Reflexes

Question 1

What is a monosynaptic reflex

Answer 1

Is when the sensory receptor is activated and action potential triangles down sensory nerve fibre to ventral root of spinal cord

Loops out dorsal via motoneurone to the muscle

Question 2

Why if you record activity of nerve following stimulation do you get multiple peaks

Answer 2

Because different axon types conduct at different speeds

Question 3

What motor neurones (CNS motor outflow) control skeletal muscle

Answer 3

Alpha motor neurones

Large diameter and transmits with conduction of 70-120m/s

Aa type nerves

Innervated skeletal muscle

Question 4

What is spatial summation?

Answer 4

Where increasing signal strength is transmitted using progressively greater number of fibres

Question 5

What is temporal summation?

Answer 5

Increasing strength of signal via increasing frequency of nerve impulses in each fibre

Question 6

What does motor unit consist of

Answer 6

Alpha motoneurone and the muscle fibres it innervates

Question 7

What neurotransmitter does all motor units use

Answer 7

ACh as neurotransmitter

They are all excitatory

Question 8

Smallest innervated and largest innverate of motor units

Answer 8

Smallest 5-10 muscle fibres per unit

Largest <1000 muscle fibres per motor neurone

Anatomical muscle will have motor units ranging between large and small

Question 9

Spectrum of motor unit sizes within muscle depends on?

Answer 9

1. Precision of control required (small motor units gives high precision such as fingers and eyes)
2. Force of contraction required or a low precision (large motor units i.e. Postural muscles or calf muscles)

Question 10

Intensity of muscle contraction is graded by

Answer 10

1. Alterations in frequency with which any single motor neurone fires action potentials
2. Recruitment of alpha motor neurones

Question 11

How does increasing the number of motor units recruited increase tension

Answer 11

There is large variety of alpha motor neurone axons ranging in size from 12-20 giving velocity of 70-120

Motor neurones at smaller end form smaller motor units and are more readily excited- small motor neurones innervate slow oxidative muscle fibres so can give low power but sustained effort

Motor neurones are larger end form larger motor units and are harder to activate - large motor neurones innervated fast glycolysis muscle fibres five high power but fatigue quickly

Question 12

Smaller motor units innervate

Answer 12

Slow oxidative muscle fibres

Low power sustained effort

Question 13

Large motor neurones innervate

Answer 13

Fast glycolysis muscle fibres

High power fatigue quick

Question 14

Why are larger alpha motor neurones harder to recruit

Answer 14

As there is a larger threshold for activation for larger motor neurones