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67 Cards in this Set

  • Front
  • Back
skeletal muscle
striated, voluntary – boundaries of cells are not well defined, multinucleated
• Span joints, attach to bone in two places (origin and insertion)
• Responsible for all locomotion
cardiac muscle
striated, involuntary – boundaries of cells are well defined, single nucleus
• Muscle of the heart
smooth muscle
no striations, involuntary
• Found only in the walls of visceral organs (ie: airways of lungs, blood vessels, digestive, urinary, reproductive tracts)
muscle plasma membrane
cytoplasm of a muscle fiber cell
muscle fiber
sheath of connective tissue that surrounds skeletal muscle,
fused to the periosteum (exists on the outer surface of the muscle)
-extend past the muscle to form tendons
sight of attachment to immovable bone of joint
sight of attachment to movable portion of joint
the three connective tissue sheaths that surround a skeletal muscle and hold it together
organizes muscle fibers into fascicles – interior portion of muscle - surrounds a group of muscle fibers
wraps around individual muscle fibers – exists inside muscles
3 different types of skeletal muscle fibers
slow oxidative
fast oxidative
fast glycolytic
slow oxidative
one of the types of skeletal muscle fibers
-have slow twitch (use ATP slowly)
- fatigue resistant
– used to maintain posture
fast oxidative
one of the types of skeletal muscle fibers
-have fast twitch (use ATP quickly)
–moderate resistance to fatigue
– used for non-exertive movement
fast glycolytic
one of the types of skeletal muscle fibers
-have fast twitch (use ATP quickly)
– easily fatigued
– used for more powerful movement
transverse tubules
portion of sarcolemma that fold inward toward center of fiber
how does the sarcolemma generate action potentials?
contains both Na+ and K+ voltage-gated channels
Sarcoplasmic Reticulum
-found in skeletal muscle fibers
-physically associated with transvers tubules
-storage site for intracellular calcium
-responds to an action potential in t-tubules by releasing Ca into sarcoplasm to increase level of calcium
-triggers contraction of muscle fiber
what is the Nerve-Muscle Functional Unit?
motor neurons from the CNS attach to muscle fibers, can generate action potentials to trigger contraction
Motor Unit
the anatomical relationship between a motor neuron and all skeletal fibers that it causes to contract
Motor Neuron
part of the nerve-muscle functional unit
-can branch many times to form many axon termini
-one motor neuron can stimulate many skeletal muscle fibers to contract
Neuromuscular Junction
a synapse which is the site at which exocytosis of neurotransmitters from a motor neuron cause the generation of an action potential
Small Motor Unit
small number of muscle fibers in that unit
-control fine movements (ie: fingers, eyes)
Large Motor Unit
several hundred muscle fibers in one unit
-control the movements of large, weight-bearing muscles (ie: back)
-controls gross movements (ie: arms and legs)
Acetylcholine (ACh)
a neurotransmitter contained in the synaptic vesicles of the axon termini
Motor End Plate
a portion of the sarcolemma where the ACh receptors are located
contraction & relaxation of a muscle fiber to a single brief threshold stimulus by a motor neuron
3 phases of a muscle twitch
Latent Period
Contractile Period
Relaxation Period
Latent Period
"lag" period of a muscle twitch
-time between the stimulation by a motor neuron and the beginning of contraction (only a few milliseconds)
Contractile Period
2nd period of a muscle twitch
-when contractile proteins in the fiber hydrolyze ATP causing the fiber to shorten (contract)
-results in an increase in tension (force)
Relaxation Period
3rd period of a muscle twitch
-when the fiber lengthens
-results in a decrease in tension
2 types of skeletal muscle contractions
Isometic Contraction
Isotonic Contraction
Isometric Contraction
"same length"
-muscle contracts and produces tension but does NOT shorten, load is NOT moved
-occurs if the load is GREATER than the tension the muscle can develop
Isotonic Contraction
"same tension"
-muscle contracts and produces tension
-muscle shortens and MOVES the load
How are skeletal muscle contraction varied?
1. by altering the frequency of muscle stimulation (lower frequency of action potentials tells muscle not to work as hard)

