Ch 2: Structure and Function of the Nervous System

Question 1

What are the primary external features of a neuron?

Answer 1

Soma

Treelike dendrites

Single axon extending from soma, that carries electrical signals to the axon terminals

Question 2

Describe the characteristics of axon terminals

Answer 2

Contain synaptic vesicles filled with neurotransmitter molecules that are released into the synapse between cells when the action potential arrives.

Question 3

Describe dendrites, and the abnormalities of dendrites in people with schizophrenia

Answer 3

The dendrites of a neuron are covered with minute spines that increase the receiving surface area of the cell. Spines/dendrites contain thousands of receptors that respond to neurotransmitters

Spines are reduced in SIZE in individuals with intellectual impairment

Spines are reduced in NUMBER in those with schizophrenia.

Question 4

What is the axon hillock?

Answer 4

located at the juncture of soma and axon and is responsible for summation (or integration) of the multiple signals required to generate an action potential

Question 5

Describe the role of myelin and 4 types of glial cells

Answer 5

Conduction of the action potential along the axon is enhanced by the insulating property of the myelin created by nearby glial cells

4 types of glial cells

Schwann cells: produce myeline (PNS)

Oligodendroglia cells: produce Myeline (CNS)

Astrocytes: regulate the extracellular environment of the neurons and provide physical support and nutritional assistance.

Microglia act as phagocytes to remove cellular debris and provide immune function.

Question 6

Describe the protein synthesis process

Answer 6

Protein synthesis occurs in the nucleus of the cell, located within the soma

Transcription of the genetic code for a specific protein by mRNA occurs within the nucleus, and translation of the “recipe,” carried by the mRNA, occurs on the ribosomes in the cytoplasm.

Ribosomes link together appropriate amino acids to create the protein.

New proteins are packaged into vesicles in the soma and are moved by motor proteins that slide along the neuron’s microtubules (part of the cytoskeleton) to the terminals (anterograde transport). Protein waste and cell debris are transported from the terminals back to the soma (retrograde transport) for recycling.

Changes in synaptic activity increase or decrease the production of particular proteins by activating transcription factors in the nucleus.

Question 7

Define epigenetics, and list two types of effects

Answer 7

Epigenetics is the study of how environmental demands such as diet, environmental toxins, stress, prenatal nutrition, and many others turn on or turn off the expression of specific genes. Although epigenetic markers do not modify DNA, they can last a lifetime and may be transmitted to future generations.

Two common markers are DNA methylation and chromatin remodeling.

Question 8

Describe the resting potential of a neuron

Answer 8

At rest, neurons have an electrical charge across the membrane of –70 mV (resting potential), with the inside being more negative than the outside.

The resting potential results from the balance between two competing forces on K+ ions:

• Electrostatic pressure moves K+ inward because it is attracted by negatively charged molecules trapped inside
• The concentration gradient for K+ pushes ions out of the cell

Question 9

What is the function of the Na+K+ pump?

Answer 9

helps to maintain the negative membrane potential by exchanging three Na+ ions (moved out of the cell) for two K+ ions (taken in).

Question 10

What is an Excitatory Postsynaptic potential? (EPSP)

Answer 10

DEPOLARIZATION (POSITIVE) - > ready for fire

Occurs when ligand-gated Na+ channels open and allow Na+ to enter the cell on its concentration gradient, making it slightly more positive and bringing the membrane potential closer to the threshold for firing.

Question 11

What is an Inhibitory Post Synaptic potential?

Answer 11

HYPERPOLARIZATION (MORE NEGATIVE) -> Not ready for fire

When Cl– channels open allowing Cl– to enter on its concentration gradient, this makes the cell more negative and farther from the threshold

When ligand-gated K+ channels open, K+ exits on its concentration gradient, leaving the cell more negative inside and farther from the threshold producing an IPSP.

