muscle physiology

Question 1

What is a reflex

Answer 1

A rapid automatic and predictable response provided by a neuronal pathway in response to a stimulus.

Question 2

What are the components of a reflex arc

Answer 2

Receptor/sensory organ -> Afferent sensory neurone -> Synapse or Interneurone -> Efferent motor neurone -> Effector organ

Question 3

What is the difference between monosynaptic and polysynaptic reflexes

Answer 3

Monosynaptic - sensory and motor neurones are directly connected through the spinal cord. The muscle spindle may also synapse directly with inhibitory interneurones which inhibit the antagonistic muscle.

Polysynaptic - sensory and motor neurones are connected by an interneurone

Question 4

Describe a withdrawal reflex

Answer 4

1) Receptor senses pain, action potential generated via sensory neuron
2) Via dorsal horn it then synapses with an interneuron within the spinal cord
3) The interneuron may synapse with multiple efferent motor neurones
e.g. - Bicep muscle agonism to withdraw the arm
- Tricep muscle antagonism to aid in withdrawal of arm and prevent extension
4) Motor efferent neurones stimulated in the ventral horn - action potential to neuromuscular junction to have desired effect of withdrawal.
Known as reciprocal innervation

Question 5

What do muscle spindles monitor and maintain

Answer 5

Muscle spindles are responsible for monitoring stretch of muscle fibres, and maintain constant length of muscles despite changes in load.

Question 6

What is the function of golgi tendon organs

Answer 6

GTO are responsible for monitoring and maintaining tension of muscle fibres, limiting tension and preventing damage.

Afferent activity in response to contraction and increased muscle tension -> inhibitory interneurone -> motor neuron inhibited to increase stretch of muscle fibre and reduce tension. Antagonistic muscle contracts.

Question 7

Function of A nerves
Aa
aB
a gamma
a delta
Diameter and velocity

Answer 7

Aa - motor, proprioception 100m/s, 10-20um
aB - Touch/pressure - 50m/s, 5um
agamma - Muscle spindle motor - 25m/s, 2-5um
a delta - Pain, touch, temperature - 25m/s, 2-5um

Question 8

Function of
B fibres
C fibres

Answer 8

B - preganglionic autonomic nerves
C - Pain/temperature OR post-ganglionic sympathetic

Question 9

How are velocity and diameter related between myelianted and unmyelianted nerves

Answer 9

Velocity proportional to diameter if myelinated,
Velocity proportional to sq.root diameter if unmyelinated

Question 10

Describe a sarcomere
What happens to the zones during contraction

Answer 10

• Z lines get closer to one another
• H band and I band reduced width
• A band doesnt change in size (myosin thick units)