Man and his environment Dr. Elriah M. Makie 0122858517
Nervous Tissue BSc.M.Sc.MBBS
Introduction The nervous system is divided into two main parts: The central nervous system (CNS) comprising the brain and spinal cord. The peripheral nervous system (PNS) comprising the nerves which run between the CNS and other tissues, together with nerve 'relay stations' termed ganglia
Introduction The nervous system is designed to deliver rapid and precise communication between different parts of the body by the action of specialised nerve cells called neurones. These highly specialised cells are interconnected and function togather and process information and then generate appropriate response signals.
Introduction Functionally, the nervous system is divided into the somatic nervous system which is involved in voluntary functions and the autonomic nervous system which exerts control over many involuntary functions. Histologically, the entire nervous system merely consists of variations in the arrangement of neurones and their supporting tissues.
Histology of neural tissue Two types of neural cells in the nervous system: Neurons - For processing, transfer, and storage of information Neuroglia For support, regulation & protection of neurons
Neuroglia (glial cells) CNS neuroglia: astrocytes oligodendrocytes microglia ependymal cells PNS neuroglia: Schwann cells (neurolemmocytes) satellite cells
Classification of neurons Structural classification based on number of processes:
Multipolar neuron multiple dendrites & single axon most common type
Bipolar neuron two processes coming off cell body one dendrite & one axon only found in eye, ear & nose
Unipolar (pseudounipolar) neuron single process coming off cell body, giving rise to dendrites (at one end) & axon (making up rest of process)
Classification of neurons Functional classification based on type of information & direction of information transmission: Sensory (afferent) neurons transmit sensory information from receptors of PNS towards the CNS most sensory neurons are unipolar, a few are bipolar Motor (efferent) neurons transmit motor information from the CNS to effectors (muscles/glands/adipose tissue) in the periphery of the body all are multipolar Association (interneurons) transmit information between neurons within the CNS; analyze inputs, coordinate outputs
Anatomical organization of neurons Neurons of the nervous system tend to group together into organized bundles The axons of neurons are bundled together to form nerves in the PNS & tracts/pathways in the CNS. Most axons are myelinated so these structures will be part of white matter The cell bodies of neurons are clustered together into ganglia in the PNS & nuclei/centers in the CNS. These are unmyelinated structures and will be part of gray matter
Anatomical structure of Nerves
Myelin Sheath is formed by 2 types of Glia The myelin sheath is the wrapping seen around the axons of some neurons. Oligodendrocytes form myelin sheaths on axons in the CNS Schwann cells form myelin sheaths on axons in the PNS Gaps between myelin sheath cells are the Nodes of Ranvier. 21
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