Transcript Central Nervous System

The Central Nervous System
The Story of Phineas Gage
On 13th. September 1848, an accidental explosion of a charge he had set blew
his tamping iron through his head.
The tamping iron was 3 feet 7 inches long and weighed 13 1/2 pounds. It was 1 1/4
inches in diameter at one end (not circumference as in the newspaper report) and
tapered over a distance of about 1-foot to a diameter of 1/4 inch at the other. The
tamping iron went in point first under his left cheek bone and completely out through
the top of his head, landing about 25 to 30 yards behind him. Phineas was knocked
over but may not have lost consciousness even though most of the front part of the
left side of his brain was destroyed. Dr. John Martyn Harlow, the young physician of
Cavendish, treated him with such success that he returned home to Lebanon, New
Hampshire 10 weeks later.
I. Formation of the Central Nervous System(CNS)
A. The CNS develops from the neural tube (extending
down the dorsal median plane of an embryo).
1. The neural tube eventually becomes the brain and
spinal cord.
B. By the fourth week the tube begins to expand and
form the brain.
C. The opening of
the neural tube
becomes the
ventricles
1. There are four
ventricles which act
as chambers in the
brain.
2. The ventricles are
filled with
cerebrospinal fluid.
Protection: the CSF protects the brain from damage by "buffering" the brain. into
other words, the CSF acts to cushion a blow to the head and lessen the
impact.
Buoyancy: because the brain is immersed in fluid, the net weight of the brain is
reduced from about 1,400 gm to about 50 gm. Therefore, pressure at the base
of the brain is reduced.
Excretion of waste products: the one-way flow from the CSF to the blood takes
potentially harmful metabolites, drugs and other substances away from the
brain.
Endocrine medium for the brain: the CSF serves to transport hormones to other
areas of the brain. Hormones released into the CSF can be carried to remote
sites of the brain where they may act.
II. Functional Anatomy of the Brain
A. There are four main regions of the brain
which include:
Cerebral hemispheres (Cerebrum), diencephalon,
brain stem and the cerebellum
B. The Cerebral Hemispheres: The paired left and
right superior parts of the brain and make up more
than half the mass of the entire brain! This part of
the brain involves conscious behaviors including;
speech, memory, emotional responses, and
voluntary movement, personality.
1. The surface is made of ridges (gyri) and
grooves (sulci)
2. Fissures (deep grooves) divide the
cerebrum into lobes
3. The outermost area of the cerebrum is
made of gray matter (covering an underlying
layer of white matter), and called the cerebral
cortex. The remaining cerebral hemisphere
tissue- the deeper white matter- is composed
of bundles of nerve fibers carrying the
impulses to or from the cortex.
a. One large fiber tract
(bundle of nerves)
called the corpus
callosum, connects
the right and left
cerebral
hemispheres
b. The basal nuclei is
an internal island of
gray matter deep
within the cerebral
cortex. It helps
regulate the
voluntary motor
activities.
Lobes of the Cerebum
4. Surface lobes of the
cerebrum include:
a. Frontal lobe
1) Primary motor areaallows
us to move
our skeletal muscles
under conscious control
2) Broca’s area- motor
speech
area that
directs muscles involved
in speech, usually only
present in left
hemisphere.
3)High level intellectual
reasoning are also
believed to be in the
anterior portion of the
frontal lobe
b. Parietal lobe
1. Somatic sensory areas- allows you to recognize
pain, coldness and touch
- The left side of the sensory cortex interprets
impulses from the right side of the body and vice
versa.
c. Occipital lobe
1)Visual interpretation
d. Temporal lobe1) Auditory interpretation,
speech, memory, Wernicke’s
area (language intrepretation)
Specialized areas of the Cerebrum:
Temporal lobe
Explain what type of impairment
a person might experience if..
