Download THE CEREBRUM (sah REB brum) LOCATION The cerebrum is the

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THE CEREBRUM
(sah REB brum)
LOCATION
The cerebrum is the largest and highest part of the brain. It occupies the whole upper part of the
skull.
DESCRIPTION:
It weighs about two pounds. and makes up about 85% of the brain. It is covered by a thin layer
gray matter called the cerebral cortex. This surface is completely covered with furrows and
ridges. Nerve cells connect the cerebral cortex with other parts of the brain: the cerebellum, the
brain stem and the spinal cord.
The cerebrum is divided into two hemispheres right and left.
Each hemisphere is divided into four lobes: the frontal, parietal, occipital, and temporal lobe.
Fissures in the cortex divide the lobes
FUNCTIONS
Each lobe of the cerebral hemispheres controls different types of functions, Figure 8-6.
1. Frontal lobe: at the front (Motor cortex )
a. Voluntary muscles. Cells in the right hemisphere activate the left side of the
body; the left hemisphere controls the right side.
b. Speech. usually in the left hemisphere Damage to this area means that you
may know what to say, but you cannot vocalize the words.
2. Parietal lobe - in the middle (sensory cortex)
pain,
touch, heat, and cold.
the determination of distances, sizes, and shapes.
3. Occipital lobe- at the rear (visual cortex), located over the cerebellum,
eyesight.
The speech area which allows us to recognize words and to interpret the
meaning, spoken or read, is located at the junction of the temporal, parietal,
and occipital lobes.
4. Temporal lobe- at the lower side
Hearing
Smelling
 The cerebral cortex also controls conscious thought. Judgment, memory, reasoning,
and will power. This high degree of development makes the human the most
intelligent of all animals. (What lobe is not designated).
 World Book: “The Association Cortex analyzes, processes, and stores information,
and so makes possible all of our higher mental abilities. such as thinking,
speaking, and remembering.
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THE THALAMUS
DESCRIPTION
The thalamus is a spherical mass of gray matter.
LOCATION: It is found deep inside each of the cerebral hemispheres, lateral to the third
ventricle.
MECHANICS
The thalamus acts as a relay station for incoming and outgoing nerve impulses.
It receives direct or indirect nerve impulses from the various sense organs of the body (with the
exception of olfactory sensations). These nerve impulses are then relayed to the cerebral cortex.
The thalamus also receives nerve impulse? from the cerebral cortex, cerebellum, and other areas
of the brain.
FUNCTION: Damage to the thalamus may result in increased sensibility to pain, or total loss of
consciousness.
HYPOTHALAMUS
LOCATION The hypothalamus lies below the thalamus. It forms part of the lateral walls and
floor of the third ventricle.
MECHANICS; A bundle of nerve fibers connects the hypothalamus to the posterior pituitary
gland, the thalamus, and the midbrain. The limbic system is that part of the brain which is
associated with emotional control.
The hippocampal gyri of the limbic system helps to store and retain short term memory. The
hypothalamus is part of the limbic system and is considered to be the “brain” of the brain.
Through the use of feedback, the hypothalamus stimulates the pituitary to release its hormones
FUNCTIONS
. Nine vital functions are performed by the hypothalamus:
1. Autonomic nervous control-Regulates the parasympathetic and sympathetic systems of the
autonomic nervous system.
2. Cardiovascular control-controls blood pressure regulating the constriction and dilation of
blood vessels and the beating of the heart.
3. Temperature control-Helps in the maintenance of normal body temperature (37°C or
98.6°P).
4. Appetite control-Assists in regulating the amount of food we ingest. The “feeding center,”
found in the lateral hypothalamus is stimulated by hunger “pangs,” which prompt us to eat.
In turn, the “satiety center” in the medial hypothalamus becomes stimulated when we have
eaten enough.
5. Water balance-Within the hypothalamus, certain cells respond to the osmotic pressure of
the blood. When osmotic pressure is high, due to water deficiency, the antidiuretic hormone
(ADH) is secreted. A “thirst area” is found near the satiety area, becoming stimulated when
the blo~d’s osmolality is high. This causes us to consume more liquids.
6. Manufacture of oxytocin-Contracts the
uterus during labor.
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7. Gastrointestinal control-Increases intestinal peristalsis and secretion from the intestinal
glands.
8. Emotional state-Plays a role in the display of emotions such as fear and plea
9. Sleep control: Helps keep us awake when necessary.
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THE CEREBELLUM
(sara BELL um)
LOCATION
The cerebellum is located lowest part of brain, at the rear below the cerebrum (see Figure 85).
