Chapter 10
what are the 2 types of smooth muscle tissue?
visceral (single unit) smooth muscle tissue and multiunit smooth muscle tissue
the body makes ATP all the time, but make more ATP when?
when sleeping, because we are not using the ATP
neuromuscular junction (NMJ)
where muscle action potentials arise. the synapse between a somatic motor neuron and a skeletal muscle fiber.
skeletal muscle fibers that have a low myoglobin content are?
white muscle fibers and appear lighter
thin filaments are anchored to?
z-discs
where do muscle action potentials travel?
Along the sarcolemma and through the T tubules, spread throughout the muscle fiber.
how long do twitches of the skeletal muscle fiber last?
20-200 msec
each molecule of glucose catabolized under aerobic condition yields?
30 or 32 molecules of ATP
the cardiac muscle has a longer refractory period lasting how long?
300 msec
the skeletal muscle has a short refractory period lasting how long?
5 msec
electrical excitability
A property of both muscle and nerve cells, is the ability to respond to certain stimuli by producing electrical signals called action potentials.
in skeletal muscle, about 300 molecules of myosin form what?
A single thick filament. each myosin molecule is shaped like 2 golf clubs twisted together
the contraction cycle consists of what 4 steps?
ATP hydrolysis, attachment of myosin to actin to form cross bridges, power stroke, and detachment of myosin from actin
Activation of ACh receptors
Binding of two molecules of ACh to the receptor on the motor end plate opens an ion channel in the ACh receptor. Once the channel is open, small cations, most importantly Na, can flow across the membrane.
release of acetylcholine
Arrival of the nerve impulse at the synaptic end bulbs stimulates voltage-gated channels to open. Because calcium ions are more concentrated in the extracellular fluid, Ca2 flows inward through the open channels. The entering Ca2 in turn stimulates the synaptic vesicles to undergo exocytosis. During exocytosis, the synaptic vesicles fuse with the motor neuron's plasma membrane, liberating ACh into the synaptic cleft. The ACh then diffuses across the synaptic cleft between the motor neuron and the motor end plate.
generating heat
As muscular tissue contracts, it produces heat, a process known as thermogenesis. the heat generated by muscle is used to maintain normal body temperature. Involuntary contractions of skeletal muscles, known as shivering, can increase the rate of heat production.
Detachment of myosin from actin
At the end of the power stroke, the cross-bridge remains firmly attached to actin until it binds another molecule of ATP. As ATP binds to the ATP- binding site on the myosin head, the myosin head detaches from actin.
body storing and moving substances within the body
Storage is accomplished by sustained contractions of smooth muscle called sphincters, which prevent outflow of the contents of.a hollow organ. cardiac muscle contractions of the heart pump blood through the blood vessels of the body. Contraction and relaxation the walls of blood vessels help adjust blood diameter and thus regulate the rate of blood flow. smooth muscle contractions also move food and substances, push gametes through the passageways of reproductive systems, skeletal muscle contractions promote the flow of lymph and aid blood return from veins to the heart.
Termination of ACh activity
The effect of ACh binding lasts only briefly because ACh is rapidly broken down by an enzyme called acetylcholinesterase (AChE) This enzyme is attached to collagen fibers in the extracellular matrix of the synaptic cleft. AChE breaks down ACh into acetyl and choline, products that cannot activate the ACh receptor. have to get rid of acetyl and choline, so we don't stay contracted
Attachment of myosin to actin to form cross-bridges
The energized myosin head attaches to the myosin-binding site on actin and releases the previously hydrolyzed phosphate group. When the myosin heads attach to actin during contraction, referred to as cross-bridges.
Production of muscle action potential
The inflow of Na+ (down its electrochemical gradient) makes the inside of the muscle fiber more positively charged. This change in the membrane potential triggers a muscle action potential. Each nerve impulse normally elicits one muscle action potential. The muscle action potential then propagates along the sarcolemma into the system of T tubules. This causes the sarcoplasmic reticulum to release its stored Ca2+ into the sarcoplasm and the muscle fiber subsequently contracts.