1. A sharp blow to the back of the head
2. Damage to the left frontal lobe just superior to
the temporal lobe and anterior to the primary
motor cortex
3. Stroke which damages the primary motor
cortex closest to the temporal lobe
4. Prefrontal lobotomy
5. Damage to the hypothalamus
6. Damage to the brainstem directly at the pons
Question of the Week:
What causes people to have a stuttering
problem?
• Normal speech development. Young children may stutter when
their speech and language abilities aren't developed enough to keep
up with what they want to say. Most children outgrow developmental
stuttering within four years.
• Inherited brain abnormalities. Stuttering tends to run in families. It
appears that stuttering results from inherited (genetic) abnormalities
in the language centers of the brain.
• Stroke or brain injury. Stuttering can sometimes result from a
stroke, trauma or other brain injury.
• Mental health problems. In isolated cases, emotional trauma or
problems with thoughts or reasoning lead to stuttering. This was
once believed to be the main cause of stuttering, but it's now known
that it's uncommon.
Factors that increase the risk
of stuttering include:
• Having relatives who stutter. Stuttering tends to run in
families.
• Delayed childhood development. Children who have
developmental delays or other speech problems are
more likely to stutter.
• Being male. Males are much more likely to stutter than
are females.
• Stress. High parental expectations or other types of
pressure
• http://serendip.brynmawr.edu/exchange/node/1683
Recent research on stuttering
• PET imaging study was
performed comparing
stutterers’ brains and nonstutterers’ brains. This study
showed that stutterers may be
using the right hemisphere of
their brain when they are
talking, which means that the
left hemisphere (the one
usually responsible for speech)
is being interrupted
Research on stuttering
• In the PET scans of the brain, the
stutterers’ brains showed decreased
activity in the auditory cortex and
hyperactivity in the speech center
while reading, which means that
stutterer is actually tuning himself out
when he is talking, so that he cannot
hear the stammering .
Research on stuttering
• One group of researchers found a
connection between the functioning of the
lateral and medial areas of the brain and
stuttering. The lateral area of the brain
controls the formation of words (Broca’s
area), muscle movements (motor areas)
and the understanding of language
(Wernicke’s area) in what is known as
closed-loop motor control.
Cerebral Lobe Review
http://www.youtube.com/watch?v=snO68aJTOpM
C. The Diencephalon or Interbrain
1. Sits on top of the brain
stem and is enclosed by the
cerebral hemispheres.
2. Composed of three main
parts: Thalamus, epithalamus,
and hypothalamus
a. Thalamus- A relay station
for sensory impulses, allows
us to recognize a sensation as
pleasant or unpleasant, the
impulse is eventually sent to
the sensory cortex for
localization and interpretation
of the sensation
b. Hypothalamus- An
important part of the
autonomic system. Its
job is regulating body
temperature, water
balance, appetite, and
metabolism. Also
includes the Limbic
system- our emotional
brain. The Limbic
system is involved in
our appetite, thirst,
pain, sex, and pleasure
centers. The pituitary
gland is attached to the
hypothalamus.
• c. EpithalamusForms the roof of
the third ventricle.
Important parts
include the pineal
body(produces
melatonin into
regulate
sleep/wake cycles)
and choroid plexus
(forms
cerebrospinal
fluid).
D. The Brain Stem
1. Attaches to the spinal cord.
2. There are three parts of the brain stem:
midbrain, pons and medulla oblongata.
a. Midbrain- is mostly composed of nerve
fiber tracts. It also contains the cerebral
aqueduct which is a tiny canal that
connects the third and fourth ventricle.
The corpora quadrigemina is dorsally
located with rounded protrusions that are
reflex centers for vision and hearing.
b. Pons- The bulging part of the brain stem
that is composed mostly of nerve fiber
tracts. It houses important nuclei that
control our breathing.
***also important because it contains
nerve fibers connecting the cerebellum to
the rest of the brain, and allows facial
expressions
c. Medulla Oblongata- The lowest
part of the brain stem that merges
into the spinal cord. It controls
important centers
that help
control blood pressure, heart rate,
breathing, swallowing, and vomiting.
E. Reticular Formation
1. Gray matter that runs along the
brain stem.
