1. Label the major structures found in a neuron and describe their functions
a. Dendrite: short, highly branched signal receptive regions of nerve cell. They convey
incoming message toward cell bodies
b. Nucleus: The
...
1. Label the major structures found in a neuron and describe their functions
a. Dendrite: short, highly branched signal receptive regions of nerve cell. They convey
incoming message toward cell bodies
b. Nucleus: The nucleus of the neuron contains the genetic material in this form of
chromosomes. It contains the genes which consist of DNA which contains the cell history,
which are necessary in the manufacturing of protein characteristics of that cell.
c. Cell body: Neuron part that contains most of the cytoplasm and the nucleus.
d. Node of ranvier: Node of Ranvier, periodic gap in the insulating sheath (myelin) on the axon
of certain neurons that serves to facilitate the rapid conduction of nerve impulses.
e. Axon: is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically
conducts electrical impulses known as action potentials, away from the nerve cell body.
f. Axon hillock: a specialized part of the cell body of a neuron that connects to the axon. The
axon hillock is the last site in the soma where membrane potentials propagated from
synaptic inputs are summated before being transmitted to the axon.
g. Myelin sheath: the insulating covering that surrounds an axon with multiple spiral layers of
myelin, that is discontinuous at the nodes of Ranvier, and that increases the speed at which a
nerve impulse can travel along an axon.
h. Schwann cell: A glial cell that makes up sections of myelin sheath. (1 schwann cell= 1 section
of myelin sheath)
i. Axon terminal: is the very end of a branch of a nerve axon, a long slender nerve fiber that
conducts electrical signals to a nerve synapse (the gap between nerve cells). The signal then
moves across the synapse to another axon by means of a neurotransmitter (an
electrochemical substance).
j. Synapse: is a structure that permits a neuron to pass an electrical or chemical signal to
another neuron or to the target effector cell.
2. What are the differences between axons and dendrites?
Axons = generating and sends information
Dendrites = Convey incoming message toward the cell bodies
3. What is myelin and what is its primary function?
Myelin is a whitish, fatty protein layer. It serves to protect and electrically insulate axon. It increases
the speed of transmission of nerve impulses
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4. Along the axons of myelinated neurons there are gaps in the myelin where the axolemma (cell membrane
of the axon) is exposed. What is the name given to these gaps in myelin? What is the significance of these
gaps in the myelin sheath?
Nodes of Ranvier are gaps in the myelin sheath coating on the neural axon. The myelin allows the
electrical impulse to move quickly down the axon. The nodes of Ranvier allow for ions to diffuse in
and out of the neuron, propagating the electrical signal down the axon.
5. What is meant by the term “polarity” in regards to the cell membrane of a neuron?
spatial differences in the shape, structure, and cell function
6. How do sodium and potassium leak channels play a role in the development of the negative membrane
potential of the axolemma (plasma membrane of the axon)?
Outside positive and inside negative; resting is 70Mv
7. Compare and contrast the three types of ion channels.
Chemically gated = Na+ channel that opens in response to the ACh at a binding site
Volted gated = Na+ channel that responds to changes in the transmembrane potential
Mechanically gated = opens in response to distortion of the membrane
8. What is meant by the term “propagation” in regards to an axon?
What triggers action potential. The action potential generated at the axon hillock propagates as a
wave along the axon. The currents flowing inwards at a point on the axon during an action potential
spread out along the axon, and depolarize the adjacent sections of its membrane. If sufficiently
strong, this depolarization provokes a similar action potential at the neighboring membrane patches.
9. Explain each of the following terms (making sure to include which ions are moving in which direction)
AND draw/recognize them on a graph:
a. Membrane potential: The potential inside a cell membrane measured relative to the fluid
just outside; it is negative under resting conditions and becomes positive during an action
potential.
b. Action potential: Demonstrates how changes in the membrane can constitute a signal. It is a
momentary reversal in electrical potential across a plasma membrane (as of a neuron or
muscle fiber) that occurs when a cell has been activated by a stimulus. It is the point of
stimulation, includes depolarization, repolarization, absolute refractory period, relative
refractory period.
c. Resting period: he resting membrane potential of a neuron is about 70 mV (mV=millivolt)
this means that the inside of the neuron is 70 mV less than the outside. At rest, there are
relatively more sodium ions outside the neuron and more potassium ions inside that neuron.
d. Threshold: is the critical level to which a membrane potential must be depolarized to initiate
an action potential. Threshold potentials are necessary to regulate and propagate signaling
in both the central nervous system (CNS) and the peripheral nervous system (PNS).
e. Activation gates: opens when the membrane potential crosses −55 mV. When a cell is at rest,
the activation gate is closed however, when the threshold is reached, the activation gate
opens, allowing Na
+ to rush into the cell. During repolarization, no more sodium can enter
the cell. When the membrane potential passes −55 mV again, the activation gate closes. After
that, the inactivation gate reopens, making the channel ready to start the whole process over
again.
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