Transcript CNS Neuroglial Cells

CNS Neuroglial Cells
• Greatly outnumber neurons in the CNS
(think worker ants vs. Queen ant)
1. Microglial cells
– Scattered throughout CNS
– Support neurons and phagocytize
bacterial cells and cellular debris
2. Oligodendrocytes
– Occur in rows along nerve fibers
– Provide layers of myelin around axons
within brain and spinal cord
CNS Neuroglial Cells,
continued….
3. Astrocytes
– Found between neurons and blood
vessels
– Provide structural support, help regulate
nutrients and ions in tissues
– Form scar tissue to fill spaces after CNS
injuries
4. Ependymal cells
– Form epithelial-like membrane in parts of
the brain (choroid plexuses)
– Form inner linings that enclose ventricles
in the brain and central canal in the spinal
CNS Neuroglial Cells
PNS Neuroglial cells
1. Schwann cells: form myelin sheath
around axons
Neurons
•
Vary in size and structure, but have
common features:
1. Cell Body
2. Dendrites
3. Axon
•
Mature neurons do not divide, but
neural stem cells can divide and form
neurons or neuroglial cells.
1. Cell Body
• Contains normal cellular structures
(golgi apparatus, mitochondria,
cytoplasm, cell membrane, etc.)
• Neurofibrils – fine threads that extend
into the axon
• Nissl bodies (chromatophilic
substances)
– Membranous sacs in the cytoplasm
– Similar to rough ER
– Ribosomes on Nissl bodies synthesize
2. Dendrites
• Usually short and highly branched
(dendr = ?)
• The main receptive surfaces for
receiving communication from axons of
other neurons
3. Axons
• Arise from a slight elevation of the cell
body, called the axonal hillock.
• Conduct nerve impulses away from the
cell body
• Contains many mitochondria,
microtubules, and neurofibrils
• Originates as a single structure, but
may have branches, especially at the
end to interact with receptive surfaces
of other cells
PNS Axons
• Enclosed in myelin sheaths composed
of many Schwann cells
• Myelin is a lipoprotein.
• Neurilemma sheath surrounds the
myelin sheath
• Nodes of Ranvier – narrow gaps in the
myelin sheath between the Schwann
cells
Classification of Neurons
• Classification based on Structural
differences:
• Bipolar neurons
• Unipolar neurons
• Multipolar neurons
• Classification based on Functional
differences:
• Sensory neurons (afferent neurons)
• Interneurons (association or internuncial
neurons)
Structural Differences
• Sketch the neurons below. Notes on the
next 3 slides:
Structural Differences,
cont…..
1. Bipolar:
– 2 processes
•
•
Axon
Dendrite
– Found in specialized parts of the eyes,
nose, and ears
Structural Differences,
cont…..
2. Unipolar:
– 1 process divides into 2 branches, which
function as a single axon
•
•
1 branch (peripheral process) associated with
dendrites
Other branch (central process) enters brain or
spinal cord
Structural Differences,
cont…..
3. Multipolar:
– Many processes arising from cell body:
•
•
1 axon
Many dendrites
– Most neurons whose cell bodies lie in the
brain or spinal cord are multipolar.
• Direction of impulse is ALWAYS from
dendrites to axon.
Functional Differences
1. Sensory (afferent) neurons
– From peripheral body parts to the brain or
spinal cord
– Have specialized receptor ends at the tips
of their dendrites OR
– Dendrites closely associated with receptor
cells in the skin or sensory organs.
– Most are unipolar, but some are bipolar.
Functional Differences,
cont…..
2. Interneurons (association or internuncial
neurons)
– Lie entirely in the brain or spinal cord
– Multipolar and link other neurons
– Transmit impulses from one part of the brain
or spinal cord to another
3. Motor (efferent) neurons
– Multipolar
– Carry nerve impulses from brain or spinal
cord to effectors
– Stimulate muscles or glands