Basic Development of CNS
Written by D C MorganThe nervous system is dervied from ectoderm except microglia, which is mesodermal.
The CNS i.e., the brain and spinal cord develop from an elongated hollow ectodermal tube, the neural tube (Fig. 20). In its formation, first there appears a neural plate, which is a thickened ectodermal area on the dorsum of the embryo. This plate becomes […]
Tags: CNS, mesodermal, neuropores
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How does the Nervous system work
Written by D C MorganThe CNS receives a variety of sensory data. In response it issues a series of motor messages which are designed to cope with the situation. There are two ways in which this is done. The first is automatic— reflexes; the second involves consciousness— reactions.
A reaction is a complicated affair always involving consciousness. It requires an […]
Tags: CNS, Memory Traces, Stimuli
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The axons of efferent neurons
Written by D C MorganThe axons of efferent neurons (Ill)
leave the spinal cord by way of ventral roots (or leave the brain stem by way of cranial nerves) to end in relation to an effector, which may be either a muscle or a gland.
It may be noted that except for the effector neurons, the central nervous system mainly comprises […]
Tags: CNS
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Basic Neural Mechanism
Written by D C MorganWhile a neuron is the structural and func¬tional unit of nervous system, the structural and functional unit of basic neural mechanism is a reflex.
Reflexes : A reflex is an involuntary auto-matic response brought about by a sensory stimulus. It represents the first order of nervous activity in the body. The reflexes are mediated through neuron […]
Tags: CNS, Neuron, reflex arc
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Degeneration & Regeneration
Written by Dr.ChrisThe first reaction of a nerve cell to injury (physical trauma or loss of blood supply) is loss of function. In PNS when a nerve fibre i.e., axon is cut the following degenerative changes take place : (a) in the distal portion of severed axon, (b) in the proximal part of the axon, and (c) […]
Tags: CNS, PNS
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Environmental Sensory nerve endings receptors
Written by Dr.ChrisExteroceptors : respond to stimuli arising from external environment and are placed at or close to the surface of the body. They include :
General (cutaneous) receptors e.g., naked nerve endings, Pacinian corpuscles,
Meissner’s corpuscles, organs of Ruffini, end bulb of Krause.
Special receptors for special sense organs: rods and cones for vision; hair cells of the […]
Tags: CNS
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Supporting Cells of Nervous System
Written by Dr.ChrisThe supporting cells of nervous system include neuroglia and ependyma in CNS; satel¬lite cells and Schwann cells (p. 6) in PNS.
Neuroglia: Neurons in central nervous system are supported by a framework of non-conducting cells called neuroglia (Fig. 12). They are necessary for normal functioning of nervous sys¬tem. Neuroglial cells are far more numerous but much […]
Tags: Astrocyfls, CNS, Ependyma, Microglia, Neuroglia, Oligodendrocytes
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Transneuronal (Transynaptic) degeneration
Written by Dr.ChrisTransneuronal (Transynaptic) degeneration: In this, section of a nerve is followed by de-generation of the nerve cells with which they are in synaptic relation. Ex : cells of lateral geniculate body degenerate in section of optic nerve.
There is no regeneration of the cell bodies of the neurons, either inside or outside CNS; for once a […]
Tags: Chromatolysis, CNS, Neuroglia
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Sheath of Schwann
Written by D C MorganSheath of Schwann is a delicate transparent membrane composed of Schwann cells and lies outside the myelin sheath. It pro-vides nutrition to the axon. It is derived from neural crest (ectodermal).
(iv)Outside the sheath of Schwann each nerve fibre is surrounded by endoneurium de-rived from connective tissue (mesodermal).
In central nervous system myelin sheath is formed from […]
Tags: central nervous system, CNS, mesodermal
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Nodes of Ranvier
Written by D C MorganNodes of Ranvier (seen in longitudinal section and in teased preparations only) : An axon comes in contactwith many Schwann cells along its length. Each Schwann cell forms myelin sheath over a short segment of the axon. At the junction of any two such segments there is a short gap in the myelin sheath. Thus […]
Tags: CNS, Myelin sheath
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Ganglia
Written by Dr.ChrisGanglia
A ganglion is a collection of nerve cells located outside the CNS. There are two types of ganglia.
· Sensory ganglia (ganglia of conduction)
All sensory ganglia contain unipolar neurons except vestibular and cochlear ganglia, which are bipolar cells. Each ganglion has a thin connective tissue capsule within which the nerve cells are peripherally placed. Each ganglion […]
Tags: CNS, ganglia of conduction, ganglia of synapse, neurons
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Motor (efferent) neurons
Written by Dr.Chris Motor (efferent) neurons are also multipolar cells. They are found in the grey matter of CNS. Their dendrites lie within CNS, but the axons leave the CNS to run in peripheral nerves to supply skeletal muscles.
Within the skeletal muscle each axon breaks up into a […]
Tags: ANS, CNS, neurons
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Internuncial (association) neurons
Written by Dr.Chris Internuncial (association) neurons are multipolar cells. They are also termed interneurons.
They are confined within CNS and transmit nerve impulses from sensory to motor neurons and also connect different groups of nerve cells within CNS.
Tags: CNS, neurons
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Sensory (afferent) neurons
Written by Dr.ChrisSensory (afferent) neurons are mostly unipolar neurons except vestibular and cochlear ganglia, which are bipolar neurons. They bring information from sense organs to the CNS. The cell bodies of afferent neurons lie outside the CNS in sensory ganglia of cranial nerves and dorsal root ganglia […]
Tags: Bipolar neurons, CNS, neurons
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ANATOMY OF NEURON
Written by Dr.ChrisA neuron is the structural and functional unit of nervous system composed of a cell body and one or more processes. The neurons are specialized for the receipt, processing and transmission of information. The processes are the axon and the dentrite. Each neuron has only one axon, while the dendrite may be one or many(Figs. […]
Tags: CNS, nervous system, neurons, Perikaryon
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