The Muscular System

Muscle tissue found everywhere in the body

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

Skeletal Muscle Structure Skeletal muscle Bundle of muscle fibers Actin Myosin Sarcomere Z disc Muscle fiber (cell) Myfibril

Muscle Contraction 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 Biceps (relaxed) Triceps (contracted) Biceps (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 –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 Hair follicle Sweat pore Nerves Hair Epidermis Dermis Subcutaneous layer Muscle Sweat gland Fat Sebaceous gland