ATP hydrolysis
The myosin head includes an ATP-binding site and an ATPase, an enzyme that hydrolyzes ATP into ADP and a phosphate group. This hydrolysis reaction reorients and energizes the myosin head. the products of ATP hydrolysis—ADP and a phosphate group—are still attached to the myosin head.
myasthenia gravis
an autoimmune disease that causes chronic, progressive, damage of the neuromuscular junction
fasciculation
an involuntary, brief twitch of an entire motor unit that is visible under the skin; it occurs regulatory and is not associated with movement of the affected muscle
smooth muscle is what?
autorhythmic
microscopic feature of cardiac muscle (muscular tissue)
branched cylindrical fiber with 1 centrally located nucleus, intercalated disc joining neighboring fibers, striated
fascia
a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body
cramp
a painful spasmodic contraction. caused by inadequate blood flow to muscles, overuse of a muscle, dehydration, injury holding a position for prolonged periods, and low blood levels of electrolytes, such as potassium
synapse
a region where communication occurs between 2 neurons, or between a neuron and a target call
troponin
a regulatory protein that is a component of the thin filament.
tremor
a rhythmic involuntary, purposeless contraction that produces a quivering or shaking movement
what is the main component of thin filaments?
actin protein. individual actin molecules join to form an actin filament that is twisted into a helix.
smooth muscle tissue are?
activated involuntarily
what does a neuromuscular junction include?
all of the synaptic end bulbs on one side of the synaptic cleft, plus the motor end plate of the muscle fiber on the other side
central fatigue
caused by changed in the central nervous system (brain and spinal cord) comes from a person having feelings of tiredness and the desire to cease activity
there are no transverse tubules in smooth muscle tissue, there are small pouch-like invaginations of the plasma membrane known as?
caveolae: contain extracellular Ca2+ that can be used for muscular contraction.
thin filaments
composed of actin protein
thick filaments
composed of protein myosin
skeletal muscle fibers are not all alike in?
composition and function ex: muscle fibers vary in their content of myoglobin, the red-colored protein that binds oxygen in muscle fibers
multiunit smooth muscle tissue
consists of individual fibers, each with its own motor neuron terminals and with a few gap junctions between neighboring fibers. found: in the walls of large arteries, in airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye.
the ATP present inside muscle fibers is enough to?
power contraction for only a few seconds
what are the 4 functions of the muscular tissue?
producing body movement, stabilizing body positions, storing and moving substances within the body, and generating heat
motor proteins
pull various cellular structures to achieve movement by converting the chemical energy in ATP to mechanical energy of motion, that is, the production of force.
a huge amount of ATP is needed to power the contraction cycle in order to?
pump Ca2+ into the sarcoplasmic reticulum, and for other metabolic reactions involved in muscle contraction
junctional folds
receptors are abundant deep grooves in the motor end plate that provide a large surface area for ACh
myogram
record of muscle contraction
skeletal muscle fibers that have a high myoglobin content are?
red muscle fibers and appear darker
when a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a period of time, what is this period of lost excitability called?
refractory period is a characteristic of all muscle and nerve cells. The duration of the refractory period varies with the muscle involved.
a nerve impulse (nerve action potentials) elicits a muscle action potential in what steps?
release of acetylcholine, activation of ACh receptors, production of muscle action potential, and termination of ACh activity
subcutaneous layer (hypodermis)
separates muscles from skin. composed of areolar connective tissue and adipose tissue. provides a pathway for nerves, blood vessels, and lymphatic vessels to enter and exit muscles
stabilizing positions
skeletal muscle contractions stabilize joints and help maintain body positions postural muscles contract continuously when awake
muscle tone
skeletal muscle exhibits. a small amount of tautness or tension in the muscle due to weak, involuntary contractions of it's motor unit
sliding filament mechanism
skeletal muscle shortens during contraction because the thick and thin filaments slide past one another
what are the 3 types of muscular tissue?
skeletal, cardiac, smooth
Filaments (myofilaments)
smaller protein structures within myofibrils
tic
spasmodic twitching made involuntarily by muscles that are usually under voluntary control ex: twitching of the eyelids and facial muscles
most of the excess ATP is used to synthesize what?
creatine phosphate: an energy-rich molecule that is found in muscle fibers
latent period (1st phase of twitch contraction)
delay lasts 2 msec. during this period, the muscle action potential sweeps over the sarcolemma (down into T-tubules) and calcium ions are released from the sarcoplasmic reticulum
how does the sarcoplasm appear?
