Spinal Cord & Sensory Pathways Flashcards
Spinal Cord Basics
Spinal Cord: runs from the brainstem to L2 vertebra
- runs in the spinal column of the vertebrae
- ends at cons medullaris then rootlets continue on to the cauda equina
- the filum terminale anchors the SC to the pelvis through Pia Mater
on a cross section view…
The middle of the SC = grey matter (cell bodies)
the edges of the SC = white matter (cell tracts/axons)
Ventral Horn (anterior) = Motor Neurons here
Dorals Horn (posterior) = Sensory Neurons here
Lateral Horn = Autonomic Neurons here
remember, the neuronal bodies are the grey matter aka the horns –> so the horns contain the bodies of these specific types of neurons whether its sensory (dorsal) or motor (ventral)
what are the denticulate ligaments
what is the filum terminale
denticulate ligaments: pia mater pieces between dorsal and ventral rootlets: anchor the SC to the arachnoid mater
think = pia mater which anchors laterally
Filum Terminale: the end of the SC which anchors the SC to the coccyx via pia mater
think = pia mater anchoring posteriorly
Cervical Vertebrae
C1 and C2 Specifics
Cervical Nerves
Cervical Vertebra: C1-C7
C1 = atlas
C2 = Axis (with dens/odontoid process) which is what C1 swivles on
all vetebra
- spinous process
- lamina connecting to the transverse processes
- transverse process connecintg to the body via pedicles
- articular processes: connect above and below pieces together
Cervical Nerves
- C1- C8 (C1 exits ABOVE the C1 vertebra, then C8 exists above T1 below C7)
- the rest of the nerves (T, L) exit below the same numbered vertebrae
- cervical nerves: exit via the superior vertebral notch)
- all otehr nerves exit via the inferior vertebral notch
How do spinal nerve roots exit the SC and vertebrae
Spinal Cord
- exits to the dorsal or ventral rootlets
- come together to form either dorsal or ventral roots (dorsal = sensory, ventral = mixed)
- the dorsal root becomes the dorsal root ganglion (collection of cell bodies from peripheral sensory nerves) because these carry sensory nerves, which synapase to allow for peripheral nerves to transfer their information to the central nerves)
- becomes a spinal nerve (which now is mixed, motor and sensory innervation)
- spinal nerve then becomes dorsal or ventral rami (dorsal going to the back) (ventral going to the front and limbs)
ventral rami v dorsal rami
Mixed nerves off of spinal cord nerves (so its a mixed of motor and sensory and ANS)
ventral = nerves that go to supply the upper and lower limbs, and the front of the trunk
plexuses include
- cerivcal (C1-C4)
- brachial (C5-T1)
- Lumbar (T12- L4)
- Sacral (L5-S4)
Thoracic nerves still considered ventral rami but dont form plexuses
Dorsal Rami (rarely named)
- supply the deep back mucles, joints and skin on back
Blood Supply to the SC
what arteries
what veins drain
Anterior SC
- anterior spinal artery
- arising from the vertebral arteries up in the cervical spine, so the ASA travels down the anterior aspect of the SC
- gives rise to sulcal arteries which go interior within the SC
Posterior SC
- Posterior Spinal Arteries (2 of them)
- arise from the vertebral or the PICA
Anterior and Posterior Segmental Meduallar Arteries
- also supply the SC and enter the SC via spinal nerve root entrances
Venous Drainage
- Venae Commitantes = small veins which have same name as the artery they accompany
- can be 2-3 spinal veins for each artery
- they sit close, and use the pulsaion of the artery to help propel the blood
Described the Sensory Spinal Tracts and their somatotopic organization in the spinal cord
Sensory Tracts: will travel from the SC up to the Brain (delivering the sense they experienced to the brain to process)
if it is traveling in the Dorsal Column it is a sense of (VIBRATION, PRESSURE or PROPRIOCEPTION) aka discrimiative touch
- the dorsal column tract sits in the dorsal SC –> with the lower extremity signals being medial (LE = faciculuc Gracillis) , and the upper extremities being lateral (UE = faculus cuneatus)
- this pathway travels up the spinal cord, synpases and crosses over at the level of the medulla
if it is traveling in the Spinothalamic tract (anteriolateral system) it is the sense of (PAIN OR TEMPERATURE) or light touch (but thats both sensory tracts)
- the spinothalamic tract is organized with the UE being medial, and the LE being lateral
