptor to the trigger zone to generate an AP

axons generally associated with nociceptors are the C- and Aδ- fibers

Question 7

What are the 4 features of pain?

Answer 7

Quality (nature of stimulus like touch, noxious, warmth),

Intensity (perceived strength of the stimulus),

Duration and Location (perceived duration for which the stimulus was applied and the location of the stimulus)

Question 8

Explain where afferent and efferent nerves originate and carry signal towards.

Answer 8

• Afferent nerves carry signals from the periphery to the CNS (A = into the CNS)
• Efferent nerves carry signals from the CNS to the periphery (E = exit the CNS)

Question 9

After being processed by the CNS, which 2 areas can the signal go towards (and what functions do these systems serve)?

Answer 9

via the efferent division that may affect either:

somatic NS (for movement via skeletal muscles)

autonomic NS (homeostasis such as heart contraction)

Question 10

What is a Pacinian corpuscle?

Answer 10

the enclosed nerve ending with layers of connective tissue are at the area of the skin such as the fingertip (receptor region)

Question 11

State the types of fibres involved in touch and pain and describe their thickness.

Answer 11

Touch: Aβ thick myelinated

Pain: unmyelinated axons (C fibre) or with thin myelin (Aδ fibre)

Question 12

What is a possible cause for congenital insensitivity to pain with anhidrosis (CIPA)

Answer 12

absence of NGF-dependent C or Aδ fibres from loss of function mutations in the NTRK1 gene

(NGF = nerve growth factor)

Question 13

What are the postsynaptic targets for excitatory and inhibitory synapses?

Answer 13

dendrite for an excitatory synapse

soma for an inhibitory synapse

Question 14

Explain what happens in a synapse (4)

Answer 14

AP depolarises the membrane (negative to positive),

triggers the opening of voltage-gated Ca channels

Ca enters the presynaptic terminal, triggering the vesicles to fuse with the membrane of the presynaptic terminal, releasing excitatory neurotransmitters

they bind to receptors on the postsynaptic terminal to transmit the signal to a dendrite and depolarise the postsynaptic membrane

Question 15

What two regions can the grey and white matter be divided into?

Answer 15

Grey matter: dorsal horn and the ventral horn

White matter: dorsal column and ventrolateral column (or ventrolateral quadrant)

Question 16

Where are efferents particularly located in?

Answer 16

ventral horn of the grey matter
(VHGM)

Question 17

Describe the balance of ions at RMP

Answer 17

at RMP:
Outside: Na+, Cl- and Ca2+ are high
Inside: K+ is high

Question 18

Describe the movement of K+ at RMP and equilibrium MP

Answer 18

At the RMP of -65mV, there is more K+ inside of the cell

Conc gradient causes K+ to move out of the cell
Electrical gradient causes K+ to move in of the cell

The pull in either direction is balanced at -97mV (equilibrium potential), which is more negative than RMP

Question 19

Explain how hypokalemia results in paralysis (with relation to K+ movement)

Answer 19

hypokalemia (for example with the use of diuretics) leads to hyperpolarisation of the membrane, making the cell less excitable,

when the K+ outside the cell is depleted, the electrochemical gradient becomes sharper, causing K+ to diffuse out

as K+ leaves the cell, the membrane becomes hyperpolarised (more negative)

Question 20

Explain what may happen if a patient takes too many multivitamins containing K+

Answer 20

Increased serum K+, leading to depolarisation

Question 21

& Describe the events that occur at the Pacinian corpuscle (and its structure) that lead to the generation of an AP (4)

Answer 21

The Pacinian corpuscle has channels that are interlinked at the skin

Upon pressure, the interlinked channels unlink slightly and allow positive ions to pass through them, causing depolarisation

This initial depolarisation travels down the axon and reaches the trigger zone (at the start of the first myelinated area)

When it reaches the trigger zone, an AP is generated

Question 22

Describe how touch signals are sensed through contralateral representation (4)

Answer 22

The first order neuron (afferent) receives the signal,

transmitting it to the second order neuron in the medulla (that crosses over to the other side)

this is sent to a third order neuron in the thalamus and

sent to the somatosensoty cortex for sensation

Question 23

How does the pain signal sensation differ from touch signal sensation?

