its neuroanatomy of cells of nervous system

1. CELLULAR ORGANIZATION OF
THE NERVOUS SYSTEM
PRESENTED BY
MUHAMMAD UZAIR KHAN
DPT
IPM&R-KMU

2. The highly specialized and complex nervous system consists of only two principal categories of cells,
(a) neurons
(b) neuroglia
Neurons:
Are the basic structural and functional units of nervous system.
The are specialized for reception, integration, interpretation, and onward transmission of
information.
Each neuron consists of a cell body also called soma or perikaryon or nerve cell body and its
processes called neurites.
A collection of nerve cell bodies in CNS are called nuclei, and out side the CNS ganglia.
The axons are generally referred to as nerve fibers.
CELLULAR ORGANIZATION OF THE NERVOUS SYSTEM

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4. ANATOMICAL CLASSIFICATION:
Pseudo unipolar neurons:
possess oval cell bodies, a single process emerges from the cell body that bifurcates into peripheral and central process.
They are found in dorsal root ganglia of spinal nerves and sensory ganglia of some cranial nerves.
Bipolar neurons:
They possess spindle shaped cell body from each end of body, thus have two processes one dendrite and one axon.
Found in olfactory epithelium of nasal cavity, retina of the eye ball, and sensory ganglia of vestibulocochlear nerves.
Multipolar neurons:
Have multipolar cell body from which emerges several dendrites and a single axon.
Mostly found in CNS e.g. motor neurons to skeletal muscles.
CLASSIFICATION OF NEURONS

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6. According to relative length of processes:
Golgi type I Neurons:
They have long axons, numerous and short dendrites.
Form tracts and peripheral nerves, e.g. pyramidal cells of cerebral cortex, purkinje cells of
cerebellum, and motor anterior cells of spinal nerves.
Golgi type II Neurons:
Axons of these neurons are morphologically similar to that of dendrites.
They are stare shaped and establish synaptic contacts with large number of neurons in their
neighbor hood. Found in cerebral and cerebellar cortex.
CLASSIFICATION OF NEURONS

7. Functional classification:
Sensory neurons:
Carry impulses from receptor to CNS.
TYPES:
Primary sensory neurons: cell bodies of these neurons lie outside the CNS.
Secondary neurons: cell bodies in CNS.
Tertiary neurons: cell bodies in thalamus.
Motor neurons:
Impulses from CNS to muscles and glands. Cell bodies of these neurons lie within the CNS, except those of
postganglionic neurons of autonomic nervous system.
CLASSIFICATION OF NEURONS

8. Types of motor neurons:
Divided into two types
Upper motor neurons:
The have cell bodies and axons in CNS. They form descending tracts of the brain and synapse
with the motor neurons of the cranial nerve nuclei in the brainstem and motor neurons of the
spinal nerves in the anterior horns of the spinal cord.
Lower motor neurons: have their cell bodies located in the brainstem and spinal cord.
Preganglionic neurons: the cell bodies of these neurons lie in the brain and spinal cord
Postganglionic neurons: the cell bodies of these neurons lie outside the CNS in lateral and
terminal autonomic ganglia.
CLASSIFICATION OF NEURONS

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10. The neuroglia are the interstitial or supporting cells of the nervous system.
Neuroglia in the central nervous system
Astrocytes:
Are the largest and most numerous, and form the main supporting tissue of the nervous system.
They are star-shaped as the name implies and possess many fine dendrite like processes with small swellings called foot-
processes.
They fill up most of the extracellular spaces among the neurons and their processes contact the surfaces of neurons and
capillaries of CNS.
They store glycogen, and also help in establishment of blood brain barrier.
Types
Cytoplasmic astrocytes: are found in the gray matter. Their processes are thicker and more branched than fibrous
astrocytes.
Fibrous astrocytes: are found mainly in the white matter. Their processes are long, slender, smooth and less branched.
Neuroglia

12. Ependymal cells:
Lines the ventricles of brain and central canal of spinal cord. They are of three types.
A) EPNDYMOCYTES: are cuboidal and columnar in shape with tuft of cilia on their luminal surfaces and
constitute the majority of the ependymal cells. The cilia helps in movement of CSF in cavities of brain
B) CHOROIDAL CELLS: present in choroid plexuses, secrete cerebrospinal fluid.
C) TANYCYTES: Ependymal cells in floor of fourth ventricle have long basal processes called tanycytes.
Neuroglia

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14. Oligodendrocytes:
Are smaller than astrocytes and as the name implies have fewer processes. They are found in clusters around the
neurons of gray matter, and along myelinated nerve fibers in white matter.
They form myelin sheath around axons in central nervous system.
Microglias: are smallest of the glial cells, capable of migrating through neural tissues. Microglia are derived from
phagocytic white blood cells that migrate from the blood into nervous system before birth.
They involve in inflammation and remove cell debris, wastes and pathogens that invade the CNS by phagocytosis.
Neuroglia

15. SATELLITE CELLS:
Surround nerve cell bodies in Peripheral ganglia and provide support and nutrition to them
SCHAWAN CELLS:
Form myelin sheath around axons in PNS.
Neuroglia in PNS

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17. Sensory Receptors
§ Structures specialized to respond to stimuli
§ Activation of sensory receptors results in depolarizations that trigger
impulses to the CNS
§ The realization of these stimuli, sensation and perception, occur in the
brain
Receptors

18. Receptor Classification by Stimulus Type
§ Mechanoreceptors – respond to touch, pressure, vibration, stretch,
and itch
§ Thermoreceptors – sensitive to changes in temperature
§ Photoreceptors – respond to light energy (e.g., retina)
§ Chemoreceptors – respond to chemicals (e.g., smell, taste,
changes in blood chemistry)
§ Nociceptors – sensitive to pain causing stimuli
Receptors

19. Receptor Class by Location: Exteroceptors
§ Respond to stimuli arising outside the body
§ Found near the body surface
§ Sensitive to touch, pressure, pain, and
temperature
§ Include the special sense organs

20. Receptor Class by Location: Interoceptors
§ Respond to stimuli arising within the body
§ Found in internal viscera and blood vessels
§ Sensitive to chemical changes, stretch, and
temperature changes

21. Receptor Class by Location: Proprioceptors
§ Respond to degree of stretch of the organs they occupy
§ Found in skeletal muscles, tendons, joints, ligaments, and
connective tissue coverings of bones and muscles
§ Constantly “advise” the brain of one’s movements
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