Chapter 8: Central Nervous System
Theory Lecture Outline
Objectives
1. Describe the functions of the central nervous system
2. List the main divisions of the central nervous system
3. Identify the parts of the brain
4. Describe the structure of the brain and spinal cord
5. Describe the functions of the parts of the brain
6. Describe the functions of the spinal cord
7. Describe disorders of the brain and spinal cord
8. Define the key words that relate to this chapter
Introduction
The nervous system is the major controlling, regulatory and communicating system in the body. It is the
center of all mental activity, including thought, learning and memory. Together with the endocrine
system, the nervous system is responsible for regulating and maintaining homeostasis. Through its
receptors, the nervous system keeps us in touch with our environment, both external and internal. Like
other systems in the body, the nervous system is composed of organs, principally the brain, spinal cord,
nerves and ganglia. These, in turn, consist of various tissues, including nerve, blood and connective
tissues. Together these carry out the complex activities of the nervous system.
Divisions of the Nervous System
The nervous system can be divided into three divisions: the central, peripheral and autonomic nervous
system
• Central nervous system
a. Brain
b. Spinal cord
• Peripheral nervous system
Consist of nerves of the body
a. 12 pairs of cranial nerves extending out from brain
b. 31 pairs of spinal nerves extending out from spinal cord
• Autonomic nervous system
a. Part of the peripheral nervous system
b. Includes peripheral nerves and ganglia
Ganglia are collections of nerve cell bodies outside the CNS
c. Supplies heart muscle, smooth muscle and secretory glands with nervous impulses as
needed; usually involuntary in action
CNS Functions
• Communication and coordination system in the body
a. Receives messages from stimuli all over the body
b. Brain interprets the message
c. Brain responds to the message and carries out an activity
• Seat of intellect and reasoning
The Nerve Cell
The central nervous system is the most highly organized system of the body, consisting of the brain and
spinal cord
• Called the neuron
o Transmits messages from one cell to the next
• Basic components
a. Nucleus, cytoplasm, and cell membrane
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
b. Dendrites
1. Extensions or fibers that project from the cell body and are the paths along
which nerve impulses travel
2. Carry messages to the cell body
c. Axons (only one per cell)
1. Specialized covering
o Neurilemma or myelin sheath
2. Carry messages away from the cell body
Nervous Tissue/Cells
• Two major types of nerve cells
a. Neuroglia
1. Type of cells that insulate, support and protect the neurons
2. Sometimes call glial cells or “nerve glue”
b. Neurons
Conducting cell that transmits impulses
1. Sensory or afferent neuron
o Emerge from the skin or sense organs and carry messages or impulses
toward the spinal cord and brain (from peripheral sense receptors to the
CNS)
2. Motor or efferent
o Carry messages from the brain and spinal cord to the muscles and glands
3. Associative or interneurons
o Carry impulses from the sensory neuron to the motor neuron (located
entirely within the CNS)
• Membrane excitability
Excitability is the ability to respond to a stimulus; conductivity is the ability to transmit an
impulse from one point to another; all the functions associated with the nervous system, including
thought, learning and memory are based on these two characteristics
a. Resting membrane is the cell membrane of a nonconducting, or resting, neuron
1. There are large amounts of potassium (K+) ions inside the cells but not many
sodium (Na+) ions
2. An active transport mechanism, the sodium-potassium pump, maintains a
difference in concentration of these ions on the two sides of the membrane
3. The inside of the cell is more negatively charged than the outside
b. Stimulation of a neuron
1. Stimulus changes the membrane so that it becomes permeable to sodium ions,
which diffuse into the cell
2. Positively charged sodium ions rapidly diffuse through the membrane to the
inside of the cell which becomes more positive until the membrane potential is
reversed also known as depolarization
3. The membrane is impermeable to sodium but permeable to potassium ion
4. Next potassium gates open and large amounts of K+ diffuse out of the cell thus
restoring the polarity of the membrane restoring sodium and potassium to resting
conditions also known as repolarization
c. When this action occurs in one part ofh te cell membrane, it spreads to adjacent
membrane regions, continuing away from the original site of stimulation, sending
“messages” over the nerve; this cycle is completed millions of times a minute throughout
the body
Synapse
• When messages go from one cell to the next cell
• Synaptic cleft
a. Space between the axon of one cell and the dendrite of another
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
•
b. Location of message transfer from cell to cell
Neurotransmitters
a. Chemicals, namely epinephrine, norepinephrine and acetylcholine accommodate
conduction between the cells
b. Acetylcholine is found between muscle cells and the nervous system
The Brain
The adult human brain is a highly developed, complex and intricate mass of soft nervous tissue
• Weighs about 1400 grams or 3 pounds
• 100 billion neurons
• Without oxygen, brain damage occurs within 4-8 minutes
• Protection provided by:
a. Bony cranial cavity
b. Meninges
o 3 membranous coverings
c. Cerebrospinal fluid (CSF)
o Fluid formed in the brain that serves as a
liquid shock absorber
• 4 major parts
a. Cerebrum
b. Diencephalon
c. Cerebellum
d. Brain stem
Memory
• Brain is our Storage of old and new information
o No one area of the brain stores all memories, because the storage site depends on the type
of memory
• Hippocampus
