Transcript Nervous System

MARCH 4, 2013
STANDARD: SAP3
WARM-UP:
Complete ARG 50.2-Write the answers only
in your composition notebook.
Nervous System
Part II
The Central Nervous System
The Brain
• During embryonic development the CNS
first appears as a neural tube – the
anterior end starts to expand at four weeks
and brain formation begins.
The Four Parts of the Brain:
•
•
•
•
Cerebrum
Diencephalon
Brain Stem
Cerebellum
Cerebrum
• Left and right paired hemispheres
• Hemispheres connected by bridge of
nerve fibers that allows them to
communicate with each other – corpus
callosum
• The cerebrum is the largest area – it
covers all other regions of the brain
• Gyri (elevated ridges) and sulci (shallow
grooves) increase surface area of brain to hold
more neurons
• Fissures – deeper grooves
– Longitudinal fissure – divides cerebrum into
hemispheres (left & right)
– Other fissures divide hemispheres into lobes (frontal,
parietal, temporal, occipital)
• Lobes – are named for cranial bones that life
over them
• Functions of cerebrum
– Speech, memory, logical and emotional
response, consciousness, interpretation of
sensation, voluntary movement
Functional areas of cerebrum:
• Frontal lobe – primary motor area
– This area controls voluntary movement of
skeletal muscle
• Prefrontal cortex – judgement
– This area is not completely wired until
adulthood
• Broca’s area – speech
– Only in one hemisphere
• Sensory and motor pathways are crossed
– left side of brain receives impulses from
right side of the body
• Cerebral cortex – thin outer layer of brain
composed of gray matter (cell bodies)
– Only 3-4 mm thick.
– Where the conscious mind is located
• White matter – located beneath cerebral
cortex; tracts that connect cell bodies of
cerebral cortex with other parts of nervous
system
Basal Nuclei of Cerebrum
• Islands of gray matter in white matter.
– Located in deepest parts of the brain.
• Two diseases associated with abnormal
function of basal nuclei:
– Huntington’s chorea
• Too much dopamine produced by neurons.
• Continuous movement
– Parkinson’s disease
• Not enough dopamine produced by neurons.
• Slowed movement, tremors
Diencephalon
• Located at the top of the brain stem
• Covered by cerebrum
• Hypothalamus
– Thermoregulation, water balance, metabolism
– Controls thirst, appetite, sex, pain
– Contains pleasure center
– Regulates pituitary gland
Brain Stem
• Midbrain, pons, medulla oblongata
• Medulla oblongata
– Merges with spinal cord at foramen magnum
– Contains centers that control heart rate, blood
pressure, breathing, swallowing and vomiting
Cerebellum
• Looks like cauliflower
• Balance and equilibrium
• Ataxia – clumsy and disorganized
movements caused by damage to
cerebellum – cannot touch finger to nose
with eyes closed; may be confused with
drunkenness
The effect of alcoholism on the
cerebellum
Hemisphere Dominance Inventory
1. ____ If you had to give someone directions to your house, which of the following methods would you
most likely use?
a. Write a paragraph that explains where and when to turn
b. Draw a road map
2. ____Which of the following are you better at solving?
a. Jigsaw puzzle
b. Crossword puzzle
3. ____Do you remember faces easily? a. Yes
b. No
4. ____Do you think you’d earn higher grades in a geometry class or in an algebra class?
a. geometry
b. algebra
5. ____Imagine that you’re vacationing at a resort. Which of the following would you most likely do?
a. Obtain a brochure of local attractions and plan what you’d like to do for the day
b. Drive around without a plan and decide what you’d like to do as you drive along
6. ____Was it usually easy or difficult to learn grammar in school? a. difficult b. easy
7. ____Imagine enrolling in a music coarse. You and a partner in the course must write a song. Which
of the following would you prefer to do?
a. Write the lyrics
b. Compose the melody
8. ____When you read a new chapter in a textbook, which of the following are you most likely to do?
a. Skim through the entire chapter first to get a general idea of what the chapter is about
b. Read the chapter from beginning to end without doing much skimming
9. ____ In which of the following English classes would you most likely enroll?
a. Journalism
b. Creative writing
10. ____ Imagine that you volunteered to work for the school newspaper. Which of the following would
you rather do?
