principles

Question 1

what is skeletal muscle contraction initiated by?

Answer 1

stimulation of alpha motor neurons

-> neurogenic initiation of contraction

Question 2

what is meant by the term motor unit?

Answer 2

a single alpha motor neuron + al the skeletal muscle fibres it innervates

-> the number of muscle fibres per motor unit depends on the function of the muscle

Question 3

what is the most abundant component of cartilage extracellular matrix?

Answer 3

water (75%) - articular cartilage (hyaline) composed of water

15% = type II collagen
10% = proteoglycan - made up of GAGs

avascular - receives nutrients via synovial fluid

Question 4

what are the dark and light parts of striated muscle?

Answer 4

dark = myocin

light = actin

Question 5

what is the functional unit of skeletal muscle?

Answer 5

sarcomere

smallest component capable of performing all the functions

Question 6

where is the Ca2+ used in muscle contraction derived from?

Answer 6

derived entirely from sarcoplasmic reticulum in skeletal muscle

Question 7

what is ATP needed for in contraction + relaxation?

Answer 7

contraction - to power cross bridges

relaxation - release cross bridges + to pump Ca2+ back into sarcoplasmic reticulum

Question 8

what are the 2 primary types of skeletal muscle contraction and what are they used for?

Answer 8

isotonic contraction - body movements + moving objects

isometric - supporting objects in fixed positions + maintaining body posture

–> contractions of both is transmitted to bone via elastic components of muscle

Question 9

what are the different types of muscle fibres and when are they used?

Answer 9

• Slow oxidative type I (slow twitch)
  o Used for low work aerobic activities – maintaining posture
  o Resistant to fatigue
  o Often called red fibres
• Fast oxidative type IIa (intermediate twitch)
  o Use both aerobic + anaerobic metabolism
  o Used in prolonged moderate work - jogging

-	Fast glycolytic type IIx (fast twitch)
o	Use anaerobic metabolism
o	Short term high intensity – jumping
o	Fatigue easily
o	Often called white fibres

Question 10

give examples of cartilaginous joints

Answer 10

intervertebral discs
pubic symphysis
costochondral joints

-> limited movement

Question 11

how does normal synovial fluid compare to inflammatory synovial fluid?

Answer 11

normal

• viscosity = high
• colour = colourless

inflammatory

• low viscosity
• colour = straw to yellow

Question 12

how is end plate potential generated?

Answer 12

Na enters and K leaves when nicotinic ACh receptors are open (activated by ACh)

Na influx is greater than K efflux so end plate potential is generated by simultaneous opening of many receptors
-> if meets threshold it triggers opening of voltage-activated Na+ channels causing action potential

Question 13

how does the action potential propagate from the sarcolemma (surface membrane) to the sarcoplasmic reticulum?

Answer 13

transverse (T)-tubules

Question 14

how is a neuromuscular transmission terminated?

Answer 14

hydrolysis of ACH by acetylcholinestererase (AChE)

choline - taken up by choline transporter
acetate - diffuses from synaptic cleft

Question 15

what are nociceptors?

Answer 15

specific primary sensory afferent neurones normally activated by intense noxious stimuli
–> first order neurones

Question 16

how do nociceptors transmit sensory info to the thalamus?

Answer 16

propagate info to spinal cord via DORSAL horn where they release pain neurotransmitters eg substance P

second order neurone recieves info + crosses to opposite side of spinal cord where it travels to thalamus via spinothalamic tract or spinoreticular tract

from thalamus third order neurones take info to primary sensory cortex