2. Involved in motor control of
visceral organs. It also contains a
special group of neurons called the
reticular activating system that plays
a role in consciousness and
awake/sleep cycles.
(RAS alerts a person when a friend
speaks and enables that person to
ignore other sounds and focus on
the one sound.
F. The cerebellum
1. Projects dorsally from under the occipital
lobe of the cerebrum. It also contains two
hemispheres with convoluted surfaces.
2. Its job is providing involuntary control of
body movements (balance), and posture.
II. Protection of the Central Nervous System
A. The scalp and skin provide the first layer of protections.
B. The skull and vertebral column provide the second
layer.
C. A layer of connective tissue called the meninges
provides the final protection for the CNS. There
are three meningeal layers.
1. Dura mater- the outermost layer that is tough
and hard.
2. Arachnoid mater- the middle web-like layer
3. Pia Mater- internal layer that clings to the
surface of the brain
The picture below shows a brain with the dura removed from the cortex
exposing the arachnoid membrane. The tiny protruding white parts seen near
the center of the photo are the visible arachnoid granulations. The transparent
membrane over the entire brain surface is the arachnoid membrane.
• Four Regions of the brain
• Use your notes to write down the four
main brain regions
Are you feeling brainy today?
D. Cerebrospinal fluidthe fluid that
forms a watery
cushion to
protect the brain.
1. Its
composition is
similar to blood
plasma
2. Formed by the
choroids plexus
3. Circulated in
arachnoid space,
ventricles, and
central canal of
the spinal cord
You tube:
Cerbrospinal fluid
circulation
MRI showing pulsation
Of CSF:
Hydrocephalus
• Imbalance in
CSF produced
and amount
absorbed
• Obstruction
• Poor
absorption
• Overproduction
E. Blood Brain Barrier- The barrier
that keeps neurons separated
from blood borne substances.
The brain is dependent upon the
constant internal environment
more than any other organ in
your body.
1. The barrier is created by
the least permeable
capillaries in the body.
2. The astrocytes contribute
to creating this barrier.
3. Exclusion of many
substances helps maintain
the delicate balance required
by the brain. However, the
barrier fails to prevent the
following substances from
entering:
Fats and fat soluble
molecules, Respiratory gases,
Alcohol, Nicotine, Anesthesia
Blood Brain Barrier
Meningitis
Meningitis is an inflammation of
the membranes that surround the
brain and spinal cord (these
membranes are known as
meninges). Meningitis is most
commonly caused by infections
with various pathogens,
examples of which are
Streptococcus pneumoniae and
Haemophilus influenzae.
III. Traumatic Brain Injuries
A. Concussion- a slight brain
injury, victim may be dizzy, or lose
consciousness briefly but there is
no permanent brain damage.
B. Contusion- nervous tissue
destruction occurs and the tissue
does not regenerate. A severe
brain stem contusion would cause
someone to go into a coma.
How are they different?
Contusions are localized, while
concussions are widespread.
* Contusions are macroscopic,
while concussions are
microscopic.
BOTH are due to head trauma
BOTH are serious, BOTH are
common
C. Cerebral Edema
(swelling) or
hemorrhage
(bleeding) - Swelling
or bleeding of the
brain due to an
inflammatory
response. This places
pressure on brain
tissue- this is a serious
situation.
D. Cerebrovascular Accident (CVA) - commonly
called a stroke. It is the result of a ruptured
blood vessel supplying a region of the brain.
The brain tissue that is supplied with oxygen
from the vessel will die. The loss of function
depends on the area of the brain affected and
the severity of the stroke.
E. Alzheimer’s disease- A
progressive
degenerative disease
affecting the brain.
Victims experience
memory loss, and
confusion. (caused by
plaques –protein
deposits- in between
the neurons)
F. Parkinson’s disease- A
basal nuclei problem
resulting from the
degeneration of
dopamine releasing
neurons. Patients
experience tremors, a
shuffling gait, trouble
getting their muscle
going, and head
nodding.
