Chapter 2: Structure and Function of the Nervous System

Question 1

What is a neuron?

Answer 1

A neuron is a nerve cell that has the main function of transmitting information in the form of electrical signalling over long distances. Neurons are surrounded by a cell membrane and are filled with cytoplasm and the organelles needed for optimal functioning.

Question 2

What are the types of neurons?

Answer 2

1. Sensory neurons
2. Motor neurons
3. Interneurons

Question 3

What is a sensory neuron?

Answer 3

Sensory neurons convert physical stimuli from the external world around us as well as our internal environment into an electrical signal.

Question 4

What is an interneuron?

Answer 4

Interneurons are nerve cells in the brain and spinal cord that receive information from sensory neurons. They form complex interacting neural circuits. Interneurons are responsible for “conscious sensations, recognition, memory, decision making, and cognition.”

Question 5

What is a motor neuron?

Answer 5

Motor neurons direct the biobehavioural response.

Question 6

What are the main external parts of a neuron?

Answer 6

1. Dendrites
2. Soma
3. Axon
4. Synaptic terminal

Question 7

Describe dendrites?

Answer 7

Dendrites receive information from other cells and are connected to the soma. Dendrites have receptors on them that respond to the neurochemicals released by other neurons. Dendrites are covered with dendritic spines which increase the surface area for receiving information.

Question 8

What makes dendrites and dendritic spines change?

Answer 8

Dendrites and dendritic spines can change in size and shape throughout the lifespan in response to changes in synaptic transmission. These changes allow people to learn as we interact with our environments. Smaller and less dense dendritic spines are associated with poorer connectivity, learning, and brain functioning.

Question 9

Describe the soma.

Answer 9

The soma is the cell body of the neuron which contains the nucleus and is responsible for metabolic care of the neuron. The soma is responsible for synthesizing proteins required for cell growth and maintenance. This includes transcription of the genetic code for proteins by mRNA and the linking of amino acids into a protein by ribosomes.

Question 10

Describe axons.

Answer 10

The axon is the single tubular extension from the soma that transmits the electrical signal to the synaptic vesicles on the axon terminals. Most axons have myelin which is an insulating sheath made of glial cells. The thicker the myelin sheath, the faster electrical signals are conducted along the axon.

Question 11

Describe the synaptic terminal.

Answer 11

The synaptic terminal is the membrane-bound sphere at the end of the axon (axon terminal) from which neurotransmitters are stored and released into the synapse between cells to transmit information to adjacent cells or the target orgran. Neurotransmitters are released when the action potential arrives.

Question 12

What are the four types of glial cells?

Answer 12

1. Schwann cells
2. Oligodendroglia
3. Astrocytes
4. Microglia

Question 13

What are Schwann cells?

Answer 13

Schwann cells form the myelin sheath on a single axon in the peripheral nervous system. They also help with axon regeneration by releasing growth factors after damage to neurons and they provide a pathway for the axon to regenerate toward the target tissue.

Question 14

What are oligodendroglia?

Answer 14

Oligodendroglia form the myelin sheath on axons in the central nervous system and, unlike Schwann cells, can wrap around multiple axons at once. Also unlike Schwann cells, they inhibit regrowth of axons because they do not provide growth factors following damage nor do they provide a path for growth.

Question 15

What are astrocytes?

Answer 15

Astrocytes provide structural support by intertwining with neurons. They also help maintain the ionic and chemical environment by taking up excess neurochemicals that could cause damage to the cells. Additionally, astrocytes perform gliosis, regulate central nervous system blood flow, and coordinate reciprocal glia-neuron activity.

Question 16

What are microglia?

Answer 16

Microglia remove dying cells from sites of neuron damage (phagocytosis) and provide the primary source of immune response in the central nervous system.

Question 17

What is resting potential?

Answer 17

Resting potential refers to the difference in electrical charge inside a neuron compared to outside a neuron. The inside of neurons are more negative than the outside making them polarized in the resting state (at -70 millivolts).

Question 18

What maintains the resting potential of cells?

Answer 18

The resting potential is maintained by the concentration gradient of potassium ions (K+) and the Na+-K+ ion pump.

Question 19

What causes epileptic seizures?

Answer 19

In healthy people, neurons fire at different times but when someone has an epileptic seizure, the neurons all fire at the same time. The abnormal action potential spreads from the origin to neurons and synaptic pathways connected to the original site. The neurons themselves are not abnormal; rather, it is the regulation of the neurons’ firing that is abnormal. Seizures spontaneously end after 15 seconds to 5 minutes when the neurons become depleted of the ATP required to maintain the high rate of firing.

Question 20

What are the functions of the spinal cord?

Answer 20

The functions of the spinal cord are analysis and integration of sensory and motor information sent by peripheral nerves (in the peripheral nervous system). The central nervous system (brain and spinal cord) then responds by sending signals to regulate muscle and organ function.

Question 21

What are the distinct regions of the CNS?

Answer 21

1. spinal cord
2. myelencephalon
3. metencephalon
4. mesencephalon
5. diencephalon
6. telencephalon

Question 22

What are the major parts of the limbic system?

