Muscle Physiology Flashcards
what are 4 purposes of skeletal muscle?
voluntary and reflexive movements like
1. maintaining posture
2. respiration
3. communication
4. produce body heat
what is the purpose of smooth muscle?
constriction and dilation of organs, vessels, and aperatures
what is the purpose of cardiac muscle?
heart constriction and relaxation
what does skeletal muscle require for contraction?
MUST be innervated
do cardiac and smooth muscle require innervation to contract?
no; they have intrinsic contraction
what is a muscle fiber?
single muscle cell
what is a myofibril?
organized protein fiber within the muscle cell
what is a sarcomere?
the unit of the myofibril that shortens to cause muscle contraction
what are thick filaments made up of?
myosin
what are thin filaments made up of?
actin; which contains troponin and tropomyosin
what are transverse (T) tubules? function?
invaginations of the sarcoplasm into the muscle fiber; important in helping the spread of the action potential
what is the sarcoplasmic reticulum? function?
modified endoplasmic reticulum with TONS of calcium; important source of calcium and for rapid release and reuptake of calcium
what is the motor unit?
the alpha motor neuron and all the muscle fibers it innervates
what is the neuromuscular junction?
the synapse between the neuron and the muscle fiber
what is the purpose of small motor units?
fine control, like the muscles in our fingers
what is the purpose of big motor units?
support/posture, like the muscles in our quads
what is the most highly developed synapse in the body?
the neuromuscular junction
how many neurons innervate each muscle fiber?
only one!!
what is the alpha motor neuron important for?
the integrity of the muscle fiber
what does loss of innervation result in?
rapid muscle atrophy
what is the major neurotransmitter released from the alpha motor neuron?
acetylcholine (ACH)
what is the primary receptor on the muscle fiber?
nicotinic, receives acetylcholine
what generates an action potential, in terms of muscle fiber parts
the cell membrane (sarcoplasm) of the muscle fibers
describe how the action potential moves through parts of the muscle fiber and what is results in
AP enters the T tubule system and initiates calcium release from the sarcoplasmic reticulum
why is it good to have a channel coupled to a receptor?
it always opens when you want!
give the 8 steps of an action potential moving through the neuromuscular junction
- motor neuron fires an action potential
- calcium enters its voltage-gated channels
- acetylcholine is released
- sodium enters the muscle fiber
- local current is established between the depolarized end plate and the adjacent muscle plasma membrane
- muscle fiber initiates action potential
- propagated action potential in muscle plasma membrane
- acetylcholine degradation
what is acetylcholinesterase and what is its use?
allows efficient termination of acetylcholine; allows synapses to only respond when AP is traveling down/through a synapse
give the 4 steps of calcium release from the sarcoplasmic reticulum
- the DHP receptor is voltage sensitive and activated by the passing action potential
- the DHP receptor has a calcium channel which allows calcium to enter the muscle cell
- activation of the DHP receptor causes calcium release from the sarcoplasmic reticulum
- calcium from the sarcoplasmic reticulum will bind to troponin of the thin filament
give the 7 steps of the power stroke/cycling of the myosin head
- calcium bonds to troponin and causes a conformation change in tropomyosin to expose myosin binding sites
- the myosin head binds to a site and ADP is released
- stored energy is released, causing the myosin head to change conformation resulting in the power stroke and the thin and thick filaments slide past each other
- ATP binds to myosin, causing it to release from the actin protein
- the ATP os hydrolyzed to ADP + Pi, resulting in the myosin head changing conformation (re-cocking)
- if calcium is still binding troponin and the myosin binding site on the actin molecule is still exposed, the cycle repeats
- if the action potentials cease, the calcium is rapidly pumped back into sarcoplasmic reticulum
how long will the myosin head cycle continue?
as long as BOTH ATP and calcium are present
how many ATP are used per power stroke?
one
what happens to a muscle if no ATP is present? why and what is this called?
the muscle is locked in its contracted state/AKA rigor mortis; ATP allows relaxation (binds to myosin causing it to release from actin)
what happens to skeletal muscle if it loses innervation?
rapid muscle atrophy; lose all reflexivity and muscle become flaccid
what is muscle associated with and how does this relate to muscle shortening?
muscle is associated with lots of connective tissue that must be tightened before muscle shortens
what is important in generating some muscle tone?
the activity of the alpha motor neurons to the muscle; generates some resting tension/muscle tone plus the myotatic reflex
what 2 things are required to get movement from a muscle?
- contract the desired muscle
AND - relax its antagonistic muscle
what are the 2 actions of muscle? describe
- static: generation of force with no movement of the joint
- dynamic: results in joint movement
what are the 2 types of dynamic muscle movement?
- concentric: shortening of the muscle (more common)
- eccentric: lengthening of the muscle
does the action potential and generation of tension occur simultaneously? why or why not?
action potential first, generation of tension slightly lags after due to calcium release, protein interactions, and tensing of elastic elements that all has to occur
how does the length of the sarcomere relate to tension in muscle?
the resting length is optimal for max tension generation; if sarcomere is too long, there is minimal interaction between the thin and thick filaments; if too short, too much/too cramped interaction and less tension is generated
can you generate tension if you can’t shorten the sarcomere?
nope
how does the number of muscle fibers relate to strength? why?
more fibers results in more strength, usually because more motor units are involved
which generates more tension: when motor units fire together or individually?
when they fire together
what does all muscle have for contraction?
actin and myosin
describe how calcium is related to contraction in all muscle types?
calcium is involved in contraction in all 3 muscle types, but the source of calcium differs between the types
is troponin found in smooth muscle?
NO!
list the 6 steps of the contraction cycle in smooth muscle
- action potential enters voltage-gated calcium channels
- calcium enters smooth muscle cell and activates calmodulin
- the calcium-calmodulin activated myosin light chain kinase (MLCK) is formed
- MLCK phosphorylates the myosin light chain in the myosin head
- this causes the head to bind to the actin protein and elicit a power stroke
- the power stroke releases the phosphate and the cycle starts over as long as calcium is present
if you gave a calcium channel blocker, would smooth muscle contraction increase or decrease? why? give a practical application
decrease because most calcium for smooth muscle comes from extracellular sources (not the sarcoplasmic reticulum like in skeletal muscle); drugs that work this way are used to relax arterioles to decrease blood pressure
is smooth muscle organized into sarcomeres?
nope!
how is smooth muscle organized? contrast contraction motion to skeletal muscle
like drawstrings; scrunch/constrict contraction instead of linear
