Advance Muscle Physiology Week 3 Smith Flashcards
Skeletal Muscle overview
Striated Cells voluntary multinucleated Not self stimulating high energy requirement fast contracting fatigues easily typically attached to bone (not tongue)
Main events in skeletal muscle contraction
- AP initiated and propagates through motor neuron
- AP triggers ACh release at presynaptic mem. of neuromuscular junction
- ACh diffuses across synaptic cleft from axon terminal to postsynap. mem in muscle fiber
- Na+ influx=K+ efflux, local depolarization occurs(aka end plate potential EPP)
- EPP triggers AP in muscle cell that propagates into t-tublules
- AP triggers Ca++ release from sarcoplasmic reticulum (SR)
- Ca++ binds to troponin on actin and shifts tropomyosin to allow cross bridge
- energized myosin heads bind to actin and rotate causing shortening and contraction.
Role of Ca+ in muscle contraction (3)
- promotes presynaptic neurotransmitter release
- Ca+ released from SR binds to troponin to initiate sliding filaments
- Ca+ promotes glycogen breakdown and ATP synthesis by activating essential enzymes.
free cytosolic ATP provides how many seconds of intense activity?
5 to 6 seconds
Creatine Phosphate
CP and ADP rxn leads to creating and ATP
15 sec of exercise and 1 ATP/CP
Glycogenolysis (anaerobic Respiration)
No oxygen present
2 ATP per glucose
lactic acid by product
provides 30-60 of exercise
Cellular (Aerobic) repiration
oxygen required
energy sources: glucose, pyruvic acid, fatty acids, AAs
38 ATP and hours of energy and CO2 and H20 as byproducts
What is oxygen debt
the amount of O2 needed to convert the accumulated lactic acid to glucose and to restore the supplies of ATP and Creatine phosphate (CP)
Define: Twitch
the single, brief contraction of a muscle in response to a single AP on its motor neuron
What causes a twitch
a single brief stimulus at a the threshold value to produce a quick all or nothing cycle of contraction and relaxation
All-or-none response of motor units
when the motor neuron fires, all of the muscle fibers innervated by its nerve(muscles in that motor unit) will contract.
laten period
delay between stimulus and onset of twitch
contraction phase
period during which tension develops and muscle shortens. no new stimulus can happen during this phase
relaxation phase
shows a loss of tension and return of muscle to resting length
refractory period
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.
Multiple motor unit summation or recruitment
increasing the strength of the stimulus at a constant frequency to recruit additional motor units and thereby increase the tension developed.
Maximal stimulus
when you have reached the max amount of neural stimuli to produce a contraction
Wave (temporal) Summation
increasing the frequency of a stimulus that is held at a constant intensity.
Treppe
form of incomplete fusion of the wave summation at a frequency just below tetanus but still below max tension
Tetanus
complete fusion of wave summation, or no relaxation between stimuli(result of depleting calcium)
Fatigue
the result of exhaustion of ATP, buildup of waste products such as lactic acid and loss of tension despite continuing stimuli
Tension
the force exerted on an object by a contracting muscle
Load
the force exerted on the muscle by an object
Isotonic contraction
- the tension generated by the muscle is greater than the load and muscle shortens.
- During relaxation, the muscle is re-extended by the load
Isometric contraction
the load exceeds the tension so the muscle doesn’t shorten.
Optimal sarcomere length
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
What is fractionation?
means that all motor units do not need activation for every load. But the more the motor units activated the greater the tension
Henneman’s Size Principle
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!!
Slow twitch fibers
continuously firing regardless of intensity.
Slow fibers=prolonged activity( maintaining posture, marathons)
Fast twitch
fast fibers=rapid powerful action jumping, short distance running.
two types type IIa and IIb
6 basic components of reflexes
- A sensory receptor
- An afferent neuron
- An integration center (CNS)
- An interneuron
- A motor efferent neuron
- An effector muscle
Stretch reflexes
- 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
Difference between extrafusal fibers and intrafusal fibers
extra: make up bulk of muscle, innervated by alpha-motor neurons, provide force for muscle contraction
Intra: innervated by gamma-motor neurons
Golgi (deep) tendon reflex
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.
Difference between muscle spindle(measures muscle length) and Golgi Tendon Organ(measures muscle tension)
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.
