BPK 105 Midterm: Module 4 - Objectives - Part 3
27 Apr 2018
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Module 4 - Objectives - Part 3
● Explain the role that myelination plays in the function of an axon.
-Myelin sheaths = specialized layers that wrap around the axons of some neurons.
- myelin sheaths are formed by the cell processes of oligodendrocytes in the CNS and
Schwann cells in the PNS (figure 8.5).
- Axons with these myelin sheaths are called myelinated axons (figure 8.6a).
- Each oligodendrocyte process or Schwann cell repeatedly wraps around a segment of
an axon to form a series of tightly wrapped cell membranes.
- Myelin = excellent insulator that prevents almost all ion movement across the cell
membrane.
- Gaps in the myelin sheath (nodes of Ranvier) occur about every millimeter b/w the
oligodendrocyte segments or b.w individual Schwann cells.
- Ion movement can occur at the nodes of Ranvier.
- Myelination of an axon increases the speed and efficiency of action potential generation
along axon.
- Unmyelinated axons lack the myelin sheaths
- axons rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in
the PNS (figure 8.6b).
- typical small nerve (consists of axons of multiple neurons) usually contains more
unmyelinated axons than myelinated axons.
● Describe the structure and function of a synapse.
- is where the axon of one neuron interacts with another neuron or with cells of an effector
organ (muscles or glands) --> synapse to transfer electric activity (information) from one
cell to another.
- synapse= junction where axon of one neuron interacts w dendrite or cell body of another
neuron
- A synapse = a junction where the axon of one neuron interacts with another neuron or
with cells of an effector organ, such as a muscle or gland (figure 8.12).
- end of the axon forms a presynaptic terminal.
- The membrane of the dendrite or effector cell = postsynaptic membrane
- space separating the presynaptic and postsynaptic membranes = synaptic cleft.
- Chemical substances called neurotransmitters stored in synaptic vesicles in the
presynaptic terminal.
- When an action potential reaches the presynaptic terminal, voltage-gated Ca2+
channels open, and Ca2+ moves into the cell.
- influx of Ca2+ causes the release of neurotransmitters by exocytosis from the
presynaptic terminal.
- The neurotransmitters diffuse across the synaptic cleft and bind to specific receptor
molecules on the postsynaptic membrane.
