Anatomy Chapter 10 Muscle and Tissue Organization

Tetanus

A form of spastic paralysis caused by a toxin produced by the bacterium Clostridium tetani only under anaerobic conditions. It blocks he release of an ininhibitory neurotransmitter called glycine in the spinal cord, resulting in overstimulation of the muscles and excessve muscle contraction.

Epimysium

A layer of dense irregular CT that surrounds the whole skeletal muscle.

Antagonist

A muscle whose actions oppose those of the agonist. If the agonist produces extension, the antagonist produces flexion. Ex. When the triceps brachii acts as an agonist to extend the forearm, the biceps brachii on the anterior side of the humerus acts as an antagonist to stabilize the movement and produce the opposing action, which is flexion of the forearm.

Actin

A thin filament. Double-stranded contractile protein, forms a helical shape. In each helical strand of actin, many small, spherical molecules are connected to form a long filament resembling a string of beads. Each spherical molecule is called G (Globular) actin, and each filament composed of a strand of G-actin molecules is called F (filamentous) actin. Function: Binding site for myosin to shorten sarcomere.

Superficial Fascia

Also called subcutaneous layer. Composed of areolar and adipose CT that separates muscle from skin.

Third Class Lever

An effort is applied between the resistance and the fulcrum. Ex. Forceps. ex. Mandible

Tendon

At the ends of muscle, the CT layers merge to form a fibrous tendon, which attaches the muscle to bone. Usually have a thick, cordlike structure.

Myofacial pain syndrome (MPS)

Common disorder usually associated with excessive use of the postural muscles. Pain results when bands of muscle fibers tighten and then twitch after the overlying skin is stimulated.

Intermediate Fibers

Contract faster than slow fibers and slower than fast fibers. Aerobic Extensive capillaries. Red fibers High resistance to fatigue Lower limbs Many mitochondria Lots of myoglobin

Striations (I and A bands)

Due to size and density differences between thick filaments and thin filaments. A bands: Dark bands. Contain the entire thick filament. I bands: Light bands. Located on either side of the A bands. Contain thin filaments but no thick filaments.

Muscle Fiber (muscle cell)

Elongated, multinucleated, cylindrical fiber (cell); contains myofibrils, separated from other fibers by delicate layer of areolar CT; exhibits striations. CT Covering-Endomysium

Parallel Muscle FIbers

Fascicle are parallel to the long axis of the muscle. Body of muscle increases in diameter with contraction. High endurance, not very strong. Ex. Rectus Abdominis

Titin

Filaments of an elastic protein. Function: Help return myofilaments to resting position after contraction; maintain positions of myofilaments in sarcomere.

Thin Filament

Fine protein myofilament composed of actin, troponin, and tropomyosin. Function: Thick filaments bind to it and cause contraction.

Thick filament

Fine protein myofilament composed of bundles of myosin. Consists of two strands; each strand has a free, globular head and an attached, elongated tail. They are oriented on either end of the filament so that the long tails point toward the center of the filament and the heads point toward the edges of the filament and project outward toward the surrounding thin filaments. Function: Bind to thin filament and cause contraction. During a contraction, myosin heads form crossbridges by binding thick filaments to actin in the thin filaments.

Smooth muscle: Location

Found in walls of hollow organs (e.g. intestines, blood vessels); and in iris and ciliary body of eye.

First Class Lever

Has a fulcrum in the middle, between the effort and the resistance. Ex. Scissors Ex. Atlanto-occipital joint of the neck.

Cardiac Muscle

Has autorhythmicity Moderate contraction speed Involuntary control

Cardiac Muscle: Location

Heart wall

Cardiac Muscle: Sarcomere Protein Organization

Highly organized; revealed by striations

ACh receptors

In the motor end plate act like doors that normally are closed. ACh is the only "key" to open these receptor doors.

Tendonitis

Inflammation of either a tendon or a synovial sheath surrounding the tendon. Results in overuse of the tendon.

Endomysium

Innermost CT layer. Delicate, areolar CT layer that surrounds and electrically insulates each muscle fiber. It has reticular fibers to help bind together neighboring muscle fibers and support capillaries near these fibers.

Myofibril

Long, cylindrical contractile element within muscle fiber; as long as the muscle fiber itself; composed of myofilaments; exhibits striations. No CT Covering

Insertion

More mobile attachment of the muscle. Usually the insertion is pulled towards its origin.

Duchenne Muscular Dystrophy (DMD)

Most common form of dystrophy. Results from the expression of a sex-linked recessive allele. In males only.

Myofilaments

Myofibrils consist of bundles of short myofilaments.

