Chapter 9:
Cells in CNS and PNS are of 2 kinds: nerve cells (neurons) and glial cells.
Membrane polarization: reacting to stimuli by reversal of ionic gradient and propagation.
Action potential (depolarization wave or nerve impulse): capable of traveling long distance
transmitting signals to other neurons, muscles and glands.
Development of nerve tissues:
o Develops from the outermost layer of embryonic layers the ectoderm
o Signals from notochord ectoderm on the mid-dorsal side of the embryo thickens to
form the epithelial neural plate. fuse to form neural tube. cells of this tube give
rise to the entire CNS, including neurons and most glial cells.
Neurons:
o Functional unit in both CNS and PNS
o Has 3 main parts:
Cell body (perikaryon): contains nucleus and most of cell’s organelles and serves
as the synthetic or trophic center for the entire neuron.
Dendrites: numerous elongated processes extending from the perikaryon and
specialized to receive stimuli from other neurons at unique sites called
synapses.
Axon: single long process ending at synapses specialized to generate and
conduct nerve impulses to other cells.
o Classification of neurons:
Multipolar neurons:
1 axon and two or more dendrites
Bipolar neurons:
1 dendrite and one axon
Mostly found in sensory organs (eye, ear…)
Unipolar (pseudounipolar) neurons:
Single process that bifurcates close to the perikaryon with the longer
branch extending to a peripheral ending and the other toward the CNS.
Found in spinal ganglia and cranial ganglia.
Anaxonic neurons:
Many dendrites but no true axon.
Do not produce action potentials but regulate electrical changes of
adjacent neurons.
o Most neurons are multipolar.
o Can also be divided to afferent (sensory neurons that receive stimuli from the receptors
throughout the body) and efferent (motor neurons that send impulses to effector
organs).
The autonomic motor nerves control the “involuntary” activities while somatic
motor nerves control voluntary.
o Interneurons establish relationships among other neurons forming complex functional
networks (circuits). They are generally multipolar or anaxonic and include 99% of the
neurons in human CNS.
, o Cell bodies are in gray matter. Axons are concentrated in white matter.
o In PNS, cell bodies are found in ganglia and in some sensory regions while axons are
bundled in nerves.
o 3 parts:
Cell Body:
Its cytoplasm has highly developed TRT with many parallel cisternae and
neighboring polyribosomes active production of cytoskeletal proteins
and proteins for transport and secretion.
Chromatophilic substance (Nissi bodies): concentrated RTR and other
polysomes that appear basophilic.
Golgi apparatus only found in cell body while mitochondria can be
found along the cell.
Neurofilaments: intermediate filaments found in both the perikarya (cell
body) and processes.
They also have microtubules.
Dendrites:
They increase the receptive area of the cell
Dendritic spines: short blunt structures projecting at points along
dendrites where synapses impinging on neurons occur.
They are important in neural plasticity underlying adaptation, learning
and memory.
Axons:
Most neurons have only 1 axon
Originate from pyramid-shaped region of cell body called axon hillock,
Axolemma: plasma membrane of axon
Axoplasm: contents of axon.
o Contains mitochondria, microtubules, neurofilaments, cisternae
of smooth ER, NO polyribosomes or RER. (it depends on
perikaryon for maintenance)
Initial segment: area just beyond axon hillock which sums excitatory and
inhibitory signals, deciding which to propagate.
Distal end of axon forms a terminal arborization.
Collaterals: branches from axons of interneurons and some motor
neurons that end at synapses influencing the activity of many other
neurons.
Terminal bouton: ending of each branch that contacts another neuron
at a synapse.
Bidirectional transport of small and large molecules:
o Anterograde transport: organelles and macromolecules
synthesized in the cell body move from there to synaptic
terminals.
o Retrograde transport: opposite direction carries certain
macromolecules from periphery to cell body.
Cells in CNS and PNS are of 2 kinds: nerve cells (neurons) and glial cells.
Membrane polarization: reacting to stimuli by reversal of ionic gradient and propagation.
Action potential (depolarization wave or nerve impulse): capable of traveling long distance
transmitting signals to other neurons, muscles and glands.
Development of nerve tissues:
o Develops from the outermost layer of embryonic layers the ectoderm
o Signals from notochord ectoderm on the mid-dorsal side of the embryo thickens to
form the epithelial neural plate. fuse to form neural tube. cells of this tube give
rise to the entire CNS, including neurons and most glial cells.
Neurons:
o Functional unit in both CNS and PNS
o Has 3 main parts:
Cell body (perikaryon): contains nucleus and most of cell’s organelles and serves
as the synthetic or trophic center for the entire neuron.
Dendrites: numerous elongated processes extending from the perikaryon and
specialized to receive stimuli from other neurons at unique sites called
synapses.
Axon: single long process ending at synapses specialized to generate and
conduct nerve impulses to other cells.
o Classification of neurons:
Multipolar neurons:
1 axon and two or more dendrites
Bipolar neurons:
1 dendrite and one axon
Mostly found in sensory organs (eye, ear…)
Unipolar (pseudounipolar) neurons:
Single process that bifurcates close to the perikaryon with the longer
branch extending to a peripheral ending and the other toward the CNS.
Found in spinal ganglia and cranial ganglia.
Anaxonic neurons:
Many dendrites but no true axon.
Do not produce action potentials but regulate electrical changes of
adjacent neurons.
o Most neurons are multipolar.
o Can also be divided to afferent (sensory neurons that receive stimuli from the receptors
throughout the body) and efferent (motor neurons that send impulses to effector
organs).
The autonomic motor nerves control the “involuntary” activities while somatic
motor nerves control voluntary.
o Interneurons establish relationships among other neurons forming complex functional
networks (circuits). They are generally multipolar or anaxonic and include 99% of the
neurons in human CNS.
, o Cell bodies are in gray matter. Axons are concentrated in white matter.
o In PNS, cell bodies are found in ganglia and in some sensory regions while axons are
bundled in nerves.
o 3 parts:
Cell Body:
Its cytoplasm has highly developed TRT with many parallel cisternae and
neighboring polyribosomes active production of cytoskeletal proteins
and proteins for transport and secretion.
Chromatophilic substance (Nissi bodies): concentrated RTR and other
polysomes that appear basophilic.
Golgi apparatus only found in cell body while mitochondria can be
found along the cell.
Neurofilaments: intermediate filaments found in both the perikarya (cell
body) and processes.
They also have microtubules.
Dendrites:
They increase the receptive area of the cell
Dendritic spines: short blunt structures projecting at points along
dendrites where synapses impinging on neurons occur.
They are important in neural plasticity underlying adaptation, learning
and memory.
Axons:
Most neurons have only 1 axon
Originate from pyramid-shaped region of cell body called axon hillock,
Axolemma: plasma membrane of axon
Axoplasm: contents of axon.
o Contains mitochondria, microtubules, neurofilaments, cisternae
of smooth ER, NO polyribosomes or RER. (it depends on
perikaryon for maintenance)
Initial segment: area just beyond axon hillock which sums excitatory and
inhibitory signals, deciding which to propagate.
Distal end of axon forms a terminal arborization.
Collaterals: branches from axons of interneurons and some motor
neurons that end at synapses influencing the activity of many other
neurons.
Terminal bouton: ending of each branch that contacts another neuron
at a synapse.
Bidirectional transport of small and large molecules:
o Anterograde transport: organelles and macromolecules
synthesized in the cell body move from there to synaptic
terminals.
o Retrograde transport: opposite direction carries certain
macromolecules from periphery to cell body.