Meningial Layers
Protection for the CNS
IV. Spinal Nerves
A. There is a pair of spinal nerves at the level of each
vertebra for a total of 31 pairs
B. Spinal nerves are formed by the combination of the
ventral and dorsal roots of the spinal cord
C. Spinal nerves are named for the region from which they
arise
A dermatome is an area of skin that is
mainly supplied by a single spinal nerve.
Nerve Plexuses
D. Complex networks of
nerves called
plexuses serve the
motor and sensory
needs of the limbs.
1. Cervical plexusorigin of nerves- C1C5, control mainly
the
muscles of the
shoulder and neck.
2. Brachial plexus- C5 – C8 and T1, control
mainly the arm
A “stinger” or a “burner”
The pain in his shoulder and neck is
intense, and the arm feels numb.
Feeling returns within a few minutes. (it is
more serious if it lasts more than 5
minutes.
• 3. Lumbar plexus- L1 – L4, controls the
lower abdomen, buttocks, leg and thigh
Innervates
muscles in the
calves, knees,
groin, thighs,
abdomen, and
lower back.
• 4. Sacral plexus- L4 –L5 and S1 – S4,
posterior surface of thigh, and leg, lower
leg, foot, and gluteus medius. This plexus
includes the sciatic nerve- largest in the
body.
V. Cranial Nerves
A. Twelve pairs of cranial
nerves extend from the brain to
serve the head and neck region.
The exception is the vagus
nerve which extends into the
thorax and abdomen.
B. Most cranial nerves are
mixed nerves; however three
pairs are purely sensory. The
optic (vision), olfactory (smell),
and vestibulocochlear (balance
and hearing). There is a chart
on pg. 231- 232 that identify
each cranial nerve by number,
origin, function and how to test
the nerve.
•
•
•
•
•
•
•
•
•
•
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Corpus callosum
Pineal gland/epithalamus
Cerebellum
Pons
Medulla oblongata
Cerebral cortex
Broca’s area
Thalamus
Hypothalamus
Frontal lobe
Choroid plexus
Identify the following brain structures
1
2
9
3
8
7
4
6
5
Question of the week: Why Do I
Sometimes See Stars?
Answer: "Seeing stars" is a common visual complaint, but it is usually a normal and
harmless occurrence. If you close your eyes and rub them, you will probably see
spots and flashes of light. These images you see are called "phosphenes," an
entoptic phenomenon characterized by the experience of seeing light without
light actually entering the eye. Phosphenes are produced by pressure on the
eyes. The pressure is translated into various patterns by the optic nerve.
These stars, or spots of light, that you see can occur after a sneeze, a deep cough, a
blow to the head or low blood pressure (such as standing up too quickly).
Some people see flashes or lines of light that often last up to 10 to 20 minutes. These
flashes of light are generally caused by a spasm of blood vessels in the brain,
called a "migraine." If a headache follows the flashes, it is called a "migraine
headache." If these flashes or lines of light occur without a headache, it is called an
"ophthalmic migraine," or migraine without a headache.
While usually harmless, frequent flashes of light can be a warning sign of something
more serious. A comprehensive eye examination will be needed to determine the
cause.
Brain Dissection Structures
External Anatomy
__ Spinal Cord
__ Cerebellum
__ Cerebrum
__ Gyri
__ Sulci
__ Olfactory bulb
__ occipital lobe
__ Optic chiasm
__ frontal lobe
__ parietal lobe
__ temporal lobe
Internal Anatomy
__ corpus callosum
__ pons
__ pituitary gland
__ lateral ventricle
__ pineal gland
__ midbrain
__ hypothalamus
__ thalamus
__ medulla oblongata
Sheep Brain
Cross-section Anatomy
Group Assignment
• Use the half sheet for a list of LABELS
(flags) you will need to identify in the
sheep brain
• INIVIDUAL assignment:
– On a separate sheet of paper, list these
structures as you tag them and write down
their functions
Study for your test!