Anatomy Test #2.5 Muscle Tissue

Explain the neuromuscular junction

-Excitable cells (muscle and nerve) make contact and communicate with one another at specialized regions called synapses. -At each synapses a small gap, called the synaptic cleft, separates the two excitable cells. (not touching) -The first cell, the motor neuron, communicates with the second cell, the skeletal muscle, across the synaptic cleft via a chemical messenger called the neurotransmitter. -The type of synapse formed between the motor neuron and the skeletal muscle cell is called the neuromuscular (myoneural) junction. -At the synapse, the motor neuron branches into clusters of bulb-shaped axon terminals (end bulbs), each cluster forming a synapse with a group of muscle cells (motor unit) -The region of the muscle cell membrane that participates in the synapse with the axon terminal is the motor end plate.

Explain process of ATP attachment during muscle contraction

-Myosin CANT bind to actin when it has ATP attached -ATP releases P to from ADP+P (cocked position) -ADP+P is released and it can now attach, tug, and swivel -Then a new ATP comes in a restarts the process. Myosin head will stay there until new ATP comes to separate it. (ATP detaches myosin head).

Describe the sliding filament theory of muscular contraction.

-Skeletal muscle shortens during contraction because the thin and thick myofilaments slide past one another. -During muscle contraction, the thick myofilaments attach to, then pull on, the thin myofilaments, causing them to slide inward towards each other. -As the cross bridges apply force to the thin myofilaments, the thin myofilamentss move towards the center of the sarcomere. This may occur so far that their tips overlap each other. -As the thin myofilaments "slide" inward, they pull the Z discs toward each other, and the sarcomere shortens, but the lengths of the myofilaments stay the same. (H zone and I band get smaller (HI) but A-band do NOT change) -The shortening of the sarcomeres, all in series, causes the shortening of the whole muscle fiber, and ultimately of the entire muscle itself, producing force used for work.

Describe the electrical and chemical events of skeletal muscle relaxation?

-Two changes are necessary to permit a muscle to relax after it has contracted. ACh is rapidly broken down in the synaptic cleft by the enzyme acetlycholinesterase (AChE) present on the motor end plate; this stops the generation of the muscle membrane electrical message. -Secondly, calcium ions are pumped into the sarcoplasmic reticulum, where they are bound to the molecule calsequestrin, thus removing them from the sarcoplasm -Without calcium, the tropomysoin-troponin complex moves back over the actin, covering the myosin-binding sites. This prevents binding of myosin cross bridges to actin. Release of the actin by the cross bridges allow the thin myofilaments to slip back to their resting position so that the sarcomere resumes its resting length. The muscle is now relaxed. (Titan assist with bringing the sarcomere back to normal shape)

Describe the use of acetylcholine

-Within each axon terminal are many membrane-enclosed vesicles called synaptic vesicles containing thousands of neurotransmitter molecules. -The neurotransmitter used exclusively by motor neurons for skeletal muscles is acetylcholine (ACh). -The nerve impulse (1) reaching the axon terminal, triggers exocytosis of the synaptic vesicles (2), releasing the ACh into the synaptic cleft. -ACh diffuses through the extracellular fluid in the synaptic cleft and approaches the motor end plate. -On the motor end plate are ACh receptors (20-50 million). These are integral proteins specific for ACh. They recognize the molecule and bind specifically to it, causing Na+ channels to open (3). -Binding of ACh to its receptors on the motor end plate initiates an electrical message in the motor end plate, and therefore in the muscle cell membrane (4). -In most skeletal muscles there is a single neuromuscular junction per cell, located near the cell's midpoint. -Stimulation of the membrane in this way spreads from the midpoint of the muscle cell towards its ends and therefore causes almost simultaneous contraction of all parts of the cell.

What are the four basic characteristics of muscle tissue?

1)Excitability 2)Contractibility 3)Extensibility 4)Elasticity

What is the amount of force (tension) a muscle can generate based on?

