9 Nervous Tissue

Question 1

The nervous system includes what 7 features?

Answer 1

The brain
Cranial nerves
Spinal cord
Spinal nerves
Ganglia
Enteric plexuses
Sensory receptors

Question 2

What are the basic parts of a neuron?

Answer 2

Several dendrites, a cell body, and a single axon.

Question 3

A multipolar neuron had __ processes extending from the cell body, a bipolar neuron has __, and a unipolar neuron has __.

Answer 3

Many; two; one

Question 4

The electrical signals produced by neurons and muscle fibres rely on ion channels such as:

Answer 4

Leak channels and voltage-gated channels

Question 5

The resting membrane potential is due to a small buildup of __ charged ions, mainly organic phosphates and proteins, in the cytosol just inside the membrane and an equal buildup of __ charged ions, mainly sodium ions, in the extracellular fluid just outside the membrane.

Answer 5

Negatively; positively

Question 6

An action potential consists of __ and __ phases.

Answer 6

Depolarizing and repolarizing

Question 7

Unmyelinated axons exhibit __ conduction, and myelinated axons exhibit __ conduction.

Answer 7

Continuous; saltatory

Question 8

What are dendrites?

Answer 8

Dendrites are extensions of the cell body that transmit impulses to the cell body.

Question 9

What are ependymal cells?

Answer 9

Epithelial cells (often ciliated) that line the ventricles of the brain. They produce cerebrospinal fluid (CSF).

Question 10

Describe the structure of a myelin sheath.

Answer 10

Consists of many layers of phospholipid membrane that belong to the Schwann cells. This sheath wraps around the axons on the myelinated neurons.

Question 11

What is a threshold stimulus?

Answer 11

Is a stimulus that causes the membrane of a neuron to depolarize to a critical level (-55mV) to generate an action potential.

Question 12

Define the term ganglia.

Answer 12

Are clusters of nerve cell bodies outside the CNS.

Question 13

What is the function of the afferent neurons?

Answer 13

To conduct impulses from the sensory cells to the CNS.

Question 14

What is a neurotransmitter?

Answer 14

Is a chemical released by a presynaptic neuron from the purpose of stimulating or inhibiting the postsynaptic neuron.

Question 15

What is the function of the microglia?

Answer 15

They act as phagocytic cells.

Question 16

What is the advantage of saltatory conduction?

Answer 16

Is very fast and requires less energy expenditure of the sodium-potassium pump.

Question 17

Name the 2 subdivisions of the autonomic nervous system:

Answer 17

Sympathetic and parasympathetic nervous system

Question 18

What is the refractory period?

Answer 18

Is the period of time following an initial stimulus during which a neuron cannot be stimulated to conduct a second impulse.

Question 19

Identify the functions of the nervous system.

Answer 19

Sensory: senses changes within the body and the environment.
Motor: initiates muscle movement or glandular secretion.
Integrative: interprets sensory information and determines the appropriate motor response.

Question 20

What is the role of the sodium potassium pump?

Answer 20

It actively carries sodium out of the cell and potassium into the cell. It is powered by ATP.

Question 21

How does a neuron become depolarized?

Answer 21

The rapid influx of sodium ions through the nerve cell membrane causes depolarization.

Question 22

Define white and grey matter.

Answer 22

White matter: groupings of the myelinated processes of many neurons.
Grey matter: contains nerve cell bodies, dendrites, and axon terminals of unmyelinated axons and neuroglia.

Question 23

Why does the synaptic conduction of an impulse occur only in one direction?

Answer 23

Transmission must be unidirectional because neurotransmitters are released only from presynaptic terminals, and because only postsynaptic membranes have appropriate neurotransmitter receptors.

Question 24

What is the meaning of the term resting membrane potential?

Answer 24

Is the potential difference that exists across a nerve cell membrane when it is not conducting an impulse, usually about -70mV.

Question 25

Which neuroglia produce myelin in the CNS?

Answer 25

Oligodendrocytes

Question 26

Which of the gated ion channels opens to a change in membrane potential?

Answer 26

Voltage

Question 27

The most important factors that determine the speed of impulse propagation are:

Answer 27

Fibre diameter and and the presence or absence of the myelin sheath.