Muscle Phys - Review

Question 1

Major physiological functions of skeletal muscle

Answer 1

Execute body movement
Establish and maintain posture
Accomplished by shortening or lengthening muscle distance between connections to bone

Question 2

Key properties of all muscle types

Answer 2

Contractibility
Excitability
Extensibility
Elasticity

Question 3

Skeletal muscle

Answer 3

Attaches to bones
Voluntary and involuntary control
Multinucleated (peripheral location)
Striated, bands perpendicular to long axis of fibers

Question 4

Cardiac muscle

Answer 4

Single nucleus, centrally located
Striated, involuntary contraction, intercalated disks

Question 5

Smooth muscle

Answer 5

Walls of hollow organs, blood vessels, eyes, glands, skin
Single nucleus, centrally located
Not striated, involuntary contraction, gap junctions in visceral smooth

Question 6

Coordination in muscle function

Answer 6

Receiving an excitatory stimulus via intracellular signal
Activates shortening machinery in cell (contraction)
Relaxation removes the extra/intracellular stimuli to contract & reverses excitation coupling
Muscles relaxed can stretch passively

Question 7

Depolarization

Answer 7

Action of ACh signaling the NMJ to transit Na & K to depolarize the resting membrane potential. This leads to muscle excitability and contraction & can cause adjacent voltage sensitive Na channels to depolarize & spread the signal, propagating down the cell

Question 8

Depolarization
Repolarization
Hyperpolarization

Answer 8

De - influx of Na into the cell
Re - efflux of K out of cell
Hyper - overshoot of K efflux out of cell

Question 9

Excitation - contraction coupling involves

Answer 9

Is a mechanism which spreading action potential is coupled to muscle fiber contractions
Sarcolemma
T tubules
Release of Ca from sarco retic

Question 10

Dihypropyridine receptor

Answer 10

In sarcolemma or t tubules
Voltage sensitive channel, opens w depolarization
Allows slow influx of calcium from extra cell
Interacts w and activates RyR

Question 11

Ryanodine receptor (RyR)

Answer 11

In sarco retic
Opens when directly activated by DHPR
Allows release of Ca++ stores in SR into sarcoplasm where it can activate contractile machinery

Question 12

Contractile machinery

Answer 12

Thin myofilaments - actin, anchored by z disks
Thick myofilaments - myosin

Question 13

Pathway of action potential to muscle contraction

Answer 13

Action potential enters sarcolemma via t tubules
Ca++ is released from the SPR into the plasma
Ca interacts with sarcomere: binds to troponin, activates/reveals the G actin binding site, myosin attaches to active sight forming a cross bridge

Question 14

Cross bridge cycling

Answer 14

Resting fiber cross bridge not attached to actin
Ca enters and cross bridge binds to actin
Power stroke involves change in orientation of myosin head cross-bridge & dissociation of ADP & P
New ATP binds to myosin head, allowing it to release from actin
ATP is hydrolyzed, causing cross bridge to return to its original orientation

Question 15

What mechanisms account for variation in force in muscle contraction?

Answer 15

Engaged number of motor units
Alteration of frequency of stimulation
Length of muscle prior to arrival of stimulus to contract
Adaptation to exercise

Question 16

Motor unit

Answer 16

Motor neuron plus all muscle fibers with which it forms synapses

Question 17

Graded contractions

Answer 17

Varying degrees of force generation, produced by variations in the number of motor units activated - controlled by CNS

Question 18

Innervation ratios

Answer 18

Fibers per neuron, vary anatomically consistent with the functional requirements of muscle in question

Question 19

Length tension relation in single muscle fiber

Answer 19

Tension generation varies based on length of muscle when signal was received.
Opportunity for greatest contraction is at resting length

Question 20

Length tension relation in muscle unit + tendons

Answer 20

Force generation capacity increases when muscle initially is slightly stretched. Active tension supplements the recoils of passive tension that has been stretched

Question 21

Fast fibers

Answer 21

High myosin ATPase activity, rapid cross bridge cycling & high shortening velocity. Rapid fatigue

Question 22

Slow fibers

Answer 22

Low myosin ATPase activity & lower shortening velocity. Fatigue slowly

Question 23

Oxidative fibers

Answer 23

Have numerous mitochondria, high capacity of oxidative phosphorylation. ATP production dependent on blood borne oxygen & fuel; contain myoglobin, increase rate of oxygen capture in fiber

Question 24

Glycolytic fibers

Answer 24

Fewer mitchondria, high concentration of glycolytic enzymes & glycogen. Larger w more thick/thin filaments = more tension. Fatigue rapidly

Question 25

Effects of exercise on skeletal muscle

Answer 25

Contractile activity increases (hypertrophy, # if myofilaments, capacity for ATP production)
Low intensity = oxidative fiber (^ mitochondria & cap)
High intensity = glycolytic fibers (^diameter of actin/myosin, ^ production of glycolytic enzymes