Spinal Cord and Plexuses (Ch. 16) Flashcards
What is the spinal cord a part of (CNS or PNS)?
CNS
What are fxns of the spinal cord?
Sensory and motor innervation of body
Two-way conduction pathway for signals between body and brain
Major center for reflexes
Where does the Spinal Cord travel?
Extends from foramen magnum (occipital bone) to level of L1 or L2 (lumbar vertebrae)
How many pairs of spinal nerves are there (part of PNS)?
31 pairs of spinal nerves
What are the 2 enlargements of the spinal cord? Why do they exist?
Cervical and Lumbar enlargements for nerves supplying upper and lower limbs
What is the inferior end of the actual spinal cord?
Conus Medullaris
The nerve roots at the inferior end of the vertebral canal is called the ______ _______?
Cauda Equina
What is the Filum Terminale?
A long filament the extends past Conus Medullaris and attaches to coccyx
What protects the spinal cord?
Bone, meninges, and CSF
What is the Epidural Space?
Filled with fat and veins
Are the subdural space, arachnoid mater, subarachnoid space, and pia mater the same in the spinal cord as the brain?
Yes
What are the Denticulate Ligaments?
Anchor spinal cord to dura mater
Where is an Epidural Nerve Block inserted? Why? What is it used for?
Needle between L4 and L5 vertebrae permits injection of anesthesia into epidural space without risk of damage to spinal cord. The Cauda Equina gets “pushed” out of the way if necessary.
Epidural. Commonly used during childbirth
Spinal Cord Gray Matter
Gray matter forms an “H,” surrounded by white matter
Gray commissure is composed of unmyelinated axons crossing from one side of the CNS to the other
Central canal is the central cavity (hollow) of the spinal cord
Dorsal (posterior) arms of H are dorsal horns
Ventral (anterior) arms are ventral horns
Anterior (Ventral) and Posterior (Dorsal) Roots
Dorsal horns receive info from sensory neurons (cell bodies located in dorsal root ganglia)
Signal from sensory neurons reach spinal cord via dorsal roots.
Ventral horns send out info to skeletal muscle. Signals going out to motor neurons travel via ventral roots
Spinal Nerves
Dorsal and Ventral roots merge to form spinal nerve
Spinal nerve has BOTH sensory and motor axons
Exits vertebral column at intervertebral foramina
Immediately splits into dorsal and ventral rami
Dorsal (Posterior) and Ventral (Anterior) Rami
Ventral and Dorsal Rami carry both sensory and motor fibers
Ventral rami innervate most of the body, including trunk and limbs. Dorsal rami innervate small portion of the back
Reflexes
Very simple neuron chain
Basic structural plan of NS
Reflexes EXCLUDE brain; rapid, automatic, unlearned motor response to stimulus
Can be somatic (hot stove) or visceral (vomiting)
Signal comes in and synapses at interneurons. Interneurons stimulate and inhibit as appropriate
What are Dermatomes?
Area of skin supplied by a single spinal nerve. All spinal nerves EXCEPT C1
Numbness can pinpoint spinal cord injuries
What is Referred Pain?
(Dermatomes)
When pain from an organ is mistakenly referred to dermatome.
ex: Appendicitis starts as pain in T10 dermatome
Nerve Plexuses
A network of nerves…formed by VENTRAL rami only
All spinal nerves except T2-T12 branch and rejoin
Each muscle in a limb receives its nerve supply from more than one spinal nerve…damage to one spinal nerve cannot completely paralyze any limb muscle
What are the 4 nerve plexuses?
- Cervical plexus (C1-C5)
- Brachial plexus (C5-T1)
- Lumbar plexus (L1-L4)
- Sacral plexus (L4-S4)
Cervical Plexus
Ventral rami of first 4 cervical nerves
Most branches are cutaneous sensory. Some motor to anterior neck
Phrenic Nerve receives fibers from C3, C4, and C5; innervates diaphragm for respiration
Brachial Plexus
Partly in neck, partly in axilla
Gives rise to most nerves of the upper limb.
