Pg 8-10 Flashcards
In a synapse formed between two neurons, what part of the second
neuron do the terminal knobs of the first neuron synapse with?
The dendrites
b. What important happens at this same location?
Depolarizations or hyperpolarizations are produced, depending upon the type of
neurotransmitter is released onto the dendrites.
- Two types of neuroglial cells wrap around neuron cell axons to form
myelin sheaths.
a. Which of these neuroglial cells does this within the CNS?
Oligodendrocytes
b. In what two ways is this neuroglial cell different from the second neuroglial
cell in the way it makes myelin sheaths?
The other cell that forms myelin sheaths is the Schwann cell. Each Oligodendrocyte
forms myelin sheaths on up to 15 different neurons while each Schwann cell forms only 1
myelin sheath. Schwann cells also form myelin sheaths in the peripheral nervous
system (PNS), not the CNS.
Neurons that have a myelin sheath around their axons are known as
white matter. Those that do not are known as gray matter.
:-)
a. What is the purpose of white matter?
Myelinated neurons (white matter) can conduct action potentials at much faster speeds
than nonmyelinated neurons (grey matter). This means, for example, that APs in the
white matter that cause muscle contraction are moving at speeds up to 300 mph.
In contrast, APs in the grey matter of sensory nerves to your skin travel as slow as 2
mph.
b. What are the Nodes of Ranvier that are found in the myelin sheath?
The nodes are areas of the neuron’s axon that are NOT covered by the myelin sheath.
In other words, the Nodes of Ranvier are gaps in the myelin sheath where the axon is
visible.
See diagram—top neuron.
c. How are the Nodes of Ranvier related to Saltatory Conduction of the
action potential?
The action potential hops or jumps from node to node as it moves down the axon.
This is known as Saltatory Conduction. See diagram.
d. What causes Saltatory Conduction in myelinated neurons?
The action potential is forced to hop from node to node because it cannot flow through
the areas where the myelin sheath covers the axon. This is because the myelin sheath
is an insulating device against electrical currents (action potentials). Since the AP
has to hop over the myelin sheath (hopping from node to node), it moves at a much
faster speed than it would if it had to move through the entire axon.
**A “insulator” is anything that blocks movement through the protected area. Insulation in
the walls of your house prevents the air inside your house from escaping through the
walls to the outside & vice versa. Instead of blocking air movement, the myelin sheath
blocks electricity.**
Within the CNS, where are myelinated nerves found?
In the brain, white matter (myelinated nerves) is found in the medulla (center/core or
inner layer.) In the spinal cord, white matter is found in the cortex (outer layer)
Think of it this way: The outside of the spinal cord looks white but the outside of the brain
it looks grey. (Cortex of brain is grey matter but cortex of spinal cord is white matter.)
*There are, however, round areas (nuclei) of grey matter in the center of the brain too.
What is another name for the Motor division of the Peripheral Nervous
System (PNS)?
The Efferent Division
b. Through what root do these nerves attach to the spinal cord?
Ventral root (attaches to the front of the spinal cord) See diagram next page.
c. In what direction do action potentials (APs) move through motor nerves?
In motor nerves, APs start in the brain and move to the body (the skeletal muscle).
Efferent means “to exit” or “to exit the brain.”
Action potentials exit the brain and go out to skeletal muscle to cause contractions.
(The actual meaning of efferent is “to carry away.”)
d. What is the Afferent Division of the PNS?
Afferent nerves are sensory nerves.
In sensory nerves, APs start in the body and move to the brain.
For example, sensory nerves in the skin send APs to the brain to provide information
about touch and pressure.
Afferent means “to come in” or “to come into the brain.”
(The actual meaning of afferent is “to carry toward.”)
