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					                 Chapter 14
        The Brain and Cranial Nerves




• Largest organ in the body at almost 3 lb.
• Brain functions in sensations, memory, emotions, decision
  making, behavior                                  14-1
    Principal Parts of the Brain
• Cerebrum
• Diencephalon
  – thalamus &
    hypothalamus
• Cerebellum
• Brainstem
  – medulla, pons &
    midbrain


                                   14-2
Protective Coverings of the Brain
                 • Bone, meninges & fluid
                 • Meninges same as around
                   the spinal cord
                   – dura mater
                   – arachnoid mater
                   – pia mater
                 • Dura mater extensions
                   – falx cerebri
                   – tentorium cerebelli
                   – falx cerebelli

                                       14-3
           Blood Supply to Brain
• Arterial blood supply is branches from circle of Willis
  on base of brain
• Vessels on surface of brain----penetrate tissue
• Uses 20% of our bodies oxygen & glucose needs
   – blood flow to an area increases with activity in that area
   – deprivation of O2 for 4 min does permanent injury
      • at that time, lysosome release enzymes
• Blood-brain barrier (BBB)
   – protects cells from some toxins and pathogens
      • proteins & antibiotics can not pass but alcohol & anesthetics do
   – tight junctions seal together epithelial cells, continuous
     basement membrane, astrocyte processes covering capillaries
                                                                       14-4
     Cerebrospinal Fluid (CSF)
• 80-150 ml (3-5oz)
• Clear liquid containing glucose, proteins, & ions
• Functions
  – mechanical protection
     • floats brain & softens impact with bony walls
  – chemical protection
     • optimal ionic concentrations for action potentials
  – circulation
     • nutrients and waste products to and from bloodstream
                                                            14-5
                     Origin of CSF




• Choroid plexus = capillaries covered by ependymal cells
   – 2 lateral ventricles, one within each cerebral hemisphere
   – roof of 3rd ventricle
   – fourth ventricle
                                                                 14-6
    Drainage of CSF from Ventricles




• One median aperture & two lateral apertures allow CSF to
  exit from the interior of the brain
                                                     14-7
Flow of Cerebrospinal Fluid




                              14-8
               Reabsorption of CSF




• Reabsorbed through arachnoid villi
   – grapelike clusters of arachnoid penetrate dural venous sinus
• 20 ml/hour reabsorption rate = same as production rate
                                                              14-9
       Medulla Oblongata
•   Continuation of spinal cord
•   Ascending sensory tracts
•   Descending motor tracts
•   Nuclei of 5 cranial nerves
•   Cardiovascular center
    – force & rate of heart beat
    – diameter of blood vessels
• Respiratory center
    – medullary rhythmicity area sets basic rhythm of breathing
• Information in & out of cerebellum
• Reflex centers for coughing, sneezing, swallowing etc
                                                             14-10
Ventral Surface of Medulla Oblongata

                 • Ventral surface bulge
                    – pyramids
                    – large motor tract
                    – decussation of most fibers
                       • left cortex controls right muscles
                 • Olive = olivary nucleus
                    – neurons send input to
                      cerebellum
                    – proprioceptive signals
                    – gives precision to movements
                                                14-11
Dorsal Surface of Medulla Oblongata




• Nucleus gracilis & nucleus cuneatus = sensory neurons
   – relay information to thalamus on opposite side of brain
• 5 cranial nerves arise from medulla -- VIII thru XII
                                                               14-12
XII = Hypoglossal Nerve
              • Controls muscles of
                tongue during speech
                and swallowing
              • Injury deviates tongue
                to injured side when
                protruded
              • Mixed, primarily
                motor

                                14-13
XI = Spinal Accessory Nerve
              • Cranial portion
                 – arises from medulla
                 – skeletal mm of throat & soft
                   palate
              • Spinal portion
                 – arises from cervical spinal
                   cord
                 – sternocleidomastoid and
                   trapezius mm.


                                       14-14
X = Vagus Nerve
        • Receives sensations
          from viscera
        • Controls cardiac muscle
          and smooth muscle of
          the viscera
        • Controls secretion of
          digestive fluids



                            14-15
IX = Glossopharyngeal Nerve
                • Stylopharyngeus m.
                  (lifts throat during
                  swallowing)
                • Secretions of parotid
                  gland
                • Somatic sensations &
                  taste on posterior 1/3
                  of tongue


                                  14-16
VIII = Vestibulocochlear Nerve
               • Cochlear branch ends in
                 medulla
                  – receptors in cochlea
                  – hearing
                  – if damaged deafness or
                    tinnitus (ringing) is produced
               • Vestibular branch ends in
                 pons
                  – receptors in vestibular
                    apparatus
                  – sense of balance
                  – vertigo (feeling of rotation)
                  – ataxia (lack of coordination)
                                        14-17
Pons

