Overview of Muscle Tissue & How it Contracts Anatomy & Physiology

Overview of Muscle Tissue & How it ContractsAnatomy & 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. Movement 2. Posture /Balance3. Stabilizing Joints4. Generating Heat

Skeletal Muscle Microanatomy•Sarcolemma: plasma membrane•Sarcoplasma: cytoplasm•Myofilaments: actin or myosin•Myosin: 1 of 2 principle contractile

proteins•Actin: 2nd principle contractile protein•Sarcoplasmic Reticulum: SER •T-Tubules: ordered invaginations of

sacroplasmic reticulum into sarcoplasma

Skeletal Muscle Properties1. Irritability

▫ ability to receive & respond to stimuli2. 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.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__function_of_the_neuromuscular_junction__quiz_3_.html

•http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP2804

•http://faculty.massasoit.mass.edu/whanna/201/201_content/topicdir/muscle/muscle_media/muscle_VD/page142/page142.html

Mechanisms of Muscle Contraction

Sliding Filaments Animation•http://www.sci.sdsu.edu/movies/actin_myo

sin_gif.html

•http://www.3dotstudio.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