Spinal Cord 1/14

1

• Spinal Cord 1/14
• CNS tissue is enclosed within vertebral column
  begins at foramen magnum and ends at L1 or L2
• Functions
• Provides two-way communication to and from brain
• Contains spinal reflex centers
• Protected by bone, meninges, and CSF

2

• Ends in conus medullaris
• Filum terminale (fibrous extension of conus
  medullaris) covered with pia mater which extends
  to coccyx and anchors the cord so it is not
  damaged by movements
• Cauda equina
• Collection of nerve roots at inferior end of
  vertebral canal

3

• Spinal nerves (Part of PNS)
• 31 pairs
• Spinal nerves split into dorsal and ventral
  branches or rami almost as soon as they leave
  vertebral column.
• Spinal nerves are often named for bone or
  structure they pass near
• Plexuses are groups of spinal nerves.

4

• Cervical plexus (C1 to C4) serves muscles and
  skin of neck, except for phrenic nerve which
  stimulates diaphragm.
• Brachial plexus (C5-8, T1) serves skin and
  muscles of arm shoulder area
• Lumbar plexus (L1-4) serves skin and muscles of
  (upper) leg pelvic area.
• Sacral plexus (L4, L5, S1-4) serves skin and
  muscles of (lower) leg pelvic area.

5

• Cross-sectional Anatomy
• Two lengthwise grooves partially divide cord into
  right and left halves
• Ventral or Anterior median fissure
• Dorsal or Posterior median sulcus

6

• Gray Matter-consists of cell bodies,
  non-myelinated processes and neuroglia
• In cross section, looks like H or a butterfly
• Gray commissureconnects masses of gray matter
  encloses central canal
• Dorsal horns - interneurons that receive somatic
  and visceral sensory input
• Ventral horns - some interneurons somatic motor
  neurons axons exit cord via ventral roots
• Lateral horns (only in thoracic and superior
  lumbar regions) - sympathetic neurons
• Dorsal roots sensory input to cord
• Dorsal root (spinal) gangliacell bodies of
  sensory neurons

7
White Matter

• Divided into three white columns (funiculi) on
  each side
• Dorsal, lateral, and ventral
• Each spinal tract composed of axons with similar
  destinations and functions
• The tracts in funiculi are typically named for
  start and end points of their axons?Ascendingspin
  al cord ? brain
  Descendingbrain ? spinal cord.
• Lateral funiculi have a mix of ascending and
  descending tracts.
• Distribution primarily sensory tracts in
  posterior descending motor tracts in the
  anterior (recall that sensory information comes
  in back side (dorsal root), and motor responses
  go out front door (ventral root).

8

• Spinothalamic Pathways (Ascending)
• Lateral and ventral spinothalamic tracts
• Provide discriminatory touch (pain, temperature,
  coarse touch, pressure) and conscious
  proprioception
• Spinocerebellar Tracts (Ascending)
• Ventral and dorsal tracts terminate in cerebellum
  
• Convey information about muscle or tendon stretch
  to cerebellum
• Used to coordinate muscle activity

9

• Dorsal ColumnMedial Lemniscal Pathways
  (Ascending)
• Composed of paired fasciculus cuneatus and
  fasciculus gracilis in spinal cord and medial
  lemniscus in brain (medulla to thalamus)
• Transmit input to somatosensory cortex for
  discriminative touch and vibrations

10

• Descending Pathways
• Reticulospinal and vestibulospinal
  tractsmaintain balance
• Rubrospinal tractscontrol flexor muscles
• Tectospinal tracts mediate head movements in
  response to visual stimuli

11

• Reflexes
• rapid, involuntary, predictable motor response to
  stimulus
• Can involve just peripheral nerves and spinal
  cord or may also involve higher brain centers
• Direct transfer of stimulus from sensory neuron
  to motor neuron (sometimes with an interneuron in
  between) allows for rapid response to stimuli.
• May be
• Inborn (intrinsic)
• Example maintain posture, control visceral
  activities
• Can be modified by learning and conscious effort
• --Learned (acquired) reflexes result from
  practice or repetition,
• Example driving skills

12

• Input travels along one pathway, called a reflex
  arc, to a specific destination
• System works in all-or-none manner to produce
  specific response
• Particular stimulus always causes same response

13
Reflex Arc

• Components
• 1. Receptorsite of stimulus action
• 2. Sensory neurontransmits afferent impulses to
  CNS
• 3. Integration centereither monosynaptic or
  polysynaptic region within CNS
• 4. Motor neuronconducts efferent impulses from
  integration center to effector organ
• 5. Effectormuscle fiber or gland cell that
  responds to efferent impulses by contracting or
  secreting

14

• Stretch and Tendon Reflexes
• To smoothly coordinate skeletal muscle, nervous
  system must receive constant proprioceptor input
  about
• Length of muscle (from muscle spindles)
• Muscle tone Amount of tension in muscle and
  tendons
• allows muscle to maintain correct muscle tone and
  adjust it reflexively

15

• LABWORK
• Describe the important structures of spinal
  cord.
• 2. Describe cross-sectional features of spinal
  cord (models and cross-section slide).
• 3. Describe spinal nerves and plexuses associated
  with the spinal cord (models).
• 4. Describe reflexes and basics of reflex
  physiology.