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Development& Functions Of Various Parts Of Cns
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Development& Functions Of Various Parts Of Cns

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  • 1. CNS
    • Consists of:
      • Brain.
      • Spinal cord.
    • Receives input from sensory neurons.
    • Directs activity of motor neurons.
    • Association neurons maintain homeostasis in the internal environment.
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  • 2. Embryonic Development
    • Groove appears in ectoderm to fuse to form neural tube by 20 th day after conception. Neural tube eventually forms the CNS.
    • During 5 th week, modified:
      • Forebrain: telencephalon and diencephalon.
      • Midbrain: unchanged.
      • Hindbrain: metencephalon and myelencephalon.
    • Part of ectoderm where fusion occurs becomes neural crest .
      • Neural crest forms ganglia of PNS.
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  • 3. Embryonic Development (continued) www.freelivedoctor.com
  • 4. Embryonic Development (continued)
    • Telencephalon grows disproportionately forming 2 the hemispheres of the cerebrum.
    • Ventricles and central canal become filled with cerebral spinal fluid (CSF).
    • CNS composed of gray and white matter.
      • Gray matter consists of neuron cell bodies and dendrites.
      • White matter (myelin) consists of axon tracts.
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  • 5. Cerebrum
    • Only structure of the telencephalon.
    • Largest portion of brain (80% mass).
    • Responsible for higher mental functions.
    • Corpus callosum:
      • Major tract of axons that functionally interconnects right and left cerebral hemispheres.
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  • 6. Cerebrum (continued) www.freelivedoctor.com
  • 7. Cerebral Cortex
    • Characterized by numerous convolutions.
      • Elevated folds: gyri.
      • Depressed groves: sulci .
    • Frontal lobe:
      • Anterior portion of each cerebral hemisphere.
      • Precentral gyri:
        • Contains upper motor neurons.
        • Involved in motor control.
    • Body regions with the greatest number of motor innervation are represented by largest areas of motor cortex.
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  • 8. Cerebral Cortex (continued) www.freelivedoctor.com
  • 9. Cerebral Cortex (continued)
    • Parietal lobe:
      • Primary area responsible for perception of somatesthetic sensation.
      • Body regions with highest densities of receptors are represented by largest areas of sensory cortex.
    • Temporal lobe:
      • Contain auditory centers that receive sensory fibers from cochlea.
      • Interpretation and association of auditory and visual information.
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  • 10. Cerebral Cortex (continued)
    • Occipital Lobe:
      • Primary area responsible for vision and coordination of eye movements.
    • Insula:
      • Implicated in memory encoding.
      • Integration of sensory information with visceral responses.
      • Coordinated cardiovascular response to stress.
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  • 11. Visualizing the Brain
    • X-ray computed tomography (CT):
      • Complex computer manipulations of data obtained from x-ray absorption by tissues of different densities.
        • Soft tissue.
    • Positron-emission tomography (PET):
      • Radioisotopes that emit positrons are injected into blood stream.
        • Collision of positron and electron result in emission of gamma rays.
          • Pinpoint brain cells that are most active.
            • Brain metabolism, drug distribution.
    • Magnetic resonance imaging (MRI):
      • Protons (H + ) respond to magnetic field, which align the protons.
        • Emit a radio-wave signal when stimulated.
          • Brain function.
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  • 12. Electroencephalogram (EEG)
    • Measures synaptic potentials produced at cell bodies and dendrites.
      • Create electrical currents.
    • Used clinically do diagnose epilepsy and brain death.
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  • 13. EEG Patterns
    • Alpha:
      • Recorded from parietal and occipital regions.
        • Person is awake, relaxed, with eyes closed.
          • 10-12 cycles/sec.
    • Beta:
      • Strongest from frontal lobes near precentral gyrus.
        • Produced by visual stimuli and mental activity.
        • Evoked activity.
          • 13-25 cycles/sec.
    • Theta:
      • Emitted from temporal and occipital lobes.
        • Common in newborn.
        • Adult indicates severe emotional stress.
          • 5-8 cycles/sec.
    • Delta:
      • Emitted in a general pattern.
        • Common during sleep and awake infant.
        • In awake adult indicate brain damage.
          • 1-5 cycles/sec.
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  • 14. EEG Sleep Patterns
    • 2 types of EEG patterns during sleep:
      • REM (rapid eye movement):
        • Dreams occur.
        • Low-amplitude, high-frequency oscillations.
        • Similar to wakefulness (beta waves).
      • Non-Rem (resting):
        • High-amplitude, low-frequency waves (delta waves).
        • Superimposed on these are sleep spindles:
          • Waxing and waning bursts of 7-14 cycles/sec.
          • Last for 1-3 sec.
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  • 15. Basal Nuclei (basal ganglia)
    • Masses of gray matter composed of neuronal cell bodies located deep within white matter.
    • Contain:
      • Corpus striatum:
        • Caudate nucleus.
        • Lentiform nucleus:
          • Putman and globus pallidus.
    • Functions in the control of voluntary movements.
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  • 16. Cerebral Lateralization
    • Cerebral dominance:
      • Specialization of one hemisphere.
    • Left hemisphere:
      • More adept in language and analytical abilities.
      • Damage:
        • Severe speech problems.
    • Right hemisphere:
      • Most adept at visuospatial tasks.
      • Damage:
        • Difficulty finding way around house.
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  • 17. Language
    • Broca’s area:
      • Involves articulation of speech.
      • In damage, comprehension of speech in unimpaired.
    • Wernicke’s area:
      • Involves language comprehension.
      • In damage, language comprehension is destroyed, but speech is rapid without any meaning.
    • Angular gyrus:
      • Center of integration of auditory, visual, and somatesthetic information.
      • Damage produces aphasias.
    • Arcuate fasciculus:
      • To speak intelligibly, words originating in Wernicke’s area must be sent to Broca’s area.
        • Broca’s area sends fibers to the motor cortex which directly controls the musculature of speech.
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  • 18. Emotion and Motivation
    • Important in the neural basis of emotional states are hypothalamus and limbic system.
    • Limbic system:
      • Group of forebrain nuclei and fiber tracts that form a ring around the brain stem.
        • Center for basic emotional drives.
    • Closed circuit (Papez circuit):
      • Fornix connects hippocampus to hypothalamus, which projects to the thalamus which sends fibers back to limbic system.
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  • 19. Emotion and Motivation (continued)
      • Areas or the hypothalamus and limbic system are involved in feelings and behaviors.
      • Aggression:
        • Amygdala and hypothalamus.
      • Fear:
        • Amygdala and hypothalamus.
      • Feeding:
        • Hypothalamus (feeding and satiety centers).
      • Sexual drive and behavior:
        • Hypothalamus and limbic system.
      • Goal directed behavior (reward and punishment):
        • Hypothalamus and frontal cortex.
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  • 20. Memory
    • Short-term:
      • Memory of recent events.
    • Medial temporal lobe:
      • Consolidates short term into long term memory.
    • Hippocampus is critical component of memory.
    • Acquisition of new information, facts and events requires both the medial temporal lobe and hippocampus.
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  • 21. Long-Term Memory
    • Consolidation of short-term memory into long-term memory.
      • Requires activation of genes, leading to protein synthesis and formation of new synaptic connections.
        • Altered postsynaptic growth of dendritic spines in area of contact.
    • Cerebral cortex stores factual information:
      • Visual memories lateralized to left hemisphere.
      • Visuospatial information lateralized to right hemisphere.
    • Prefrontal lobes:
      • Involved in performing exact mathematical calculations.
        • Complex, problem-solving and planning activities.
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  • 22. Long-Term Potentiation
    • Type of synaptic learning.
      • Synapses that are 1 st stimulated at high frequency will subsequently exhibit increased excitability.
    • In hippocampus, glutamate is NT.
      • Requires activation of the NMDA receptors for glutamate.
        • Glutamate and glycine or D-serine binding and partial depolarization are required for opening of channels for Ca 2+ and Na + .
    • May also involve presynaptic changes:
      • Binding of glutamate to NMDA receptors and simultaneous depolarization, open receptor channels for Ca 2+ .
        • Ca 2+ causes long-term potentiation in postsynaptic neuron, release of NO from postsynaptic neuron.
          • NO acts as a retrograde messenger, causing release of NT.
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  • 23. Neuronal Stem Cells in Learning and Memory
    • Neural stem cells:
      • Cells that both renew themselves through mitosis and produce differentiated neurons and neuroglia.
    • Hippocampus has been shown to contain stem cells (required for long-term memory).
    • Neurogenesis:
      • Production of new neurons.
    • Indirect evidence that links neuogenesis in hippocampus with learning and memory.
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  • 24. Thalamus and Epithalamus
    • Thalamus:
      • Composes 4/5 of the diencephalon.
      • Forms most of the walls of the 3 rd ventricle.
