BRAIN

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BRAIN

• CHAPTER 14

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THE BRAIN

• Human brain only weighs about 3 lb.
• Contains more than 100 billion neurons.
• It does more than think and make decisions.
• Bodys main key to homeostasis, regulating body
  processes.
• Nerves and specialized receptors may receive the
  message, but you actually experience the
  sensation in your brain.

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PARTS AND MENINGES

• The principal parts of the brain are
• Brainstem the brain minus the cerebrum,
  cerebellum, and diencephalon.
• Cerebellum located inferior to the cerebrum and
  posterior to the brainstem second largest part
  of the brain, a motor area involved in
  coordination, maintenance of posture and balance.

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PARTS OF BRAIN

• Diencephalon a division of the brain that
  includes the epithalamus, thalamus and
  hypothalamus
• Cerebrum the largest portion of the brain,
  composed of the cerebral hemispheres, includes
  the cerebral cortex, the cerebral nuclei and the
  internal capsule.

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MENINGES

• Cranial meninges membranes surrounding the
  brain. This includes the tough outer dura mater,
  the middle web-like arachnoid layer and the
  thinner pia mater. Provide the necessary
  physical stability and shock absorption. Blood
  vessels branching within these layers also
  deliver oxygen and nutrients.

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Cerebrospinal Fluid

• The four CSF-filled cavities within the brain are
  called the ventricles-2 lateral, third and
  fourth.
• It completely surrounds and bathes the exposed
  surfaces of the CNS.
• Cushions delicate neural structures
• supports the brain
• transports nutrients, chemical messengers and
  waste products.
• A spinal tap can provide useful clinical
  information concerning CNS injury, infection or
  disease.

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Formation of CSF

• The site of production are the choroid plexuses
  which are network of capillaries in the walls of
  the ventricles.
• The capillaries are covered by ependymal cells
  that form CSF from blood plasma by filtration and
  secretion.
• There are tight junctions here-formation of
  blood-brain barrier. This allows for certain
  substances to enter the CSF and excludes others.

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Formation of CSF

• The CSF formed in t he choroid plexuses of each
  lateral ventricle flows into the third ventricle.
• More CSF is added by choroid plexuses of the
  third ventricle.
• The fluid then flows through the cerebral
  aqueduct into the fourth ventricle. This
  contributes mors fuid.
• Then it enters the subarachnoid space.
• It then circulates in the central canal of the
  spinal cord.
• CSF is gradually reabsorbed into the blood
  through arachnoid villi. Normally CSF is
  reabsorbed as rapidly as it is formed. Hence the
  pressure of CSF is constant.

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Hydrocephalous

• A condition resulting from excessive production
  of or inadequate drainage of CSF. The total
  volume of CSF and blood must remain at a stable
  level. If blood and CSF increases, the volume of
  the brain must compensate by decreasing its
  volume. An increase in the brains fluid volume
  compression and distortion of the brain. This in
  turn causes swollen facial features.
  Hydrocephalous is basically a condition in which
  intracranial pressure in altered.

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Adequate Blood Supply

• Neurons have a high demand for energy. They do
  not have energy reserves from lipids or CHOs or
  oxygen reserves. Therefore neurons depend on
  blood to transport oxygen to them. Hb gives red
  blood cells to transport oxygen in t he blood.
  Blood which irrigates the brain does so by means
  of arterial carotid arteries and vertebral
  arteries. The blood then leaves the brain
  through the internal jugular veins. Lack of
  oxygen has several medical complication from
  fainting to CVA.

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Medulla Oblongata

• That part of the brain stem that connects the
  pons and the root of the brain to the spinal
  cord. All the afferent and efferent tracts from
  the spinal cord either pass through or terminate
  here. It also contains nerve centers
  instrumental to the regulation and control of
  breathing, swallowing, coughing, sneezing and
  vomiting. Other centers in the medulla regulate
  arterial blood pressure, thereby exerting control
  over the circulation of blood.

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Pons

• The pons is a broad band of white matter located
  anterior to the cerebellum and between the
  midbrain and medulla oblongata. The pons
  contains fiber tracts linking the cerebellum and
  medulla to higher cortical areas two-way
  conduction pathway between areas of the brain and
  other areas of the bodyinfluences respiration.

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Mid-Brain

• Located between the forebrain and hind brain.
  Contains a number of large afferent and efferent
  pathways connecting major motor areas of the fore
  and hind brain. Also found in the mid brain are
  four small masses of gray cells-corpora
  quadrigemina. The upper two called superior
  colliculi are associated with visual reflexes and
  tracking movements of the eyes. The lower two,
  inferior colliculi are involved with the sense of
  hearing.

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Thalamus

• This is the largest of the two divisions of the
  diencephalon and is actually two large masses of
  grey cell bodies joined by a third or
  intermediate mass. It serves as a relay center
  for all sensory impulses (except olfactory) being
  transmitted to the sensory areas of the cortex.
  Besides its sensory function the thalamus also
  relays motor impulses from the cerebellum and
  basal ganglia to motor areas of the cortex. Some
  impulses related to emotional behavior are also
  passed from the hypothalamus through the thalamus
  to the cerebral cortex.

