Download Cell Compartments

Histology
of
Nervous Tissue
Cells of nervous tissue
Neurons and supporting cells
Neurons
Functional units of the nervous system
- relay sensory (afferent) stimuli from the internal and external
environments
- process, store and integrate information
- transmit information to other neurons, muscles and glands
Composed of a cell body, dendrites, axon and its terminal
arborization and synapses
Form complex and highly integrated circuits
Astrocyte
Supportive cells
Highly outnumber neurons
CNS:
Astrocytes
Structural support
Metabolic support
Homeostasis
Oligodendrocyte
Oligodendrocytes
Insulation (myelin sheath)
Microglia
Phagocytosis
Immunomodulation
Ependymal cells
PNS:
Schwann cells
Microglia
Myelin
Functional compartments
of the neuron
Cell body
Dendrites
Axon
Synapses
Functional compartments
of the neuron
Cell body
Dendrites
Axon
Synapses
Functional compartments
of the neuron
Cell body
Dendrites
Axon
Synapses
Functional compartments
of the neuron
Cell body
Dendrites
Axon
Synapses
Cell body
(Soma, Perikaryon)
Nucleus
Neuronal Cytoskeleton
Neurofilaments
Neurofilaments (8-10 nm)
Microtubules (20-25 nm)
Gives shape and support for the cell
(Neurofilaments)
Facilitates intracellular transport
(Microtubules)
SER
Microtubules
Cross section
Microtubules
Neurofilaments
Longitudinal section
Nissl bodies
RER + polysomes
Nissl
RER
Polysomes
Dendrites
Form majority of receptive field
Usually multiple and branched at
acute angles
May possess spines
Transmit toward cell body
(receptor potentials, graded)
Organelles (similar to cell body)
Dendritic spines
Dendrites
Form majority of receptive field
Usually multiple and branched at
acute angles
May possess spines
Transmit toward cell body
(receptor potentials, graded)
Organelles (similar to cell body)
Axon
Usually singular
Smaller caliber and often longer
than dendrites
Right angle branching
Organelles
Lacks Nissl
High cytoskeleton content
Originates at the axon hillock
Transmits action potentials away
from cell body
Neurons
Muscles and glands
Terminal arborization
Terminal buton
Pre-synaptic element
Initial segment
of the axon
Comparison of axon and dendrite
Chemical synapses
Chemical synapses
Classified according to post-synaptic structure
Dendrite (Axodendritic)
Cell body (Axosomatic)
Axon (Axoaxonic)
Muscle cell (neuromuscular junction)
Chemical
synapses
Pre-synaptic terminal (buton)
Neurotransmitter (synaptic) vesicles
Mitochondria
Synaptic cleft
Post-synaptic cell with postsynaptic density
Terminal
buton
Synaptic
vesicles
Active zone
on presynaptic
membrane
Transmitter release
Synaptic cleft
Postsynaptic
density
Dendritic
spine
Post synaptic
density
Classification of neurons
By shape and function
Multipolar
Most numerous and
heterogeneous group
Efferent or association
Pseudounipolar
Sensory (afferent)
Bipolar
Sensory, organs of special
sense
Developmental stage for
all neurons
Motor (efferent)
Association
Multipolar
Types of neurons
Sensory (afferent)
Pseudounipolar
Bipolar
Pseudounipolar
Segregation of axons and cell bodies in the nervous system
In both CNS and PNS cell bodies are found in clusters and neuron processes
travel in bundles. Such groupings are based on common function and/or common
connections.
CNS
Gray matter - composed primarily of neuron cell bodies and supporting cells
Cortex - neuronal cell bodies arranged in layers covering the outer layers of
the brain, e.g., the cerebrum and cerebellum
Nucleus - group of neuron cell bodies in the interior of the CNS
White matter - regions of CNS rich in myelinated axons
Appears white in fresh tissue due to presence of lipid-rich myelin
Composed of tracts - bundles of axons that course together
W
G
W
G
W
G
W
G
Segregation of axons and cell bodies in the nervous system
PNS
Ganglia (singular = ganglion) - groups of cell bodies with a similar function
Nerves (both cranial and spinal nerves) - bundles of axons coursing together
Nerve
Ganglion
Reflex arc
(Multipolar)
(Pseudounipolar)
(Multipolar)
Supporting Cells
• CNS
–
–
–
–
Astrocytes
Oligodendrocytes
Ependymal cells
Microglia
• PNS
– Schwann cells
Neuroglial cells
(neural ectoderm)
Astrocytes
• Stellate morphology
– Fibrous
– Protoplasmic
• Functions
–
–
–
–
–
–
Physical support
Nutritional support
Ion homeostasis
Transmitter uptake
Scar formation
Immune function
Cell of origin for some brain
tumors (astrocytomas)
Fibrous
Cap
Protoplasmic
Perivascular
end foot
Cap
Oligodendrocytes
• Interfascicular and satellite
• Interfascicular oligodendrocytes
form the myelin sheath in the
CNS
Interfascicular
Satellite
Ependymal cells
Line the ventricles and central
canal of brain and spinal cord
Cilia
Microglial cells
"Brain macrophages“
Derived from mesoderm
Schwann cells
Satellite Schwann cells
Surround cell bodies
Ensheathing Schwann cells
Surround axons
Myelin sheath
• Segmental, multilamellar, lipid-rich wrapping of axons formed by
the plasma membranes of:
- Oligodendrocytes in CNS (interfascicular)
- Schwann cells in PNS
• Functions to increase speed of conduction (saltatory conduction)
by insulating the axon
Myelin sheath
Node of Ranvier
Internode
Internode:
Single myelin segment
Node of Ranvier: Specialized region of the axon between internodes, rich
in sodium channels; site where depolarization occurs
Myelin
Axon
Cross section
of a myelinated axon
Myelin
Axon
Myelin sheath
– Oligodendrocytes in CNS
CNS
PNS
Multiple internodes per cell
Multiple axons per cell
– Schwann cells in PNS
One internode per cell
One axon per cell
Schwann cells
Oligodendrocyte
Myelination in the PNS – Schwann cells
Unmyelinated axons
Schwann cell
nucleus
Myelination in the CNS - Oligodendrocytes
Connective tissues
in the peripheral and central
nervous systems
Peripheral nervous system
Endoneurium
Perineurium
Epineurium
Ep
P
En
Central nervous system
Meninges (meningitis)
Dura mater
Arachnoid membrane
Pia mater
Dura mater
Arachnoid
membrane
Pia mater
Brain
Dura mater
Arachnoid
membrane
Pia mater
Blood vessel
Brain