Control of Skeletal Muscle Function

Question 1

List the three type of muscles and two similarities

Answer 1

• Skeletal
• Cardiac
• Smooth
  All three use ATP and changing Ca2+ concentrations to contract

Question 2

Function of skeletal muscles… (3)

Answer 2

Move bones via muscle pairs

Used for movement, breathing, posture

Question 3

Structure of skeletal muscle from the muscle to individual components (5)

Answer 3

1) Skeletal Muscle
2) Muscle fibres
3) Transverse (T) tubules
4) Myofibrils
5) Sarcomere - contractile unit

Question 4

Define Sarcomere
What is composed of
What are the specific regions called

Answer 4

a functional unit of a muscle fibre consisting of myofilaments
Actin (thin filaments) and myosin (thick filament) - both together are myofilament
H Zone: middle region of sarcomere; only contains myosin
A Band: zone of whole thick filament (myosin); includes overlapped regions of myosin and actin
I band: zone of thin filament (actin) only
M line: centre of A band therefore middle of sarcomere
Z disc: lateral borders of sarcomere

Question 5

What happens within the sarcomere when the muscle contracts and relaxes?
Do the A band, I band, H zone increase/stay the same/decrease in length

Answer 5

Whole sarcomere shortens, 
H zone decreases 
I band decreases 
A band stay the same
Vice versa when muscle relaxes

Question 6

What are the distinguishable features of muscle cells? (sarco……) What are muscle cells aka?

Answer 6

Muscle cells = large bundles of long cells = muscle fibres
○ Cell membrane of muscle fibre aka sarcolemma
○ Sarcoplasm = muscle cell’s cytoplasm
○ Sarcoplasm folds inwards creating T tubules; aid spread of electrical impulses
○ Sarcoplasmic reticulum runs through sarcoplasm; contain Ca2+
Can be multinucleate
○ Contain long cylindrical ORGANELLES called myofibrils

Question 7

Molecular level - Steps of Contraction in muscle (8)

Answer 7

1. Ca2+ binds to troponin
2. causing conformational changes of actin specifically tropomyosin
3. Leading to exposure of actin-myosin binding sites on actin
4. Therefore myosin heads can bind to binding sites on actin
5. Form actin-myosin cross bridge
6. Ca2+ activate ATPase breaking ATP so get ADP+ Pi + energy, energy used to move myosin head
7. Movement of myosin head pulls actin filament along
8. Aka the power/working stroke

Question 8

Molecular level - Steps of relaxation in muscle (2)

Answer 8

1. ATP provided to break cross-bridge (this occurs once the actin filament has moved forward post power stoke)
2. Myosin reattaches to new am.b.site future down actin

Question 9

Process of AP movement across Neuromuscular junctions (8)

Answer 9

1. AP travels down motor neuron depolarising the pre-synaptic bulb
2. Depolarisation of nerve ending leads to voltage gated Ca2+ open and Ca2+ moves in down it’s concentration gradient
3. ACh released via exocytosis (cholinergic synaptic vesicles bind with membrane)
4. Diffuses across neuromuscular junction and binds to nAChRs on muscle
5. nAChR’s ion channels open so Na+ rushes in depolarising the muscle
6. Initiating action potential in muscle fibre
7. This AP is propagated in the plasma membrane
8. Ach degraded so propagation stopped

Question 10

Pathway of the AP in muscle cell (4) (improve this question when my brain works )

Answer 10

1. AP propagated along sarcolemma and down T tubules
2. AP triggers Ca2+ release from sarcoplasmic reticulum
3. Ca2+ binds to troponin… “Molecular level - Steps of Contraction and relaxation”
4. To end contraction, Ca2+ pumps in sarcoplasmic reticulum use ATP to force Ca2+ back into them, muscle relaxes

Question 11

Summary of ATP use during muscle contraction (3)

Answer 11

• Power-stroke on actin-myosin cross bridge
• Returning myosin to resting position
• Active transport of Ca2+ into SR

Question 12

What is Muscle Proprioception

Answer 12

sense of limb position and movement

Question 13

What are proprioceptors and give their three locations

Answer 13

type of sensory receptor located in skeletal muscle, joints and ligaments
Muscle Spindles
Golgi Tendon Organs
Joints and skin sensors

Question 14

What are two types of skeletal muscle fibres? And their function.

Answer 14

Intrafusal: sensory and monitor changes in muscle length
Extrafusal: generate force for contraction aka contractile fibres

Question 15

What is the role of muscle spindles?
What type of receptor is are they?
What type of skeletal muscle fibres do they contain?
What ….. endings are stimulated when muscle stretches?

Answer 15

monitor muscle length and prevent overstretching
Stretch
Intrafusal
Afferent nerve endings

Question 16

Where are Golgi tendon Organs (GTOs) located?

Answer 16

between skeletal muscle and a tendon

Question 17

What are Golgi tendon Organs (GTOs) made of?

Answer 17

connective tissue capsule and filled with collagen fibres surrounding sensory nerve endings

Question 18

Function of Golgi tendon Organs (GTOs)?

Answer 18

Respond to muscle tension OVERCONTRACTION

Question 19

What are the names of the four autonomic reflex controls of muscle movement?

Answer 19

Stretch Reflex (aka myotatic or deep tendon reflex)
Golgi Tendon reflex (aka inverse myotatic) 
Flexion reflex (withdrawal) 
Flexion and Crossed-Extension reflex

Question 20

Give an example of a stretch reflex

Answer 20

knee jerk reflex

Question 21

What proprioceptor is stimulated during a stretch reflex?

Which one is contracted and relaxed out of muscle initially stimulated and of the antagonistic muscle?

Answer 21

Muscle spindles

○ Muscle spindle stimulated and signals contraction of muscle and relaxation of antagonistic (opposing) muscle

Question 22

Normally during autonomic reflex controls of muscle movements, how many nerves of motor and sensory are stimulated?

Answer 22

2 motor

1 sensory

Question 23

What is reciprocal inhibition?

Answer 23

when one muscle is signalled to contract and other relaxes

Question 24

What proprioceptor is stimulated during a Golgi tendon reflex?
Which one is contracted and relaxed out of muscle initially stimulated and of the antagonistic muscle?

Answer 24

GTO

Muscle is inhibited (relax) and antagonistic muscle is activated (contract)

Question 25

Function of flexion reflex?

What type of receptor is stimulated?

Answer 25

to pull limbs away from painful stimuli

Nociceptors

Question 26

During a flexion reflex nociceptor send signal to spinal cord so …. motor neurones cause …… of flexors and …… of extensors

Answer 26

Alpha
Contraction
Relaxation

Question 27

Function of Flexion and Crossed-Extension reflex

Answer 27

Postural reflex to maintain balance i.e. When stepping on something sharp

Question 28

During a flexion reflex and Crossed-Extension nociceptor send signal to spinal cord so flexors ….. and extensors …… in one leg and vice versa for other

Answer 28

Contract
Relax
(order of answer doesn’t matter)