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The Nervous System
I.
Divisions
a. Central Nervous System
i. Consists of the brain and spinal cord
ii. Brain
1. Protected by cranium
2. Centers of thought
3. Weighs about 3 lbs
4. Constantly receives messages from senses
5. Uses all this information to form ideas, decisions, and give
commands to the body
6. Communicates with most of the body through spinal cord
7. 12 pairs of cranial nerves
a. Branch directly off brain
b. Eyes, ears, mouth, face, scalp
iii. Spinal cord
1. thick bundle of nerves
2. attaches to brain at brain stem
3. spinal nerves pass through gaps in vertebrae
4. 31 pairs of spinal nerves
5. tapers off at upper portion of lumbar region
6. 10 pairs of nerves pass through lumbar vertebrae and sacrum
iv. Meninges
1. triple layer of protection on spinal cord and brain
2. outer layer - dura mater
a. one of strongest tissues in body
b. flexible, protective layer
3. middle layer – arachnoid
a. thin fibers like spider’s web
b. 3-D network around brain
c. cerebrospinal fluid circulates in fibers and acts like
cushion if you bump your head
4. inner layer - pia mater
a. delicate layer that lays against brain and cord
v. 2 kinds of nerve cells
1. glial cells - support and insulate the cell
2. neurons
a. actual cell
b. very different from other cells
vi. Neurons
1. long fibers that branch out
2. cell body
a. contains nucleus
b. most of cytoplasm
3. dendrites
a. branching structure
b. receives messages
c. myelin sheath – fatty substance that surrounds and protects
fibers
4. axon
a. long extension
b. carries impulse away from cell body
5. axon terminals
a. hair like ends
b. end of the axon
6. myelin sheath
a. protective layer
b. formed around axon
7. node of Ranvier
a. gaps in the myelin sheath
b. allow better transmission
8. Schwann’s cells
a. produce myelin
b. located in myelin sheath
9. types of neurons
a. sensory - take information from body to brain
b. motor - take message from brain to body
c. interneurons
i. only found in central nervous system
ii. relay information between neurons
vii. Gray matter
1. largely cell bodies of neurons
2. lack myelin (which is white)
viii. White matter
1. mostly axons and glial cells (myelin coated)
ix. Nerve cell bodies found only in
1. Brain
2. spinal cord
3. ganglion - mass of cell bodies
a. large nerve mass called a plexus
b. these plexus better control muscles (like in hands)
x. automatic nervous system
1. cranial and spinal nerves control body’s functions
2. heart beat, breathing, digestion
3. frees your mind to think on other things
4. every organ and gland needs to be turned on or off at times - this
control comes from hypothalamus of brain
a. sympathetic - generally turns on system
i. increases heart rate, breathing, blood supply
ii. for emergency situation or increases activity, stress
b. parasympathetic - generally turns off syste
i. slows it back down
ii. blocks action of sympathetic
c. Stomach is opposite
b. Peripheral Nervous System
II.
i. Cranial and Spinal nerves
1. bundles of nerve fibers (axons)
2. branch off from brain and spinal cord
3. sciatic nerve
a. longest nerve in body
b. runs from base of spinal cord to leg
4. 12 pairs cranial nerves
5. 31 pairs spinal nerves - each pair supply body part
6. most nerves carry both types of fibers – motor and sensory
a. sensory carries from body to brain
b. motor carries from brain to body
c. cell bodies of sensory fibers located in ganglia outside
spinal cord
i. enter through rear nerve root
d. cell bodies of motor fibers located in gray matter of spinal
cord
i. leave spinal cord through front root
e. all impulses travel up and down through spinal cord
How Nerves Work
a. Function of Typical Nerve
i. Sensory nerve fibers carry information
1. up skin
2. To spinal cord
3. To brain
ii. Brain processes the information
1. Temperature
2. Pressure
3. Pain
iii. Brain passes information
1. Down spinal cord
2. Through motor nerve fibers
3. Tells muscle or body how to react
b. Structure of nerve
i. Nerve consists of bundles of nerve fibers
ii. Nerves are embedded in connective tissue
iii. In bundles lie nerve fibers (axons)
1. imbedded among glial cells
2. protected by myelin sheath
3. each axon is either motor or sensory - never both
iv. Blood and lymph and cushioning of fatty tissue help to nourish and
protect fibers
c. Nerve Cells
i. Majority of nerve tissue is glial cells
ii. Neurons are the only cells responsible for nerve impulse
iii. They do not reproduce - never replaced
iv. Alcohol and drugs kill cells that will never be replaced
v. Dendrite pick up information
vi. Passes through cell body
vii. Information travels out through the axon
1. they are surrounded by special glial cells called Schwann cells
2. these produce myelin sheathing which acts as insulation on
electrical wire
3. there are gaps in the Schwann cells called nodes of Ranvier
4. myelinated axons transmit impulses faster than those with no
covering
a. why does some have no covering?
