Advance Muscle Physiology Week 3 Smith

Question 1

Skeletal Muscle overview

Answer 1

Striated Cells
voluntary
multinucleated 
Not self stimulating
high energy requirement
fast contracting 
fatigues easily
typically attached to bone (not tongue)

Question 2

Main events in skeletal muscle contraction

Answer 2

1. AP initiated and propagates through motor neuron
2. AP triggers ACh release at presynaptic mem. of neuromuscular junction
3. ACh diffuses across synaptic cleft from axon terminal to postsynap. mem in muscle fiber
4. Na+ influx=K+ efflux, local depolarization occurs(aka end plate potential EPP)
5. EPP triggers AP in muscle cell that propagates into t-tublules
6. AP triggers Ca++ release from sarcoplasmic reticulum (SR)
7. Ca++ binds to troponin on actin and shifts tropomyosin to allow cross bridge
8. energized myosin heads bind to actin and rotate causing shortening and contraction.

Question 3

Role of Ca+ in muscle contraction (3)

Answer 3

1. promotes presynaptic neurotransmitter release
2. Ca+ released from SR binds to troponin to initiate sliding filaments
3. Ca+ promotes glycogen breakdown and ATP synthesis by activating essential enzymes.

Question 4

free cytosolic ATP provides how many seconds of intense activity?

Answer 4

5 to 6 seconds

Question 5

Creatine Phosphate

Answer 5

CP and ADP rxn leads to creating and ATP

15 sec of exercise and 1 ATP/CP

Question 6

Glycogenolysis (anaerobic Respiration)

Answer 6

No oxygen present
2 ATP per glucose
lactic acid by product
provides 30-60 of exercise

Question 7

Cellular (Aerobic) repiration

Answer 7

oxygen required
energy sources: glucose, pyruvic acid, fatty acids, AAs
38 ATP and hours of energy and CO2 and H20 as byproducts

Question 8

What is oxygen debt

Answer 8

the amount of O2 needed to convert the accumulated lactic acid to glucose and to restore the supplies of ATP and Creatine phosphate (CP)

Question 9

Define: Twitch

Answer 9

the single, brief contraction of a muscle in response to a single AP on its motor neuron

Question 10

What causes a twitch

Answer 10

a single brief stimulus at a the threshold value to produce a quick all or nothing cycle of contraction and relaxation

Question 11

All-or-none response of motor units

Answer 11

when the motor neuron fires, all of the muscle fibers innervated by its nerve(muscles in that motor unit) will contract.

Question 12

laten period

Answer 12

delay between stimulus and onset of twitch

Question 13

contraction phase

Answer 13

period during which tension develops and muscle shortens. no new stimulus can happen during this phase

Question 14

relaxation phase

Answer 14

shows a loss of tension and return of muscle to resting length

Question 15

refractory period

Answer 15

period when muscle will not respond to new stimulus. very short period 2-3 msec. also the same motor units involve in the twitch response cannot be fired during this brief phase.

Question 16

Multiple motor unit summation or recruitment

Answer 16

increasing the strength of the stimulus at a constant frequency to recruit additional motor units and thereby increase the tension developed.

Question 17

Maximal stimulus

Answer 17

when you have reached the max amount of neural stimuli to produce a contraction

Question 18

Wave (temporal) Summation

Answer 18

increasing the frequency of a stimulus that is held at a constant intensity.

Question 19

Treppe

Answer 19

form of incomplete fusion of the wave summation at a frequency just below tetanus but still below max tension

Question 20

Tetanus

Answer 20

complete fusion of wave summation, or no relaxation between stimuli(result of depleting calcium)

Question 21

Fatigue

Answer 21

the result of exhaustion of ATP, buildup of waste products such as lactic acid and loss of tension despite continuing stimuli

Question 22

Tension

Answer 22

the force exerted on an object by a contracting muscle

Question 23

Load

Answer 23

the force exerted on the muscle by an object

Question 24

Isotonic contraction

Answer 24

• the tension generated by the muscle is greater than the load and muscle shortens.
• During relaxation, the muscle is re-extended by the load

Question 25

Isometric contraction

Answer 25

the load exceeds the tension so the muscle doesn’t shorten.

Question 26

Optimal sarcomere length

Answer 26

the muscle is slightly stretched and there is slight overlap between the myofibrils allowing maximum overlap of actin and myosin.
80-120% sarcomere length is optimal

Question 27

What is fractionation?

Answer 27

means that all motor units do not need activation for every load. But the more the motor units activated the greater the tension

Question 28

Henneman’s Size Principle

Answer 28

motor units are recruited in the order of the size of the motor unit based on the force/resistance needed.
always recruited small fibers to large!!

Question 29

Slow twitch fibers

Answer 29

continuously firing regardless of intensity.

Slow fibers=prolonged activity( maintaining posture, marathons)

Question 30

Fast twitch

Answer 30

fast fibers=rapid powerful action jumping, short distance running.
two types type IIa and IIb

Question 31

6 basic components of reflexes

Answer 31

1. A sensory receptor
2. An afferent neuron
3. An integration center (CNS)
4. An interneuron
5. A motor efferent neuron
6. An effector muscle

Question 32

Stretch reflexes

Answer 32

• initiated at receptors called muscle spindles which are sensitive to length of muscle as it is stretched.
• Stretching depolarizes muscle spindles, sends AP to CNS and activates alpha motor neuron to contract stretched muscle.
• *monosynaptic**
  eg. knee-jerk

Question 33

Difference between extrafusal fibers and intrafusal fibers

Answer 33

extra: make up bulk of muscle, innervated by alpha-motor neurons, provide force for muscle contraction
Intra: innervated by gamma-motor neurons

Question 34

Golgi (deep) tendon reflex

Answer 34

initiated at golgi tendon organs(GTOs) that are sensitive to tension in tendon caused by muscle contraction.

• GTOs depolarize in response to the tendon being stretched, but inhibit alpha motor neuron.
• Stimulates contracted muscle to relax relieving tension on the tendon
• Prevents tendon damage
• disynaptic- on neuron to antagonist and one to stretched muscle.

Question 35

Difference between muscle spindle(measures muscle length) and Golgi Tendon Organ(measures muscle tension)

Answer 35

MS: stretch activates efferent alpha motor neurons when muscle is stretched causing contraction of the muscle
GTO: inhibits efferent alpha motor neuron when the muscle is contracted causing relaxation of the muscle to prevent injury.