The Brain and Cranial Nerves

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The Brain and Cranial Nerves
Slides accompany Chapter 14 and 15 of your
text, Fundamentals of Anatomy Physiology by
Frederic H. Martini
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Midbrain (mesencephalon)

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

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Structures of the Mesencephalon

• Tectum
• 2 pairs of sensory nuclei (corpora quadrigemina)
• superior colliculus (visual)
• inferior colliculus (auditory)

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Relationship of mesencephalon to pons and
cerebellum
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Structures of the Mesencephalon

• Tegmentum
• red nucleus (many blood vessels)
• substantia nigra (pigmented gray matter)

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Structures of the Mesencephalon

• Cerebral peduncles
• nerve fiber bundles on ventrolateral surfaces
• contain
• descending fibers to cerebellum
• motor command (pyramidal) fibers

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Mesencephalon in Section

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

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The Mesencephalon
Figure 148a
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Midbrain(mesencephalon of the brainstem)
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Summary The Mesencephalon
Table 14-4
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Reticular Formation (Dont forget this diffuse
structure!)

• Motor function helps regulate muscle movements
• Sensory function Reticular activating system
  (RAS)
• Stimulation ? increased cortical activity
• Inactivation ? sleep

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Reticular Activating System

• RAS filters out repetitive, weak, irrelevant
  stimuli.
• LSD removes the filtering effect ?
  sensory-overload.
• Head Trauma (eg., lightweight boxers)
• ? concussion (mild, transient loss of
  consciousness)
• ? coma (loss of consciousness, hours to
  lifetime).

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The Cerebellum
Figure 147a
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Cerebellum

1. Adjusts postural muscles
2. Fine-tunes conscious and subconscious movements

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Cerebellar Peduncles

• Three paired fiber tracts
• Superior peduncles connect the cerebellum to the
  midbrain
• Middle peduncles connect the pons to the
  cerebellum
• Inferior peduncles connect the medulla to the
  cerebellum and carry ascending and descending
  cerebellar tracts from the spinal cord.
• All fibers in the cerebellum are ipsilateral

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Structures of the Cerebellum
Figure 147b
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Structures of the Cerebellum

• Cerebellar hemispheres
• separated at midline by vermis
• Vermis
• narrow band of cortex
• Flocculonodular lobe
• below fourth ventricle

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Structures of the Cerebellum

• Folia
• surface of cerebellum
• highly folded neural cortex
• Anterior and posterior lobes
• separated by primary fissure

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Arbor Vitae
Cerebellum
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Arbor Vitae

• Highly branched, internal white matter of
  cerebellum
• Cerebellar nuclei
• embedded in arbor vitae
• relay information to Purkinje cells

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Purkinje Cells

• Large, branched cells
• Found in cerebellar cortex
• Receive input from up to 200,000 synapses

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Disorders of the Cerebellum

• Ataxia
• damage from trauma or stroke
• intoxication (temporary disturbance)
• disturbs muscle coordination

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Summary The Cerebellum
Table 14-3
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What are the main components of the diencephalon
and their functions?
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The Diencephalon

• Integrates sensory information and motor commands

• Filters ascending sensory information for primary
  sensory cortex
• Relays information between basal nuclei and
  cerebral cortex

Figure 145a
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The Diencephalon

• Thalamus, epithalamus, and hypothalamus

Figure 149
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The Third Ventricle

• Separates left thalamus and right thalamus
• Intermediate mass
• projection of gray matter
• extends into ventricle from each side

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Thalamic Nuclei

• Lateral geniculate nucleus relays visual
  information
• Medial geniculate nucleus relays auditory
  information
• Lateral group involved in emotional states and
  integration of sensory information

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Summary Thalamic Nuclei
Table 14-5
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Hypothalamus

• Located below the thalamusit caps the brainstem
  and forms the inferolateral walls of the third
  ventricle
• Mammillary bodies
• Small, paired nuclei Relay station for
  olfactory pathways
• control reflex eating movements
• Infundibulum stalk of the hypothalamus
  connects to the pituitary gland

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The DiencephalonHypothalamus
Diencephalon
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The Hypothalamus

• Lies below thalamus

Figure 1410a
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8 Functions of the Hypothalamus

1. Provides subconscious control of skeletal muscle
2. Controls autonomic function
3. Coordinates activities of nervous and endocrine
   systems

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Functions of the Hypothalamus

• Secretes hormones
• antidiuretic hormone (ADH) by supraoptic nucleus
• oxytocin (OT) by paraventricular nucleus

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Functions of the Hypothalamus