b. areas that allow exchanging of positive and negative
charges to the nerve
d. How neurons work
i. Electrochemical process
ii. Nerve cell at rest - ion pumps give it a slightly negative charge
iii. Cell membrane has billions of voltage sensitive gates that transmit nerve
impulses
iv. When one is opened by a signal (change in charge) causes a chainreaction and they all open
v. Electrochemical impulse races along nerve
vi. After impulse passed, cell goes back to original balance
e. Synaptic Transmission
i. Axons of sensory neurons and interneurons usually end in synapse
1. enclosed junction between axon of one neuron and dendrites of
another
2. When impulse reaches synapse - special chemical is released
known as neurotransmitter into synapse
3. When sensors in receiving neuron detect the neurotransmitter it
generates electric signal
4. The message is passed along the neurons
5. Peripheral nerves constantly relaying messages to and from the
central nervous system
6. In central nervous system things don’t automatically fire, they
process the info and determine what to do
f. Inhibitors of nerve impulses
i. Local anesthetic - novacain - blocks nerve impulses
ii. Botulinum B toxin
1. powerful poison
2. most deadly type of food poisoning
3. one of most toxic substances known to man
4. destroys a protein inside motor nerve synapses preventing motor
discharge - causing paralysis
5. when it reaches muscles involved in breathing - death by
suffocation
6. Botox
Doctors warn patients of 'backstreet Botox' dangers
Ian Sample, science correspondent
Wednesday November 22, 2006
The Guardian
Doctors have urged patients to avoid "backstreet" Botox treatments after four people were
hospitalised
following injections with an unlicensed product.
The patients were admitted to hospital with life-threatening botulism days after receiving
injections from a batch
of botulinum toxin A not approved for human use.
The patients, who received between four and six injections into muscles around the eyes,
forehead and nose, quickly developed severe fatigue and neurological problems and had to be
put on ventilators to support their breathing. Each was given an antidote and spent a minimum
of 40 days in hospital.
Interviews with the patients revealed they had received the injections at a private clinic which
had acquired a 100 microgramme vial of pure botulinum A neurotoxin, clearly labelled as
suitable only for laboratory research.
Further investigations revealed that one of the patients was a doctor working at the clinic
despite having had his medical licence revoked. He had diluted the neurotoxin before injecting
it into himself and three patients.
The incident is described in the Journal of the American Medical Association by doctors at the
US Centres for Disease Control and Prevention in Atlanta. The researchers believe the patients
may have received up to 2,857 times the amount of toxin believed to be lethal if injected
directly into the bloodstream.
"These patients would have died if they had not been put on life support. It's a wake-up call to
physicians that this stuff is out there," said study leader Chris Braden. "During this investigation
we've learned about a rather surprising grey or black market for this type of product," he added.
Writing in the journal, the doctors said there was an urgent need for fresh controls to ensure
research-grade botulinum toxin was only shipped to laboratories that could prove their
credentials.
They estimated that the vial obtained by the clinic contained enough botulinum toxin to
kill 14,286 adults.
The doctor responsible for administering the injections has since been jailed for three years.
In August, British health inspectors announced a crackdown on beauty clinics after evidence
emerged that clients had been disfigured by rogue operators offering improperly administered
Botox injections, laser therapy and anti-wrinkle skin fillers.
Faulty injections of Botox can paralyse the wrong muscles, but the effect is usually temporary.
g. Reflex Action
i. Simplest nerve pathway is a reflex arc
1. as few as 2 or 3 nerve cells
III.
