Muscle System

Ch 9

Muscle Properties

• 4 basic properties– Contractability– Excitability– Extensibility– Elasticity

Contractability

• Cells capable of decreasing along a longitudinal axis– Shorten & thicken

• Produce force– Pull or create tension

Contractability

Excitability

• Ability to respond to external stimulation

• Stimulation initiated by – Hormonal cues– nerves

• Motor nerves

Extensibility

• Ability to “stretch” without loss of function

Elasticity

• Ability to regain original shape following contraction

Muscle Types

• Skeletal• Cardiac• Smooth

Skeletal

• Aka muscle fiber• Primary muscle type

– 700+

• Voluntary – Only consciously controlled tissue

• Move & stabilize the skeleton• Striated

– Contractile proteins produce movement (contraction), striated in appearance

• Large, multinucleate cells• Long thin cells= myofibers• Some regeneration

Striation

Skeletal Muscle Function

• By mean of contractions..

Skeletal Muscle Functions

• Produce skeletal movement

• Maintain posture & position

• Support soft tissue (pelvic floor & abdominal wall)

• Regulate entering & exiting of material– Digestive & urinary tract

• Thermogenic– Produce body heat

Motor Control• Controlled by higher

brain regions (Cerebrum)

• Allow for conscious control of muscles

Smooth• Aka visceral• Non-striated aka smooth• Involuntary

– Not consciously controlled

• Small spindle shaped cells– Microfibers with random arrangement

• Uninucleate• Regenerative• Functions in transporting fluids & solids through the body

– Ex digestive system, urinary structures, blood vessels, glands, reproductive tract

Cardiac• Involuntary striated

– Self stimulating• Only in heart• Small, uninucleate,

interconnected, branched cells• Intercalated discs

– Visible cellular connections• Gap junctions• Desmosomes

• Functions to push blood through blood vessels

• No regeneration

Cardiac

Skeletal Muscle Anatomy

• Specialized cells- Myofibers

• Long slender fiber like cells

• Mature cells multinucleate– NOT capable of mitotic division

• Cellular development– Fusion of many embryonic stem cells form

long multinucleate cells• myoblasts

Myofiber

Myofibers

Skeletal Muscle Cellular Development

Myofibers

Myofiber Structure

• Sarcolemma – Myofiber cell membrane

• Sarcoplasm– Myofiber cytoplasm

• Made up of bundles of myofibrils– Made up of micrfilaments aka myofilaments

• Satallite cells– Muscle stem cells– Resident myoblasts in adult tissue– Tissue repair

• Fascicle– Connective tissue holds together for organization– Contains bundles of myofibers

Myofiber

Sarcolemma

Sarcoplasm

Satellite Cells

Myofibers are made of bundles of Myofibrils

Aka Fascicle

Myofibrils are bundles of Myofilaments

Muscle Connective Tissue

• Connective tissue surrounds, supports, & attaches muscle

• 3 layers of connective tissue– Endomysium– Perimysium– Epimysium

Endomysium

• “Within”

• CT surrounding & binding together individual myofibers

• Delicate network of reticular fibers– Holds myofibers together– Supports blood vessels

• House satellite cells

Endomysium surrounds & binds together individual myofibers

Endomysium

Endomysium- Normal Cells

Perimysium• “around”• CT surrounding & binding groups of

myofibers• Fascicles

– Stringiness of meat• Collagen & elastic fibers• Houses blood vessels & nerves

Perimysium- Cross Section

Perimysium- Longitudinal Section

Perimysium anchors blood vessels & nerves

Perimysium bundles a fascicle

Epimysium• “above”• Dense irregular CT • Surrounds & binds fascicles together• Holds together Individual muscles into discrete units

– Ex biceps, triceps, deltoid

Epimysium

Tendons & Aponeurosis

• CT attaching– Muscle to bone– Muscle into CT of another muscle

• Combination of CT fibers from all levels of muscle organization– Endomysium– Perimysium– Epimysium

• CT fibers are continuous w/ periosteum & osseous matrix= strong muscle attachments– Bones more likely to break before tendon tears away from bone

• All CTs merge to form attachments– Tendon- strong cord or rope– Aponeurosis- flattened sheet

Tendon

Aponeurosis

Attachment

• Origin– Point of attachment to the fixed bone– Site that remains stationary during muscle

contraction– Typically proximal

• Insertion– Point of attachment to the moving bone– Typically distal

Deltoid

Teres Major

Teres Minor

Muscle function

• Prime movers & Agonists– Key muscle in motion, primarily responsible

• Antagonists– “Reverse” motion

• Synergists– Aid prime mover

• Fixators– Specialized synergists– Immobilize origin of prime mover– Maximize motion

Prime Mover aka AgonistBiceps Brachii

Antagonist- Triceps Brachii

Synergist- Brachialis

Synergist- Pronator Teres

Supinator