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The Nervous System
By:Dr.ISAM ZABIBA
I. Neurons
II. Glial Cells
III. CNS
IV. PNS
V. ANS
Neuron Consists of:
• A Cell Body – contains nucleus, mitochondria, no reproductive apparatus
• Dendrites: highly branched extensions of the cell body. Conduct impulses towards the
cell body
• Axon: a single long process. Conducts impulses away from the cell body.
Its cytoplasm= axoplasm ,
plasma membrane=axolemma.
I. Neurons
F. Perikaryons
1. large nucleus
2. rER
a. Nissl bodies
3. Golgi complex
4. mitochondria
5. neurofilaments
6. lipofuscin
Structural of Neurons
1. multipolar neurons: more than two processes one is the axon and the rest are denderites
eg. motor neuron
2. bipolar neurons: have two processes one is axon and other one is denderites
eg.olfactory cells.
3. pseudounipolar neurons : have a single process close to the perikaryon.
eg. Dorsal root gangalia.
Neurons location
• Bipolar neurons
1. cochlear & vestibular ganglia
2. retina
3. olfactory epithelium
• Pseudounipolar neurons
1. dorsal root ganglia
2. sensory cranial ganglia
• Multipolar neurons
1. All other neurons
Neurons Functional types
1. sensory (afferent)
a. pseudounipolar
2. Interneurons
a. multipolar
3. motor (efferent)
a. multipolar
Types of Synapses
• Axodendritic
– Between axon terminals of one neuron and dendrites of another
– Most common type of synapse
• Axosomatic
– Between axons and neuronal cell bodies
• Axoaxonic, dendrodendritic, and dendrosomatic
– Less common types of synapses
– Function not as well understood
Structure of the Neuron
Myelin Sheath
-a white, multi layered, fatty covering for some nerve processes.
- arranged in segments, separated by Nodes of Ranvier (enables salutatory conduction)
Function
Insulation of nerve process
Increased speed of conduction
Neurilemma(Schwann cells)
outer layer of myelin sheath
essential for regeneration
II. Glial Cells
A. Oligodendrocytes:
Produce myeline sheath in CNS
B-Schwann cells
Produce myeline sheath in PNS
Wrap around portion of only one
axon to form myelin sheath
C. Astrocytes
Regulate extracellular brain fluid
composition
Promote tight junctions to form
blood-brain barrier
D. Ependymal cells:
Line brain ventricles and spinal
cord central canal
Help form choroid plexuses that
secrete CSF
E. Microglia:
Phagoctic cells in nervous tissue.
F. Satellite cells
Surround neuron cell bodies in
ganglia,
provide support and nutrients
III. Choroid Plexus
The choroid plexus is located along ventricular walls in the CNS where the wall is composed
only of pia mater and cuboidal epithelium. The choroid plexus produces CSF. It is located in
the lateral, third, and fourth ventricles.
IV. CNS
A. Grey matter & white matter
1. perikaryons (cell soma)
2. myelinated axons
B. Cerebral Cortex
1. 6 layers from pia to WM
2. cytoarchitectonics
3. pyramidal neurons
a. apical dendrite
b. basal axon
C. Spinal Cord
1. central canal (ependymal cells)
2. dorsal horn
3. ventral horn
a. motor neurons
4. dorsal, lateral, ventral white columns
D. Cerebellum
1. molecular layer
2. Purkinje cell layer
3. granular layer
E. Meninges
1. Dura mater
2. Arachnoid membrane
a. subarachnoid space
b. CSF
3. Pia mater
4. Layers are visible around the optic nerve
V. PNS
A. Nerve fibers
1. nuclei = Schwann cells
B. Sensory ganglia
1. dorsal root ganglion
2. cranial nerve ganglia
a. geniculate ganglion
3. pseudounipolar neurons
4. satellite cells
Nerves
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Endoneurium – layer of delicate connective tissue surrounding the axon
Nerve fascicles – groups of axons bound into bundles
Perineurium – connective tissue wrapping surrounding a nerve fascicle
Epineurium – whole nerve is surrounded by tough fibrous sheath