o Regulates and decides the significance of events and determines where in the brain the
information should be stored
• Memory can be Short or long term
o Determined by how much attention we pay to an event, how many times we repeat an
activity and the kinds of memory associations
Coverings of the Brain
• Three meninges
a. Dura mater
o Outer brain covering inside of the skull
b. Arachnoid mater
o Middle layer
c. Pia mater
1. Covers the brain surface
2. Consists of blood vessels held together by fine connective tissue
Ventricles of the Brain
• Four lined cavities, called cerebral ventricles, filled with cerebrospinal fluid
a. 1st and 2nd
o Right and left lateral ventricles
b. 3rd
o Connected to the lateral ventricles by the interventricular foramen
th
c. 4
o Connected to the 3rd by the cerebral aqueduct
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
•
Choroid plexus
o Specialized capillary networks within the ventricles which helps in the formation of
cerebrospinal fluid
CSF (cerebrospinal fluid)
• Formed inside the four ventricles
o Serves as a liquid shock absorber protecting the delicate brain and spinal cord
• Transports nutrients to, and removes metabolic waste products form, the brain cells
• Blood-brain barrier
o Capillaries of the choroid plexus have selective permeability that can prevent substances
from penetrating the brain tissue
• CSF fluid bathes the brain and the spinal cord ultimately circulating into the bloodstream via the
venous structures in the brain
• Lumbar puncture
a. Removal of CSF with a needle inserted between the third and fourth lumbar vertebrae
b. CSF is used to detect some defects or disease of the brain
Parts of the Brain
Cerebrum
• Largest part of the brain
• Weighs about 2 pounds and occupies the whole upper part of the skull
• Cerebral cortex
o Gray matter that covers the upper and lower surfaces of the cerebrum
• Two hemispheres
a. Right and left
b. Divided by a longitudinal fissure
c. Each hemisphere is divided into four lobes
Cerebral Functions
Each lobe controls specific functions
• Frontal lobe
a. Anterior portion
b. Controls voluntary muscle movement and makes speech possible
1. Right hemisphere activates movement of the left side of the body
2. Left hemisphere activates movement of the right side of the body
• Parietal lobe
a. Located behind the frontal lobe
b. Receives and interprets nerve impulses form the sensory receptors for pain, touch, heat,
cold and balance
• Occipital lobe
a. Located over the cerebellum
b. Houses the visual area controlling eyesight
• Temporal lobe
a. Beneath the frontal and parietal lobes
b. Olfactory (smell) area and auditory area
• Limbic lobe or system
a. Located at the center of the brain beneath the other four lobes and encircles the top of the
brain stem
b. Influences unconscious and instinctive behaviors that relate to survival
c. Hippocampus is part of the limbic system
The cerebral cortex also controls conscious thought, judgment, memory, reasoning and willpower
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Diencephalon
• Located between the cerebrum and the midbrain
• Two major structures
a. Thalamus
o Relay station for incoming and outgoing nerve impulses
b. Hypothalamus
o Part of the limbic system and is considered the be the “brain” of the brain
Hypothalamus
Vital functions performed:
• Autonomic nervous control
• Cardiovascular control
• Temperature control
• Appetite control
• Water balance
o ADH secretion and “thirst area”
• Manufacture of oxytocin
o Contracts the uterus during labor
• Gastrointestinal control
• Emotional state
• Sleep control
• Mind-over-body experiences
Cerebellum
• Located behind the pons (bridge that serves as a two-way conductive pathway fro nerve impulses
between the cerebrum, cerebellum and other areas of the nervous system) and below the
cerebrum
• Right and left cerebellar hemispheres connected by vermis (median connecting lobe)
• Communicates with the rest of the CNS by three pairs of tracts called peduncles (myelinated
nerve fibers that carry nerve messages in and out of the cerebellum)
Cerebellar Function
Any and all information relating to skeletal muscle activity is carried to the cerebellum
• Maintenance of balance
• Maintenance of muscle tone
• Coordination of muscle movements
o Voluntary movement is initiated in the cerebral cortex but execution is the role of the
cerebellum
Brain Stem
Three parts:
• Midbrain
o Contains the nuclei for reflex centers involved with vision and hearing
• Pons
a. Conductive pathway for nerve impulses between the cerebrum, cerebellum and other
areas of the nervous system
b. Site for emergence of four pairs of cranial nerves
• Medulla oblongata
a. Located between the pons and the spinal cord
b. Vital functions
1. Heart rate
2. Rate and depth of respiration
3. Regulates blood pressure
4. Center for swallowing and vomiting
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Spinal Cord
• Begins at foramen magnum of the occipital bone (at the base of the skull)
• Ends at the second lumbar vertebrae
• 31 pairs of spinal nerves
• Protected by meninges and other tissues
o Cerebral fluid circulates to bathe the spinal cord
• Functions
a. Carry messages from the sensory neurons to the brain for interpretation and the response
is carried back from the brain through the motor neurons to the muscles and glands
b. Serve as the reflex center for the body
Effects of Aging
• Slowing nerve conduction
• Loss of brain size
• Slowing of reaction time
• Changes in sleep patterns
Disorders
Read through the disorders to become familiar with the terminology associated with the nervous system
• Meningitis
• Encephalitis
• Epilepsy
• Cerebral palsy
• Poliomyelitis
• Hydrocephalus
• Parkinson’s disease
• Essential tremor
• Multiple sclerosis
• West Nile virus
• Dementia
• Alzheimer’s disease
• Brain tumors
• Hematoma
• Spinal cord injuries
a. Quadriplegia
b. Paraplegia
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition