muscles Flashcards
what are the four general muscle functions?
- movement of bones or fluids
- maintaining posture and body positions
- stabilizing joints
- heat generation
what are the special characteristics of muscle tissue?
excitability, contractility, extensibility, elasticity
what is excitability?
ability to receive and respond to stimuli
what is contractility?
ability to shorten when stimulated
what is extensibility?
ability to be stretched
what is elasticity?
ability to recoil to resting length
muscle fiber=
muscle cell
my/o, mys/o, sarc/o
used to reference muscles
sarcolemma
plasma membrane of muscle fiber
sarcoplasm
cytoplasm of muscle fibers
what are the 2 myofilaments?
actin and myosin
fascicles
a muscle made up of densely packed groups of elongated cells
muscle fibers
smaller units in a fascicle
myofibrils
a muscle fiber made into even smaller units
sacromeres
myofibril made fo repeating units which are made up of two types of filaments
what are the structures of a skeletal muscle big to small?
muscle, fascicles, muscle fiber, myofibrils, sarcomere
epimysium
dense regular connective tissue surrounding entire muscle
perimysium
fibrous connective tissue surrounding groups of muscle fibers
endomysium
fine loose connective tissue surrounding fascicles
sarcoplasmic reticulum
surrounds myofibrils and stimulates muscle contractions
each myofibril is made up of repeating units called _____________
sarcomeres
a sarcomere is a functional unit of a ____________
muscle fiber
the sarcomere is composed of which two types of myofilaments?
thick and thin
_______ is a thick filament
myosin
__________ is a thin filament
actin
what does. myosin look like?
it has globular heads coming off of it, each head is attached to ATP
what does actin look like?
a twisted molecule with binding sites for myosin heads
A band:
contains only actin filaments giving them a lighter appearance
Z-line:
anchors the actin filaments and connects myofibrils to one another, represents edges of sarcomeres
H zone:
region where you find only myosin
M line:
line of protein that anchors myosin filaments together during a muscle contraction
how does skeletal muscle contract?
the movement of actin and myosin bands over eachother
which theory explains how a muscle contracts?
sliding filament theory
what does the sliding filament theory state?
that thin filaments slide across thick filaments, thereby shortening the sarcomere
what are the two requirements for skeletal muscle contractions?
activation and excitation-contracting coupling
what is activation?
neural stimulation at a neuromuscular junction
what is excitation-contraction coupling?
generation and propagation of an action potential along the sarcolemma
what is the final trigger in excitation-contraction coupling?
a brief rise in intracellular calcium levels
in order for muscles to contract they have to receive a ________ from the nervous system
stimulus
the place a muscle receives a stimulus from is the ______________
neuromuscular junction
skeletal muscles are stimulated by?
motor neurons
where do axons of motor neurons travel?
from the central nervous system to skeletal muscles
the place where an axon enters a muscle is called?
a motor end plate
4 steps to activation of skeletal muscle contraction:
- nerve impulse is sent to the neuromuscular junction
- calcium channels open and calcium enters the axon terminal, stimulating synaptic vesicles to release the neurotransmitter acetylcholine into the synaptic cleft
- acetylcholine binds to receptors on the motor end plate
- this causes the action potential to be sent through the muscle tissue
7 steps of excitation contraction coupling of skeletal muscle contraction:
- as the action potential is sent through the muscle tissue it passes through the T-tubules and into the sarcoplasmic reticulum
- calcium ions are released from the sarcoplasmic reticulum and invade the sarcolemma
- calcium ions bind to the troponin on actin and cause it to change shape
- tropomyosin now moves, which exposes the binding sites on the actin filaments
- the myosin kicks off the hydrolyzed ATP which allows the ADP to bond to actin
- the myosin heads pull the actin toward the m-line, shortening the sarcomere
- when calcium levels decrease the contraction stops and sarcomere lengthens
how long does acetylcholine continue to stimulate action potentials?
until it is destroyed
what destroys acetylcholine?
acetylcholinesterase
what is acetylcholinesterase?
enzyme released into the synaptic cleft that destroys acetylcholine and prevents continued muscle fiber contraction
what is a motor unit?
a motor neuron and all muscle fibers it innervates
small motor units
found in muscles that control fine units
what are examples of small motor units?
fingers and eyes
what are large motor units?
found in large weight-bearing muscles
what are examples of large motor units?
thighs and biceps
motor units in a muscle usually contract _____________
asynchronously
why do motor units contact asynchronously?
to prevent muscle fatigue
what is a muscle twitch?
a motor unit’s response to a single electrical impulse sent through the motor neuron
what does a muscle twitch cause?
muscle fibers to quickly contract then relax
muscle twitches can be recorded in the lab on a _________
myogram
what are the 3 phases of a twitch?
latent period, period of contraction, period of relaxation
what is the latent period?
events of excitation-contraction coupling
what is the period of contraction?
cross-bridge formation; tension increases
what is the period of relaxation?
calcium re-entry into SR; tension declines to a zero
what are graded muscle responses?
variations in the degree of muscle contraction
what are graded muscle responses required for?
proper control of skeletal movement
what are the 2 graded muscle responses?
