Myology Amanda Dunne

Learning outcomes By the end of the session you will be able to: Differentiate between the structure and function of the different types of muscle Describe the process of muscle contraction

Introducing: the muscular system Three types of muscle tissue. Muscle cells are called fibres Shortening/contracting of fibres causes movement. Muscle movement results from conversion of chemical energy (ATP) into mechanical energy.

Muscle tissue types SMOOTH - moves substances (food stuffs, urine, blood) along internal passageways. Involuntary control. Located mainly in the walls of hollow organs. CARDIAC - as it contracts, it propels blood into circulation. Involuntary control. Located in the walls of the heart. SKELETAL - voluntary movement, locomotion, manipulation of the environment, facial expressions and voluntary control. Located in skeletal muscle attached to bones or occasionally to skin.

Skeletal muscle Attaches to and moves skeleton Longest fibres Voluntary Tires easily, yet powerful Contains several nuclei Stimulated by motor nerve impulses Skeletal muscle is voluntary, but also subconscious and can be activated by reflexes

Smooth (visceral) muscle Involuntary muscle No striations when seen under a microscope Found in walls of hollow visceral structures such as digestive tract, blood vessels, and ureters.

Skeletal muscle

Cardiac (heart) muscle Involuntary muscle Striated Branched Doesn’t tire Independent of the nervous system Characterized by intercalated disks. Interconnected nature of cardiac muscle fibers allows heart to contract as a unit.

Muscles – the inside story Fascia extends past muscles to form tendons and intertwine with fibres of periosteum

Elongated cylindrical shape Exceptionally large (10x normal somatic cell size) Multi-nucleated Cell membrane = sarcolemma Cytoplasm = sarcoplas m Skeletal muscle fibre (cell)

Muscle fibres contain: Myoglobin to store oxygen glycosomes to store glycogen Densely packed with myofibrils (80% of cell) Rich in mitochondria Myofibrils contain contain the contractile unit called sarcomere Skeletal Muscle fibre (cell)

Skeletal muscle contracts when thin protein filaments (actin) slide past and overlap with thick protein filaments (myosin) in the sarcomere It’s the Organisation of these contractile fibres which produces alternating dark and light striations characteristic of skeletal muscle Sliding filament modal of contraction

Nervous control Nervous system stimulates muscular contraction Somatic motor neurons in brain and spinal chord extend via axons to the muscle they serve Axons divide as it reaches the muscle Nerves and muscle meet at the neuromuscular junction

Neuromuscular junction

Important terms to remember Axon – end of neuron that stimulates muscle fibre Synaptic cleft – actual space between muscle fibre and neuron Synaptic vesicles – little sacs containing chemicals that will signal muscle to contract called neurotransmitters Motor unit – one neuron and all the fibres that it controls Response = muscle impulse Acetylcholine = neurotransmitter that is released into synaptic cleft and stimulates muscle fibre

Neurotransmitter (Ach) is released into synaptic cleft and binds to the sarcolemma (muscle cell membrane) Sarcolemma (membrane) changes permeability to ions and calcium is released into the sarcoplasm Calcium enables the actin to bind with myosin cross bridges causing the sliding movement of contraction. Steps in muscle contraction

Nerve impulse ceases: Acetylcholine in the synaptic cleft is decomposed by enzymes Ca+ ions are pumped back into the sarcoplasmic reticulum which released them Ca+ decrease stops the cross bridges binding to actin Stimulation to sarcolemma and fibre ceases. This also requires ATP In muscle relaxation

Muscle cramp! Lactic acid causes fatigue and muscle cramps

KEEP FIT! Physically fit people make less lactic acid because strenuous activity causes new capillary growth supplying an increased amount of oxygen and nutrients; also extra mitochondria are made which can make more ATP

Muscle tone When a muscle is at rest, sustained contractions are occurring in a certain number of fibres Important in maintaining posture When muscle tone is suddenly lost, like when we lose consciousness, the body collapses

Types of contraction ISOTONIC For coordination and purposeful movement When muscles shorten when they work to move an object (eg picking up a book) its concentric When the muscles generate force, they lengthen and this is eccentric (e.g. calf muscle when walking up hill)

Types of contraction ISOMETRIC Muscle contracts but there is no movement E.g. push against a wall Increase in tension but muscle remains the same length Important in maintaining posture

Fast Twitch Can contract rapidly but tend to fatigue easily High concentration in hand and eye Jumping, running for the bus, catching a ball Fewer myoglobin Also known as white fibres Types of muscle fibres

Slow Twitch Good contract for along time without tiring Mainly found in lower leg and back Endurance activities, cycling long distance running Abundant myoglobin Sometimes called red fibres Types of muscle fibres

Muscle Attachments Tendons – fibrous connective tissue that usually connects muscle to bone Ligaments – connect bone to bone and help to stabilize joints