Download THE MUSCULAR SYSTEM

THE MUSCULAR SYSTEM
TYPES OF MUSCLE
• 1. Cardiac- found only in the heart; striated, involuntary. Contracts
forcing blood to be pumped by the heart. Unique in the fact it
normally does not fatigue.
• Smooth- (visceral) found in the walls of hollow organs. Involuntary,
non-striated. Also found in blood vessels (arteries) and in
sphincter muscles which help control blood pressure, circulation,
heat loss, and digestion.
• Skeletal Muscle- striated, voluntary; contraction causes movement
of the skeleton with the joints acting as a fulcrum and the bones as
levers. Also creates body heat by giving off heat created by
contraction and the consumption of ATP.
Types of muscle fibers
Characteristics of Skeletal Muscle
• 1. Irritability-(excitability) ability to react to a stimulus
• 2. Contractility- ability to shorten when stimulated
• 3. Extensibility- ability to stretch
• 4. Elasticity- ability to return to a normal length after stretching
Skeletal Muscle Attachments
• All muscles are encased by connective tissue sheath and connective
tissue attachments at each end of the muscle.
• Fascia- each individual muscle is encased by the fibrous connective
tissue sleeve.
• Tendon-FCT band that attaches muscle to the bone.
Origin- the attachment with the least or no movement
Insertion- the attachment that moves the most on contraction
• Aponeurosis- broad fibrous sheet of connective tissue that attaches a
muscle to another band of muscle.
Types of connective tissue
attachments for muscles
Origin and Insertion of the biceps brachii
Individual Muscle C. T. coverings
• Epimysium- covers the whole muscle
• Perimysium-surrounds and separates a large group of fibers of
a muscle called a fasiculus.
• Endomysium-surrounds each individual muscle fiber
MUSCLE STRUCTURE
• Each muscle cell is called a fiber. Very large cell,
multinucleated.
• Sarcolemma- muscle cell membrane
• Sarcoplasm- cytoplasm of a muscle cell
• Each fiber is composed of smaller fibers called myofibrils.
• Myofibrils are composed of even smaller fibrous proteins
called Actin and Myosin these are called myofilaments.
• These proteins are arranged in repeating units called the
SARCOMERE.
skeletal muscle.
The contractile or functional unit of
MUSCLE MICROANATOMY
THE SLIDING FILAMENT THEORY
• Proposed in the 1950’s by T. J. Huxley, he explained that
actin filaments are pulled over myosin filaments by
cross-bridges which form the between the proteins. He
later received the Nobel Prize for his theory.
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When the muscle fiber is stimulated to contract:
1. The I-band disappears
2. A-band remains unchanged
3. M or H zone disappears
4. Z-lines are drawn closer together.
• Each muscle fiber is made up of thousands and thousands of
sarcomeres and when each of these multitudes of sarcomeres
each shorten it results in the whole muscle shortening or as
we call it contracting.
Myosin is 2 protein strands wrapped around one another
in which globular proteins project.
• globular proteins on myosin react with actin forming
cross-bridges
• This reaction generates the force necessary to shorten
myofibrils
Actin is a double strand twisted into a helix. It has ADP
molecules on its surface and this is what forms the crossbridges with myosin.
THE NEUROMUSCULAR JUNTION
• Each muscle fiber is connected to a nerve cell fiber called a motor
neuron.
• The site where the nerve fiber and muscle fiber join is called the
neuromuscular junction.
• The muscle fiber membrane is specialized to form a motor end
plate.
• Muscle contraction is stimulated by the secretion of acetylcholine
at the neuromuscular junction. Acetylcholine is a
neurotrasmitter.
• Motor unit = motor neuron + muscle fibers controlled by it.
Neuromuscular junction
Stimulus for Muscle Contraction
• Acetylcholine secreted at the NMJ stimulates muscle
contraction by causing depolarization of the myofibril.
• Ca++ ions have to be present for muscle contraction to occur.
• Ca++ ions are stored in the sarcoplasmic reticulum which
surrounds each myofibril.
• Acetylcholine stimulates the release of Ca++ ions which in
turn stimulates shortening of the sarcomeres causing
contraction of the muscle fiber.
