Central Nervous System (CNS)

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• Central Nervous System (CNS)
• CNS consists of brain and spinal cord
• Surface anatomy includes cerebral hemispheres,
  cerebellum and brain stem

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• Embryonic Development
• Ectoderm (outermost of the three primary germ
  layers of an embryo) forms a neural plate which
  invaginates, forming a groove with neural folds
  at each side
• By week four of embryonic development, the neural
  groove fuses dorsally and forms the neural tube
• Brain grows faster than membranous skull
• Folds to occupy available space
• Forebrain moved toward brain stem (midbrain,
  pons, medulla oblongata)
• Cerebral hemispheres double back and envelop
  diencephalon and midbrain while creasing and
  folding to increase surface area

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• Brain regions
• Cerebral hemispheres
• Diencephalon
• Brain stem (midbrain, pons, and medulla)
• Cerebellum

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• Regions and Organization of the CNS
• Spinal cord
• Central cavity surrounded by gray matter
• Gray matter will become the processing part of
  brain
• External white matter composed of myelinated
  fiber tracts
• White matter is generally protective in nature
• Brain
• Cerebral hemispheres and cerebellum
• Outer gray matter called cortex
• in brain stem we see scattered gray matter nuclei
  amid white matter

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• Ventricles of the Brain
• Central cavity of neural tube enlarges and forms
  4 brain
• ventricles
• Ventricles filled with cerebrospinal fluid (CSF)
• Lined by ependymal cells
• Connected to one another and to central canal of
  spinal cord and to subarachnoid space
• Lateral ventricles--paired, C-shaped
• Separated anteriorly by septum pellucidum
• Third ventricle in diencephalon
• Fourth ventricle in hindbrain

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• Cerebral Hemispheres
• 3 basic regions cortex, white matter and basal
  nuclei
• Surface markings increase surface area and thus
  brain activity
• Ridges (gyri), shallow grooves (sulci), and deep
  grooves (fissures)
• Longitudinal fissure separates two hemispheres

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• Cerebral Hemispheres
• Deep sulci divide the hemispheres into 5 lobes
• Frontal
• Parietal
• Temporal
• Occipital
• Insula--function associated with visceral
  functions, integrates autonomic information

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Cerebral Hemispheres

• Cerebral cortex--40 mass of brain
• gray matter superficially, white matter
  internally
• Basal nuclei- islands of gray matter deep within
  white matter
• Site of conscious mind conscious behavior
  involves the entire cortex no functional area
  acts alone
• Enables awareness, sensory perception, voluntary
  movements, communication, memory storage,
  understanding
• Each hemisphere concerned with contralateral
  (opposite) side of body
• Lateralization or specialization of cortical
  function in each hemisphere

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• Functional areas
• Motor areascontrol voluntary movement
• Sensory areasconscious awareness of sensation
• Association areasintegrate information
• Cerebral Cortex--Motor Areas
• Frontal lobe--controls voluntary movement
• Primary (somatic) motor cortex
• Premotor cortex anterior
• Broca's area-speech musculature comprehension

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• Parietal lobes somatosensory lobe and some
  association areas
• Receives sensory information from skin and
  proprioceptors of skeletal muscle, joints, and
  tendons
• spatial discrimination identification of body
  region being stimulated
• Occipital lobe visual lobe, includes association
  areas

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• Temporal lobes auditory lobes and includes
  association areas
• Interprets information including pitch, loudness,
  and location
• Stores memories of sounds and permits perception
  of sound stimulus
• Wernickes area--can speak, but speech often
  incoherent and makes no sense

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• Networks of neurons that span wide areas of brain
  BUT work together
• Limbic system Includes parts of diencephalon and
  some brain stem structures
• emotional or affective brain gives emotional
  responses to odors
• Example skunks smell bad
• Reticular formation- governs brain arousal

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• Reticular Formation governs brain arousal
• includes RAS
• Reticular activating system (RAS)
• Sends impulses to cerebral cortex to keep
  conscious and alert
• Filters out repetitive, familiar, or weak stimuli
• damage in this brain area causes inability to
  distinguish between valuable and not valuable
  information
• Inhibited by hypothalamic sleep centers, alcohol,
  drugs
• Severe injury results in permanent
  unconsciousness (coma)

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• Diencephalon
• Consists of 3 structures
• Thalamus
• Hypothalamus
• Epithalamus (Pineal gland)
• Structures enclose third ventricle

