The spinal cord
The longitudinal cord of nerve tissue enclosed in the spinal canal. It serves not only as a pathway for nerve impulses to and from the brain, but also as a center for operating and coordinating reflex actions independent of the brain.
Spinal Nerves
dorsal roots
contains the axons of the sensory neurons
dorsal root ganglion
contains the cell bodies of sensory neurons
ventral roots
contain the axons of motor neurons (somatic & autonomic)
Cervical
8 cervical nerves
Thoracic
12 thoracic nerves
Lumbar
5 lumbar nerves
Sacral
5 sacral nerves
Coccyx
1 coccygeal nerve
Protection of the Spinal Cord
The spinal cord is protected from mechanical forces by:
- vertebral column
- cerebrospinal fluid - also nourishes the neural.
tissue & removes waste products
- spinal meninges
The Spinal Meninges
Internal Anatomy of the Spinal Cord
The neural tissue (neurons & neuroglia) of the spinal cord:
- is divided into a left and right side by two grooves
- anterior (ventral) median fissure
- posterior (dorsal) median sulcus
- is organised into areas of gray matter & white
matter
- identical arrangement of gray & white matter, and the structures within them, on each side of the spinal cord
Gray Matter
Sensory Nuclei of the Posterior Gray Horns
Contain the cell bodies of spinal cord interneurons
Somatic Motor Nuclei of the Anterior Gray Horns
Contain the cell bodies of lower motor neurons
Autonomic Motor Nuclei of the Lateral Gray Horns
Contain the cell bodies of preganglionic neurons
Spinal Reflexes
Gray matter is the site of integration for spinal reflexes.
Reflex integration centres:
* receive & interpret incoming sensory input
* decide on & generate the motor output that causes the reflex response
These reflexes rapidly and involuntarily stimulate:
- skeletal muscle contractions = somatic reflex (e.g. patellar reflex)
- smooth muscle contractions of visceral organs (e.g. bladder) or gland secretions = autonomic reflex
White Matter ”conduction highway”
Spinal Cord Tracts of the White Matter
Fasciulus gracilis
Fasciulus cuneatus
Lateral spinothalamic
anterior spinocerebellar
posterior spinocerebellar
Anterior spinothalamic