The Muscular System

The Muscular System Muscle tissue found everywhere in the body Tendons connect muscle to bone

Muscle Types Three types of muscle tissue – skeletal, smooth, and cardiac Smooth Skeletal Cardiac

Skeletal Muscle Usually attached to bones and are responsible for voluntary movement (voluntary muscle) Striated/striped – light and dark bands Cells very large with many nuclei

Smooth Muscle Muscles not under voluntary control (involuntary muscle) One nucleus in cells and not striated Found in organs and blood vessels Helps move food through digestive tracts, decrease size in pupils, as well as operate other organs in the body

Cardiac Muscle Muscle found in heart Small, striated cells with one to two nuclei Involuntary muscle found ONLY in the heart

Muscle Bundle of Nuclei muscle fibers Single muscle fiber (cell) Figure 27.31 Muscle Bundle of muscle fibers Nuclei Single muscle fiber (cell) Myofibril Light band Light band Dark band Sarcomere Thick filaments (myosin) TEM Light band Dark band Light band Thin filaments (actin) Sarcomere

Muscle Contraction Striations in skeletal muscle cells are formed by alternating patterns of thick and thin filaments Thick filaments = myosin protein Thin filaments = actin protein Tiny myosin and actin filaments are the force-producing engines that cause muscles to contract A muscle contracts when the thin filaments (actin) slide over the thick filaments (myosin) Myosin forms cross-bridge with actin and pulls the actin, making the muscle contract Energy for muscle contraction is supplied by ATP

Muscle Contraction (continued) Relaxed Muscle Myosin Actin Z disc Movement of Actin Filament Actin Cross-bridge Sarcomore Binding sites Contracted Muscle Myosin Cross-bridges Z disc

Motor Neurons: Control of Muscle Contraction are part of the central nervous system, release neurotransmitters that cause muscle muscle fibers to contract, and can branch to a number of muscle fibers. A motor unit consists of a neuron and all the muscle fibers it controls.

Muscle Contraction (continued) Contraction of a single muscle fiber is an all-or-none process – either the fiber completely contracts or it doesn’t The NUMBER of fibers stimulated by the nervous system to contract varies with the amount of work/strength needed Muscle fatigue caused by not enough ATP getting to muscle Lactic cid fermentation kicks in = burning sensation in muscles

How Muscles and Bone Interact Individual muscles can only PULL in one direction, so how does your arm move in two directions? Skeletal muscle is joined to bones by tendons, which pull on bones and make them work Several muscles surround each bone joint to allow pulling in different directions

How Muscles and Bone Interact (continued) Muscles work in opposing pairs – when one contracts, the other relaxes. Ex. Upper arm with biceps and triceps Biceps contracts = bend elbow (triceps relaxes) Triceps contracts = extend elbow (biceps relaxes) Exercise is important to keep muscles firm and working properly; however, too much exercise all at once can tear and stress muscles and be painful

Opposing Muscle Pairs Movement Movement Biceps (relaxed) Biceps (contracted) Triceps (contracted) Triceps (relaxed)

The Skin

The Skin – aka Integumentary System Largest sense organ in the body – deals with the sense of touch

Functions of the Skin Regulate internal body temperature (warming, cooling, sweating, etc.) Block the sun’s radiation with melanin Sense organ Produces essential vitamins – Vitamin D Protective layer to underlying tissues (invasion of microbes, chemicals, etc.)

Two Layers of the Skin Epidermis Dermis Outermost layer – dead cells slough off Has melanin pigments = skin color Dermis Innermost layer Helps insulate body Contains blood vessels, nerves, nerve endings, sweat glands, hair follicles, oil glands

Two Layers of the Skin Nerves Hair Sweat pore Hair follicle Epidermis Dermis Subcutaneous layer Muscle Sweat gland Fat Sebaceous gland