Download NAME:OLUWATIMEHIN OLUWAWEMIMO MATRIC NUMBER :14

NAME:OLUWATIMEHIN OLUWAWEMIMO
MATRIC NUMBER :14/MHS01/112
ANA 203
DEPARTMENT : MEDICINE AND SURGERY
Muscle tissue is a soft tissue that composes muscles in animal bodies, and gives rise to muscles' ability to contract. This is opposed to other
components or tissues in muscle such as tendons or perimysium. [clarification needed] It is formed during embryonic development through a
process known as myogenesis
Muscle function:
1. contraction for locomotion and skeletal movement
2. contraction for propulsion
3. contraction for pressure regulation
Muscle classification: muscle tissue may be classified according to a morphological classification or a functional classification.
Morphological classification (based on structure)
There are two types of muscle based on the morphological classification system
1. Striated
2. Non striated or smooth.
Functional classification
There are two types of muscle based on a functional classification system
1. Voluntary
2. Involuntary.
Types of muscle: there are generally considered to be three types of muscle in the human body.
Skeletal muscle: which is striated and voluntary
Cardiac muscle: which is striated and involuntary
Smooth muscle: which
skeletal muscle muscle fiberfasicleendomysiumperimysium epimysiumsarcolemmasarcoplasmic reticulummotor unitneuromuscular
junctionacetylcholinemyofibrilsI-band A-band Z-line H-band M-line myofilamentthick filamentthin filamentsarcomereT-tubuleterminal cisternae
slow-twitch muscle fiber myoglobinred fiberfast-twitch muscle fiber white fibersmooth muscle involuntary muscleadhesion density focal density
cardiac muscle intercalated discfunctional syncytiumfascia adherensdesmosomesgap junction Purkinje fiber
Muscles are multicellular contractile units. They are divided into three types:
skeletal muscle
smooth muscle
cardiac muscle
Skeletal muscle
Skeletal muscle is mainly for the movement of the skeleton, but is also found in organs such as the globe of the eye and the tongue. It is a
voluntary muscle, and therefore under conscious control. Skeletal muscle is specialized for rapid and forceful contraction of short duration.
Skeletal muscle cells contain similar components and structures as other cells but different terms are used to describe those components and
structure in skeletal muscle cells. The plasma membrane of skeletal muscle is called the sarcolemma; its cytoplasm is known as sarcoplasm; the
endoplasmic reticulum is called the sarcoplasmic reticulum.
Each muscle cell is defined by a sarcolemma and contains many nuclei along its length. The nuclei are displaced peripherally within a cross
section of the sarcoplasm while a large number of longitudinal myofibrils, groups of arranged contractile proteins, occupy most of the center
space. The myofibril contains several important histological landmarks:
The myofibril is composed of alternating bands. The I-bands (isotropic in polarized light) appear light in color and the A-bands (anisotropic in
polarized light) appear dark in color. The alternating pattern of these bands results in the striated appearance of skeletal muscle.
The Z-lines (Zwischenschieben) bisect the I-bands.
A light band called the H-band (Heller) sits within each A-band.
The M-line (Mittelschiebe) bisects each A-band (and, in doing so, bisects each H-band).
Each myofibril can be understood as a series of contractile units called sarcomeres that contains two types of filaments: thick filaments,
composed of myosin, and thin filaments, composed of actin. The individual filaments do not change in length during muscle contraction; rather
the thin filaments slide over the thick filaments to shorten the sarcomere. The nature of these filaments can be understood in the context of the
histological landmarks of the myofibril.
The thick filaments are a bipolar array of polymerized myosin motors. The motors on one side of the filament are oriented in the same direction
whereas the motors on the other side of the filament are oriented in the opposite direction. The center of the filament lacks motors; it contains
only the coiled-coil region of the myosins. A set of proteins crosslinks each myosin filament to its neighbors at the center of the filament. These
proteins make up the M-line.
The thin filaments are attached to a disc-like zone that appears histologically as the Z-line. The Z-lines contain proteins that bind and stabilize the
plus ends of actin filaments. Z-lines also define the borders of each sarcomere.
The I- and H-bands are areas where thick and thin filaments do not overlap (this is why these bands appear paler under the microscope). The Iband exclusively contains thin filaments whereas the H-band contains exclusively thick filaments.
Skeletal muscles are divided into two muscle fiber types:
Slow-twitch (type I) muscle fibers contract more slowly and rely on aerobic metabolism. They contain large amounts of mitochondria and
myoglobin, an oxygen-storage molecule. The reddish color of myoglobin is why these fibers may be referred to as red fibers. These muscles can
maintain continuous contraction and are useful in activities such as the maintenance of posture.
Fast-twitch (type II) muscle fibers contract more rapidly due to the presence of a faster myosin. Type II fibers can be subdivided into those that
have large amounts of mitochondria and myoglobin and those that have few mitochondria and little myoglobin. The former primarily utilize
aerobic respiration to generate energy, whereas the latter rely on glycolysis. The lack of myoglobin results in a paler color than the slow-twitch
muscles, and fast-twitch fibers may therefore be referred to as white fibers. These muscles are important for intense but sporadic contractions;
for example, those that take place in the biceps.
Most muscles contain a mixture of these extreme fiber types. In humans, the fiber types cannot be distinguished based on gross examination,
but require specific stains or treatments to differentiate the fibers.
