Muscular System Flashcards
special characteristics of muscle tissue
excitability (irritability/responsiveness)
contractility
extensibility
elasticity
function of skeletal muscles
producing movement maintain posture/body position stabilize joints generate heat protect abdominal organs link the body and the external environment (manipulation)
function of cardiac muscles
pump blood
involuntary contractions of the heart
functions of smooth muscles
peristalsis-alternating contractions and relaxations that mix and squeeze substances thru the lumen of hollow organs
propulsion of substances
is each skeletal muscle an organ
yes
it is made up of several different tissues (skeletal muscle fibers, bv, nerve fibers, connective tissue) working together to perform a common function
endomysium
fine sheath of areolar connective tissue
reticular fibers that surround each muscle fiber
perimysium
fibrous connective tissue that surrounds groups of muscle fibers called fascicles
epimysium
overcoat of dense irregular connective tissue that surrounds the entire muscle
origin
the muscles attachment to the immovable/less moveable bone
insertion
the attachment of the muscle to the moveable bone
sarcolemma
plasma membrane of muscle
sarcoplasm
cytoplasm of muscle cells that usually contains large amounts of glycosomes and myoglobin
glycosomes
granules of stored glycogen that provide glucose during muscle cell activity
myoglobin
red pigment that stores and binds oxygen
what attaches muscles to bones
tendons
sarcoplasmic reticulum
elaborate smooth endoplasmic reticulum w interconnecting tubules surrounding each myofibril
functions in the regulation and storage of intracellular calcium levels
excitability
irritability/responsiveness
the ability to receive and respond to a stimuli- any change in the inside/outside envt
contractility
the ability to shorten forcibly when adequately stimulated
extensibility
the ability to extend or stretch even beyond resting length when relaxed
elasticity
ability of a muscle to recoil and resume its resting length after stretching
location of skeletal muscles
attached to bones/skin/other muscles
location of cardiac muscle
in the heart
location of smooth muscle
hollow visceral organs and blood vessels
structure of skeletal muscle
multinucleated
long
striated
cylindrical
structure of cardiac muscle
uninucleated short branching striated cylindrical intercalated disks- gap junx
structure of smooth muscle
uninucleated
long
spindle like
gap junx
ctrl of skeletal muscle
voluntary
ctrl of cardiac muscle
involuntary
ctrl of smooth muscle
involuntary
reproduction of skeletal?
no
reproduction of cardiac?
minimal
reproduction of smooth?
yes
myofibrils
rodlike contractile elements that make up most of the muscle volume (hundreds to thousands in a single fiber) has striations (perfectly aligned repeating series of dark A bands, and light I bands)
T-tubules
continuation of sarcolemma that protrudes deep into the cell forming an elongated tube that increases muscle fibers surface area, and conducts nerve impulses to the deepest regions of the muscle cell
allows every sarcomere to open voltage sensor proteins which release calcuim from adj SR terminal cisternae
triad
the relationship that occurs bt the paired SR terminal cisternae and T-tubule
T-tubule proteins act as
voltage sensors, so they can change shape when there is an electrical impulse to to open calcium ion channels on the SR
smallest contractile unit of Skeletal and cardiac muscles is
Sarcomere- located between two successive Z disks
z-disk
coin shaped sheet of proteins that anchors thin filament
m-line
middle line that anchors the myosin
A-band
dark
contains thick and thin filaments
actin+myosin
I-band
light
only thin filaments
actin
H-zone
only thick filaments
myosin
3 filaments in a sarcomere
thick filament
thin filament
elastic filament
thick filament
myosin
extends entire length of A band
thin filament
actin, troponin, tropomyosin
extends across the I band and partially into the A band
elastic filament
made of titin
extends from Z disk to M line and holds thick filaments in place
assists muscle cell to spring back after stretching
sliding filament mechanism
proposes that changes in overall fiber length are directly associated with changes in overlap between the 2 sets of filaments
H-zone disappears as actin and myosin slide over eachother in contraction
neuromuscular junx: AXON TERMINAL
the branched end of a neurons axon that contains synaptic vesicles w the neurotransmitter ACH
neuromuscular junx: SYNAPTIC CLEFT
small space separating axonal terminals with the motor end plate of the muscle fiber
neuromuscular junx: MOTOR END PLATE
specific part of the sarcolemma looking towards the axon terminal; contains ACH receptors
first thing to happen at the neuromuscular junx
nerve impulse reaches the axon terminal and travels down the T-tubules
second thing to happen at the neuromuscular junx
voltage gated calcium channels on the SR open and release calcium down the electrochemical gradient
3rd thing to happen at the neuromuscular junx
calcium entry causes ACH (neurotransmitter) to be released via exocytosis and diffuse across the synaptic cleft
4th thing to happen at neuromuscular junx
2 ACH bind to the ACH receptors on the NaK chemical gated channels at the motor end plate