       • One inch long
       • White fiber tracts
         ascend and descend
       • Pneumotaxic &
         apneustic areas help
         control breathing
       • Middle cerebellar
         peduncles carry
         sensory info to the
         cerebellum
       • Cranial nerves V thru
         VII             14-18
VII = Facial Nerve

           • Motor portion
             – facial muscles
             – salivary & nasal and
               oral mucous glands &
               tears
           • Sensory portion
             – taste buds on anterior
               2/3’s of tongue



                                 14-19
VI = Abducens Nerve

           • Lateral rectus eye
             muscle




                                  14-20
V = Trigeminal Nerve
           • Motor portion
             – muscles of mastication
           • Sensory portion
             – touch, pain, &
               temperature receptors of
               the face
                • ophthalmic branch
                • maxillary branch
                • mandibular branch



                                  14-21
Midbrain

           • One inch in length
           • Extends from pons to
             diencephalon
           • Cerebral aqueduct
             connects 3rd
             ventricle above to
             4th ventricle below



                         14-22
                 Midbrain in Section




• Cerebral peduncles---clusters of motor & sensory fibers
• Substantia nigra---helps controls subconscious muscle activity
• Red nucleus-- rich blood supply & iron-containing pigment
   – cortex & cerebellum coordinate muscular movements by sending
     information here from the cortex and cerebellum
                                                                    14-23
       Dorsal Surface of Midbrain




• Corpora quadrigemina = superior & inferior colliculi
   – coordinate eye movements with visual stimuli
   – coordinate head movements with auditory stimuli
                                                       14-24
IV = Trochlear Nerve
             • Superior oblique eye
               muscle




                             14-25
III = Oculomotor Nerve
             • Levator palpebrae raises
               eyelid
             • 4 extrinsic eye muscles
             • 2 intrinsic eye muscles
                – accomodation for near
                  vision (changing shape
                  of lens during reading)
                – constriction of pupil



                                 14-26
         Reticular Formation
• Scattered nuclei in medulla, pons & midbrain
• Reticular activating system
  – alerts cerebral cortex to sensory signals (sound of
    alarm, flash light, smoke or intruder) to awaken
    from sleep
  – maintains consciousness & helps keep you awake
    with stimuli from ears, eyes, skin and muscles
• Motor function is involvement with
  maintaining muscle tone
                                                  14-27
                      Cerebellum




• 2 cerebellar hemispheres and vermis (central area)
• Function
   – correct voluntary muscle contraction and posture based on
     sensory data from body about actual movements
   – sense of equilibrium                                   14-28
                    Cerebellum




• Transverse fissure between cerebellum & cerebrum
• Cerebellar cortex (folia) & central nuclei are grey matter
• Arbor vitae = tree of life = white matter
                                                      14-29
                 Cerebellar Peduncles




• Superior, middle & inferior peduncles attach to brainstem
   – inferior carries sensory information from spinal cord
   – middle carries motor fibers from cerebral cortex & basal ganglia
   – superior carries motor fibers that extend to motor control areas
                                                               14-30
Diencephalon Surrounds 3rd Ventricle




  • Surrounds 3rd ventricle
  • Superior part of walls is thalamus
  • Inferior part of walls & floor is hypothalamus
                                                     14-31
                     Thalamus




• 1 inch long mass of gray mater in each half of brain
  (connected across the 3rd ventricle by intermediate mass)
• Relay station for sensory information on way to cortex
• Crude perception of some sensations
                                                    14-32
                Thalamic Nuclei




• Nuclei have different roles
   – relay auditory and visual impulses, taste and somatic sensations
   – receive impulses from cerebellum or basal ganglia
   – anterior nucleus concerned with emotions, memory and acquisition
     of knowledge (cognition)
                                                                 14-33
                      Hypothalamus




