Skeletal muscle control

Question 1

a-motorneurones

Answer 1

Motor neurones of the spinal cord
Cell bodies in the ventral horn
Axons project out to skeletal muscles
Synapse with muscle fibres = neuromuscular junction

Question 2

Motor unit

Answer 2

single α motoneurone and all the muscle fibres it innervates

Question 3

Focal innervation

Answer 3

Each muscle fibre receives input from a single a-motorneurone

Question 4

Safety feature of nerve terminals

Answer 4

Nerve terminals always release 8-10x more ACh than necessary so we always get muscle contraction with a single action potential

Question 5

Smooth contraction

Answer 5

Each α-motoneurone innervates muscle fibres that are spread throughout the muscle
α-motoneurones fire asynchronously

Question 6

Innervation ratio

Answer 6

number of muscle fibres innervated by each individual α-motoneurone
Innervation ratio is inversely correlated with contractile precision

Question 7

Type I muscle fibres features

Answer 7

Slow twitch
Low force of contraction
High resistance to fatigue
Oxidative energy source
Red in colour
Function: posture

Question 8

Type II muscle fibre features

Answer 8

Fast twitch
High force of contraction
Low resistance to fatigue
Glycolytic energy source
White in colour
Function: Rapid movements

Question 9

Increasing the force of contraction via a-motorneurones

Answer 9

Recruit more α-motoneurones
Increase the action potential firing rate of α-motoneurones
Summation of muscle contractions
Maximum summation (tetanus) = 3.5kg/cm2 force in all muscles

Question 10

3 ventral horn neurones

Answer 10

a-motorneurones
renshaw cells
y-motorneurones

Question 11

Renshaw cells

Answer 11

Inhibitory interneurons
Release glycine
Synapse with α-motoneurones (inhibit their activity)
Lateral inhibition = prevents overactivity and enables fine control of movement
Target site of tetanus bacteria toxin

Question 12

y-motorneurones

Answer 12

Innervate muscle spindles

Question 13

Mechanoreceptors

Answer 13

Stretch receptors

Question 14

Sensory neurones

Answer 14

Innervate middle section of intrafusal muscle

Question 15

Types of intrafusal muscle

Answer 15

Ia = absolute stretch and change in stretch
II = absolute stretch

Question 16

Knee jerk reflex steps

Answer 16

Strike patellar tendon with a hammer
Stretches the muscle spindle in the quadricep
Action potentials project along Ia afferents to spinal cord
Synapse (excitatory, glutamate) with α-motoneurone in ventral horn that innervates the quadricep
α-motoneurone releases Ach at NMJ causing contraction of quadricep
Collateral synapse (excitatory, glutamate) with Renshaw cell in ventral horn
Renshaw cell (inhibitory, glycine) synapses with α-motoneurone that innervates hamstring
Reciprocal inhibition of hamstring
Leg raises

Question 17

The gamma (y) loop

Answer 17

Monitors muscle contraction and corrects when required

Question 18

Golgi tendon organs

Answer 18

Mechanoreceptors
Tendons (between the muscle and bone)
Innervated by Ib sensory neurones
When the muscle stretches so do the Golgi tendon organs

Question 19

Golgi tendon reflex

Answer 19

Protects the muscle from overloading - inverse stretch reflex