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Muscle System
The word muscle means little mouse in Latin from the
fancied resemblance of the muscle body contracting
beneath the skin.
Three Types of Tissues
Skeletal: striated, voluntary, multinucleated
Three Types of Tissues
Cardiac: striated, involuntary, single nucleus per
cell, and intercalated disks.
Three Types of Tissues
Smooth: nonstriated, involuntary, single nucleus,
found in organ walls and blood vessel walls
Functions of the Muscle System
Produces body movements
Stabilizes body positions
Regulates organ volume
Moves substances through the body
Produces Heat
75% of the energy of muscles becomes heat
25% of the energy of muscles produces movement
Muscles have a large blood supply
At rest: 15-20% of the blood in the body goes to the
muscles
Maximum exertion: 80-85% of the blood in the body
goes to the muscles
Muscles have their own nerve supply
Every muscle cell gets its own motor nerve ending
Sensory neurons goes from the muscle to
the spinal cord to the brain
Properties of Muscle Tissues
Electrical Excitability
Ability to respond to certain stimuli by producing
electrical signals
Contractility
Ability to shorten
Extensibility
Ability to stretch
Elasticity
Ability to rebound after stretching
Shapes/Arrangements of Muscle Fiber
Parallel
Fascicles run side
by side and they
end in flat
tendons
Ex: sartorius
Fusiform
Ex. Biceps brachii
Another type of fascicle arrangement, but
the ends of the muscle taper toward the
tendons. The belly of the muscle (the
fleshy part in the middle) is more
expanded than the ends
Pennate
the muscle fibers are short and the fascicles are directed
obliquely (diagonally) toward a central tendon that runs
the length of the muscle.
fascicles insert into only
one side of the tendon, the
muscle is UNIPENNATE
Ex:Extensor digitorum
longus
fascicles insert into the tendon from both sides, so that the
muscle resembles a feather, the arrangement is BIPENNATE
Ex: Rectus
femoris
Fascicles that attach obliquely (at a diagonal) from
many directions to several tendons are called
MULTIPENNATE
Ex. deltoid
CONVERGENT (triangular) pattern,
the muscle has a broad origin and
its fascicles converge toward a
single tendon
Ex. Pectoralis major
Ex. Obicularis oculi
Circular
Fascicles are arranged to form a
circle of muscle fibers.
This arrangement is always found
surrounding an external body
opening.
Gross Anatomy
Each skeletal muscle is a separate organ composed of
fibers.
Connective tissues surround the muscle fibers and
the whole muscle.
Fascia: sheet/broad band of fibrous connective tissue
Perimysium: surrounds groups of muscle fibers
called fascicles
Endomysium: separates individual muscle fibers
Nerve and Blood Supply
Generally, an artery and 1 or 2 veins accompany each
nerve that penetrates a skeletal muscle.
Neurons that stimulate muscular contractions
are called somatic motor neuron
Microscopic Anatomy
Sarcolemma: plasma membrane that surrounds each
muscle fiber
Sarcoplasma: cytoplasm of the fiber and located within it
Myofibrils: threadlike structures that run the length of the muscle fibers
contractile elements of the skeletal muscle
composed of myofilaments
Two Types of Myofilaments
1. Myosin filament: thick and consist of a protein called myosin
2. Actin filament: thin, consist of a protein called actin
Myosin and actin filaments form repeating units called
sarcomeres.
Basic unit of muscle contraction
Hundreds of sarcomeres join end to end to
form a myofibril
Joined at the ends by interweaving filaments
called Z line
Filaments overlap producing striation
A Band: darker middle portion of the sarcomere and
extends the entire length of the myosin
I Band: lighter area of the sarcomere, contains only
actin
H Zone: located in the center of of each A band and
contains only myosin
M Line: supporting proteins holding the myosin at
the center of the H zone
Zebras In A Hot Motel
Z line, I band, A band, H Zone, M line
Zebras In A Hot Motel
Z line, I band, A band, H zone, M line
Sarcoplasmic reticulum: fluid-filled system of membranous sacs that
encircle each myofibril.
Stores calcium (Ca 2+ ) during muscle relaxation
Releases calcium to trigger muscle contraction
Terminal cisterns : dilated end sacs of the sarcoplasmic reticulum
T tubules and terminal cisterns form a triad of the sacroplasmic reticulum
Troponin
tropomyosin
Muscle Metabolism
Muscle fibers have 3 sources for ATP production:
Creatine phosphate
Anaerobic cellular respiration
Aerobic cellular respiration
Creatine Phosphate
Energy rich molecule unique to muscle fibers
Provides enough energy for muscles to
contract maximally for about 15 minutes. Ex:
100 meter dash.
Anaerobic Cellular Respiration
ATP producing reactions that do not require oxygen
Produces energy for about 30-40 seconds of
maximal muscle activity. Ex: 200 meter race
Aerobic Cellular Respiration
Oxygen-requiring reactions that produces ATP
Used when muscle activity lasts longer than
half a minute.