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Hypothalamus

• This lies beneath the thalamus. Is a principal
  regulator of ANS activity and is associated with
  behavior and emotional expression. It also
  produces neurosecretions for the control of water
  balance, sugar and lipid metabolism, regulation
  of body temperature, sleep-cycle control,
  appetite and sexual arousal. It also produces
  hormones for the post. Pituitary gland.

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Cerebrum

• Represents seven eighths of the brains total
  weight. It contains nerve centers that govern
  all sensory and motor activity, including sensory
  perception, emotions, consciousness, memory and
  voluntary movements. It is divide by
  longitudinal fissure into two cerebral
  hemispheres the right and left are joined by
  large fiber tracts (corpus callosum)that allow
  for information to pass from one hemisphere to
  another. The surface or cortex of each
  hemisphere has been divided into lobes as a means
  of identifying certain locations. These lobes
  correspond to the overlying bones of the skull an
  are the frontal, parietal, temporal and occipital
  lobes.

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Cerebellum

• This is the largest part of the hindbrain. It
  occupies a space in the back of the skull
  inferior to the cerebrum and dorsal to the pons
  and medulla oblongata. The cerebellum is oval in
  shape and is divided into deep fissures. The
  surface of the ceebellum has a cortex of grey
  cell bodies and its interior contains nerve
  fibers, white matter, connecting it to every part
  of the CNS. The cerebellum plays an important
  part in the coordination of voluntary movements.

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RAS

• One of the most important brain stem components
  is a diffuse network in the reticular formation
  known as the reticular activating system (RAS).
  This network extends from the midbrain of the
  medulla oblongata. The output of the RAS
  projects to thalamic nuclei that influence large
  areas of the cerebral cortex. When the RAS is
  inactive, so is the cerebral cortex. When the
  area is active, many impulses pass upward into
  the thalamus and disperse to widespread areas of
  the cerebral cortex. The effect is a generalized
  increase in cortical activity making one more
  alert and attentive.

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Pyramids

• Pyramids are thick bonds visible along the
  ventral surface of the medulla oblongata.
• Decussation is the movement of the axon from the
  left side to the right side and vice versa.
• The nucleus gracilis and nucleus cuneatus both
  pass sensory information to the thalamus.

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Pyramids

• The wall of the diencephalon are composed of the
  left and right thalamus. Each thalamus contains
  relay and processing centers for sensory
  information. The brain stem includes the
  mesencephalon, pons and the medulla oblongata.
• The pneumotaxic centers of the pons are paired
  nuclei that adjust the output of the respiratory
  rhythmicity centers.

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Blood-Brain Barrier

• Endothelial cells that line CNS capillaries
  create this BBB. This isolates the CNS from
  general circulation. The barrier exists because
  these cells contain tight junctions and they
  prevent diffusion of materials. Astrocytes
  maintain this barrier by providing structural
  support. They also regulate ion, nutrient, and
  dissolved gas concentrations. If the astrocytes
  are damaged or stop stimulating the endothelial
  cells, the blood brain barrier disappears.

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Cerebellum and Skeletal Muscle activities

• The cerebellum is involved in synergic control of
  skeletal muscles and plays an important role in
  the coordination of voluntary muscular movements.
  It receives afferent impulses and discharges
  efferent impulses but does not serve as a reflex
  center in the usual sense, however it may
  reinforce some reflexes and inhibit others. The
  cerebellum does not initiate movements, it
  interrelates with many brain stem structures in
  executing a variety of movements including proper
  posture and balance, walking, running, fine
  voluntary movements as required in writing,
  dressing, eating and playing musical instruments.
  The cerebellum controls the property of movement
  such as speed, acceleration and trajectory.

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LOBES

• Temporal lobe lobe of the cerebrum located
  laterally and below the frontal and occipital
  lobe. Contains auditory receptive areas.
• Frontal lobe four main convolutions in front of
  the central sulcus of the cerebrum.
• Parietal lobe the division of each side of the
  brain lying beneath each parietal bone.
• Occipital lobe posterior lobe of the cerebral
  hemisphere that is shaped like a three-sided
  pyramid.

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Convolutions

• In anatomy one of the many folds on the surface
  of the cerebral hemispheres. They are separated
  by sulci or fissures.
• Gyri outward folds of the cerebral cortex.
• Sulci shallow grooves betweeb folds of the
  cerebral cortex.
• Fissures deep grooves located between folds of
  the cerebral cortex.

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Fissures

• Parieto-occipital fissure fissure between the
  occipital and parietal lobes o9f the brain.
• Longitudinal fissure two cerebral hemispheres
  are almost completely separated by a deep
  longitudinal fissure.
• Central sulcus on each hemisphere the central
  sulcus a deep groove divide the anterior frontal
  lobe.
• Lateral sulcus this separates the frontal lobe
  from the temporal lobe.
• Postcentral situated or happening behind a
  center(gyrus)
• Precentral in front of a center, as a central
  fissure of the brain (gyrus).