stuffed with little threads
terminal cisterns
dilated end sacs of the sarcoplasmic reticulum the butt against the T tubule from both sides
both thin and thick filaments are?
directly involved in the contractile process
What are the 4 properties of muscle tissue?
electrical excitability, contractility, extensibility, elasticity
everything ending in "-ase" is an?
enzyme
microscopic feature of smooth muscle (muscular tissue)
fiber thickest in middle, tapered at each end, and with 1 centrally positioned nucleus, not striated
sarcoplasmic reticulum (SR)
fluid-filled system of membranous sacs that encircle each myofibril; stores and releases calcium ions
what are the 3 ways muscle fibers produce ATP?
from creatine phosphate, anaerobic glycolysis, and aerobic respiration
the fibers of smooth muscle connects to 1 another by what?
gap junctions, forming a network through which muscle action potentials can spread.
contractile protein
generate force during contraction
slow oxidative (SO) fibers
have a sloe speed of contraction. appear dark red because they contain large amounts of myoglobin and many blood capillaries. they have large mitochondria, SO fibers generate ATP by aerobic respiration. are slow because the ATPase in the myosin heads hydrolyzes ATP relatively slowly and the contraction cycle proceeds at a slower pace.
fast glycolytic fibers (FG)
have low myoglobin content, relatively few blood capillaries, and few mitochondria, and appear white in color. They contain large amounts of glycogen and generate ATP mainly by glycolysis. Due to their ability to hydrolyze ATP rapidly, FG fibers contract strongly and quickly.
what does the fascia do?
holds muscles with similar functions together. also allows free movement of muscles, carries nerves, blood vessels, and lymphatic vessels, and fills spaces between muscles
neurotransmitters
how one cell communicates with another by releasing this chemical messenger. cells do not physically touch, the action potential can not "jump the gap" from one cell to another
aerobic respiration
if the sufficient oxygen is present, the pyruvic acid formed by glycolysis enters the mitochondria, where is undergoes this a series of oxygen-filling reactions that produces ATP, carbon dioxide, water, and heat
why does a muscle fiber contract?
in response to one or more actions potentials propagating along it's sarcolemma and through it's system of T-tubules
what does connective tissue do?
surrounds and protects muscular tissue
synaptic vessels
suspended in the cytosol within each synaptic end bulb are hundreds of these membrane-enclosed sacs.
wherever there is a z-disc there is a?
t-tubule
myosin head
the 2 projections of each myosin molecule (gold club heads). the heads project outward from the shaft in a spiraling fashion, each extending toward 1 of 6 thin filaments that surround each thick filament
when a 2nd stimulus occurs after the refractory period of the 1st stimulus is over, but before the skeletal muscle fiber has relaxed what happens?
the 2nd contraction will be stronger than the 1st
what happens as the thin filaments slide inward?
the I band and H zone narrow and eventually disappear altogether when the muscle is contracted
contractility
the ability of muscular tissue to contract forcefully when stimulated by an action potential
elasticity
the ability of muscular tissue to return to its original length and shape after contraction or extension
extensibility
the ability of muscular tissue to stretch, within limits without being damaged
at the NMJ, the end of the motor neuron is called?
the axon terminal, which divides into a cluster of synaptic end bulbs: the neutral part of the NMJ
what does the adipose tissue of the subcutaneous layer store?
the body's triglycerides serve as an insulating layer that reduces heat loss and protects muscles from physical trauma.
twitch contraction
the brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron
acetylcholine
inside each synaptic vesicle are thousands of these molecules the neurotransmitter released at the NMJ
calsequestrin
inside the SR, molecules of a calcium-binding protein
what do smooth muscle fibers also contain?
intermediate filaments
the use of creatine phosphate for ATP production?
is unique to muscle fibers
wave summation
is which stimuli arriving at different times cause larger contractions
what do the 3 layers of connective tissue do?
it extends from the fascia to protect and strengthen skeletal muscle
why does the heart beat?
it has a natural pacemaker that initiates each contraction. the built-in rhythm is called autorhythmicity
when a skeletal muscle fiber is stimulated at a rate of 20-30 times per second what happens?
