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Development& Functions Of Various Parts Of Cns


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Development& Functions Of Various Parts Of Cns

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