Chapter 12 Study- Nervous Tissue

Question 1

What are the two anatomical subdivisions of the nervous system? Which ones houses the brain and spinal cord?

Answer 1

Central nervous system (CNS)—brain and spinal cord​
​Peripheral nervous system (PNS)—nerves and ganglia​

Question 2

What are the 2 divisions of the PNS?

Answer 2

1. Sensory (afferent) division—carries signals from receptors (sense organs) to CNS
2. Motor (efferent) division—carries signals from CNS to effectors (glands and muscles that carry out the body’s response)

Question 3

Compare somatic to visceral

Answer 3

Somatic motor division—carries signals to skeletal muscles; causes voluntary muscle contraction and automatic reflexes
Visceral motor division (autonomic nervous system, ANS)—carries signals to glands, cardiac and smooth muscle; no voluntary control; responses called visceral reflexes

Question 4

What are the 3 functional classes of neurons? Compare afferent (sensory) neurons to efferent (motor)

Answer 4

1. Sensory (afferent) neurons—detect stimuli and transmit information about them toward the CNS
2. Interneurons—receive signals from other neurons, process this information, and make resulting “decisions”
3. Motor (efferent) neurons—send signals out to muscles and gland cells (the effectors)
   the next cell

Question 5

Be able to differentiate between multipolar, bipolar, unipolar, and anaxonic neurons.

Answer 5

Multipolar neuron—one axon and multiple dendrites; most common type in body, most neurons in CNS
*Bipolar neuron—one axon and one dendrite; examples include olfactory cells, some neurons of retina, sensory neurons of ear
*Unipolar neuron—single process leading away from cell body, splits into peripheral process and central process
Both processes comprise the axon; only short receptive endings of peripheral process are considered dendrites
*Anaxonic neuron—many dendrites but no axon; found in brain, retina, and adrenal gland

Question 6

Compare anterograde to retrograde transport

Answer 6

Anterograde transport—movement away from cell body, down the axon
Retrograde transport—movement up the axon toward the cell body

Question 7

List the 6 neuroglial cells and each of their functions. Which are found in the CNS and which are found in the PNS?
1. Oligodendrocytes—form myelin sheaths in CN

Answer 7

1. Oligodendrocytes—form myelin sheaths in CNS
2. Ependymal cells—line internal cavities of brain; secrete and circulate cerebrospinal fluid (CSF)
3. Microglia—macrophages; engulf debris, provide defense against pathogens
4. Astrocytes—most abundant type; wide variety of functions
   PNS
   1 . Schwann cells—envelop axons of PNS, form myelin sheath, and assist in regeneration of damaged fibers
5. Satellite cells—surround nerve cell bodies in ganglia of PNS; provide insulation around cell body and regulate chemical environment

Question 8

What is myelin? Which cells secrete this? What are the gaps between myelin called?

Answer 8

spiral layers of insulation around an axon

Question 9

What is MS?

Answer 9

Multiple sclerosis (MS) -Oligodendrocytes and myelin sheaths in CNS deteriorate

Question 10

How does size and myelin effect how fast signals travel down an axon?

Answer 10

Diameter: larger axons have more surface area and conduct signals more rapidly (faster the signal)
Presence or absence of myelin: myelin speeds signal conduction

Question 11

Define RMP. How does the ICF of a resting cell compare to the ECF

Answer 11

Resting membrane potential (RMP)—charge difference across plasma membrane intracellular fluid (ICF) becomes relatively negative to the extracellular fluid (ECF)

Question 12

Compare depolarization to hyperpolarization

Answer 12

Depolarization- Polarity is reduced, voltage is less negative
Hyperpolarization- (membrane more negative) is inhibitory—makes a neuron less likely to produce an action potential

Question 13

Define action potential

Answer 13

Action potential—rapid up-and-down change in voltage produced by the coordinated opening and closing of voltage-gated ion channels

Question 14

Describe the 3 important characteristics of action potentials listed

Answer 14

All-or-none law—if threshold reached, neuron fires up to maximum voltage; if threshold not reached, it does not fire
Non decremental—do not get weaker with distance
Irreversible—once started, an action potential travels all the way down the axon cannot be stopped

