Chp 12: The Brain Part 2; Spinal Cord

5. ganglion

a cluster of cell bodies associated with nerves in the PNS 1. First-order neurons, whose cell bodies reside in a ganglion, conduct impulses from the cutaneous receptors of the skin and from propioceptors to the spinal cord or brain stem, where they synapse with second-order neurons. 2. Ganglia associated with afferent nerve fibers contain cell bodies of sensory neurons.

3. dorsal root

the branch of a nerve that enters the dorsal side of the spinal cord. 1. Afferent fibers carrying impulses from peripheral sensory receptors form the dorsal roots of the spinal cord that fan out as the dorsal rootlets before they enter the spinal cord. 2. The cell bodies of the associated sensory neurons are found in an enlarged region of the dorsal root called the dorsal root ganglion.

2. central canal

a small hole in the center of the H crossbar 1. The brain ventricles are continuous with one another and with the central canal of the spinal cord.

10. spinal cord

an extension of the brainstem that begins at the foramen magnum and continues 1. The spinal cord is held in position at its inferior end by the filum terminale, an extension of the pia mater that attaches to the coccyx. 2. Along its length, the spinal cord is held within the vertebral canal by denticulate ligaments, lateral extensions of the pia mater that attach to the dural sheath.

9. sensory (afferent) tract

ascending pathway that transmits sensory information from various parts of the body to the brain. 1. For example, in an ascending sensory tract, fibers transmitting inputs from sensory receptors in superior body regions lie lateral to those conveying sensory information from inferior body regions.

7. motor (efferent) tract

descending pathway that transmits nerve impulses from the brain to muscles and glands 1. Motor pathways involve two neurons, referred to as the upper and lower motor neurons. 2. The indirect pathways include brain stem motor nuclei and all motor pathways except the pyramidal pathways.

8. pia mater

meninx composed of delicate connective tissue and invested with tiny blood vessels 1. The filum terminale, a fibrous extension of the conus covered by pia mater, extends inferiorlly from the conus medullaris to the coccyx, where it anchors the spinal cord so it is not jostled by body movements. 2. Furthermore, saw-toothed shelves of pia mater called denticulate ligaments secure the spinal cord to the tough dura mater meninx throughout its length.

1. arachnoid mater

middle meninx 1. It is separated from the dura mater by a narrow serous cavity, the subdural space which contains a film of fluid 2. The subarachoid space is filled with cerebrospinal fluid and also contains the largest blood vessels serving the brain. Because the arachnoid mater is fine and elastic, these blood vessels are poorly protected.

6. gray matter

mostly cell bodies 1. The two dorsal projections of the gray matter are the dorsal (posterior) horns, and the ventral pair are the ventral (anterior) horns. 2. All neurons whose cell bodies are in the spinal cord gray matter are mainly interneurons.

13. white matter

myelinated and nonmyelinated nerve fibers that allow communication between different parts of the spinal cord and between the cord and brain. 1. Ascending and descending tracts make up most of the white matter. 2. The white matter on each side of the cord is divided into three white columns, or funiculi, named according to their position as dorsal, lateral, and ventral funiculi.

4. dura mater

strongest meninx 1. The single-layered spinal dura mater is not attached to the bony walls of the vertebral column. 2. Between the bony vertebrae and the spinal dura mater is an epidural space filled with a soft padding of fat and a network of veins.

12. ventral root

the branch of the nerve that enters the ventral side of the spinal cord 1. Ventral roots contain motor nerve axons, transmitting nerve impulses from peripheral regions to the spinal cord. 2. Because the ventral roots contain both somatic and autonomic efferent fibers, they serve both motor divisions of the peripheral nervous system.

11. spinal nerves

the dorsal and ventral roots fused laterally 1. Spinal nerves emerge in pairs, one from each side of the spinal cord along its length. 2. This strange arrangement [cauda equina] reflects the fact that during fetal development, the vertebral column grows faster than the spinal cord, forcing the lower spinal nerve roots to "chase" their exit points inferiorly through the vertebral canal.