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76 terms

anatomy

muscle tissue
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skeletal muscle
is striated muscle and is voluntary (it can be controlled consciously). It can only be stimulated by the nervous system.
cardiac muscle
is striated muscle. It is involuntary (no conscious control). It can be stimulated or inhibited by either the nervous or the endocrine systems.
smooth muscle
is nonstriated and also involuntary. It also can be stimulated or inhibited by either the nervous or endocrine function.
three functions of muscle tissue
motion, stabilize body positions and regulate organ volume, thermogenesis
characteristics of muscle tissue
excitability, contractility, extensibility, elasticity
fascia
refers to a sheet or broad band of fibrous connective tissue beneath the skin or around muscles and organs of the body. There are two types.
superficial fascia
(subcutaneous layer or hypodermis) lies immediately deep to the skin. It is composed of adipose and areolar tissues.
Four functions of Superficial fascia
store fat, insulation, mechanical protection, pathway for nerves and blood vessels
deep fascia
formed of dense irregular connective tissue. It lines the body wall and extremities and holds muscles together, separating them into functional groups. allows free movement of muscles, carries nerves, blood vessels, and lymph vessels, and fills the spaces between muscles.
epimysium
is the outermost layer of deep fascia, wrapping the entire muscle.
perimysium
is formed by invaginations of the epimysium, dividing the muscle into bundles of cells called fascicles (fasciculi).
endomysium
is formed by invaginations of the perimysium that penetrate the fascicle and wrap each muscle cell, completely insulating it from the others.
tendon
All three layers may extend beyond the muscle as a cord of dense connective tissue that attaches the muscle to the peristeum of a bone.
tendon sheath
Some tendons, particularly those in high stress areas like the ankle and wrist, are wrapped in a layer of synovial membrane
aponeurosis
When the three connective tissue components extend from the muscle as a flat sheet, rather that a round cord,
myofiber
Within a typical skeletal muscle there are thousands of individual, very long, cylindrical cells called muscle fibers, bundled together as fascicles. They lie in parallel to one another.
sarcolemma
the cell membrane of a muscle cell. surrounds the sarcoplasm.
mitochondria
lie in rows throughout the muscle fiber, located close to the muscle proteins that use ATP for the contraction-relaxation sequence.
Nuclei in skeletal muscle
cells are multinucleated, due to fusion of precursor cells during embryogenesis; the nuclei are located along the periphery of the cell, out of the way of the contractile elements within the sarcoplasm.
myofibrils
lie parallel to each other and extend lengthwise throughout the myofiber. give skeletal muscles their striations due to their areas of light and dark. The contractile element of skeletal muscle. Are made up of myofilaments.
sacromere
functional (contracting) unit of skeletal muscle.
Z line
a dense material found at each end of a sarcomere, separating it from the next sacromere in line.
thin myofilaments
extending from each z line towards the middle of the sacromere
thick myofilaments
suspended within the sarcoplasm, between the thin myofilaments, and not attached to the z line
Actin
the main component of a thin myofilament, each molecule of which looks like a kidney bean.
myosin binding site
upon each actin filament that is twisted to form a helical strand.
tropomyosin troponin complex
In relaxed muscle, covers the myosin-binding sites on the actin molecules. This blocks the myosin-binding sites and prevents the attachment of the thick myofilaments, thus preventing contraction of the sarcomere.
Mysoin
Each thick myofilament is composed of about 200 molecules of a protein. is shaped like two golf clubs twisted together. The tail of the molecule extends to the center of each sarcomere. The projecting "head," called a cross bridge, extends out towards the thin myofilaments.
Titin
elastin myofilament, anchor the thick myofilaments in position and to play a role in recovery of the resting sarcomere length when a muscle cell is stretched or contracted. accounts for most of the extensibility and elasticity of the myofibrils
sarcoplasmic reticulum
A fluid filled system of tubules that encircles each myofibril. In relaxed muscle stores calcium ions by sequestering them from the sarcoplasm.
transverse tubules
are tunnel like enfolding of the sarcolemma. They penetrate the myofiber at right angles to the sarcoplasmic reticulum and the myofilaments. Are open to the outside of the muscle fiber and therefore filled with extracellular fluid.
terminal cisternae
dilated end sacs of the sarcoplasmic reticulum connected on both sides of the transverse tubule.
Muscle triad
a transverse tubule together with its two terminal cisternae.
motor neuron
originating in the brain or spinal cord, delivers the nervous stimulus that ultimately causes a muscle tissue to contract.
motor unit
One motor neuron plus ALL of the skeletal muscle cells it stimulates. On average, a single motor neuron makes contact and thus stimulates about 200 individual skeletal muscle cells. All the cells contract and relax together, as a unit.
precise movement
muscles that have as few as 2-3 muscle cells per motor neuron.
gross movement
muscle that have as many as 2,000 muscle cells per motor neuron.
total strength
the number of motor units being used at any given time.
recruitment
the process of increasing the number of active motor units within a given skeletal muscle.
synapses
Excitable cells (muscle and nerve) make contact and communicate with one another at specialized regions
synaptic cleft
at each synapses a small gap, separates the two excitable cells.
