


















Muscles are separated by fascia.
Tendons connect muscles to bones, aponeuroses are broad sheets that connect to
muscles.
Muscle cells are called fibers.
Endomysium surrounds and individual muscle fiber.
Fibers are bundled to form a fascicle. Fascicles are surrounded by the perimysium.
Fascicles are bundled to form a muscle. Muscles are surrounded by the epimysium.
Muscles are often contained within a compartment along with nerves and blood
vessels. Increased pressure within the compartment can cause compartment
syndrome.
There are three types of muscle; skeletal, cardiac, and smooth.
Skeletal muscle cells are cylindrical, multinucleated, voluntary, striated. Found attached
to the bones.
Cardiac muscle cells are striated, branched, involuntary, single nucleus, and have
intercalated discs. Found only in the heart.
Smooth muscle cells are tapered or spindle-shaped, nonstriated, involuntary, with a
single nucleus. Found in hollow internal organs.
Myofibrils make up a muscle cell. There are thick filaments (myosin) and thin filaments
(actin, troponin, and tropomyosin).
These filaments make up the sarcomere, which is the contractile unit of the muscle cell.
The actin attaches to the z-discs and extend inward toward each other. The myosin sits
in the middle of the sarcomere. Mysoin contains crossbridges used to attach on to the
actin to pull the z-discs inward toward the middle of the sarcomere.
The neuromuscular junction is the connection between the motor neuron and the
muscle fiber. The motor unit is the actual neuron and whatever muscle fibers it
connects to. In the eyes, it may be 10 fibers. In the back, it may 1000 fibers. The
synaptic cleft is the gap in between the two cells.
When an impulse reaches the end of a motor neuron, achetylcholine is released from
the vesicles as the neurotransmitter. It diffuses across the synapse and attaches onto
the sarcolemma of the muscle fiber. The impulse causes calcium ions to be released
from the T-tubules. The calcium ions attach onto the troponin and cause the
tropomyosin to move out of the way, exposing bing sites for the myosin crossbridges to
attach to. This requires ATP. The myosin pulls the actin inward toward the middle,
causing the sarcomere to shorten. Since the muscle cell is made of repeating
sarcomeres connected end to end, the entire muscle fiber shortens. This causes the
muscle to contract.
When the impulse stops, calcium ions are released from the troponin and return to the
T-tubules. The crossbridges are broken off the actin. Tropomyosin returns to its original
position. The actin slides back out to cause the muscle cell to relax. This also requires
ATP. This process is referred to as the sliding-filament theory of muscle contraction.
Acetylcholinesterase breaks down the remaining Ach in the synapse.
Muscle fibers follow the all-or-none principle. If a threshold stimulus is received, it will
contract 100%, or it won’t contract at all. Muscles do not follow this. The strength of
contraction can be determined by the number of fibers that are recruited. The more
fibers recruited, the stronger the contraction. This is usually based on our past
experiences.























Isometric contractions change the tension, but the length of the muscle does not
change. This is seen in pushing against the wall or pulling on a fixed object.
Isotonic contractions maintain the same tension, but the length of the muscle changes
and movement occurs. Free weights are a good example.
One way energy can be supplied for muscle contraction is by creatine phosphate
donating a phosphate to ADP to make ATP.
Energy can also be supplied anaerobically, but this supplies very little energy and it
runs out within 20-30 seconds. In anaerobic conditions, lactic acid begins to build up in
the muscles and leads to the muscle shutting down. Oxygen is required to break down
the lactic acid. During exercise, oxygen is used up faster than normal, creating an
oxygen debt. This results in rapid breathing to repay the debt.
The majority of energy produced for muscle contractions is done so by aerobic cellular
respiration.
Psychological fatigue means you feel tired and want to stop. Physiological fatigue is
when the muscle cannot continue to contract.
Muscles produce heat as a by-product of cellular respiration.
A threshold stimulus is the minimal stimulus required to cause a muscle cell to
contract.
A twitch is a contractile response in a single muscle fiber.
The time between the stimulus and the contraction is the latent period.
The force of a muscle contraction depends on: the frequency at which the individual
muscle fibers are stimulated and how many fibers take part in the overall contraction.
Summation is the process by which the force of individual twitches combine. When the
resulting contraction is forceful and sustained it is a tetanic contraction.
The more muscle fibers that are stimulated by a single motor neuron the less precise
the movement. The fewer stimulated, the more precise the movement. (Eye muscles1/10, back muscles-1/1000.
Muscle tone is a continuous partial muscle contraction. It leads to definition or that
ripped look. It is important in maintaining posture.
Fast-twitch fibers contract very quickly but fatigue easily. They are also called white
fibers due to lack of myoglobin and oxygen. Found in the eyes. (forms dark meet seen
in breast meat of migratory birds, chicken legs)
Slow-twitch fibers are fatigue-resistant. They are slow to contract but do not fatigue.
Also called red fibers due to large amounts of myoglobin and oxygen. Seen in our
posture muscles. (forms breast meat in chickens and turkeys)
Intermediate fibers are fatigue resistant fast twitch fibers. Found in muscles that move
the limbs.
1st class lever-fulcrum is between the force and resistance. (trapezius pulling the head
back)
2nd class lever-resistance is between the force and fulcrum. (raising up on your toes)
3rd class lever-force is between the fulcrum and resistance (biceps curl)
Origin is the stationary end of a muscle whereas the insertion is the movable end. The
insertion moves toward the fulcrum.
Prime mover is the muscle that does the main action. The synergist helps it. The
antagonist does the opposite action and may even resist it. Remember, muscles only
pull, they do not push. Fixators help stabilize the prime mover as well as the joint.
Flexion decreases the joint angle and extension increases it.











Abduction moves a part away from the midline and adduction moves it toward it.
Rotation turns the part on an axis.
Supination turns palm upward and pronation turns it downward.
Inversion turns the sole of the foot inward. Eversion turns it outward.
Plantar flexion points the foot. Dorsiflexion brings the foot toward the shin.
Atrophy is a decrease in muscle size. Muscles will atrophy over time. Also caused by
casting, paralysis, and bed rest. Hypertrophy is an increase in size of the muscle.
Muscles increase in size by increasing the amount of protein fibers in the cells rather
than by making more cells.
You must work out once a week to maintain your current strength.
If you want to build strength, use heavier weights and do fewer reps. If you want to
build endurance, use less weight and do more reps.
A bruise is bleeding in a muscle.
A strain is a tear to a muscle or tendon.
Myoglobin, ATP, and creatine phosphate levels decline as we age.By age 80, nearly 50%
of your muscle mass will have atrophied.