Spinal Cord and Spinal Nerves (Ch 16) Flashcards
What are the functions of the spinal cord?
- sensory/motor innervation of body
- two way conduction pathway for signals between brain and body
- major center for reflexes (don’t need to go to brain to process)
Spinal Cord location
extends from foramen magnum to level of L1/L2
How many pairs of spinal nerves are there?
31
What are the cervical and lumbar enlargements?
enlargements for nerves of upper/lower limbs
conus meullaris
the inferior end of the spinal cord (in L1 and L2)
cauda equina
nerve roots at inferior end of vertebral canal
“horses tail”
film terminale
long filament (of pia mater) that extends past conus medullaris and attached to coccyx "anchor"
deep gray matter of spinal cord
forms “H” at center
- posterior (dorsal) arms of “H” are dorsal horns: contain sensory neurons
- anterior arms of “H” are ventral horns: contain motor neurons
What is the spinal cord protected by?
bone, meninges, and CSF
dural mater of spinal cord
spinal dural sheath
epidural space
filled with fat and veins
denticulate ligaments
anchor spinal cord to dura mater (pieces of pia mater, pierce the arachnoid, and anchor to dura)
Epidural Nerve Block
needle between L4-L5 permits injection of anesthesia into epidural space without risk of damage to spinal cord
-cauda equina pushed out of way if necessary
Anterior (Ventral)/Posterior (Dorsal) Roots
- dorsal horns receive info from sensory neurons (cell bodies located in the dorsal root ganglia)
- signals 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/ventral roots merge to form spinal nerve
- has sensory/motor axons
- exits vertebral column at intervertebral foramina
- immediately splits into dorsal/ventral rami
Dorsal (Posterior) and Ventral (Anterior) Rami
- both carry sensory/motor fibers
- ventral rami: innervate most of body including trunk/limbs
- dorsal rami: innervate small portion of back
Reflexes
- very simple neuron chain
- basic structural plan of NS, usually preprogrammed
- exclude brain: rapid, automatic, unlearned motor response to stimulus
- can be somatic (hot stove) or visceral (vomiting)
- signal comes in and synapses at interneurons in spinal cord
Dermatomes
area of skins applied by a single spinal nerve
- all spinal nerves except C1
- numbness can pinpoint a spinal nerve injury
- referred pain: when pain from an organ is mistakenly referred to as a dermatome (ex. appendicitis)
Nerve Plexuses
a network of nerves formed only by VENTRAL RAMI
- all spinal nerves expect T2-T12 branch and rejoin
- each muscle in a limb receives it’s nerve supply from more than one spinal nerve –> damage to one spinal nerve cannot paralyze limb
- -> four different plexuses (cervical, brachial, lumbar, sacral)
Cervical Plexus
C1-C5
- ventral rami of first 4 cervical nerves
- most branches innervate skin
- some motor to anterior neck
- phrenic nerve
phrenic nerve
*in cervical plexus
receives fibers from C3, C4, C5 and innervate diaphragm for respiration
“C3, C4, C5…keep the diaphragm alive”
Brachial Plexus
C5-T1
- partly in neck, partly in axilla
- gives rise to most nerves of upper limb
- mixing of ventral rami of C5-C8 and most of ventral ramus of T1
What are the components of the brachial plexus?
- Ventral Rami (“roots”)
- Trunks
- Divisions
- Cords
- Branches
Anterior Division of Brachial Plexus
nerves that innervate anterior compartment muscles of upper limb and skin
Posterior Division of Brachial Plexus
nerves that serve posterior compartment muscles of upper limb and skin
What are the terminal branches of the brachial plexus?
