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NERVOUS TISSUE

NERVOUS TISSUE. Forms the nervous system which is divided into: Central Nervous System (CNS): Brain Spinal cord Peripheral Nervous System (PNS): Cranial nerves Spinal nerves Neurons (nerve cells): The units of nervous tissue. They receive and transmit impulses.

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NERVOUS TISSUE

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  1. NERVOUS TISSUE • Forms the nervous system which is divided into: • Central Nervous System (CNS): • Brain • Spinal cord • Peripheral Nervous System (PNS): • Cranial nerves • Spinal nerves • Neurons (nerve cells): The units of nervous tissue. They receive and transmit impulses. • Neuroglialcells: do not receive or transmit impulses; instead, they support neurons.

  2. NEURONS • The units of nervous tissue. They receive and transmit nerve impulses to & from the CNS. • A neuron = nerve cell body + all its processes: • One axon. • One or more dendrites.

  3. Types of Neurons • Unipolar. • Bipolar. • Multipolar.

  4. Unipolar Neurons • Formerly called pseudounipolar. • Only one process that divides into a peripheral branch (dendrite) and a central branch (axon). • Present in the dorsal root ganglia of spinal nerves.

  5. Bipolar Neurons • Two processes: a single dendrite and a single axon. • Present in: • Nasal cavity (olfactory epithelium). • Inner ear. • Retina.

  6. Multipolar Neurons • The most common type. • Multiple dendrites and a single axon. • Present throughout the nervous system: e.g. • Stellate cells: motor neurons in spinal cord. • Pyramidal cells: in cerebral cortex. • Purkinje cells: in cerebellum.

  7. Nerve Cell Body • Nucleus: spherical, central with prominent nucleolus. • Cytoplasm: • Abundant rER & polyribosomes. • Prominent Golgi. • Many mitochondria. • Only 1 centriole. • Microtubules, neurofilaments. Nissl bodies

  8. Nerve Cell Processes

  9. Nerve Fibers • A nerve fiber = any long process of a nerve cell (axon or dendrite). • Types of nerve fibers: • Myelinated: • Covered by myelin sheath formed by Schwann cells in PNS and oligodendrocytes in CNS. • In white matter of CNS and all peripheral nerves. • Unmyelinated: • Not covered by myelin sheath. • In grey matter of CNS and terminal parts of all peripheral nerve fibers.

  10. Peripheral Nerve Trunk • The whole nerve is covered by a C.T. covering, the epineurium. • Consists of parallel myelinated nerve fibers, arranged in bundles, separated by C.T. septa, the perineurium. • The individual nerve fibers are separated by C.T., endoneurium. Epineurium Perineurium Endoneurium

  11. NEUROGLIAL CELLS • Supportive and protective to neurons. They do not receive or transmit nerve impulses. • All are present in CNS except Schwann cell (in PNS). • Types: • Astrocytes: nutritive function. • Oligodendrocytes: formation of myelin in CNS. • Microglia: phagocytic (defence). • Schwann cells: formation of myelin in PNS.

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