Answer 23

Touch: 2nd order neuron in medulla

Pain: 2nd order neuron in dorsal horn of spinal cord

Question 24

Where is the primary somatosensory cortex located

Answer 24

Post central gyrus

(neurons are arranged in a somatosensory homunculus)

Question 25

What are the 4 principles underlying sensory processing?

Answer 25

1. The relay uses AP as a signal to relay properties of the stimulus
2. The signal travels along topographic lines
3. The signal travels along a labelled line (between receptor and its primary afferent)
4. The signal along the relay line encodes for properties of the stimuli such as intensity

Question 26

Describe the pain pathophysiology:

where does the signal go after the free nerve endings receive the painful stimulus? (2)

Answer 26

Free nerve endings (painful stimulus) lead to a C fibre (first order neuron) which then synapses with the spinothalamic neuron (second order neuron)

Question 27

In the touch pathophysiology:

Which fibre takes which path to relay signal to the brain

Answer 27

The touch fibres lead to a Aβ fibre (first order neuron) and leads to the spinal cord where it turns upwards along the doral column pathway

Question 28

What are the two places that the Aβ fibre is in contact with

Answer 28

Spinal cord
inhibitory neuron

Question 29

How does inhibition work? (3)

Answer 29

The inhibitory transmitter GABA acts on the spinothalamic tract neurons,

this opens up Cl- channels, causing Cl- to move from the outside to the inside of the cell

and hyperpolarise the spinothalamic tract neuron (becomes less excited)

Question 30

How does pain modulation work?
(2 locations, 1 interneuron)

Answer 30

Context suppresses pain and excites neurons in the prefrontal cortex which will excite neurons in the midbrain (periaqueductal grey, PAG) which then inhibits the pain pathway

The E interneuron (enkephalin) within the spinal cord is the one that ultimately inhibits the spinothalamic neuron

Question 31

What are the 3 types of generated movement?

Answer 31

• Reflexes (involuntary) (eg. removing hand in response to hot surface)
• Rhythmic motor patterns (require voluntary initiation and termination) (eg. walking)
• Voluntary (goal-directed) (of own desire)

Question 32

Which part of the brain controls voluntary movement?

Answer 32

Cortex

Question 33

Which part of the brain controls rhythmic motor patterns?

Answer 33

Brain stem

Question 34

Which two areas in the brain are important for voluntary behiaviour

Answer 34

Primary motor cortex
Premotor area

Question 35

Explain the function of the cerebellum (involves 2 other brain parts)

Answer 35

It indirectly affects movement by adjusting the output of the efferents via the cortex and the brain stem

Question 36

State the function of the basal ganglia

Answer 36

initiation of movement and selection of appropriate motor programme

Question 37

What are some effects of basal ganglia damage? (2 classes)

Answer 37

movement disorders (tremors at rest, rapid flicking movements, violent flailing/ballism, slow writhing or twisting, bradykinesia)

posture disorders (rigidity)

Question 38

What are the 4 ingredients for voluntary movement?

Answer 38

1. knowledge where the body is in space,
2. where it intends to go
3. selection of a plan to get it there, plan held in memory until the appropriate time
4. instruction to implement the plan

Question 39

Which part of the brain controls “knowledge where the body is in space”

Answer 39

posterior parietal cortex

Question 40

Which part of the brain controls “Where it intends to go and what to do”

Answer 40

anterior frontal lobes

Question 41

Which part of the brain controls “Selection of a plan and holding it until execution”

Answer 41

premotor cortical areas

Question 42

Which part of the brain controls “implementation”

Answer 42

primary motor complex