Smooth Muscle: Myofibrils

None

Resistance

Rotation occurs when an effort applied to one point on the lever exceeds a resistance located at some other point.

Interaction between T-tubules and terminal cisternae

Spread of a muscle impulse along the T-tubule membrane causes calcium ions to leak out of the terminal cisternae into the sarcoplasm of the muscle fiber. These calcium ions diffuse throughout the sarcoplasm and attach to the troponin.

Isometric Contraction

The length of the muscle does not change because the tension produced by this contracting muscle never exceeds the resistance (load). Tension is generated, but it is not great enough to move the load.

Origin

The less mobile attachment of the muscle is the origin.

Second Class Lever

The resistance is between the fulcrum and the applied effort. Ex. Wheelbarrow Ex. When the foot is depressed (plantar flexion) so that a person can stand on tiptoe.

Synaptic vesicles

The synaptic knob cytoplasm houses numerous synaptic vesicles (small membrane sacs) filled with molecules of the neurotransmitter acetylcholine (ACh).

Convergent Muscle Fibers

Triangular muscle with common attachment site. Direction of pull of muscle can be changed. Does not pull as hard as equal-sized parallel muscle. Ex. Pectoralis major

Triad

Two terminal cisternae and a centrally placed T-tubule form a triad.

Cardiac Muscle: Regeneration capacity

Very limited or none

Sarcoplasm

Cytoplasm of a muscle fiber. Function: Site of metabolic processes for normal muscle fiber activities.

Smooth Muscle: Sarcoplasmic retculum, transverse tubules

SR: Almost none TT: None

Cardiac Muscle: Sarcoplasmic Reticulum/ Transverse Tubules

SR: Moderate TT: Extensive; aligned with Z disc

Myofilaments

Short contractile proteins of two types: thick (composed of myosin) and thin (composed of actin, tropomyosin, and troponin). No CT Covering

Perimysium

Surrounds the fascicles. Dense irregular CT sheath of the perimysium contains extensive arrays of blood vessels and nerves that branch to supply each individual fascicle.

Z disc

(Also called Z line) A thin transverse protein structure in the center of the I band that serves as an attachment site for thin filament ends. Although the Z disc is circular, when viewed "head-on," only the edge of the circle is visible, so it sometimes looks like a line. Connectins: Z disc proteins that anchor and interconnect the thin filament ends at either end of a sarcomere.

Functions of Skeletal Muscle Tissue

-Body movement (coordinated movement between muscles, bones, and joints) -Maintenance of posture (Contractions of muscles stabilize joints) -Temperature Regulation (Energy is required for muscle tissue contraction, and heat is always the byproduct. This heat maintains normal body temperature) -Storage and movement of materials (Sphincters contract as the openings (orifices) of gastrointestinal and urinary tracts. Voluntarily close and open). -Support (Flat sheets or layers, such as along the walls of abdominal cavity. Holds your abdominal organs in place).

Properties of Muscle Tissue

-Excitability (Responsive to input from stimuli) -Contractility (Stimulation of muscle cells generates tension within the cell, which may cause the cell to shorten) -Elasticity (Its ability to return to its original length when tension is released. -Extensibility (Capability of extending in length in response to the contraction of opposing muscle cells)

Fascicle

A bundle of muscle fibers separated from other bundles of fibers by a dense irregular CT covering. CT Covering- Perimysium

Muscular Dystrophy

A collective term for several hereditary diseases in which the skeletal muscles degenerate, lose strength, and are gradually replaced by adipose and fibrous CT.

Step 1 of muscle contraction

A nerve impulse triggers release of ACh from the synaptic knob into the synaptic cleft. ACh binds to ACh receptors in the motor end plate of the neuromuscular junction, initiating a muscle impulse in the sarcolemma of the muscle fiber.

H zone

A light, central region in the A band. Lighter because only thick filaments are present- there is no thin filaments overlapping the thick filaments in the H zone in a relaxed muscle fiber. At maximal contraction, the thin filaments and keeps the thick filaments are pulled into this zone, and then H zone disappears.

Synergist

A muscle that assists the agonist in performing its action. The contraction of a synergist usually either contributes to tension exerted close to the insertion of the muscle or stabilizes the point of origin. Usually most useful at the start of a movement when the agonist is stretched and cannot exert much power. Ex. The biceps brachii and the brachialis muscles of the arm. They work together to flex the elbow joint.

Botulism

A potentially fatal muscular paralysis caused by a toxin produced by the bacterium Clostridium botulinum. The toxin prevents the release of ACh at the neuromuscular junctions and leads to muscular paralysis.