2. by altering the number of muscle fibers that will contract (determined by the number of motor units generating action potentials to the muscle)
Incomplete Tetanus
occurs with rapidly delivered stimuli, multiple muscle twitches, tension does not return to baseline
Complete Tetanus
occurs when stimuli are given quickly enough that individual twitches blend together and maximum contractile force is reached
when more motor units are activated as a result of an increase in stimulus strength
Maximum Force
is reached when all motor units are activated. it is the most force a muscle is capable of generating, even if stimulus continues to increase
Oxidative v. Glycolytic Fibers
-oxidative fibers contain greater amounts of mitochondria
-oxidative fibers contain myoglobin
found in oxidative skeletal muscle fibers
-maintains a high concentration of oxygen within a fiber for aerobic resp.
-similar in struction to hemoglobin
-provides red color to oxidative fibers
-absence of myoglobin in glycolytic fibers results in white color
contractile proteins found in skeletal muscle fibers
long bundles of Myofilaments arranged within the sarcoplasm
-composed of 2 myofilaments that overlap: THIN and THICK
the arrangement of myofilaments within myofibrils that creates the look of STRIATIONS
-thousands of sarcomeres per myofibril
Banding patterns of myofilaments
caused by the arrangement of thin and thick filaments within a sarcomere
-Z disc
-A band
-I band
-H (bare) zone
Z disc
banding pattern of a sarcomere
- constitutes one end of a sarcomere
- anchors the thin filaments
A band
banding pattern of a sarcomere
- the length of the thick filaments (both overlapping and not overlapping with thin)
I band
banding pattern of a sarcomere
- the length of the thin filaments that is NOT overlapping with the thick filaments
H (bare) zone
banding pattern of a sarcomere
-the length of thick filaments that is NOT overlapping with the thin filaments
What happens to the filaments of a sarcomere during contraction and relaxation?
-in a relaxed state, thin and thick filaments overlap only slightly
-upon stimulation, thick filaments pull thin filaments toward center of sarcomere, filaments overlap greatly, sarcomere shortens

**as all of the sarcomeres in a muscle shorten, the entire muscle shortens
What is the structure of thin filaments?
composed of 3 proteins:



-Troponin C
What is the structure of thick filaments?
-composed of many molecules of the protein MYOSIN
-each myosin has a tail and two heads
Myosin heads
-portion of the protein myosin, exists in thick filaments
-hydrolyzes a molecule of ATP to get energy to contract
-temporarily binds to actin (of thin filament) pulls on actin to shorten sarcomere
one of the 3 proteins found in thin filametns
-- helical, binding site for myosin head of thick filaments
one of the 3 proteins found in thin filametns
**blocks interaction between actin (of thin filaments) and myosin (of thick filaments)

-prevents an unstimulated muscle from contracting
Troponin C
one of the 3 proteins found in thin filametns
- attached to tropomyosin
-binds to Ca in sarcoplasm during contraction
Excitation-Contraction Coupling
-binding of ACh opens Na+ and K+ channels
-results in depolarization
-opens volatge-gated Na+ and K+ channels to generate action potential
-action potentials move along sarcolemma into t-tubules
-action potentials in t-tubules cause release of Ca from sarcoplasmic reticulum into sarcoplasm which causes a contraction
At the myofilament level, what causes muscle fiber shortening?
Myosin (of thick filaments) pulls on Actin (of thin filaments) in a repetitive ratching fashion
Cross Bridge Cycling
-events of Contraction
What occurs during activation of the Myosin head, and when does this happen?
-a molecule of ATP is hydrolyzed, energy is then used to change shape of myosin into the high energy state

-this occurs during muscle fiber shortening when thin filaments are pulled towards the center of the sarcomere
What is Cross Bridge Formation?
-myosin cross bridge attaches to Actin

-occurs after activation of myosin head
What is Power Stroke?
-Myosin head pivots and pulls thin filament over thick filament

-occurs after cross bridge formation
What is Cross Bridge Detachment?
-binding of a molecule of ATP to the myosin head, detaches from Actin

-occurs after power stroke
What occurs during muscle fiber relaxation?
-motor neuron stops the exocytosis of ACh
-remaining ACh is hydolyzed into acetate and choline
-ACh receptors close
-membrane potential returns to resting
-Ca is pumped back into SR = decrease in Ca in sarcoplasm