Download LESSON 1.2 WORKBOOK How does brain structure impact its function?

LESSON 1.2 WORKBOOK
How does brain structure impact its
function?
DEFINITIONS OF TERMS
Central nervous system (CNS) –
contains the brain and spinal cord.
Peripheral nervous system
(PNS) – includes all the nerves outside the brain and spinal cord.
For a complete list of defined
terms, see the Glossary.
In this lesson, you’ll be dissecting a sheep’s brain.
During the dissection you’ll localize and identify major
brain structures. By understanding where these
structures are localized you’ll begin to appreciate how
the brain is organized spatially. Once you understand
spatial organization we can begin to investigate how
the different parts connect to control behavior.
If you have an iphone or an ipad you can download a great free app that will allow you to
look at the structures of the brain in 3D. These pictures are worth a thousand words as
we examine more closely how the brain is organized. The app is available FREE from the
itunes store. Just search ‘3D brain’.
How can we study our brains?
Before we get too much further in our discussion of how the brain is organized, let’s take a short tour of
the nervous system as a whole to orient you on all the different parts, how they’re classified and what
their functions are.
First of all we need to remember that your nervous system has basically three functions – it receives
information via our various sensory systems; it makes sense of these sensations and decides what an
appropriate response should be; and it executes that response. To complete these three functions, our
nervous system uses its two main branches - the central nervous system (CNS) and the peripheral
nervous system (PNS).
Wo r k b o o k
Lesson 1.2
Sensations come in from the environment via the PNS. The PNS delivers this information to the CNS
which then evaluates the information and decides how to respond. Finally, the CNS sends a signal the
PNS in order to be able to execute the response. Your central nervous system (CNS) includes your
brain and spinal cord while your peripheral nervous system includes all the nerves in your head, body
and limbs that lie outside the brain and spinal cord (Figure 4). Let’s start by briefly talking about the
peripheral nervous system and spinal cord, then we can concentrate on the brain for the remainder of
this lesson.
What are the three basic functions of your
nervous system?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
What is the CNS?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
What is the PNS?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
8
LESSON READING
Your Peripheral Nervous System (PNS)
The PNS can be further divided into the somatic nervous system, which controls voluntary muscles,
and the autonomic nervous system, which controls the function of organs and glands. The autonomic
nervous system has two divisions:
•
Sympathetic nervous system is nicknamed the “fight-or-flight” system because it prepares our
body when energy expenditure is necessary, such as during times of stress or excitement. This
system increases heart rate and blood pressure, stimulates secretion of adrenaline, and increases
blood flow to the skeletal muscles.
•
Parasympathetic nervous system helps our body conserve and store energy for later use. This
system increases salivation, digestion, and storage of glucose and other nutrients, as well as slowing
the heart and decreasing respiration.
DEFINITIONS OF TERMS
Peripheral nervous system
(PNS) – includes all the nerves outside the brain and spinal cord.
Somatic nervous system - part
of the PNS that controls voluntary
movement.
Autonomic nervous system –
part of the PNS that controls the
function of organs and glands.
For a complete list of defined
terms, see the Glossary.
Overall, the peripheral nervous system connects with
non-neuronal cells at one end and the central nervous
system at the other. The neurons of the PNS can be
divided into two classes:
•
•
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Which part of your autonomic nervous
system is working as you are reading this
page? What about if you heard a fire alarm?
Sensory neurons bring sensations such as
smell, touch, hearing, taste and pain to the CNS
where they are evaluated to determine what response is needed.
Motor neurons execute those responses. Motor
neurons of the somatic nervous system control
voluntary responses such as muscle contractions, whereas motor neurons of the autonomic
nervous system control involuntary responses
such as changes in heart rate.
Peripheral nerves are protected by the organs they
travel through, and in cases of injury or disease peripheral nerves are able to regenerate.
Wo r k b o o k
Lesson 1.2
Are you aware of your somatic nervous
system? What about your autonomic nervous system?
Figure 4: Peripheral and central
nervous systems. The CNS is in pink,
and contains all neurons in the brain
and spinal cord. The PNS is in blue,
and contains all neurons not in the
brain or spinal cord.
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
9
LESSON READING
Your Central Nervous System (CNS)
DEFINITIONS OF TERMS
Cerebrospinal fluid (CSF) - the
fluid that bathes the brain and
spinal cord.