11. ____ After reading a new chapter in a textbook, which of the following would you rather do?
a. summarize the chapter
b. outline the chapter
12. ____ if you had an important project due in a class, would you prefer to work? a. in a group
b. alone
13. ____Which of the following classroom situations do you prefer?
a. A teacher announces assignments on a weekly basis and sets specific weekly due
dates
b. A teacher announces all the assignments at the beginning of the course and allows
you to complete them at any time before the end of the course
14. ____ Which of the following statements best applies to you?
a. I’m good at guessing a person’s mood by his or her body language
b. I’m not good at guessing a person’s mood by his or her body language
15. Which of the following would you rather play? a. Scrabble
b. Checkers
16. With which of the following statements do you most agree?
a. We should continue exploring outer space since one day this exploration may
benefit us
b. We should continue exploring outer space only if we can be sure ahead of time of
certain benefits we would receive
Scoring
How many “a” answers did you have for odd-numbered questions? ___________
How many “b” answers did you have for even-numbered questions? ___________
LEFT HEMISPHERE TOTAL
_______________
How many “a” answers did you have for even-numbered questions? ___________
How many “b” answers did you have for odd-numbered questions? ___________
RIGHT HEMISPHERE TOTAL
_______________
CRANIAL NERVES
(12 PAIRS)
Oh - Olfactory (smell)
Oh - Optic (vision)
Oh – Oculomotor (eye muscles)
To – Trochlear (external eye muscle)
Touch – Trigeminal (skin of face, chewing muscles)
And – Abducens (lateral muscle of eye)
Feel – Facial (facial expression)
Very – Vestibulocochlear (balance, hearing)
Good – Glossopharyngeal (throat, swallowing, saliva)
Velvet – Vagus (pharynx, larynx, heart)
Ah – Accessory (sternocleidomastoid and trapezius)
Hypoglossal (tongue movements)
Protection of the CNS
• Four elements of protection:
– Bones of dorsal cavity
– Meninges
– Cerebrospinal fluid
– Blood-Brain Barrier
Bones of Dorsal Cavity
• Skull
– Helmet-like protection of brain
• Vertebral Column
– Cervical, thoracic, and lumbar vertebrae
Meninges
• Protective connective tissue membranes
• Three layers wrap brain and spinal cord
Dura mater
• Leathery outer layer
• Ends in sac below the layer of the spinal cord
– Arachnoid mater
• Web-like (spider) middle layer
• Thread-like extensions extend into sub-arachnoid
space which contains cerebrospinal fluid (CSF)
– Pia mater
• Most delicate layer which clings to the surface of
the brain
• Pathologies:
– Meningitis – inflammation of meninges
caused by bacteria or viruses; can spread to
CNS.
– Encephalitis – inflammation of brain (West
Nile Virus).
Figure 28-21 Pyogenic meningitis. A thick layer of suppurative exudate covers the brain stem and cerebellum and thickens the leptomeninges. (From Golden JA, Louis
DN: Images in clinical medicine: Acute bacterial meningitis. N Engl J Med 333:364, 1994.)
Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 7 April 2005 12:46 AM)
© 2005 Elsevier
Cerebrospinal Fluid (CSF)
• Watery fluid – similar to blood plasma.
• Cushions brain and cord, protecting fragile
nervous tissue from trauma.
• Fills subarachnoid space, ventricles of
brain, and central canal of spinal cord.
• Volume – about ½ cup.
• Lumbar puncture (spinal tap) – diagnostic
tool to check for bacteria or viruses in CSF
(meningitis).
• Needle is inserted between L3-L4 or
L4-L5.
• Spinal cord ends around level of L1-L2.
CSF Pathologies
• Subdural hematoma
– Blood from brain injury collects in space
between dura and arachnoid mater.
– Pressure can kill brain tissue.
• Hydrocephalus
– CSF drainage is obstructed.
– CSF accumulates and puts pressure on the
brain.
Subdural hematoma
Figure 28-12 A, Large organizing subdural hematoma attached to the dura. B, Coronal section of the brain showing compression of the hemisphere underlying the
hematoma.
Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 7 April 2005 12:46 AM)
© 2005 Elsevier
Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 7 April 2005 12:46 AM)
© 2005 Elsevier
JOURNAL : Match the following terms with the correct region or
description of the brain.
A.
B.
C.
D.
Brain stem
Cerebellum
Cerebrum
Diencephalon
1.
2.
3.
4.
5.
6.
7.
controls balance and equilibrium
location - Basal nuclei
controls blood pressure
Broca’s speech area
composed of the midbrain, pons and medulla oblongata
contains gray and white matter
divided into left and right hemispheres
Blood-Brain Barrier
• The brain is absolutely dependent on a
constant internal environment.
– Fluctuations in sodium and potassium levels
can result in uncontrollable firing of neurons.
• Blood Brain Barrier:
– The cells of the brain are separated from
substances in the blood by the least
permeable capillaries in the body.
• These capillaries are the thickest capillaries in the
body.
What substances can cross the
blood-brain barrier?
• Water soluble substances that can cross the
barrier:
– Water, glucose, essential amino acids.
• BBB is useless against fat-soluble substances:
– This is why alcohol, nicotine, and anesthetics can
affect the brain.
• This barrier often prevents antibiotics from
reaching the brain or CSF in sufficient
concentrations to battle infections, such as
meningitis.
