Ch. 10 Muscle Tissues and Organization

Properties of Muscle Tissue

excitability, conductivity, contractility, elasticity, extensibility

Excitability

ability to respond to a stimuli

Conductivity

ability to transmit an electrical charge along the sarcolemma

Contractility

ability to generate tension via shortening cell length (allows for movement)

Elasticity

ability of muscle to return to original (resting) length

Extensibility

ability to be stretched beyond resting length (lengthening of muscle cell)

Skeletal muscle is considered an ____

organ

Features of Skeletal Muscle Tissue

striated (actin/myosin)

usually attached to bones

various shapes and sizes of skeletal muscles

Primary functions of Skeletal Muscle

Movement, Maintaining posture, Protection/support, Regulation of materials, Heat production

Movement

bones move when skeletal muscle contracts

Maintaining posture

contraction of muscles keep head and neck up

Protection/support

arrangement of fibers

Regulation of material

sphincters located at orifices of GI and urinary tracts (allows for expulsion of feces and urine)

Heat production

energy for contraction → heat

Muscle sizes

muscle, fascicle, fiber, myofibril

Fascicle

makes up the muscles

made up of muscle fibers

Muscle Fiber/muscle cell

makes up the fascicle

made up of myofibrils

Myofibrils

makes up the fascicle

made up of myofilaments

Myofilaments

short contractile proteins

composed of thick and thin filaments (actin and myosin)

Function of Connective Tissue (CT)

provides protection, sites for blood vessels and nerves, attachments to skeleton

distributes tension to attachment sites

3 layers of CT

Endomysium (within)

Perimysium (around)

Epimysium (upon)

Endomysium

surrounds each fiber

Areolar CT with reticular fibers

Perimysium

surrounds each fascicle

dense irregular connective tissue

Epimysium

surrounds entire skeletal muscle

dense irregular connective tissue

Deep fascia

sheet of dense irregular CT

Purpose of the Deep Fascia

separates individual muscles

binds together muscles with similar functions

distributes vessels (nerves blood)

Superficial fascia

areolar and adipose CT (subcutaneous layer)

Purpose of the Superficial Fascia

separates skin from muscle

Tendons

attaches muscle to bone, skin or another muscle

(CT layers merge to form tendons)

Aponeurosis

tendon that forms a thin, flattened sheet

Muscle Attachments

skeletal muscles extend over a joint and attach to bones on either side of the joint

origin, insertion

Origin of Muscle Attachments

less mobile attachment site

Insertion of Muscle Attachments

more mobile attachment site

Blood Vessels

travel/extend through perimysium and epimysium

What are the functions of blood vessels

deliver nutrients and oxygen to muscles

remove waste products

Nerves

controlled by somatic (voluntary) motor neurons

axons

Axons of somatic motor neuron

pass through all 3 layers of CT to create junctions with skeletal muscle fibers

Components of muscle cells (muscle fibers)

Sarcolemma

Sarcoplasm

Mitochondria (-300 per fiber)

Multinucleated

Satellite cells

Transverse tubules

Sarcoplasmic reticulum

Satellite cells

help with repair and regeneration of skeletal muscle tissue

Transverse tubules (T-tubules)

invaginations of the sarcolemma that extend into the sarcoplasm

carries impulses from sarcolemma

Sarcoplasmic reticulum (SR)

internal membrane complex

stores Ca²⁺

Terminal cisternae

Terminal cisternae

expanded ends of SR that are in contact with T-tubules

Triad(2 per 1 t-tubule)

Myofilaments

strands of proteins which allow for contraction

thick - myosin

thin - actin

Thick filaments (myosin)

composed each myosin has 2 strands

heads form cross-bridges with thin filaments during contraction

Cross-bridges

temporary connection formed between the myosin head (from a thick filament) and the actin filament (thin filament) within a muscle cell

Thin filaments (actin)

2 twisted protein strands wrapped around each other

Regulatory proteins:

• Tropomyosin

• Troponin

Tropomyoisin

protein that covers binding sites for myosin heads

Troponin

attached to actin and provides binding site for calcium

Sarcomere

functional unit of skeletal muscle fibers

in skeletal and cardiac muscles

Z disc (Z lines)

ends of sarcomere

serves as anchors for thin filaments

I band

extend from Z discs

contains only thin filaments (actin)

A band

central region of sarcomere

where thin and thick filaments partially overlap

H zone

most central portion of A band

contains only thick filaments

M line

thin transverse protein meshwork in center of H zone

attachment site for thick filaments

Sliding Filament Theory

sarcomeres shorten when the thick filaments attach to the thin filaments and pull them towards the center of the sarcomere

Motor unit

single motor neuron and all the muscle fibers it innervates

Size principle

size of the motor unit and indicates degree of control

• Big MU - quadriceps femoris

• Little MU - eyeball

All-or-Nothing Principle

when a motor unit is stimulated, all muscle fibers within it contract

Type 1 Muscle Fiber

slow oxidative (aerobic)

Type 2a Muscle Fiber

fast oxidative/glycolytic

Type 2b Muscle Fiber

fast glycolytic (anaerobic)

Cardiac Muscle (involuntary)

in myocardium (wall of heart)

autorhythmic

striated

mitochondria (aerobic)

controlled by automatic nervous system

Autorhythmic

able to generate electrical impulses without nerve stimulation

Smooth muscle (involuntary)

controlled by automatic nervous system and in walls of viscera and blood vessels

one central nucleus

Muscular hypertrophy

increase in muscle size (not number

Muscular dystrophy

decrease/wasting of muscle tisue

Rigor Mortis

skeletal muscles lock into a contracted position a few hours after the heart stops beating

• calcium remains bound to troponin

• ATP is not available (cross-bridges can’t detach)