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MUSCLE ANATOMY
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LEARNING GOALS
• I will understand the anatomy of the muscle.
• I will understand the simple neurology of the muscle.
BASIC UNIT
• Skeletal muscles are made up of cylinder shaped cells called fibres.
• Each fibre is made up of long slender cells (myofibrils) ranging from 1mm to 50
mm in length
• In each muscle, fibres are grouped together in bundles.
• Bundles of muscle fibre are called fasciculi
• The arrangement of the bundle determines the shape and size of each muscle.
EPIMYSIUM
• Skeletal muscles are sheathed by a tough layer of connective tissue called the
epimysium.
• Envelopes the entire muscle
• Extends beyond muscle to become tendon
• Tendon becomes bone’s periosteum
• This is the attachment site of muscles: origin and insertion
PERIMYSIUM
• Sheath of connective tissue binding groups of muscle fibres together
ENDOMYSIUM
• Connective tissue surrounding a muscle fibre
• In between fibres
SARCOLEMMA
• Plasma membrane that lies beneath the endomysium
• Contains the muscle cell’s cytoplasm
SARCOPLASM
• Muscle cell’s cytoplasm
• Large amounts of stored glycogen
• Protein myoglobin
• High concentration of Ca2+ and mitochondria
SARCOMERES
• Repeating structural units or compartments containing proteins ‘actin’ and
‘myosin’
• Myosin (thick filament) and Actin (thin filament)
• Myosin (looks like golf club) head has an attachment site for Actin
• Actin has a binding site for Myosin
• Actin has two other proteins: troponin (Ca) and tropomyosin (covers binding
site on actin)
SARCOPLASMIC RETICULUM
• Network of web like channels involved in muscle activation
• Release Ca
• Actin and myosin slide across one another during muscle contraction
NEUROMUSCULAR FUNCTION
NERVOUS ARE YOU?
• Skeletal muscle is activated by the nervous system.
• The nervous system can be divided into
• central (spinal cord)
• peripheral (away from spinal cord)
• The nervous system can also be divided into
• sensory (collects information from sensors and sends information to brain)
• motor (sends signals to activate muscle contraction)
• Motor nerves extend from spinal cord to muscle fibers
MOTOR UNIT
• A single nerve that activates a group of fibers is called a motor unit.
• Large muscles may have hundreds of fibers in each unit (quads)
• Small muscles may have as little as 10 fibers in each unit (muscles of the eye)
• The smaller the motor unit the more precise the movement.
• Nerves transmit impulses in “waves” that ensure smooth movements.
• A single nervous impulse and the resulting contraction is called a muscle
twitch.
• One neuron or nerve (called the “motor neuron”) may be responsible for
stimulating a number of muscle fibres.
ALL OR NONE PRINCIPLE
• An impulse from the CNS needs to be of a certain magnitude to cause fibers to
contract.
• A smaller impulse does not result in a smaller contraction.
• Once the needed magnitude is reached, the muscle contracts.
• This is called the all-or-none principle.
When a motor unit contracts it will
contract completely or not at all.
• In other words, if a motor unit consists of 10 muscle fibres (or 800 muscle fibres)
and they are “turned on,” either all fibres will contract or none will contract.
INTRAMUSCULAR COORDINATION
• Increased strength requires more motor units being activated.
• This is called intramuscular coordination.
• Trained athletes are able to recruit more motor units than untrained
individuals (Olympic weight-lifters – 85%, untrained individuals – 60%).
• Trained athletes can further increase strength only by increasing muscle
diameter.
INTERMUSCULAR COORDINATION
• Recruiting motor units from different muscles allows for improved
performance.
• This is called intermuscular coordination.
• A high performance athlete has trained all agonists and antagonists to work
together for a fluid skill movement.
RECIPROCAL INNERVATION
• Muscles seldom work alone.
• In almost all cases muscles work in pairs or groups to produce movement.
• When you move your body, a coordinated action of several muscles must
occur.
• Different muscles attached around the joint cooperate to produce a smooth
efficient movement.
• Reciprocal innervation is a process which produces the exact amount of
relaxation in the antagonist to balance the amount of contraction generated in
the agonist.
• For example, in the human arm, the triceps acts to extend the lower arm
outward while the biceps acts to flex the lower arm inward.
• In order to reach optimum efficiency, contraction of opposing muscles must be
inhibited while muscles with the desired action are excited.
• This reciprocal innervation occurs so that the contraction of a muscle results
in the simultaneous relaxation of its corresponding antagonist.
LEARNING GOALS
• I will understand the anatomy of the muscle.
• I will understand the simple neurology of the muscle.