- Musculotaneous Nerve
- Ulnar Nerve
- Median Nerve
- Axillary Nerve
- Radial Nerve
Musculotaneous Nerve
- terminal branch of brachial plexus
- sensory innervation: skin sensation for lateral forearm
- motor innervation: anterior compartment of arm
Ulnar Nerve
*terminal branch of brachial plexus
“Funny Bone Nerve”
-sensory innervation: skin of medial hand, medial digit 4, and all of digit 5
-motor innervation: flexors and intrinsic hand muscles
Median Nerve
- terminal branch of brachial plexus
- sensory innervation: skin of lateral palm, digits 1-3, and lateral side of digit 4
- motor innervation: anterior compartment of forearm (with ulnar), intrinsic muscles of lateral palm, and muscles that oppose the thumb
Median Nerve Lesion
“Carpal Tunnel Syndrome”
- affects motor nerve –> thenar muscles
- pain/numbness in lateral palm
- form compression of nerve near hand
Axillary Nerve
- terminal branch of brachial plexus
- sensory innervation: shoulder joint and skin on part of deltoid
- motor innervation: teres minor and deltoid
Radial Nerve
- terminal branch of brachial plexus
- sensory innervation: skin over doors-lateral arm, forearm, and hand
- motor innervation: posterior compartment of arm and forearm (extensors)
What are divisions of the Lumbar Plexus?
L1-L4
- Femoral Nerve
- Obturator nerve
Femoral Nerve
- divison of lumbar plexus
- sensory innervation: skin of antero-medial thigh, skin of medial leg/foot
- motor innervation: muscles of anterior thigh (quads, thigh flexors/leg extensors)
Obturator Nerve
- division of lumbar plexus
- sensory innervation: skin of medial thigh
- motor innervation: muscles of medial thigh (adductors - adductor longus, gracilis, adductor magnus/brevis)
Sciatic Nerve
- part of sacral plexus
- tibial nerve + common fibular nerve together in a common sheath
- longest/thickest nerve of the body
- serves all of lower limb except anterior/medial thigh
What are the nerves of the sacral plexus?
- Sciatic Nerve
- Common Fibular Nerve
- Tibial Nerve
Common Fibular Nerve
- part of sacral plexus (posterior division)
a. k.a. peroneal nerve - sensory innervation: skin of antero-lateral leg, skin of dorsal on foot
- motor innervation: muscles of anterior leg (deep fibular) and muscles of lateral leg (superficial fibular)
Fibular Nerve Lesion
= “foot drop”
- common fibular nerve is cut/bruised –> affects muscles
- most commonly injured due to superficial location on lateral knee
Tibial Nerve
- part of sacral plexus (anterior division)
- sensory innervation: skin of postero-lateral leg, skin of sole of foot (subdivides into plantar nerves)
- motor innervation: muscles of posterior thigh/leg + adductor magnus (w/obturator) and biceps femurs (w/common fibular)
Nerve Lesion: Phrenic
motor innervation: diaphragm
deficit: inability/difficulty breathing
Nerve Lesion: Axillary
motor innervation: deltoid
deficit: difficulty abducting arm to 90 degrees
Nerve Lesion: Musculotaneous
motor innervation: anterior arm
deficit: weakness flexing elbow
Nerve Lesion: Median
motor innervation: anterior arm/thumb
deficit: weakness flexing wrist, difficulty opposing thumb, carpal tunnel syndrome
Nerve Lesion: Radial
motor innervation: posterior arm/forearm
deficit: difficulty extending elbow, wrist drop
Nerve Lesion: Ulnar
motor innervation: deep hand muscles
deficit: can’t adduct/abduct fingers
“funny bone”
Nerve Lesion: Femoral
motor innervation: anterior thigh muscles
deficit: walking problems, knee buckles
Nerve Lesion: Tibial
motor innervation: posterior thigh/leg
deficit: shuffling gait, difficulty with plantar flexing
Nerve Lesion: Common Fibular
motor innervation: anterior/lateral leg
deficit: foot drop
gray commissure
- in gray matter of spinal cord
- composed of unmyelinated axons crossing from one side of CNS to the other
central canal
- in gray matter of spinal cord
- central cavity (hollow) of spinal cord
