Download Muscle Tone

Functions of Muscles
• 1. Produce movement – all movements
of the human body are produced by
muscles
• 2. Maintain posture – some muscles are
in a partial state of contraction at all times
• 3. Stabilize joints – muscle tendons
reinforce and stabilize joints
• 4. Generate heat – ¾ of the energy used
to contract muscles is lost as heat.
Needed to maintain body temperature
Skeletal Muscle Characteristics
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Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by
connective tissue called Fascia
Smooth Muscle Characteristics
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Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs
Cardiac Muscle Characteristics
• Has striations
• Usually has a single nucleus
• Joined to another muscle cell at an intercalated
disc
• Involuntary
• Found only in the heart
General Structure of Muscles
• A muscle is composed of bundles of muscle
fibers called fascicles separated by connective
tissue (perimysium)
• Fascicles are surrounded by a tough connective
tissue layer called the Epimysium, which covers
the entire muscle
• The epimysia extend beyond the end of the
muscle and form the Tendon which connects it
to bone
• The epimysia can also form a broad sheet-like
connection to an adjacent muscle called an
Aponeurosis
• Each fasciculi is composed of bundles of
smaller fibers that are the individual
muscle cells.
• Each cell is composed of smaller fibers
called myofibrils surrounded by a cell
membrane (sarcolemma)
• The myofibrils are made of filaments of
actin and myosin protein arranged in units
called sarcomeres
Neuromuscular Junction
• Sarcolemma is folded to form the motor end
plate. Many Mitochondria in the region
• Nerve fiber forms Synaptic Clefts into the
recesses of the sarcolemma. The nerve
contains synaptic vesicles that contain
neurotransmitter
• When a nerve impulse reaches the junction it
causes the release of the neurotransmitters
• The specific neurotransmitter that stimulates
skeletal muscle cells is acetylcholine
Skeletal Muscle Contraction
• 1. Nerve impulse causes the release of
acetylcholine by the synaptic vessels into the
synaptic cleft
• 2. The acetylcholine stimulates a muscle impulse
along the length of the sarcolemma
• 3. The impulse cause the sarcoplasmic reticulum
to release Calcium ions into the sarcoplasm of the
muscle cell
• 4. Ca++ ions cause an attractive force between
actin and myosin and the sarcomere becomes
shorter
• 5. Ca++ ions are removed by active transport and
acetylcholine is decomposed by an enzyme
Energy for Contractions
• Energy for the contraction comes from
ATP. ATP→ADP + Energy
• 4 – 6 seconds worth of ATP is stored in
muscles
• Another 20 seconds worth can be
generated from Creatine Phosphate
• The rest must be generated via aerobic
and anaerobic respiration.
• Aerobic respiration is slow but efficient (36
ATP per molecule of glucose
• Anaerobic respiration is fast but inefficient
(2 ATP per glucose molecule)
• Muscle Fatigue - Muscle loses the ability
to contract. Due mainly to the buildup of lactic
acid from anaerobic respiration
• Myoglobin – Reddish brown pigment
found in muscles that combines with oxygen to
store it in muscles
• Cramps – Muscle contracts but does not
relax. Caused by lack of ATP. Can’t move Ca++
ions out.
• Muscle Tone – Sustained contraction that
occurs in some fibers of most muscles.
Maintains Posture. Involuntary
• Twitch Contraction – Quick contraction
(fraction of a second) in response to a single
stimulus. Example - Eye blink
• Tetanic Contraction – Sustained
contraction in response to continuous stimuli.
Most muscle contractions are tetanic.
• Origin – Point of attachment to the
immovable or less movable bone.
• Insertion – Point of attachment to the
movable bone
• Muscle Atrophy – Decrease in the size of the
muscle due to disuse
• Muscle Hypertrophy – Increase in the size of
muscles from exercise
• Muscles Act In Groups
• Prime mover – is responsible for most of a
certain movement
• Synergist – assist the prime mover
• Antagonist – capable of resisting the prime
mover’s action. Responsible for movement in
the opposite direction.