Unit 5: The Nervous System
Unit 5
The Nervous System
(4 hours LEC/6 hours LAB)
Introduction
This unit describes one of the very complex organ systems of
the body – the nervous system. This begins in looking at an overview
of the structures of the nervous system to understand how many of
these functions are possible. It presents its two major divisions, namely
the central nervous system and peripheral nervous system. Though
each subdivision is also called a "nervous system," all of these smaller
systems belong to the single, highly integrated nervous system where
each subdivision has structural and functional characteristics that
distinguish it from the others.
Learning Outcomes
At end of this unit, you are expected to:
a. discuss the division of the Nervous System;
b. identify the gross structure and function of the Central
Nervous System;
c. identify the gross structure and function of the
Peripheral Nervous System;
d. list the cranial nerves in order of anatomical location
and provide the central and peripheral connections;
e. list the spinal nerves by vertebral region and by which
nerve plexus each supplies;
f. correlate the problems of the nervous system with its
effect on the respiratory system;
g. enumerate the neurotransmitters and their function;
and
h. describe the neuronal pathway
Presentation of Contents
It is probably difficult for us to understand how possible it is for us
to think, feel, control our body movements and even control the
things you don’t think about, like the beating of your heart, and
breathing. So let us take a ​snapshot of the nervous system which
tries to control these things. And, eventually it will make it easier for
us to understand the whole complex system.
The nervous system is generally characterized as the body’s
communication network that consists of all nerve cells. Also, it is a
major controlling and regulatory system of the body and the center
of all mental activity.
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Unit 5: The Nervous System
The nervous system is intricate with numerous parts and various
new vocabulary words. It might even seem overwhelming at first
but you can get it through the figures and a little study reading
VanPutte, Regan & Russo (2019); Marieb E. & Keller (2019) or
Rizzo D. (2016).
Figure 1. Major division and subdivision of the nervous system.
Figure 2. Organization of the nervous system
Application:
1. Identify five general functions of the nervous system.
Explain these functions and give examples each.
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Unit 5: The Nervous System
2. Discuss briefly each component of the nervous system as
presented in Figure 1.
3. Explain the communication between the central nervous
system and peripheral nervous sytem as presented in
Figure 2.
Your readings might have introduced you already of the
different structures making up the nervous system. And though the
nervous system has been characterized as a complex system it
only composed of two main types of cells in nerve tissue,
specifically; the ​neuron (nerve cell) and the ​neuroglia (glial cell)​.
The former is the "conducting" cell and has three significant parts;
the ​cell body, the dendrites and the axon, and are further classified
as ​multipolar, bipolar and pseudo-unipolar​. While the latter is the
“supporting” cells because it carry out different functions that
enhance the functions of the neurons. They are also classified
according to type based on location, for the CNS we have the
astrocytes, ependymal cells, microglia and oligodendrocytes and
for the glial cells of the PNS, we have the ​Schwann cells​.
A localized collection of neuron cell bodies in the CNS is referred to
as a nucleus. In the PNS, a cluster of neuron cell bodies is referred
to as a ganglion. A bundle of axons, or fibers, found in the CNS is
called a tract whereas the same thing in the PNS would be called a
nerve.
The cells in the nervous system communicate through electrical
signals and neuronal pathways. All cells exhibit electrical
properties. Neuron as described are similar to a light switch being
turned on, but, “what flips the light switch on?” This change is a
result of ​resting membrane potentials, action potentials a
​ nd
communication in between ​synapse.​
Moreover, within the CNS are organized to form pathways. The
simplest are the ​converging and diverging pathways.​ Within the
CNS and in many PNS synapses, it takes more than a single action
potential to have an effect. The ​reflex arc on the other hand, is the
neuronal pathway by which reflex occurs and generally has five
basic components, to be exact are the ​sensory receptor, sensory
neuron, interneuron, motor neuron and the effector organ​.
To understand further these processes, read and appreciate the
illustrations presented in VanPutte, Regan & Russo (2019); Marieb
E. & Keller (2019) or Rizzo D. (2016).
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Unit 5: The Nervous System
1. Describe the neuron as a “conducting cell”. Define its
structures.
2. Differentiate the types of neurons and give examples for
each.
