Module 1 Lesson 4 - 3
Completion requirements
Lesson 4 — The Structure and Organization of the Nervous System
The Central Nervous System
The central nervous system is composed of the brain and the spinal cord.
The Brain
Read pages 386 - 395
The blood from the circulatory system does not enter the brain and the spinal cord directly because of the tight junctions at the blood-brain barrier. This highly selective permeable barrier protects the brain from toxins and bacteria while allowing oxygen, glucose, and other lipid-soluble substances to pass through.
The cerebrospinal fluid (CSF) is a clear, colourless fluid that surrounds the brain and the spinal cord. It acts as a cushion to protect the central nervous system from injury. It is produced and replaced constantly throughout the day and transports nutrients, white blood cells, and hormones.
Try This
The brain and spinal cord are essential structures in communicating and keeping the body in balance. They must be protected. The following activity reviews the roles of the skull, meninges, and cerebrospinal fluid and indicates what happens when the brain
becomes scrambled.
Use two transparent plastic containers (with lids) that are a little larger than an egg. Put an uncooked egg into each container. Fill one container with water. Close each container firmly with the lid. Shake the containers. Record your observations. Consider what parts of this demonstration illustrate the skull, the meninges, the cerebrospinal fluid, and the brain. What was the role of the water?
The skull is the plastic container, water is the cerebrospinal fluid, the egg shell is the meninges, and the egg yolk is the brain.
Use two transparent plastic containers (with lids) that are a little larger than an egg. Put an uncooked egg into each container. Fill one container with water. Close each container firmly with the lid. Shake the containers. Record your observations. Consider what parts of this demonstration illustrate the skull, the meninges, the cerebrospinal fluid, and the brain. What was the role of the water?
The skull is the plastic container, water is the cerebrospinal fluid, the egg shell is the meninges, and the egg yolk is the brain.
Did You Know?
The brain has no pain receptors. This means neurosurgeons can perform brain surgery while the patient is awake and conscious throughout the procedure.
Forebrain, Midbrain, and Hindbrain
The hindbrain consists of a wrinkled ball at the base of the brain called the cerebellum and the upper part of the brain stem, which includes the medulla oblongata and the pons. The pons is a relay centre for the brain. It connects the cerebrum
to the cerebellum. The medulla oblongata controls involuntary movements such as breathing, heart rate, blood pressure, and swallowing. The cerebellum controls body movement and balance.
The midbrain is above pons and controls eye movement muscles and other skeletal muscles.
The forebrain is the most developed part of the brain and consists of the cerebrum, thalamus, and hypothalamus. The thalamus is another relay centre for the brain. It connects the neurons in the PNS to the brain. The hypothalamus maintains homeostasis (body temperature, blood volume, water balance, blood pressure, and thirst), regulates emotions, and controls the pituitary gland. The cerebrum is the largest part of the brain and is split into two hemispheres. It has the centres for intellect, memory, consciousness, and language.
The midbrain is above pons and controls eye movement muscles and other skeletal muscles.
The forebrain is the most developed part of the brain and consists of the cerebrum, thalamus, and hypothalamus. The thalamus is another relay centre for the brain. It connects the neurons in the PNS to the brain. The hypothalamus maintains homeostasis (body temperature, blood volume, water balance, blood pressure, and thirst), regulates emotions, and controls the pituitary gland. The cerebrum is the largest part of the brain and is split into two hemispheres. It has the centres for intellect, memory, consciousness, and language.
Skull and brain sagittal section. © 2006 Patrick J. Lynch, medical illustrator; C. Carl Jaffe, MD, cardiologist. http://creativecommons.org/licenses/by/2.5/ labels added by ADLC
The Cerebrum
Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 390, fig. 11.29. Reproduced by permission.
The cerebrum is divided into left and right hemispheres that communicate through a thick bundle of nerves at the base of the division, which is called the corpus callosum. The left hemisphere is responsible largely for language ability, and
the right hemisphere controls reasoning, spatial abilities, and visual recognition.
Two neurologists in the 1800s noticed that damage to two areas in the left hemispheres led to speech and language problems, which led to the discovery of Broca’s area and Wernicke’s area. Damage to Broca’s area in the frontal lobe results in inability to speak, and damage to the Wernicke’s area in the temporal lobe affects the understanding of language.
The location of the Broca's and Wernicke's areas is largely dependent on the dominant hemisphere of the cerebrum. For approximately 90% of right-handed individuals and 70% of left-handed individuals, the left hemisphere is dominant and this is where the two language areas will be located.
Two neurologists in the 1800s noticed that damage to two areas in the left hemispheres led to speech and language problems, which led to the discovery of Broca’s area and Wernicke’s area. Damage to Broca’s area in the frontal lobe results in inability to speak, and damage to the Wernicke’s area in the temporal lobe affects the understanding of language.
The location of the Broca's and Wernicke's areas is largely dependent on the dominant hemisphere of the cerebrum. For approximately 90% of right-handed individuals and 70% of left-handed individuals, the left hemisphere is dominant and this is where the two language areas will be located.
The cerebrum has four major lobes: frontal lobe, parietal lobe, occipital lobe, and temporal lobe.
- The frontal lobe is responsible for intellect, learning, memory, personality, emotions, creativity, and voluntary motor movement. It also contains Broca's area.
- The parietal lobe is responsible for processing sensory information (touch and taste) and proprioception (the body's position and orientation).
- The occipital lobe is mainly responsible for processing visual information.
- The temporal lobe is mainly responsible for processing auditory information and contains Wernicke’s area. It is also responsible for retrieving visual and verbal memories.
The Spinal Cord
Read pages 385 - 386
White matter is composed of extensions of neurons called dendrites and axons; grey matter is composed of cell bodies and interneurons. In the spinal cord, the white matter is on the outside, and grey matter is on the inside. In the virtual dissection of the brain, this is reversed: the grey matter is on the exterior and the white matter is on the interior in the brain.
The central canal is filled with cerebrospinal fluid. The meninges, which are three layers of coverings that wrap around the brain, are also around the spinal cord.
The spinal cord has two special types of nerves.
- Sensory nerves (dorsal root) communicate messages from the body to the brain for interpretation.
-
Motor nerves (ventral root) communicate messages from the brain to effectors (muscles) that initiate responses.
Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 386, fig. 11.23. Reproduced by permission.
Positron-Emission Tomography (PET) and Magnetic Resonance Imaging (MRI)
A PET scan looks at the function of the brain; an MRI scan examines the structure of the brain (as well as other parts of the body). In a PET scan, a radioactive substance is tagged to glucose and ingested. The PET image shows various colours and brightness according to the activity levels in the brain. An MRI scan uses magnets and radio signals to produce clear images of organs.
Did You Know?
In 1848, Phineas Gage suffered an injury while working at a railroad construction site. A heavy iron rod was driven through his left frontal lobe. He survived the accident, but the damage to his brain resulted in a radical personality change.
FMRI scan during working memory tasks
John Graner, Neuroimaging Department, National Intrepid Center of Excellence, Walter Reed National Military Medical Center. Public Domain.
John Graner, Neuroimaging Department, National Intrepid Center of Excellence, Walter Reed National Military Medical Center. Public Domain.
PET scans showing the differences between the brain of a normal older adult and the brain of an older adult afflicted with Alzheimer's disease
Health and Human Services Department, National Institutes of Health, National Institute on Aging : p.24. Public Domain.
Health and Human Services Department, National Institutes of Health, National Institute on Aging : p.24. Public Domain.