Answer 22

1. amygdala
2. hippocampus
3. basal ganglia
4. cingulate gyrus.

Question 23

What does the amygdala do?

Answer 23

The amygdala (almond-shaped) is known as the emotional centre of the brain. It is responsible for the fight-flight-freeze response as well as learning on the basis of reward or punishment.

Question 24

What does the hippocampus do?

Answer 24

The hippocampus (seahorse-shaped) is important for making new long-term memories.

Question 25

Describe the basal ganglia.

Answer 25

The basal ganglia is made up of the caudate, putamen and globus pallidus and organizes motor behaviour. It is also involved with rule-based habit learning, inhibiting undesired movements and allowing desired movements, choosing from potential actions, motor planning, sequencing, predictive control, working memory, and attention.

Question 26

What does the cingulate gyrus do?

Answer 26

The cingulate gyrus connects smells and sights with pleasant memories of previous emotions. It is also involved in emotional reaction to pain and regulating aggressive behaviour.

Question 27

Describe the characteristics of the cell membrane.

Answer 27

The cell membrane is a phospholipid bilayer that does not allow materials to pass unless they are lipid-soluble. The membrane has receptors (large protein molecules) in it that are the initial sites of action of ligands (i.e., neurotransmitters, hormones, drugs). Cell membranes also have ion channels and transporters (another group of proteins) that move ionized molecules across the membrane. Channels can be one of three types: gated channels, ligand-gated channels, or voltage-gated channels.

Question 28

What is a local potential?

Answer 28

Local potentials are small, local changes in ion distribution and electrical potential differences caused by momentary opening of ligand-gated ion channels in response to stimuli disturbing the membrane. Local potentials are graded, decremental, can be depolarization or hyperpolarization, and can be either spatial and temporal summation.

Question 29

What is an action potential?

Answer 29

Action potential is when the threshold of -50mV is reached opening the voltage-gated Na+ channels, allowing large amounts of Na+ to enter the cell membrane depolarizing it. The action potential is transmitted down the axon by sequential opening of voltage-gated Na+ channels. It is nondecremental, all-or-none and the intensity of the stimulus is coded by rate of firing.

Question 30

What are the divisions of the nervous system?

Answer 30

1. Central nervous system

2. Peripheral nervous system

Question 31

What makes up the central nervous system?

Answer 31

1. Brain

2. Spinal cord

Question 32

Describe the peripheral nervous system.

Answer 32

The peripheral nervous system connects all parts of the body to the central nervous system and is further subdivided into the autonomic nervous system and the somatic nervous system.

Question 33

Describe the autonomic nervous system.

Answer 33

The autonomic nervous system is made up of the sympathetic and parasympathetic divisions and regulates the internal environment.

Question 34

What does the sympathetic nervous system do?

Answer 34

The sympathetic division predominates at times when energy expenditure is necessary (e.g. when stressed). The sympathetic nervous system consists of nerves that carry sensory and motor information from (input information) the external environment and body senses and to (output information) the skeletal muscles.

Question 35

What does the parasympathetic nervous system do?

Answer 35

The parasympathetic nervous system predominates when energy can be conserved and reserved for later.

Question 36

Explain the division of the cerebral cortex.

Answer 36

The cerebral cortex is divided into four lobes in each hemisphere: the parietal lobe, occipital lobe, temporal lobe and the frontal lobe. The first three lobes are sensory in function and the last (frontal lobe) is responsible for movement and executive planning.

Question 37

What are the main differences between rat and human brains?

Answer 37

1. absolute and relative size
2. rat brains have relatively bigger olfactory bulbs and midbrains
3. human brains have expanded secondary and tertiary association areas of the cerebral cortex that allow for human’s greater capacity for cognitive processing, reasoning, abstract thinking, and decision making

Question 38

What is an axon hillock?

Answer 38

The axon hillock is 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 39

What enhances conduction of the action potential along the axon?

Answer 39

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

Question 40

What is epigenetics?

Answer 40

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 41

What are EPSPs?

Answer 41

Excitatory postsynaptic potentials (EPSPs), or depolarizations, occur when ligand-gated Na+ channels open and allow Na+ to enter the cell on its concentration gradient, making the cell slightly more positive and bringing the membrane potential closer to the threshold for firing.

Question 42

What are IPSPs?

Answer 42

Opening Cl– channels allows Cl– to enter on its concentration gradient, making the cell more negative and farther from the threshold, causing hyperpolarizations called inhibitory postsynaptic potentials (IPSPs). 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 43

What is the absolute refractory period?

Answer 43

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.

Question 44

What is the relative refractory period?

Answer 44

As the cell becomes more positive inside, 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.

Question 45

What are neurotropic factors?

Answer 45

Neurotrophic factors are neuronal growth factors that guide the development of neurons, regulate dendritic growth and retraction, and aid in survival of neurons.

Question 46

What are the main similarities between human and rat brains?

Answer 46

Rat and human brains have the same major subdivisions, which are topographically organized in similar locations.