Download Neurons

Kharkov National
Medical University
LECTURE for dentistry students
Department of
Histology, cytology and
embryology
Nervous Tissue
consists of
– 2 types of cells
• Neurons• Neuroglia-
– Embryogenesis
• Neural tube
• Neural crest – cranial, spinal, autonomic ganglia,
neuroendocrine cells (APUD),
Shwann cells of neuroglia
• Monoblast – microglia
Neurons. Structure
 Neurons = nerve cells
 Specialized to perception, excitement and
transmition messages
 Cell body
 Processes – that extend from the cell
body (dendrites and axons)
 Nerve endings (synapses and others)
Slide 4
Neuron
 Cell body
Slide 5
Neurofibrils:
A network of neurofibrils is in the perikaryon and
in the dendrites and axon. Is unique to neurons.
Support, drainage.
Nissl body
clumps of basophilic material
is unique to neurons.
an aggegation of
the rough endoplasmic
reticulum and free
ribosomes.
Neuron processes
dendrite
 Extensions
outside the cell
body
axon
 Dendrites –
conduct
impulses toward
the cell
 Axons – conduct
impulses away
from the cell
(only 1!)
Slide 8
Classifications of neurons
(1) According to amount of processes –
structural classification:
Unipolar neurons
Pseudounipolar neurons
Bipolar neurons
Mutipolar neurons
Slide 11
(2) Functional Classification
• 1. Sensory (afferent) neurons
Carry impulses from the sensory receptors
• 2. Motor (efferent)
•
Carry impulses from the central nervous
system
• 3. Interneurons (association)
-99,9%
In the central
nervous system
Connect sensory and motor neurons
(2). Neuron Classification
Support Cells (Neuroglia)
Macroglia
Ependymal cells
Astrocytes
Schwann cells
Microglia
Nerve fibers –
processes, covered by sheaths
1. Unmyelinated
2. Myelinated
Unmyelinated nerve fiber
Processes are invaginated in Schwann cell cytoplasm
cytoplasm
N.c. process
nucleus
N.c. process
Myelinated nerve fibers
2 sheaths: myelin and Schwann (neurilemma)
nucleus
process
cytoplasm
nucleus
process
myelin
process
cytoplasm
The Nervous Tissue
• Nerve endings
I. Synapses
Peripheral:
II. Sensory
III. Motor
NERVOUS System
Nervous system
consists of:
 Central nervous system (CNS)
 --Brain
 --Spinal cord
 Peripheral (PNS):

- ganglia

- nerves
Nervous system
consists of:
 Somatic – innervates skeletal muscles
Autonomic – innervates viscera:

- sympathetic

- parasympathetic
PNS
• Ganglia are aggregations of nerve cells
• Sensory ganglia lie on the dorsal root of
the spinal cord, contain sensory neurons
• Autonomic ganglia lie near or inside
organs, contain motor neurons
PNS
Nerves
 Nerve = bundle of myelinated and unmyelinated fibers
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Structure of a Nerve
Figure 7.20
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Connective tissue in the nerve:
• individual nerve fibres are covered by
loose connective tissue - endoneurium.
• Bundles of Nerve fibres, fascicles, are
surrounded by perineurium.
• The entire nerve is surrounded by a thick
layer of dense connective tissue, the
epineurium.
PNS
• ganglia are
surrounded
by a c.t.
capsule,
• Neurons
• N.fibers
CNS
consists of Gray and white matters.
- Gray matter – neurons and
unmyelinated fibers
- white matter – fibers
– Clusters of neurons form Nuclei
Spinal Cord- participates in formation of reflex
arcs and connects body with the brain cortex
 Nerves begin from:
Dorsal root
Ventral root
Spinal Cord
grey matter
Dorsal horn
Ventral horn
white mater –
conduction tracts
Anterior horn:
• two motor nuclei: medial and lateral
• The axons of motor neurons form anterior
root
Posterior horn
two integrative (intercalated) nuclei of
somatic nervous system:
• proper nucleus and Klark’s nucleus.
Lateral horn
• medial and lateral nuclei
• intercalated neurons of ANS (mostly SNS)
Somatic reflex arc
• 1-st neuron – sensory
ganglion
• 2-d neuron – dorsal horn
• 3-d neuron – ventral horn
• Target – skeletal muscle
Testing Patellar Reflex
Somatic reflex arc
Sympathetic reflex arc
• 1-st: sensory neuron - in the spinal ganglion)
• 2-d: intercalated (preganglionic) neuron – in the
lateral horn of the thoracic and upper lumbar
segment of spinal cord.
Its axon is called preganglionic fiber.
• 3-d, motor (efferent) neuron is located in the
sympathetic ganglion. The axon of the ganglion
cell is called the postganglionic fiber,
carries impulse to the effector
Parasympathetic reflex arc
• 1-st: sensory neuron (in the spinal
ganglion)
• 2-d neuron: is in the sacral spinal cord
segments and in the brain stem.
• 3-d neuron is in the parasympathetic
ganglia, which lie close to the viscera or
into wall of viscera.
Cerebellum
 Two hemispheres form ’’arbor vitae’’
 Provides involuntary coordination of
body movements
Cerebellum
Cerebellar cortex
1)Molecular layer
2)Purkinje cells
layer – main,
Receive all information
3)Granular layer
Cerebral cortex
Trough spinal cord receives all the
information,
analyzes it,
forms respond
Cerebral cortex = grey matter
Cerebral cortex
1)molecular layer
2)external granular
layer
3 )pyramidal layer
4)internal granular layer
5)ganglionic layer
6)multiform layer
Main =Pyramidal cells
the biggest Betz cells
Structural unit – module =
vertical column = processes of
neurons around neuroglial cell