Transcript Nervous System II

Nervous
System II
Chapter 12
Major Organs
• Brain
• Spinal Cord
• Cranial Nerves
• Spinal Nerves
Brain
• May appear
somewhat
unimpressive at first
glance.
• Average adult brainMale 3.5 lbs the
Female 3.2 lbs.
• Quivering pink tissue
with the appearance
of cold oatmeal.
Brain
• Functions- contains
nerve centers
associated with sensory
functions and is
responsible for
sensations and
perceptions. (motor
functions, memory,
reasoning, nerve
pathways)
Cerebrum
• The cerebrum, which develops from the
anterior portion of the brain, is the
largest part the mature brain.
• It consists of two large masses or
cerebral hemispheres.
• Together they account for about 83%
of total brain mass.
Cerebrum
• A deep bridge of nerve
fibers called the corpus
callosum connects the
cerebral hemispheres.
• This is the structure
that is located beneath
the Cerebrum in the
pictures.
Cerebrum
• Many ridges called
Gyri or
(convolution,)
separated by
grooves, mark the
cerebrum.
• A shallow to
somewhat deep
groove is called a
sulcus.
• A very deep grove is
called a fissure.
• The pattern of
these elevations and
depressions is
complex, and it is
distinct in all normal
brains.
Cerebrum
Cerebrum
Cerebrum
• You need to be able to located the following
sulcus and fissures on the brain.
• Central Sulcus (Separates the frontal and
parietal lobes)
• Lateral Sulcus (Separates the temporal lobe
from the parietal and frontal lobes)
• Transverse Fissure (Is anterior to the
cerebellum)
• Longitudinal Fissure (Separates the left
and right hemispheres)
Cerebrum
• Each Cerebral hemisphere has three
basic regions
– Cortex Matter- A superficial layer that
looks gray in fresh brain tissue.
– Internal White Matter-internal layer.
– Basal Nuclei- islands of gray matter
situated deep within the white matter.
They relay motor impulses originating in
the cerebral cortex and aid in controlling
motor activities.
Cerebrum
Cerebrum
• The cerebral cortex
is the “executive
suite” of the nervous
system, where our
conscious mind is
found.
Cerebrum
• A think layer of gray matter called the
cerebral cortex, constitutes the
outermost portion of the cerebrum.
• It covers the gyri or convolutions.
Cerebral Cortex
• The cerebral cortex contains nearly
75% of all the neuron cell bodies in the
nervous system.
• The cerebral cortex has sensory, motor
and association areas.
Functions of The Cerebrum
• The cerebrum provides higher brain
functions: interpreting impulses from
sense organs, initiating voluntary
muscular movements, storing
information as memory, and retrieving
this information in reasoning.
• The cerebrum is also the seat of
intelligence and personality.
Frontal Lobe of the Cerebral
Frontal Lobe of the Cerebral
• Functions: Motor areas control
movements of voluntary skeletal
muscles
• Association areas carry on higher
intellectual processes for concentration,
planning complex problem solving, and
judging the consequences of behavior.
Parietal Lobe of the Cerebral
Parietal Lobe of the Cerebral
• Functions: Sensory areas provide
sensations of temperature, touch,
pressure, and pain involving the skin.
• Association areas function in
understanding speech and in using
words to express thoughts and feelings.
Temporal Lobe of the Cerebral
Temporal Lobe of the Cerebral
• Functions: Sensory areas are
responsible for hearing
• Association areas interpret sensory
experiences and remember visual
scenes, music, and other complex
sensory patterns.
Occipital Lobe of the Cerebral
Occipital Lobe of the Cerebral
• Functions: Sensory areas are
responsible for vision.
• Association areas combine visual
images with other sensory experiences.
Dominant Hemisphere
• Both cerebral hemispheres participate in
basic functions, such as receiving and
analyzing sensory impulses, controlling
skeletal muscles on opposite sides of
the body.
• However, 90% of the population is left
hemisphere dominant for the languagerelated activities of speech, writing, and
reading.
Diencephalon
• The diencephalon forms the central
core of the forebrain and surrounded by
the cerebral hemispheres….. contains
the thalamus, hypothalamus, and
epithalamus.
Thalamus
• The thalamus selects incoming
sensory impulses and relays them to
the cerebral cortex
Hypothalamus
• The Hypothalamus is important in
maintaining the homeostasis.
• Helps maintain the following….Autonomic
control center, center for emotional response,
body temperature regulation, regulatin of
food intake, water intake, and thirst, sleep
cycles,etc.
• Pituitary Gland- secrets at least 9
hormones. Size and shape of a pea. Located
below the hypothalamus. (add to notes)
Hypothalamus
Epithalamus
• The Epithalamus is the most dorsal
portion of the diencephalon forms the
roof of the third ventricle.
• It works in close association with the
Hypothalamus and pineal gland.
• The Pinal Gland secrets melatonin
which plays a role in the sleep/wake
cycle. (yes, you have to adjust your notes here)
The Brain Stem
• The brain stem extends from the base
of the brain to the spinal cord.
• The brain stem consists of the midbrain,
pons, and medulla oblongata.
The Brain Stem
The Brain Stem
• The midbrain contains reflex centers
associated with eye and head
movement
The Brain Stem
• The pons transmits impulses between
the cerebrum and other parts of the
nervous system and contains centers
that help regulate rate and depth of
breathing.
• The medulla oblongata transmits all
ascending and descending impulses and
contains several vital and non-vital
reflex centers. (blood pressure, heart
rate, and respiration)
Cerebellum
• The cerebellum consists of two
hemispheres connected by the vermis.
