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Describe the characteristics of muscle tissue Compare the structures and functions of the

three forms of muscle tissue and give examples of each.

List the components of a muscle cell. Given a diagram of a sarcomere, label its

components. Describe the sliding filament theory of

excitation- contraction coupling. Describe the structure and function of the

neuromuscular junction. Given a diagram, label the major muscles of

the body.

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(Course Name and Number)

Describe the functions of those muscles directly involved with the cardiovascular system.

Explain the role of muscle as it relates to homeostasis.

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(Course Name and Number)

Characteristics of Muscle Tissue Forms of Muscle Tissue Muscle Cell Organizational Structure of

Skeletal Muscle Sarcomere Action Potential Neuromuscular Junction

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Sliding Filament Theory Major Muscles of the Body Cardiovascular System Muscle

Functions Role of Muscles Lab/Practical Practical Test/Performance

Evaluation

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Excitability◦ A property of both muscle and nerve cells.◦ Ability to respond to a certain stimuli by

producing electrical signals called action potential (impulses)

◦ For muscle cells the stimulus that triggers these action potentials are chemicals called neurotransmitters

Conductivity◦ Ability of a muscle cell to propagate or conduct

an action potential along the plasma membrane

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Contractility◦ Ability of the muscle to shorten and thicken

(contract) therefore generating the force to do work.

Extensibility ◦ Muscle can be extended (stretched) without

damaging the tissue Elasticity

◦ Muscle tends to return to its original shape after contraction or extension

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Three forms of muscle tissue:◦ Skeletal muscle o Striated

Band-like appearance Multi–nucleated

‒ Voluntary tissue Under conscious control Function

‒ Movement of body parts ‒ 85% heat ‒ Provide posture for the body

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Three forms of muscle tissue (continued)◦ Cardiac muscle o Striated o Involuntary o Single nucleus per cell o Not under conscious control o Function

Provide circulation of blood flow to and from all body parts through cardiac contraction

◦ Smooth muscle o Non-striated

Shredded appearance

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‒ Smooth Muscle Tissueo Involuntary o Central single nucleus o In hollow organs of body – blood vessels,

digestive tract, bladder or uterus o Maintain lumen size of blood vessels o Key in maintenance of blood pressureo Aid in the expulsion of urine o Rhythmic contractions of the uterus lead to

childbirth

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•04/21/23 •14Source: Principles of Anatomy and Physiology, 12th Edition, Gerard J. Tortora and Bryan Dickerson, John Wiley and Sons, Figure 10.2

Sarcolemma ◦ Cell or plasma membrane

Sarcoplasm ◦ Cytoplasm of a muscle cell ◦ More abundant than most other cells

Sarcoplasmic reticulum ◦ Endoplasmic reticulum of muscle tissue ◦ Intracellular transport ◦ Support ◦ Storage network ◦ T-tubules

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Sarcoplasmic Reticulum cont◦ T-Tubules

Deep invaginations of the sarcolemma Provide for more rapid communication of

extracellular ions/electrolytes Storage and transport site for Ca++ L-tubules

Longitudinal tubules Encircle the myofibrils of the cell Contain dilated sacs (Terminal cisterns) that

store Ca++ Not as abundant in skeletal muscle

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Triad◦ The union of a T-tubule and two ends of the

L-tubules constitutes a triad. Storage site for Ca++ Allows for the transference of substances from

one system to another Explains in part how electro/chemical

stimulation affects the entire cell at the same time Speeds conduction through the cell Affords contraction of the whole cell, vice a portion

at a time

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Nucleus ◦ Smooth muscle and cardiac muscle both

have a single centrally located nucleus. ◦ Skeletal muscle contains several peripherally

located nuclei. Mitochondria

◦ Much larger in both size and number than in any other cell Due to the high energy requirements

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Contractile elements ◦ Myofibrils◦ Contraction of many muscle cells at the same

time◦ Breakdown of a muscle to the contractile

elements

◦ Myofilaments Interconnecting proteins Actin Myosin

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◦ Sarcomeres Compartments of myofilaments Repeating units of contraction

Specialized Properties of Cardiac Muscle tissue◦ Intercalated discs

Irregular thickening of sarcolemma Contains Desmosomes

Provides enhanced strength needed for contraction

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(Intercalated discs continued)

Constitutes the longitudinal boundaries of the cardiac cell

Offset itself at the level of one full sarcomere Provides for direct cell to cell communication Provides low-resistance bridges Efficient spread of excitation

Speeds the conduction velocity of cardiac tissue

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Skeletal Muscle◦ Fascicles: Consists of bundles of muscle fibers

surrounded by the perimysium (a type of connective tissue)

