Biology | Answers to Review Questions

Author Dr. George B. Johnson, Washington University
Author Dr. Peter H. Raven, Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer, Carleton College
Contributor Dr. Jonathan Losos, Washington University

Answers to Review Questions

Chapter 54 (p. 1102)

1. Sensory neurons carry impulses from sensors to the CNS. Motor neurons carry impulses from the CNS to effectors. Association neurons (interneurons) are located ion the brain and spinal cord and comprise the CNS. All of these neurons have a cell body with a nucleus, cytoplasmic extensions called dendrites that receive stimuli, and an axon through which impulses pass from the cell body.

2. K⁺ is more highly concentrated inside the cell; Na⁺ is more highly concentrated outside the cell membrane. These concentration differences are maintained by active transport during a nerve cell's resting potential.

3. A voltage-gated ion channel is a channel that will open or close when triggered by the appropriate membrane potential.

4. Action potentials remain the same throughout transmission of the impulse, creating a "domino effect." Myelination and increase in nerve diameter increase the velocity at which an action potential is conducted. The region between Schwann cells (produce insulating myelin) is the node of Ranvier. These nodes are in direct contact with the intercellular fluid, and the action potential jumps from node to node.

5. The transmission of a nerve impulse down a myelinated axon occurs "domino fashion," with each action potential triggering another action potential. When the action potential reaches the presynaptic vesicle, it cannot continue. Instead, it triggers a series of events that allow a neurotransmitter to flow across the synaptic cleft to stimulate the postsynaptic cell. The postsynaptic cell is stimulated by a neurotransmitter, not an action potential.

6. Basal ganglia are regions of grey matter located deep in the white matter of the cerebrum. They receive sensory information from ascending tracts and motor commands from the cerebral cortex and cerebellum. Outputs of the basal ganglia are sent along the spinal cord to help control skeletal muscles and body movement.

7. Short-term memory is transient and easily lost; its storage in the brain may be as a transient impulse. Long-term memory may involve structural changes in the cortex.

8. Sympathetic axons leave the top and bottom of the spinal cord; parasympathetic ones come off the spinal cord in the chest and abdominal areas. In both systems, the preganglionic neurons are in the CNS, and the postganglionic neurons synapse with the viscera.