Chapter 11.5 - Muscular System Flashcards by Aditi Iyer

Where is smooth muscle found

walls of our organs, airways, blood vessels

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Smooth muscle is not:

striated

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smooth muscle contracts and relaxes:

involuntarily

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What gives muscles a striated appearance?

sarcomeres

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cardiac muscle contracts and relaxes:

involuntarily

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cardiac muscle has __ nucleus/nuclei per cell

1 nucleus

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Which muscles are striated?

skeletal and cardiac

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Which muscle contains intercalated discs?

cardiac cells

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Intercalated discs contain:

desmosome and gap junction

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Gap junction allows for:

cells can pass ions quickly allowing heart to depolarize and contract in unison

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skeletal muscle cells are:

long, multinucleated, striated

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Smallest to largest unit of skeletal muscle

myofibril –> muscle fiber –> fascicles –> muscle

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protective sheath encasing the muscle fiber:

sarcolemma

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Cytoplasm of muscle fiber

sarcoplasm

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Epimysium

The most superficial sheath. Covers the muscle itself

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Perimysium

Covers the muscle fascicles

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Endomysium

the deepest sheath, covers muscle fibers

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Myofibril contain many repeating units called:

sarcomeres

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Functional unit of muscle fibers

sarcomeres - shorten to faciliatte muscle contraction

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Neuromuscular junction

space between the presynaptic motor neuron and postsynaptic muscle fiber

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When a motor neuron sends an action potential, it releases ___ into the ___ ___

acetylcholine; neuromuscular junction

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Steps to transfer action potential to muscle

acetylcholine released at neuromuscular junction, binds to voltage gated Na+ channels
graded potential created (small depolarization)
opens more Na+ channels
creates action potential in muscle

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T-tubules

invaginations in the sarcolemma - allow the action potential initiated on the muscle fiber to spread throughout the cell very quickly, ensuring a coordinated contraction

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Muscles contract across:

a joint

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Muscles __ the bone they ___ upon closer to the bone they ____ from

pull; insert; originate

Muscle contraction is always:

a pull motion

The sarcolemma is:

muscle fiber's cell membrane

sarcomeres contain:

array of long filament proteins (myofilaments)

Examples of myofilaments

thin actin filaments, thick myosin filaments

neuromuscular junction

space between the presynaptic motor neuron and postsynaptic muscle fiber

Which NT is released by a motor neuron?

Acetylcholine

What does acetyl choline do once it is released by motor neuron?

creates graded potential - facilitates the opening of ligand gated sodium channels on the muscle fiber

Invaginations in the sarcolemma

T-tubules

Sarcoplasmic reticulum

specialized ER that stores calcium ions in muscle fibers

What causes voltage gated Ca2+ channels to open?

Depolarization traveling across T-tubules

When Ca2+ is released, it travels from ___ to ___

sarcoplasmic reticulum; sarcoplasm

actin's binding site for myosin is covered by:

tropomyosin

Tropomyosin is held in place by

troponin

How does tropomyosin move away from myosin binding site?

Ca2+ in sarcoplasm binds to troponin

Troponin has _ binding sites:

3; A, C, T

troponin A site

binds actin

troponin C site

binds Ca2+

troponin T site

binds tropomyosin

How does myosin form cross bridge?

hydrolyzes ATP to extract energy, enters high energy state to bind to actin forming cross bridge

What happens when myosin releases ADP and Pi?

power stroke

rigor mortis

happens in dead animals, no ATP being produced --> myosin released from actin --> maintains contraction

Z line

periphery (ends) of each sarcomere

M line

midpoint of each sarcomere

I bands

areas where only actin is present (including where Z line is)

A bands

areas where myosin and actin overlap

H zone

where only myosin is present

Which band does not shorten during muscle contraction?

A band

Small motor units

few muscle fibers, innervated by single motor neuron

Precision movements are created by:

small muscles containing many motor units

large motor units have:

many muscle fibers, innervated by one motor neuron

How are powerful movements created? (how many motor units)

large muscles with few motor units

What is a twitch contraction?

brief contraction a muscle fiber experiences as the result of a single action potential stimulating an entire motor unit

All-or-none principle of muscle contraction

Either the depolarization is above threshold in which all fibers twitch, or it is below threshold and none twitch

Phases of twitch

latent; contraction; relaxation

Muscle fiber types

1. slow oxidative fibers 2. fast oxidative-glycolytic fibers 3. fast glycolytic fibers

___ fibers have the slowest acting myosin ATPase

Type I

Type I fibers = ___

slow oxidative fibers

Type II-a fibers:

Fast oxidative-glycolytic fibers

type II-b fibers

Fast glycolytic fibers

Describe slow oxidative fibers

- small diameter (weak contractions) - dark red - aerobic respiration - efficient - resistant to fatigue

Describe fast oxidative glycolytic fibers

- intermediate diameter - dark red - an/aerobic respiration - reasonably efficient but susceptible to fatigue

Describe fast glycolytic fibers

- white - anaerobic respiration - strongest contractions - somewhat inefficient, fatigues quickly

True or false: since twitch will always be the same size, overall force of contraction remains the same

false - contraction varies due to wave summation/ motor unit summation

wave summation

refers to the process of depolarizing muscle fibers in a motor unit again during their relaxation period

Tetanus

process where the muscle fibers of a motor unit are being maximally stimulated by a motor neuron and tension can no longer increase

Tetanus usually happens when:

sending action potentials down a motor neuron with such a high frequency that we don’t experience any relaxation

Motor unit summation affects force of contraction because:

action potentials are traveling to different motor units at different times

Muscle tone (tonus)

due to weak and involuntary twitches of small groups of motor units within a muscle, due to a continuous output of action potentials from the brain and spinal cord

True or false: continuous muscle tonus causes fatigue

False - we never feel fatigued by our tonus because different motor units of a muscle are being stimulated at different times

Which muscle has no inherent muscle tone?

cardiac muscle tone

Hypotonicity

muscles lose tone and thus feel flaccid. occurs as the result of damage to PNS/reduced electrolytes

hypertonicity

when muscles gain tone and thus feel spastic and rigid; occurs as the result of damage to the central nervous system.