◦ Muscle fibers (Myofibers) Long cylindrical bundles lying parallel Cells lie end to end, side by side and range from 10-

100 μm in diameter Cardiac muscle fibers may branch Contain many threadlike structures called myofibrils

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◦ Myofibrils Contractile elements of skeletal muscle 1-2 μm in diameter Extend lengthwise within the muscle fiber Prominent alternating light and dark bands

called cross striations Contains smaller structures called filaments

(myofilaments) Actin Myosin

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◦ Myofilaments Actin (thin filament) 8nm in diameter Myosin (thick filament) 16nm in diameter Can overlap each other depending on state of

muscle contraction These filaments do not extend the entire length

of a muscle fiber Arranged in compartments called sarcomeres

which are the basic functional units of striated muscle tissue

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Thick Myofilaments ◦ Composed of the protein myosin◦ Occupies the center of the sarcomere◦ Contains spine-like processes that extend out

toward the thin filaments actin Cross-bridges bind with receptor sites on Actin

filament during contraction Primary mechanism of muscle contraction

◦ Middle of myosin presents as a nodule

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M Line◦ Thin Myofilaments ◦ Composed predominately of the protein actin◦ Bound with a troponin-tropomyosin complex

which Inhibits the actin filament from interacting with the myosin cross bridges in the absence of intracellular calcium (relaxation)

◦ Contains receptor sites for myosin cross bridge attachments

◦ There are six actin filaments surrounding each myosin filament

◦ Each actin filament receives cross bridges from three myosin filaments

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◦ Thin filaments originate from the Z lines (Z-Disc). Extend toward center of the sarcomere Overlap partially with myosin filament when

relaxed When contraction takes place the actin

filaments may completely overlap one another Z Line

◦ Transverse dense material where the thin filaments originate

◦ Two Z lines (Z-Discs) in horizontal succession constitute the limits of one sarcomere

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I band ◦ Area on both sides of the Z line◦ Only thin myofilaments are found

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Source: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mcb&part=A5208&rendertype=figure&id=A5208

A band ◦ Center area of the sarcomere where thick and

thin myofilament overlap◦ Encompasses the length of the myosin filament

H zone ◦ Center of the sarcomere where there are only

thick filaments (relaxed)◦ Disappears during contraction as the Z lines

are drawn together◦ Causes the sarcomere to become shorter

and fatter

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Wave of negativity occurs along the surface membrane of a cell causing a rapid change in membrane potential, which involves depolarization and re-polarization.

Phase: “0” Phase: “1” Phase: “2” Phase: “3” Phase: “4”

Phase 0◦ Upon stimulation, acetycholine changes the

membrane permeability to Na+.

◦ The large influx of Na+ causes the cell to depolarize.

◦ This is termed a “threshold”:-70mV (nerve cell)-60mV (“automatic” cardiac cell)-90mV (“non-automatic” cardiac cell)

•Phase O startsPhase O starts•herehere

•Phase 1Phase 1

Phase 1◦ “Overshoot” of Na+ causing the inside of the

cell to become momentarily positive.◦ Termed “Depolarization”

Phase 2 “Plateau Phase” cell undergoes a continuous

influx of Ca++ From -50mV through phase 1 of the action

potential Allows for sustained contraction (or whatever

that cell’s particular function is)

•Phase 2Phase 2

Phase 3◦ Cessation of impulse stimulation, ◦ The beginning of acetylcholinestrase

activity (neuromuscular junction)◦ The membrane undergoes increased

permeability to K+.

This causes an efflux of K+ from the cell.

•Phase 3 areaPhase 3 area

Phase 4

◦ Restoring resting membrane state.

◦ Na+ / K+ pumps are powered by ATP and easily restore the low concentration of Na+ inside the cell

•Phase 4 Phase 4 •aka.. Resting Potentialaka.. Resting Potential

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The neuromuscular junction consists of: ◦ A muscle ◦ Terminal telodendria of a motor neuron

The terminal end of the nerve axon has fine filament extensions called synaptic end bulbs◦ Lie in very close proximity with the

sarcolemma of the muscle cell ◦ Contain synaptic vesicles

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When a nerve stimulation reaches the terminal axon ◦ Calcium activates the synaptic end bulbs to

release neurotransmitters by exocytosis

Neurotransmitter (Ach) is liberated from the synaptic vesicles◦ Travels into the synaptic gutter ◦ Located between the telodendria and the

muscle fiber

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Causes an action potential to occur on the sarcolemma

◦ Changes membrane permeability◦ Spreads the impulse◦ Nearly simultaneous activation of acetylcholine

receptors and contraction of the muscle

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A motor unit ◦ A motor neuron with all the muscle fibers it

stimulates May innervate from 1 up to 3000 muscle fibers All fibers within a motor unit contract or none

do. When the nerve impulse reaches the terminal

end of the motor nerve Myoneural junction (Neuromuscular junction) Causes acetylcholine to be released

