Human Histology: Muscle, Nervous, and Bone Tissue Explained
Muscle Tissue Structure and Function
Large cylindrical cells are called fibers. These cells contain a large number of mitochondria due to high energy expenditure, are multinucleated, and possess a specialized membrane (sarcolemma) and cytoplasm (sarcoplasm). Electron microscopy reveals repeating structures called sarcomeres, which contain ordered protein fibrils forming distinct bands.
Muscle Contraction Mechanics
When a muscle contracts, fibers slide past one another, decreasing the sarcomere length and causing the H-band to almost completely disappear.
Types of Muscle Tissue
- Skeletal Muscle: Characterized by rapid, voluntary contraction. These fibers are elongated and composed of myofibril proteins (actin and myosin).
- Cardiac Muscle: Features rapid, involuntary contraction with a striated appearance.
- Smooth Muscle: Characterized by slow, involuntary contraction. Located in the walls of blood vessels and hollow organs such as the stomach, bladder, and uterus.
Nervous Tissue
Nervous tissue functions via nerve impulses, which are electrochemical currents. It is composed of two primary cell types: neurons and glia.
Neurons: The Functional Unit
Neurons are the structural and functional units of the nervous system. Once mature, they lose their ability to divide; the number of neurons is established at birth, and they cannot regenerate if they die.
Bone and Hematopoietic Tissue
Compact Bone Tissue
Located in the shafts of long bones and the exterior of all bones, compact bone is organized into the Haversian System:
- Haversian Canal: Contains blood vessels for nourishment and nerves for sensation. These canals communicate via Volkmann's canals.
- Osteocytes: Bone cells arranged in concentric lamellae, communicating through small channels called canaliculi.
Hematopoietic Tissue
This tissue is responsible for blood cell formation. It is primarily located in the spleen, lymph nodes, thymus, and red bone marrow, which serves as the most important hematopoietic center.