Transcript No Slide Title

The Brain
Prepared by Hugh Potter
Biology Department
Union County College
Source of Images: ADAM, Inc
BRAIN - LATERAL VIEW
COVERINGS OF THE BRAIN
A. THE CRANIUM
B. THE MENINGES
B
A
The Meninges
The Meninges are tough, moist membranes surrounding the brain and
spinal cord. Infection of meninges is called meningitis.
1. Dura mater – outermost membrane. Very tough, protective layer
consisting of:
a. The Periosteal layer – thick, outer portion, continuous with the
periosteum of the cranial bone.
b. Meningeal layer- thin, inner portion. The spinal dura mater
consists only of this layer.
2. Arachnoid layer – a fibrous, delicate middle zone. Below this layer
is the subarachnoid space filled with cerebrospinal fluid.
3. Pia mater – innermost of the meningeal layers. It is closely adherent
to the surface of the brain and spinal cord.
Cerebrospinal Fluid and the Ventricles of the Brain
CSF is manufactured by specialized blood vessels, the choroid plexi.
These vessels are located within spaces of the brain called the ventricles.
The brain contains four ventricles:
The Lateral ventricles – Each cerebral hemisphere contains a lateral
ventricle (ventricles I and II). They are separated from one another by a
thin partition called the septum pellucidum.
The Third Ventricle – This ventricle is found below the lateral
ventricles in the diencephalon. Each lateral ventricle is connected to
ventricle III by a narrow opening – the Foramen of Monro.
The Fourth Ventricle – This ventricle is found between the brain stem
and the cerebellum. The III and IV ventricles are connected by a channel
called the Aqueduct of Sylvius. The floor of the IV ventricle has three
small holes which allow the CSF to leave the inside of the brain and pass
into the subarachnoid space
The Cerebral Cortex
The cerebral cortex is a structure within the brain that
plays a key role in memory, attention, perceptual awareness,
thought, language, and consciousness. In non-living, preserved
brains, the outermost layer of the cerebrum has a gray color, hence
the name gray matter.
Gray matter is formed by neurons and their unmyelinated
fibers, whereas the white matter below the gray matter of the cortex
is formed predominantly by myelinated axons interconnecting
different regions of the central nervous system. The human cerebral
cortex is 2-4 mm (0.08-0.16 inches) thick.
The surface of the cerebral cortex is folded in large
mammals, wherein more than two-thirds of the cortical surface is
buried in the grooves, called “sulci."
Connections of the Cerebral Cortex to other Brain Regions
The cerebral cortex is connected to various structures such as
the thalamus and the basal ganglia, sending information to
them along efferent connections and receiving information
from them through afferent connections. Most sensory
information is routed to the cerebral cortex from the thalamus.
Olfactory information, however, passes through the olfactory
bulb to the olfactory cortex directly. The vast majority of
connections are from one area of the cortex to another rather
than to subcortical areas.
The cortex is commonly described as comprising three
parts: sensory, motor, and association areas.
Sensory areas
The sensory areas are the areas that receive and process
information from the senses. Parts of the cortex that receive sensory
inputs from the thalamus are called primary sensory areas. The senses
of vision, audition, and touch are served by the primary visual cortex,
primary auditory cortex and primary somatosensory cortex,
respectively.
In general, the two hemispheres receive information from the
opposite (contralateral) side of the body. For example the right primary
somatosensory cortex receives information from the left limbs, and the
right visual cortex receives information from the left visual field. Areas
with lots of sensory innervation, such as the fingertips and the lips,
require more cortical area to process finer sensation.
Association areas
Association areas function to produce a meaningful
perceptual experience of the world, enable us to interact effectively,
and support abstract thinking and language. The parietal, temporal,
and occipital lobes organize sensory information into a coherent
perceptual model of our environment centered on our body image.
The frontal lobe or prefrontal association complex is
involved in planning actions and movement, as well as abstract
thought. Our language abilities are localized to the association areas
of the parietal-temporal-occipital complex, typically in the left
hemisphere.
Two of these areas are most important:
1. Wernicke’s area relates to understanding the meaning of
language, facial expressions and body language.
2. Broca’s area controls the muscles of the tongue, lips and larynx
that we use to produce speech.
Motor areas
The motor areas are located in both hemispheres of the
cortex. They are shaped like a pair of headphones stretching from
ear to ear. The motor areas are very closely related to the control of
voluntary movements, especially fine fragmented movements
performed by the hand. The right half of the motor area controls the
left side of the body, and vice versa.
