2. The Nervous system has three major functions:
Sensory – monitors internal & external environment through presence
of receptors
Integration – interpretation of sensory information (information
processing); complex (higher order) functions
Motor – response to information processed through stimulation of
effectors
muscle contraction
glandular secretion
5. Histology of neural tissue
Two types of neural cells in the nervous system:
Neurons - For processing, transfer, and storage of information.
Organization
Cell body or soma or perikaryon
Dendrites: Input
Axons: Output
Neuroglia or supporting cells – For support, regulation & protection of
neurons
6. • Neurons have 2 special properties:
1. Excitability:
ability to respond to physical or chemical stimuli by generating
an electrical impulse.
2. Conductivity:
ability to conduct electrical impulse to other parts of body.
11. •Most axons of the nervous system are surrounded
by a myelin sheath (myelinated axons)
•The presence of myelin speeds up the
transmission of action potentials along the axon
•Myelin will get laid down in segments
(internodes) along the axon, leaving unmyelinated
gaps known as “nodes of Ranvier”
•Regions of the nervous system containing
groupings of myelinated axons make up the
“white matter”
•“gray matter” is mainly comprised of groups of
neuron cell bodies, dendrites & synapses
(connections between neurons)
of Ranvier
12. • Dendritic spines: site for synapse
• Collateral branch: axons side branching
• Nissl bodies: RER+Ribosome (clumps of basophilic material)
• Owl’s eye appearance: prominent nucleolus in nucleus.
• Cytoskeleton: consist of neurofilaments & microtubules
• Dendrites donot have Golgi apparatus
15. Unipolar (pseudounipolar)
neuron
• single process coming off
cell body, giving rise to
dendrites (at one end) &
axon (making up rest of
process)
•Found in dorsal root of
spinal nerve & sensory
ganglia.
16. Bipolar neuron
• two processes coming off
cell body – one dendrite &
one axon
• only found in eye, ear &
nose
17. Multipolar neuron
• multiple dendrites & single
axon
• most common type i.e.
pyramidal cells of cerebral
cortex, purkinje cells of
cerebellar cortex & anterior
horn cells of spinal cord.
18. 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
• are the most common type of neuron (20 billion)
• are all multipolar
19. Classification of neurons
• A/c to Length of their Axons:
• Golgi type I:
possess many dendrites & a very long axons that
leaves the grey mattar & passes to other
regions in CNS.
• Golgi type II:
possess many dendrites & a short axons that
donot leaves the grey mattar
20. The Synapse
• Junction between two cells
• Site where action potentials in one cell cause action
potentials in another cell.
• Impulse transmission at synapses can occur
- Chemically
- Electrically
21. chemical synapse:
- a presynaptic knob or axonal ending of one neuron it contains besides mitochondria and
neurofilaments a great number of synaptic vesicles, in which neurotransmitters are
stored.
• a synaptic cleft - there is narrow space, about 20 nm, separating membrane of
presynaptic from post synaptic membrane.
- a postsynaptic membrane - there is a membrane of the next neuron and/or effector cell
in w/c N.T are released.
22.
23. • Electrical Synapse:
- besides chemical synapses, in which a chemical
substance mediates the transmission of the nerve
impulse, there are the electrical synapses
- nerve cells are linked through a gap junction
- electrical synapses are not numerous as chemical
synapses
24. Types of synapses
• Axodendritic = axon to dendrite
• Axosomatic = axon to cell body
• Axoaxonic = axon to axon
25.
26. Peripheral Nerves
• Composed of bundles of nerve fibres.
• Epineurium:
- Each P.N is surrounded by a sheath of dense irregular C.T.
• Perineurium:
- Nerve fibres are arranged in bundles or fascicles w/c are surrounded
by C.T tissue sheath.
• Endoneurium:
- Each nerve fibres is surrounded by thin layer of C.T.
27.
28. Ganglia
• Collection of nerve cell bodies outside the CNS.
• Two types:
• Sensory ganglia.
• Autonomic ganglia.
29. Neuroglia (glia cells)
• Supporting cells
• 2 types:
1. Neuroglia proper:
consist of neuroglial cells that occur b/w
neurons.
2. Ependymal cells:
lines cavities in the brain & spinal cord
32. Astrocytes
• Star shaped cells with many branching processes.
• Numerous & largest
• Large, central, spherical nuclei.
