Download What is a neuron?

Nervous System Histology
Week 9
SB fall 2011
What is a neuron?
Neuron = Nerve
cell
Reflex Arc
Objective 1:
Neuron Structure
Main parts of a neuron
Dendrites (receive)  Cell Body (process)  Axon (send)  Axon Terminals
(transfer)
Cell
Body
Axon
Terminals
Multipolar Neuron model
Dendrites and Cell Body
Dendrites
(receptive
regions)
Cell body (Soma)
(biosynthetic center
and receptive region)
Neuron
cell
body
Nissl bodies
(rough ER)
Dendrite
Neurofibrils
Nucleus
Nucleolus
Axon
(impulse generating
and conducting region)
Impulse
direction
Axon
Axon hillock
Impulse
direction
Axon
Neurilemma
(sheath of Schwann)
Schwann cell
(one internode)
Node of Ranvier
Schwann cells - supporting cells of the PNS that myelinate axons
• Myelin sheath – whitish lipoprotein that surrounds and insulates the
axon (nerve fiber)
• Neurilemma - external layer containing bulk of cytoplasm with
nucleus and organelles (cell membrane)
myelin sheath
neurilemma
Schwann
cell
nucleus
axon
Node of
Ranvier
•Schwann cells myelinate axons
•Gaps between successive
Schwann cells along the length
of the axon are nodes of Ranvier
What you need to draw and label
Axon
Node of
Ranvier
Neurilemma
Neuron Pathology: Multiple Sclerosis
MS is thought to be an autoimmune
disease in which the myelin is lost in
multiple areas, leaving scar tissue
called sclerosis. These damaged areas
are also known as plaques or lesions.
Sometimes the nerve fiber itself is
damaged or broken.
Myelin not only protects nerve fibers,
but makes their job possible. When
myelin or the nerve fiber is destroyed
or damaged, the ability of the nerves
to conduct electrical impulses to and
from the brain is disrupted, and this
produces the various symptoms of MS.
Axon Terminals
Impulse
direction
Terminal branches
(Telodendria)
Axon terminals
(secretory component)
Remember this?
Axon (branches)
Muscle fibers
Axon terminals
Axon Collateral
Axon Collateral
What you need to draw and label
(Nuclei)
Cell Body
Spinal Cord Smear – Motor Neuron
Objective 2:
Neuron Classification
Pseudounipolar (unipolar) neurons
•
include most sensory neurons
•
have a short process which emerges from the cell body and
divides into proximal and distal branches
soma
Distal process (toward periphery)
Proximal process (toward CNS)
Pseudounipolar Cell Bodies in the
Dorsal Root Ganglion of a Spinal Nerve
“This is a low power slide of the Dorsal
Root Ganglion. The key to knowing that
you are looking at Neurons in the DRG is by
looking for the CENTRALLY LOCATED
NUCLEI, indicated by the Red arrows.
These large neurons are Pseudounipolar,
Sensory (Afferent) Neurons. They are
responsible for conveying information to the
Central Nervous System. You can tell that
these Neurons have huge cell bodies. These
are some of the largest cells in the body.
The larger the cell body, the further away
the information is coming from.”
Red arrows - Central Nuclei of Sensory
Neurons
UMDNJ histsweb
Bipolar neurons
Human retina
• are found in special sense organs (eye, ear)
• have a single axon & a single dendrite which
are attached to opposite sides of the cell body
bipolar
neurons
dendrite
axon (branched)
Multipolar neurons:
• include most neurons including all motor neurons and most CNS neurons
• have multiple dendrites and a single axon
Purkinje cell of the cerebellum
Neuron from the cerebral cortex
Pyramidal cell of
the hippocampus
Silver Stained Neuron In Gray Matter
Spinal Cord - Anterior Horn
Glial cell nuclei
Multipolar neuron
Multipolar neurons you will be drawing
Pyramidal cell
Hippocampus & Cerebral cortex
Purkinje cell
Cerebellum
(Pseudo)unipolar neuron
Most sensory neurons
Cell body located in
Dorsal Root Ganglion
(spinal nerves)
Multipolar neurons
Most neurons
Most CNS neurons
(interneurons)
All motor neurons
Cell bodies located in
Spinal cord & Brain
Objective 3:
Nerves are structures of
the peripheral nervous
system (PNS) that
consist of axons and
dendrites bundled
together by connective
tissue
Nerves
Epineurium:
tough, fibrous connective
tissue sheath surrounding
a nerve
Perineurium: loose areolar connective
tissue sheath surrounding a
fascicle (a bundle of axons or
dendrites)
Endoneurium: delicate connective tissue
wrapping around each nerve
fiber which electrically
insulates each nerve fiber
Perineurium
Endoneurium
Fascicle
Epineurium
Electron micrograph image
Nerve fiber
(axon)
a = epineurium
b= perineurium
perineurium
endoneurium
axon
EN = endoneurium
Ax = axon
NR = node of Ranvier
My = myelin sheath