Summary

This document explains the different types of muscle tissue in the human body, including their structures and functions. It covers skeletal, smooth, and cardiac muscle, emphasizing their roles in movement and vital processes. The document is very detailed.

Full Transcript

# 7. TEJIDO MUSCULAR ## 7.1 DEFINICIÓN - Un músculo es un órgano contráctil - Tiene la propiedad de disminuir su longitud mediante un estimulo - It is part of the human and animal body - It is composed of muscle tissue - The muscles are connected to the skeleton or form part of the structure of org...

# 7. TEJIDO MUSCULAR ## 7.1 DEFINICIÓN - Un músculo es un órgano contráctil - Tiene la propiedad de disminuir su longitud mediante un estimulo - It is part of the human and animal body - It is composed of muscle tissue - The muscles are connected to the skeleton or form part of the structure of organs and apparatuses. - The word muscle comes from the diminutive Latin musculus, mus (rat) and the diminutive ending -culus - This comes from the fact that Romans thought muscles looked like little rats contracting. - Muscles are surrounded by a membrane of connecting tissue called fascia. - The functional and structural unit of the muscle is the muscle fiber. - The muscular system contains more than 600 muscles - They are responsible for generating voluntary or involuntary movement - Skeletal muscles and visceral muscles - Some muscles can be categorized as mixed. ## 7.2 CLASSIFICATION OF MUSCLE TISSUE - The muscular system is formed by muscles and tendons - The main function of the muscles is to contract in order to generate movement and accomplish vital functions. - There are three groups of muscles, according to their arrangement: ## 7.2.1 STRUCTURE OF THE STRIATED MUSCLE - The basic unit of every muscle is the myofibril, a thin thread-like structure - This structure is very small - It is formed by complex proteins. - Each muscle cell or fiber contains several myofibrils. - These are composed of two types of filaments: thick and thin - These filaments are arranged regularly. - Each thick filament contains hundreds of myosin protein molecules. - The thin filaments contain two chains of the protein actin. - The myofibrils are formed by rows that alternate between thick and thin filaments - These filaments are located end-to-end with their ends overlapping - During muscle contractions, these rows interdigitate. - They slide over each other by means of cross bridges which act as wheels - The energy needed for this movement comes from dense mitochondria that surround the myofibrils. - **Sarcomere:** The anatomical and functional unit of the muscle. - It is enclosed by two Z lines - The sarcomere includes an A zone (anisotropic) and two I half zones (isotropic): - **Thick filaments:** They are formed by a protein called myosin - They are located in the A bands - **Thin filaments:** They are composed of another protein called actin - They are attached to each Z line - They extend to the center of the sarcomere from the I bands to the A bands. - **I bands:** They only contain thin actin filaments - **A bands:** They contain both thin and thick filaments - Thick and thin filaments are connected by bridges. - **Z lines:** The muscle fiber is separated by an outer membrane called sarcolema or cell membrane - This membrane exhibits invaginations along the Z lines of the sarcomeres. ## 7.2.2 SMOOTH MUSCLE - Smooth muscle forms the walls of the viscera - It is not under voluntary control - It does not contain striations. - It has a similarity with skeletal muscle - It does not have a Z line. - Instead, it has dense spheres - These replace the Z lines. - Smooth muscle can be unitarian or multiunitarian. - **Unitarian:** There is a connection (gap junctions) between every fiber. - **Multiunitarian:** There is no connection between the fibers, so they act independently. - Smooth muscle and its function are very important. - For example, smooth muscle exists in the gastrointestinal tract - This smooth muscle is responsible for peristalsis. - Smooth muscle contraction is much more prolonged than skeletal muscle contraction - This is because it does not consume as much energy - The contraction phase is longer than the skeletal muscle contraction phase. - This is despite the fact that smooth muscle uses the same number of steps in the process - However, smooth muscle consumes less energy (the same amount of ATP, but less energy consumption) - It has a slower metabolism and energy expenditure than skeletal muscle. - The time and distance of smooth muscle contraction is greater than that of the skeletal muscle. - Smooth muscle contraction and relaxation are controlled by the enteric and autonomic nervous system - In addition, it is controlled by acetylcholine and adrenaline. ## 7.2.3 CARDIAC MUSCLE: MYOCARDIUM - Myocardium (mio: muscle and cardo: heart) is the tissue that makes up the heart - This is the muscle that is responsible for contracting the heart - Cardiac muscle is responsible for pumping blood throughout the circulatory system. - It contains an abundance of capillaries - These are necessary for supplying the heart with energy needs. - Cardiac muscle typically functions involuntarily and rhythmically - It does not require nerve stimulation - This is because it is a myogenic muscle, also known as autoexcitable. - There different specialized cardiac muscle tissues - These include, the auricular muscle, ventricular muscle, and conduction muscle. - These tissues can be grouped into two sections: - **Contraction muscle:** Auricular and ventricular muscle - **Cardiac conduction muscle:** Conduction muscle. ## 7.2.4 FUNCTION