Question 12

Define action potential

Answer 12

When the threshold (–50 mV) is reached, voltage-gated Na+ channels open, allowing large amounts of Na+ to enter the cell to produce the massive depolarization

At the peak of the action potential (+40 mV), voltage-gated Na+ channels close and cannot be opened until they reset at the resting potential, so no action potential can occur during this time (the absolute refractory period).

The action potential moves down the length of the axon by sequential opening of voltage-gated Na+ channels.

Question 13

What happens during the relative refractory period?

Answer 13

voltage-gated K+ channels open and K+ exits from the cell, bringing the membrane potential back toward resting levels. The overshoot by K+ causes the cell to be more polarized than normal, so it is more difficult to reach the threshold to generate another action potential (relative refractory period).

Question 14

Describe the nervous system break downs

Answer 14

1. CNS
   - brain, spinal chord
2. PNS
   a) Somatic nervous system - sensory motor
   b) Autonomic nervous system- smooth muscles, organs
   i) Sympathetic
   ii) Parasympathetic

Question 15

What are the layers of the CNS?

Answer 15

1) Dura
2) Arachnoid
3) Pia

+ Cerebrospinal fluid

Question 16

What are neurotrophic factors?

Answer 16

growth factors that

• guide the development of neurons
• regulate dendridic growth and retraction
• aid in survival of neruons

Question 17

What are the six regions of the CNS?

Answer 17

• each contains multiple nuclei, which form interconnecting neural circuits

1) Spinal cord
2) Mylencephalon (medulla)
3) Metencephalon (cerebellum and pons)
4) Mesencephalon (mid brain)
5) Diencephalon (thalamus and hypothalamus)
6) Telencephalon (Cerebral cortex and basal ganglia)

Question 18

Differentiate between gray matter and whole matter

Answer 18

GRAY: constitutes cell bodies that receive sensory information and cell bodies of motor neurons that serve muscles.

WHITE: tracts of myelinated axons that carry signals in the ascending direction to the brain and descending tracts for cortical control of the spinal cord.

Question 19

Describe the Mylencephalon (MEDULLA)

Answer 19

contains nuclei that serve vital functions for survival, such as respiration, heart rate, and vomiting.

Question 20

Describe the Metencephalon (Cerebellum and pons)

Answer 20

Cerebellum: posture and balance and provides fine motor control and coordination.

Pons: contains several nuclei that represent the origins of most of the tracts utilizing the neurotransmitters norepinephrine (the locus coeruleus) and serotonin (the raphe nuclei).

Question 21

What is the reticular formation?

Answer 21

Beginning in the medulla, running through the pons, and extending into the midbrain

a network of interconnected nuclei that control arousal, attention, and survival functions.

Question 22

Describe the mesencephalon (midbrain)

Answer 22

Contains nuclei that control sensory reflexes such as pupillary constriction.

Other nuclei (substantia nigra and ventral tegmental area) are the cell bodies of neurons that form three major dopaminergic tracts.

The peri-aqueductal gray organizes behaviors such as defensive rage and predation and serves as an important pain-modulating center.

Question 23

Describe the diencephalon (thalamus; hypothalamus)

Answer 23

important for maintaining homeostasis of physiological functions and for modulating motivated behaviors, including eating, aggression, reproduction, and so forth. The many nuclei that constitute the hypothalamus control both the autonomic nervous system and the endocrine system.

Question 24

Describe the telencephalon (cerebral cortex, basal ganglia, limbic system)

Answer 24

The basal ganglia modulate movement.

The limbic system is made up of several brain structures with perfuse interconnections that modulate emotion, motivation, and learning. Some of the prominent limbic structures are the amygdala, hippocampus, nucleus accumbens, and limbic cortex.

Question 25

Differentiate between human brains and rat brains

Answer 25

rat and human brains have the same major subdivisions that are topographically organized in similar locations.

Rat brains have relatively larger olfactory bulbs and midbrains.

Human brains have expanded secondary and tertiary association areas of the cerebral cortex that serve higher-order sensory perception and cognitive functions.