Energy Sources for Contraction
• Like all cells of the body muscle ultimately relies on
ATP -----ADP to supply energy for contraction
• Glycogen is stored in muscles and the liver
• Glycogen ------- glucose which then enters glycolysis
• Pyruvic acid, the end product of glycolysis, when oxygen is
present , enters the Kreb’s cycle ATP------- ADP
• Myoglobin, a protein in muscle stores oxygen.
• During periods of intense activity, oxygen cannot be supplied
to muscle fibers fast enough and not enough ATP can be
supplied by oxidative metabolism.
• Without enough oxygen pyruvic acid formed from glycolysis is
then converted to lactic acid which diffuses out of the muscle
fibers and into the blood stream.
• Muscles store a compound called creatine phosphate this
provides a means of reforming ATP rapidly.
• An oxygen debt is built up during periods of intense muscular
activity when nonoxidative sources of ATP (glycolysis and
creatine phosphate) are used to support muscle contraction.
• This debt is paid back by an elevated rate of respiration during
the period following exercise.
• The elevated rate of respiration provides oxygen required to
produce ATP for the resynthesis of creatine phosphate and to
convert lactic acid back to glucose and glycogen.
• During exercise these reactions take place:
glucose---------lactic acid + ATP
creatine phosphate-------- creatine + phosphate + energy
• After exercise:
ADP + P-------- ATP
creatine + phosphate------- creatine phosphate
1/5 lactic acid + oxygen ------- carbon dioxide + water
4/5 lactic acid + ATP ------ glucose
Muscle Fatigue
• Muscle fatigue results in the loss in the ability to contract the
muscle.
• Caused by:
blood supply interruption
exhaustion of acetylcholine
lactic acid build up (pH changes)
lack of ATP, K+, Na+, or Ca++
Muscle Response
Muscle response is measured on a kymograph producing a
myogram.
• All or None Law- A muscle fiber will contract fully or not at all.
• Threshold stimulus- the weakest stimulus that will elicit a response.
(contraction of a muscle fiber)
• Subthreshold stimuli can be additive and can stimulate a contraction this is
called summation.
Latent period .01sec
Contraction phase .04sec
Relaxation phase .05sec
Frog gastrocnemius in kymograph
Types of Muscle Contractions
• Concentric – contraction in which the muscle shortens
• Eccentric- contraction of the muscle when the muscle is stretched.
• Isometric –contraction in which there is no movement.
• Isotonic-contraction which produces movement, resistance is
variable (due to gravity and lever action of the skeleton)
• Isokinetic-contraction with movement, resistance will vary
depending on the force applied. (machines only)
• Hypertrophy- muscle enlargement due to increase in fiber size
• Atrophy-muscle shrinkage due to disuse or paralysis or nerve
impairment.
• Tetany (tetanus) a sustained contraction resulting from too many
stimuli, will last until oxidation and removal of lactic acid occurs
within the muscle.
• Tonus (tone) some muscle fibers will be contracted while others
remain relaxed. Then other muscle fibers will contract while
others are relaxed.
Antagonistic Pairs
opposite pairs of muscles.
• Agonist (prime mover) muscle contracting producing movement
• Antagonist opposite muscle being stretched due to the contraction
of the agonist.
• Examples biceps-triceps, quadriceps-hamstring
Diseases and Disorders of the Muscular System
• Myasthenia gravis-severe muscle fatigue, drooping eyelids,
double vision due to low acetylcholine production or
acetylcholine receptors malfunction.
• Muscle strain- stretching or tearing of muscle fibers or the
tendons which connect them. 1st degree, 2nd degree, 3rd degree
Structural and Functional Characteristics of the 3 Types
of Skeletal Muscle Fibers
Speed of Cont.
Enzyme act.
Pathway for ATP syn
Myoglobin content
Glycogen stores
Recruitment
Rate of fatigue
Slow oxidative
Slow
Slow
aerobic
high
low
1st
slow
Activites best suited
endurance
Color
Fiber diameter
Mitochondria
Capillaries
red
small
many
many
Fast oxidative
fast
fast
both
high
intermed.
2nd
intermed.
Fast glycolytic
fast
fast
anaerobic
low
high
3rd
fast
intermed
intense
red to pink
intermed
many
many
white
large
few
few
Muscle fiber comparison X-sect.