(neurotransmitter) Acetylcholine bridges the synaptic cleft and

stimulates the sarcolemma to undergo a change

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Upon stimulation of a muscle fiber by a motor nerve there is a series of reactions that sequentially takes place causing the muscle cell to contract◦ Ach causes the nerve impulses to spread

across the entire sarcolemma which changes the membrane permeability to Na+ which initiates an action potential (depolarization)

The action potential stimulates the sarcoplasmic reticulum and releases the calcium that is stored in the triads (T-tubules, L-tubules) to quickly enter the sarcoplasm

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The released Calcium ions bind with the troponin/tropomyosin complex ◦ Calcium shift the troponin/tropomyosin complex

off of the actin binding sites◦ Allows myosin cross bridges to interact with the

actin filaments and perform “power stroke” ◦ Cross bridges interaction with the action filaments

pulls them toward the center of the sarcomere ATP is then utilized to break the bond

between the myosin head and the actin site repowering the myosin cross bridge for another power stroke if the binding sites are still exposed ◦ ATP hydrolyzed into ADP + Phosphate

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Termination of contraction ◦ Acetylcholine is rapidly deactivated by the

enzyme acetylcholinesterase (Neuromuscular junction).

◦ Nerve impulse and stimulation ceases◦ Calcium is pumped back out of the sarcoplasm by

active transport pumps on the Sarcoplasmic Reticulum membrane into the SR (T & L Tubules). Troponin/tropomyosin complex shifts back over the

actin filament binding sites

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Cardiac excitation contraction coupling ◦ Cardiac muscle contracts and relaxes

continuously Rhythmically normally 60 to 100 times a minute Major difference between cardiac and skeletal

muscleo Cardiac muscle contracts without

outside stimulus o Remains contracted longero Longer refractory period after each cell depolarizes

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Cardiac excitation contraction coupling ◦ Impulse propagates through the

transverse tubules to inside of cell◦ Sliding-filament theory process takes place

as in the skeletal muscle◦ The T-tubules are located at the Z lines◦ Cardiac muscle fibers form two separate

networks Atria Ventricular

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Muscles are named according to:◦ Their anatomic location ◦ Their principle action◦ Number of origin sites or number of tendons

of origin◦ Description of the overall muscle mass in

comparison to another muscle

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•04/21/23 •62Source: Principles of Anatomy and Physiology, 12th Edition

•04/21/23 •63Source: Principles of Anatomy and Physiology, 12th Edition

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Diaphragm ◦ Forms floor of thoracic cavity◦ Moves downward during inspiration

Increasing vertical size of thoracic cavity

External intercostals ◦ Principle muscle of ventilation

Lifts ribs up and out on inspiration

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Internal intercostals ◦ Pull ribs down and in on expiration

Rectus abdominus ◦ Accessory muscle of expiration

Forced expiration (ex. Pulmonary function test)

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Smooth muscle of the vasculature ◦ Regional blood flow ◦ Blood pressure ◦ Very easily manipulated with medications

Skeletal muscles of the lower extremities◦ Contraction aids in venous return

Heart ◦ Responsible for pumping blood throughout the

blood vessels by repeated, rhythmic contractions

◦ Primary mechanism for maintaining cellular perfusion through circulation of oxygenated blood

◦ Cardiac Output: Determined by two factors

HR (Chronotrope) Stroke Volume (amount of blood ejected from the

ventricles per beat)

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Source: Principles of Anatomy and Physiology, 12th Edition, Gerard J. Tortora and Bryan Dickerson, John Wiley and Sons, Figure 20.2

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• Motion◦ To produce movement of body parts in a

coordinated manner Running, walking

Moving Substances within the body◦ Circulation◦ Ingestion ◦ Digestion ◦ Absorption ◦ Respiration

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Heat production ◦ As Skeletal muscle contracts to perform work, a

by-product is heat◦ Assist in the maintenance of normal body temp.◦ Generate approximately 85% of all body heat

Stabilizing body positions and organ volume◦ Partially contracted neck muscles to hold the

head upright◦ Smooth muscle sphincters to prevent outflow of

contents within a hollow organ

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Worksheet Activity

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WorksheetActivity

Student Guide

Characteristics of Muscle Tissue Forms of Muscle Tissue Muscle Cell Organizational Structure of Skeletal

Muscle Sarcomere Action Potential Neuromuscular Junction Sliding Filament Theory Major Muscles of the Body Cardiovascular System Muscle Functions Role of Muscles

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Complete Quick Check

Student Guide

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