Chapter 12-Intro to Nervous System

Microglial cells

Phagocytic cells in the CNS

Satellite Cells

Surround the cell bodies of neurons in the PNS.

Certain inhaled anesthetic agents are thought to open Cl- channels in the membranes of postsynaptic neurons in the brain, an effect that causes IPSPs. Why might this action put a person "to sleep" during anesthesia?

The inhibitory potentials summate, which prevents action potentials from being generated in affected neurons, effectively putting them "to sleep."

Astrocytes

Anchor neurons and blood vessels, maintain extracellular environment around neurons, assist in formation of the blood-brain barrier.

An action potential is generated at the _________ _______________.

Axon hillock

You are examining a neuronal process and you find that it generates action potentials. Is this an axon or a dendrite? How can you tell?

This must be an axon, because by definition only axons generate action potentials.

The main function of an axon is to _________________________.

generate and transmit signals in the form of action potentials.

Ependymal cells

Ciliated cells in the CNS that form and circulate cerebrospinal fluid.

What is the difference between an excitatory postsynaptic potential and an inhibitory postsynaptic potential?

An excitatory postsynaptic potential creates a local depolarization in the membrane of the postsynaptic neuron that brings it closer to threshold. An inhibitor postsynaptic potential does the opposite; it hyperpolarizes the membrane and brings it farther away from threshold.

Where are synaptic vesicles located?

Axon terminals

Predict what would happen if the calcium ion channels in the axon terminal were blocked. Explain.

Blocking calcium ion channels in the axon terminal would inhibit exocytosis of neurotransmitters into the synaptic cleft. This would shut off synaptic transmission between two neurons.

Schwann Cells

Create the myelin sheath in the PNS

Oligodendrocytes

Form the myelin sheath in CNS

The bacterium Clostridium tetani produces a toxin called tetanospasmin, the causative agent of the disease tetanus. The toxin prevents the release of inhibitory neurotransmitters in the CNS and so blocks the resulting IPSPs they would normally generate. What are some of the functions of inhibitory synapses? Considering this, what symptoms would you expect from the disease tetanus, and why?

Inhibitory synapses perform several functions, including preventing antagonist muscles from contracting while agonist muscles are simultaneously contracting. When inhibitory synapses are prevented by tetanospasmin, antagonist and agonist muscles contract at the same time. This leads to painful muscle contractures, a situation in which all muscles are in spasm and movement is impossible.

A damaged axon in the PNS may be able to regenerate only if the cell body is intact. Why do you think that the cell body must be intact for regeneration to occur?

The cell body contains the nucleus and most of the other cellular machinery necessary for protein synthesis. In addition, organelles like the smooth endoplasmic reticulum, which synthesizes membrane phospholipids, are located in the cell body. Unless these structures are intact, a neuron cannot make new cellular parts to repair itself.

What triggers exocytosis of synaptic vesicles?

The influx of calcium ions into the axon terminal.

Multiple sclerosis is a demyelinating disease, in which the patient's immune system attacks and destroys the cells that form the myelin sheath in the central nervous system. What types of symptoms would you expect from such a disease? Why? Would Schwann cells or oligodendrocytes be affected? Explain.

The myelin sheath increases the speed of action potential conduction within the CNS. As MS results in the destruction of the myelin sheath, it causes slowing of action potential conduction. This causes muscle weakness and eventual paralysis and can cause cognitive impairment. MS affects oligodendrocytes because these neuroglial cells myelinate axons of the CNS.

You are examining another neuron, and find that it has two processes, both of which generate action potentials. What is the structural class of this neuron? How did you come to this conclusion?

This is a pseudounipolar neuron, in which it has two axons, a central process and a peripheral process. Both processes are capable of generating action potentials, and so both are axons.