Chapter 14 The Brain and Cranial Nerves

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Chapter 14The Brain and Cranial Nerves
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Objectives

• Understand how the brain is protected and
  nourished.
• Develop an overall view on how the brain is
  organized.
• Identify the functions of particular brain areas.
• Identify the cranial nerves and what they
  innervate.
• Develop an understanding of brain development.

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Major parts of the brain

• Brain stem
• Medulla oblongata Pons
• Midbrain
• Cerebellum
• Diencephalon
• Thalmus
• Hypothalamus
• Pineal gland
• Cerebrum

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Cranial meninges
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Cranial meninges

• Falx cerebriseparates hemispheres of cerebrum
• Falx cerebelliseparates hemispheres of
  cerebellum
• Tenorium cerebelliseparates cerebrum from
  cerebellum

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Blood flow in the brain

• Carotid arteries
• Jugular veins
• Dural venous sinuses located between two dural
  layers
• Vessels sheathed in pia mater as they penetrate
  the brain

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Energy needs for the Brain

• Brain represents 2 of body weight but consumes
  20 of the oxygen and glucose.
• The brain uses only aerobic respiration and uses
  glucose. Also likes to use ketones.
• No glucose is stored so it must be replenished
  from blood flow
• Increased activity in a brain region increases
  the use of glucose.

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Blood Brain Barrier

• Tight junctions with thick basement membrane seal
  endothelial cells.
• Astrocytes interact with capillaries and secrete
  chemicals that affect permeability of tight
  junctions.
• Lipid soluble substances more permeable than
  water soluble.

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Cerebral spinal fluid (CSF)

• Found in four ventricles

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CSF

• Compositionglucose, proteins, lactic acid,
  cations, anions, and white blood cells
• Total volume is 80-150mL in adults
• CSF continuously circulates.
• Contributes to brain homeostasis
• Mechanical protection
• Chemical protection
• Circulates and interacts with blood tissue

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Formation of CSF

• Produced in choroid plexus
• Network of capillaries in the walls of the
  ventricles.
• A bilayer of cuboidal epithelial cells take blood
  plasma, filter it and secrete it into ventricles.
• BloodCSF barrier also functions to chemically
  protect brain.

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Circulation of CSF
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Circulation of CSF
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Circulation of CSF

• CSF production is 20mL/hr.
• It is reabsorbed at the same rate it is produced.
• Thus CSF pressure remains constant.
• Hydrocephalus

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The brain stem

• Medulla oblongata
• Relays sensory and motor function
• Regulates respiration and cardiovascular function
• Nuclei for cranial nerves VIII-XII
• Raphesite of serotonergic neurons

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The brain stem

• Pons
• Relays sensory and motor function
• Nuclei for cranial nerves V-VIII
• Midbrain
• Reflex centers for visual and auditory activity
• Substantia nigrasite of dopaminergic neurons
• Reticular formation
• Helps maintain consciousness, muscle tone

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Cerebellum

• Contains ½ neurons found in brain
• Evaluates motor movements initiated by cerebrum.
• Handles coordination of skilled movement
• Regulates posture and balance
• Cognitive and language processing

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Diencephalon

• Thalamuspaired oval masses of gray matter with
  interspersed tracts of white matter.
• Major relay station for sensory input
• Transmits information from cerebellum and basal
  ganglia to primary motor cortex
• Plays a role in autonomic function and
  consciousness

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Diencephalon

• Hypothalamusmajor regulator of homeostasis

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Diencephalon hypothalamus

• Controls and regulates activities of ANS
• Production of hormones
• Regulation of emotional and behavioral patterns
• Regulation of eating and drinking
• Control of body temperature
• Regulation of circadian rhythms and states of
  consciousness.

