Anatomy and Physiology Ch 6 Muscular System

Muscle Types Skeletal Muscle –Attach to the skeleton (skeletal)‏ –Striated –Voluntary Reflexes though! –Long multinucleated cells –Strong and quick but tired easily

Skeletal Muscle Structure Cells are fragile alone just like all cells Individual cells are covered in endomysium 1000’s of cells wrapped by perimysium to form fasicle Fasicles are wrapped by epimysium to form the muscle Epimesium blends in to tendons

Muscle Types Smooth Muscle –Non-striated –Involuntary –Found in the walls of hollow organs (visceral)‏ –Spindle shaped with single nucleus –Two layers; one circular one longitudinal –Slow contraction but sustained

Muscle Types Cardiac Muscle –Only in the heart (Cardiac)‏ –Striated –Involuntary –Branching cells joined by intercalated discs

Muscular System Applied only to skeletal muscle Functions –Movement Muscle contraction –Posture –Joint Stabilization Shoulder –Generation of heat 75% of muscle contraction energy lost as heat 40% of body mass

Microscopic Anatomy of Skeletal Muscle Plasma membrane = sarcolemma Cell filled with myofibrils Alternating light (I) bands and Dark (A) bands Shows the working structure of a cell Myofibril are chains of sarcomeres made up of myofiliments (actin and myosin)‏

Skeletal Muscle Properties Irritability- the ability to receive and respond to stimuli Contractility- can shorten when stimulated Extensibility- can be stretched Elasticity- can return to resting length

Nerve Stimulus and Action Potential Muscles need to be stimulated by nerve impulses One neuron and the muscle cells it stimulates is a motor unit The axon branches and forms the axon terminals Terminal joins the sarcolemna forming the neuromuscular junction

Neuromuscular junction Axon terminus and muscle cells don’t touch When nerve impulse reaches the terminus a neurotransmitter is released into synapse –Acetylcholine (ACh) stimulates muscles ACh receptors in sarcolemma receive neurotransmitter ACh causes change in the permeability of the cell membrane (Na + in K + out)‏

Action Potential Cell interior is normally negative More Na + flows in than K + flows out causing a change (+) This change in charge conducts the electrical signal The muscle cell contracts ACh breaks down into choline and acetic acid to end the stimulation –K + diffuses out and Na + /K + pump restore cell

Muscle Contraction Sliding filament theory Thick filaments (myosin) grab onto the thin filaments (actin)‏ Actin is then “walked” to the center of the sarcomere shortening the muscle cell Myosin attachment requires Ca 2+ released by action potential

Muscle contraction Cells are all or none, but not the whole muscle The entire muscle has a graded response –Change the frequency of stimulation –Recruit more cells

Types of Muscle Contractions Isotonic –When the tension in the muscle results in movement Ex- Doing Squats Isometric –When the muscle cells are trying to contract but are held without movement Ex- Planking Muscle Tone –Motor units are randomly stimulated –In the case of spinal cord injury muscle tone is lost

Graded Response A single stimulus causes a twitch –Not normal – caused by nervous system error Series of stimuli not allowing relaxation is summed No relaxation is called fused or complete tetanus

Energy for Muscle Contraction