3. Discuss the structure and function of the four glial cells.
4. Explain the resting membrane potential. Describe the role of
the potassium leak channel and the sodium- potassium
pump.
5. Put in a diagram the events that generate an action potential.
6. Describe the events that happen in between synapse. Start
with an action potential in the presynaptic neuron and end
with the generation of an action potential in the postsynaptic
neuron.
7. List the different neurotransmitters. Describe their primary
function.
8. Compare and contrast the converging and diverging
pathways. Give an example for each.
One easy approach to activate your understanding of the
structure of the nervous system is to start with the large divisions
and then going through a more in-depth learning of its specific
structures.
The ​Central Nervous System consists of the brain and spinal cord,
which are located in the dorsal body cavity. The brain is surrounded
by the cranium, and the spinal cord is protected by the vertebrae.
The brain is continuous with the spinal cord at the foramen
magnum. In addition to bone, the CNS is surrounded by connective
tissue membranes, called meninges, and by cerebrospinal fluid.
The brain is divided into the cerebrum, diencephalons, brain stem,
and cerebellum. The largest and most obvious portion of the brain is
the cerebrum, which is divided by a deep longitudinal fissure into
two cerebral hemispheres and is connected by an arching band of
white fibers, called the corpus callosum. Each cerebral hemisphere
is divided into five lobes, four of which have the same name as the
bone over them: the fontal lobe, the parietal lobe, the occipital lobe,
and the temporal lobe. A fifth lobe, the insula or Island of Reil, lies
deep within the lateral sulcus. The diencephalon is centrally located
and is nearly surrounded by the cerebral hemispheres. It includes
the thalamus, hypothalamus, and epithalamus. The brain stem is
the region between the diencephalons and the spinal cord. It
consists of three parts: midbrain, pons, and medulla oblongata. The
cerebellum, the second largest portion of the brain, is located below
the occipital lobes of the cerebrum. Three paired bundles of
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Unit 5: The Nervous System
myelinated nerve fibers, called cerebellar peduncles, form
communication pathways between the cerebellum and other parts of
the central nervous system. A series of interconnected, fluid-filled
cavities are found within the brain. These cavities are the ventricles
of the brain, and the fluid is cerebrospinal fluid (CSF).
The spinal cord extends from the foramen magnum at the base of
the skull to the level of the first lumbar vertebra. The cord is
continuous with the medulla oblongata at the foramen magnum.
Like the brain, the spinal cord is surrounded by bone, meninges,
and cerebrospinal fluid.
The spinal cord is divided into 31 segments with each segment
giving rise to a pair of spinal nerves. At the distal end of the cord,
many spinal nerves extend beyond the conus medullaris to form a
collection that resembles a horse's tail. This is the cauda equina. In
cross section, the spinal cord appears oval in shape. The spinal
cord serves as a conduction pathway for impulses going to and from
the brain. Sensory impulses travel to the brain on ascending tracts
in the cord. Motor impulses travel on descending tracts.
On the other hand, the ​Peripheral Nervous System ​consists of the
nerves that branch out from the brain and spinal cord. These nerves
form the communication network between the CNS and the body
parts. It is further subdivided into the somatic nervous system and
the autonomic nervous system. The somatic nervous system
consists of nerves that go to the skin and muscles and is involved in
conscious activities. While the autonomic nervous system consists
of nerves that connect the CNS to the visceral organs such as the
heart, stomach, and intestines which mediates unconscious
activities.
A nerve contains bundles of nerve fibers, either axons or dendrites,
surrounded by connective tissue. Sensory nerves contain only
afferent fibers, long dendrites of sensory neurons. Motor nerves
have only efferent fibers, long axons of motor neurons. Mixed
nerves contain both types of fibers.
Twelve pairs of cranial nerves emerge from the inferior surface of
the brain. The cranial nerves are designated both by name and by
Roman numerals and most of the nerves have both sensory and
motor components.
There are thirty-one pairs of spinal nerves emerge laterally from the
spinal cord. Each pair of nerves corresponds to a segment of the
cord, specifically; there are 8 cervical nerves, 12 thoracic nerves, 5
lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve.