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• Thalamus-- Function
• Gateway to cerebral cortex-is the relay station
  for brain
• Sorts, edits, and relays ascending input
• Impulses from hypothalamus for regulation of
  emotion and visceral function
• Impulses from cerebellum and basal nuclei to help
  direct motor cortex
• Impulses for memory or sensory integration
• Impulses from visual and auditory centers
• Essential role in mediating sensation, motor
  activities, cortical arousal, learning, and
  memory
• When afferent stimuli reach thalamus, we have a
  recognition of the stimulus as pleasant or
  unpleasant

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• Hypothalamus
• Located below the thalamus
• Primarily involved in hormone production
• Infundibulumstalk that connects it to pituitary
  gland
• Hypothalamic Function
• Controls autonomic nervous system
• Controls endocrine system
• Physical responses to emotions
• Perception of pleasure, fear, and rage, and in
  biological rhythms and drives
• Regulates body temperature, hunger, thirst
• Regulates sleep-wake cycles
• Biological clock

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• Epithalamus or Pineal gland (body)
• secretes melatoninhelps regulate sleep-wake
  cycle
• Helps regulate body cycles by monitoring length
  of day via input from optic nerve
• Choroid Plexus
• Hang from roof of each ventricle produce CSF at
  constant rate keep in motion

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• Brain Stem
• Consists of 3 regions
• Midbrain
• Pons
• Medulla oblongata
• Controls automatic behaviors necessary for
  survival
• Provides pathway for nerve tracts connecting
  higher and lower brain centers
• Pons
• Bulging brainstem area between midbrain and
  medulla oblongata
• helps maintain normal rhythm of breathing

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• Medulla Oblongata
• Most inferior portion of the brain stem joins
  spinal cord at foramen magnum
• Cardiovascular center
• Cardiac center adjusts force and rate of heart
  contraction
• Vasomotor center adjusts blood vessel diameter
  for blood pressure regulation
• Respiratory centers
• Generate respiratory rhythm
• Control rate and depth of breathing (with pontine
  centers)
• Vestibular nuclei (pons and medulla)mediate
  responses that maintain equilibrium

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• Medulla Oblongata
• Additional centers regulate
• Vomiting Hiccupping Sneezing
• Swallowing Coughing
• Cerebellum
• Subconscious input from cortex, brain stem and
  sensory receptors to allow smooth, coordinated
  movements of skeletal muscles
• Arbor vitaetreelike pattern of cerebellar white
  matter
• May compare actual with predicted movement
  sequences and adjust movement accordingly

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• Meninges--3 protective connective tissue
  membranes enclose brain and spinal cord
• Dura mater is outermost and strongest layer
• Arachnoid mater is middle layer has spidery
  extensions which secure it to innermost layer.
• Pia mater is innermost layer and clings tightly
  to CNS.

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• Cerebrospinal Fluid (CSF)
• Composition
• Watery solution formed from blood plasma
• Contains less protein and different ion
  concentrations than plasma
• Constant volume
• Functions
• Gives buoyancy to CNS structures
• Reduces weight by 97
• Protects CNS from blows and other trauma
• Nourishes brain and carries chemical signals

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• Hydrocephalus
• Obstruction blocks CSF circulation or drainage
• Fontanelles at skull in newborn allow enlargement
  of head
• Brain damage in adult due to rigid adult skull
• Treated by draining with ventricular shunt to
  abdominal cavity

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• Blood Brain Barrier
• Helps maintain stable environment for brain
• Separates neurons from most bloodborne substances
• Selective barrier
• Allows nutrients to move by facilitated diffusion
• Metabolic wastes, proteins, toxins, most drugs,
  small nonessential amino acids, K denied
• Allows any fat-soluble substances to pass,
  including alcohol, nicotine, and anesthetics
• Absent in some areas, e.g., vomiting center and
  hypothalamus, where necessary to monitor chemical
  composition of blood

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• LABWORK (includes next slide)
• 1. Identify and describe the meninges and
  structures of the brain stem.
• 2. Identify and describe the cerebellum and
  structures of the diencephalon.
• 3. Identify and describe the structures of the
  cerebrum.
• State the function of the cranial nerves.
• 5. Locate the following on diagrams, human brain
  models, the sheep brain
• Ventral view olfactory bulb, pituitary gland,
  mammillary body, trigeminal nerve, pons,
  cerebellum, medulla oblongata, oculomotor nerve,
  optic tract, optic chiasma, optic nerve, cerebrum

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• Midsagittal view corpus callosum, thalamus,
  hypothalamus, optic chiasma, pituitary gland,
  pons, cerebellum, arbor vitae, corpora
  quadrigemina (midbrain), pineal body, cerebral
  hemisphere.
• On the human brain models, Locate the lobes of
  the cerebrum, gyri, sulci, and fissures.