ANATOMY & PHYSIOLOGY Chapter 12 THE NERVOUS SYSTEM AND NERVOUS

Image Slideshow

both anatomical and functional
Describe the functional and structural differences between

gray matter and white matter structures
Name the parts of the multipolar neuron in order of polarity
List the types of glial cells and assign each to the proper division of the nervous system, along with their function(s)
Distinguish the major functions of the nervous system: sensation, integration, and response
Describe the components of the membrane that establish the resting membrane potential
Describe the changes that occur to the membrane that result in the action potential
Explain the differences between types of graded potentials
Categorize the major neurotransmitters by chemical type and effect

Add:
Be able to discuss normal development and selected aging issues
Be able to discuss selected, associated disorders

Objectives
Identify the anatomical and functional divisions of the nervous system
Central

(CNS)
Peripheral (PNS)
or
Somatic (SNS)
Autonomic (ANS)
Relate the functional and structural differences between gray matter and white matter structures of the nervous system to the structure of neurons
List the basic functions of the nervous system
Sensation (Input / Afferent signaling)
Integration (Analysis)
Response (Output / Efferent signaling)

are referred to as ganglia and nerves, which can be

seen as distinct structures. The equivalent structures in the CNS are not obvious from this overall perspective and are best examined in prepared tissue under the microscope.

autopsy, with a partial section removed, shows white matter surrounded

by gray matter. Gray matter makes up the outer cortex of the brain. (credit: modification of work by “Suseno”/Wikimedia Commons)

its protons and neutrons.
The nucleus of a cell is the

organelle that contains DNA.
A nucleus in the CNS is a localized center of function with the cell bodies of several neurons, shown here circled in red. (credit c: “Was a bee”/Wikimedia Commons)

of the eye to the brain shows the optic nerve

extending from the eye to the chiasm, where the structure continues as the optic tract. The same axons extend from the eye to the brain through these two bundles of fibers, but the chiasm represents the border between peripheral and central.

N.B.:
In Figure 12.5, the two colors differentiate the left/right origin of the visual stimuli – not whether the structures are peripheral (nerves) or central (tracts)!

structures include the spinal nerves, both motor and sensory fibers,

as well as the sensory ganglia (posterior root ganglia and cranial nerve ganglia). Autonomic structures are found in the nerves also, but include the sympathetic and parasympathetic ganglia. The enteric nervous system includes the nervous tissue within the organs of the digestive tract.

Pearson.
Relationships between the subdivisions of the nervous system

neuron
Identify the different types of neurons on the basis of

polarity
List the glial cells of the CNS and describe their function
List the glial cells of the PNS and describe their function

are labeled on a multipolar neuron from the CNS.
N.B.: the

axon’s initial segment is more often called “axon hillock” in the literature.
N.B. The synaptic end bulbs are also called “terminal boutons”.

includes both the axon and dendrite. Bipolar cells have two

processes, the axon and a dendrite. Multipolar cells have more than two processes, the axon and two or more dendrites.

N.B.: The type of unipolar neuron above is often referred to as “pseudo-unipolar.”

on the basis of other criteria. (a) The pyramidal cell

is a multipolar cell with a cell body that is shaped something like a pyramid. (b) The Purkinje cell in the cerebellum was named after the scientist who originally described it. (c) Olfactory neurons are named for the functional group to which they belong.

Also have an important role in establishing the blood-brain barrier

(BBB)

microglia, and ependymal cells that support the neurons of the

CNS in several ways.

Image source:
Science Photo Library, accessed 07/2017.

Adapted from Marieb’s Anatomy and Physiology, 9th edition, Pearson.

and Schwann cells.

cell membrane around the cell membrane of an axon segment.

A single Schwann cell insulates a segment of a peripheral nerve, whereas in the CNS, an oligodendrocyte may provide insulation for a few separate axon segments. EM × 1,460,000. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

nervous system:
sensation
integration
response
List the sequence of events in a simple

sensory receptor–motor response pathway

of the water.

and the integration in the CNS, a motor response is

formulated and executed.

membrane that establish the resting membrane potential
Describe the changes that

occur to the membrane that result in the action potential

of a phospholipid bilayer and has many transmembrane proteins, including

different types of channel proteins that serve as ion channels.

acetylcholine, binds to a specific location on the extracellular surface

of the channel protein, the pore opens to allow select ions through. The ions, in this case, are cations of sodium, calcium, and potassium.

surrounding tissue, such as pressure or touch, the channel is

physically opened. Thermoreceptors work on a similar principle. When the local tissue temperature changes, the protein reacts by physically opening the channel.

around them. Amino acids in the structure of the protein

are sensitive to charge and cause the pore to open to the selected ion.

