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and engulf foreign material.
(d) Astrocytes are supportive cells anchoring neurons
to capillaries and supporting the blood-brain
barrier. They also help repair brain tissue after
injury. They have many processes to connect the
neurons and capillaries. Transmission of Nerve Impulses (page 78)
1. An action potential passes along a nerve because
the depolarization occurring in one region of the axon
makes the next region of the axon more permeable to
sodium ions (and more likely to conduct the impulse). 2. Because the refractory period makes the neuron
unable to respond for a brief period after an action
potential has passed, the impulse can pass in only
one direction along the nerve (away from the cell
body). 3. The nervous system interprets nerve impulses
correctly because it records where they have
come from and “knows” where they go to. Different
regions of the brain are responsible for sorting out,
interpreting, and integrating the nerve impulses from
different sources. Chemical Synapses (page 79)
1. A synapse is a junction between the end of one axon
and the dendrite or cell body of a receiving neuron.
Biozone International 2009 Photocopying Prohibited 13
Note: A synapse can also occur between the end of
one axon and a muscle cell (neuromuscular junction).
2. • Arrival of a nerve impulse at the end of the axon
causes an influx of calcium. This induces the vesicles
to release their neurotransmitter into the cleft. • 2. Any one of:
• Drug can act as an indirect agonist, preventing the reuptake of norepinephrine by the presynaptic
cell, thereby prolonging the response in the
postsynaptic cell, e.g. cocaine and amphetamines.
• Drug can act as a direct antagonist, competing for adrenergic β receptors on the postsynaptic
membrane and blocking impulse transmission,
e.g. β blockers used to treat hypertension. Delay at the synapse is caused by the time it takes
for the neurotransmitter to diffuse across the gap
(synaptic cleft) between neurons. 4. (a) Neurotransmitter (NT) is degraded into
component molecules by enzyme activit...
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This document was uploaded on 01/28/2014.
- Winter '13