OF MUSCLE TISSUE - The main function of muscle tissue is movement - There are three types of movement: - **Movement of the internal structures:** Composed of smooth muscle. - This includes vessels, visceral walls, and glands. - **External movement:** Characterized by manipulation and movement in our environment. - This is made up of striated muscle. - **Automatic movement:** The muscle works on its own. - This is the cardiac muscle, which is striated. - Muscle is a tissue with a contrast in movement, it is divided into striated, smooth, and cardiac. - Striated muscle is voluntary - This muscle is found throughout the body, attached to long bones (such as the femur). - Smooth muscle is visceral and involuntary. - It can be found in the viscera and other internal organs. - Cardiac muscle is more important. - It can be found in the heart - It is made up of clear and dark fibers - It functions involuntarily. - The main purpose of this muscle is to maintain tone in the viscera and blood vessels - It helps us maintain posture - It is responsible for movement. - The muscles of the extremities (skeletal muscle) contract - They are able to move the bones. - The flexors contract - This causes the limb to bend. - The extensors contract - This causes the limb to straighten. - The heart and artery muscles contract - This causes the blood to be mobilized. - The muscles of the intestines, stomach, and esophagus contract rhythmically - This helps food move through the digestive tract. ## 7.3 NERVOUS TISSUE ## 7.3.1 GENERALITIES - The nervous system is a group of organs, ganglia, and nerve fibers. - They are dispersed throughout the body. - Their function is to regulate the body's functions. - The anatomical and functional unit at the microscopic level is the neuron. - These specialized cells form the nervous tissue. ## 7. 3.2 NERVOUS CELL OR NEURON - Each nerve cell or neuron consists of a central part or cell body - This body contains the nucleus and perikaryon. - The perikaryon is the cytoplasm that surrounds the nucleus. - The neuron also contains two types of extensions, dendrites and axons. - **Dendrites:** These are short extensions from the neuron's cell body. - They are responsible for receiving stimuli. - **Axon:** An elongated extension from the neuron's cell body. - It is important in transmitting impulses from the neuron's cell body to other cells. ## 7. 3.3 TYPES OF NEURONS - There are three types of neurons: - **Unipolar neurons:** They only have one extension. - They can be found in the ganglia of the posterior root of the spinal nerve. - **Pseudounipolar neurons:** These neurons are bipolar. - However, these extensions fuse as they approach the cell body - They form one single extension. - **Bipolar neurons:** These neurons emit an extension from each end of the cell body. - These can be found in the bipolar cells of the retina and the cells of the vestibular and cochlear ganglia. - **Multipolar neurons:** They have a large number of dendrites in addition to the axon. - Examples include: - Pyramidal neurons of the Betz cell, in the cerebral cortex. - Bottle-shaped neurons of Purkinje, in the cerebellum. - Star-shaped neurons of the anterior horn, in the spinal medulla. ## 7.3.4 NEUROGLIA OR GLIA - The name suggests its function - This is the glue that holds the nervous tissue together. - It is composed of supportive cells - There are more supportive cells than neurons. - These include the ependyma. - There are four types of supporting cells. - **Astrocytes:** These cells have a star shape. - There are two types of astrocytes: - **Protoplasmic astrocytes:** They are found mainly in the gray matter. - They have highly branched extensions - **Fibrous astrocytes:** They have long and thin extensions. - They are found mainly in the white matter. - **Oligodendrocytes:** These glial cells have fewer extensions and these extensions are shorter than astrocytes. - They form and maintain the myelin sheaths of the fibers of the central nervous system. - **Microglia:** These small cells have a reduced nucleus. - They have a large number of thin extensions. - They are phagocytic cells. - Their function is to defend the nervous system against infection and injury. - **Ependyma:** Composed of cuboidal epithelium. - It lines the cavities of the brain and the central canal of the spinal cord. ## 7. 3.5. COVERING OF NERVE FIBERS - A nerve fiber is a single axon with its corresponding nerve sheaths. - All peripheral axons are surrounded by a sheath of Schwann cells. - In the case of larger peripheral axons, Schwann cells develop a layer called the myelin sheath. - This distinguishes between myelinated and non-myelinated nerve fibers. - **Myelinated nerve fibers:** There is a small opening called the Node of Ranvier between two adjacent myelinated segments. - **Non-myelinated fibers:** They only have Schwann cells covering them. - These Schwann cells form the sheath of Schwann. ## 7. 3.6 GANGLIA - A ganglion is a cluster of neuronal cell bodies located outside the central nervous system. - They are classified into: - **Sensory ganglia:** These are spindle-shaped enlargements. - They are located in the posterior root of each spinal nerve and along the path of the cranial nerves V, VII, VIII, IX, and X. - **Autonomic ganglia:** These ganglia are irregularly shaped. - They are found along the path of the efferent fibers of the autonomic nervous system - They are located in the paravertebral sympathetic chains. - They surround the roots of the large visceral arteries in the abdomen. - They are near or embedded in the walls of several visceral organs.

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