- changing the frequency of a stimulation
- changing the strength of a stimulus
what does a response to change in stimulus frequency do?
a single stimulus results in a single contractile response- a muscle twitch
if the frequency of stimuli is ________ the muscle doesn’t have to completely relax between stimuli
increased
what is a temporal (wave) summation?
calcium release stimulates further
what is an infused (incomplete) tetanus?
a further increase in stimulus frequency
if stimuli are given quickly enough, _________ occurs
fused tetany
what is response to change in stimulus strength?
each muscle fiber has a threshold stimulus
what is a threshold stimulus?
stimulus strength at which the first observable muscle contraction occurs
a muscle contracts more vigorously as stimulus strength is increased above threshold due to more ________ being stimulated
motor units
what is contraction force and what does it do?
it is precisely controlled by the recruitment of motor units, which brings more muscle fibers into action
what is size principle?
motor units with larger and larger fibers that are recruited as stimulus intensity increases
the constant state of slight contraction is called what?
muscle tone
isotonic
muscle contracts and shortens
what is an example of isotonic?
occurs when we walk or lift objects
isometric
tension increases but muscle doesn’t shorten
what is an example of isometric?
tensing the abdominal muscles
our ___________ can change in size depending on our level of activity
muscle fibers
atrophy
the shrinking of muscles from not using them
hypertrophy
enlarged muscles due to overuse or over-excercise
when muscles get bigger they increase in size, and there is/is not an increase in the number of muscle cells
is not
___ is the only source of energy used to power muscle contractions
ATP
how fast are available stores of ATP depleted?
4-6 seconds
what are the 3 ways ATP is regenerated by?
- direct phosphorylation by creating phosphate
- anaerobic pathway
- aerobic respiration
anaerobic pathway is at __% of maximum contractile activity
70
what compresses blood vessels?
bulging muscles
in an anaerobic pathway oxygen delivery is __________
impaired
in anaerobic pathway which acid is converted into lactic acid?
pyruvic acid
what are 3 traits of lactic acid?
- diffuses into the bloodstream
- used as a fuel by the liver, kidneys, and heart
- converted back into pyruvic acid by the liver
aerobic pathway produces __% of ATP during rest and light to moderate excercise
95%
what are some fuels of aerobic pathway?
- stored glycogen
- blood borne glucose
- pyruvic acid from glycolysis
- free fatty acids
what is muscle fatigue?
physiological inability to contract due to overuse of the muscle
what is muscle fatigue caused by?
oxygen reserves, glycogen stores, ATP and CP reserves, conversion of lactic acid back to pyruvic acid
what are some effects of training on muscle efficiency?
- improved motor unit/ muscle coordination
- improved functioning of the respiratory and circulatory system
- elimination or reduction of excess fat
- improved joint movement
what are some effects of training on muscle strength?
- increase in muscle size
- improved muscle coordination
- improved functioning in the cortical brain region
muscles only ______
pull
what attaches muscles to bones?
tendons
what is the part of the skeletal muscle attached to a fixed bone?
orgin
what part of a muscle does not move during a muscle contraction?
the orgin
what part of a muscle is attached to a moveable part?
insertion
what part of the muscle moves during muscle contraction?
insertion
the ______ produces movement in a singe direction
prime mover
the muscle being contracted is an example of which pair?
prime mover
the ______ moves bone in opposite direction
antagonist
what is an example of an antagonist?
muscle that relaxes
_________ help to steady a movement or stabilize joint activity
synergists
how are muscles named by location?
some names indicate the bone that the muscle is attached to
how are muscles named by shape?
some refer to the shape of the muscle
how are muscles named by size?
some refer to maximus and minimus
______ muscles have muscle fibers that run parallel to the midline
rectus
_____ muscles have muscle fibers that run perpendicular to the midline
transverse
______ muscles have muscle fibers that run diagonally
oblique
how are skeletal muscles name by number of orgin?
biceps vs triceps vs quadriceps
how are muscles named according to the point of attachments?
named according to point of origin and insertion
how are muscles named due to muscle action?
named for the type of movement they produce
