Muscular System Flashcards by Connor Lucas

Contractility

shorten forcibly

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Functions of muscular system

Body movement
Maintenance of posture
Respiration
Production of body heat
Communication (speaking, writing, etc)
Constriction of organs & vessels
Heartbeat

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Excitability

to receive & respond to stimuli

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Extensibility

Can be stretched beyond its normal resting length & is still able to contract

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Elasticity

to recoil to its original resting length after it’s been stretched

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Skeletal muscle

bones
multinucleated 
striated 
voluntary
involuntary (reflexes)

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Smooth muscle

walls of hollow organs, blood vessels, eyes, glands, skin
single nucleus
nonstriated
involuntary

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Cardiac muscle

branching fibers
single nucleus
striated
involuntary

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Fascia

connective tissue sheets; outermost layer

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Epimysium

dense collagen;

surrounds entire muscle

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Fascicle

bundle of muscle fibers

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Perimysium

surrounds fascicles; fibrous connective tissue

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Endomysium

surrounds each muscle fiber;

fine sheath of connective tissue composed of reticular fibers

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Myofibril

bundles of protein filaments within muscle cells; extend along length of muscle fiber (long)

myofilament- individual protein filaments: actin & myosin

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Connective tissue functions

associated with muscles

surround & protect muscle tissue
binds & holds muscles together
free movement of muscles
supports nerves & blood vessels
fills spaces between muscles

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Sarcolemma

muscle cell plasma membrane

-> T tubules- indentations of sarcolemma; allows sarcolemma to extend to interior of muscle fiber

Sarcoplasm

cytoplasm of muscle cell, fills sarcolemma;
consists of organelles OTHER than myofibrils:
-sarcoplasmic reticulum
-mitochondria
-glycogen granules

Sarcoplasmic reticulum

endoplasmic reticulum;

stores & pumps Ca+ ions

Actin (thin) myofilament

strands of pearls
Fibrous (F actin) = strand
Globular (G actin) = pearls
  -> active site where myosin binds
troponin molecules are attached along actin, have Ca+ binding sites

Myosin binding site is covered on G actin by:

tropomyosin when Ca+ is absent;
when present, site is uncovered for myosin to bind

MUST HAVE Ca+ FOR MUSCLE CONTRACTION & MYOSIN TO BIND

Myosin (thick) myofilament

golf clubs
head- deep cleft, binds to active site on G actin (forming cross-bridge)
hinge- enables movement of head
rod- attach to each other; oriented so heads are at end of myosin myofilament

Actin moves along

myosin

think of pulling a rope

Sarcomere

unit of actin & myosin filaments

basic functional unit of striated muscle fibers

arrangement of actin & myosin = banded appearance

Z disk

separates sarcomeres;
attachment site for actin
holds actin filaments in place
(blue zig zag line)

Z disks move toward each other during contraction

A band

extends entire length of myosin; contains H zone (AH) does not narrow/change in sarcomere shortening (contraction)

I band

connects end of one actin to beginning of other; Z disk in middle; contains 2 different sarcomeres; extends to ends of myosin narrows in contraction

H zone

center of A band (sarcomere) ONLY myosin narrows & disappears in contraction (actin meets & overlaps)

M line

middle of H zone; holds myosin filaments in place --> Titin

What gives striated appearance under the microscope?

alternating A & I bands

Myofilaments (actin & myosin) do not change _______ during muscle contraction

length; they just "slide" over each other

Contraction begins with:

head of myosin bound to actin. Ca+ must be present

Fully contracted muscle

H zone disappears | I band narrows

Nervous system stimulates muscles through:

action potential (nerve impulses) action potential -> inside of membrane becomes + all or none principal -> going to happen or not -> must break threshold or muscle will not respond

Ligand-gated ion channels

gates open in response to a ligand binding to a receptor binding of a ligand allows ions to flow; absence of ligand = gates closed majority of ligands are NEUROTRANSMITTERS

Voltage-gated ion channels

open & close in response to changes in voltage

Axons of motor neurons enter muscles & send out branches each branch =

neuromuscular junction (synapse) | an axon branch joins a muscle fiber