Lesson 20 The Muscular Tissue Flashcards
what is the purpose of muscles?
to contract and become small!
what does the muscular system refer to?
skeletal muscles. NOT cardiac or smooth muscles
what characteristics do muscle cells have?
- excitability (responsiveness)
- conductivity
- contractility
- extensibility
- elasticity
what is the difference between conductivity and excitability?
excitability is the responsiveness to chemical signals, stretch, and electrical changes across the plasma membrane
conductivity is the local electrical excitation that sets off a wave of excitation that travels along the muscle fiber
what are 2 other ways to call skeletal muscle cells?
muscle fibers or myofibers
what are the 6 functions of skeletal muscle tissue?
- produce skeletal movement
- maintain posture and body position
- support soft tissues
- guard entrances and exits
- maintain body temperature
- store nutrient reserves
what fibrous connective tissues does the skeletal muscle contain (deep to superficial)?
endomysium: surrounds each muscle fiber (thin layer)
perimysium: bundles muscle fibers into fascicles (thick layer)
epimysium: surrounds entire muscle, blends with fascia and deeper connective tissues
what is fascia?
a sheet of connective tissue between muscles or muscle groups
where does the endomysium, perimysium, and epimysium come together and what does it form?
it comes together at the ends of muscles and forms connective tissue attachment to bone matrix (ex. tendon (bundle) or aponeurosis (sheet))
name the components of a muscle fiber
- sarcolemma: plasma membrane of fiber
- sarcoplasm: cytoplasm of fiber
- sarcoplasmic reticulum: smooth ER (stores calcium)
- terminal cisterns: sacs of SR crossing the fiber from one side to another (calcium reservoir)
- transverse tubules: tubular infoldings of sarcolemma; funnels action potentials generated towards terminal cisterns
- myoblasts: stem cells forming the fiber
- myosatellite cells: unspecialized myoblasts remianing between muscle fiber and endomysium
why do skeletal muscle cells have multiple nuclei?
myoblasts contribute one nucleus. multiple myoblasts cause for multiple nuclei in the cell.
what is inside the sarcoplasm?
- myofibrils: long protein cords (occupy most of sarcoplasm)
- glycogen: carbohydrate stored to provide energy for exercise
- myoglobin: red pigmented protein; storage for oxygen and provides some for muscle activity
what are myofibrils composed of?
muscle filaments (myofilaments)
what are the 3 kinds of myofilaments?
- thick filaments: made of several hundred myosin molecules
- thin filaments: made of 3 protein types
- elastic filaments: made of huge springy protein called titin
what is myosin?
a motor protein
what 3 proteins make up thin filaments?
- fibrous (F) actin: 2 intertwined strands of globular (G) actin
- tropomyosin: regulatory protein that blocks the active sites on G actin subunits
- troponin: small, calcium binding protein on each tropomyosin molecule
what is a contractile protein and what are 2 examples?
contractile proteins do the work of contraction
myosin and actin are contractile proteins
what is a regulatory protein and what are 2 examples?
regulatory proteins act like a switch that determines when the muscle fiber can and cannot contract
tropomyosin and troponin act as regulatory proteins
how does contraction occur?
contraction is activated by the release of calcium from the SR into the sarcoplasm, which then binds onto troponin.
troponin changes shape and moves tropomyosin off active sites on actin allowing myosin head to bind onto actin
why are there striations on muscles?
myosin and actin are organized in a precise array that account for striations
what are striations made up of?
A-bands (dark) and I-bands (light)
what is an A-band?
a dark band where thick filaments overlap a hexagonal array of thin filaments.
what is the H band and the M line?
the H band is not as dark and is the middle of the A band; thick filaments only
the M line is a dark, transverse protein in the middle of the H band
what is the I-band?
a light band; only thin filaments
what is the Z disc (Z line)?
a protein complex that provides anchorage for thin filaments and elastic filaments
what is a sarcomere?
a segment from Z disc to Z disc; functional contractile unit of muscle fiber
how do muscle cells shorten?
they shorten because individual sarcomeres shorten. Z discs are pulled closer together as thick and thin filaments slide past each other
do thick and thin filaments change length during shortening?
NO. only the amount of overlap changes as the thin filaments are pulled towards the M line
what is the zone of overlap?
the area of the A band minus the H band (where thin and thick filaments overlap)
this zone increases during muscle contraction
what is denervation atrophy?
shrinkage of paralyzed muscle when nerve remains disconnected. the motor neuron is no longer stimulating the muscle cell
how are nerves and muscles related?
skeletal muscles cannot contract unless they’re stimulated by a nerve. if nerve connections are severed or poisoned, muscle is paralyzed.
what neurons move skeletal muscle cells?
somatic motor neurons. axons of these motor neurons are somatic motor fibers, leading to the skeletal muscle.
what is a motor unit?
one nerve fiber and all the muscle fibers innervated by it; they behave as a functional unit
how do the muscle fibers of one motor unit act?
they contract in unison and produce weak contraction over a wide area. they provide the ability to sustain long term contraction as the motor units take turns contracting.
true or false: effective contraction requires contraction of several motor units at once
TRUE
what is the difference between small motor units and large motor units?
small motor units provide a fine degree of control (less muscle fibers)
large motor units provide more strength than control (more muscle fibers)
what is a synapse?
the point where a nerve fiber meets its target cell
what is the synapse called when the target cell is a muscle fiber?
neuromuscular junction (NMJ) or motor end plate
