Exam 4 - chapter 9 Flashcards
3 basic types of muscle tissues
skeletal, cardiac, smooth
4 functions of muscle tissue
- movement of bones or fluids (e.g., blood)
- maintaining posture and body position
- stabilizing joints
- heat generation (esp. skeletal muscle)
gross structure of a skeletal muscle
epimysium - surrounds entire muscle (blends with fascia)
perimysium - surrounds fascicles (groups of muscle fibers)
endomysium - between individual muscle fibers
microscopic anatomy of a skeletal muscle fiber
- long cylindrical cell
- multiple peripheral nuclei
- sarcolemma - plasma membrane
- sarcoplasm (cytoplasm)
- myofibrils
- sarcoplasmic reticulum
- t tubules
myofibrils
- densely packed, rodlike elements
- 80% of cell volume
- contain sarcomeres (contractile units)
- exhibit striations - perfectly aligned repeating series of dark A bands and light I bands
sarcoplasmic reticulum (SR)
- network of smooth endoplasmic reticulum surrounding each myofibril
- pairs of terminal cisternae form perpendicular cross channels
- functions in regulation of intracellular calcium levels (stores & releases calcium)
t tubules
- continuations of sarcolemma
- lumen continuous with extracellular space
- increase muscle fiber’s surface area
- penetrate cell’s interior at each A band & I band junction
- associate with paired terminal cisterns to form triads that encircle each sarcomere
which band does not change in width during muscle contraction
i bands shorten, z discs closer, h zones disappear
‘A’ BANDS LENGTH STAYS THE SAME
relate i bands, a bands, h zone, and z lines to the arrangement of thick and thin myofilaments in sarcomeres
I bands are light,
A bands are dark,
h zones: lighter region in midsection of dark A band where filaments do not overlap
Z lines are coin-shaped sheets of proteins on midline of light I band that anchors thin filaments and connects myofibrils to one another
explain how muscle fibers are stimulated to contract by describing events that occur at the neuromuscular junction
- action potential arrives at axon terminal of motor neuron
- voltage-gated calcium ion channels open and calcium ion enters axon terminal moving down the gradient.
- calcium ion causes ACh (neurotransmitter) to be released.
- ACh difusses across the synaptic cleft and binds to receptors on cell membrane.
- ACh binding opens ion channels in the receptors that allow sodium in and potassium out.
- ACh effects are terminated by acetylcholinesterase and diffuse away from junction.
sliding filament model of contraction
during contraction, the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree.
when nervous system stimulates muscle fibers, the myosin heads on the thick filaments latch onto myosin-binding sites on actin in the thin filaments, and the sliding begins.
these cross bridge attachments form and break several times during a contraction, acting like tiny ratchets to generate tension and propel the thin filaments toward center of sarcomere.
as this occurs, muscle cell shortens
i bands shorten, z discs get closer together, h zones disappear
‘A’ BANDS LENGTH STAYS THE SAME
events of excitation-contraction coupling that lead to cross bridge activity
- action potential propogates along the sarcolemma and down t-tubles.
- calcium ions released
- calcium binds to troponin and removes the blocking action of tropomysin
- contraction begins.
motor unit
motor neuron and all muscle fibers it supplies (4-several hundred)
smaller motor units = fine control. (eyes, fingers)
larger motor units = weight-bearing, larger muscles (hip muscles)
muscle twitch
motor unit’s response to single action potential of its motor neuron. simplest observable in lab, recorded as myogram
events in a muscle twitch
latent period - events of excitation-contraction coupling, no muscle tension
period of contraction: cross bridge formation; tension increases
period of relaxation: calcium ion reentry into SR; tension declines to zero