Cerebellum
• A thin cortex of gray
matter surrounds the
white matter of the
cerebellum
• The arbor vitae (Latin
for "Tree of Life") is the
cerebellar white matter,
so called for its
branched, tree-like
appearance.
Cerebellum
Cerebellum
• The cerebellum functions primarily as a
reflex center, coordinating skeletal
muscle movements and maintaining
equilibrium.
Optic Chiasma
• A point near the thalamus and
hypothalamus at which portions of each
optic nerve cross over.
• We will try to find this in a sheep brain!
Optic Chiasma..in the human brain!
Olfactory Bulb
• One of two enlargements at the
terminus of the olfactory nerve at the
base of the brain just above the nasal
cavities
Olfactory Bulb
• Again this is something that we will
really observe in the sheep brain.
Larger in sheep than humans!
Cerebrospinal Fluid
• The entire surface of central
nervous system is bathed by a
clear, colorless fluid called
cerebrospinal fluid (CSF).
• The CSF is contained within a
system of fluid-filled cavities called
ventricles.
Cerebrospinal Fluid
• Found in and around the brain and spinal cord
• Reduces brain weight by 97% and prevents
the brain from crushing under its own weight.
• Protection: the CSF protects the brain from
damage by "buffering" the brain. In 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.
Cerebrospinal Fluid
• Excretion of waste products: the oneway 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.
Cerebrospinal Fluid
• The CSF is formed by the choroid
plexuses that hang from the roof of
each ventricle…primarily the first
and second ventricles. (lateral)
• CSF is replaced in an average
human once about every 8 hours.
Cerebrospinal Fluid
• CSF flows from the lateral ventricle
to the third ventricle through the
interventricular foramen (also
called the foramen of Monro).
• The third ventricle and fourth
ventricle are connected to each
other by the cerebral aqueduct
Cerebrospinal Fluid
Cerebrospinal Fluid
Spinal Cord
• The spinal cord is a
nerve column that
extends from the brain
into the vertebral canal.
• Consists of 31
segments, each of
which gives rise to a
pair of spinal nerves.
• Divided into right and
left halves.
Functions of the Spinal Cord
• The spinal cord is the center for spinal
reflexes (1) Reflexes are automatic,
subconscious responses to changes. (2) They
help maintain homeostasis. (3) The knee-jerk
reflex employs only two neurons. (4)
Withdrawal reflexes are protective actions
• The cord provides a two-way communication
system between the brain and structures
outside the nervous system.
Spinal Nerves
• Consists of thirtyone pairs of spinal
nerves
• Functions- they
provide two way
communication
between the spinal
cord and parts of
the upper and lower
limbs, neck and
trunk
Cranial Nerves
• There are twelve
pairs of cranial
nerves
• Functions- consists
of sensory fibers
(smell and vision)
and motor fibers
(controls muscles
and glands)
Protection of the Brain
• Nervous tissue is soft and delicate and
neurons are injured by even slight
pressure.
• However the brain is protected in 4
keys ways.
Protection of the Brain
• 1.) Skull- we will go into more detailed
in the Skeletal System
• 2.) Membranes (Meniges)
• 3.) Watery Cushions (Cerebrospinal
Fluid)
• 4.) Blood-brain Barrier.
Protection of the Brain
• Membranes (Meniges)- are three
connective tissue membranes that lie
just external to the CNS
• Functions
– Cover and protect the CNS
– Protect blood vessels and enclose venous
sinuses
– Contain CSF fluid
– Form partitions in the skull
Protection of the Brain
• The leathery Dura Mater, meaning
“tough mother” is the strongest meninx
• Surrounds the brain
• Two-layered sheet of fibrous connective
tissue.
• The two other meninges are the
Arachnoid and Pia Mater.
Protection of the Brain
• Meningitis? Inflammation of the
meninges…serious threat to the brain
because a bacterial or viral meningitis
may spread to the CNS..
• Meningitis is diagnosed by obtaining a
sample of CSF via a lumbar tap.
Protection of the Brain
• Blood-Brain Barrier (BBB) is semipermeable; that is, it allows some
materials to cross, but prevents others
from crossing.
Protection of the Brain
• The BBB functions are…
• Protects the brain from "foreign
substances" in the blood that may injure
the brain.
• Protects the brain from hormones and
neurotransmitters in the rest of the body.
• Maintains a constant environment for
the brain.
Degenerative Brain Disorders
Alzheimer's Disease
• Alzheimer is a progressive degenerative
disease of the brain that ultimately
results in dementia.
• Alzheimer’s patients represent about ½
of the people living in a nursing home.
• Extreme memory loss, shortened
attention span, disorientation, and
eventually memory loss.
Degenerative Brain Disorders
Alzheimer's Disease
• Examination of brain tissue reveal senile
plaques littering the brain like shrapnel
between neurons. The presence of
neurofibrillary tangles inside neurons
have also been identified. Both of
these seem to be a malfunction of key
proteins.
Degenerative Brain Disorders
Parkinson’s Disease
• Typically striking people in their 50’s
and 60’s
• Afflicted individuals have a persistent
tremor at rest, forward-bent walking
posture and shuffling gait, and stiff
facial expression.
Degenerative Brain Disorders
Parkinson’s Disease
• PD results from a degeneration of the
dopamine-releasing neurons of the
sustantia nigra.
• As those neurons deteriorate the
dopamine-deprived basal nuclei they
target become overactive.
Degenerative Brain Disorders
Huntington’s Disease
• Huntington’s Disease is a fatal
hereditary disorder that strikes during
middle age.
• HD is caused by a mutant Huntington
protein that accumulates in brain cells
and the tissue dies.
• Symptoms include wild jerky
movements, mental deterioration and is
usually fatal within 15 years of onset. .