Question 15

Compare the absolute refractory period to the relative refractory period

Answer 15

Refractory period—period of resistance to stimulation; has two phases:
Absolute refractory period—no stimulus of any strength will trigger another AP
*Caused by inactivation of voltage-gated Na+ channels
Relative refractory period—an unusually strong stimulus is needed to trigger a new AP
*During hyperpolarization, a larger depolarization (local potential) is required to reach threshold

Question 16

Compare conduction in unmyelinated and myelinated axons

Answer 16

Unmyelinated axons and continuous conduction: Slower
Unmyelinated axons have voltage-gated channels along their entire length
Chain-reaction continues down axon
Myelinated axons and saltatory conduction: Faster
Action potentials can only be generated at the nodes, where voltage-gated ion channels are concentrated
Electrical signal must spread passively between nodes
Action potential seems to “jump” from node to node

Question 17

What molecules link 2 neurons together across the cleft?

Answer 17

Each neuron has cell-adhesion molecules (CAMs) reaching into the cleft

Question 18

Describe the functions of a neurotransmitter. Compare the 3 different examples of synapses

Answer 18

Some neurotransmitters are excitatory, others inhibitory, and sometimes a transmitter’s effect differs depending on type of receptor on postsynaptic cell
Example1: An excitatory cholinergic synapse
Cholinergic synapse—acetylcholine (ACh) is the neurotransmitter
Example 2: An inhibitory GABA-ergic synapse
Example 3: An excitatory adrenergic synapse
Adrenergic synapse—norepinephrine (NE) is the neurotransmitter

Question 19

List 3 ways that neurotransmitter can be cleared from a synaptic cleft.

Answer 19

Neurotransmitter degradation—enzyme in synaptic cleft breaks down neurotransmitter
Reuptake—neurotransmitter or its breakdown products reabsorbed into axon terminal
Diffusion—neurotransmitter or its breakdown products simply away from synapse into nearby ECF

Question 20

What is a neuromodulator? List an example

Answer 20

Neuromodulators—chemicals secreted by neurons that have long term effects on groups of neurons
Exsample: Relaxing smooth muscle

Question 21

Compare EPSPs to IPSPs

Answer 21

Excitatory postsynaptic potential (EPSP)—voltage change from the RMP toward threshold
Inhibitory postsynaptic potential (IPSP)— voltage becomes more negative that it is at rest

Question 22

Compare temporal summation to spatial summation

Answer 22

Temporal summation—a single synapse generates EPSPs so quickly that each is generated before the previous one fades
Spatial summation—EPSPs from several different synapses add up to threshold at an axon hillock

Question 23

Compare presynaptic facilitation to inhibition

Answer 23

Presynaptic facilitation—occurs when one presynaptic neuron enhances another one
Presynaptic inhibition—occurs when one presynaptic neuron suppresses another on

Question 24

Identify the 4 different neural circuit types

Answer 24

Diverging circuit—one nerve fiber branches and synapses with several postsynaptic cells
Converging circuit—input from many different nerve fibers can be funneled to one neuron or neural pool
Reverberating circuit—neurons stimulate each other in linear sequence but one or more of the later cells restimulates the first cell to start the process all over
Parallel after-discharge circuit—input neuron diverges to stimulate several chains of neurons

Question 25

Compare serial and parallel processing

Answer 25

Serial processing—neurons and neural pools relay information along pathway in relatively simple linear fashion​
Parallel processing— information is transmitted along diverging circuits through different pathway that act on it simultaneously, for different purposes
driving steering and vision (looking around)

Question 26

Can process only one flow of information at a time​

Answer 26

Serial processing—neurons and neural pools relay information along pathway in relatively simple linear fashion
Read a book or watch a television movie—you cannot do both simultaneously​
May jump back and forth between one and the other, or only half understanding each

Question 27

Compare AD to Parkinson disease.

Answer 27

Alzheimer disease (AD)
Memory loss, moody, combative, and lose ability to talk, walk, and eat​
Acetylcholine (ACh) and nerve growth factor (NGF) deficiencies

Parkinson disease (PD)—progressive loss of motor function due to degeneration of dopamine-releasing neurons​
Dopamine normally prevents excessive activity in motor centers (basal nuclei