2. short circuit - allows impulses to bypass the brain when a speedy
response is necessary
ii. Purpose - to prevent severe damage to tissues
iii. How it works
1. sensory neurons transmit pain to interneurons in spinal cord
2. interneurons transmit emergency signal to appropriate motor
neurons
3. body part is jerked away from danger
4. by the time the parietal section of brain registered pain, you
already had jerked away from object
The Brain
a. 3 Main Parts
i. Cerebrum - upper part that coordinates thought, memory, and learned
behaviors
ii. Cerebellum - lower back part that helps control balance and coordinate
voluntary muscle activity
iii. Brain stem - connects the brain to the spinal cord and controls
involuntary muscles and activities of autonomic nervous system
b. The Incredible Design of Brain
i. Contains about 100 billion neurons each linked to an average of 100,000
other forming more than 10,000,000,000,000,000 connections
ii. Packing all that into a 3 pound brain is like taking all the telephone
systems of the world and putting them into a thimble
iii. It is beyond comprehension
iv. Evolution or intelligent design?
c. Cerebrum
i. Consciousness, memory, voluntary actions, thinking, and intelligence
ii. Largest part of the brain - divided into right and left hemisphere
1. split in half by longitudinal fissure
2. right hemisphere
a. controls left side body (left-handed)
b. see big picture
c. music, artistic, 3-D perception, intuition, imagination
3. left hemisphere
a. controls right side (right-handed)
b. see details
c. science, math, language, logical thinking
iii. Corpus Callosum - two hemispheres communicate through here
iv. Gray and White matter in Cerebrum
1. gray matter
a. made up mostly of cell bodies
b. lack the white myelin coating
c. most located in cerebral cortex
i. outer layer of cerebrum
ii. about 1/8 inch thick
d. convolutions (deep grooves)
i. allow for maximum amount of gray matter in
limited amount of space
ii. you have about 16 square feet of surface area
(about size of beach ball)
2. white matter
a. interior of the brain
b. bundles of myelin-covered nerve fibers
c. messages generated in cortex travel along nerve fibers to
other areas of brain, spinal cord, or body parts
d. messages also travel to the cortex of the brain from the
sense organs so they can be acted upon
v. Cerebral lobes
1. through observation of injury, neurosurgery in the 1960’s, now
brain mapping they can tell what happens in each lobe
2. frontal lobe
a. front - personality, judgment, and self-control
b. back - motor area of voluntary skeletal muscles
3. parietal lobe - analyze senses of body and handle actions
4. occipital lobe - eye sight
5. temporal lobe - hearing, taste, smell
d. Cerebellum - muscle coordination
i. Location and structure
1. 2nd largest part of brain
2. behind the brain stem and below occipital lobe of cerebrum
3. right and left hemisphere
4. gray and white matter
5. convolutions are smaller
a. cortex of cerebellum more dense
ii. Function and purpose
1. coordinates skeletal muscle activity
2. relieves the cerebrum from so much work
3. don’t have to think about walking, driving, brushing your teeth
4. swimming
a. uses about every skeletal muscle
b. when learning cerebrum things about every movement so
you won’t drown
c. as you become more coordinated your cerebellum is being
trained
d. when you are good cerebellum does the work without you
thinking about it
e. Brain Stem - Involuntary Functions
i. Located between the cerebrum and spinal cord
1. all nerve cells that go from brain to spinal cord go through this
2. 3 parts
a. medulla oblongata
b. pons
c. midbrain
ii. Medulla oblongat
1. lowest part of brainstem
2. centers that regulate and monitor
a. breathing
b. temperature
c. blood pressure
d. heartbeat
e. other vital functions
3. it triggers sneezing and swallowing
4. all major pathways (sensory and motor) cross over here giving
you right brain - left hand
iii. The pons
1. just above medulla
2. Latin word for bridge
3. links cerebrum to cerebellum
4. regulates breathing
5. helps coordinate some eye movement and facial expressions
iv. The midbrain
1. above the pons
2. nerve centers in the midbrain help movement of both eyes, adjust
pupils to respond to light, help lens to focus
v. The Master Switch - reticular formation
1. network of neurons
2. causes you to wake up - switch on cerebral cortex
3. causes you to go to sleep - switches off cerebral cortex
4. keeps you alert and attentive to your surroundings
5. puts you on high alert when you hear a sudden, loud noise or feel
pain to help protect you from danger
6. if damaged a person may slip into comma (prolonged state of
unconsciousness)
7. keeps your body upright and balanced when not moving
f. Limbic System - Coordinating Emotions
i. Several structures lying in the brain core
ii. Coordinate the activity in different parts of your brain
iii. Generate and regulate emotions and desires in coordination with
incoming sensory info and the powers of reason in the cerebrum
iv. The organs
1. Thalamus
a. located at core of brain
b. acts like a switchboard sending signals from the reticular
formation and sensory nerves to the right place on cerebral
cortex
2. hypothalamus
a. right below thalamus
b. control unit for automatic systems
i. automatic nervous system through the brain stem
ii. endocrine system through the pituitary gland
c. monitors temperature, pressure, composition of blood and
makes adjustments
d. responsible for physical effects of emotions like rage and
fear
IV.
