Tejido Muscular PDF

# 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.