Lower Motor Neurons and Spinal Reflexes

Tract

axons within the central nervous system

What makes voluntary motor movement

UMN

True or False: The more motor units activated the stronger the force f contraction

TRUE

How does sensory information travrl

through the dorsal horn

Reflexes

involuntary or automatic action produced by CNS pathways in response to particular stimuli

What do reflexes test?

all portions of the reflex arc

List the clinical subdivisions od the spinal cord.

C1-C5 = neck

C6 - T2 = thoracic limb

T3-L3= Thoracolumbar

L4-S1 = Pelvic Limb

S1-S3 = Sacrocaudal

Monosynaptic Reflex

aka myotactic reflexes, muscle strecth reflex, or deep tendon reflex

• sensory axon synapses directly onto the LMN

Polysnaptic Neuron

multiple synaptic contacts within the CNS between sensory input anf LMN output where interneurons are necessary

What is the most reliable reflex?

Patellar Reflex

Patellar Reflex: nerve, segment, response

Nerve: femoral

Segment: L4-L6

Response: single quick extension of the stifle

List all the Myotactic reflexes and what nerve they test

Patellar Reflex

Biceps Reflex: segment C6-C8 → musculocutaneous nerve

Triceps Reflex: C7-T1 → radial nerve

Extensor Carpi Radialis Reflex: C7-T1 → radial nerve

Cranial Tibial: L6-L7 → Fibular / Peroneal branch of sciatic

Gastrocnemius: L7-S1 → Tibial Branch of Sciatic

What does 0 mean when grading reflexes?

Absent

What does 4 mean when grading reflexes?

Hyperreflexive

What are examples of Polysnaptic Reflex Arcs

• Withdrawal

• Cutaneous trunci

• Perineal Reflex

what nerves and segments does the withdrawal reflex test?

Throacic: all nerves and C6-T2

Pelvic: sciatic nerve and femoral (digit 1); L6-S1

If a crossed extensor reflex is present, it indicates _____

Chronic UMN or UMN Tract Lesion

True or False: A normal patient in lateral recumbency should not have the crossed extensor reflex.

TRUE

What does the crossed extensor reflex test?

Ipsilateral flexion and contralateral extension

Where is the sensory nerves for the cutaneous trunci reflex?

2 vertebral bodies in front of where you are pinching

What motor nerve is involved in the cutaneous trunci reflex?

Lateral Throacic Nerve (C8-T1)

What nerves and spinal segments are involved in the perineal reflex?

Nerves: Pudendal (sensory) & Caudal rectal branch of pudendal (Motor)

Segments: S1-S3

para-

back legs

tetra-

all four limbs

mono-

one leg

hemi-

one side

paretic

decreased but visible motor

-Plegic

NO MOTOR SEEN

What do you specify for a paretic patient versus a plegic patient?

Paretic: Ambulatory/not

Plegic: DP±