The autonomic nervous system is a visceral efferent system, which
means it sends motor impulses to the visceral organs. It functions
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Unit 5: The Nervous System
automatically and continuously, without conscious effort, to
innervate smooth muscle, cardiac muscle, and glands. It is
concerned with heart rate, breathing rate, blood pressure, body
temperature, and other visceral activities that work together to
maintain homeostasis. The autonomic nervous system has two
parts, the sympathetic division and the parasympathetic division.
To add up to this knowledge, complement this by reading VanPutte,
Regan & Russo (2019); Marieb E. & Keller (2019) or Rizzo D.
(2016).
1. Name the three layers of meninges around the brain and
spinal cord. Describe each layer.
2. Elaborate the function of the brain structures.
a. Cerebrum
- right and left hemispheres
- lobes: frontal, parietal, temporal, occipital, insula
b. Diencephalon
- thalamus, hypothalamus, and epithalamus
c. Brain stem
- midbrain, pons, and medulla oblongata
d. Cerebellum
3. Discuss the structure of the spinal cord. Explain how the
spinal nerve is connected to the spinal cord.
4. Trace the CSF pathway.
5. List the different cranial nerves. Describe the mode of
assessment for each.
6. Differentiate the function of the sensory neuron and motor
neuron.
7. List the innervation of each spinal nerve.
8. Compare and contrast sympathetic from parasympathetic
response.
An essential role of sensory receptors is to help us explore
and learn about the environment around us, or the state of our
internal environment. The ​senses a
​ re the means by which the brain
receives information about the environment and the body. The
process initiated by stimulating sensory receptors is termed as
sensation,​ while the conscious awareness of hose stimuli is
perception.​ Stimuli in the environment activate specialized receptor
cells in the peripheral nervous system. Different types of stimuli are
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Unit 5: The Nervous System
sensed by different types of receptor cells. Receptor cells can be
classified into types on the basis of three different criteria: cell type,
position, and function.
Ask anyone what the senses are, and they are likely to list the five
major senses—taste, smell, touch, hearing, and sight. However,
these are not all of the senses. The most obvious omission from this
list is balance.
A general sense is one that is distributed throughout the body and
has receptor cells within the structures of other organs.
Mechanoreceptors in the skin, muscles, or the walls of blood vessels
are examples of this type. General senses often contribute to the
sense of touch, as described above, or to proprioception (body
movement) and kinesthesia (body movement), or to a visceral sense,
which is most important to autonomic functions.
A special sense is one that has a specific organ devoted to it, namely
the eye, inner ear, tongue, or nose. Each of the senses is referred to
as a sensory modality.
Gustation is the special sense associated with the tongue. The
receptor cells are sensitive to the chemicals contained within foods
that are ingested, and they release neurotransmitters based on the
amount of the chemical in the food. Neurotransmitters from the
gustatory cells can activate sensory neurons in the facial,
glossopharyngeal, and vagus cranial nerves.
Like taste, the sense of smell, or olfaction, is also responsive to
chemical stimuli. As airborne molecules are inhaled through the
nose, they pass over the olfactory epithelial region and dissolve into
the mucus.
Hearing, or audition, is the transduction of sound waves into a neural
signal that is made possible by the structures of the ear. The auricle,
ear canal, and tympanic membrane are often referred to as the
external ear. The middle ear consists of a space spanned by three
small bones called the ossicles. The three ossicles are the malleus,
incus, and stapes, which are Latin names that roughly translate to
hammer, anvil, and stirrup. The middle ear is connected to the
pharynx through the Eustachian tube, which helps equilibrate air
pressure across the tympanic membrane. Along with audition, the
inner ear is responsible for encoding information about equilibrium,
the sense of balance.
Somatosensation is the group of sensory modalities that are
associated with touch, proprioception, and interoception. These
modalities include pressure, vibration, light touch, tickle, itch,
temperature, pain, proprioception, and kinesthesia.
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Unit 5: The Nervous System
Vision is the special sense of sight that is based on the transduction
of light stimuli received through the eyes. Tears are produced by the
lacrimal gland. Movement of the eye within the orbit is accomplished
by the contraction of six extraocular muscles that originate from the
bones of the orbit and insert into the surface of the eyeball. Four of
the muscles are arranged at the cardinal points around the eye and
are named for those locations. They are the superior rectus, medial
rectus, inferior rectus, and lateral rectus.
Photoreceptor cells have two parts, the inner segment contains the
nucleus and other common organelles of a cell, whereas the outer
segment is a specialized region in which photoreception takes place.