Pathology of the CNS
• Concussion – caused by a blow to the
head.
– Patient may lose consciousness briefly.
– May be accompanied by vomiting and blurred
vision.
Headaches
• Although brain tissue lacks pain receptors,
the meninges and blood vessels are well
supplied with them.
• Tension headaches
– Muscular headaches
– Prolonged contraction of skeletal muscle.
– Related to stress, anxiety, frustration.
Migraine Headaches
• Vascular headaches (blood vessels)
• Initial vasoconstriction of blood vessel causes
aura of light and/or numbness of limbs.
– When the vessel becomes smaller, it restricts blood
flow to an area.
• Reflex vasodilation of affected vessel results in
intense pain, usually unilateral.
– When the vessel expands, it presses on nerve fibers.
Brain Tumors - Gliomas
• Brain tumors are not composed of neurons
because neurons can’t divide.
– Brain tumors are almost always composed of
neuroglial cells.
• Grade I Tumor
– Usually only symptom is seizure.
– Good prognosis
– Usually found in children and young adults.
• Grade IV
– Glioblastoma
– Most malignant tumor
– Infiltrate brain tissue with fingers that cannot
be removed surgically.
– Prognosis: 51 weeks with most aggressive
treatment.
Cerebrovascular Accident (CVA)
• May be a stroke or an aneurysm.
• Blood circulation to an area of the brain is
blocked and brain tissue dies.
• Ischemia – loss of blood supply; oxygen
and glucose are blocked.
• Most common cause: blood clot.
• Aneurysm – ballooning of blood vessel.
– Vessel is weakened and prone to rupture.
Alzheimer’s Disease
• Primarily affects individuals over 65 years
of age.
• Gradual loss of short term and long term
memory.
• Beta-amyloid plaques form between
neurons in the brain.
• Neurofibrillary tangles form inside
neurons, causing their destruction.
Normal brain vs. Alzheimer’s
Effects of Drugs on the Brain
• The Pleasure Center is a small bundle of
nervous tissue located inside the hypothalamus.
– This area reinforces our drives to eat, drink and
reproduce.
– Our ability to feel good involves neurotransmitters
such as dopamine, norepinephrine, endorphins and
serotonin.
– Recreational drugs work by artificially stimulates the
reward pathways in the pleasure center.
CNS Stimulants
• Result in increased vasoconstriction, leading to
increased heart rate and blood pressure.
• Amphetamines
– Cause increased secretion of norepinephrine
and/or dopamine which stimulates the sympathetic
nervous system (similar to adrenalin).
– The more you take artificially, the less your body
makes; can quickly lead to dependence or addiction.
Meth Mouth
• Cocaine
– Blocks reabsorption of dopamine
– It stays in the synapse and continues to stimulate
receptor cells so that the drug’s effects are felt for an
extended period.
– Dopamine is washed away from the synapse instead
of being reabsorbed into axonal terminals – neuron
runs out of dopamine.
– User becomes anxious and unable to experience
pleasure without the drug.
– Highly addictive.
Hallucinogens - LSD
• Acts as artificial neurotransmitter that
stimulates the brain.
• Synesthesia – hearing colors or seeing
sound.
• Hallucinations – false sensory perceptions.
CNS Depressants
• The CNS is depressed, resulting in
lowered heart rate and blood pressure.
• Include barbiturates (sleeping pills), pain
killers and tranquilizers.
• Effects range from calming to sleep to
respiratory distress to coma to death.
• Opiates – heroin, morphine, codeine,
dilaudid; pain relievers.
• Marijuana – euphoria and distorted
perception of time and space.
• Alcohol – slows down reflexes, disrupts
coordination, impairs judgement.
– Ataxia – alcohol easily crosses into the
cerebellum.
Spinal Cord
• Begins where the nervous tissue leaves
the cranial cavity at the foreman magnum.
• Terminates between the 1st and 2nd lumbar
vertebrae.
• Structure:
– 31 segments – each gives rise to a pair of
spinal nerves.
– Spinal nerves branch out to body parts,
connecting them to CNS.
Functions of the Spinal Cord
1. Conduction of nerve impulses
– The spinal cord is a two-way communication
system between the brain and parts of the
body.
2. Serve as a center for spinal reflexes.
Spinal Cord Injuries
• 10,000 per year; mostly in males 18-30.
• If the spinal cord is damaged, loss of
function may be only temporary. If function
does not return within 48 hours, paralysis
is permanent in most cases.
• If nerve fibers are severed, function is
likely to be completely lost.
• Transection (cutting) of the spinal cord at
any level results in motor and sensory loss
in body regions inferior to the site of
damage.
• The loss is bilateral (both sides).
– Paraplegia – T1-L1, both lower limbs are
paralyzed.
– Quadriplegia – cervical region; all 4 limbs
affected.