it is only partially relaxed between stimuli
where are the multiple nuclei of a skeletal muscle located?
just beneath the sarcolemma
structural proteins
keep the thick and thin filaments in the proper alignment
relaxation period (3rd phase of twitch contraction)
lasts 10-100 msec. Ca2+ is actively transported back into the sarcoplasmic reticulum, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin and tension in the muscle fiber decrease
contraction period (2nd phase of twitch contraction)
lasts 10-100 msec. during this period, Ca2+ binds to troponin, myosin-binding sites on actin are exposed and cross-bridges form. peak tension develops in the muscle fiber
Perimysium
layer of dense irregular connective tissue, and surrounds 10-100 or more muscle fibers, separating them into bundles called fascicles.
what are the ACh receptors?
ligand-gated (chemical) ion channels
fascicles
little bundles. are large enough to be seen with the naked eye. have the characteristics of "grain" when ripping apart along the fascicles.
myoglobin
located in the sarcoplasm and contains red-colored protein. found: only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid
smooth muscle tissue
located in the walls of hollow internal organs (blood vessels, airways, and most organs in the abdominopelvic) nonstriated, involuntary
acetylcholine receptors
located within each motor end plate, 30-40 million of them integral transmembrane proteins to which ACh specifically bonds
microscopic feature of skeletal muscle (muscular tissue)
long cylindrical fiber with many peripherally located nuclei, unbranched, striated
red muscle fibers contain?
more mitochondria and are supplied by more blood capillaries
the presence of muscles=
more muscle fibers being contracted
skeletal muscle tissue
most of the skeletal muscles move the bones of the skeleton. striated, works in a voluntary manner
producing body movements
movements of the whole body are a result of muscular contractions; rely on the integrated functioning of skeletal muscles, bones, and joints
what are 2 terms for the same structure?
muscle cell=muscle fiber
Each of your skeletal muscles is a separate organ composed of cells that are called?
muscle fibers due to their elongated shape
what are the 2 types of contractile proteins in muscles?
myosin and actin. both are composed of thick and thin filaments.
why does muscle contraction occur?
myosin heads attach to a "walk" along the thin filaments at both ends of the sarcomere, progressively pulling the thin filaments towards the m-line
in a relaxed muscle what is blocked?
myosin is blocked from binding to actin because strands of tropomyosin cover the myosin-binding sites on actin
what is on each actin molecule?
myosin-binding site, where a myosin head can attach
z-discs
narrow, plate-shaped regions of dense material that separate one sarcomere from the next
somatic motor neurons
neurons that stimulate skeletal muscle fibers to contract has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscles fibers
cardiac muscle tissue
only contains the heart and forms most of the heart wall. striated, action is involuntary
myoglobin
only found in muscle cells
hemoglobin
only found in red blood cells
what are the 2 sources of oxygen for muscular tissue?
oxygen that diffuses into muscle fibers from the blood and oxygen released by myoglobin within muscle fibers
myoglobin and hemoglobin are what?
oxygen-binding proteins that bind oxygen when it is plentiful and release oxygen when it is scarce
Endomysium
penetrates the interior of each fascicle and separates individual muscle fibers from 1 another. mostly reticular fibers
sarcolemma
plasma membrane of a muscle cell
myosin tail (twisted gold club handles)
points towards the m-line in the center of the sarcomere. tails of neighboring myosin molecules lie parallel to one another, forming the shaft of the thick filaments
myofibrils
the contractile organelles of skeletal muscle
once the binding sites are "free" what happens?
the contraction cycle: the repeating sequence of events that causes the filaments to slide
sarcoplasm (within the sarcolemma)
the cytoplasm of a muscle fiber. includes: large amount of glycogen, which is a large molecule composed of many glucose molecules. glycogen can be used for synthesis of ATP.
muscle fatigue
the inability of a muscle to maintain a force of contraction after prolonged activity. results from changes within muscle fibers
fast oxidative glycolytic fibers (FOG)
the largest fibers. contain large amounts of myoglobin and many blood capillaries, and have a dark red appearance. fibers can generate considerable ATP by aerobic respiration, which gives them a moderately high resistance to fatigue. fibers are "fast" because the ATPase in their myosin heads hydrolyzes ATP three to five times faster than the myosin ATPase in SO fibers, which makes their speed of contraction faster
Epimysium
the outer layer, encircling the entire muscle. consists of dense irregular connective tissue
excitation-contraction coupling
the steps that connect excitation to contraction
a brief delay occurs between application of what?