1)Frequency of stimulation of muscle fiber by motor neurons 2)Length of muscle fibers before they begin to contract 3)The number of muscle fibers contracting at any one given time (number of activate motor units)(recruitment) 4)Structural components of the muscle itself.

What does calcium do?

1)It binds to troponin, causing the tropomyosin-troponin complex to move, exposing the myosin bind sites on the actin. 2)It activates ATP on the myosin heads, causing them to bind to the actin. (ATP gets myosin ready and supplies energy for the "tug")

What are the three functions of muscle tissue?

1)Motion 2)Stabilize body positions and regulate organ volume 3)Thermogenesis

What are the three types of muscle tissue?

1)Skeletal Muscle 2)Cardiac Muscle 3)Smooth Muscle

What are the four functions of superficial fascia?

1)Store fat and therefore water 2)Insulation 3)Mechanical protection 4)Pathway for nerves and blood vessels

What are the two types of fascia?

1)Superficial fascia 2)Deep fascia

What are the 3 physiological classes of muscle fibers?

1)Type I fibers 2)Type IIb fibers 3)Type IIa fibers

Explain thermogenesis (function of muscle tissue)

A by-product of muscle contraction is heat production and is therefore important in homeostasis of body temperature.

What is the Z disc (line?

A dense material called the Z disc is found at each end of a sarcomere, separating it from the next sarcomere in line.

Describe the sarcoplasmic reticulum and calcium flux

A fluid-filled system of tubules called the sarcoplasmic reticulum encircles each myofibril. In a relaxed muscle cell, the sarcplasmic reticulum stores calcium ions by sequestering them from the sarcoplasm. Calcium ions released through calcium channels back into the sarcoplasm around the thin and thick myofilaments trigger muscle contraction.

Describe myosin

A molecule of myosin is shaped like two golf clubs twisted together. The tail of the molecule extends to the center of each sarcomere. The projecting "head" called a cross bridge, extends out towards the thin myofilaments. The "head" is the part that will eventually attach to the actin-binding site.

How does the all-or-none principle fit with the concept of the motor unit?

A motor neuron delivers a threshold stimulus to all of the cells of the motor unit and each cell contracts fully and completely. There is no partial contraction of the motor unit.

What is a motor neuron?

A motor neuron delivers the nervous stimulus that ultimately causes a muscle tissue to contract. Also stimulates glands to secrete.

What is a functional syncytium?

A network of muscle cells. If one cell is stimulated all cells of the network become stimulated.

Describe titan

A third component of the sarcomere is the elastin filament (also known as titan). The role of titan is to anchor the thick myofilaments in position and to play a role in recovery of the resting sarcomere length when a muscle cell is stretched or contracted.

What is a twitch contraction?

A twitch contraction is a brief contraction of all muscle fibers in a motor unit in response to a single threshold stimulus from a motor neuron. As seen by the myogram, there are three distinct phases in a simple twitch contraction.

Describe the electrical and chemical events of skeletal muscle contraction.

Acetylchonline released by the motor neuron at the neuromuscular junction diffuses across the synaptic cleft and binds its receptors on the motor end plate. -This binding initiates formation of an electrical message in the sarcolemma that spreads in all directions, passing downy the transverse tubules and out into the sarcoplasmic reticulum, causing calcium channels there to open, allowing calcium to diffuse into the sarcoplasm. Calcium then: 1)It binds to troponin, causing the tropomyosin-troponin complex to move, exposing the myosin bind sites on the actin. 2)It activates ATP on the myosin heads, causing them to bind to the actin. (ATP gets myosin ready and supplies energy for the "tug") Binding of myosin heads to actin causes the hinge regions to tilt, pulling the thin myofilaments across the thick myofilaments, thus causing the sarcomeres to shorten and the muscle cells to contract.

What is the main component of a thin myofilament?

Actin

What are intercalated discs?

