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functions of skeletal muscle
- heat generation
- movement
- posture
- breathing
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properties of skeletal muscle
- excitability/irritability
- contractility
- extensibility
- elasticity
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excitability/irritability
ability to respond to a stimulus
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contractility
ability to shorten if stimulated
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extensibility
ability to stretch if pulled
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elasticity
ability to return to original shape after stretching
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muscle facts
- usually work in pairs
- work together or oppose each other
- only pull - never push
- should only shorten - never extend beyond original length
- insertion should only move toward origin
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insertion
- most movable part of a muscle that is attached to the most movable bone
- usually farthest from trunk
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origin
- least movable part of a muscle that is attached to the least movable bone
- usually closest to the trunk
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gaster
- aka body / belly
- middle main part of a muscle
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agonist
- aka prime mover
- muscle in a group that produces a desired movement
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antagonist
muscle in a group that reverses a specific movement
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agonist/antagonist facts
- usually on opposite sides of a joint over which they act
- when prime mover contracts, agonist relaxes
- may stay partially contracted to produce smooth movement
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synergists
muscles that help prime movers and antagonists function and help eliminate unnecessary movement at the joint
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fixators
muscles that stabilize the prime mover to cause the desired movement
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epimysium
membrane that covers the entire muscle
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fascicles
bundles of skeletal muscle fibers
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perimysium
membrane that surrounds fascicles
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muscle fibers
muscle cells
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endomysium
membrane that surrounds individual muscle fibers
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myofibrils
contractile organelles of skeletal muscle
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sarcomere
smallest part of a muscle that is capable of contracting
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sarco- / myo-
prefix for muscle
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sarcolemma
cell membrane of a muscle cell
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sarcoplasm
muscle cytoplasm
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sarcoplasmic reticulum
ER of a muscle cell
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Z disk
dense region of cytoplasm that separates sarcomeres in a muscle
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actin
thin protein filaments that directly attach to z-disk
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myosin
thick protein filaments that slightly overlap actin on each side
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titin
thin elastic protein that attaches myosin to Z disk
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I band
contains actin and titin (no myosin)
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A band
contains myosin and overlapping actin
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H zone
part of A band containing only myosin
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M line
imaginary line through middle of sarcomere
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active sites
only in I band
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tropomyosin
covers active sites in relaxed sarcomere
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cross bridges
golf club shaped proteins on myosin
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motor unit
motor neuron plus part of muscle that it stimulates
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neuromuscular junction
- where neuron and muscle join
- composed of axon terminal, synapse, and motor end plate
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motor neuron
any nerve cell that carries impulses from brain out to a muscle
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axon terminal
distal expanded part of an axon
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synaptic end bulb
expanded end of the axon
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synaptic vesicles
tiny sacs inside bulbs filled with chemicals called neurotransmitters (NT)
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neurotransmitters
allow neurons to communicate with muscle
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acetylcholine
only NT associated with muscle
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synapse
space between axon terminal and muscle
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T tubles
deep indentations in sarcolemma
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motor end plate
part of muscle directly across from axon terminal that stimulates it
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naming of muscles
- by location
- by function
- by origin and insertion
- by # of origins
- by shape
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fascia
- CT associated with muscles
- bind muscles together and stabilizes blood vessels and nerves as they enter/exit muscle
- 2 types: superficial and deep
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superficial fascia
subcutaneous skin
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deep fascia
- dense irregular tissue that surrounds muscle, fasciles, and fiber
- (epimysium, perimysium, endomysium)
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arrangements of fascicles
- circular
- fusiform: nearly parallel and tapered on ends
- unipennate: short, attach to central tendon at an angle
- bipennate: short, attach to central tendon at an angle on both sides
- multipennate: short, attach to central tendon at an angle on many sides
- parallel: attach to tendon top and bottom
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direct muscle attachment
- epimysium attaches directly to periosteum of bone
- ex: intercostals
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indirect muscle attachment
- epimysium extends beyond muscle and turns into connective tissue cord which attaches muscle to other structures
- cord can be tendon, aponeurosis, or tendon sheath
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tendon
attaches muscle to bone
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aponeurosis
broad flat tendon that attaches muscle to bone, skin, or other structure
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tendon sheath
- CT structure that secretes synovial fluid
- only found in a joint
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muscle contratction
- must be stimulated by motor neuron
- nerve impulse reaches axon terminal
- Ach released from synaptic vessicles
- Ach bridges synapse - allows impulse to cross synapse and reach sarcolemma
- impulse moves down T tubules to sarcoplasmic reticulum
- calcium ions dump into sarcoplasm
- acetylcholinesterase enzyme (found on sarcolemma) is activated
- calcium binds to troponin to form Ca-troponin complex
- Ca-troponin complex attaches to tropomyosin to form tropomyosin blockade
- tropomyosin tipped off active sites
- ATP pivots cross bridges upward (power stroke)
- cross bridges attach to exposed active sites
- thin filaments slide over thick myosin
- Z disk get closer together
- I bands get smaller
- A band unchanged
- H zone almost completely disappears
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ATP
- major energy source for muscle contraction
- muscle cells only contain a small amount
- body must replenish to keep muscles contracting
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creatinine phosphate
- ADP converted to ATP for energy
- provides small amount of ATP for initial activity
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glycogen
- carbs stored in muscle fibers converted to ATP
- source is limited but can keep muscles functioning temporarily
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cellular respiration
- sugar, protein, amino acids converted to ATP
- used for long term, extreme muscle activity
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types of muscle fibers
- type 1: slow twitch - vascular, tend to resist fatigue
- type 2: fast twitch - light in color (less vascular), fatigue easily
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isotonic
- muscle shortens and contracts
- work is being done because there is movement
- produces bulk and definition
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isometric
- muscle fibers become less tense but don't shorten
- no work being done
- produces muscle tone
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oxygen debt
- O2 supply to a muscle is reduced
- muscle stops contracting
- feel burning and cramping sensation
- muscle will stay cramped until O2 supply restored
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fatigue
muscle cannot maintain strength of its contraction due to decreased O2 and decreased ATP
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twitch
pathological response of a single muscle cell to a stimulus that is not strong enough to cause a contraction
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tetanus
smooth sustained muscle contraction
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threshold
stimulus that is strong enough to cause a muscle to contract
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subthreshold
- weak stimulus
- muscle can't contract
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muscle tone
smooth sustained partial contraction
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all or none
if a muscle cell contracts, it always contracts completely or not at all
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summation
when a muscle receives rapid stimulation from several neurons, the strength of contraction increases
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