Meninges – protective membranes that cover the brain and
spinal cord
Ventricles - the spaces inside the
hollow brain and spinal cord that
are gilled with cerebro spinal fluid.
The central nervous system (CNS) is also divided into different parts - the spinal cord and
the brain. The sensations that are received
in the periphery via sensory neurons first
enter the spinal cord and then pass into the
brain. Then once the brain has decided on a
response, output from the brain passes into
the spinal cord before it exits to the somatic
or autonomic peripheral motor neurons in the
periphery.
The central nervous system is protected from
damage by the bony skull and vertebrae.
Both the brain and spinal cord are cushioned
by sheets of protective membranes called
meninges (Figure 5).
The brain also contains a series of hollow, interconnected chambers called ventricles which are filled with
cerebrospinal fluid (CSF). The largest of these chambers are the lateral ventricles which are located in
the center of the brain (Figure 6). The CSF serves two main functions - it provides the brain with nutrients
and it cushions the meninges to protect the brain.
For a complete list of defined
terms, see the Glossary.
Lateral ventricles Fourth ventricle Wo r k b o o k
Lesson 1.2
Figure 5: Meninges. The brain is protected in part
by the meninges which are fluid filled membranes
covering the brain. (A) The meninges have three
layers: the pia mater, the arachnoid, and the dura
mater. (B) Meningitis results from inflammation of
the meninges.
Third ventricle Figure 6: Ventricles. The ventricles are interconnected chambers that are filled with cerebrospinal fluid (CSF).
Despite these multiple levels of protection, in
cases of injury or disease, the CNS is unable
to regenerate.
What is the role of the meninges?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
What are two functions of the cerebrospinal fluid?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
10
LESSON READING
What is the function of the spinal cord?
Your Spinal Cord (CNS)
DEFINITIONS OF TERMS
Myelin – fatty substance that insluates most nerves.
White matter – portions of the nervous system that appear white in
color because they are composed
of myelinated axons.
Grey matter – portions of the
nervous system that appear grey in
color because they are composed
of neuron cell bodies and unmyelinated axons.
For a complete list of defined
terms, see the Glossary.
The spinal cord is a long, conical structure,
approximately as thick as your little finger. Its
main function is to act as a two-way track that
collects the sensory information from the periphery to pass it onto the brain, and then to
collects the motor responses from the brain
to pass onto the somatic and autonomic nervous systems.
We can divide the spinal cord into four regions, each controlling a specific region of
the body. Starting from the top (Figure 7):
• The cervical region serves the neck and
arms.
• The thoracic region serves the trunk.
• The lumbar region serves the legs.
• The sacral region serves the bowels and
bladder.
B. Brainstem Spinal cord Cervical Vertebra A. Thoracic Lumbar Sacral Figure 7: The spinal cord. The spinal cord is segmentally arranged. The segments are grouped into
4 major divisions: cervical, thoracic, lumbar, and
sacral. (A) The spinal cord is encased in vertebral
bone. (B) The spinal cord has pathways along which
sensory information can be conveyed to the brain
(indicated in red), and motor information can be
transmitted from the brain to the body (indicated in
blue).
The spinal cord is arranged so the neurons traveling up into the brain and down out of the brain are arranged on the outside. These neurons are coated with a layer of fatty insulation that appears white, called
myelin. As we will see later, myelin makes the signals that are transmitted along neurons move more
efficiently. Because of this white appearance, this area of the spinal cord is referred to as white matter.
The area where connections between the peripheral and central nervous system neurons are made is in
the middle of the spinal cord, and lacks myelin. Because of this it appears grey in comparison to the white
matter. So, this area is referred to as grey matter.
Crossing over
Wo r k b o o k
Lesson 1.2
One interesting thing to note about the neurons traveling up and down the spinal cord is that they cross
over from one side to another. Because of this cross, each side of the brain receives sensory information
from the opposite side of the body. Similarly, the spinal cord output neurons also cross from one side of
the body to the other so that each side of the brain also controls the responses of the opposite side of
the body.
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
What side of the brain controls the left
side of the body? What side of the brain
controls the right side of the body?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
11
LESSON READING
Your Brain
The brain is also organized into areas of white matter where neurons travel and gray matter where connections between different neurons are made. In addition it can also be divided into distinct areas, each
of which perform a specific function. Starting from the region where the spinal cord connects to the brain,
these areas are called the brainstem, diencephalon, cerebellum, and cerebrum (Figure 8). We will take a
look at each of these areas in turn.