Two areas of the cortex are commonly referred to as motor:
1. Primary motor cortex, which executes voluntary movements
2. Premotor cortex, Regulates skilled motor activities. This area
“instructs” the Primary Motor cortex.which then selects voluntary
movements.
THE BRAIN - SAGITTAL VIEW
A
A. The Cerebrum
B. The Cerebellum
B
D
C
C. The Pons
D. The Medulla Oblongata
THE BRAIN - LATERAL VIEW
I The Cerebrum
A - Frontal Lobe
B
A
B - Parietal Lobe
C - Temporal Lobe
D - Occipital Lobe
II The Cerebellum
D
C
II
CEREBRUM - FRONTAL LOBE
1. The frontal lobe initiates motor
activities.
2. It controls the movements of the
tongue leading to speech through Broca’s
area.
3. The frontal lobe controls the formation
of thought and emotions and stores
memory.
4. The frontal lobe is the region from
which our personality and intelligence
originates.
CEREBRUM - PARIETAL LOBE
The Parietal lobe receives
sensory nerve information from
various regions of the body,
especially the skin. This is
called general sensation. The
parietal lobe is also responsible
for interpreting this
information
Cerebrum - Temporal Lobe
1. The temporal lobe is responsible
for the perception and
interpretation of auditory input.
2. An Olfactory Area receives and
interprets odors.
3. Wernicke’s area allows us to put
words to auditory, visual or even
touch sensations (Braille). This
area turns these sensations into
meaningful ideas.
Temporal lobe
CEREBRUM - OCCIPITAL LOBE
The Occipital lobe contains the
Visual Area responsible for the
interpretation of visual input or
sight. It is the destination of
the optic nerve.
CORPUS CALLOSUM
The Corpus callosum is a
flat, sheet-like nerve tract
connecting the right and left
cerebral hemispheres. It
contains more than 200
million axons.
Basal Cerebral Ganglia
1. Nuclei buried deep in the cerebrum just superior to the
thalamus. A nucleus is a group of nerve cell bodies
found together in a specific area of the central nervous
system
2. The basal ganglia control the background, gross,
intentional body movements which are always associated
with the more precise movements of arms, hands, fingers
and feet. For example, when you are picking up a pencil,
the conscious reach and grasp actions are performed by
the arm, hand and fingers. The cerebral nuclei position
your shoulder and stabilize the arm to make the grasp
more precise.
Limbic System
The limbic system is found along the border between the
cerebrum and the diencephalon. The limbic system links the
conscious functions of the cerebral cortex with the unconscious and
autonomic functions of the lower brain. It plays a very large role in
memory storage and retrieval.
Temporal lobe
hippocampus
Components of the Limbic System
1. Hippocampus is a sea horse shaped region responsible for
establishing new memories, especially those that are
emotionally charged.
2. Mamillary body processes sensory information and
movements associated with eating, e.g., chewing, licking and
swallowing.
3. Amygdala is crucial in the formation of emotions. It is
highly connected to our learning and memory centers. The
amygdala is central to most brain events involving fear.
4. The Fornix is a tract of white matter that connects the
hippocampus with the hypothalamus.
The hippocampus is located
in the medial portion of the
temporal lobe of the
cerebrum. It is part of a
nerve tract called the limbic
system. The name is based
on its shape – like a sea
horse.
Why should you care about the hippocampus? Here are
three good reasons.
First, this part of the brain appears to be absolutely
necessary for making new memories. If you didn't have
it, you couldn't live in the present: you'd be stuck in the
past of old memories. Alzheimer's disease affects the
hippocampus first and very severely, before other parts
of the cortex (later, the frontal lobes too). So memory is
usually the first thing to start to falter in Alzheimer's -the ability to make new ones, that is. Who visited
yesterday? Where did I put the car keys? Why isn't
there any mail today (when you brought it in 3 hours
ago)?
Secondly, the hippocampus seems to be involved in severe
mental illnesses. In both schizophrenia and some severe
depressions, the hippocampus appears to shrink. However,
there is recent evidence that this shrinkage can be reversed
and perhaps prevented in people with depression and
bipolar disorder, with effective treatment.
Third, the hippocampus is known to be directly affected
by estrogen. Estrogen increases "synaptic density" -- the
number of connections to other nerve cells -- in the
hippocampus. There is some evidence that estrogen may
play a role in preventing Alzheimer's.
