Evaluate and distinguish between the anatomical and functional divisions of the nervous system.

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Neurology - The medical science that deals with the nervous system and disorders affecting it.

Central Nervous System (CNS) - The gross anatomical subdivision of the nervous system consisting of the brain and spinal cord housed in the dorsal body cavity and protected by the bones of the skull and vertebral column and the three connective tissue meninges; this system is the major rapid response control system for the entire organism.

Peripheral Nervous System (PNS) - The gross anatomical subdivision of the nervous system consisting of the nerves (with sensory = afferent and motor = efferent components) which project from the brain and spinal cord, along with the various visceral ganglia and the various sensory receptors distributed throughout the body.

Somatic Nervous System (SNS) - A functional subdivision of the nervous system; those neurons which respond to stimuli from the external environment and conduct somatic afferent sensory impulses from cutaneous and special sense receptors (exteroreceptors) to the CNS, and those somatic efferent motor neurons which conduct impulses from the CNS to skeletal muscle tissue.



Autonomic Nervous System (ANS) - A functional subdivision of the nervous system; those visceral sensory neurons (interoreceptors) which respond to stimuli from the internal environment and conduct impulses from visceral organs to the CNS, and, especially, those visceral motor neurons which convey impulses from the CNS to smooth and cardiac muscle tissue, and glands; the motor part of the ANS consists of the sympathetic division and the parasympathetic division.



Parasympathetic Division of ANS - The functional subdivision of the ANS which dominates in controlling the body for metabolic "business as usual"; its preganglionic fibers originate in brain stem and exit with certain cranial nerves or in the lateral horns of the sacral spinal cord (thus its alternative label of the "craniosacral" division), have relative long axons, and synapse with their postganglionic sympathetic neurons in the parasympathetic ganglia located in the walls of visceral effector organs (smooth muscle, cardiac muscle, endocrine glands or exocrine glands); its postganglionic axons are relatively shorter and synapse with various effector organs; all parasympathetic cells, preganglionic and postganglionic, are cholinenergic, i.e., they release the neurotransmitter acetylcholine.

Sympathetic Division of ANS - The functional subdivision of the ANS which prepares the body for muscular exertion or stressful activities ("fight or flight"); its preganglionic fibers originate in the lateral horns of the thoracic and lumbar spinal cord (thus its alternative label of the "thoracolumbar" division), have relative short axons, and synapse with their postganglionic sympathetic neurons in the sympathetic chain/trunk ganglia or the celiac or mesenteric ganglia; its postganglionic axons are relatively longer and synapse with various visceral effector organs (smooth muscle, cardiac muscle, endocrine glands or exocrine glands); most sympathetic postganglionic cells are adrenergic, i.e., they release the neurotransmitter norepinephrine; the exception being cholinergic stimulation of sweat glands.

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ldkirk

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Anatomical divisions of nervous system: Nervous system is made up of two principle populations namely, neurons and supporting cells. Supporting cells are called as “neuroglia (glia = glue) or glial cells.” The nerve cells of the neurons form the gray matter and the nerve fibres from the white matter. Human brain contains more supporting cells (glial cells) than neurons.

Brain and spinal cord together form the central nervous system. So, motor and sensory neurons enter and leave brain, and they are not abundant cell type of brain.

Central neuroglial cells: There are four types of glial cells in the CNS. They are                                                                                                           

Microglia (smallest neuroglial cells derived from monocytes)

Astrocytes (star shaped cells present throughout the brain)

Oligodendrocytes and (they produce myelin sheath around the nerve fibres)

Ependymal cells.

Peripheral neuroglial cells: PNS contains two types of glial cells. They are,

Schwann cells (major glial cells of PNS and prove myelin sheath around the nerve fibres)

Satellite cells (they present on the exterior surface of the PNS neurons and provide physical support).

The functional unit of nervous system is neuron.

A typical neuron consists of,

Nerve cell

Axon

Dendrite
Dendrites: These are the short fibres arising from the body of the nerve cell. They act as receptors of impulses and conduct impulses towards the cell body. The junction between the axon of one neuron and the dendrite of another neurone is called as synapse. Neurone above the synapse is called presynaptic neuron and neuron below the synapse is called post synaptic neuron.

Nerve cell: Nerve cell or cell body has a nucleus and highly specialised protoplasm. The body of the nerve gives rise to nerve fibres. The nerve cells of the neurons form the gray matter, which is found in the periphery of the CNS, sometimes they are also found in ganglia (group of neurons outside the CNS).

Axon: Also called nerve fibre and this arises from the body of each nerve cell. The impulse generation and conduction occurs here. Axons conduct impulses in one direction only (towards the axon terminals). Axonal terminals contain stored neurotransmitters. The nerve fibres form the white matter, which is found inside the CNS.

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