Muscle anatomy Copy only the red text!

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.

When a motor unit contracts it will 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.