Adjacent cell membranes contact one another at thickened areas called intercalated discs; it is through these structures that adjoining cells communicate. (Gap junctions)

Explain the treppe contraction phenomenon

After the first few contractions, the muscle reaches its peak performance and can undergo its strongest contractions. One explanation may be similar to that for tetanus--build-up of calcium ions in the sarcoplasm during the repeated stimulations. It may also be part due to "loosening up" of the connective tissue elements.

Describe a tendon

All three layers (epimysium, perimysium, endomysium) may extend beyond the muscle as a cord of dense connective tissue, called a tendon, that attaches the muscle to the periosteum of a bone. Strong, rope-like

What does deep fascia do?

Allows free movement of muscles, carries nerves, blood vessels, and lymph vessels, and fills the spaces between muscles.

Explain excitability (characteristic of muscle tissue)

Also known as irritability. This is the ability to receive and respond to certain stimuli by producing electrical messages.

Explain the tropomyosin-troponin complex

Also present on the thin myofilament are two regulatory molecules called tropomyosin and troponin. In relaxed mules, the tropomyosin-troponin complex covers the myosin-binding site on the actin molecules. This blocks the myosin-binding sites and prevents the attachment of the thick filaments, thus preventing contracting of the sarcomere.

Explain myofilaments

Are found inside the myofibril but do not extend the length of the myofiber, but rather are stacked into repeating units (compartments) called sarcomeres.

How is muscle tone accomplished?

At any given moment a few motor units are contracting, while all the others remain relaxed.

Explain contractility (characteristic of muscle tissue)

Contractility is the ability to shorten and thicken (contract), thus generating force to do work.

What happens at the T-tubules?

Current flows through the T-tubules and the terminal cistern recognize it and release calcium.

Describe deep fascia

Deep fascia is formed of dense irregular connective tissue. It lines the body wall and extremities and holds muscles together, separating them into functional groups.

What is the main component of thick myofilament?

Each thick myofilament is composed of about 200 molecules of a protein called myosin.

Explain Elasticity (characteristic of muscle tissue)

Elasticity is the ability to return to original shape after contraction or extension.

Describe the Endomysium

Endomysium is formed by invaginations of the perimysium that penetrates the fascicle and wrap each muscle cell, completely insulating it from the others.

Where are the thin and thick myofilametns located in the sarcomere?

Extending from each Z disc towards the middle of the sarcomere are the thin myofilaments. Suspended within the sarcoplasm, between the thin myofilaments, and not attached to the z discs, are the thick myofilaments

Explain extensibility (characteristic of muscle tissue)

Extensibility is the ability to stretch without damaging the tissue

What is fascia?

Fascia refers to a sheet or broad band of fibrous connective tissue beneath the skin or around muscles and organs of the body. There are two types.

Explain Type IIb fibers

Fast glycolytic, fast twitch, white -poor in mitochondria, myoglobin, and capillaries, rich in enzymes of the phosphagen and glycogen pathways -vast sarcoplasmic reticulum (rapid Ca++ movement), anaerobic reparation, fatigue quickly

Describe the aerobic system in a muscle cell

For continued activity with sufficient oxygen, mitochondria completely catabolizes glucose to carbon dioxide, water, and a net 36 ATPs. When the oxygen supply is outstripped by the activity, glucose is incompletely catabolized to lactic acid. This leads to fatigue and oxygen debt. (most productive, takes most time)

Describe the perimysium

Formed by invaginations of the epimysium, dividing the muscle into bundles of cells called fascicles.

The prime function of muscle is used for?

Generate force, perform work, and produce movements

What is a major reason for muscle fatigue?

High levels of ADP+P which limits the sarcoplasmic reticulum from releasing calcium.

What is incomplete tetany?

If a muscle receives multiple stimuli very quickly (20-30 per second), it can only relax partially before its next wave summation. The result is a sustained contraction called incomplete tetany, during which the muscle is contracting maximally but relaxing only partially.

Describe wave summation

If a second stimulus is applied to an excited cell after the refractory period, but before the cell has finished resting from the first stimulus, the second contraction will be greater than the first. This phenomenon, in which stimuli arrive at different times and cause larger contractions, is called wave summation.