• Cytoplasm contain bundles of intermediate filament w/c extend
in to processes.
• Few processes end in small expansions called perivascular end
feet.
33. • 2 sub types:
1. Protoplasmic:
found in grey matter of brain & spinal cord.
processes are short, thick but branched.
2. Fibrous:
found in white matter.
fewer branch processes, thinner, straighter &
longer than those of protoplasmic astrocytes.
34. Functions
• Create supportive framework for neurons
• Create “blood-brain barrier”
• Monitor & regulate interstitial fluid surrounding neurons
• Secrete chemicals for embryological neuron formation
• Stimulate the formation of scar tissue secondary to CNS injury
(fibrous astrocyte)
• Exchange O2, CO2 & nutrient b/w BV & neurons.
35. Oligodendrocytes
• Smaller cells, contain smaller, rounder & denser nuclei.
• Shorter & fewer processes.
• No perivascular feet.
• No intermediate filament.
• Astrocyte & oligodendrocyte are collectively called Macroglia.
36. • A/c to location, D/D in to 2 subtypes:
1. Interfascicular:
found in white matter lying b/w nerve fibres.
create myelin sheath around axons of neurons
in the CNS.
2. Perineuronal:
also called satellite oligodendrocyte.
found in grey matter.
closely a/s with perikarya of neurons.
37. Microglia
Small, elongated cells with rod shaped nuclei.
No intermediate filament.
Have delicate tortuous processes w/c bear spines.
Present in grey as well as white matter & in close
relation with BV.
phagocytize cellular wastes & pathogens.
“brain macrophages”
Secrete immunoregularory cytokines.
38. Ependymal cells
Cuboidal or low columnar cells.
line ventricles of brain & central canal of spinal
cord called ependyma. (As epithelium)
produce, monitor & help circulate CSF
(cerebrospinal fluid)
Cells are bounded with junctions located at apical
surface.
Also contain microvilli as well as cilia.
Microvilli absorp whereas Cilia facilitate
movement of CSF.
39. Schwann cells
surround all axons of neurons
in the PNS creating a
neurilemma around them.
Neurilemma allows for potential
regeneration of damaged axons
creates myelin sheath around
most axons of PNS
Satellite cells
support groups of cell
bodies of neurons within
ganglia of the PNS
40. Grey & White Matter
• Grey Matter consists mainly of nerve cell bodies, also
contain unmyelinated & myelinated nerve fibres (mostly
unmyelinated)
• White Matter consist of unmyelinated & myelinated
nerve fibres (mostly myelinated) but donot have nerve
cell bodies.
41. • The central nervous system is divided into gray matter and
white matter, reflecting the concentration of perikarya.
• Gray matter contains the perikarya of neurons and their
closely related processes, whereas white matter is composed
chiefly of bundles or masses of axons and their surrounding
sheaths.
• In the spinal cord, gray matter has a central location
surrounded by white matter; in the cerebral and cerebellar
cortices, gray matter is at the periphery and covers the white
matter.
42. Blood brain barrier
• Highly selective functional barrier.
• Prevents the passage of antibiotics, bacterial toxins, toxic drugs
etc from blood streams to the neural tissues.
• It depends on tight junctions b/w endothelial cells lining the
blood capillaries.
• Perivascular end feet of astrocyte maintain the junctions b/w
endothelial cells of continuous capillaries of brain & spinal cord.
43. Cerebral Cortex
• The neuronal cells of the cortex consist of six main cell types.
These are the pyramidal cells (the main output neurons of the
cerebral cortex), fusiform cells, stellate (granular) cells, basket
cells, horizontal cells of Cajal-Retzius and cells of Martinotti.
• Starting at the periphery of the cerebral cortex, the general
organization of neurons is molecular layer (I), external
granular layer (II), external pyramidal layer (III), internal
granular layer (IV), internal pyramidal layer (V), and
multiform layer (VI).
44. Cerebellar Cortex
• The cerebellar cortex is organized in three laminae: molecular
layer, Purkinje cell (PC) layer, and granular layer
(GL). Purkinje, Golgi, stellate, and basket cells are
inhibitory neurons; granule and unipolar brush cells are
excitatory.
• Two types of afferent nerve fibers enter the cerebellar cortex
from outer regions of the central nervous system.
• These are the mossy fibers, which synapse with granule cells,
and the climbing fibers, which enter the molecular layer and
wind about the dendrites of Purkinje cells.
