CHAPTER 12 - SPINAL CORD & SPINAL NERVES

I. SPINAL CORD - links brain to P.N.S.

            A. GENERAL STRUCTURE (Fig. 12.1, p. 408)

                        1. Foramen magnumè2nd Lumbar vertebra

                        2. Cervical enlargementèarm

                        3. Lumbar enlargementèleg

                        4. CAUDA EQUINA

                                    a. CONUS MEDULLARIS

                                    b. FILUM TERMINALE – coccyx

            B. MENINGES - C.T. layers around C.N.S. (Fig. 12.2, p. 409)

                        1. DURA MATER - “tough mother”, outermost, THECAL SAC

                                    a. 2 over brain w/sinuses, contin. w/ periosteum

                                    b. 1 over spinal cord, epidural space between periosteum

                        2. ARACHNOID MATER

                                    a. Thin, delicate & web-like

                                    b. SUBARACHNOID SPACE - C.S.F.

                        3. PIA MATER - “delicate mother”, innermost

a.    DENTICULATE ligaments - hold pia to dura in cord

            C. CROSS SECTION (Fig. 12.3, p. 410)

                        1. WHITE MATTER - outer, axons, 2 halves each with:

                                    a. ANTERIOR/VENTRAL COLUMN/FUNICULUS

                                    b. LATERAL    “

                                    c. POSTERIOR/DORSAL    “

                                    d. Columns composed of FASCICULI = Tracts

                                    e. White Commissure connects L & R halves

                        2. GRAY MATTER - inner, bodies & dendrites

                                    a. ANTERIOR/VENTRAL HORN - Motor output

                                    b. LATERAL    “    - A.N.S. output

                                    c. POSTERIOR/DORSAL   “    - Sensory input

                                    d. Gray Commissure connects L & R halves

                        3. ROOTS (Fig. 12.4, p. 411)

                                    a. DORSAL   - sensory/afferent to dorsal horn

                                                            - dorsal root ganglia

                                                            - “In back door” from P.N.SèC.N.S.

                                    b. VENTRAL  - motor/efferent from anterior horn

                                                            - “Out front door” from C.N.SèP.N.S.

II. REFLEXES

A.   DEFN =

1.    SIMPLEST FUNCTIONAL UNIT OF N.S.

                                    - UNCONSCIOUS integration

                                    - STEREOTYPICAL response - always same

                        2.  5 COMPONENTS minimum = REFLEX ARC  (Fig. 12.5, p. 412)

                                    a. RECEPTOR/SENSOR

                                    b. AFFERENT/SENSORY NEURON

                                    c. INTERNEURON (may also go to brain)

                                    d. EFFERENT/MOTOR NEURON

                                    e. EFFECTOR - muscle or gland

3. CAN BE TRAINED TO BE FASTER - boxer, fencer

                        4. CAN BE OVER-RIDEN - “hot antique dish"

                        5. HOMEOSTATIC - prevent damage

                        6. INTEGRATION - synapse in C.N.S.

                                    a. SPINAL CORD

                                    b. BRAIN

            B. TYPES

                        1. STRETCH REFLEX - “knee jerk” (Fig. 12.6, p. 413)

                                    a. Simplest reflex arc - 5 components

                                    b. Excitatoryècauses contraction, maintains posture

                        2. GOLGI TENDON REFLEX (Fig. 12.7, p. 414)

                                    a. ê tension in muscles, relaxes muscle (i.e. weight lifter)

                                    b. Inhibitoryèprevents damage due to excessive tension

                        3. WITHDRAWAL REFLEX - response to pain, “Step on a tack” (p. 415)

                                    a. RECIPROCAL INNERVATION - to catch balance in same leg

                                    b. CROSSED EXTENSOR - prevents falling if you trip, other leg stim.

                                                                                                                                    (p. 416)

III. SPINAL PATHWAYS - Tracts (Fig 12.3c, p. 410 & 12.11, p. 417)

            A. ASCENDING - sensory input

            B. DESCENDING - motor output

IV. STRUCTURE OF PERIPHERAL NERVES bundles of nerve axons (Fig. 12.12, p. 418)         

            A. ENDONEURIUM - surrounds each fiber

            B. PERINEURIUM - surrounds FASCICLES - bundles of fibers

            C. EPINEURIUM - surrounds 1 nerve, bundle of fascicles

V. SPINAL NERVES [1-31] - ARISE FROM SPINAL CORD

            A. REGIONS (Fig. 12.13, p. 418 & Fig. 12.14, p. 419)

                        1. CERVICAL C1-C8

                        2. THORACIC T1-T12

                        3. LUMBAR L1-L5

                        4. SACRAL S1-S5

                        5. COCCYGEAL Co or Cx

            B. PATHWAY: Each w/ DORSAL & VENTRAL ROOT (Fig. 12.15, p. 420)

                        1. SPINAL CORD

                        2. ROOTLETS (6-8) per VENTRAL or DORSAL ROOT

                        3. DORSAL ROOT

                                    a. SENSORY/AFFERENT

                                    b. “IN BACK DOOR”

                                    c. DORSAL ROOT GANGLION

                        4. VENTRAL ROOT

                                    a. MOTOR & A.N.S./EFFERENT

                                    b. “OUT FRONT DOOR”

                        5. VENTRAL & DORSAL ROOTS FUSE = SPINAL NERVE!

                                    a. 2 RAMI (Branches) per spinal nerve

                        6. DORSAL RAMUS

                                    a. MOTOR to DEEP MUSCLES of back

                                    b. SENSORY from MIDLINE of back

                        7. VENTRAL RAMUS 

                                    a. join w/ other ventral ramiè 4 PLEXUSES (Braids)

b.    EXCEPT in THORACIC, no PLEXUSES = INTERCOSTAL n.

            C. PLEXUSES – 4 (Fig. 12.13, p. 418)

                        1. CERVICAL C1èC4 (Fig. 12.16, p. 422)

                                    a. most of PHRENIC n. - diaphragm

                        2. BRACHIAL C5èT1 – ARMS (Fig. 12.17, p. 423)

                                    - part of PHRENIC n.

                        A         a. AXILLARY n. - shoulder

                        R         b. RADIAL n. - arm, forearm, middle, index & thumb front

                        M         c. MUSCULOCUTANEOUS - motor arm, sensory forearm

                        U         d. ULNAR - pinkie & ring fingers, “funny bone”

                        M         e. MEDIAN - back of thumb

                        3. LUMBOSACRAL L1èS4 – LEGS (Fig. 12.23, p. 429)

                                    a. OBTURATOR - adducts upper thigh

                                    b. FEMORAL - Flexes thigh, extends leg

                                    c. ISCHIADIC (SCIATIC) - largest nerve in body

                                                i. TIBIAL          - MEDIAL PLANTAR

                                                                        - LATERAL PLANTAR

                                                ii. COMMON PERONEAL   - DEEP PERONEAL

                                                                                                - SUPERFICIAL PERONEAL

                        4. COCCYGEAL - skin over coccyx

            D. DERMATOME - map of cutaneous innervation (Fig. 12.14, p. 419)

            *E. READ & KNOW CLINICAL IMPACTS & PREDICT QUESTIONS!!!