Nerve, Junction, Muscle Flashcards
how many spinal vertebrae are there
33
how many spinal nerves are there
31 spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal)
in the cervical region, where do nerve roots come out, relative to their named vertebrae
nerves come out ABOVE their named vertebrae
in the thoracic and lumbar regions, where do spinal nerves come out, relative to their named vertebrae
spinal nerves come out BELOW their named vertebrae
where does the C7 nerve root come out
C6-C7 vertebrae
where does the C8 nerve root come out
C7-T1 vertebrae
where does the L5 nerve root come out
L5-S1 vertebrae
where does the L4 nerve root come out
L4-L5 vertebrae
what spinal nerves contribute to the brachial plexus
C5-T1
what are the terminal divisions of the brachial plexus
MARMU: musculocutaneous, axillary, radial, median, and ulnar nerves
long thoracic nerve
*comes off the roots of the brachial plexus
*innervates serratus anterior
*damage = winged scapula
dorsal scapular nerve
*comes off the roots of the brachial plexus
*innervates the rhomboid muscles
pinching of the lateral femoral cutaneous nerve causes ?
meralgia paresthetica (tingling, numbness, burning pain in anterolateral thigh)
what does the femoral nerve innervate
1) quadriceps muscles
2) sensation down the medial aspect of the leg (distal to the knee)
what does the sciatic nerve innervate
1) hamstrings
2) muscles distal to knee
*splits into fibular (peroneal) and tibial nerves
epineurium
outside of nerve (wraps multiple fascicles together)
perineurium
creates fascicles (wraps multiple nerves together)
*strongest blood-nerve barrier
endoneurium
wrapped around each axons
resting potential of a nerve
-70 mV inside the nerve (polarized)
*lots of Na+ outside the membrane, compared to lots of K+ inside the membrane
3 things that contribute to the resting potential of the nerve
1) Na+/K+ pump
2) negatively charged proteins within the cell
3) permeability to K+ of the cell (lots of K+ inside the cell)
action potential of a nerve
1) stimulus changes the resting potential, and once it reaches -55 mV (threshold), then channels open and Na+ rushes IN
2) inside of the cell becomes positive (depolarized)
3) K+ flows OUT, allowing re-polarization, completing the action potential (nerve impulse)
motor unit
a nerve AND all the muscle fibers it innervates
steps for a nerve to stimulate a muscle
1) action potential propagates along the neuron to the axon terminal
2) voltage-gated calcium channel opens and calcium floods in
3) calcium interacts with SNARE proteins, causing fusion of the vesicle and subsequent release of the neurotransmitter (acetylcholine) into the synaptic cleft
4) acetylcholine binds to the acetylcholine receptor, opening an ion channel
5) sodium rushes in, and an action potential propagates along the muscle
6) acetylcholinesterase degrades acetylcholine in the synaptic cleft
gross anatomy of a muscle (in general)
bone - tendon - skeletal muscle - tendon - bone
muscle fiber
syncytium of cells, made of many myofibrils
*epimysium, perimysium, and endomysium
myofibrils
composed of a series of repeating functional contractile units called sarcomeres
sarcomere
spans from Z-disk to Z-disk
A band (of sarcomere)
correspond to the fixed length of the myosin thick filaments
I bands (of sarcomere)
*correspond to the zone of thin filaments that are NOT overlapping the thick filaments
*exclusively contains thin filaments
Z-line
*contains proteins that bind and stabilize the ends of actin filaments
*define the borders of the sarcomere
H-band
*a light band that sits within each A band
*contains exclusively THICK filaments
*SHORTENS during muscle contraction
M line
*bisects the sarcomere, each A-band, and each H-band
which portions of the sarcomere change during muscle contraction
*lengths of H band and I bands change in proportion to the degree of sarcomere relaxation or contraction
*z lines come closer to each other
which portion(s) of the sarcomere remain constant during muscle contraction
the length of the A band always remains the same
what happens at the micro level during muscle contraction
1) the thin filaments slide past the thick filaments as a result of cross-links that form between actin and myosin
2) the binding of Ca2+ to troponin C causes a steric movement such that tropomyosin shifts out of the groove of the actin helix, EXPOSING THE MYOSIN HEAD BINDING SITE
3) tension pulls the thin filaments toward the thick filaments
steps of muscle contraction
- acetylcholine binds to the post-synaptic receptor
- sodium flows in, starting an action potential
- action potential travels down t-tubules
- calcium channels open and calcium flows from sarcoplasmic reticulum into the sarcoplasm
- calcium bids to troponin C portion of actin thin filaments
- this causes tropomyosin to change configuration (move out of the way to open up binding sites for myosin)
- myosin heads (thick filaments) with ADP can now bind actin and pull thin filaments toward the middle of sarcomere (power stroke)
what happens in rigor mortis
unbinding of the myosin head requires ATP; in rigor mortis, there is no ATP, so the myosin head cannot unbind from actin, leading to stiffness