DESCRIPTION:
It is composed of two hemispheres or wings: the right cerebellar hemisphere and the left
cerebellar hemisphere. These two hemispheres are connected to a central portion called the
vermis. The cerebellum consists of gray matter on outside the white matter on the inside.
The . white matter on the inside of the cerebellum is marked with a tree-like pattern. This
pattern is called arbor vitae (tree of life).
MECHANICS
The cerebellum communicates with the rest of the central nervous system by three pairs of
tracts called peduncles.
These three peduncles are composed of "incoming" axons that carry nerve messages" into
the cerebellum and "outgoing" axons that transmit messages out of the cerebellum.
FUNCTIONS
The incoming axons carry messages to the cerebellum regarding
 movement within joints, muscle tone, position of the body, and the tightness of
ligaments and tendons. This information reaches the cerebellum directly from
sensory receptors including the inner ear, the eye, and the proprioceptors of the
skeletal muscle. The "outgoing" axons carry nerve messages to the different parts of
the brain that control skeletal muscles.
The cerebellum controls all body functions that have to do with skeletal muscles.
 Maintenance of balance. If the body is imbalanced, sensory receptors in the inner ear
send nerve messages to the cerebellum. There the cerebellum carries impulses to the
motor controlling areas of the brain. These brain areas, in turn, stimulate muscle
contraction that restores balance.
 Maintenance of muscle tone. The cerebellum transmits nerve impulses to the red nucleus
that, in turn, relays them to the spinal cord and then to the skeletal muscles.
 Coordination of muscle movements. Any voluntary movement is initiated in the cerebral
cortex. However, once the movement is started, its smooth execution is the role of the
cerebellum.
 The cerebellum allows each muscle to contract at the right time, with the right strength,
and for the right amount of time so that the overall movement is smooth and flowing.
 This is important when doing complex or skilled movements such as speaking, walking,
writing; even simple movements need the coordinating abilities of the cerebellum. A
simple action such as raising the hand to the face to avoid a blow requires the
synchronized action of 50 or more muscles. These muscles then act on 30 separate bones
of the arm and hand.
The removal of or injury to the cerebellum results in motor impairment.
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THE BRAIN STEM
DESCRIPTION AND LOCATION
The brain stem is made up of three parts:
the midbrain, pons, and the medulla. The pons is located in front of the cerebellum,
between the midbrain and the medulla oblongata. Gray matter extends the whole length of
the brain stem.
MECHANICS
The brain stem provides a pathway for messages that neurons take to and from the cerebrum.
These are the neurons that are involved in the sleep-wake cycle. It contains interlaced
transverse and longitudinal myelinated, white nerve fibers mixed with gray matter.
The pons has three essential functions: 1) It is a pathway for nerve impulses which connect
the cerebrum, cerebellum, and other areas of the nervous system. It is the site for the
emergence of four pairs of cranial nerves. And 3) It controls respiration.
The midbrain extends from mammillary bodies to the pons. The cerebral aqueduct travels
through the midbrain. It contains the nuclei for reflex centers involved with vision and
hearing.
The medulla oblongata is a bulb-shaped structure found between the pons and the spinal
cord. It lies inside the cranium and above the foramen magnum of the occipital bone. The
medulla is white on the outside, just like the pons, because of the myelinated nerve fibers
which serve as a passageway for nerve impulses between the brain and spinal cord. It
contains the nuclei for vital functions such as the heart rate, the rate and the depth of respiration, the vasoconstrictor center which affects blood pressure, and the center for
swallowing and vomiting.
SUMMARY OF THE FUNCTIONS OF THE BRAIN STEM
1. It connects to several other brain parts, including the cerebrum, cerebellum, mid
brain, spinal cord,
2. Controls respiration
3. Vision and hearing
4. Heart rate, blood pressure
5. Swallowing and vomiting
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SPINAL CORD
LOCATION
The spinal cord continues down from the
brain. The spinal cord begins at the foramen magnum of the occipitalq.one and continues to
the second lumbar vertebrae.
DESCRIPTION It is white and soft and lies within the vertebrae of the spinal column. Like
the brain, the spinal cord is submerged in cerebrospinal fluid and is surrounded by the three
meninges. The gray matter in the spinal cord is located in the internal section; the white
matter composes the outer part, Figure 8-7.
MECHANICS
In the gray matter of the cord, connections can be made between incoming and outgoing
nerve fibers which provide the basis for reflex action.
FUNCTION
The spinal cord functions as a reflex center and as a pathway to and from the brain.