Motor Unit

A single motor neuron typically controls numerous muscle fibers in a muscle. This motor neuron has a neuromuscular junction with each muscle fiber it controls. Most muscles have many motor units, which means that many motor neurons are needed to innervate (supply) an entire muscle. The smaller the motor unit, the finer the control.

Fibromyalgia

A syndrome of chronic severe pain involving both the muscles and the skeleton, and accompanied by fatigue, morning stiffness, and sometimes psychological depression.

Tropomyosin

A thin filament. Double-stranded regulatory protein. A short, thin, twisted filament that covers small sections of the actin strands. Function: Covers the active sites on actin, preventing myosin from binding to actin when muscle fiber is at rest.

Troponin

A thin filament. Regulatory protein that holds tropomyosin in place and anchors to actin. Function: When calcium ions bind to one of its subunits, troponin changes shape, causing the tropomyosin to move off the actin active site, and this permits myosin binding to actin. 1) Attaches to actin to anchor itself in place. 2) Attaches to tropomyosin to hold it in place over the surface of the actin 3) Functionally, troponin provides a binding site for calcium ions.

M line

A thin transverse protein meshwork structure in the center of the H zone of a relaxed fiber. Serves as an attachment site for thick filaments and keeps the thick filaments aligned during contraction and relaxation.

Lever

An elongated, rigid object that rotates around a fixed point called the fulcrum. Ex. A seesaw. Lever: Longbone Fulcrum: Joint Effort: muscle

Acetylcholinesterase (AChE)

An enzyme that resides in the synaptic cleft, rapidly breaks down molecules of ACh that are released into the synaptic cleft. Thus, AChE is needed so that ACh will not continuously stimulate the muscle.

Blood Vessels and Nerves

An extensive network of blood vessels and nerve fibers extends through both the epimysium and the perimysium. The blood vessels deliver to the muscle fibers nutrients and oxygen needed for the production of ATP. They also remove waste products produced by the muscle fibers.

Hypertonia

An increase in muscle stiffness that presents as either spasticity or rigidity. Spasticity: Associated with an increase in tendon reflexes and certain pathologic reflexes, such as the Babinski sign, in which the great toe extends when the sole of the foot is stroked. Rigidity: An increased in muscle tone but does not involve reflexes.

Step 2 of muscle contraction

As the muscle impulse spreads quickly from the sarcolemma along T-tubules, calcium ions are released from terminal cisternae into the sarcoplasm.

Rigor Mortis

At death, circulation ceases, and all body tissues are immediately deprived of oxygen and nutrients. Some tissues continue to "live" for as long as an hour as they metabolize stored energy reserves. Rigor mortis continues for about 15-24 hours. This is due to the lack of ATP availability. The crossbridges between thick and thin filaments cannot detach. All skeletal muscles lock into a contracted position, and the deceased individual becomes rigid.

Smooth Muscle

Autorhythmicity: In some types only Contraction speed: Slow Nervous system control: involuntary

Development of Skeletal Muscles

Begins during the 4th week of development Portions of the mesoderm form somites. They appear superior to inferior (start at cranial end of embryo) Differentiate into three distinct regions: Sclerotome: gives rise to the vertebral skeleton Dermatome: forms the connective tissue of the skin Myotome: forms the skeletal muscles

Smooth Muscle: Ca Source, Junctions, and Neuro

Ca source: Sarcoplasmic Reticulum and interstitial fluid Junctions: Gap junctions in some types only Neuro junctions: In some types only

Cardiac Muscle: Calcium source, junctions, and neuromuscular junctions

Ca source: Sarcoplasmic reticulum and interstitial fluid. Junctions: Intercalated discs contain gap junctions and desmosomes Neuromuscular Junction: NONE

Step 3 of muscle contraction

Calciium ions bind to troponin. Troponin changes shape, moving tropomyosin on the actin to expose active sites on actin molecules of thin filaments. Myosin heads of thick filaments attach to exposed active sites to form crossbridges.

Naming of Skeletal Muscles

Can be named by: Action Ex. Adductor magnus, adducts. Specific Body Region Ex. Obicularis oris, mouth Muscle attachments Ex. Sternocleidomastoid, sternum and clavicle. Orientation of muscle fibers Ex. Rectus abdominis, straight. Muscle shape and size Ex. Deltoid, triangular Muscle heads / tendons of origin Ex. Biceps femoris, two heads.

