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
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)
Critical Thinking (1) What functional advantages might a neuron with SEVERAL dendrites have over a neuron with only ONE dendrite?
(1) Axon (signal sent AWAY) • EXTENSION of soma (cell body), transmits NERVE IMPULSES between neurons of CNS and PNS.
(2) Central Nervous System (CNS) • Includes BRAIN and SPINAL CORD, nerves ENCASED in axial skeleton.
(3) Peripheral Nervous System (PNS) • 32 PAIRS of NERVES that EXTEND spinal cord, receiving AND transmitting IMPULSES throughout BODY.
(4) Afferent Neurons (i.e., SENSORY neurons “What do we have here?”) • COLLECT data from SENSES and transmit impulses TOWARDS CNS [via dorsal roots].
(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].
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.
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?
(1) Cerebral Hemispheres (L (Speech and Language), R (Reasoning) • Connected by CORPUS CALLOSUM and contain cerebral CORTEX.
(2) Corpus Callosum • THICK BAND of AXONS of many INTERCONNECTED neurons of 2 cerebral HEMISPHERES.
(3) Cerebral Cortex (wrinkled OUTER layer—contains FOUR lobes) • OCCIPITAL Lobe (vision), PARIETAL Lobe (tactile senses), TEMPORAL Lobe (hearing), and FRONTAL Lobe (problem-solving).
(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)
(B) Upper Brain Stem (Diencephalon—hypothalamus AND thalamus) • LINKS cerebrum WITH spinal cord, contains RELAY centers for data ENTERING and EXITING cerebrum.
(1) Thalamus (upper RELAY center FOR SENSES) • DIRECTS incoming SENSORY signals to proper LOBE of cerebral cortex. (NOTE: Hypothalamus—assists w/hormone production/homeostasis)
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?
(2) Limbic System (includes diencephalon & PRIMITIVE brain) • Plays a role in EMOTION, MEMORY, REFLEXES, and MOTIVATION.
(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.
(1) Midbrain (innervates optic AND auditory nerves—SEE RED BELOW) • Relay center for VISUAL (occipital lobe) and AUDITORY (temporal lobe) data.
(2) Pons (critical region for GYMNASTS) • Relay center between neurons of CEREBRUM and CEREBELLUM.
(3) Medulla Oblongata (BOTH relay AND control center—involuntary) • Regulates HEART and BREATHING rates—homeostatic activity of body.
(4) Reticular Formation (network of neurons THROUGHOUT brain stem) • A FILTER that separates IMPORTANT sensory signals FROM UNIMPORTANT signals to CEREBRUM.
(D) Cerebellum (tied into PONS and CEREBRUM) • Works with brain MOTOR CENTERS to coordinate responses (i.e., muscle contractions, movements, BALANCE, and body posture)
(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.
(2) Dura Mater (OUTER layer, SEE BLUE BELOW) • Consists of connective tissue, blood vessels, and neurons.
(3) Arachnoid Layer (MIDDLE layer, SEE GOLD BELOW) • Elastic and WEB-LIKE, provides FLEXIBILITY to spinal cord.
(4) Pia Mater (INNER layer, SEE LIGHT PINK BELOW) • Thin layer ADHERING to CNS, rich in blood vessels and neurons.
(5) Cerebrospinal Fluid (CSF, fills inner and middle meninges) • Provides protective CUSHION and transport MEDIUM for neurotropins.
(6) Ventricles (FOUR interconnected CAVITIES in brain) • Filled with CSF, acting as CHAMBERS for transport medium and cushion.
(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).
Critical Thinking (4)Why might an injury to the LOWER spinal cord cause a loss of sensation in the LEGS?
(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).
(2) Sensory Receptor (data FROM receptor to spinal cord—DORSAL roots) • AFFERENT neuron to detect a STIMULUS, (pressure, heat, or pain).