What is the function of the following brain
structures? What symptoms would you
see if they were damaged? Would the patient survive?
Medulla
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Pons
Figure 8: Main brain areas. The brain can be subdivided into the brainstem, diencephalon, cerebellum, and cerebrum (or cerebral
hemisphere).
The Brainstem
The brainstem is an evolutionarily old area of the brain where the spinal cord and the brain connect. Part
of the brainstem consists of sensory neurons that are traveling into the brain, and motor neurons that are
traveling out of the brain. But the brainstem also has its own functions, that divide it into 3 parts, from the
bottom, closest to the spinal cord, to the top, closest to the brain itself.
Wo r k b o o k
Lesson 1.2
•
The medulla controls breathing, heart rate and digestion. As you can imagine these are critical functions, and it is difficult to survive when the medulla is damaged.
•
The pons (from the Latin that means bridge) is a part of the brainstem that acts like a bus station
connecting upper levels of the brain (the cortex) with the spinal cord and a part of the brain called the
cerebellum. These connections allow the brain not only to give instructions about which movements
to make, but also to monitor those movements as they are happening.
•
The midbrain is also involved with coordinating movements. In this case it coordinates eye movement responses to visual and auditory stimulation.
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Midbrain
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
12
LESSON READING
What is the function of the following brain
structures? What symptoms would you
see if they were damaged? Would the patient survive?
Thalamus
The Diencephalon
Moving on upwards, the diencephalon is located at the upper end of the brain stem. It has two parts
that perform functions that are critical for life:
•
•
The thalamus acts as a relay station (like a post office) where all the major ascending sensory
pathways from spinal cord and brainstem connect to neurons destined for the upper parts of the
brain in the cortex. There are also reciprocal connections from the cortex to the thalamus. The
thalamus is thought to be the first area in the brain where consciousness can be experienced.
We’ll talk more about the thalamus and how important these connections are when we talk about
epilepsy and seizures.
The hypothalamus is tiny! Only 1 oz. in adult humans, yet it is the master regulator of homeostasis – controlling heart rate, blood pressure, blood composition, eating behaviors, and body
temperature to name but a few of its functions. It also links body responses to emotions. We’ll talk
more about the hypothalamus when we talk about sleep.
The Cerebellum
Wo r k b o o k
Lesson 1.2
The cerebellum lies behind and on top of the pons (Figure 9). It communicates with both the spinal cord and
the cortex. The cerebellum monitors how the intention to
perform a motor movement compares with how well the
movement is actually being executed. It can then adjust
the response to make sure the intention is being executed accurately. Amazingly, you are completely unaware of
the cerebellum as it works – it functions below the level
of consciousness.
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Hypothalamus
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Cerebellum
Cerebellum Figure 9:The cerebellum. The
cerebellum lies just behind the pons
and is critical for controlling motor
movements.
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
13
LESSON READING
What is the function of the following brain
structures? What symptoms would you
see if they were damaged? Would the patient survive?
The Cerebrum
The cerebrum forms the bulk of the CNS
(Figure 10). The cerebrum consists the
three deep-lying structures surrounded by
the cerebral cortex. These three structures
also have distinct functions.
Corpus callosum •
Corpus callosum Cingulate cortex Thalamus Basal ganglia Cingulate cortex The basal ganglia are involved in the
intention to move (like when you’re lying in bed and then suddenly you’re up,
but you haven’t consciously jumped
out of bed and put your feet on the
Hypothalamus floor).
Amygdala Basal ganglia
Basal ganglia Thalamus Cerebral cortex Cerebral cortex Hypothalamus Amygdala Hippocampus Hippocampus •
The hippocampus is involved with
making memories, as we saw with
H.M.
•
The amygdala is involved in creating
emotional states. It then works with the
hippocampus to coordinate the emotional states with the correct hormonal
responses (think fight or flight).
Figure 10: The Cerebrum. The cerebrum consists
of the cerebral cortex and three deep-laying structures: basal ganglia, hippocampus, and amygdala.
The two hemispheres of the cerebral cortex are
connected via the corpus callosum. (The thalamus
and hypothalamus, which together compose the diencephalon, are also shown for spatial reference.)
