Neuro physiology

Question 1

What type of neurone are most:

a) sensory neurones
b) motor neurones

Answer 1

a) unipolar/pseudounipolar, with cell bodies lying in the dorsal root ganglion
b) multipolar

Question 2

Cells which myelinate axons in a) the CNS and b) the PNS

Answer 2

a) oligodendrocytes

b) Schwann cells

Question 3

Which cells are the “macrophages” of the CNS?

Answer 3

Microglia

Question 4

What are the main support cells in the CNS?

Answer 4

Astrocytes- wide range of functions including maintenance of the BBB

Question 5

Epithelial cells which line the ventricles?

Answer 5

Ependymal cells

Question 6

What is the resting transmembrane potential of a neurone?

Answer 6

Around -70mV

Question 7

Equilibrium potential for a) K+ and b) Na+

Answer 7

a) -90mV- cell is permeable to potassium

b) 66mV- cell is not very permeable to sodium

Question 8

What are the main cations and anions of a) the ICF and b) the ECF

Answer 8

a) cation- potassium, anions- phophate and proteins

b) cation- sodium, anion- chloride

Question 9

Describe how an action potential is generated (3)

Answer 9

Opening of a sodium channel brings an area of membrane to threshold (-60mV)
Voltage-gated sodium channels are opened causing an influx and depolarisation
Voltage gated sodium channels are inactivated at 30mV, and voltage gated potassium channels are opened causing K+ efflux, repolarizing the membrane potential

Question 10

What is the transmembrane potential during the relative refractory period?

Answer 10

Hyperpolarized- needs a greater than normal stimulus to become depolarized again

Question 11

Two main factors which influence speed of AP propagation

Answer 11

myelination of the axon and axon diameter

Question 12

What information is carried by the fastest axons?

Answer 12

Proprioception

Question 13

Describe how an AP is transmitted at a cholinergic synapse (5)

Answer 13

Arrival of AP depolarizes the synaptic knob opening calcium channels and causing an influx of calcium
Calcium causes the exocytosis of neurotransmitter vesicles (ACh)
ACh diffuses across,binds to receptors and induces a depolarizing potential
ACh is removed by acetylcholinesterase inhibitors

Question 14

Types of acetylcholine receptors (2)

Answer 14

Nicotonic-initiate a fast epsp at skeletal muscle by direct ion gating
Muscarinic-initiate a slow epsp by closing Potassium channels (in parasympathetic axons)

Question 15

Neurotransmitters in the CNS:

a) main excitatory
b) main inhibitory and its mechanism
c) inhibits antagonist motoneurone in spinal reflexes

Answer 15

a) glutamate
b) GABA- opens chloride and potassium channels to hyperpolarize the membrane
c) glycine

Question 16

Receptors which sense

a) light touch
b) pressure
c) pain

Answer 16

a) Meissners, Merkel
b) Pacinian, Ruffini
c) noiceptors

Question 17

Types of nociceptor (4)

Answer 17

Mechanoreceptors
Thermal (heat/cold)
Chemical (prostaglandin/bradykinin/histamine)
Polymodal- respond to at least two of the above

Question 18

A-delta fibres respond to…and mediate….

Answer 18

Respond to noxious mechanical and thermal stimuli- mediate first pain

Question 19

C-fibres respond to….and mediate…

Answer 19

Respond to all noxious stimuli- mediate second pain

Question 20

How can receptive field be demonstrated?

Answer 20

Two point discrimination test

Question 21

What does a motor unit consist of?

Answer 21

A motor neurone and all the muscle fibres it innervates

Question 22

What does a motor pool consist of?

Answer 22

A muscle and all the motor neurones that innervate it

Question 23

How is excitation coupled to contraction?

Answer 23

ACh binds to nicotinic receptors
This causes release of calcium from the sacroplasmic reticulum
Calcium binds troponin, unveiling cross-bridging sites on actin
Actin-myosin cross bridges are formed and ATP powers filament sliding, shortening the muscle

Question 24

What is the muscle stretch reflex also known as?

Answer 24

The myotatic reflex

Question 25

What is the organ responsible for detecting muscle stretch?

Answer 25

The muscle spindle

Question 26

What is reciprocal inhibition?

Answer 26

Relaxation of the antagonist muscle during the stretch reflex e.g. in the knee jerk reflex, the relaxation of the hamstring muscles

Question 27

What name is given to the reflex which opposes excessive muscle tension rather than stretch?

Answer 27

Golgi reflex

Question 28

Which type of motor neurones

a) keep the muscle spindle fom going “slack”
b) contact the muscle being stretched to oppose the stretch

Answer 28

a) gamma

b) alpha