Properties Of The Motor Unit Wk3

Question 1

What is the motor system of the body?

Answer 1

• constituted from those tissues of the body that work together to:
  : set muscle tone of the body (small level contraction = posture)
  : bring about voluntary movements = exaggeration of posture

Question 2

How to examine for motor tone?

Answer 2

• any resistance?
• any force applied?
• what force required?
• is there a range of motion?

Question 3

What does a motor unit have?

Answer 3

• Motorneurone (neuronal) & skeletal muscles (muscular) & neuromuscular junction (interface)
• Defined as a somatic efferent plus all the muscle fibres it supplies
• More strictly, it compromises of 1 alpha-motorneurone, all extrafusal muscle fibres it supplies (extra-ocular muscles (10 fibres) and quadriceps (1000 fibres))

Question 4

What is the mechanical efficiency of skeletal muscle?

Answer 4

~20%

Question 5

What is the importance of skeletal muscle?

Answer 5

• movement
• posture
• stability of joins:muscles arranged antagonistically around a joint i.e. extension of full flexion: flexed muscles paralysed and exterior muscles activated
• heat generation: core temp, 57 degrees generated, when elderly lose muscle they get cold

Question 6

What is muscles from cells?

Answer 6

• Myocytes - muscle cells
• They collect to form a fasciculus or fascicle
• Fasciculi collect to form a muscle as we know it

Question 7

What are the tissue envelopes of skeletal muscles?

Answer 7

OUTSIDE IN

• Epimysium
• Perimysium
• Endomysium (between fibres)
• Fascicle (wrapped by perimysium) (7 fascicles) - blood vessels between vascicles

Question 8

What is a tendon?

Answer 8

• organised tough band of fibrous connective tissue mass that forms a point of confluence of contraction by single myocytes of a muscle
• it is not always present in all muscles of the body
• where present, it brings together single contractions of myofibrils, hence myocytes to produce combined actions at a single point (usually joint)
• the manner in which myofibrils (hence myocytes) converge their pulling actions depends on the architecture of the muscle itself

Question 9

What do common assemblies of fascicles include?

Answer 9

Convergent muscle
Strap muscles
Circular muscles
- also known as sphincters
Fusiform muscles
Penates muscles
- unipennate
- bipennate
- multipennate

Question 10

What do myofibrils appear as under microscopes?

Answer 10

Appear as alternating dark and light bands of tissue

Question 11

What is a summary muscle stimulation and contraction?

Answer 11

1. AFTER : Action potential arrives at many neuromuscular junctions simultaneously
2. CRACKHEAD : causing calcium ion protein channels to open and calcium ions to diffuse into the synaptic knob.
3. PUPPETS: Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine into the synaptic gap
4. ASK: Acetylcholine diffuses across the synaptic cleft and binds with receptors on the
5. SHITTY: muscle sarcolemma causing depolarisation
6. TEACHERS: AP travels down the T tubule and causes Ca2+ to be released from the sarcoplasmic reticulum
7. THE: Ca2+ causes tropomyosin molecules that were blocking
8. ALPHABET: binding site on the actin filament to pull away, unlocks binding site on the actin
9. CRACKHEADS: allowing actin myosin cross bridge to form
10. CALL: ADP molecules attached to the myosin head mean they are in a state to bind to the actin filament and form a cross bridge
11. PEACOCKS: once attached to the actin filament, the myosin heads change their angle, pulling the actin filament along as they do so, releasing ADP and Pi - power stroke!
12. DEAD: An ATP molecule attaches to the myosin head, causing it to detach from the actin filament
13. ANIMALS: The calcium ions then active ATPase, which hydrolyses the ATP to ADP + Pi
14. OVER: The hydrolysis provides the energy for the myosin head to return to its original position
15. REPLICATING: The myosin head, once more with an attached ADP molecule then reattaches itself further along the actin filament
16. HIPPOS: and the cycle is repeated as long as the concentration of calcium ions remain high

Question 12

What is the gross anatomy of mammalian spinal grey matter in X-section?

Answer 12

• Somatic motor efferent with a cell body in either:
  : lamina IX of the spinal cord (i.e. spinal motor nucleus)
  : cranial nerve motor nucleus (such as a CNVII motor nucleus; i.e. cranial motorneurone)
• It’s axon supplies skeletal muscles of the body directly

Question 13

What does a motor unit contain?

Answer 13

• 1 alpha-motorneurone
• extrafusal muscle fibres it supplies - numbers of fibres being variable (extra-ocular muscles (10 fibres) and quadriceps (1000 fibres))
• Each muscle cell receives motor supply from only 1 motorneurone

Question 14

What are characteristics of muscle fibres of a motor unit?

Answer 14

• they have the same physiological profile (contraction speeds, susceptibility fatigue)
• they have the same histochemical profile (myosin fibre typing: enzyme expression profile, metabolic profile)

Question 15

What do characteristics of motor unit allow for?

Answer 15

• uniform development of force throughout the muscle
• the nervous system to regulate the rate and speed of contraction of movements it may choose
• muscle contraction to be distributed throughout the muscle