N.B.: The voltage-gated sodium channels of the axolemma have two gates: an activation gate and a deactivation gate.

the membrane randomly. The particular electrical properties of certain cells

are modified by the presence of this type of channel.

electrode is inserted into the cell and a reference electrode

is outside the cell. By comparing the charge measured by these two electrodes, the transmembrane voltage is determined. It is conventional to express that value for the cytosol relative to the outside.

membrane against time, the action potential begins with depolarization, followed

by repolarization, which goes past the resting potential into hyperpolarization, and finally the membrane returns to rest.

cell membrane against time, the events of the action potential

can be related to specific changes in the membrane voltage. (1) At rest, the membrane voltage is -70 mV. (2) The membrane begins to depolarize when an external stimulus is applied. (3) The membrane voltage begins a rapid rise toward+30 mV. (4) The membrane voltage starts to return to a negative value. (5) Repolarization continues past the resting membrane voltage, resulting in hyperpolarization. (6) The membrane voltage returns to the resting value shortly after hyperpolarization.

ions move through
voltage-gated
channels.
Depolarization
is caused by Na+
flowing into the

cell.

Repolarization is
caused by K+ flowing
out of the cell.

Hyperpolarization is caused by K+ continuing to
leave the cell.

1

2

3

4

Image source: Adapted from Marieb’s Anatomy and Physiology, 9th edition, Pearson.

“Initial segment” of the axon ≈ “axon hillock”.

types of graded potentials
Categorize the major neurotransmitters by chemical type

and effect

voltage, the characteristics of which depend on the size of

the stimulus. Some types of stimuli cause depolarization of the membrane, whereas others cause hyperpolarization. It depends on the specific ion channels that are activated in the cell membrane.

N.B.: Graded potentials form along dendrites,
but also on the neuron’s soma (although not at the axon hillock).

is the overall change in the membrane potential. At point

A, several different excitatory postsynaptic potentials add up to a large depolarization. At point B, a mix of excitatory and inhibitory postsynaptic potentials result in a different end result for the membrane potential.

mV, the inside becoming less
negative (more positive).
Time (ms)
+50
0
–50
–70
–100
0
1
2
3
4
5
6
7
Image source: Adapted

from Marieb’s Anatomy and Physiology, 9th edition, Pearson.

EPSP

inside becoming more negative.
Resting
potential
Hyper-
polarization
Image source: Adapted from Marieb’s Anatomy and

Physiology, 9th edition, Pearson.

IPSP

depolarizes.
Image source: Adapted from Marieb’s Anatomy and Physiology, 9th edition,

Pearson.

Graded Potentials (1/2): Generation

with distance: Because current is lost through the “leaky” plasma

membrane, the voltage declines with distance from the stimulus (the voltage is decremental). Graded potentials are short- distance signals.

–70

Graded Potentials (2/2): Decay

Image source: Adapted from Marieb’s Anatomy and Physiology, 9th edition, Pearson.

from thousands of other neurons
A single EPSP cannot induce an

AP
EPSPs and IPSPs can summate to influence postsynaptic neuron:
Temporal summation
Spatial summation

AP occurs only if ( ∑ EPSPs + ∑ IPSPs ) ≥ AP threshold

and Physiology, 9th edition, Pearson.

9th edition, Pearson.

9th edition, Pearson.

Marieb’s Anatomy and Physiology, 9th edition, Pearson.

synapse increases ability of presynaptic cell to excite postsynaptic neuron
Ca2+

concentration increases in presynaptic terminal and postsynaptic neuron
Ca2+ activates kinase enzymes that promote more effective responses to subsequent stimuli

abundant in embryo
Two-way signal transduction

Chemical
A gap separates the pre- post-synaptic

elements (synaptic cleft)
Signal switches from electric to chemical to electric again
Increasingly abundant in fetus and the majority of synapses after birth
One-way signal transduction only

neuron and its target cell (which is not necessarily a

neuron). The presynaptic element is the synaptic end bulb of the axon where Ca2+ enters the bulb to cause vesicle fusion and neurotransmitter release. The neurotransmitter diffuses across the synaptic cleft to bind to its receptor. The neurotransmitter is cleared from the synapse either by enzymatic degradation, neuronal reuptake, or glial reuptake.

and Physiology, 9th edition, Pearson.

Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal.
Image

source: Adapted from Marieb’s Anatomy and Physiology, 9th edition, Pearson.

vesicles to release neurotransmitter by exocytosis
4- Neurotransmitter diffuses across
the synaptic

cleft and binds to specific
receptors on the postsynaptic membrane.

Image source: Adapted from Marieb’s Anatomy and Physiology, 9th edition, Pearson.

resulting in graded potentials.
6- Neurotransmitter effects are terminated by reuptake

through…

…enzymatic degradation,
or diffusion away from the synapse.