neurotransmitter
chemical that is released from a nerve cell which thereby transmits an impulse from a nerve cell to another nerve, muscle, organ, or tissue
at the skeletal muscle fiber level ACH the neurotransmitter
allows the NaK gates to open and begin depolarization of the sarcolemma
neurotransmitter used in skeletal muscle contraction
Acetylcholine
termination of ACH caused by
acetylcholinesterase
an enzyme in the synaptic cleft that breaks down ACH into acetic acid and choline
prevents continued contraction
resting potential
the potential difference (-70mv) across the membrane of a resting neuron/skeletal muscle
the outside (extracellular face) is positive
the inside face is negative
resting potential is generated by
difference in concentration of Na, K, Cl, proteins, and anions
sodium is the major
extracellular ion
potassium is the major
intracellular ion
depolarization
when Na+ enters the cell causing it to become more positive (or less negative)
change from -70mv until cell reaches -55mv threshold
at -55mv
the Na+ voltage gated channels open and only sodium floods in until sarcolemma reaches +30mv
at +30mv
an action potential is created
sodium gates close
potassium gates open to let K+ out
repolarization begins
repolarization
Na+ voltage gated channels close
K+ voltage gated channels open and K+ diffuses out
electrical polarity -70mv becomes restored in the sarcolemma
action potential is started when
depolarization brings sarcolemma to -55mv
Na+ voltage gated channels open only Na comes in
action potential formed when
cell reaches +30mv
carried down T-tubules
action potential causes the opening of
Ca++ voltage gated channels
the calcium binds to troponin
the binding of calcium to troponin causes
troponin to move tropomyn exposing the myosin binding sites
action potential is all or nothing because
either threshold is reached or not, no in between
how is electrical imbalance restored
thru repolarization
ionic imbalance is restored thru
the sodium potassium pump
3 Na+ out
2 K+ in
absolute refractory period
part of the refractory period where the Na+ channel is resetting and another AP cannot be generated
relative refractory period
part of the refractory period where as long as it is under -55mv a second action potential can be generated
importance of calcium in muscle contraction
binds to troponin removing the tropomyosin blockage
cross bridge formation
working powerstroke-myosin head piviots and pulls actin filament towards m-line
calcium is stored in the
sarcoplasmic reticulum
when nervous system stimulation ceases calcium
is actively pumped back into the extracellular fluid for storage and later use
importance of ATP in muscle contraction
attaches to myosin head
allows detaching of cross bridge
becomes hydrolzyed to ADP and Pi and cocks myosin head back to high energy state
motor unit
motor neuron and all the muscle fibers it supplies (nerve/muscle functional unit)
has muscle fibers spread thru the muscle insulated by endomysium
so contraction of a single motor unit cause weak contraction of the whole muscle
muscle twitch
the response of a musce to a single action potential of its motor neuron
muscle tone
constant slightly contracted state of all muscles due to spinal reflexes that activate groups of motor units alternately in response to input from stretch receptors in muscles
keeps muscles healthy, firm, ready to respond
twitch myogram: LATENT
1st few ms after stimulation from depolarization to calcium release 2ms
twitch myogram: CONTRACT
cross bridges form
muscle shortens
10-100 ms
twitch myogram: RELAX
calcium is reabsorbed
muscle tension goes to zero
10-100ms
3 ways ATP can regenerate
interaction w creatine phosphate
aerobic respiration
lactic acid fermentation
interaction of ADP w creatine phosphate
1atp per 1cp
unique high energy molc stored in muscles that supplies ATP in exercising until muscles metab adj itself to the demand
aerobic resp
95%
32atp
glucose-pyruvic acid-krebs cycle-ETC
uses glucose 1st 30 min then fat for energy
lactic acid fermentation
2 atp
glucose-pyruvate-lactic acid-blood-fuel-pyruvic acid
used in anaerobic resp when bulging muscles compress bv and impair 02 delivery
pain causing discontinuation of exercise is
from lactic acid build up in liver
only 40% of energy released in muscle activity is
useful as work
remaining 60% given off as heat
differences of smooth muscle
thin short spindle shaped fibers connective tissue is only endomysium less developed SR no myofibrils/ T-tubules actin and myosin present but not arranged in sarcomere gap junctions calcium binds to CALMODULIN which activates MYOSIN KINASE which phosphorylates myosin, activating myosin ATPases that provide energy for contraction contractions/relaxations take longer
similarities bt skeletal and smooth muscle
actin and myosin in sliding mechanism
CALCIUM IS FINAL TRIGGER
ATP IS ENERGY SOURCE
differences of cardiac muscle
behaves as a functional synctium-intercalated disks
cells are mechanically, chemically, electrically connected
autorhythmic cells-self excitable and can initiate own depol
use Ca influx rather than Na to create AP
more mitochondria
ability to switch to whatever nutrient supply is readily available (fat drops on top)
20% Ca comes from ecf
danger of lack of o2 not nutrients
slower
