Skeletal muscle control (systems)

Question 1

What are α-motor neurones?

Answer 1

They are the motor neurones of the spinal cord

Question 2

Where are the cell bodies of α-motor neurones found?

Answer 2

Cell bodies in the ventral horn

Question 2

Where do α-motor neurones project to?

Answer 2

Out to the skeletal muscles

Question 3

What do α-motor neurones synapse with?

Answer 3

Synapse w muscle fibres = neuromuscular juction

Question 4

What is a motor unit?

Answer 4

Single α motorneurone & all the fibres it innervates

(Made up of α-motoneurones & muscle fibres)

Question 5

What are skeletal muscles made up of?

Answer 5

Bundles of muscle fibres

Question 6

How many muscle fibres can an α motorneurone synapse w?

Answer 6

Each α motorneurone can synapse w multiple muscle fibres

Question 7

What is focal innervation?

Answer 7

Each muscle fibre receives input from a single α motorneurone - this is focal innervation

Question 8

What is a safety feature muscle have?

Answer 8

Nerve terminals always release 8-10x more ACh than necessary so we always get muscle contraction w a single AP

Question 9

See flashcard on the NMJ (in another deck not sure which one) and ACh reuptake

Answer 9

thank u c

Question 10

What is tubocurarine?

Answer 10

• Nicotinic receptor antagonist
• Some South American hunters use this to hunt animals

Question 11

What is smooth contraction?

Answer 11

• Each α-motorneurones innervates muscle fibres that are spread throughout the muscle
• α-motorneurone fire ascynchronously

Question 12

What is innervation ratio?

Answer 12

No. muscle fibres innervated by each individual α-motorneurone

Question 13

What is innervation ratio is inversely correlated with?

Answer 13

Contractile precision

Question 14

Give some examples of innervation ratio being inversely correlated w contractile precision:

Answer 14

Fingers = very dexterous, 5-15 fibres per α-motorneurone

Abdominal muscles = coarse movements, 200-1500 fibres per α-motorneurone

Question 15

What are the 2 types of muscle fibres?

Answer 15

• Type I
• Type II

Question 16

What are type I muscle fibres AKA?

Answer 16

Slow twitch

Question 17

What are type II muscle fibres AKA

Answer 17

Fast twitch

Question 18

What are the the following like for type I muscle fibres:

• Contraction
• Force of contraction
• Resistance to fatigue

Answer 18

• Contraction = slow (0.1s)
• Force of contraction = low
• Resistance to fatigue = high

Question 19

What are the the following like for type II muscle fibres:

• Contraction
• Force of contraction
• Resistance to fatigue

Answer 19

• Contraction = fast (0.01s)
• Force of contraction = high
• Resistance to fatigue = low

Question 20

What are the the following for type I muscle fibres:

• Energy source
• Colour
• Function

Answer 20

• Energy source = oxidative
• Colour = red
• Function = posture

Question 21

What are the the following for type II muscle fibres:

• Energy source
• Colour
• Function

Answer 21

• Energy source = glycolytic
• Colour = white
• Function = rapid movements

Question 22

What is an example of a type I muscle fibre?

Answer 22

Anti-gravity muscles e.g. abdominal muscles

Question 23

What is an example of a type II muscle fibre?

Answer 23

Eye muscles

Question 24

What sort of muscle fibre are muscles made up of?

Answer 24

Made up of both type I and II muscle fibres α-motoneurones only innervate one type of muscle fibre`

Question 25

How do muscle fibre types increase the force of a contraction?

Answer 25

- Generally, slow twitch are recruited first - Heavy loads also req fast twitch muscle fibres --> glycolytic fatigue happens quickly

Question 26

How do α-motoneurones increase the forceof contraction?

Answer 26

Recruit more α-motoneurones Inc the AP firing rate of α-motoneurones - Summation of muscle contractions - Max summation (tetanus) = 3.5Kg/cm^2 force in all muscles

Question 27

What are the 3 types of ventral horn hormones?

Answer 27

- α-motoneurones - Renshaw cells - γ-motoneurones

Question 28

What do γ-motoneurones do?

Answer 28

Innervate muscle spindles

Question 29

What do α-motoneurones do?

Answer 29

- Innervate muscle fibres - Release ACh - Cause contraction of muscle fibres via nAChRs

Question 30

What do Renshaw cells do?

Answer 30

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

Question 31

What are mechanoreceptors?

Answer 31

Stretch receptors

Question 32

What are muscle spindles?

Answer 32

- Mechanoreceptors - Intrafusal muscle fibres - Attached to the extrafusal muscle fibres - γ-motoneurones innervate ends of intramural muscles - Sensory neurones innervate middle section of intrrafusal muscles

Question 33

What are the types of intrfusal muscles?

Answer 33

- Dynamic nuclear bag fibre - Static nuclear bag fibre - Nuclear chain fibre

Question 34

What are annulospiral sensory endings also called and what do they do?

Answer 34

Ia = absolute stretch & change in stretch

Question 35

What are flower spray sensory endings also called & what do they do?

Answer 35

Il = absolute stretch

Question 36

What is the process of the knee jerk reflex?

Answer 36

1 - Strike patellar tendon w a hammer 2 - Stretches the muscle spindle in the quad 3 - APs project along Ia afferents to spinal cord 4 - Synapse (excitatory, glutamate) w -motoneurones

Question 37

What is the process of the knee jerk reflex?

Answer 37

1 - Strike patellar tendon w a hammer 2 - Stretches the muscle spindle in the quad 3 - APs project along Ia afferents to spinal cord 4 - Synapse (excitatory, glutamate) w α-motoneurones in ventral horn that innervates that quadricep --> α-motorneurone releases ACh at NMJ causing contraction of quad 5 - Collateral synapse (excitatory, glutamate) w Renshaw cell in ventral horn ---> Renshaw cell (inhibitory, glycine) synapses w α-motorneurone that innervates hamstring --> Reciprocal inhibition of hamstring 6 - Leg raises

Question 38

What is the gamma (γ) loop?

Answer 38

Monitors muscle contraction & corrects when required

Question 39

What are golgi tendon organs?

Answer 39

- Mechanoreceptors - Tendons (Between the muscle & bone) - Innervated by Ib sensory neurones - When the muscle stretches so do the Golgi tendon organs

Question 40

What is the golgi tendon reflex?

Answer 40

Protects the muscle from overloading - inverse stretch reflex

Question 41

Summarise γ-motorneurones:

Answer 41

- Muscle spindles - Monitor muscle stretch - Stretch reflex (activates muscle contraction) γ-loop (monitors & correct contraction)

Question 42

Summarise α-motorneurones:

Answer 42

- Extrafusal msucle fibres - Muscle contraction

Question 43

Summarise golgi tendon organ:

Answer 43

- Monitor muscle tendon - Golgi tendon organ reflex (protects muscle from overload - inhibits contraction)