Muscle Physiology: Lecture 1 Flashcards
each muscle consists of ______ to ______ of individual contractile fibers
hundreds to thousands
connective tissue is made up of mostly…
mostly collagen, some elastin
epimysium
tough coat of tightly woven bundles of collagen which surround entire muscle, separating it from other muscles and structures
myotendinous junction
ends of the muscle where epimysium connects with the sarcolemma
why is there extensive folding of both the epimysium and sarcolemma?
more surface area?
perimysium
tough and thick
- divides muscle fibers into fascicles, or bundles
- provides pathway for arteries, veins and nerves
endomysium
- surrounds each muscle fiber
- connects both the perimysium and the basement membrane
sarcolemma
consists of a
- basement membrane
- plasmolemma or cell membrane
basement membrane
several compounds, mostly proteins, glycoproteins, and collagen
conduit arteries and veins
parallel along surface of muscle
perforating arteries and veins dive into the belly of muscle in ______
parallel (in the belly)
arterioles lead to a ______ which surrounds each fiber
capillary network
a capillary network surrounds ______
each fiber
nerves usually run in _______ with the arteries and veins
parallel
what makes up 60% of the nervous innervation of skeletal muscle?
motor nerves
what represents the final nerve in the path from the motor centers In the cerebrum to the target muscle?
motor nerves
what produces muscle contraction when stimulated
motor nerves
motor nerve impulses travel in an ______ direction
efferent direction
efferent means
away from the spinal cord/central nervous system
impulses travel very fast along an axon because of ____
the myelin sheath
the region of muscle plasmalemma under the terminal axon
motor end plate
what kind of nerves represent 40% of the nerves in skeletal muscles
sensory nerves
sensory nerve impulses travel in an ____ direction
afferent direction
afferent means
toward the spinal cord/central nervous system
what is the purpose of sensory nerves?
they relay a variety of touch, pain, and muscle tension and contraction information
skeletal muscles appear _____
striated
____ is the cell membrane surrounding each cell
sarcolemma
______ is a membranous network that surrounds each myofibril.
sarcoplasmic reticulum
what is one of the primary roles of the of the sarcoplasmic reticulum?
the release of Ca++ which initiates the contraction process
_____ are membranous channels that extend inward from the sarcolemma and pass completely through the fiber
transverse tubules
the transvers tubules pass between enlarged portions of the SR called ______.
cisternae
each ______ is long and rod-like in shape, it consists of a 3 dimensional arrangement of the contractile elements.
myofibril
the basic unit of the contractile element is the ______. each is separated from the next by connective tissue called a Z line.
sarcomere
myosin filaments
thicker, make up the dark A band
actin filaments
thin, and extend in both directions from the Z line
-constitute the lighter region of the sarcomere called the I band
H zone
at the center of the sarcomere
-represents the area of only myosin, between the actin filaments extending from the Z line at each end of the sarcomere
actin
double helix of spherical molecules which contain sites for binding to myosin
tropomyosin
helical molecule that wraps around the actin strand to cover up the myosin binding sites
troponin
sits on the tropomyosin strands
-has a binding site for Calcium
titin
the largest proteins in our bodies (keeps myosin in place)
- found in cardiac and skeletal muscle fibers
- acts like a giant spring
- thethers the myosin filament within the sarcomere
- source of much of the passive force in skeletal muscle
- the major mechanism for the frank-starling mechanism in the heart
motor-end plate
the site where the alpha motor neuron ends and transmits depolarization signal to the muscle
true or false: the alpha motor neuron physically touches the sarcolemma of the muscle cell
false: it does not touch the sarcolemma of the muscle cell
neuromuscular junction or synaptic cleft
where the sarcolemma inviginates around the alpha motor neuron synapse
steps in excitation contraction coupling ECC
- alpha motorneuron depolarization wave (action potential)leads to the release of acetylcholine ACh from nerve ending (nerve bouton)
- ACh binds to ACh binding site, causing Na+ entry into cell, leading to depolarization of muscle cell membrane (sarcolemma): called the end-plate potential
- depolarization wave on sarcolemma is transmitted down the t-tubules
- this leads to the release of calcium from the sarcoplasmic reticulum
- Calcium then binds to troponin initiating contraction process
- to restore the cell to its pre contraction state, calcium is pumped back into the SR by the SR Calcium ATP-ase
- ACh is broken down by enzyme acetylcholinesterase
consequence of excitation contraction coupling
there has to be continual motorneuron activity to cause continued muscle contraction
muscle contraction – the sliding filament theory
- rest
- excitation coupling
- active contraction
- recharging system
- subsequent response dependent on presence of Calcium
step 1. rest of sliding filament theory
a. myosin heads extended, but not contacting actin
b. Calcium stored in sarcoplasmic reticulum
c. myosin head is energized by breakdown of ATP
Step 2. excitation coupling
of the sliding filament theory
a. nerve impulse from motor neuron leads to depolarize of sarcolemma, SR.
b. Calcium released from SR into cytosol
c. Calcium binds to troponin, causes tropomyosin to shift, exposing myosin binding sites on actin
d. myosin binds to active site on actin
Step 3: active contraction
of the sliding filament theory
a. myosin heads flex, causing myosin chain to move along the actin filament, resulting in shortening of the sarcomere
b. force is developed
c. ADP and Pi are released from the myosin head
Step 4: recharging system
of the sliding filament theory
a. ATP binds to myosin, causing release of actin myosin bond
b. ATP is then broken down, resulting in charging of the myosin head, and production ADP and Pi
Step 5: subsequent response dependent on presence of calcium
of the sliding filament theory
a. if calcium is still present, means nerve stimulation still occurring, muscle contraction, repeat steps 2-4.
b. if nerve depolarization ceases, Calcium can be resequestered in SR by calcium ATPase. this leads to muscle resting in step #1.
