Thread by @drokane

Mini Neuro Tweetorial #2 : Cord and Cauda
Spinal Cord
👉 Starts at Foramen magnum.
👉 Ends at lower edge of L1 vertebra
👉 So can LP below L1.
👉 Whole cord C8/T12/L5/S5/C1 31 nerves.
👉 7 Cervical vert but 8 nerves. C1 goes over the top.

👉 Cord much shorter than the canal.
👉 Cord has corticospinal tract (CST)
👉 CST is Upper motor neuron (UMN).
👉 CST Synapses at anterior horn cell to form
👉 Motor Roots which are Lower motor neuron (LMN)
👉 These exit cord anterior. Forms root.
👉 Exits canal at foramina

👉 In cord we correlate clinical findings primarily with dermatomal and myotomal level. Secondarily with side.
👉We need to know our myotomal /dermatomal landmarks
👉 Highest dermatome ? C2 back of head
👉 Lowest dermatome ? S5 Perianal

See Derm maps. Some think it is head to foot - it is not
Back of head: C2
Shoulders: C4
Lateral arm: C5/6
Fingers: C7 Middle finger
Medial arm: C8/T1
Chest: T4 nipple
Abdomen: T10 umbilicus L1 inguinal
Front legs: L2/3/4/5
Sole feet: S1
Back legs: S2/3
Perianal /Genital: S4/5

Myotomal maps: I won't do details here but generally
👉C5-T1 Upper limb
👉L1-S2 Lower Limb
👉S3-5 Anal sphincter, Bowels/Bladder

Cord Injury at T4. No motor or sensory below T4 MOTOR LEVEL
👉 Bilateral weak legs but normal arms
👉 Increased tone both legs and clonus
👉 Upgoing plantars
👉 Increased ankle and knee reflexes

In some cases acute spinal shock can cause initial pattern to be flaccid areflexia

SENSORY LEVEL
👉 Loss of sensation everywhere below the nipple both sides chest, abdomen, legs, buttocks
👉 Loss of sensation bowels/bladder
AUTONOMIC
👉 Labile Blood pressure, tachycardia, hypotension
SPHINCTERS
👉 Urinary retention. Bowel and bladder dysfunction

A Cord lesion at or above T1 will cause UMN upper limb signs in both arms and legs. The higher it goes will lead to a quadriplegia. A high cervical cord lesion can cause difficulty with breathing in addition.

Cauda Equina
This is the bundle of nerve roots which have exited the cord which has ended at L1 and sit in the lumbar cistern awaiting their foramina through which to exit. Contains sensory/motor nerve roots to L2-5, S1-5 and C1. These are Lower motor neurons.

What if there is a knife/bullet/disc/tumour/clot at L3 which compresses this bundle of nerve what will we find
👉 Flaccid bilateral weak legs
👉 Reduced tone areflexia, absent plantars
👉 Weak anal bladder sphincters with incontinence
👉 Lack sensation saddle area anus genitals

PS Brown Sequard: hemisection of cord - 1 motor pathway 2 sensory: Cord lesion
👉I/L UMN lesion below up plantar, clonus, inc reflex
👉I/L Vibn Propn loss below lesion (Post columns)
👉C/L Pain temp loss below lesion (spinothalamic)

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