Download Nervous System Chapter 11 Answers

Nervous System Chapter 11 Answers
1. What are the 3 functions of the nervous system?
 Senses changes inside and outside the body.
 Interprets those changes.
 Responds to the interpretations by initiating action in the form of muscular
contractions or glandular secretions.
2. Outline the organization of the nervous system
3. Which neuroglias form the myelin sheath?
Oligodendrocytes in the C.N.S.
Schwaan cells in the P.N.S.
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4. What is a neuron?
Nerve cells, which are the structural unit of the nervous system
Special characteristics of neurons:
1. Last a lifetime (100+ years)
2. Lose ability to divide (When they die they cannot renew or be replaced)
3. Have HIGH metabolic rates (Consume mucho glucose and oxygen)
5. A cluster of cell bodies in the C.N.S. is called _Nuclei_?
6. A cluster of cell bodies in the P.N.S. is called _Ganglia_?
7. What is white matter? Gray matter?
White matter consists of the parts of the brain and spinal cord innervated with
myelinated neurons
Gray matter consists of the parts of the brain and spinal cord innervated with
UNmyelinated neurons
8. Differentiate between afferent and efferent neurons.
Afferent neurons: collect and send sensory input to the brain (Three types)
1. Proprioceptors –found in the joints, muscles, tendons, & middle ear; are
responsible for body position and movement
2. Exteroceptors – Found in the skin; collects and sends sensory input from the
external environment e.g. Heat, pressure, touch, pain, sight, hearing, or smelling
3. Interoceptors – Found in blood vessels and visceral organs; sends sensory input
from inside the body e.g. Hunger, thirst, pain, pressure, nausea, or fatigue
9. What causes transmitter gated and voltage gated channels to open?
Neurotransmitters and changes in membrane potential
10. What is an electrochemical gradient?
Chemical gradient is formed when ions diffuse across a membrane (High to low
concentration)
Electrical gradient is formed when ions move toward an area of opposite charge
An electrochemical gradient occurs on neural membranes due to BOTH chemical &
electrical gradients
11. What is the resting membrane potential and why is the membrane polarized?
The net ion charge inside and outside of a neuron at rest is its’
resting membrane potential (~ -70 mV)
The membrane is polarized because:
 Anions (Proteins) are too large to move across the
membrane

Sodium/Potassium pumps exchange 3 Na+ for 2 K+
placing more cations outside of the membrane
12. Differentiate between depolarization, hyperpolarization, and repolarization.
Depolarization – a reduction in membrane potential (The inside of the membrane
becomes LESS negative…Approaches 0 mV)
Hyperpolarization – an increase in RESTING membrane potential (The inside of the
membrane becomes MORE negative > -70 mV)
Repolarization – an increase in membrane potential AFTER an action potential (The
inside of the cell becomes MORE negative e.g. 0 mV increases to -70 mV
Depolarization to -55 mV results in an action potential
-55 mV is the membrane THRESHOLD (When potassium and sodium exchange is equal)
13. What is the state (open or closed) of sodium and potassium channels during
resting state, depolarization, repolarization, and after hyperpolarization?
Resting state: Sodium & Potassium channels are closed
Depolarization: Sodium channels are open & Potassium channels are closed
Repolarization: Sodium channels are closed & Potassium channels are open
Hyperpolarization: Sodium channels remain closed & Potassium channels are slow to
close so the resting membrane potential is overshot the Potassium channels close and
some potassium diffuses across the membrane until the resting membrane potential is
established
14. How is an action potential propagated?
 Depolarization of the neuron membrane
 Repolarization of the neuron membrane
 Hyperpolarization of the neuron membrane
 Resting potential is re-established in the neuron membrane
15. What is the all-or-nothing phenomenon?
An action potential occurs completely, or not at all (THRESHOLD must be reached
to open up sodium channels)
16. What variables influence the conduction velocity of a neuron?
 Axon diameter (Larger diameter results in faster conduction of impulse)
 Degree of myelination (Continuous conduction vs. Saltatory conduction)
17. Describe the events of the propagation of an action potential through a synapse
to the next dendrite.
1. Propagation of impulse to the axon terminal of the pre-synaptic neuron results
in calcium channels opening and calcium ions binding to neurotransmitter vesicles
2. The calcium addition to the neurotransmitter vesicles causes them to fuse to
the pre-synaptic neuron and release the neurotransmitters into the synaptic
cleft (space) by exocytosis
3. Calcium is removed by calcium pumps (Small amounts of calcium are used in the
mitochondria also)
4. The neurotransmitters diffuse across the synaptic space and bind to receptors
on the post-synaptic neuron membrane
5. The neurotransmitter changes the shape of the protein channel allowing sodium
or calcium ions to cross the post-synaptic membrane which opens sodium
channels and propagates the action potential