Download What is a neuron?

Nervous System Histology
In Lab Today:
• Draw & identify the portions of a
multipolar neuron from slides
• Draw & differentiate between
pseudounipolar, bipolar & multipolar
neurons from slides
• Identify the components of the nerve
cross section using diagrams & slides
• Identify the portions of a multipolar
neuron from the models
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)
Multipolar Neuron model
Cell
Body
Axon
Terminals
Dendrites
(receptive
regions)
Cell body
(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 hillock
Impulse
direction
Axon
Neurilemma
(sheath of Schwann)
Schwann cell
(one internode)
Node of Ranvier
Impulse
direction
Terminal branches
(Telodendria)
Axon terminals
(secretory component)
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
Schwann cell
myelin sheath
nucleus
axon
neurilemma
Node of
Ranvier
Nodes of Ranvier Gaps between successive Schwann cells along the length
of the axon
Microscopic Views
What you need to draw and label
Axon
Node of
Ranvier
Neurilemma
What you need to draw and label
Cell Body
Spinal Cord Smear – Motor Neuron
Objective 2:
Neuron Classification
>
Receptive
Endings
Distal process
(toward periphery)
A short process (axon) emerges from
the cell body and divides into proximal
and distal branches
Proximal process
(toward CNS)
Has a single axon and a single
dendrite attached to opposite sides
of the cell body
<
dendrite
>
dendrites
axon
axon (branched)
Has multiple dendrites and a single axon
(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
Bipolar neurons
Found in
special sense organs
(eye, ear, nose, tongue)
Example: Retina
HISTOLOGY
(Pseudo)uipolar
neurons
Bipolar
neurons
Multipolar neurons
Pseudounipolar cell bodies
in the dorsal root ganglion of a
spinal nerve
Centrally located nuclei
Dorsal Root
Ganglion
Spinal
Cord
Pseudounipolar
cell bodies
Bipolar neurons in the human retina
Bipolar
neurons
Bipolar
neuron
nuclei
axons
Note: Multipolar neurons have diverse morphologies
You do not need to memorize all these
Some Examples of Motor Neurons
Neurons from the spinal cord
(smear)
Neuron from the
cerebral cortex
Multipolar neurons you will be drawing
Pyramidal cell
Hippocampus & Cerebral cortex
Purkinje cell
Cerebellum
Pyramidal cell
(Low Power – Cerebrum)
Purkinje cell
(Low Power - Cerebellum)
Recap: Neuron Classifications
Be able to identify each type of neuron by classification
Objective 3:
Nerves are
structures of the
PNS that
consist of axons and
dendrites bundled
together by
connective tissues
Nerve Structures
NERVE
Epineurium: tough, fibrous connective
tissue sheath surrounding
a nerve
Perineurium: loose, areolar connective
tissue sheath surrounding
fascicles
Fascicle: a bundle of axons or dendrites
Endoneurium: delicate connective tissue
wrapping around each nerve
fiber; the endoneurium
electrically insulates each
nerve fiber
Perineurium
Endoneurium
Fascicle
Epineurium
Electron micrograph image
Nerve fiber
(axon)
LAB ACTIVITY:
Draw and label the components of the nerve cross section