CAM101 Lecture 19: Nervous Tissue
Characteristics
• Exists as part of the central nervous system (CNS; brain and spinals cord) or peripheral nervous
system (PNS; nerves, sensory receptors, ganglia)
• Cells (neurons) are widely scattered with only limited contact at the extremities
• Ability to transmit a signal (action potential) along a cell by reversing polarity of cell
membrane (excitable cells)
• Cells of nervous tissue are characterised by having many cellular processes (cytoplasmic
extensions)
• Depending upon where you're looking (CNS or PNS) nervous tissue can have different
characteristics
Rule of Two's
Cells of Neurons
• Neurons
• Glial Cells (Supporting)
• Oligodendrocytes
• Astrocytes
• Microglia
• Ependymal cells
• Schwan cells
• Satellite cells
• Blue = CNS Green = PNS
Neuronal Types
Multipolar Neuron
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All Neurons
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Bipolar Neuron: exists in the organs of special sense (taste, hearing & sight)
Unipolar Neuron: exists in sensory organs everywhere else ( i.e. Pain)
Neuronal cell bodies (soma) exist only in:
• The CNS
• Accumulation of neuronal cell bodies in PNS called ganglia
Nerve cell bodies are NOT found in peripheral nerves!
Myelin
Oligodendrocytes produce myelin in the CNS
Schwann cells produce myelin in the PNS
Myelin is a wrapping of the axon by cell membrane (phospholipid-rich) from either an
oligodendrocyte or a Schwann cell.
Voltage-gated ion channels accumulate on the axon cell membrane at the spaces between myelin
sheaths in spaces called Nodes of Ranvier.
Myelin, then, acts as an insulator. An action potential 'jumps' from one node of ranvier to the next.
This speeds up conduction of the signal. This is called saltatory conduction.
Oligodendrocytes
• In the CNS
• May myelinate many different axons at once (or same axon multiple times)
• Done via long cytoplasmic processes that wrap around axons.
Schwann Cells
• In the PNS
• Only myelinate one part of an axon
• Always intimately associated with their axons unlike oligodendrocytes
• One axon may have up to 10000 Schwann cells depending upon its length
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Document Summary
Cells of neurons: neurons, glial cells (supporting, oligodendrocytes, astrocytes, microglia, ependymal cells, blue = cns green = pns. Bipolar neuron: exists in the organs of special sense (taste, hearing & sight) Unipolar neuron: exists in sensory organs everywhere else ( i. e. pain) Neuronal cell bodies (soma) exist only in: the cns, accumulation of neuronal cell bodies in pns called ganglia. Nerve cell bodies are not found in peripheral nerves! Myelin is a wrapping of the axon by cell membrane (phospholipid-rich) from either an oligodendrocyte or a schwann cell. Voltage-gated ion channels accumulate on the axon cell membrane at the spaces between myelin sheaths in spaces called nodes of ranvier. An action potential "jumps" from one node of ranvier to the next. In the cns: may myelinate many different axons at once (or same axon multiple times, done via long cytoplasmic processes that wrap around axons.
