Chapter 12 The Spinal Cord

Question 1

Features of the Spinal Cord:

Answer 1

o Extends from the foramen magnum of the skull to the first or second lumbar vertebra.
o Provides a two-way conduction pathway to and from the brain.
o Major reflex center with it’s reflexes being initiated and completed at the spinal cord level.
o Protected by bone, meninges, and cerebrospinal fluid.
o Typically ends between Lumbar 1 or 2; because of this the subarachnoid space is the ideal point for removal of CSF for medical testing (called a lumbar puncture or tap).

Question 2

Spinal Dura Mater:

Answer 2

Not attached to the bony walls of the vertebral column.

Question 3

Epidural Space:

Answer 3

• Between the bony vertebrae and the spinal dura mater.
• Filled with soft padding of fat and a network of veins.
• Cerebrospinal fluid fills the subarachnoid space between the arachnoid and pia mater meninges.

Question 4

Conus Medullaris:

Answer 4

The tapering cone-shaped area at which the spinal cord terminates.

Question 5

Filum Terminale:

Answer 5

• A fibrous extension of the conus medullaris covered with pia mater.
• Extends inferiorly from the conus meduallaris to the coccyx where it anchors the spinal cord so it isn’t damaged or rotated during movement.

Question 6

Denticulate Ligaments:

Answer 6

Secure the spinal cord to the tough dura mater meninx throughout it’s length.

Question 7

Cervical and Lumbar Enlargements:

Answer 7

Enlarged portions of he spinal cord where the nerves serving the upper and lower limbs arise.

Question 8

Cuada Equina:

Answer 8

• The collection of nerve roots at the inferior end of the vertebral canal.
• Also referred to as the “horse’s tail” due to it’s resemblance.

Question 9

The Two Grooves that Mark the Surface of the Spinal Cord:

Answer 9

o Ventral (Anterior) Median Fissure

o Dorsal (Posterior) Median Sulcus

Question 10

Gray Commissure:

Answer 10

A crossbar of gray matter that encloses the central canal.

Question 11

Dorsal (Posterior) Horns:

Answer 11

Two dorsal projections of gray matter.

Question 12

Ventral (Anterior) Horns:

Answer 12

Two ventral projections of gray matter.

Question 13

Lateral Horns:

Answer 13

• The additional pair of gray matter columns in the thoracic and superior lumbar segments of the spinal cord.
• Consist mostly of cell bodies of autonomic (sympathetic) division.

Question 14

Ventral Roots:

Answer 14

• Ventral rootlets that fuse together via motor neurons being sent out to the skeletal muscles.
• Contain both somatic and autonomic efferent fibers.
• Serve both motor divisions of the PNS.

Question 15

Dorsal Roots:

Answer 15

• Formed by afferent fibers carrying impulses from peripheral sensory receptors.
• The cell bodies of dorsal roots are found in the dorsal root ganglion or spinal ganglion.
• After entering the cord, the axons take different routes.
• Some enter the dorsal white matter of the cord while others synapse with interneurons in the dorsal horns of the spinal gray matter at their entry level.

Question 16

Spinal Nerves:

Answer 16

Combination of the dorsal and ventral roots that fuse laterally.

Question 17

The 4 Divisions of Spinal Gray Matter:

Answer 17

The spinal gray matter is divided according to its neurons’ relative involvement in innervating the somatic and visceral regions of the body.

o Somatic Sensory
o Visceral Sensory
o Visceral (autonomic) motor
o Somatic Motor

Question 18

White Matter of the Spinal Cord:

Answer 18

Composed of myelinated and nonmyelinated nerve fibers that allow communication between different parts of the spinal cord and between the cord and the brain.

Question 19

The Directions in Which White Spinal Nerve Fibers Run:

Answer 19

o Ascending: Up to the higher centers (sensory inputs). More Common.

o Descending: Down to the cord from the brain or within the cord to lower levels (motor inputs). More Common.

o Transverse: Across from one side of the cord to the other (commissural fibers). Less Common.

Question 20

Funiculi:

Answer 20

• Three white columns that are named according to their position (dorsal (posterior), lateral, and ventral (anterior) funiculi).
• Each contains several fiber tracts, and each tract is made up of axons with similar destinations and functions.

Question 21

Four Key Generalizations of Neuron Progression and Details of Each:

Answer 21

o Decussation: Most pathways cross from one side of the CNS to the other (decussate) at some point along their journey.
o Relay: Most pathways consist of a chain of two or three neurons (a relay) that contribute to successive tracts of the pathway.
o Somatotopy: Most pathways exhibit somatotopy, a precise spatial relationship among the tract fibers that reflects the orderly mapping of the body.
o Symmetry: All pathways and tracts are paired symmetrically (right and left), with a member of the pair present on each side of the spinal cord or brain.

Question 22

Neuron Orders and Details of Each:

Answer 22

o First-Order Neurons: Cell bodies reside in a ganglion and conduct impulses from the cutaneous receptors of the skin and from proprioceptors to the spinal cord or brain stem, where they synapse with second order neurons.
o Second-Order Neurons: Cell bodies reside in the dorsal horn of the spinal cord or in medullary nuclei. They transmit impulses to the thalamus or to the cerebellum where they synapse.
o Third-Order Neurons: Have cell bodies in the thalamus. Relay impulses to the somatosensory cortex of the cerebrum.

Question 23

Paralysis/Paresthesias:

Answer 23

Any localized damage to the spinal cord or its roots leads to some functional loss.

Question 24

Flaccid Paralysis:

Answer 24

Severe damage to ventral root or ventral horn cells result in this. This occurs because nerve impulses don’t reach the muscle served.

Question 25

Spastic Paralysis:

Answer 25

When only the upper motor neurons of the primary motor cortex are damaged. Spinal motor neurons remain intact and spinal reflex activity continues to stimulate the muscles irregularly.

Question 26

Paraplegia:

Answer 26

Transection of the spinal cord between Thoracic 1 and Lumbar 1. Both lower limbs are affected.

Question 27

Quadriplegia:

Answer 27

Transection of the spinal cord in the cervical region. All four limbs affected.

Question 28

Hemiplegia:

Answer 28

Paralysis of one side of the body usually due to brain damage rather than spinal injury.

Question 29

Spinal Shock:

Answer 29

A transient period of functional loss that follows the injury. Immediately depresses all reflex activity caudal to the lesion site.

Question 30

Poliomyelitis:

Answer 30

Results from the poliovirus which usually enters the body in feces-contaminated water and destroys the ventral horn motor neurons.

Question 31

Postpolio Syndrome:

Answer 31

Extreme lethargy, sharp burning pains in the muscles, and progressive muscle weakness or atrophy.

Question 32

Amyotrophic Lateral Schlerosis (ALS):

Answer 32

Devastating neuromuscular condition that progressively destroys ventral horn motor neurons and fibers of pyramidal tracts.

Question 33

CNS Development Starting at the 3-Week Old Embryo:

Answer 33

o 1: The neural plate forms from surface ectoderm. Invaginates, forming the neural groove flanked by neural folds.
o 2: Neural fold cells migrate to from the neural crest, which will form much of the PNS and many other structures.
o 3: The neural groove becomes the neural tube, which will form CNS structures.

Question 34

Anencephaly:

Answer 34

The cerebrum and part of the brain stem never develop because neural folds fail to fuse rostrally.

Question 35

Spina Bifida:

Answer 35

Results from incomplete formation of the vertebral arches and typically involves the lumbosacral region.