Ch. 17 Spinal Cord & Spinal Nerves Flashcards
Intro
- contains neural circuits that control quickest reactions to environmental changes
- site for integration of neuronal stimulation
- relay sensory nerve impulses
- continuous with brain and together constitute the CNS
Spinal Cord Anatomy
spinal meninges: cover spinal nerves up to the point of exit from spinal column through the intervertebral foramina
cerebrospinal fluid: serves as shock absorber and suspension system for spinal cord and brain
denticulate ligaments: thickenings of pia mater that project and fuse with arachnoid mater and inner surface of dura mater between anterior and posterior nerve roots of spinal nerves on either side
Meninges
Dura mater: most superifical, composed of dense, irregular connective tissue
- also protected by cushion of fat and connective tissue in epidural space
Arachnoid mater: middle layer and avascular covering; delicate collagen fibres and some elastic fibres
- betweendura mater and arachnoid mater is thin subdural space which contains interstitial fluid
Pia mater: innermost connective tissue layer that adheres to surface of spinal cord and brain
External Anatomy
cervical enlargement: extends from fourth cervical vertebra to first thoracic vertebra
lumbar enlargement: inferior enlargement, extends from ninth to twelfth thoracic vertebra
- inferior to lumbar enlargment, spinal cord terminates as a tapering, conical structure called conus medullaris
- conus modulars ends at level of intervertebral disc between first and second lumbar vertebra in adults
- arising from concur modulars is hilum terminal
Internal Anatomy
- 2 grooves penetrate white matter of spinal cord and divide into right and left sides
- anterior median fissure is a wide groove on anterior side
- posterior median sulcus is narrow groove on posterior side
- gray matter of spinal cord is shaped like latter H and surrounded by white matter
- gray matter consists of cell bodies of neutrons, neuroglia, unmyelinated axons, and dendrites of interneurons and motor neurone
- white matter consists of bundles of myelinated axons of sensory neutrons, interneurons and motor neurons
Gray Horns
- gray commissure forms crossbar of H; in centre is small space called central canal, extends entire length of spinal cord and contains CSF
- gray matter on each side of spinal cord is subdivided into horns
1. anterior (ventral) gray horn: contain somatic motor nuclei; clusters of cell bodies of somatic motor neurone that provide skeletal muscles
2. posterior (dorsal) gray horns: contain cell bodies and axons of interneurons as well as axons of incoming sensory neutrons
3. lateral gray horns: present only in thoracic, upper lumbar, and sacral segments of spinal cord; lateral horns contain cell bodies of autonomic motor nuclei that regulate activity of smooth muscle, cardiac muscle and glands
White Matter
- anterior and posterior gray horns divide white matter
- anterior to gray commissure is anterior white commissure, which connects white matter of right and left sides of spinal cord
Spinal Nerves
- part of PNS
- connect CNS to sensory receptors, muscles, and glands
- 31 pairs of spinal nerves
- 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral, 1 pair of coccygeal
Branches of Spinal Nerve
- sensory posterior root and motor anterior root project laterally; converge to form a mixed nerve and spinal nerve trunk
- spinal nerve trunk runs for a short distance before branching into two large branches and a a variable series of smaller branches
- large branch is called a ramus
Ramus
anterior ramus and posterior rams are somatic branches that run in musculoskeletal system
- posterior ramus serves: deep muscles and skin of posterior
- anterior ramus: serves muscles and structures of upper and lower limbs and muscles and skin of lateral and anterior regions of trunk
- smaller visceral branches, such as meningeal branch and communicating rami, form autonomic pathways to smooth muscles and glandular tissue
