Unit V: Movement Muscle Tissue Chapter 4 – pg Chapter 9 – pg

Characteristics of All Muscle Tissue Excitibility (Responsiveness, irritability) Conductivity – local electrical change triggered by stimulation – results in contraction Contractility Extensibility Elasticity

Skeletal Muscle General Properties Long, cylindrical, unbranched cells Multinucleated Striations Not capable of mitosis Voluntary –movement, posture, breathing, swallowing, facial expression, speech, and excretion

Cardiac Muscle General Properties Striations Short branched cells –One nuclei Intercalated discs Not capable of mitosis Pumping of blood by cardiac (heart) muscle Nucleus Cardiac muscle cells Intercalated discs Striations LM x 450

Smooth Muscle General Properties Nonstriated Short fusiform cells −One central nucleus Capable of mitosis Located in viscera –digestive, respiratory, urinary tracts, blood vessels, uterus Forms adjacent layers –one encircling organ –one longitudinal

The Muscle Fiber

Types of Myofilaments Thick filaments – myosin

Types of Myofilaments Thin filaments – F-actin (fibrous actin) – G-actin (globular actin) binds to head of myosin molecule – Tropomyosin – Troponin F-actin G-actin Tropomyosin Troponin Active site

Types of Myofilaments Elastic filaments – Titin – keeps filaments aligned – resist over-stretching – recoil of muscle cells

Individual myofibrils Sarcomere I band A band I band A band H band M line H band Thick filament Titin Thin filament Elastic filament (a) (b) Z disc Nucleus Z disc M line Striations A band –dArk and darker areas I band –lIght area Z disc –sarcomere

Spinal cord Cell bodies of motor neurons Axons of motor neurons Motor nerve KEY Motor unit 1 Motor unit 2 Motor unit 3 Nerve-Muscle Relationship Single somatic motor neuron – may branch 200 times Motor Unit – somatic motor neuron + all the muscle fibers it innervates – muscle fibers of a motor unit are NOT clustered together – Result: weak contraction over a wide area Fine control – small motor units contain as few as 20 muscle fibers per nerve fiber

Neuromuscular Junction Synapse between a neuron and muscle fiber Motor end plate Junctional Folds Acetylcholinesterase Neuromuscular junction Motor nerve fibers Muscle fibers (a) 100 m Victor B. Eichler

Neuromuscular Toxins Pesticides and nerve agents –cholinesterase inhibitors –bind to acetylcholinesterase –spastic paralysis Clostridium bacteria –Tetanus or “lockjaw” (spastic paralysis) blocks glycine release from motor neurons –botulism blocks release of ACh flaccid muscle paralysis (limp muscles) Arrow poison curare –competes with ACh –Flaccid paralysis