There are two types of photoreceptors—rods and cones—which
differ in the shape of their outer segment. There are three cone
photopigments, called opsins, which are each sensitive to a
particular wavelength of light. The wavelength of visible light
determines its color. The pigments in human eyes are specialized in
perceiving three different primary colors: red, green, and blue.
VanPutte, Regan & Russo (2019); Marieb E. & Keller (2019) or Rizzo
D. (2016). will help you further in understanding the concepts of the
special senses.
1. Describe structural receptor types and functional receptor
types.
2. Discuss the functional parts of the five senses. Name and
identify their specific receptors.
3. Indicate the action of the extrinsic eye muscle.
4. Identify assessment methods for the special senses
Unit Summary
Here is what you have learned from the Nervous system:
- The nervous system is the major controlling, regulatory, and
communicating system in the body and the center of all
mental activity.
- The various activities of the nervous system generally
includes; sensory, integrative, and motor function.
- Neurons are the nerve cells that transmit impulses. Supporting
cells are neuroglia.
- A neuron is composed of a cell body or soma, one or more
afferent processes called dendrites, and a single efferent
process called an axon.
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Unit 5: The Nervous System
-
-
The central nervous system consists of the brain and spinal
cord.
The peripheral nervous system consists of cranial nerves,
spinal nerves, and ganglia.
The afferent division of the peripheral nervous system carries
impulses to the CNS; the efferent division carries impulses
away from the CNS.
There are three layers of meninges around the brain and
spinal cord, the dura mater, arachnoid, and the pia mater.
The spinal cord functions as a conduction pathway and as a
reflex center.
Sensory impulses travel to the brain on ascending tracts in the
cord. Motor impulses travel on descending tracts.
The major senses are taste, smell, touch, hearing, sight and
also the sense of balance.
Feedback
Part 1: Test for Critical Thinking. ​Read and analyze the problems
carefully. From your readings and understanding answer the
questions concisely and in no more than 300 words.
1. It had been a busy week for you. You had taken various
exams and activities recently, and as if that wasn't stressful
enough, plus you spend much of your time helping out at
home. By the end of the week, you decided to go for a walk
and some genuine relaxation. The day was warm you took off
her shoes when at home. Halfway up the stairs, you stepped
on something extremely sharp and withdrew your foot in pain.
You hopped around on one foot, rubbing the other to ease the
pain, and then sat on the sofa. This incident is a simple event
and may have happened to you. In terms of the neural
pathways, this reaction requires a complex neural net. Explain
what happened?
2. Reflex output is initiated by an input stimulus and result in an
output response. Reflex activity ranges from simple to
complex. In a table format, list the different types of reflex and
how to assess these functions.
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Unit 5: The Nervous System
3. John encountered a motor vehicular accident when returning
home from work. Upon assessment he said he has lost his
consciousness for quite a while. On the basis of what you
learned about the brain function. Discuss the symptoms that
would likely to occur if John had cerebellar damage?
Part 2: Drawing/Labelling Exercise. ​Write your answers legibly.
1. Name the following parts of the neuron as indicated. Specify
the functions of each part.
2. Illustrate and explain the reflex arc.
3. Illustrate and explain transmission of neuronal impulses
across synapse.
4. Label the parts of the brain responsible for control of
respiration.
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Unit 5: The Nervous System
References:
Textbook/Manual:
1. Tortora & Derrikson (2016). Principles of Anatomy and
Physiology, 15​th​ Edition.
2. VanPutte C., Regan J., Russo A. (2019). Seeley’s Essentials
of Anatomy and Physiology 10th Edition
3. Gunstream S. (2003), Anatomy & Physiology, 3​rd​ Ed. McGraw
Hill
4. Marieb E. & Keller S., (2019). Essentials of Human Anatomy &
Physiology,12​th​ Ed, Pearson
5. Rizzo D. (2016). Fundamentals of Anatomy & Physiology, 4​th
Ed. Pearson
6. Hapan M.F., Domingo J., Sadang M.G. (2015). Human
Physiology and Anatomy Laboratory Manual 2​nd​ Edition C&E
Publishing
Online Sources:
https://courses.lumenlearning.com/suny-ap1/
https://training.seer.cancer.gov/anatomy/
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