- this pathway travels with the sense entering the SC and IMMEDIATELY crossing over to the contralateral side and synpasing right THERE then traveling up to the brain
what is contained within the dorsal root ganglion
the cell bodies of sensory nerves: those which detect nociception, mechanreceptors, visceral afferent nerves
- these are sensory nerves, that then deliver their sensation to the nerves of the CNS (spinothalamic or dorsal column)
- dorsal column: travel then cross and synapse in teh medulla
- spinothalamic: cross and synpase in the SC
3 types of sensory/afferent neruons
the receptors for the skin (mechanoreceptors, nociceptors, chem and photo)
- general sesnory afferent: skin bones and soft tissues sensory
- visceral afferent: from organs, and blood vessels of sensory information
- special afferent: the special sense; vision, hearing, smell and vestibular
Receptors of Sensation
- chemoreceptors: sense smell
- Photoreceptors: sense vision
- Mechanoreceptors: touch, pressure, vibrationand proprioception
- Nociceptors: pain
- thermoreceptors: temperature
the cutaneous receptors in the skin are mostly in the dermis layer
- pacinian: deep pressure and ibration
- Meissner: light touch
- Ruffini: deep pressure
what is the difference between temporal and spatial summation of neronal signals
Spatial Summation: input optained from a greater surface area
- all collection onto 1 neuron to take the information up
Temporal Summation: rapid sequence input at the same neuron collect then send one signal out
can lead to false neurologic testing because both of these patterns lead to an increase AP traveling down the neuron
Dermatomes
what are they
generally what areas
Dermatomes: areas of the body which are skin sensory innervated by speicifc and known nerve levels
T4 = nipple line
T10 = belly button
ARM
- C6 = deltoid and down the arm and thumb
- C7 = first two fingers
- C8: ring and pinky
- T1: up the arm to armpit
L3: never goes below the knee
L5: down the knee to the toes
S1: to the pinky toe and lateral ankle and back of calf laterally
S2: medial posterior calf and posterior medial leg to butt
difference between Radicular Pain and Radiculopathy and Referred Pain
Radicular Pain
- sharp and shooting pain which usually follows a special spinal nerve distribution
- usually a result of hte DRG between the vertebrae that is inflammed or pinched
Radiculopathy: a “progression” of pain in the sense that its a little worse because its compressing the nerve root/spinal nerve in its intierity
- thus, you may get the numbness and tingling from teh sensory issue, but you also can get muscle atrophy, wasting due to the lack of motor innervation
- can lead to atrophy and paralysis
Referred Pain
- areas of pain which are not the actual source of pain
- the actual source of pain is injury to areas with pain fibers
- but because these fibers travel into the SC and into the dorsal horn, where other sensory fibers are joining, the brain cant process “which” nerve brought the pain signal
- so it guesses and you can get pain within the same region of the nerve
- because pain fibers synpase immedaitely in the spinal cord at that level
how to localize a lesion based on symptoms
motor and sensory
if the lesion occurins abvoe the level of the deccasation: the symptoms will be on the contralateral side (in upper and lower limbs)
ex. occlusion of the left MCA at the hand area: inability to pass sensory or motor information: resulting in right sided motor and sensory deficts
if the lesion is occuring below the level of the deccasaion : the symptoms will be on the SAME side as the lesion
ex. Right SC lesion at T12: means that there will be sensory and motor losses on the right side lower legs
Fast v Slow Pain fibers
Pain fibers: sensory: spinothalamic tract: cross and synpase at the level of the SC quickly
Fast FIbers: a delta(myleinated) fibers
- pass their signal via glutamate
- synpase on the VPL nucleus in thalmus
- travel to cortex
Slow Fibers: c-fibers (unmyleinated)
- Substance P is the NT used to pass the signal
- travel to the thalmus but synpase on the intralaminar nucleli
LP and Epidural
LP: sample CSF, admin anesthesia
- at the L3/L4 or L5/L5 level
for labor and surgery epidural: L3 level to L5
spinal anesthias is quicker acting than the epidural relief