• Produces emotions and behavioral drives
• the feeding center (hunger)
• the thirst center (thirst)

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Functions of the Hypothalamus

• Coordinates voluntary and autonomic functions
• Regulates body temperature
• preoptic area of hypothalamus

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Functions of the Hypothalamus

• Controls circadian rhythms (daynight cycles)
• suprachiasmatic nucleus

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Summary The Hypothalamus
Table 14-6
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Epithalamus
Pineal Gland

• Above the thalamus
• Pineal gland
• secretes melatonina hormone involved with sleep
  regulation, sleep-wake cycles, and mood

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Questions?
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Cerebrospinal Fluid (CSF)

• 80-150 ml (about ½ cup)
• 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 blood

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CSF Composition

• Differs from plasma
• no (or very few) cells
• protein is lower
• ionic concentrations are different
• pH ? affects brain blood flow
• respiratory rate.

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Blood Brain Barrier

• Ependymal cells around choroid plexus (which
  produce CSF) have tight junctions.
• Capillaries of brain tissue have tight junctions
  between endothelial cells.
• Astrocytes wrap the small vessels.
• Many antibiotics and chemotherapy agents can not
  pass from blood to brain.

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Blood Brain Barrier details to know

• Break-Down
• radiation, infection, neoplasm (cancer), manitol
  (intentional disruption)
• facilitated diffusion
• glucose, amino acids
• simple diffusion
• Small, neutrally charged molecules (i.e., lipid
  soluble
• molecules) pass easily.
• Water, CO2, O2,
• alcohol, caffeine, nicotine, heroin
• general anesthetics

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Brain Blood Flow

• Sources
• 2 internal carotids (R and L)
• 2 vertebral arteries and Circle of Willis
• (Study in more detail in lab.)
• 14 of cardiac output, and uses 20 of oxygen
  used by body

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Brain Blood Flow
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Brain Blood Flow

• Flow depends on CO2 more than O2 concentration
• High CO2 ? increased blood flow
• Low CO2 ? decreased blood flow
• Hyperventilation ? blow off CO2 ? low blood flow
  ? dizzy spell
• Other Factors extreme blood pressures
• intracranial pressure
• blood viscosity

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Brain Blood Flow Clinical Issues

• Low blood sugar (eg., too much insulin) starves
  neurons
• Mass (tumor, blood clot) ? decreased flow
• Heart attack ? decreased flow and confusion
• 10 seconds without blood ? pass out
• 4 minutes ? permanent brain damage
• lysosomes release enzymes

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Medical Example Subdural Hematoma
An subdural hematoma is a blood collection
Between the dura and arachnoid mater (external to
the brain) Since the skull cannot expand, the
brain shifts across the midline.
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Clinical CasesBleeding in the Brain

• Epidural Bleed
• Subdural Hematoma
• Intraparenchymal Bleed

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Clinical CasesBleeding in the Brain

• Epidural Bleed
• Subdural Hematoma
• Intraparenchymal Bleed

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Clinical CasesBleeding in the Brain

• Epidural Bleed
• Subdural Hematoma
• Intraparenchymal Bleed(s)

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Medical Examples

• Meningitis is inflammation of the meninges due to
  bacterial or viral infection.
• Encephalitis is inflammation of the brain

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Parkinsons Disease

• Unknown cause.
• Basal ganglia involved.
• Tremor, rigidity.
• New therapy.

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Basal Ganglia

• Connections to red nucleus, substantia nigra
  subthalamus
• Input output with cerebral cortex, thalamus
  hypothalamus
• Control large automatic movements of skeletal
  muscles

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The Electroencephalogram
Figure 1417
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Seizure

• Is a temporary cerebral disorder
• Changes the electroencephalogram
• Symptoms depend on regions affected

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4 Categories of Brain Waves

• Alpha waves
• found in healthy, awake adults at rest with eyes
  closed
• Beta waves
• higher frequency
• found in adults concentrating or mentally
  stressed

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4 Categories of Brain Waves

• Theta waves
• found in children
• found in intensely frustrated adults
• may indicate brain disorder in adults
• Delta waves
• during sleep
• found in awake adults with brain damage

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Synchronization

• A pacemaker mechanism
• synchronizes electrical activity between
  hemispheres
• Brain damage can cause desynchronization

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Herpes Virus

• CN V (trigeminal)
• Dermatomes

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Next time

• Special Senses and Cranial Nerves (not on
  pre-midterm)
• Review of somatic sensory and motor pathways
• Integration areas of the brain
• Limbic system
• Learning and Memory

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