Muscle physiology Flashcards
name the different phases of muscle contraction?
1) resting and energized
2) excitation and contraction coupling
3) contraction (power stroke)
4) recharge
5) relaxation
what is the size principle?
Motor units are recruited in order by size
what are the characteristics of type I muscle fibers?
- more mitochondria
- more aerobic enzymes
- higher capillary density (O2 delivery)
- more myoglobin
- fatigue resistant
What are the characteristics of type II muscle fibers?
- all the opposite of type I
- greater acute force production
Describe proprioception
Proprioception is the sense of the relative position of neighboring parts of the body.
what 2 structures are key to proprioception?
Muscle Spindles and GTOs
what are muscle spindles? what is their function?
Modified muscle fibers: serve to regulate muscle contraction by responding to the lengthening of the muscle body (deformation stimulates sensory neuron; motor neuron signals muscle shortening)
where are muscle spindles located?
In the muscle belly itself
what and where are GTOs?
proprioceptors located in tendons near the myotendinous junction.
what is the function of GTOs?
protective mechanism: the sensory neuron of the GTO stimulate an inhibitory interneuron which then inhibits the motor neuron, stopping muscle from contracting
what is the innervation ratio?
efferent neurons: innervated fibers
how is force production regulated? (force gradation)
rate coding or motor recruitment
describe force gradation
Firing rate: overlapping action potentials will result in greater force (tetanus). If a small amount of force is required, then there will be more time between the synapses.
explain motor recruitment
depending on how much force is needed different numbers of motor units are recruited.
define motor unit
a single efferent neuron and all the muscle fibers it innervates
how does an efferent neuron influence the fibers
it innervates?
the type of fiber (fast or slow twitch; I or II) is dependent on the kind of efferent neuron that innervates it
afferent neurons
transmit information from the receptors to the CNS
transmit information from the CNS to the muscles
efferent
2 primary phases of nerve stimulation
depolarization and repolarization
what is the myelin sheath? what is it’s purpose?
fatty covering of the axon. conducts the action potential faster down toward the NMJ
Motor unit activation is determined by a ________
threshold
describe the all or nothing principle
it is not possible to almost reach threshold and create some force production or over achieve threshold and create more force production. Only when threshold is reached does it produce and effect, and that effect is always of the same magnitude
Slight relaxation between action potentials
incomplete tetanus
action potential at the nerve terminal causes the release of _____________.
acetylcholine
3 types of connective tissue in the muscle
Epimysium, Perimysium, Endomysium
what connects the myosin to the Z line?
titin