Interactions between thick and thin filaments

Contraction of a muscle fiber requires that the myosin heads in the thick filament bind to active sites on G-actin molecules within the thin filaments. When the muscle fiber is in a relaxed state, the tropomyosin molecules cover these active sites, preventing interaction between thick filaments and thin filaments. When the nerve impulse arrives at the muscle fiber it generates an influx of calcium ions into the sarcoplasm of the muscle fiber from the sarcoplasmic reticulum. Some calcium ions bind to troponin subunits with a binding site for calcium, causing the entire troponin molecule to change shape. As it changes shape, it moves the tropomyosin molecule to which it is attached, thus exposing the active sites on the G-actin molecules. Myosin is now able to bind to actin. When the stimulation from the nerve impulse ceases, calcium ions are pumped back into the sarcoplasmic reticulum, and the troponin-tropomyosin complex moves back to its original conformation.

Myoblasts

Embryonic cells that fuse to form single skeletal muscle fibers. Each myoblast nucleus contributes to the eventual total number of nuclei to one muscle fiber.

Deep Fascia

Endomysium, perimysium, and epimysium are ensheathed by deep fascia, an expansive sheet of dense irregular CT that separates individual muscles, binds together muscles with similar functions, and forms sheaths to help distribute nerves, blood vessels, and lymphatic vessels, and to fill spaces between muscles.

Terminal cisternae

Expanded ends of the sarcoplasmic reticulum that are in contact with the transverse tubules. Function: Site of calcium ion release to promote muscle contraction.

Smooth Muscle: Regenerative Capacity

Extensive

Cardiac Muscle: Presence of myofibrils

Extensive, but of irregular thickness

Circular Muscle Fibers

Fibers arranged concentrically around an opening. Functions as a sphincter to close a passageway or opening. Ex. orbits, mouth, anus

Hypotonia

Involved decreased or lost muscle tone. These muscles are flaccid and appear flattened.

Synaptic cleft

Is a narrow space separating the synaptic knob and the motor end plate.

Motor end plate

Is a specialized region of the sarcolemma. It has folds and indentations to increase the membrane surface area covered by the synaptic knob.

Sarcomere

Is the functional contractile unit of a skeletal muscle fiber. From Z disc to Z disc. There are numerous sarcomeres in each myofibril. Each sarcomere shortens as the muscle fiber contracts.

Satellite Cells

Myoblasts that do not fuse with other myoblasts. These embryonic-like cells remain in adult skeletal muscle tissue as satellite cells. if a skeletal muscle is injured, some satellite cells may be stimulated to differentiate and assist in its repair and regeneration.

Muscle

Multiple fascicles housing many muscle fibers, CT coverings, blood vessels, nerve fibers. CT Covering- Epimysium

Unipennate Muscle Fibers

Muscle body has one or more tendons. fascicles at oblique angle to tendon. Pulls harder than a parallel muscle of equal size. All muscle fibers are on the same side of the tendon. Ex. Extensor Digitorum

Bipennate Muscle Fibers

Muscle body has one or more tendons. fascicles at oblique angle to tendon. Pulls harder than a parallel muscle of equal size. Muscle fibers on both sides of the tendon. Ex. Rectus femoris

Multipennate Muscle FIbers

Muscle body has one or more tendons. fascicles at oblique angle to tendon. Pulls harder than a parallel muscle of equal size. Tendon branches within the muscle. Ex. Deltoid

Neuromuscular Junction

Muscle contraction begins when a newve impulse stimulates an impulse in a muscle fiber. Each muscle fiber is controlled by one motor neuron. The motor neuron transmits the effect of a nerve impulse to the muscle fiber at the neuromusclular junction, the point where a motor neuron meets a skeletal muscle fiber.

Step 4 of muscle contraction

Myosin heads pivot, moving thin filaments toward the sarcomere center. ATP binds myosin heads and is broken down into ADP and P. Myosin heads detach from thin filaments and return to their pre-pivot position. The repeating cycle of attach-pivot-detach-return slides thick and thin filaments past one another. The sarcomere shortens and the muscle contracts. The cycle continues as long as calcium ions remain bound to troponin to keep active sites exposed.

Transverse tubule (T-tubule)

Narrow, tubular extensions of the sarcolemma into the sarcoplasm, contacting the terminal cisternae; wrapped around myofibrils. Function: Quickly transports a muscle impulse from the sarcolemma through the entire muscle fiber.

Cardiac Muscle: CT components

One layer of endomysium only

Smooth Muscle: CT Components

One layer of endomysium only

Smooth Muscle: Sarcomere Protein Organizatin

None

Synaptic knob

Of a neuron is an expanded tip of an axon. When it nears the sarcolemma of a muscle fiber, it expands further to cover a relatively large surface area of the sarcolemma. A nerve impulse travels through the axon to the synaptic knob.