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Central White Matter

• Lies beneath the neural cortex and around the
  cerebral nuclei and contains 3 major groups of
  axons. Whole collection of fibers is called
  internal capsule.
• 1. Association fibers interconnects areas of
  neural cortex within a single cerebral hemisphere
  . The short association fibers are called
  arcuate fibers, are curved and pass from one
  gyrus to another. The longer fibers are the
  longitudinal fasciculi, connect the frontal lo0be
  to the rest of the lobes in the same hemisphere.

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Central White Matter

• 2. Commisural fibers interconnect and permit
  communication between the two cerebral
  hemispheres. These fibers are the corpus
  callosum, carry about 4 billion impulses per
  second and contain 200 million axons and anterior
  commisure.
• 3. Projection fibers link the cerebral cortex to
  the diencephalon, brain stem, cerebellum and
  spinal cord.

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Cerebrum

• The cerebrum is the largest region of the brain
  and is involved in the processing of somatic
  sensory and motor information. Conscious
  thoughts and all intellectual functions originate
  in its right and left hemispheres.

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Left Hemisphere

• The categorical hemisphere or left hemisphere
  contains the general interpretive and speech
  centers.
• It is responsible for language based skills.
• It performs analytical tasks.
• The premotor cortex involved with the control of
  hand movements is larger on the left side for
  right-handed than for left-handed individuals.

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Right Hemisphere

• The representational hemisphere or right
  hemisphere deals with spatial relationships,
  analyzes sensory information and releases the
  body to the sensory environment.
• Permits identification of objects by touch,
  sight, smell, feel or taste.( recognizing faces
  and understanding 3-D)
• It analyzes the emotional context of a
  conversation. (get lost is it a question or
  threat)
• individuals with a damaged right hemisphere may
  be unable to add emotional inflections to their
  own words.

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Basal Ganglia

• Basal ganglia are sections of gray matter largely
  composed of cell bodies within each cerebral
  hemisphere. They lie between the diencephalon
  and the white matter of the hemisphere. They may
  perform functions important in the maintenance of
  focused attention. They are involved in
  cognitive and motor processes. They may
  coordinate the automated processing of sensory
  inputs nd motor outputs required for
  concentration and attention. They mey also
  synchronize sequential activities required to
  analyze and respond in an integrated way.

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Limbic System

• The limbic system is composed of
• amygdaloid body-acts as an interface between the
  limbic system, the cerebrum and various sensory
  systems. It plays a role in the regulation of the
  heart rate and in the fight or flight response.
• cingulate gyrus-sits superior to the corpus
  callosum
• parahippocampal gyrus- and dentate gyrus conceal
  the hippocampus, a folded area of the cortex that
  lies inferior to the floor of the lateral
  ventricle. It appears to be important in
  learning, especially in the storage and retrieval
  of new long term memories.

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Limbic System

• Hippocampus
• mamillary bodies process sensory information
  including olfactory sensations. They lso contain
  motor nuclei that control reflexes associated
  with eating, chewing, licking and swallowing.
• Fornix is a tract of white matter that connects
  the hippocampus with the hypothalamus.

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Limbic System Functions

• Establishing emotional states and related
  behavioral drives.
• Linking the conscious, intellectual functions of
  the cerebral cortex with the unconscious and
  autonomic functions of the brain stem.
• Facilitating memory storage and retrieval.

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Functional areas in the cerebral cortex

• This map is very important as it reveals which
  part of the brain performs a specific function.
• An injury to a specific part of the cerebrum will
  be the cause of a specific neural dysfunction.
• Neurological and psychological disorders have
  been studied due to its construction.

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Thalamus and Cortex

• It is known that the cortex performs specific
  functions. The thalamus is the final relay point
  for ascending sensory information and it
  coordinates the pyramidal and extrapyramidal
  systems. (fig. 4-12 and tab 14-4).

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Waves

• Alpha waves occur in healthy people who are awake
  and disappear when they fall asleep or
  concentrate. Beta waves are of a higher
  frequency and are typical when a person is
  concentrating, under stress or in psychological
  tension. Delta waves are large in amplitude, low
  frequency. They are normal in sleeping people of
  all ages and in infants brain. They are found in
  adult awake people when tumors, vascular blockage
  or inflammation has damaged portions of the
  brain. Theta waves appear sometimes in sleeping
  adults but mostly in children and intensely
  frustrated adults. In other circumstances they
  may indicate the presence of a brain disorder
  such as tumor.

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Neurological Disorders

• Ataxia caused by problems affecting cerebellum.
  Disturbance in balance that can leave the person
  unable to stand without assistance.
• Bells palsy inflammation of facial nerve.
  There is paralysis of facial muscles on affected
  side and loss of taste from anterior 2/3 of
  tongue.
• CVA or stroke blood supply to a potion of the
  brain is cut off.
• Concussion temporary loss of consciousness and
  variable period of amnesia resulting from a head
  injury.
• Dyslexia disorder affecting comprehension and
  use of words.