What is complete tetany?

If frequency of stimulation is increased to 80-100 per second, no relaxation period occurs at all between contractions. This is complete tetany. Both types of tetany occur of the continued addition of calcium ions to the sarcoplasm without benefit of sequestering calcium between contractions.

Of what use is recruitment?

In addition to increasing strength of a muscle, it is also important because it works with short-term tetanic contractions to produce smooth movements rather than a series of jerky ones.

Explain type IIa fibers

Intermeditae fibers Somewhere in between fast and slow twitch

Explain isometric contractions

Isometric contractions occur when the muscle does not or cannot shorten, but the tension within it greatly increases. (EX: holding a book in a steady position, outstretched away from the body; the book stretches the arm and shoulder; muscle contraction counteracts the stretch; there is no motion) ("Iso"-->same; "meter"-->length)

Explain isotonic contractions

Isotonic contractions occur when you move a constant load through the range of motions possible at a joint. In this type of contraction, the tension within the muscle stays the same during the contraction, while the length of the fibers shorten. (EX: most movements of the body) (same tension; constant tension and movement)

How is muscle tone essential for maintaining posture?

It gives the muscle firmness without producing movement. This is essential for maintaining posture.

What is the neuromuscular junction

Junction between neuron and muscle cell

Explain the structure of Actin

Looks like a kidney bean. Individual molecules of actin are linked together to form the actin filament that is twisted to form a helical strand. On each molecule of actin within the helical strand is a myosin-binding site upon which the thick myofilaments will attach.

Describe a mitochondria

Mitochondria lie in rows throughout the muscle fiber, located close tot he muscle proteins that use ATP for the contraction-relaxation sequence. (very abundant)

Explain visceral (single-unit) smooth muscle

Most common type. It is found wrapped in sheets that form part of the walls of hollow organs. the cells are tightly bound to each other to form a continuous network (functional syncytium), so that stimulation of one cell results in stimulation of the entire network.

How are most voluntary movements accomplished?

Most voluntary movements are accomplished using short-term tetanic contractions, rather than simple twitch contractions. This allows the movements to be smooth and sustained over time.

Explain motion (function of muscle tissue)

Motion can be obvious body movements or less noticeable motions such as heartbeat and gut movement

What causes motion?

Motion results from the alternating contraction (shortening) and relaxation of muscles.

How are motor units different for precise and gross movements?

Muscles that control precise body movements may have as few as 2-3 muscle cells per motor neuron (eye muscles), while muscles that control gross body movements may have as many as 2,000 muscle cells per motor neuron (gluteal muscles).

Once you reach aerobic system, are all other systems stopped?

NO, other 2 systems may still be working, aerobic system is just the main source.

Explain smooth muscle

Nonstriated muscle that is involuntary. It can also be stimulated or inhibited by either the nevous or endocrine function. Walls of digestive organs and blood vessels.

What is a muscle triad?

On both sides of a T-tubule are dilated end sacs of the sarcoplasmic reticulum called the terminal cistern. A T-tubule, together with its two terminal cistern, is called a muscle triad.

Define the concept of a motor unit?

One motor neuron plus ALL of the skeletal muscle cells it stimulates is called a motor unit. On average, a single motor neuron makes contact and thus stimulates about 150 individual skeletal muscle cells. All the cells contract and relax together, as a "unit"

What is a threshold stimulus?

One that initiates the formation of an electrical impulse in the sarcolemma. No matter how high over the threshold you get, it still contracts equally.

How is recruitment accomplished?

Recruitment involves activating more and more motor units form the inactive population in order that the whole muscle can generate more force during contraction.

What is recruitment?

Recruitment is the process of increasing the number of active motor units within a given skeletal muscle.

Describe the nuclei

Skeletal muscle cells are multinucleated, due to fusion of precursor cells during embryogenesis; the nuclei are located along the periphery of the cell, out of the way of the contractile elements within the sarcoplasm.