Myofibrils

Organized bundles of myofilaments; cylindrical structures as long as the muscle fiber itself. Function: Contain myofilaments that are responsible for muscle contraction. During contraction, the myofibrils shorten as their component proteins change position. Because myofibrils are attached to the ends of muscle fiber, the shortening of the myfibrils during a contraction causes the fiber to shorten.

Sarcolemma

Plasma membrane of a muscle fiber. Function: Surrounds muscle fiber and regulates entry and exit of materials.

Agonist

Prime mover. A muscle that contracts to produce a particular movement, such as extending the forearm. Ex. The triceps brachii of posterior arm is an agonist that causes forearm extension.

Cardiac Muscle: Appearance and Shape of Cell

Short, branched cell with 1 or 2 centrally located nuclei; intercalated discs between fibers; striated.

Muscle Fiber

Single muscle cell Function: Metabolic activities; contraction.

Sarcoplasmic Reticulum

Smooth endoplasmic reticulum in a muscle fiber. Function: Stores calcium ions needed for muscle contraction.

Aponeurosis

Sometimes, the tendon forms a thin, flattened sheet.

Smooth Muscle: Appearance and Shape

Spindle-shaped; a single centrally located nucleus; no striations

All-or-none principle

States that a muscle fiber either contracts completely or does not contract at all. When a motor unit is stimulated, all its fibers contract at the same time. The total force exerted by the muscle depends on the number of activated motor units. If more motor units are activated or recruited, more muscle fibers contract and greater force is exerted. Movements that require less force need fewer activated motor units.

Resistance Arm

The part from the fulcrum to the point of resistance is the resistance arm.

Effort Arm

The part of the lever from the fulcrum to the point of effort is called the effort arm.

Muscle tone

The resting tension in a skeletal muscle. Usually, motor units are stimulated randomly so that the attached tendon maintains a constant tension, but the individual muscle fibers are afforded some relaxation time. This resting muscle tone stabilizes the position of bones and joints. As simulation begins and then increases in an active muscle, the fibers within the muscle begin to contract, generating tension in the muscle.

Isotonic Contraction

The tension produced equals or is greater than the resistance, and then the muscle fibers shorten, resulting in movement. The tension generated in the appropriate muscles equals the load, and then the muscle fibers shorten. Two types: 1) Concentric contractions: actively shorten a muscle. The load is less than the maximum tension that can be generated by the muscles in the arm; thus, the muscle shortens. 2) Eccentric contractions: actively lengthen a muscle. Simply put, an isotonic contraction of the arm muscles allows you to lift a book from the table, while an isometric contraction of the arm muscles occurs when you push against a wall.

Voluntary Muscles

They are controlled by the somatic (voluntary) nervous system and we can voluntarily move our skeletal muscles. The neurons (nerve cells) that stimulate muscle contraction are called motor neurons and are said to innervate muscle fibers within the muscle. An axon of a motor neuron transmits a nerve impulse to an individual muscle fiber. The junction between the axon and the muscle fiber is called a neuromuscular junction.

Slow fibers

Typically smaller in diameter. They contract more slowly than fast fibers, often taking two or three times longer to contract after stimulation. Specialized to continue contracting for extended periods of time. Vascular supply to slow muscle fibers is more extensive thus, the supply of nutrients and oxygen to slow fibers is markedly increased. Also called red fibers because they contain red pigmented myoglobin (a globular, oxygen-binding, reddish-appearing protein that is structurally related to hemoglobin. Resting slow muscle fibers contain substantial oxygen reserves that can be mobilized during a contraction to provide the needed ATP. They have relatively large number of mitochondria. Aerobic.

Fast Fibers

Uses ATP quickly Anaerobic Sparse capillaries White color Fast velocity Low resistance to fatigue Upper limbs Largest in size Fewer mitochondria Small amount of myglobin Sort duration, intense movement.

Sliding Filament Theory

When a muscle contracts, thick and thin filaments slide past each other, and the sarcomere shortens. -Width of the A band remains constant, but the H zone disappears. -Z discs in one sarcomere move closer together. -Sarcomere narrows or shortens in length. -I band narrow or shorten in length.

Biomechanics

When analyzing muscle contraction, anatomists often compare it to the mechanics of a lever; this practice of applying mechanical principles to biology is called biomechanics.

Fibrosis

When the elasticity of skeletal muscle decreases as muscle mass is replaced by dense regular (fibrous) CT, a process called fibrosis. This decreases the flexibility of muscle; an increase in collagen fibers can restrict movement and circulation.

Step 5 of muscle contraction

When the impulse stops, calcium ions are actively transported into the sarcoplasmic reticulum, tropomyosin re-covers active sites, and filaments passively slide back to their relaxed state.