Spinal Cord and Peripheral Nerves

General Objectives:

1. Be able to describe the nervous and protective components of the spinal cord. 2. Be able to identify the different plexuses in the body and the major peripheral nerves

arising from those plexuses. 3. Be able to identify the microscopic portions of the spinal cord and the function of

each region. 4. Be able to describe the components of the dorsal roots, ventral roots, and peripheral

spinal nerves. OBJECTIVE 1: SPINAL CORD NERVES & PLEXUSES MENINGES

Dura mater Arachnoid mater Pia mater

SPINAL ROOTS Afferent and efferent nerves are combined

CAUDA EQUINA “HORSE’S TAIL”

End of the spinal cord. Begins around 1st or 2nd lumbar vertebrae

L1

L2

L3

CERVICAL PLEXUS

C3-C5 Phrenic nerve arises from these rami C1- C5 Origins of the cervical plexus

BRACHIAL PLEXUS

C5 - T1 Origins of the brachial plexus - Axillary Nerve – shoulder area - Radial Nerve – posteriolateral surface of arm, forearm, and hand - Ulnar Nerve – posteriomedial surface of arm ‘funny bone’ - Median Nerve – anteromedial surface, most flexor muscles of forearm - Musculocutaneous Nerve – flexor muscles of arm and skin

LUMBOSACRAL PLEXUS Pelvic region and lower limbs, combines two plexuses: lumbar and sacral.

L1- L4 - Origins of the lumbar plexus - Femoral Nerve –quadriceps

Median femoral nerve Anterior femoral nerve Cutaneous nerve Saphenous nerve

L4- S4 - Origins of the sacral plexus

- Sciatic Nerve – largest nerve in the body Common peroneal nerve Tibial nerve

Artery

Vein

Adipose (fat)

Nerves

OBJECTIVE 2: SPINAL CORD STRUCTURES (CROSS-SECTION) NERVE FIBER DIRECTION

Afferent - impulse travels ‘to’ brain Efferent – impulse travels ‘away’ from brain to organs, tissues, etc.

GRAY MATTER ‘Butterfly’ shape neuronal cell bodies and their dendrites, short interneurons, and glial cells

Posterior (dorsal) horn (‘pointy’ side) - Sensory nerve fibers enter here (afferent nerve fibers)

Nerve fibers enter from dorsal root - Interneurons are located here (they connect incoming and outgoing nerves)

Anterior (ventral) horn (round side)

- Somatic (muscle) efferent nerve fibers and their cell bodies

Lateral horn - Autonomic efferent fibers

Gray commissure – connects the right and left sides of the ‘butterfly’

Anterior median fissure – space that dips into cord on central anterior side

Central canal – tiny central hole contains cerebral spinal fluid

(note, the central canal on this diagram is a bit smushed due to the slicing of the spinal cord)

Posterior horn

Anterior horn

Lateral horn Lateral horn

NERVE ROOTS Tiny nerves that enter the front or back of the spinal cord

Dorsal root - Dorsal root ganglion -cell bodies of sensory neurons cluster here - Neurons on dorsal root enter spinal cord via the posterior horn impulses travel

either: Up to brain via the spinal cord

or To an interneuron in spinal cord and back out the ventral root

Ventral root

- Nerve fibers going out to body -cell bodies of sensory neurons cluster here

Spinal nerves The spinal nerves that we see coming through vertebral foramen are a combination of dorsal and ventral roots, so nerve impulses travel in both directions (to & from brain)

- Fibers are both efferent (ventral root fibers) and afferent (dorsal root fibers)