Describe role of skeletal muscle in thermogenesis and homeostasis of body temperature.

Skeletal muscle is responsible for generating a great deal of heat in a very short time in response to decreased body temperature. -During contraction, 20-30% of energy created is used. The balance is lost as body heat and is used to help maintain normal body temperature. -A decrease in body temperatures is detected by thermoreceptors in the hypothalamus of the brain and the skin. In response, the hypothalamic neurons initiate two events to occur: 1)Widespread shunting of blood from the body core to arterio-venous plexuses of the skin 2)Involuntary increase in skeletal muscle tone, causing shivering. This involuntary thermogenesis returns body temperature to within normal homeostatic range, and the process is turned off by negative feedback.

Explain Type I fibers

Slow oxidative, slow twitch, red fibers -abundant mitochondria, myoglobin, and capillaries, aerobic respiration

Describe smooth muscle

Smooth muscle is non-striated and involuntary muscle whose cells are spindle-shaped with a single nucleus. Each cell contains thick and thin myofilaments, but not arranged into sarcomeres. This permits the walls of hollow organs to stretch without increasing tension within the cells. 1)non-striated 2)no sarcomeres 3)single nucleus/cell 4)two types -visceral (functional syncytium -multiunit

Describe a tendon sheath

Some tendons, particularly those in high stress areas like the ankle and wrist, are wrapped in a layer of synovial membrane, forming a tendon (synovial) sheath.

How is the total strength of a muscle determined?

Stimulation by its motor neuron results in a simultaneous contraction of all the skeletal muscle cells in the motor unit. Accordingly, the total strength of any particular muscle is determined by the total number of motor units being used at any given time.

Explain cardiac muscle

Striated muscle that is involuntary (no conscious control). It can be stimulated or inhibited by either the nervous system or the endocrine systems.

Explain Skeletal muscle

Striated muscle that is voluntary (it can be controlled consciously). It can only be stimulated by the nervous system.

Describe superficial fascia

Superficial fascia (subcutaneous layer or hypodermic) lies immediately deep to the skin. It is composed of adipose and areolar tissues. It has four functions

Explain "stabilize body positions and regulate organ volume" (function of muscle tissue)

Sustained contractions of skeletal muscle maintain body posture without creating noticeable movement. Sustained contractions of smooth muscle prevent outflow from hollow organs and maintain them at an appropriate volume.

What is muscle tone?

Sustained, small contractions of motor units give skeletal muscles a firmness known as muscle tone. (Essential for maintaining posture)

Describe the arrangement of molecules in myosin

Tails of adjacent myosin molecules lie parallel to each other, forming the "shaft" of the thick myofilament, while the "heads" project around the shaft in a spiraling fashion.

What forms the striations of skeletal muscle?

The alternating areas of thin myofilaments, followed by areas of overlapping thin and thick myofilaments, are responsible for the striations seen in skeletal muscle.

What are myofibrils?

The contractile elements of skeletal muscle. Each is 1-2 microns in diameter and consists of three even smaller structures called myofilaments. Myofibrils give the prominent alternating light and dark bands evident give the skeletal muscle cells their characteristic striations.

Describe the contraction period

The contraction period is the time during which the myofilaments are sliding, the sarcomere is shortening, and the muscle fiber is generating force.

Explain oxygen debt

The difference between oxygen consumption at rest and oxygen consumption following exercise. This "debt" must be "repaid" in order to: 1)Replace the body's oxygen reserves 2)Replenish the phosphagen system 3)Oxidize accumulated lactic acid 4)Serve the elevated metabolic rate post-exercsie

Describe the latent period

The latent period is the time from when the stimulus is applied to the beginning of the actual shortening of the sarcomere

Describe the epimysium

The outermost layer of deep fascia, wrapping the entire muscle.

Describe the phosphagen system in a muscle cell.

The phosphagen energy system, which utilizes stored ATP and creatinine phosphate, provides enough energy for skeletal muscles to contract maximally for about 15 seconds. It is used for maximal short bursts of activity

Describe cardiac muscle

The principal constituent of the heart is cardiac muscle. It is striated like skeletal muscle, with the same arrangement of thin and thick myofilaments. Unlike skeletal muscle, each cardiac muscle cell has a single nucleus, there is no insulating endomysium, and the cells branch freely. Involuntary 1)Striated 2)Single nucleus/cell 3)Intercalated discs 4)Functional syncytium 5)Involuntary 6)Self-stimulating

What is recruitment?(motor neuron)

The process of activating more neurons in order to lift more weight.

Describe the relaxation period

The relaxation period is the time during which acetylcholinesterase is destroying acetylcholine at the synapse and the sarcomere is returning to its resting strength. (recovery)

Describe a sarcolemma

The sarcolemma is the cell membrane of a muscle cell. It surrounds the sarcoplasm, or muscle fiber cytoplasm.

What is a sarcomere?

The sarcomere is the functional (contracting) unit of skeletal muscle.

Where are myofibrils located?

The sarcoplasm are stuffed with small threads called myofibrils. Myofibrils lie in parallel to each other and extend lengthwise throughout the extent of the myofiber.

What is the function of the connective tissue specializations that surround skeletal muscle cells?

These connective tissues protect and strengthen the muscles, as well as provide attachment of the muscle to surrounding structures. All the layers are continuous with each other and surrounding deep fascia.

Explain the H band

Thick myofilaments ONLY

Explain the I band

Thin myofilaments only (lIght shaded)(Actin)

Explain multiunit smooth muscle

This consists of individual smooth muscle cells, each with its own motor neuron, so that each can contract independent of the others. Multiunit muscle is found in the walls of blood vessels, the arrestor pili of hair follicles, and in the iris of the eye. (more precise)

Why does the muscle (muscle tone) not fatigue?

This is accomplished without fatigue due to asynchronous firing of motor units. Different units are activated at different times.

What is the all-or-none principle in muscle?

This principle states that individual muscle fibers contract fully and completely or the existing conditions, or do not contract at all.--If the muscle cell generates its electron potential (All myofibrils of muscled cell will contract.)

What is the prime function of muscle?

To convert chemical energy (ATP) into mechanical energy.

Describe transverse tubules

Transverse tubules (T tubules) are tunnel-like enfolding of the sarcolemma. They penetrate the myofiber at right angles to the sarcoplasmic reticulum and the myofilaments. T tubules are open to the outside of the muscle fiber and are therefore filled with extracellular fluid.

How is cardiac muscle controlled?

Unlike skeletal muscle, cardiac muscle stimulates itself to contract; it can then be regulated by the nervous and endocrine systems.

Describe the Refractory period

When a muscle fiber receives a threshold stimulus, it temporarily loses its excitability and cannot be stimulated again. This is called the refractory period.

What are treppe contractions?

When a skeletal muscle has been fully rested and is then stimulated repeatedly by identical stimuli too far apart to cause wave summation, each of the first few contractions is a little stronger than the last. This phenomenon is known as the staircase effect or treppe.

Describe the glycogen-lactic acid system in a muscle cell

When stored ATP and creatinine phosphate are depleted, the cell catabolizes glucose to create new ATP. A series of reactions known as glycolysis creates 2 ATPs for each glucose and does so anaerobically (without oxygen). This provides energy for an additional 30-40 seconds.

Describe aponeurosis

When the three connective tissue components extend from the muscle as a flat sheet, rather that a round cord, they are called an aponeurosis. Delicate, sheet-like

Explain the A band of sarcomere

Where the thick and thin myofilaments overlap (dArk)

Describe a myofiber (muscle fiber)

Within a typical skeletal muscle there are thousands of individual, very long, cylindrical cells called muscle fibers (myofibers), bundled together as fascicles. They lie in parallel to one another, ranging in size from 10-100 microns in diameter and up to 10 cm in length.

Describe Striations

caused by the way thick and thin filament line up (light and dark)