Neuromuscular Junction and Activation of Skeletal Muscle Cells
Skeletal muscle cells are innervated by motor neurons. A motor unit is defined as the neuron and the fibers it supplies. Some motor neurons
innervate one or a few muscle cells whereas other motor neurons can innervate hundreds of muscle cells. Muscles that require fine control have
motor neurons that innervate fewer muscle cells; muscles that participate in less controlled movements may have many fibers innervated by
each neuron. Motor axons terminate in a neuromuscular junction on the surface of skeletal muscle fibers. The neuromuscular junction is
composed of a pre-synaptic nerve terminal and a post-synaptic muscle fiber. Upon depolarization, the pre-synaptic vesicles containing the
neurotransmitter acetylcholine fuse with the membrane, releasing acetylcholine into the cleft. Acetylcholine binds to receptors on the postsynaptic membrane and causes depolarization of the muscle fiber, which leads to its contraction. Typically, one action potential in the neuron
releases enough neurotransmitter to cause one contraction in the muscle fiber.
In muscle cells, the sarcolemma or plasma membrane extends transversely into the sarcoplasm to surround each myofibril, establishing the Ttubule system. These T-tubules allow for the synchronous contraction of all sarcomeres in the myofibril. The T-tubules are found at the junction
of the A- and I- bands and their lumina are continuous with the extracellular space. At such junctions, the T-tubules are in close contact with the
sarcoplasmic reticulum, which forms a network surrounding each myofibril. The part of the sarcoplasmic reticulum associated with the T-tubules
is termed the terminal cisternae because of its flattened cisternal arrangement. When an excitation signal arrives at the neuromuscular junction,
the depolarization of the sarcolemma quickly travels through the T-tubule system and comes in contact with the sarcoplasmic reticulum, causing
the release of calcium and resulting in muscle contraction.
Functions of Skeletal Muscle Tissue
Skeletal muscles function in pairs to bring about the co-ordinated movements of the limbs, trunk, jaws, eyeballs, etc.
Skeletal muscles are directly involved in the breathing process
Smooth Muscle
Smooth muscle forms the contractile portion of the wall of the digestive tract from the middle portion of the esophagus to the internal sphincter
of the anus. It is found in the walls of the ducts in the glands associated with the alimentary tract, in the walls of the respiratory passages from
the trachea to the alveolar ducts, and in the urinary and genital ducts. The walls of the arteries, veins, and large lymph vessels contain smooth
muscle as well.
Smooth muscle is specialized for slow and sustained contractions of low force. Instead of having motor units, all cells within a whole smooth
muscle mass contract together. Smooth muscle has inherent contractility, and the autonomic nervous system, hormones and local metabolites
can influence its contraction. Since it is not under conscious control, smooth muscle is involuntary muscle.
Smooth muscle fibers are elongated spindle-shaped cells with a single nucleus. In general, they are much shorter than skeletal muscle cells. The
nucleus is located centrally and the sarcoplasm is filled with fibrils. The thick (myosin) and thin (actin) filaments are scattered throughout the
sarcoplasm and are attached to adhesion densities on the cell membrane and focal densities within the cytoplasm. Since the contractile proteins
of these cells are not arranged into myofibrils like those of skeletal and cardiac muscle, they appear smooth rather than striated.
Smooth muscle fibers are bound together in irregular branching fasciculi that vary in arrangement from organ to organ. These fasciculi are the
functional contractile units. There is also a network of supporting collagenous tissues between the fibers and the fasciculi.
Functions of Smooth Muscle Tissue
Smooth muscle controls slow, involuntary movements such as the contraction of the smooth muscle tissue in the walls of the stomach and
intestines.
The muscle of the arteries contracts and relaxes to regulate the blood pressure and the flow of blood.
Cardiac Muscle
Cardiac muscle shares important characteristics with both skeletal and smooth muscle. Functionally, cardiac muscle produces strong
contractions like skeletal muscle. However, it has inherent mechanisms to initiate continuous contraction like smooth muscle. The rate and force
of contraction is not subject to voluntary control, but is influenced by the autonomic nervous system and hormones.
Histologically, cardiac muscle appears striated like the skeletal muscle due to arrangement of contractile proteins. It also has several unique
structural characteristics:
The fibers of cardiac muscle are not arranged in a simple parallel fashion. Instead, they branch at the ends to form connections with multiple
adjacent cells, resulting in a complex, three-dimensional network.
Cardiac muscle fibers are long cylindrical cells with one or two nuclei. The nuclei are centrally situated like that of smooth muscle.
Cardiac muscle sarcoplasm has a great amount of mitochondria to meet the energy demands.
Similar to the skeletal muscle, cardiac muscle cells have an invaginating network of T-tubules and sarcoplasmic reticulum.
In atrial cardiac muscle cells, secretory granules can be seen. These granules contain atrial natriuretic factor (ANF), which is released upon excess
filling of the atria and opposes the action of angiotensin II in production of aldosterone.
Collagenous tissues are found surrounding individual cardiac muscle fibers. There is abundance vascularization within this supporting tissue,
which is required to meet the high metabolic demands of cardiac muscle.
The cardiac muscle fibers are joined end to end by specialized junctional regions called the intercalated discs. The intercalated discs provide
anchorage for myofibrils and allow rapid spread of contractile stimuli between cells. Such rapid spread of contraction allows the cardiac muscles
to act as a functional syncytium. The intercalated discs contain three types of membrane-to-membrane contact:
fascia adherens, which are connected to actin filaments to transmit contraction
desmosomes, which connect to intermediate filaments of the cytoskeleton
gap junctions, which are sites of low electrical resistance that allow the spread of excitation
In addition to the contractile cells, there is a specialized system made up of modified muscle cells whose function is to generate the stimulus for
heartbeat and conduct the impulse to various parts of the myocardium. This system consists of sinoatrial node, atrioventricular node, bundle of
his and purkinje fibres.
Functions of Cardiac (Heart) Muscle Tissue
Cardiac muscle tissue plays the most important role in the contraction of the atria and ventricles of the heart.
It causes the rhythmical beating of the heart, circulating the blood and its contents throughout the body as a consequence