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Diencephalon epithalamus

• Pineal glandsecretes melatonin during darkness
  and is associated with sleep. Participates in
  setting the body clock.
• Habenulais involved with olfaction, particularly
  odors that have emotional overtones.
• Circumventricular organs lie in the walls of the
  third and fourth ventricle.
• Coordinate blood pressure, fluid balance, hunger,
  and thirst.
• Site of entry into the brain for HIV

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Cerebrum

• Made up of two hemispheres separated by the falx
  cerebri and connected by the corpus callosum.
• Outer rim of gray matter, internal region of
  white matter, and gray nuclei deep within.
• The rapid development of gray matter during
  development leads to formation of folds called
  gyri.
• Grooves between folds are fissures
• Shallower grooves are sulci

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Cerebrum
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Lobes of cerebrum
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Cerebral white matter

• Association tracts conduct APs between gyri in
  same hemisphere.
• Commissural tracts conduct APs from gyri in one
  hemisphere to corresponding gyri in other
  hemisphere.
• Projection tracts conduct APs to lower brain
  regions such as thalamus, spinal cord or
  brainstem.

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Cerebral white matter
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Basal ganglia

• Made up of three nuclei that together are also
  known as corpus striatum
• Globus pallidus
• Putamen
• Caudate nucleus
• Is functionally linked to substantia nigra and
  subthalamic nuclei.
• Regulates initiation and termination of motor
  movements and cognitive processes.

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Basal ganglia
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Basal ganglia
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Limbic system

• Plays a role in emotionpain, pleasure, fear,
  docility, affection and anger.
• Functions in memory formation.
• Components of limbic system
• Hippocampus
• Dentate gyrus
• Amygdala
• Septal nuclei
• Olfactory bulbs
• Mammillary bodies
• Fornix
• Anterior and medial nucleus of the thalalmus

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Limbic system
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Brain injuries

• Head trauma that leads to displacement or
  distortion of neural tissue.
• Gives rise to release of free radicals that can
  disrupt DNA and change membrane permeability.
• Hypoxia leads to brain injury
• Concussion
• Contusion
• Laceration

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Cerebral cortex organization

• Sensory areas
• Perception
• Conscious awareness
• Motor areas
• Initiate movement
• Integrative areas
• Memory
• Emotions
• Will
• Judgment
• Personality
• Intelligence

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Sensory areas

• Primary sensory areas get input from peripheral
  sensory receptors.
• Secondary sensory areas receive input from
  primary sensory areas and other areas of brain.
• Secondary sensory areas and sensory integrative
  areas integrate sensory information and lead to
  recognition and awareness.

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Primary somatosensory area

• Receives sensory information on pain, touch,
  proprioception, itching, and temperature.
• A map of the body is represented in this area
  (the homunculus)

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Primary sensory areas

• Primary visual, auditory, gustatory, and
  olfactory areas

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Motor areas

• Primary motor area also has a map of the entire
  musculo-skeletal system.

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Brocas speech area

• Found in the frontal lobe and in most people in
  the left hemisphere.
• Forms neural circuits with regions of premotor
  and primary motor area involved with speech
  production.
• A stroke in this area can cause aphasia.

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Association areas

• Association areas are connected to one another
  through association tracts.
• Somatosensory
• Frontal (prefrontal cortex)
• Visual
• Auditory
• Wernickes area
• Common integrative
• Premotor
• Frontal eyefield

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Association areas
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Hemispheric lateralization

• The functional asymmetry of the brain is
  lateralization.
• Left side of the brain
• controls movement on the right side of the body.
• Reasoning, numerical and scientific skills,
  spoken, written and signed language resides in
  the left hemisphere in most people.

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Hemispheric lateralization

• Right side of the brain
• Controls movement on the left side of the body.
• Musical and artistic awareness
• Spatial and pattern perception
• Recognition of faces and emotional content of
  language
• Discriminate different smells
• Generates mental images for comparisons

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Hemispheric lateralization response to olfactory
stimuli
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Brain waves

• The population of nervous impulses in the brain
  produce brain waves.
• Alpha waves
• Beta waves
• Theta waves
• Delta waves

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Cranial nerves

• Cranial nerves pass through the foramina in the
  cranium and are part of the PNS.
• Named numerically from anterior to posterior and
  according to their function or distribution.

