4 - Skeletal Muscle & Function Flashcards
muscle cells are the only cells in the body that have the property of _______, which allows them to shorten and develop tension
contractility
what are the three types of muscle tissue?
- skeletal
- cardiac
- smooth
what are the defining characteristics of skeletal muscle?
- striated
- voluntary control
what are the defining characteristics of smooth muscle?
- non-striated
- involuntary control
what are the defining characteristics of cardiac muscle?
- striated
- involuntary control
what are 4 examples of skeletal muscle function?
- maintain posture and body position
- breathing
- generate heat and maintain body temperature
- chewing food and talking
what criteria is used to name muscles? (6)
- shape
- action
- location
- divisions
- size relationships
- direction of fibers
def: bundles of muscle fibers
fasciculi
if fasciculi run parallel to long axis of muscle they give…
greater range of motion, less strength
if fasciculi insert diagonally(pennate), into a tendon running the length of the muscle they give….
smaller range of motion, greater strength
def: all fasciculi insert on one side of a tendon
unipennate, semimembranosus
def: fasiciculi insert on both sides of tendon
bipennate, rectus femoris
def: convergence of several tendons
multipennate, deltoid
def: fasciculi run parallel to the long axis of the muscle
longitudinal, sartorius, rectus abdominus
def: fibers ran out from a single attachment
radiate, pectoralis major
def: a muscle whose contraction is primarily responsible for a particular movement
prime mover
def: muscles that oppose one another upon contraction - biceps and triceps
antagonists
def: muscles that immobilize a bone or joint near the origin of the primer mover so that the prime mover can act more efficiently
fixators/stabilizers
def: less movable end of a muscle, usually proximal
origin
def: more movable end of a muscle, usually distal
insertion
def: widest portion of a muscle, between its origin and insertion
belly
T or F: all muscles insert on bones
false, some face muscles insert into skin
what are the three layers of connective tissue?
- endomysium
- perimysium
- epimysium
def: extensions beyond the end of muscle
tendons
which is stronger: tendons or muscles?
tendons
within each muscle cell are many ______.
myofibrils
each repeated array of contractile proteins is called a _______
sarcomere
what are the two major contractile proteins of the sarcomere?
actin (thin) and myosin (thick)
what is the most prominent theory of muscle contraction?
the sliding filament theory
describe the sliding filament theory?
- when muscle is activated, protruding cross bridges on myosin attach to actin
- with ATP, the cross bridge microstructure can rotate
- shortens the thin actin filament to slide over myosin
- sarcomere shortens
on average, how many capillaries are there surrounding each muscle fiber of a sedentary person?
3-4
when muscle force increases, so does _________
intramuscular pressure
training can induce ________ ________, resulting in up to 7 capillaries per muscle fiber
capillary angiogenesis
what are the two extremes in muscle fiber activation?
max force or max velocity
def: a functional unit of a muscle, consisting of a motor neuron and all the muscle fibers that motor neuron innervates
motor unit
what does the axon do when it is close to the muscle?
separates many times (bifurcates) to innervate all the muscle fibers of that particular motor unit
how many muscle fibers will the average motor unit innvervate?
200 muscle fibers
if the cell body of the motor neuron receives a strong enough stimulus, an ________ _________ is generated
action potential
what law do action potentials follow?
all-or-none law
what percent of muscles in legs and arms are slow twitch fibers?
45% - 55%
T or F: all the muscle fibers in a given motor unit will have identical contractile and metabolic properties
true
what are the two classifications of motor units?
slow twitch & fast twitch
what are the three metabolic characteristics of muscles?
slow twitch oxidative - type I
fast twitch oxidative-glycolytic - type IIa
fast twitch glycolytic - type IIx
who has a higher proportions of slow twitch muscle fibers: endurance athletes or power athletes?
endurance athletes
can slow twitch fibers and fast twitch fibers be inter-converted by physical training?
no
can FOG and FG fibers be inter-converted by physical training?
yes
what are the two methods by which a muscle can control force production?
- multiple motor unit summation
- frequency or wave summation
def: when a muscle activates a certain number of motor units depending on the amount of force needed. more force = more motor units
multiple motor unit summation
def: frequency of action potentials controlling the force.
frequency or wave summation
how is a muscle maximally activated?
when all motor units are activated and they are all activated at a high firing rate
as the muscle force requirement increases, motor units with progressively ______ _____ are recruited
larger axons
during light to moderate effort, which motor units are used?
slow twitch motor units with the lowest activation threshold are selectively recruited
which motor units are used during rapid, powerful movements?
FOG motor units and then FG until all the motor units of all types are activated
when can an isolated muscle exert its maximal force or tension?
while in a resting stretched position
as a muscle shortens, ____ tension can be exerted
less
what do sarcomeres do when a muscle is stretched or shortened?
their length also increases or decreases
within the range of sarcomere lengths there is an ______ ______ at which provides the greatest possible number of cross bridge formations
optimal length
little cross-bridges or too many cross-bridges results in…?
reduced active force production
when velocity is positive, then the muscle is shortening which is called?
concentric contraction
when the velocity is negative, then the muscle is lengthening, which is called?
eccentric contraction
when the velocity of shortening is zero, there is no change in muscle length?
isometric contraction
power is the product of ______ X _______
force X velocity
when does max muscle power output occur?
one half of max velocity and one third of max concentric force
how does muscle activity change at joint angles greater than 90 degrees?
- magnitude of rotational component of the muscle pull force decreases
- magnitude of stabilizing component of the force increases
what are the three factors that affect the expression of strength by a muscle?
- the initial length of the muscle fibers
- the speed of shortening
- the angle of pull of the muscle on the bony skeleton
def: the age related loss of skeletal muscle mass, strength, and function
sarcopenia
what are the physical characteristic of old age?
- significant decline in skeletal muscle mass and strength
- decreased physical activity
- decreased food intake
what are the causes of sarcopenia?
- neural apoptosis (cell death)
- imbalance of muscle protein synthesis/degradation
- physical inactivity
- hormonal imbalance
- food intake (insufficient protein)
what are 4 ways to prevent sarcopenia?
- strength training
- hormonal therapy
- dietary intervention
- reduction in sedentary time