i. directs adrenals to release adrenaline
ii. increases heart rate
iii. pupils dilate
iv. digestion slows
v. body readies itself for emergency
vi. gives physical desires like hunger and thirst
3. hippocampus
a. processes factual memories for storage
4. amygdala
a. at back end of hippocampus
b. generates emotions and helps process emotional memories
Neurological Health
a. Caring for the Nervous System
i. Controlling habits
1. Unhealthy food you eat, alcohol, cigarettes can destroy your
nervous system
2. Caffeine - too much stimulant
3. Loud noises - can lead to sensorineural deafness - keep music low
4. Proper rest - deep restful sleep is necessary for brain to function
properly
a. Continued late nights disrupt nervous system
b. Rest enables body to restore itself
b. Alcohol and the Nervous System
i. Loss of inhibitions
1. quickly enters blood stream
2. acts as a depressant on central nervous system
3. loss of self-control
4. behavior becomes unpredictable
5. motor neurons affected
a. clumsiness
b. slowed reactions
c. impaired judgment
d. slurred speech
e. emotionally unstable
f. can depress entire body – death
ii. Breaking down alcohol
1. liver breaks it down creating another poison acetaldehyde
2. this causes headaches and nausea – hangover
3. can take the body hours to get rid of only a few drinks
iii. Long-term effects
1. accelerated death of brain cells
2. permanent brain damage
3. nervous disorders, visual problems, tremors, neuritis
4. liver diseases - hepatitis, cirrhosis
5. pancreatis, kidney failure, heart disease, dementia, cancer, FAS in
infants
6. 70,000-80,000 people die due to alcohol related illnesses
iv. Path to dependence
1.
2.
3.
4.
addictive drug
170 million people drink alcohol
average age person first drinks – 12
10% of people who start drinking become alcoholics - 17 million
in the US
5. suicide rate among alcoholics 30 times higher
6. try to stop - withdraw symptoms
a. temporay insanity - DT’s
b. sweat profusely, speak incoherently, hallucinations
7. mental breakdowns and permanent insanity can come from years
of drinking
v. Alcohol-related accidents
1. driving requires coordination
2. alcohol interferes with reflexes (responses) and is major cause of
auto accidents
3. more than 40% of all fatal crashes - alcohol related
4. 17,000 - 20,000 Americans die each year from alcohol related
crashes
5. alcohol kills another 12,000 by accidents such as drowning, fire,
falls
vi. Alcohol and Crime
1. a person will commit acts they wouldn’t normally do
2. 49% murders
3. 52% rapes and sexual assaults
4. 68% manslaughters
5. 48% robberies
6. 62% assaults
7. 49% other violent crimes
c. Injuries to the Nervous System
i. Unrepairable
1. cell death occurs when cell body dies
2. if nerves are damaged without cell body death the nerve can grow
back
3. if the axon is severed it will regenerate
4. nerve fibers in the central nervous system don’t regenerate
5. injury to brain and spinal cord - permanently damaged
ii. Spinal cord and nerve injuries
1. whiplash
2. sciatica
3. severs from gunshot, stab wounds or accidents
iii. Brain injuries
1. stroke
a. internal blockage or rupture of blood vessel in brain
b. certain areas not supplied with blood and death occurs to
nerves cells
2. concussion - a period of paralysis to central nervous system
3. amnesia - loss of memory can come from concussion
4. coma - prolonged lose of consciousness
d. Diseases and the Nervous System
i. Blood-brain barrier - tightly closed system in your brain that doesn’t
allow things many things to pass through
ii. Meningitis
1. some germs can slip through barrier and cause meningitis
2. infection in the meninges - puts pressure on brain
3. can be fatal
iii. Multiple Sclerosis
1. immune system attacks glial cells
2. myelin sheath deteriorates and replaced with scar tissue
3. axon is not hurt but nerve impulses are slowed greatly and
sometimes short circuit
4. effects vision, sensations, movement of limbs
iv. Epilepsy
1. neurons malfunction - firing over and over again
2. disrupts normal function and causes muscle convulsions
3. continues until brain brings cerebral processes back to normal
v. Cerebral Palsy
1. damage to the cerebral motor area
2. poor speech, spastic contractions
3. may be one side or both
4. they are not mentally retarded - most are highly intelligent trapped
in a body they can’t control
vi. Many others like Alzheimers, Arteriosclerotic dementia, Parkinson’s
disease, tetanus, poliomyelitis