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Chapter 50: Nervous System and Sensory Organs
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Chapter 50: Nervous System and Sensory Organs

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  1. Chapter 50: Nervous System and Sensory Organs 50-1 Central Nervous System 50-2 Peripheral Nervous System 50-3 Transmission of Nerve Impulses 50-4 Sensory Systems

  2. 50-1 Central Nervous System I. Organization (neuron is the cell type) • TWO divisions of NERVE NETWORKS regulate our body: • CNS (MASTER headquarters) • (2) PNS (SATELLITE centers)

  3. Critical Thinking (1) What functional advantages might a neuron with SEVERAL dendrites have over a neuron with only ONE dendrite?

  4. (1) Axon (signal sent AWAY) • EXTENSION of soma (cell body),  transmits NERVE IMPULSES between neurons of CNS and PNS.

  5. (2) Central Nervous System (CNS) • Includes BRAIN and SPINAL CORD, nerves ENCASED in axial skeleton.

  6. (3) Peripheral Nervous System (PNS) • 32 PAIRS of NERVES that EXTEND spinal cord, receiving AND transmitting IMPULSES throughout BODY.

  7. (4) Afferent Neurons (i.e., SENSORY neurons  “What do we have here?”) • COLLECT data from SENSES and transmit impulses TOWARDS CNS [via dorsal roots].

  8. (5) Efferent Neurons (i.e., MOTOR neurons  “What do we do now?”) • RECEIVE orders from CNS and RELAY it to PNS (typically to MUSCLES and GLANDS) [ via ventral roots].

  9. II. Brain (conscious AND subconscious organ ~ 100 billion neurons) • 2% of body weight, BUT DEMANDS 20% of water AND glucose supply. (A) Cerebrum (controls MOTOR and SENSORY activities) • Largest portion of brain, composed of TWO hemispheres.

  10. Critical Thinking (2)Strokes result in the DEATH of neurons in the brain. How might a doctor tell WHICH AREAS of the brain have been AFFECTED if a person has suffered from a stroke?

  11. (1) Cerebral Hemispheres (L (Speech and Language), R (Reasoning) • Connected by CORPUS CALLOSUM and contain cerebral CORTEX.

  12. (2) Corpus Callosum • THICK BAND of AXONS of many INTERCONNECTED neurons of 2 cerebral HEMISPHERES.

  13. (3) Cerebral Cortex (wrinkled OUTER layer—contains FOUR lobes) • OCCIPITAL Lobe (vision), PARIETAL Lobe (tactile senses), TEMPORAL Lobe (hearing), and FRONTAL Lobe (problem-solving).

  14. (4) White Matter (and Gray Matter) • Composed of AXONS that link CORTEX with other CENTERS of brain. (NOTE: GRAY matter consists of the cell BODIES of neurons)

  15. (B) Upper Brain Stem (Diencephalon—hypothalamus AND thalamus) • LINKS cerebrum WITH spinal cord, contains RELAY centers for data ENTERING and EXITING cerebrum.

  16. (1) Thalamus (upper RELAY center FOR SENSES) • DIRECTS incoming SENSORY signals to proper LOBE of cerebral cortex. (NOTE: Hypothalamus—assists w/hormone production/homeostasis)

  17. Critical Thinking (3)Synesthesia is a puzzling phenomenon in which one type of sensory input is interpreted by the brain as another type. For example, a person hearing music might associate certain notes with certain colors. What may be happening in the central nervous system to produce this effect?

  18. (2) Limbic System (includes diencephalon & PRIMITIVE brain) • Plays a role in EMOTION, MEMORY, REFLEXES, and MOTIVATION.

  19. (C) Lower Brain Stem (i.e., midbrain, pons, AND medulla oblongata) • BELOW diencephalon, brain stem NARROWS (into midbrain, pons, and medulla oblongata) BECOMING continuous with SPINAL CORD.

  20. (1) Midbrain (innervates optic AND auditory nerves—SEE RED BELOW) • Relay center for VISUAL (occipital lobe) and AUDITORY (temporal lobe) data.

  21. (2) Pons (critical region for GYMNASTS) • Relay center between neurons of CEREBRUM and CEREBELLUM.

  22. (3) Medulla Oblongata (BOTH relay AND control center—involuntary) • Regulates HEART and BREATHING rates—homeostatic activity of body.

  23. (4) Reticular Formation (network of neurons THROUGHOUT brain stem) • A FILTER that separates IMPORTANT sensory signals FROM UNIMPORTANT signals to CEREBRUM.

  24. (D) Cerebellum (tied into PONS and CEREBRUM) • Works with brain MOTOR CENTERS to coordinate responses (i.e., muscle contractions, movements, BALANCE, and body posture)

  25. (E) Protection (in addition to SKULL) • Tissue protected by meninge CUSHION and CSF MATRIX. (1) Meninges (e.g., dura mater, arachnoid layer, and pia mater) • THREE layers SURROUNDING neurons of CNS.

  26. (2) Dura Mater (OUTER layer, SEE BLUE BELOW) • Consists of connective tissue, blood vessels, and neurons.

  27. (3) Arachnoid Layer (MIDDLE layer, SEE GOLD BELOW) • Elastic and WEB-LIKE, provides FLEXIBILITY to spinal cord.

  28. (4) Pia Mater (INNER layer, SEE LIGHT PINK BELOW) • Thin layer ADHERING to CNS, rich in blood vessels and neurons.

  29. (5) Cerebrospinal Fluid (CSF, fills inner and middle meninges) • Provides protective CUSHION and transport MEDIUM for neurotropins.

  30. (6) Ventricles (FOUR interconnected CAVITIES in brain) • Filled with CSF, acting as CHAMBERS for transport medium and cushion.

  31. (F) Spinal Cord (neural tissue—medulla THROUGH vertebral column) • OUTER sheath of WHITE matter (AXONS of neurons) surrounds an INNER core of GRAY matter (SOMA of neurons).

  32. Critical Thinking (4)Why might an injury to the LOWER spinal cord cause a loss of sensation in the LEGS?

  33. (1) Nerve (a group of BUNDLED axons) • Each SPINAL NERVE consists of a DORSAL root (carries sensory signals to CNS) and a VENTRAL root (carries signals to MUSCLES and GLANDS).

  34. (2) Sensory Receptor (data FROM receptor to spinal cord—DORSAL roots) • AFFERENT neuron to detect a STIMULUS, (pressure, heat, or pain).