The Diencephalon
The diencephalon is located directly under the corpus
callosum. The third ventricle is found in the diencephalon. The
diencephalon is composed of three major regions:
1. The Thalamus is a motor relay station for sensory information
from the spinal cord to the cerebral cortex. All sensory
information going to the brain (except for olfactory) has to make a
pit stop in the thalamus.
2. The Epithalamus is located in the most superior and anterior
portion of the diencephalon. The choroid plexus of the third
ventricle is found in the epithalamus. The pineal body is also
found here. The pineal manufactures melatonin which helps to
regualte our sleep-wake cycle.
3. The Hypothalamus is located just below the thalamus on the
floor
of the brain. It is a major center for the control of internal body
functions through the activities of several nuclei.
Regulatory Centers of the Hypothalamus
1. Preoptic nucleus – controls body temperature.
2. Supraoptic nucleus - regulates the secretion of antidiuretic hormone. This hormone helps to regulate the
balance between fluids and electrolytes in the body
(osmoregulation), as well as, blood pressure.
3. Paraventricular nucleus – manufactures the hormone
oxytocin which stimulates the smooth muscle of the
uterus.
4. Medial nuclei – produce a sense of satiety or satisfaction
from food intake due to a rise in blood sugar.
5. Lateral regions of the hypothalamus – Stimulation of
this area produces the feeling of hunger of thirst
depending on the precise location stimulated.
6. The hypothalamus exerts a great deal of control over the
CEREBELLUM
The cerebellum is located
posterior to the pons and
medulla oblongata.
Through its nerve
connections to the
cerebrum and spinal cord,
it coordinates all motor
activity of the body.
The Brain Stem
The brain stem is the last major
portion of the brain. It contains the
centers for regulating physiological
processes, e.g., respiration, blood
pressure, heart rate and wakesleep cycles.
Midbrain – is the uppermost region of
the brain stem.
The Pons – is located just superior to
the medulla oblongata and inferior
to the midbrain.
Medulla oblongata – is the last region
of the brain stem before the spinal
cord.
The Midbrain
1. the uppermost region of the brain stem.
2. located at the junction of the cerebellum and pons.
3. a relay station for motor and sensory messages between
parts of the brain and the spinal cord.
4. The tectum of the midbrain contains two pairs of
rounded bulges, the corpora quadrigemina. The
superior colliculi coordinate motor reflexes produced by
visual stimuli. The two inferior colliculi coordinate motor
reflexes due to auditory input.
5. The substantia negra is located in the midbrain. The substantia
negra controls motor tracts form the cerebrum by releasing an
inhibitory neurotransmitter, dopamine. Damage to this area leads to
Parkinson’s disease.
The Pons
The Pons is located just superior to the medulla oblongata and
inferior to the midbrain. It contains many of the longitudinal nerve
tracts passing through the brain stem:
1. Corticospinal tracts – The axons of these tracts originate at the
cerebral cortex and pass directly to the motor neurons of the
spinal cord.
2. Spinothalamic tracts – are sensory tracts carrying nerve messages
of crude touch, pain and temperature from various levels of the
spinal cord to the thalamus and then to the cerebral cortex.
The pons contains nuclei for regulating respiratory movements:
1. The apneustic center stimulates the respiratory rhythmicity center
(RRC) in the medulla oblongata to produce inspiration.
2. The pneumotaxic center inhibits the RRC producing a passive
expiration.
The Medulla Oblongata
The medulla oblongata is the last portion of the brain before the
spinal cord. The medulla contains the corticospinal and
spinothalamic nerve tracts.
1. Corticospinal tracts contain descending nerve fibers for the
control of conscious motor activity. In the lower medulla, these
tracts decussate (cross over). As a result, the left cerebral
cortex initiates motor activity on the right side of the body and
vice versa. 85% of the corticospinal tracts decussate.
2. The Spinothalamic tracts pass through the medulla and
converges on the thalamus. They carry sensory information of
crude touch, pressure and pain, as well as, thermal sensation.
There is no decussation of these messages in the medulla. This
has already occurred in the spinal cord at the level of entry to
the medulla.
Medullary Nuclei
Medullary nuclei are clusters of cell bodies within the
interior of the medulla oblongata that carry out a
variety of regulatory functions:
1. Cardiovascular centers regulate heart rate, and
vasomotion.
2. Respiratory rhythmicity center sets the breathing
pace with input from the apneustic and pneumotaxic
centers of the pons.