      • Acts as relay center through which all sensory information (except olfactory) passes to the cerebrum.
        • Lateral geniculate nuclei:
          • Relay visual information.
        • Medial geniculate nuclei:
          • Relay auditory information.
        • Intralaminar nuclei:
          • Activated by many sensory modalities.
          • Projects to many areas.
            • Promotes alertness and arousal from sleep.
    • Epithalamus contains:
      • Choroid plexus where CSF is formed.
      • Pineal gland which secretes melatonin.
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  • 25. Hypothalamus
    • Contains neural centers for hunger, thirst, and body temperature.
    • Contributes to the regulation of sleep, wakefulness, emotions, sexual arousal, anger, fear, pain, and pleasure.
    • Stimulates hormonal release from anterior pituitary.
    • Produces ADH and oxytocin.
    • Coordinates sympathetic and parasympathetic reflexes.
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  • 26. Pituitary Gland
    • Posterior pituitary:
      • Stores and releases ADH (vasopressin) and oxytocin.
    • Hypothalamus produces releasing and inhibiting hormones that are transported to anterior pituitary .
      • Regulate secretions of anterior hormones.
    • Anterior pituitary:
      • Regulates secretion of hormones of other endocrine glands.
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  • 27. Midbrain
    • Contains:
      • Corpora quadrigemina:
        • Superior colliculi:
          • Involved in visual reflexes.
        • Inferior colliculi:
          • Relay centers for auditory information.
      • Cerebral peduncles:
        • Composed of ascending and descending fiber tracts.
      • Substantia nigra:
        • Required for motor coordination.
      • Red nucleus:
        • Maintains connections with cerebrum and cerebellum.
          • Involved in motor coordination.
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  • 28. Hindbrain
    • Metencephalon:
      • Pons:
        • Surface fibers connect to cerebellum, and deeper fibers are part of motor and sensory tracts.
        • Contains several nuclei associated with cranial nerves V, VI, VII.
        • Contains the apneustic and pneumotaxic respiratory centerss .
      • Cerebellum:
        • Receives input from proprioceptors.
        • Participates in coordination of movement.
        • Necessary for motor learning, coordinating different joints during movement, and limb movements.
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  • 29. Hindbrain (continued)
    • Myelencephalon (medulla oblongata):
      • All descending and ascending fiber tracts between spinal cord and brain must pass through the medulla.
        • Nuclei contained within the medulla include VIII, IX, X, XI, XII.
        • Pyramids:
          • Fiber tracts cross to contralateral side.
      • Vasomotor center:
        • Controls autonomic innervation of blood vessels.
      • Cardiac control center:
        • Regulates autonomic nerve control of heart.
      • Regulates respiration with the pons.
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  • 30. Reticular Formation
    • Reticular Formation:
      • Complex network of nuclei and nerve fibers within medulla, pons, midbrain, thalamus and hypothalamus.
      • Functions as the reticular activating system (RAS).
        • Non specific arousal of cerebral cortex to incoming sensory information.
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  • 31. Ascending Spinal Tracts
    • Convey sensory information from cutaneous receptors, proprioceptors and visceral receptors to cerebral cortex.
    • Sensory fiber tract decussation may occur in medulla or spinal cord.
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  • 32. Descending Spinal Tracts
    • Pyramidal (corticospinal) tracts descend directly without synaptic interruption from cerebral cortex to spinal cord.
      • Function in control of fine movements that require dexterity.
    • Reticulospinal tracts (extrapyramidal):
      • Influence movement indirectly.
        • Gross motor movement.
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  • 33. Cranial and Spinal Nerves
    • Cranial nerves:
      • 2 pairs arise from neuron cell bodies in forebrain.
      • 10 pairs arise from the midbrain and hindbrain.
        • Roman numerals refer to the order in which the nerves are positioned from front of the brain to the back.
      • Most are mixed nerves containing both sensory and motor fibers.
    • Spinal nerves:
      • 31 pairs grouped into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and l coccygeal.
      • Mixed nerve that separates near the attachment of the nerve to spinal cord.
        • Produces 2 roots to each nerve.
          • Dorsal root composed of sensory fibers.
          • Ventral root composed of motor fibers.
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  • 34. Reflex Arc
    • Unconscious motor response to a sensory stimulus.
    • Stimulation of sensory receptors evokes APs that are conducted into spinal cord.
      • Synapses with association neuron, which synapses with somatic motor neuron.
    • Conducts impulses to muscle and stimulates a reflex contraction.
      • Brain is not directly involved.
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