Structures & Function of Spinal Cord

Spinal nerves

mixed motor/sensory & they will divide into dorsal & ventral rami

White matter

surrounding area consisting of tracts (axons of neurons)

Roots

ventral/anterior (motor); dorsal/posterior (sensory) attaches nerves to spinal cord

Arachnoid mater

adheres to the dura; continues with the subarachnoid of the brian and contains CSF; lumbar cistern

Pia mater

adheres to the spinal cord

FilumTerminale Internum

ataches the terminal end of the spinal cord (conus medullaries) to the dural sac; extension of pia mater

Denticulate ligaments

attach the spinal cord to the dural sac (lateral points of attachment)

Filum Terminale Externum

attaches dural sac to the coccyx

Gray matter

butterfly-shaped central area primarily consisting of neuronal cell bodies--> ventral/anterior horn (motor); dorsal/posterior horn (sensory)

Dorsal Root Ganglion

contains cell bodies on sensory neurons

Central canal

continuous with the ventricular system of the brain

Dural mater (sac) (spinal meninges)

encloses the spinal cord and is seperated from the vertebrae by the epidural space

Structure of Spinal Cord

extends from foramen magnum to L1-L2 vertebrae; consists of 31 spinal levels (31 pairs of spinal nerves)--> 8 cervical, 12 thoracic, 5 paired lumbar, 5 paired sacral, 1 paired coccygeal; Enlargements--> cervical: serves the upper limb; lumbsacral: serves the lower limb

Sensory components of spinal nerves

-Somatic afferents: carry sensory information from the body surfaces, muscles, tendons, ligaments, and joints--> exteroceptive: touch, vibration, temperature & pain; proprioceptive: information from muscles, tendons, & joints -Visceral afferents: carry sensory information from the viscera--> interoceptive: pain information from the viscera

Motor components of spinal nerves

-Somatic efferents: innervate skeletal muscles--> alpha motor neurons (extrafusal fiber); gamma motor neurons (intrafusal fiber) -Visceral efferents: innervate smooth, cardiac, and glandular epithelium--> visceral motor neurons

What are the four essential functions of the spinal cord?

1) receives and begins to integrate primary sensory input -somatosensory fibers (somatic afferents): from receptors in the skin, skeletal muscle, tendons -viscerosensory fibers (viscerosensory afferents): from receptors in thoracic, abdominal, and pelvic viscera -this information is use to mediate reflexes,is relayed to higher centers via ascending fibers, or both 2) contains motor neurons that innervate target structures -somatic motor neurons (somatic efferents): innervate skeletal muscle -visceral motor neurons (visceral efferents) these preganglionic neurons will synapse in a peripheral ganglia to influence cardiac muscle, smooth muscle or glandular epithelium 3)contains descending fibers from the cortex or brainstem that modulate the activity of spinal motor and sensory neurons 4) mediation of spinal reflexes