Transcript Chapter 7 Central Nervous System - kendrick

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.
Embryonic
development
C. The opening of the
neural tube becomes the
ventricles
1. There are four
ventricles which act as
chambers in the brain. (2
lateral ventricles, third,
and fourth)
2. The ventricles are
filled with cerebrospinal
Protection: the CSF protects the brain from damage by "buffering" the brain. into
fluid.
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 (anterior
commisure is the
bundle of nerve fibers
connecting the two
hemispheres)
b. The basal nuclei
(ganglia) is an internal
island of gray matter
deep within the cerebral
cortex. It helps
regulate the voluntary
motor activities,
learning, and action
selection (which
behavior to execute at a
given time).
4. Surface lobes of the cerebrum include:
a. Frontal lobe
1) Primary motor area- allows 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
Specialized areas of the Cerebrum:
Temporal lobe
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. Epithalamus- Forms the roof of the third ventricle.
Important parts include the pineal body(produces
melatoninto regulate sleep/wake cycles) and
choroids 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
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.
Helps prevent sensory overload!)
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
D. Cerebrospinal fluid- the 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
E. Blood Brain Barrier (The BBB)- 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
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.
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.
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
D. Complex networks of nerves called plexuses
serve the motor and sensory needs of the
limbs.
1. Cervical plexus- origin of nerves- C1- C5,
control mainly the
muscles of the shoulder and neck.
2. Brachial plexus- C5 – C8 and T1, control
mainly the arm
3. Lumbar plexus- L1 – L4, controls the
lower abdomen,
buttocks, leg and thigh
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.
Sheep brain dissection website
• http://bpweb.baypath.edu/biology/sheep%20brain/
brain-sheep.html