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Cranial nerves Olfactory (I) nerve

• Entirely sensory
• Made up of bipolar neurons that project through
  the ethmoid bone to the olfactory bulb.

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Cranial nerves Optic (II) nerve

• Entirely sensory
• Made up of the axons of ganglion cells in the
  retina that make up the optic chiasm.

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Cranial nerves Oculomotor (III) nerve

• Mixed but primarily motor nerve
• Also provides parasympathetic innervation to
  eyeball muscles
• Sensory information from proprioceptors in eyeball

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Cranial nerves Trochlear (IV) nerve

• Mixed but primarily motor nerve innervating
  superior oblique muscle
• Sensory information from proprioceptors in
  superior oblique muscle

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Cranial nerves Trigeminal (V) nerve

• Mixed with 3 branches
• Ophthalmic
• Maxillary
• Mandibular
• Sensory nerves carry touch, pain, and thermal
  info
• Mandibular branch carries motor neurons

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Cranial nerves Abducens (VI) nerve

• Mixed but primarily motor nerve innervating
  abductor muscles of the eyeball
• Sensory information from proprioceptors in
  lateral rectus muscle

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Cranial nerves Facial (VII) nerve

• Mixed with motor nerves controlling facial
  expression
• Parasympathetic neurons extend to lacrimal,
  nasal, palatine, sublingual and submandibular
  glands
• Sensory information from tastebuds and
  proprioceptors in face and scalp

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Cranial nerves Vestibulocochlear (VIII) nerve

• Mixed but mostly sensory
• Vestibular branchsignals for equilibrium
• Cochlear branchimpulses for hearing
• Sensory information from inner ear and cerebellum
• Motor axons go to hair cells of the semicircular
  canals

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Cranial nerves Glossopharyngeal (IX) nerve

• Sensory nerves from taste buds and posterior 1/3
  of tongue.
• Proprioceptors in swallowing muscles.
• Baroreceptors (stretch receptors) in the carotid
  sinus and chemoreceptors in the carotid body

• Motor neurons innervate muscles of the pharynx
  and larynx.
• Autonomic neurons innervate parotid gland

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Cranial nerves Vagus (X) nerve

• Sensory axons from skin of external ear,
  epiglottis, and pharynx
• Proprioceptors in neck and throat.
• Baroreceptors and chemoreceptors in the aorta
• Visceral sensory receptors in most organs

• Parasympathetic axons supply glands of GI tract
  and smooth muscle of respiratory tract.

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Cranial nerves Accessory (XI) nerve

• Originates from both the brain stem and spinal
  cord.
• Cranial root is motor
• Spinal root is mixedinnervates the
  sternocleidomastoid and trapezius muscles
• Sensory axons arise from proprioceptors in
  muscles of innervated by its motor neurons

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Cranial nerves Hypoglossal (XII) nerve

• Sensory axons is from proprioceptors in the
  tongue.
• Motor input to muscles of the tongue during
  speech and swallowing.

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Development of the nervous system

• Develop from ectoderm arranged in a tubular
  structure called the neural tube.

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Development of the nervous system

• Development starts at 3 weeks.
• Ectoderm thickens into the neural plate
• Raised edges become are neural folds.
• Neural folds increase in height and form the
  neural tube.

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Development of the nervous system

• Three layers of cells differentiate from the wall
  of the neural tube
• Marginal layer becomes white matter
• Mantle layer develops into gray matter
• Ependymal layer develops into lining of the
  central canal and ventricles
• Neural crest differentiates into PNS (spinal and
  cranial nerves, ganglia of spinal and cranial
  nerves, ganglia of ANS), adrenal medulla, and
  meninges.

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Development of the nervous system
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Development of nervous system
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Development of nervous system
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Development of nervous system
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Development of nervous system