the stimulus and the beginning of contraction delay
dense bodies
the thin filaments attached to structures, functionally similar to z discs in striated muscle fibers. some are dispersed throughout the sarcoplasm, and others are attached to the sarcolemma
due to T tubules being open to the outside of the fiber?
they are filled with interstitial fluid
what is the result of thin filaments sliding inward and meeting at the center of the sarcomere?
they move so far inward that their ends overlap
what happens while muscle fibers are relaxed?
they produce more ATP than they need for resting metabolism.
transverse (T) tubules
tiny invaginations of the sarcolemma. they tunnel in from the surface toward the center of each muscle fiber.
what are the smaller amounts of regulatory protein that is apart of thin filaments?
tropomyosin and troponin
the tropomyosin strands are held in place by?
troponin molecules. when calcium ions bind to troponin, it undergoes a change in shape; this change moves tropomyosin away from myosin-binding sites on actin and muscle contraction begins after myosin binds to actin.
individual lengths of the thick and thin filaments remain?
unchanged
power stroke
After the cross-bridges form, the power stroke occurs. During the power stroke, the site on the cross-bridge where ADP is still bound opens. As a result, the cross-bridge rotates and releases the ADP. The cross-bridge generates force as it rotates toward the center of the sarcomere, sliding the thin filament past the thick filament toward the M line.
triad (3)
a transverse tubule and 2 cisterns on either side of it for this to be formed
creatine
a small amino acid-like molecule that is synthesized in the liver, kidneys, and pancreas and then transported to muscle fibers
synaptic cleft
a small gap. separates the 2 cells
fibrillation
a spontaneous contraction of a single muscle fiber that is not visible under the skin, but can be recorded by electromyography. may signal the destruction of motor neurons
spasm
a sudden involuntary contraction of a single muscle in a large group of muscles
all 3 connective tissue layers may extend beyond the muscle fibers to form what?
a tendon, that attaches.a muscle to the periosteum of a bone
the epimysium, perimysium, and endomysium are all?
continuous with the connective tissue that attaches skeletal muscle to other structures, such as bone or another muscle.
what are the 3 kinds of protein that myofibrils are built from?
contractile, regulatory, and structural proteins
regulatory proteins
help switch the contraction process on and off
anarobic glycolysis
the entire process by which breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration
sarcomeres
the filaments inside a myofibril do not extend the entire length of a muscle fiber, but instead they are arranged in compartments known as this basic functional units of myofibril
myosin
the main component of thick filaments. function as a motor protein. when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, preventing myosin from binding to actin.
m-line
the middle of the sarcomere. region in the center of H zone that contains proteins that hold thick filaments together at the center of sarcomere
visceral (single unit) smooth muscle tissue
the more common found in skin & tubular arrangements that form part of the walls of small arteries and veins of hollow organs such as the stomach, intestines, uterus, and urinary bladder.
when a neurotransmitter, hormone, or autorhythmic signal stimulates 1 fiber what happens?
the muscle action potential is transmitted to neighboring fibers, which then contract in unison, as a single unit
if muscle contractions continue past the few seconds what must happen?
the muscle fibers must make more ATP
if two stimuli are applied immediately after the other what happens?
the muscle will respond to the first stimulus but not to the second.
motor end plate
the region of the sarcolemma opposite the synaptic end bulbs. the muscle fiber part of the NMJ.
rigor mortis
the resulting condition, in which muscles are in a state of rigidity (cannot contract or stretch)
at the onset of the contraction cycle what happens?
the sarcoplasmic reticulum releases calcium ions into the sarcoplasm, where they bind to troponin. troponin then moves tropomyosin away from the myosin-binding sites on actin
in a relaxed muscle fiber what happens?
the sarcoplasmic reticulum stores calcium ions. release of calcium from the terminal cisterns of the sarcoplasmic reticulum triggers muscle contraction
the thin filaments on each side of the sarcomere are attached where?
to the z discs, the thin filaments slide inward, the z discs come closer together and the sarcomere shortens
