Neuro 11 - Neuromuscular and Spinal Cord

Question 1

What is the difference between EPSP and IPSP in terms of membrane potential?

Answer 1

EPSP - makes the membrane less negative - bringing it closer to the threshold potential

IPSP - makes the membrane more negative - taking it further away from the threshold - Hyperpolarisation

Question 2

Which proteins are involved in the release of acetylcholine at the synapses?

Answer 2

SNARE proteins

Question 3

What triggers acetylcholine release?

Answer 3

Calcium influx

Question 4

If you record the post synaptic membrane potential at any one time, you will see some small changes in membrane potential. What are these caused by?

Answer 4

Miniature end plate potentials

Caused by constant dumping of acetylcholine into the synapse

but not enough to cause an action potential

Question 5

What is the difference between intrafusal and extrafusal muscle fibres?

Answer 5

intrafusal - skeletal muscle fibres that serve as sensory organs e.g. proprioceptors

Extrafusal - your bog standard skeletal muscle fibres that are innervated by alpha motor neurones and generate tension by contracting

Question 6

What are alpha motor neurones?

Answer 6

motor neurones that innervate the extrafusal fibres of skeletal muscle

Question 7

What is the name given to the sensory receptors in muscle that feedback to the CNS and allow an excitatory reflex to be generated?

Answer 7

Spindles

Question 8

What is a motor neurone pool?

Answer 8

Collection of lower motor neurones that innervate a single muscle

Question 9

Describe the arrangement of alpha motor neurones within the ventral horn?

Answer 9

Dorsal - flexors
Ventral - extensors
Medial - proximal
Lateral - distal

Question 10

What is an important rule to remember regarding the connections between alpha motor neurones and muscle fibres?

Answer 10

1 motor neurone can innervate several muscle fibres

but 1 muscle fibre can only be innervated by 1 motor neurone

Question 11

Under what conditions is the 1:1 muscle fibre:motor neurone debatable?

Answer 11

pathological conditions

e.g. severed neurone - can cause innervation of muscle fibres which are already being innervated

Question 12

Define motor unit.

Answer 12

single motor neurone together with all the muscle fibres that it innervates

smallest functional unit that can generate force

Question 13

Describe and explain the difference in innervation ratio across different muscles in the body using examples.

Answer 13

muscles that require very fine control have low innervation ratio e.g. maybe 1 fibre being innervated by 1 neurone

Question 14

What are the three types of motor unit.

Answer 14

Slow - type 1
Fast Fatigue resistant - Type 2A
Fast Fatiguable - Type 2B

Question 15

Describe the structural and functional differences between slow and fast twitch muscle fibres.

Answer 15

Slow - small diameter, smaller dendritic trees, thinnest axons, slowest condutions

Question 16

What are the 2 methods by which the brain regulated the force that a single muscle can produce?

Answer 16

Recruitment - recruiting more motor units for contraction

Rate coding - increasing the frequency of action potentials occurring

Question 17

What principle governs recruitment?

Answer 17

Size principle

smaller units recruited first aka slow ones

Question 18

Describe the order of recruitment of motor units with increasing force generation.

Answer 18

Slow — Fast fatigue resistant – fast fatiguable

Question 19

What are neurotrophic factors?

Answer 19

Factors produced within nerves and are transported throughout the nerve to maintain the integrity and function

Growth factor that prevents neuronal death

Question 20

What happens to a slow fibre when a fast nerve is transplanted into it?

Answer 20

becomes fast

this shows that the function of a nerve is determined by the nerve that innervates it

action potentials are not the only thing being transported by the nerves

Question 21

How easy is it to switch from one motor unit type to another?

Answer 21

type 2b to 2a is possible with training

slow to fast not normally possible

Question 22

How does muscle composition change with ageing?

Answer 22

loss of type 1 and type2 with preference for type 2

sarcopenia

Question 23

What tract is responsible for voluntary movements?

Answer 23

Corticospinal

Question 24

What is the role of the extrapyramidal tracts?

Answer 24

automatic movements

Question 25

What is a reflex?

Answer 25

automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre then outwards to an effector without reaching the level of consciousness

Question 26

What are the three components of a reflex arc?

Answer 26

afferent signal
relay neurone
motor neurone

Question 27

What are the two signals that are generated when the patellar ligament is tapped?

Answer 27

Excitatory to the quads

inhibitory to the hamstrings

Question 28

Why is there a difference in the time taken for these signals to reach the relevant muscles?

Answer 28

• signal going to the quads is monosynaptic

- signal going to hamstrings is inhibitory so has 2 synapses

Question 29

What are the 2 twitches that are seen when you stimulate the nerve behind the knee?

Answer 29

M wave - directly stimulating the motor neurone

H wave - action potential going to spinal cord then coming out

Question 30

Why do sensory neurones show a response at lower stimulus than motor neurones?

Answer 30

larger

Question 31

What names are given to the polysynaptic reflexes?

Answer 31

flexion withdrawal

crossed extensor

Question 32

Describe the supraspinal control of reflexes?

Answer 32

large descending control of reflexes

Question 33

What is the Jendrassik manoeuvre?

Answer 33

clenching teeth = manoeuvre 2-3x larger

Question 34

If you decerebrate an animal and test their reflexes what would you see?

Answer 34

Hyperreflexia

Increased muscle tone

Question 35

What signs are seen with upper motor neurone lesions?

Answer 35

hyperreflexia
clonus
babinski’s sign