Chapter 12-Part 2 Flashcards
(24 cards)
What is a synapse?
Place where a neuron connects to another neuron or an effector
There are two types of synapses: chemical and electrical.
What are the two types of synapses?
- Chemical synapses
- Electrical synapses
What characterizes an electrical synapse?
Presynaptic and postsynaptic neurons bound together by gap junctions
Fast: no synaptic delay in passing electrical signal.
What is a chemical synapse?
Presynaptic neuron’s axon terminal produces signal; postsynaptic neuron receives signal
Most commonly with one of its dendrites.
What is the synaptic cleft?
Small fluid-filled gap between the two neurons
What occurs during synaptic communication?
- Neurotransmitter molecules released from vesicles of synaptic knob into cleft
- Neurotransmitter diffuses across cleft and binds to postsynaptic receptors
- Binding initiates postsynaptic potential (a graded potential)
What is synaptic delay?
Time it takes for all events in synaptic communication to occur
What are glial cells?
Nonexcitable, support cells found in CNS and PNS
Smaller, but far outnumber neurons; account for about half the volume of nervous system.
What is a key function of astrocytes?
Help form blood-brain barrier by wrapping feet around brain capillaries
What do oligodendrocytes do?
Wrap around axons of neurons forming myelin sheath
What is the role of microglia?
Phagocytic cells of immune system that engulf infectious agents and remove debris
What do ependymal cells line?
Cavities in brain and spinal cord
What is the function of satellite cells?
Electrically insulate and regulate the exchange of nutrients and wastes around neuronal cell bodies in a ganglion
What do neurolemmocytes (Schwann cells) do?
Ensheath PNS axons with myelin, allowing for faster action potential propagation
What are gliomas?
Glial cell tumors that may be benign or malignant
What is myelination?
Process of wrapping an axon with myelin
What is myelin composed of?
Several layers of membrane of glial cells with high lipid content
What is the difference in myelination between PNS and CNS?
In PNS, neurolemmocyte myelinates one axon segment; in CNS, oligodendrocyte can myelinate multiple axons
What is a neurofibril node?
Gaps between neurolemmocytes, also known as nodes of Ranvier
What is multiple sclerosis?
Progressive demyelination of neurons in CNS due to autoimmune disorder
What is Guillain-Barré syndrome?
Loss of myelin from peripheral nerves due to inflammation, often with recovery
What conditions are necessary for PNS axon regeneration?
- Neuron cell body is intact
- Enough neurilemma remains
What are the steps of axon regeneration?
1) Axon severed by trauma
2a) Proximal axon seals off and swells
2b) Distal axon and sheath degenerate
3) Neurilemma and endoneurium form a regeneration tube
Why is CNS axon regeneration limited?
Oligodendrocytes secrete growth-inhibiting molecules and scars obstruct regrowth