The outer layer of the cerebrum is called the cerebral cortex. The cortex contains at least 30 billion individual cells. Approximately half are the neurons that transmit information around the nervous system. Just
like in the spinal cord the neurons are arranged in layers of white matter where neurons are traveling, and
grey matter where they are connecting. In the cortex these layers are alternating.
The cerebral cortex is divided into two hemispheres, one on the left and one on the right. Although they
superficially look the same they are neither structurally nor functionally symmetrical. Each hemisphere
receives sensory information from, and sends motor instructions to, the opposite side of the body. Even
though the two cerebral hemispheres perform somewhat different functions, our perceptions and our
memories are unified. This unity is accomplished by the corpus callosum, a large band of neurons that
travels between corresponding parts of the left and right hemispheres connecting them and providing both
sides of the cortex with the same information – “one world through two eyes”.
Wo r k b o o k
Lesson 1.2
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Hippocampus
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Amygdala
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Corpus callosum
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
14
LESSON READING
Each hemisphere of the cortex can be divided into 4 lobes, each of which has a different function (Figure
11):
•
The frontal lobe is concerned with planning for future action and with control of movement.
•
The parietal lobe is concerned with receiving sensory information and with body image.
•
The occipital lobe is concerned with vision.
•
The temporal lobe is concerned with hearing, learning and memory and emotion.
Parietal lobe
Sensation, body image
Frontal lobe
Planning, motor control
Occipital lobe
Vision
Cerebellum
Temporal lobe
Hearing, memory,
learning, emotion
Brainstem
Spinal cord
Figure 11: The four lobes of the cerebral cortex.
The cerebral cortex is divided into four lobes: frontal,
temporal, parietal and occipital.
Each lobe has many characteristic folds and grooves. The folds are called gyri (singular gyrus), and the
grooves are called sulci (singular sulcus). Together the gyri and sulci increase the area of the cortex
considerably increasing the amount of information it can handle. The two most prominent sulci are:
•
The longitudinal sulcus (or fissure) which separates the left and right hemispheres
•
The central sulcus which separates the frontal lobe from the parietal lobe
Notably, mammals lower in the evolutionary scale than humans have many fewer sulci and gyri than
humans.
Wo r k b o o k
Lesson 1.2
What is the function of the following brain
structures? What symptoms would you
see if they were damaged? Would the patient survive?
Frontal lobe
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Parietal lobe
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Occipital lobe
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
Temporal lobe
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
15
LESSON READING
Getting information into and out of the brain
As we saw before, the brain communicates with the rest of the body via the cranial nerves (that supply
the head) and the spinal nerves (that supply the body). These nerves are part of the PNS. Since we’ve
not dealt with them before, let’s end by taking a look at the cranial nerves.
There are twelve pairs of cranial nerves that attach to the bottom surface of the brain before they enter it
via the brainstem (Figure 12).
•
Many of them deal with sensory
and motor functions in the head
and neck region in the same
way that spinal neurons do.
•
Others convey what we call the
‘special senses’ (vision, smell
and taste and hearing) to the
brain. For example, the olfactory sensory neurons transmit
olfactory information from receptors in the nose to the brain,
while the optic nerve transmits
visual signals from the eye to
the brain. The optic nerves partially cross before entering the
brain at the optic chiasm.
•
Wo r k b o o k
Lesson 1.2
What are two functions of cranial nerves?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
If the vagus nerve was damaged what
symptoms would you see?
Figure 12:The cranial nerves. Twelve pairs of cranial
nerves attach to the bottom surface of the brain and innervate the head and neck region. The three we focus on
are: olfactory (CNI), optic (CNII), and vagus (CNX).
Finally, the vagus nerve is an important autonomic cranial nerve that regulates the functions of
organs of the chest and abdomen such as the heart, lungs and digestive system.
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
16
STUDENT RESPONSES
What differences are there between your central and peripheral nervous systems? (Be sure to address their overall functions,
and ability to regenerate).
_____________________________________________________________________________________________________
____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
Remember to identify your
sources
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
Given what you know about how your brain controls the function of your body, if you met a stroke patient who had difficulty
moving his left leg, what half of his brain was affected by the stroke?
____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
Wo r k b o o k
Lesson 1.2
_____________________________________________________________________________________________________
17