Nerve Tissue: Lecture 9 PDF

Nerve Tissue Anatomy Unit  Objective Understand the microscopic difference between excitable and non-excitable cells present in the nervous system.  Composition of Nerve Tissue Nerve Tissue consists of two types of cells: Neuron or nerve cell Supporting cells Cells...

Nerve Tissue Anatomy Unit  Objective Understand the microscopic difference between excitable and non-excitable cells present in the nervous system.  Composition of Nerve Tissue Nerve Tissue consists of two types of cells: Neuron or nerve cell Supporting cells Cells have very high ability to: Respond to stimuli Transmit impulses Nerve Tissue Nerve Tissue NEURON is the main nerve cell NEURON is the structural and functional unit of the nervous system. It consists of: Cell Body(3) (Perikaryon,Soma) Is the part of the neuron that contains the nucleus and surrounding cytoplasm, Dendrites (5) have many elongated processes specialized to receive stimuli Axon(1) axon (Gr. axon, axis), which is a single process specialized in generating and conducting nerve impulses to other cells (nerve, muscle, and gland cells). Motor Neuron Motor Neuron Cell body Dendrites Axon Covered by Myelin sheath  Classification of Neurons  According to the number of processes extending from the cell body: Multipolar neurons: Have one axon and two or many dendrites.Most neurons are multipolar e.g., motor neurons and interneurons Bipolar neurons: With one dendrite and one axon e.g., retina(sight), olfactory mucosa(smell), and the (inner ear) cochlear and vestibular ganglia(balance). Unipolar or pseudounipolar neurons: Have a single process that divide into two branches close to the perikaryon e.g. spinal ganglia (the sensory ganglia found with the spinal nerves) and in most cranial ganglia. Neurones According to their functional roles Motor (efferent) neurons control effector organs such as muscle fibers and exocrine and endocrine glands. Sensory (afferent) neurons are involved in the reception of sensory stimuli from the environment and from within the body. Interneurons form a communicating network between motor and sensory neurons(99.9%) Neuron Multipolar Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy Neuron's – cerebral cortex Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy Neuron's – spinal cord Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy  Cell Body The part of the neuron that contains the nucleus and surrounding cytoplasm. Nissl bodies (chromatophilic substance) : Are RER and free ribosomes which appear under the light microscope as clumps of basophilic material.  Nerve Fiber (Axon) All axons originate from a pyramid-shaped region, the axon hillock, arising from the perikaryon Nerve fibers are long nerve cell processes (axon cylinder, axon) The plasma membrane of the axon is often called the axolemma and its contents are known as axoplasm. Stain: osmium tetroxide; magnification: × 1000  Nerve Fiber (Axon) Myelinated nerve fiber, i.e., the axon is covered by a myelin sheath, which is rich in lipids. Every 0.8 to 1.0 mm, a node of Ranvier subdivides the myelin sheath into segments or internodes. Schwann cells (neurolemmocytes, peripheral glial cells) enfold the axon and form an insulating cover known as Schwann’s sheath (neurolemma). Stain: osmium tetroxide; magnification: × 1000 Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy  Nerve Organization & Coverings Endoneurium is the innermost layer of thin connective tissue surrounding a single axon immediately after Schwann. Perineurium is a connective tissue layer surrounding fascicles ( groups of axons with Schwann cells and endoneurium) Epineurium is outermost layer of dense irregular connective tissue surrounding the perineurium.  Sciatic nerve – cross section 1 Fascicle (nerve fiber bundle) 2 Perineurium 3 Epineurium 4 Artery 5 Vein 6 Adipose tissue Stain: alum hematoxylin; magnification: × 10 Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatom Glial Cells Glial cells (Neuroglia) or (Glia) (Greek "glue” Non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for the brain's neurons They occupy the entire space between neurons and separate nerve cells from blood vessels Glial Cells - Functions 1. Surround neurons and hold them in place 2. Supply nutrients and oxygen to neurons 3. Insulate one neuron from another 4. Destroy pathogens and remove dead neurons 5. Line the ventricles of the brain and central canal of the spinal cord.  Glial Cells - Types Astrocytes (macroglia) Oligodendrocytes Microgliocyte Ependymal cells Astrocytes Most abundant Deal with homeostasis – relate to vessels Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anat  Are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including : 1- biochemical support of endothelial cells that form the blood–brain barrier, 2- provision of nutrients to the nervous tissue, 3-maintenance of extracellular ion balance, 4- and a role in the repair and scarring process of the brain and spinal cord following traumatic injuries Astrocytes and nerve cells Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy Microglia(phagocytes): Microglia are the main resident immunological cells the CNS Oligodendrocytes: Closely related to neurons Provide myelin protection for CNS neurons  Ependymal Cells Are low columnar or cuboidal cells that Line the ventricles of the brain and central canal of the spinal cord Have cilia( movement of CSF) cerebrospinal fluid Long microvilli(absorption). Neurons and glial cells Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy Neuron and glial cells Kuehnel, Color Atlas of Cytology, Histology, and Microscopic Anatomy  Summary Nerve Tissue Cells: Neurons: Myelinated Non-myelintaed  Summary Neuroglial cells: Astrocytes Microglia Oligodendrocytes Ependymal cells