Image source: As before.

when the neurotransmitter binds to it.
A metabotropic receptor is a

complex that causes metabolic changes in the cell when the neurotransmitter binds to it (1). After binding, the G protein hydrolyzes GTP and moves to the effector protein (2). When the G protein contacts the effector protein, a second messenger is generated, such as cAMP (3). The second messenger can then go on to cause changes in the neuron, such as opening or closing ion channels, metabolic changes, and changes in gene transcription.

direct signaling; (M) metabotropic or indirect signaling; “E”, excitatory; “I”,

inhibitory.

for maintaining the chemical environment of the CNS tissue. If

the balance of ions is upset, drastic outcomes are possible.
Normally the concentration of K+ is higher inside the neuron than outside. After the repolarizing phase of the action potential, K+ leakage channels and the Na+/K+ pump ensure that the ions return to their original locations.
Following a stroke or other ischemic event, extracellular K+ levels are elevated. The astrocytes in the area are equipped to clear excess K+ to aid the pump. But when the level is far out of balance, the effects can be irreversible.
Astrocytes and other glial cells enlarge and their processes swell. They lose their K+ buffering ability and the function of the pump is affected, or even reversed. This Na+/K+ imbalance negatively affects the internal chemistry of cells, preventing glial cells and neurons from functioning normally.

origins can cause a demyelination of axons. As the myelin

insulation of axons is compromised, electrical signaling becomes slower.
Multiple sclerosis (MS) is an example of an autoimmune disease. The antibodies produced by lymphocytes (a type of white blood cell) mark CNS myelin as something that should not be in the body. This causes inflammation and the destruction of the myelin in the central nervous system. Scarring – sclerosis – occurs in the white matter of the brain and spinal cord. The symptoms of MS include both somatic and autonomic deficits. Control of the musculature is compromised, as is control of organs such as the bladder.
Guillain-Barré syndrome is an example of a demyelinating disease of the PNS. It is also the result of an autoimmune reaction, but the inflammation is in peripheral nerves. Sensory symptoms or motor deficits are common, and autonomic failures can lead to changes in the heart rhythm or a drop in blood pressure, especially when standing, which causes dizziness.

sequence of amino acids must fold into a three-dimensional shape

that is based on the interactions between and among those amino acids.
When the folding is disturbed, and proteins take on a different shape, they stop functioning correctly. Symptoms can arise as a result of the functional loss of these proteins, but often also because the accumulation of these altered proteins is toxic.

Alzheimer’s Disease
One of the strongest theories of what causes Alzheimer’s disease is based on the accumulation of beta-amyloid plaques, dense conglomerations of a protein that is not functioning correctly.
Creutzfeld-Jacob Disease
Creutzfeld-Jacob disease, the human variant of the prion disease known as mad cow disease, also involves the accumulation of amyloid plaques, similar to Alzheimer’s. Cerebral neurons die in small clusters, creating a “spongiform encephalopathy”.
Parkinson’s Disease
Parkinson’s disease is linked to an increase in a protein known as alpha-synuclein that is toxic to the dopamine-secreting neurons of the substantia nigra nucleus (midbrain).

an interactive game that demonstrates the use of Magnetic Resonance

Imaging (MRI) and compares it with other types of imaging technologies.
Visit this site http://openstaxcollege.org/l/troublewstairs to read about a woman that notices that her daughter is having trouble walking up the stairs. This leads to the discovery of a hereditary condition that affects the brain and spinal cord. The electromyography and MRI tests indicated deficiencies in the spinal cord and cerebellum, both of which are responsible for controlling coordinated movements.
Visit this site http://openstaxcollege.org/l/nervetissue3 to learn about how nervous tissue is composed of neurons and glial cells.
View an electron micrograph of a cross-section of a myelinated nerve fiber at http://openstaxcollege.org/l/nervefiber (U. of Michigan).
View this animation http://openstaxcollege.org/l/dynamic1 of what happens across the membrane of an electrically active cell.

virtual neurophysiology lab, and to observe electrophysiological processes in the

nervous system.
Watch this video http://openstaxcollege.org/l/summation to learn about summation.
Watch this video http://openstaxcollege.org/l/neurotrans to learn about the release of a neurotransmitter.

containing ependymal cells that line cover the outside of blood

capillaries and filter blood to produce CSF in the four ventricles of the brain

Add p.543:
Ependymal cell: glial cell type in the CNS, bearing cilia, which lines the internal cavities of the CNS; responsible for producing cerebrospinal fluid in choroid plexuses

Error p. 543:
Leakage channel: ion channel that opens randomly and remains open as it is not gated to a specific event, also known as a non-gated channel

Add p.545:
Synaptic end bulb: also known as “terminal bouton” - swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse

Reserved.
Last modified: 09/2017 / Dr. F. Jolicoeur
End

Anatomy and Physiology, 9th edition, Pearson.

Anatomy and Physiology, 9th edition, Pearson.