Anatomy of muscle tissue

which muscles under voluntary vs involuntary control?

voluntary: skeletal muscle

involuntary: smooth and cardiac muscle

which muscles are multiucleated vs uninucleated?

multinucleated cylindrical cell with nuclei in periphery of cell: skeletal muscle

uninucleated: smooth (spindle-shaped cells), cardiac (branching cell shape)

which muscles striated vs unstriated?

striated bc overlapping actin and myosin: skeletal and cardiac

unstriated: smooth muscle

where are the different types of muscle located?

skeletal: along bones

smooth: located in Gi tract, arteries, uterus, airways, eye

cardiac: located in heart

what is excitability?

ability for cells to receive and respond to a stimulus by changing its membrane potential

what is contractility?

ability to shorten with force when stimulated

what is extensibility?

ability to extend/stretch

what is elasticity?

ability for cell to return to resting length after stretching

what are muscle functions?

movement/locomotion, maintaining posture, stabilizing joints and generating heat from muscle contraction

what elements make up skeletal muscle?

skeletal muscle tissue, neurovasculature, and connective tissue sheaths

what are skeletal muscle cells called?

muscle fibers

what are the layers of connective sheaths that envelope muscle tissue?

epimysium, perimysium, and endomysium

what is the epimysium?

dense irregular CT covering the entire muscle (most superficial sheath)

what is the perimysium?

dense irregular CT covering BUNDLE of muscle fibers called FASCICLES

what is the endomysium?

AREOLAR CT surrounding INDIVIDUAL muscle fibers

compare and contrast the different muscle sheaths

write down on whiteboard when studying

what is the sarcolemma?

cell membrane of skeletal muscle fiber

what is sarcoplasm?

cytoplasm of muscle fiber that contains glycosome (granules of glycogen) and myoglobin (oxygen-storing protein)

in muscles, what is most of cell volume taken up by?

myofibrils

what are myofibrils?

chains of contractile filaments organized into functional units called sarcomeres

striation in skeletal (and cardiac) muscle arise from?

overlap or lack thereof between myofilaments (actin and myosin) result in striations of myofibrils

what are all the parts of a myofibril?

sarcomere, A band, myosin and actin, I band, H zone, M line, Z disc

what does a sarcomere do in myofibril anatomy?

extends Z disc to Z disc

what does A band do in myofibril anatomy?

contains overlap between thick filaments made from myosin and thin filaments made of actin

what does I band do in myofibril anatomy?

contains thin filaments composed primarily of actin

what does H zone do in myofibril structure?

lighter central region within A band where thin filaments do not extend

what is the M line in myofibril structure?

fine protein strands anchoring adjacent thick filaments at center of H zone

what is Z disc in myofibril structure?

sheet of proteins anchoring actin filaments. also contains elastic titin filaments to further attach thick filaments. contains dystrophin which is a structureal protein that anchors myofilaments to sarcolemma

in myofilament composition, what are thick filaments made of?

myosin molecules

characteristics of myosin molecules?

eleongated tail with globular head that binds to actin

flexible hinge region at base of head

can split ATP by itself to produce movement so acts as and ATPase

in myofilament composition, what are thin filaments mainly made of?

actin molecules

characteristics of actin?

actin molecules have binding sites for myosin heads

tropomyosin: polypeptide chain that blocks myosin-binding sites of actin during rest

troponin: Ca binding protein that connects to both tropomyosin and actin—so when Ca binds to troponin, moves tropomyosin from binding sites and allows contraction

what is the sarcoplasmic reticulum (SR) made of?

specialized smooth endoplasmic reticulum of muscle cells

what does the sarcoplasmic reticulum (SR) do?

stores calcium and releases when muscle cell stimulated to contract

run longitudinally along myofibrils and end as terminal cisters, perpendicular coross-channels at A band-I bland junctions

mitochondria closes associaated with SR tubules cause need lots of atp

what are T-tubules?

infoldings of the sarcolemma that protrudes to form elongated tubes encircling myofibrils

where are T-tubules located and what do they do?

situated in between terminal cisterns of SR at A band-I band junctions

conduct changes in sarcolema’s membrane potential to deep parts of cell

how does contraction of muscles occur?

contraction occures due to thin filaments sliding acroos thick filaments where myosin heads bind to actin and pull thin filaments closer to M line

when relaxed, where do thick and thin filaments overlap?

only at the ends of A band

what happens during contraction to I band, Z discs, H zone and A band?

I band shortens, Z discs pull closer together, H zones shorten and disappear, and neighboring A bands move closer together, length doesn’t change

contraction via sliding filament model happens in?

occurs in all sarcomeres and myofibrils of stimulated muscle cell

how are muscles stimulated?

by motor neurons

how do motor neurons work?

nuclei of motor neurons located in central nervous system

axons travel in bundles as nerves to skeletal muscles

branches of axons end as axon terminals that interact with individual muscle fibers

axon terminals of motor neurons contain synaptic vesicles filled with the neurotransmitter acetocholine (ACh)

what is a neuromuscular junction?

a synapse between axon terminal and sarcolemma

what is the synaptic cleft in neuromuscular junction?

small space between axon terminal and sarcolemma

what are the junctional folds in neuromuscular junction?

folded surface of sarcolemma at neuromuscular junction that increases surface area and is studded with ACh receptors

how do nerves communicate?

through action potentials

what is resting membrane potential at?

-70 mV

what is an action potential?

is a wave of change in membrane potential that spreads rapidly throughout cell

what happens in action potential?

1st. Na+ channels open resulting in depolarization

then: K+ channels open resulting in repolarization (go back to negative resting potential)

what happens when action potentials reach axon terminals of a nerve?

synaptic vesicles release neurotransmitters (like ACh)