Overview of Muscle Tissue How it Contracts Anatomy

Overview of Muscle Tissue & How it Contracts Anatomy & Physiology

Muscle Tissue: Comparisons • Skeletal ▫ attached to bones or skin ▫ cells singular, very long, cylindrical, multinucleated ▫ voluntary ▫ striated ▫ contractions slow to fast

Skeletal Muscle Fibers

Muscle Tissue: Comparisons • Cardiac: ▫ walls of the heart ▫ branching chains of cells connected by intercalated discs, ▫ uninucleated & striated ▫ involuntary: pacemaker & nervous system control ▫ slow contraction, rhythmic

Cardiac Muscle

Muscle Tissue: Comparisons • Smooth: ▫ ▫ walls of hollow viscera (except heart) cells singular, fusiform uninucleated, no striations involuntary, controlled by nervous system, hormones, some chemicals, & stretch ▫ contractions slow

Smooth Muscle Fibers

Muscle Fibers • all skeletal muscle cells referred to as fibers • all 3 muscle tissue type contract because of same 2 microfilaments: actin & myosin • all have subunits with prefixes: myo- or sarco-

Connective Tissue Wrappings of Skeletal Muscle

Smooth Muscle Layers in GI Tract: Circular Inner/ Longitudinal Outer

Muscle Functions 1. 2. 3. 4. Movement Posture /Balance Stabilizing Joints Generating Heat

Skeletal Muscle Microanatomy • • Sarcolemma: plasma membrane Sarcoplasma: cytoplasm Myofilaments: actin or myosin Myosin: 1 of 2 principle contractile proteins Actin: 2 nd principle contractile protein Sarcoplasmic Reticulum: SER T-Tubules: ordered invaginations of sacroplasmic reticulum into sarcoplasma

Skeletal Muscle Properties 1. Irritability ▫ ability to receive & respond to stimuli 2. Contractility ▫ ability to forcibly shorten when adequate stimulus received

Nerve Stimulus • 1 motor neuron (nerve cell that innervates a muscle fiber) may stimulate a few fibers or hundreds of them • motor unit: 1 motor neuron & all the muscle fibers it stimulates

Nerve Stimulus • axon: extension from cell body that carries the nerve impulse (action potential) to wherever neuron needs to send it • axon terminal: end of axon

Neuromuscular Junction • junction between axon terminals surface of muscle fiber • Synapse: (synaptic cleft) gap filled with interstitial fluid

NMJ • neurotransmitter : chemical (messenger molecule) released from axon terminal • synaptic vesicles: vesicles that store neurotransmitter molecules in axon bulb until action potential hits which causes vesicle exocytose • acetylcholine: neurotransmitter in all motor neurons • motor end plate: portion of sarcolemma that has receptor proteins for acetylcholine

Neuromuscular Junction

• http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/cha pter 10/animation__function_of_the_neuromus cular_junction__quiz_3_. html • http: //www. wisconline. com/objects/View. Object. aspx? ID=AP 28 04 • http: //faculty. massasoit. mass. edu/whanna/201_content/topicdir/muscle_media/ muscle_VD/page 142. html

Mechanisms of Muscle Contraction

Sliding Filaments Animation • http: //www. sci. sdsu. edu/movies/actin_myosin _gif. html • http: //www. 3 dotstudio. com/zz. html • http: //www. blackwellpublishing. com/matthews /myosin. html

Muscle Movements • Origin: muscle attachment to the immovable or less movable bone • Insertion: muscle attachment to the movable bone

Flexion • generally in sagittal plane • decreases the angle of the joint & brings 2 bones closer together • Hinge Joints • Ball-and-Socket Joints

Extension • movement that increases the distance between 2 bones or parts of the body • If > 180◦ it is hyperextension

Rotation • movement of a bone around its longitudinal axis • Ball-and-Socket Joints • Atlas/Dens (shaking head “no”)

Abduction • moving a limb away fro the midline, or median plane • includes fanning fingers or toes

Adduction • movement of a limb toward midline

Circumduction • proximal end stationary • distal end moves in a circle • limb as a whole outlines a cone

Dorsiflexion • lifting foot so the dorsum of the foot (top of foot) approaches the shin • corresponds to extension of the hand

Plantar Flexion • depressing the foot ( pointing the toes) • corresponds to flexion of the hand

Inversion of the Foot • turn sole medially

Eversion of the Foot • turn sole laterally

Supination • “turning backward” • forearm rotates laterally so palm faces anteriorly • radius &ulna are parallel

Pronation • “turning forward” • forearm rotates medially so palm faces posteriorly • radius crosses ulna

Opposition • thumb touches tips of other fingers on same hand