• Dozen or so nuclei in 4 major regions
   – mammillary bodies are relay station for olfactory reflexes;
     infundibulum suspends the pituitary gland
• Major regulator of homeostasis
   – receives somatic and visceral input, taste, smell & hearing
     information; monitors osmotic pressure, temperature of blood
                                                              14-34
   Functions of Hypothalamus
• Controls and integrates activities of the ANS which
  regulates smooth, cardiac muscle and glands
• Synthesizes regulatory hormones that control the
  anterior pituitary
• Contains cell bodies of axons that end in posterior
  pituitary where they secrete hormones
• Regulates rage, aggression, pain, pleasure & arousal
• Feeding, thirst & satiety centers
• Controls body temperature
• Regulates daily patterns of sleep
                                                14-35
Epithalamus
       • Pineal gland
          – endocrine gland the
            size of small pea
          – secretes melatonin
            during darkness
          – promotes sleepiness &
            sets biological clock
       • Habenular nuclei
          – emotional responses to
            odors
                           14-36
Subthalamus & CVO
• Subthalamus
  – small area just inferior to thalamus
  – work with basal ganglia, cerebrum & cerebellum to
    control body movements
• Circumventricular organs
  – in walls of 3rd & 4th ventricles
  – monitor changes in blood chemistry because lack
    blood brain barrier (parts of hypothalamus, pineal &
    pituitary gland)
  – sites of entry of HIV virus into brain (dementia)
                                                  14-37
          Cerebrum
    (Cerebral Hemispheres)
• Cerebral cortex is gray matter
  overlying white matter
   – 2-4 mm thick containing billions
      of cells
   – forms folds(gyri) and grooves
     (sulci or fissures)
• Longitudinal fissure separates left
  & right cerebral hemispheres
• Corpus callosum is band of white matter connecting
  left and right cerebral hemispheres
• Each hemisphere is subdivided into 4 lobes        14-38
Lobes and Fissures   • Longitudinal fissure
                     • Frontal lobe
                     • Central sulcus
                         – precentral & postcentral gyrus
                     •   Parietal lobe
                     •   Occipital lobe
                     •   Lateral sulcus
                     •   Temporal lobe
                     •   Insula




                                              14-39
Insula within Lateral Fissure




                                14-40
           Cerebral White Matter




• Association fibers between gyri in same hemisphere
• Commissural fibers between hemispheres-corpus collosum
• Projection fibers form descending & ascending tracts
                                                14-41
                   Basal Ganglia




• Connections to red nucleus, substantia nigra & subthalamus
• Input & output with cerebral cortex, thalamus &
  hypothalamus
• Control large automatic movements of skeletal muscles
                                                    14-42
              Limbic System




• Parahippocampal & cingulate gyri & hippocampus
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
                                                14-43
Sensory Areas of Cerebral Cortex




 Receive sensory information from the thalamus
   Primary somatosensory area = postcentral gyrus = 1,2,3
   Primary visual area = 17
   Primary auditory area = 41 & 42
   Primary gustatory area = 43
                                                      14-44
   Motor Areas of Cerebral Cortex




• Voluntary motor initiation
   – Primary motor area = 4 = precentral gyrus
      • controls voluntary contractions of skeletal muscles on other side
   – Motor speech area = 44 = Broca’s area
      • production of speech -- control of tongue & airway            14-45
    Association Areas of Cerebral Cortex




•   Somatosensory area = 5 & 7 (integrate & interpret)
•   Visual association area = 18 & 19 (recognize & evaluate)
•   Auditory association area(Wernicke’s) = 22(words become speech)
•   Gnostic area = 5,7,39 & 40 (integrate all senses & respond)
•   Premotor area = 6 (learned skilled movements such as typing)
•   Frontal eye field =8 (scanning eye movements such as phone book)
                                                              14-46
                          Aphasia
• Language areas are located in the left cerebral
  hemisphere of most people
• Inability to use or comprehend words = aphasia
  – nonfluent aphasia = inability to properly form words
     • know what want to say but can not speak
     • damage to Broca’s speech area
  – fluent aphasia = faulty understanding of spoken or
    written words
     • faulty understanding of spoken or written words
        – word deafness = an inability to understand spoken words
        – word blindness = an inability to understand written words
     • damage to common integrative area or auditory association
       area
                                                                      14-47
Hemispheric Lateralization
                • Functional
                  specialization of each
                  hemisphere more
                  pronounced in men
                • Females have larger
                  connections between 2
                  sides
                • Damage to left side
                  produces aphasia
                • Damage to same area
                  on right side produces
                  speech with little
                  emotional inflection
                                  14-48
Electroencephalogram (EEG)
              • Brain waves are millions
                of nerve action potentials
                in cerebral cortex
                  – diagnosis of brain
                    disorders (epilepsy)
                  – brain death (absence of
                    activity in 2 EEGs 24
                    hours apart)
              •   Alpha -- awake & resting
              •   Beta -- mental activity
              •   Theta -- emotional stress
              •   Delta -- deep sleep
                                      14-49
II -- Optic Nerve

            • Connects to retina
              supplying vision




                             14-50
I -- Olfactory Nerve

              • Extends from
                olfactory mucosa of
                nasal cavity to
                olfactory bulb
              • Sense of smell




                             14-51

				
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posted:11/17/2010
language:English
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