Chapter 25: The Nervous System

Question 1

What is the most critical functions of the nervous system?

Answer 1

Homeostasis. Requires communication between the sensors (cells that detect internal and external conditions) and the effectors (the muscles and glands that make adjustments. The nervous and endocrine system provide this essential communication

Question 2

Differences between the nervous system and the endocrine system

Answer 2

• Nervous system electrical impulses travel so rapidly. Endocrine system secretes hormones which may take hours to respond.

Question 3

Two basic cell types for nervous tissues

Answer 3

1. Interconnected neurons

2. Associated neuroglial cells

Question 4

Neurons

Answer 4

Cells that communicate with one another.

Question 5

Neuroglia (glial cells)

Answer 5

Provide physical support help maintain homeostasis in the fluid surrounding the neurons, guide neuron growth.

Question 6

What do neurons and neuroglia do?

Answer 6

Control mood, appetite, blood pressure, coordination and the perception of pain and pleasure.

Question 7

Nerve nets

Answer 7

Diffuse networks of neurons in the body walls of hydras, jellyfishes, sea amemones and other cnidarians. Stimulates muscle cells near the body surface.

Question 8

Ganglia

Answer 8

Clusters of neurons

Question 9

Nerve ladder

Answer 9

Formed by transverse nerves connect the nerve cords to each other

Question 10

Ventral nerve cord

Answer 10

Peripheral nerves branch from here so the animal can coordinate its movements.

Question 11

Central nervous system

Answer 11

Brain, and the dorsal, tubular spinal cord.

Question 12

Peripheral nervous system

Answer 12

Carries information between the central nervous system and the rest of the body.

Question 13

Neuron structure

Answer 13

• Cell body: enlarged and round contains the nucleus, mitochondria that supply ATP, ribosomes that manufacture proteins, and other organelles.
• Dendrites: short, branched extensions that transmit information toward the cell body.
• Axon: nerve fiber; a single long extension of the cell body. Each tiny terminal extension communicates with another cell at a junction called a synapse. Conducts nerve impulses from the cell body to a muscle, gland, or other neuron.
• Myelin sheath: fatty material coats sections of the axon, speeding nerve impulse conduction.

Question 14

Schwann cells

Answer 14

In the peripheral nervous system, these form the myelin sheath

Question 15

Oligoendrocytes

Answer 15

Make myelin sheaths in the central nervous system.

Question 16

Nodes of Ranvier

Answer 16

Short regions of exposed axon between sections of the myelin sheath

Question 17

Three classes of neurons

Answer 17

• Sensory neuron: brings information from the body’s organs toward the central nervous system. Responds to light, sound waves, heat, touch, odors and taste. Lies in the peripheral nervous system.
• Interneurons: 90% of neurons. Connect one neuron to another within the spinal cord and brain. Receives information from sensory neurons and generates the message that the sensory neurons carry to effector organs.
• Motor neuron: conducts its message from the central nervous system toward an effector: a muscle or gland. Cell body and dendrites reside in the central nervous system. Stimulate muscle cells to contract and glands to secrete.

Question 18

Resting potential

Answer 18

Difference in electrical charge between the inside and outside of a neuron that is not conducting a message.

Question 19

Sodium-potassium pump

Answer 19

Pumps three sodium ions out of the cell from every two K+ that enter, at a cost of one ATP molecule per cycle.

Question 20

Action potential

Answer 20

Brief depolarization that propagates like a wave along the membrane of the nerve fiber.