neurotransmitter
The first cell, the motor neuron, communicates with the second cell, the skeletal muscle cell, across the synaptic cleft via a chemical messenger
neuromuscular junction
The type of synapse formed between the motor neuron and the skeletal muscle cell
axon terminals
At the synapse, the motor neuron branches into clusters of bulb shaped, each cluster forming a synapse with a group of muscle cells (motor unit)
motor end plate
The region of the muscle cell membrane that participates in the synapse with the axon terminal
acetylcholine
the neurotransmitter used exclusively by motor neurons for skeletal muscles
synaptic vesicles
Within each axon terminal are many membrane-enclosed vesicles containing thousands of neurotransmitter molecules
sliding filament theory
it was proposed that skeletal muscle shortens during contraction because the thin and thick myofilaments slide past one another.
acetylcholiesterase
ACh is rapidly broken down in the synaptic cleft by the enzyme
calsequestrin
calcium ions are pumped into the sarcoplasmic reticulum, where they are bound to the molecule, thus removing them from the sarcoplasm
muscle tone
Sustained contractions of a few motor units in a given skeletal muscle produce a firmness, This maintains optimum length of the muscle and makes it ideally ready for action.
asynchronous firing
different units are activated at different times
phosphagen system
energy system which utilizes stored ATP and creatinine phosphate, provides enough energy for skeletal muscles to contract maximally for about 15 seconds. It is used for maximal short bursts of activity.
aerobic system
For continued activity and with sufficient oxygen, mitochondria completely catabolize glucose to carbon dioxide, water, and a net 36 ATPs. When the oxygen supply is outstripped by the activity, glucose is incompletely catabolized to lactic acid. This leads to fatigue and oxygen debt.
glycogen lactic acid system
When stored ATP and creatinine phosphate are depleted, the cell catabolizes glucose to create new ATP. A series of reactions known as glycolysis creates 2 ATPs for each glucose and does so anaerobically (without oxygen). This provides energy for an additional 30-40 seconds.
oxygen debt
the difference between the resting state of oxygen consumption and the elevated rate following an exercise.
slow oxidative fibers
abundant mitochondria, myoglobin (stores oxygen), and blood capillaries well adapted to aerobic respiration, fibers do not fatigue easily (high endurance)
fast glycolytic fibers
abundant enzymes for the phosphagen and glycolytic lactic acid pathways, extensive sarcoplasmic reticulum for rapid calcium movement, poor in mitochondria, myoglobin, and blood capillaries, twitch times as short as 7.5 sec, atigue easily (low endurance)
thermoreceptors
detect decreases body temperature in the hypothalamus of the brain and the skin.
involuntary thermogenesis
returns body temperature to within normal homeostatic range, and the process is turned off by negative feedback.
all or none principle
states that individual muscle fibers contract fully and completely for the existing conditions, or do not contract at all.
threshold stimulus
one that initiates the formation of an electrical impulse in the sarcolemma.
twitch contraction
brief contraction of all muscle fibers in a motor unit in response to a single threshold stimulus from a motor neuron.
latent period
is the time from when the stimulus is applied to the beginning of the actual shortening of the sarcomere. During this time, membrane polarization is changing, calcium is diffusing out of the sarcoplasmic reticulum, and the cross bridge of myosin are attaching to actin.
contraction period
is the time during which the myofilaments are sliding, the sarcomere is shortening, and the muscle fiber is generating force.
relaxation period
is the time during which acetylcholinesterase is destroying acetylcholine at the synapse, calcium ions are being sequestered within the sarcoplasmic reticulum, the cross bridges are releasing from actin, and the sarcomere is sliding back to its resting strength.
refractory period
When a muscle fiber receives a threshold stimulus, it temporarily loses its excitability and cannot be stimulated again.
wave summation
If a second stimulus is applied to an excited muscle cell after the refractory period, but before the cell has finished resting from the first stimulus, the second contraction will be greater than the first. This phenomenon, in which stimuli arrive at different times and cause larger contractions
incomplete tetany
during which the muscle is contracting maximally but relaxing only partially.
complete tetany
If frequency of stimulation is increased to 80-100 per second, no relaxation period occurs at all between contractions.
treppe contraction
When a skeletal muscle has been fully rested and is then stimulated repeatedly by identical stimuli too far apart to cause wave summation, each of the first few contractions is a little stronger than the last.
isotonic contractions
occur when you move a constant load through the range of motions possible at a joint. In this type of contraction, the tension within the muscle stays the same during the contraction, while the length of the fibers shortens.
isometric contractions
occur when the muscle does not or cannot shorten, but the tension within it greatly increases.
intercalated discs
Adjacent cell membranes contact one another at thickened areas, it is through these structures that adjoining cells communicate
visceral smooth muscle
It is found wrapped in sheets that form part of the walls of hollow organs. The cells are tightly bound to each other to form a continuous network (functional syncytium), so that stimulation of one cell results in stimulation of the entire network.
Multiunit smooth muscle
consists of individual smooth muscle cells, each with its own motor neuron, so that each can contract independent of the others. Is found in the walls of blood vessels, the arrector pili of hair follicles, and in the iris of the eye.