Mixing of ventral rami of C5-C8 and most of the ventral ramus of T1
Main components:
–ventral rami, trunks, divisions, cords, terminal branches
Brachial Plexus: Number of roots, trunks, divisions; Anterior and Posterior Divisions
5 roots give rise to 3 trunks which branch into 2 divisions
Anterior Division: nerves that innervate anterior compartment muscles of upper limb and skin
Posterior Division: nerves that serve posterior compartment and skin
Brachial Plexus: C5-T1
Roots: C5-T1
Trunks: upper, middle, lower
Anterior Divisions (cords): lateral and medial
–lateral (from upper trunk) –> supplies musculocutaneous nerve
–medial (from lower trunk) –> supplies medial and ulnar nerves
Posterior Division (from middle trunk): supplies radial nerve and axillary nerve
What are the terminal branches of the Brachial Plexus?
Axillary Nerve Radial Nerve Musculocutaneous Nerve Median Nerve Ulnar Nerve
Musculocutaneous Nerve
brachial plexus
Sensory innervation: skin sensation for lateral arm
Motor innervation: anterior compartment of arm
Ulnar Nerve
brachial plexus
aka “funny bone” nerve
Sensory Innervation: skin of medial hand, medial side of digit 4, all of digit 5
Motor Innervation: flexors and intrinsic hand muscles
Median Nerve
brachial plexus
Sensory Innervation: skin of lateral palm and digits 1-3 and lateral side of digit 4
Motor innervation: anterior compartment of forearm (w/ ulnar); intrinsic muscle of lateral palm, muscles that oppose the thumb
Median Nerve Lesion
aka Carpal Tunnel Syndrome
Affects motor nerve to thenar muscles
Pain/numbness in lateral palm
From compression of nerve near hand
Axillary Nerve
brachial plexus
Sensory Innervation: shoulder joint and skin on part of deltoid
Motor innervation: Teres Minor and Deltoid
Radial Nerve
brachial plexus
Sensory Innervation: skin over dorso-lateral arm, forearm, and hand
Motor Innervation: posterior compartment of arm and forearm (extensors)
Lumbar Plexuses
Ventral Rami: branches into Iliohypogastric, Ilioinguinal, Genitofemoral, and Obturator
Anterior Division
Posterior Divison: branches into Lateral Femoral Cutaneous and Femoral
Femoral Nerve
lumbar plexus
Sensory Innervation: skin of antero-medial thigh; skin of medial foot
Motor Innervation: muscles of anterior thigh (thigh flexors, leg extensors [ex: quadriceps femoris])
Phrenic Nerve
cervical plexus
Phrenic Nerve receives fibers from C3, C4, and C5; innervates diaphragm for respiration
“C3, C4, C5 keep the diaphragm alive”
Obturator Nerve
lumbar plexus
Sensory Innervation: skin of medial thigh
Motor Innervation: muscles of medial thigh
*Adductor Magnus innervated by both Obturator and Tibial Nerves
Sacral Plexus: Sciatic Nerve
Tibial Nerve and Common Fibular Nerve together in common sheath = “Sciatic Nerve”
Longest and thickest nerve of body. Senses all of lower limb except anterior/medial thigh
Sacral Plexus: L4-S4; Anterior Division
Ventral Rami: L4-S4
Anterior Division: Tibial and Pudendal
Posterior Division
Tibial Nerve
Anterior compartment of sacral plexus
Sensory Innervation: skin of postero-lateral leg, skin of sole of foot (subdivides into plantar nerves)
Motor Innervation: muscles of posterior thigh and muscles of posterior leg
–plus Adductor Magnus (w/ Obturator N.) and Biceps Femoris (w/ Common Fibular N.)
Sacral Plexus: L4-S4; Posterior Division
Ventral Rami: L4-S4
Posterior Division: Common Fibular, Superior Gluteal, Lumbosacral Trunk, Inferior Gluteal
Anterior Compartment
Common Fibular Nerve
Posterior compartment of sacral plexus
Sensory Innervation: skin of anterolateral leg, skin on dorsum of foot
Motor Innervation: muscles of anterior leg (deep fibular), muscles of lateral leg (superficial fibular)
–Common Fibular N. also innervates Biceps Femoris (w/ Tibial N.)
Fibular Nerve Lesion
Foot-Drop
Fibular Nerve = Peroneal Nerve
What is the longest and thickest nerve of the body?
Sciatic Nerve
The Sciatic Nerve serves all of the lower limb except _____?
Anterior/medial thigh
