Page 1078 - Small Animal Internal Medicine, 6th Edition

1050 PART IX Nervous System and Neuromuscular Disorders

VetBooks.ir Greater

trochanter

Ischial
tuberosity

C
A B

FIG 58.14
Assessing the sciatic nerve and spinal cord segments L6-S2. Pelvic limb withdrawal reflex:
pinching the toe (A) results in limb flexion (B). Assess flexion in all of the joints of the
limb. It may be necessary to apply a forceps to the nail base to provide adequate
stimulation. (C) Sciatic reflex: striking the sciatic nerve in the notch between the greater
trochanter of the femur and the ischial tuberosity results in limb flexion.

A B

FIG 58.15
Thoracic limb withdrawal reflex. Pinching the toe (A) results in limb flexion (B). Assess
flexion in all the joints of the limb.

limb opposite the one being stimulated is termed a crossed response should occur during digital rectal examination. The
extensor reflex. The presence of this reflex in a paralyzed bulbourethral reflex causes anal sphincter contraction in
animal or an animal that is not trying to rise or get away response to gently squeezing the bulb of the penis or the
suggests that there is a UMN lesion to the limb being vulva. LMN damage to the pudendal nerve or the S1-S3
evaluated. spinal cord segments will cause a loss of both of these
reflexes, urinary incontinence (LMN bladder), loss of tone
Perineal Reflex and Bulbourethral Reflex in the internal and external anal sphincters, and resultant
The perineal and bulbocavernosus reflexes are used to assess anal dilation and fecal incontinence.
the pudendal nerve (sensory and motor) and sacral spinal
cord segments S1-S3. In the perineal reflex the perineal skin Cutaneous Trunci Reflex (Panniculus)
is pinched with a hemostat, causing the anal sphincter to Pinching the skin of the dorsum causes a reflex contraction
contract and the tail to ventroflex (Fig. 58.16). The same of the cutaneous trunci muscles bilaterally, producing a