Download Cardiac muscle

Name: HARRISON TEMITOPE JOY
Department: MEDICINE AND SURGERY
Matric No: 14/MHS01/060
Course code: ANA 203 (HISTOLOGY OF BASIC TISSUES)
Level: 200
AN ESSAY ON THE HISTOLOGY OF MUSCLE AS A TISSUE AND ITS TYPES
Muscle tissue is a soft tissue that makes up muscles present in animals.
The term muscle is derived from the Latin word musculus meaning little mouse perhaps because of
the shape of certain muscles or because contracting muscles look like mice moving under the skin.
It is a type of tissue made up of cells with it basic property of contractility.
Origin and source of power/strength
Muscle tissues are derived from the mesoderm layer of embryonic germ cells in a process called
myogenesis and they differentiate by a gradual process of cell lengthening with abundant synthesis
of the myofibril proteins, actin and myosin. They are primarily responsible for maintaining and
changing posture, locomotion, as well as movement of internal organs, such as the contraction of
the heart and the movement of food through the digestive system via peristalsis.
Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic
chemical reactions are also used, particularly by fast twitch fibres.
Muscles contract when they receive a motor impulse from a motor nerve. These nerve impulses
serve only a limited number of muscle fibers. The muscle fibers served by a single motor neuron
make up a structure known as a motor unit. Motor units allow for selective contraction of muscle
fibers so that we may control the strength and extent of muscle contraction. Without motor units a
nerve impulse to the muscle would result in the entire muscle contracting to its full extent. That
would make every motion that we make an “all or none” motion. This type of movement would
make life nearly impossible.
a neuromuscular junction of one motor neuron with one muscle fiber. In a motor unit the motor
neuron branches to form neuromuscular junctions with several muscle fibers
General muscle function:
1. Contraction for locomotion and skeletal movement
2. Contraction for propulsion
3. Contraction for pressure regulation
Muscle terminology
myofiber or myocyte: a muscle cell
sarcolemma: the plasma membrane of a muscle cell
sarcoplasm: the cytoplasm of the muscle cell
sarcoplasmic reticulum: the endoplasmic reticulum of a muscle cell
sarcosome: the mitochondria of a muscle cell
sarcomere: the contractile or functional unit of muscle
Types of muscles
Types of muscles are based on the classification to be striated and voluntary, striated and
involuntary, non striated and involuntary (which make up the morphological and functional
classification) They include:
Skeletal muscle
Cardiac muscle
Smooth muscle, respectively.
Muscles (myocytes) are elongated cells ranging from several millimetres to about 10
centimetres in length and from 10 to 100 micrometres in width. These cells are joined
together in tissues that may be either striated or smooth, depending on the presence or
absence, respectively, of organized, regularly repeated arrangements of myofibril contractile
proteins called myofilaments. Striated muscle is further classified as either skeletal or cardiac
muscle. Striated muscle is typically subject to conscious control, while smooth muscle is not
Skeletal muscle
This type of muscle constitutes the muscle that is attached to the skeleton and controls motor
movements and posture. It is a striated muscle with cells that are elongated or tubular. They have
multiple nuclei and these nuclei are located on the periphery of the cell. Skeletal muscle fibres are a
multinucleated syncytium formed by the fusion of individual small muscle cells or myoblasts, during
development. They are filled with myofibrils of which are made up of myofilaments myosin (thick
filament) and actin (thin filament). Individual contractile units are called sacromeres. A myofibril
consists of many sacromeres. Longitudinal sections of skeletal muscle contains alternating pattern of
dark and light bands called A (anisotropic) and I (isotropic) band. The I band is bisected by a dense
zone called the Z line to which the thin filaments of the I band are attached. The nuclei are located
peripherally, immediately under the plasma. The thickness of each fiber is uniform throughout its
length and they do not branch out.
Skeletal muscle is sub-divided into two;
a) Slow twitch: These muscles are also called red muscles. They are dense in capillaries and rich in
mitochondria and myoglobin, giving the muscle its red colour. It can carry more oxygen and sustain
aerobic activity using fats or carbohydrates as fuel. They contract for a long period of time but with
little force.
b) Fast twitch: They contract quickly and powerfully but fatigue very rapidly, sustaining only short,
anaerobic bursts of activities before muscle contraction becomes painful. They contribute most to
the muscle strength and have greater potential for increase in mass. Fast twitch muscle/ Type II have
three subtypes IIa, IIx, IIb that vary in contractile speed and force generated.
Skeletal muscle is designed as a bundle within a bundle arrangement
The entire muscle is surrounded by a connective tissue called the epimysium.The muscle is made up
of smaller bundles known as fascicles. Fascicles are actually bundles of individual muscle cells
(myofibers or myocytes). These bundles are surrounded by a connective tissue sheath called the
perimysium.
Each fascicle is made up of several muscle cells known as myocytes. They may also be called
myofibers or muscle fibers. Each muscle cell is surrounded by a connective tissue sheath known as
the endomysium. This sheath is very important in the physiology of muscle contraction because it
electrically insulates the individual muscle cells from each other.
Cardiac muscle
This is the type of muscle is found in the heart and at the base of the venae cava as they
enter into the heart. Cardiac muscle cells are not as long as skeletal muscles cells and often are
branched cells. Cardiac muscle cells may be mononucleated or binucleated. In either case the nuclei
are located centrally in the cell. Cardiac muscle is also striated. In addition cardiac muscle contains
intercalated discs
Cardiac muscle also exhibit striation due to the presence of actin and myosin filaments arranged
into sacromeres. Cardiac muscle cells have only one or two nuclei that are centrally located. They
are joined to one another in a linear array. The boundary between two cells abutting each other is
called an intercalated disc. Cardiac muscle fibers branch and anastomose with one another.
Although made up of individual fibers, heart acts as a functional syncytium during contraction for
the efficient pumping of blood.
SMOOTH MUSCLE
This is the intrinsic muscle of the internal organs and blood vessels. It is also found in the iris
and ciliary body of the eye and associated with hair follicles. Smooth muscle cell are described as
spindle shaped. That is they are wide in the middle and narrow to almost a point at both ends.
Smooth muscle cells have a single centrally located nucleus. Smooth muscle cells do not have visible
striations although they do contain the same contractile proteins as skeletal and cardiac muscle,
these proteins are just laid out in a different pattern.
Smooth muscles are specialised for slow, prolonged contraction. Smooth muscle fibers are generally
arranged in bundles or sheets. Each fiber is fusiform in shape with tapered end. The single nucleus is
located in the central part of the fiber of which has a cork screw shape in longitudinal section due to
contraction of the muscle fiber during fixation. Fibers do not branch. They range enormously in size,
from 20 to 500mm. Smooth muscle fibers lie over one another in a staggered fashion. Smooth
muscle has the ability to secrete connective tissue matrix.
Function
Skeletal muscle
1.They carry out movements of the body.
2.They support the body.
3.They maintain the posture of the body.
Smooth muscle
It is responsible for the contractility of hollow organs, such as blood vessels, the
gastrointestinal tract, the bladder.
Cardiac muscle
Cardiac muscle is the muscle of the heart. It is self-contracting, autonomically regulated and
must continue to contract in rhythmic fashion for the whole life of the organism. Hence it has
special features.
Reference: Junqueira’s histology textbook
[email protected]