Chapter 16: Spinal Cord

Function of Spinal Cord

- Sensory and motor innervation of body -two way conduction pathway for signals between body and brain - major center for relec

Spinal Nerves

1)Dorsal and ventral roots merge to form spinal nerve 2)Spinal nerve has both sensory and motor axons 3)Exits the vertebral column at intervertebral foramina 4) Immediately splits into dorsal and ventral rami

How many pairs of Spinal Nerves?

31 pairs, part of the PNS even though the spinal cord itself is part of the CNS

What is the connection between the rami communicantes and the sympathetic chain ganglion?

Additional rami, called the rami communicantes, are also associated with spinal nerves. These rami contain axons associated with the autonomic nervous system (ANS). Each set of rami communicantes extends between the spinal nerve and a ball-like structure called the sympathetic trunk ganglion. These ganglia are interconnected and form a beaded necklace-like structure called the sympathetic trunk.

What is needed for a reflex?

All reflexes have similar properties: A stimulus is required to initiate a reflex. A rapid response requires that few neurons are involved and synaptic delay is minimal. A preprogrammed response occurs the same way every time. An involuntary response requires no conscious intent or preawareness of the reflex activity. Thus, reflexes are usually not suppressed.

What are spinal cord horns?

Anterior horns primarily house the cell bodies of somatic motor neurons, which innervate skeletal muscle. Lateral horns occur in the T1-L2 parts of the spinal cord only. The lateral horns contain the cell bodies of autonomic motor neurons, which innervate cardiac muscle, smooth muscle, and glands. Posterior horns are the left and right posterior masses of gray matter. The axons of sensory neurons and the cell bodies of interneurons are located in the posterior horns.

Origin and Ending of Spinal Cord

Forman Magnum-> L1 or L2 - in children ends at around L3 or 4

Gray Mater: Spinal Cord

H surrounded by white mater - unmyelinated axons cross one side of CNS to another - Dorsal (posterior)- dorsal horns - Ventral (anterior)- ventral horns

Spinal Cord

Part of the CNS

What are spinal roots? What is contained in each? How do these relate to spinal nerves?

The posterior root is the afferent sensory root and carries sensory information to the brain. The anterior root is the efferent motor root and carries motor information from the brain. The posterior root contains the cell bodies of sensory neurons. The anterior (ventral) root contains axons of motor neurons that conduct nerve impulses from the CNS to other parts of the body such as the muscles. anterior root and posterior root unite within the intervertebral foramen to become a spinal nerve

What is the posterior / anterior rami? Where do they innervate?

The rootlets extend out of the spinal cord medially and combine to form roots. The roots combine to form the spinal nerve and then they split apart again and are now called rami (ramus for singular). The dorsal root is posterior to the ventral (front) root. The posterior rami innervate the deep muscles of the back for motor control, such as the erector spinae and also a horizontal strip of skin for sensory input. The anterior rami in the thoracic region are known as the intercostal nerves.

Dorsal Horns (Posterior Roots)

recieve information from sensory neurons via dorsal roots

Ventral Horns (ventral roots)

send out info to skeletal muscle - motor neurons travel via ventral roots