Post on 22-Apr-2022
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)