10.2.96
neurology clinical correlation.
dr. betsy someone

showing film from 1957 which shows results of transecting various 
peripheral nerves. keep in mind that we all have peripheral nerves and 
they're all pretty similar. many of these nerves are palpable in the live 
animal and in ourselves. 

functional anatomy of nerves to the appendages.

all nervous activity is regulated by CNS - brain and spinal cord. but the 
peripheral nerves are what send info to and from CNS from rest of body.

typical spinal nerve- ventral and dorsal branch. 

nerve has large number of nerve fibers and cells. these fibers are of two 
kinds....afferent sensory and efferent motor fibers. any serious injury 
to peripheral nerve will affect sensation and motion.

note that all animals regardless of species have similar nerve anatomy.

each nerve controls a specific group of muscles and innervates a 
particular cutaneous area.

nerve supply to appendges of dog:

brachial plexus: formed by ventral branches of last 3 cervical and first 
two thoracic nerves. nerves of forelimb arise here.


suprascapular nerve courses cranial to neck of scapula, supplies 
supraspinatus and infraspinatus, which extend shoulder. these muscles are 
mainly supportive. transection of this nerve doesn't result in much 
clinical pathology. but the muscles do atrophy and the spine of the 
scapula becomes prominent. atrophy of these muscles in the horse is 
called sweeny.

radial nerve: functional key to pectoral appendage.. spirals around 
humerus supplying elbow extensors, then branching into deep branch, 
supplying extensors of carpus and digits, and superficial branch, sensory 
to dorsal and lateral forearm and dorsal paw. transecting superficial and 
deep branches causes animal to knuckle onto dorsal paw. elbow can be 
extended, however. this kind of injury can be seen in fx humerus cases. 
complete radial nerve paralysis causes total inability to extend all 
joints of forelimb, except shoulder. elbow can be neither extended nor 
fixed, totally non wt bearing.

musculocutaneous nerve: supplies two flexors of elbow: biceps brachii and 
brachialis. joins median nerve. cutaneous branch is sensoy to medial side 
of forearm. transection produces only a slight straightening of the angle 
of the elbow.

ulnar nerve and median nerves work as a unit. together they supply all 
flexors of carpus and digits and are sensory to carpal, metacarpal and 
digital pads. ulnar nerve sensory to skin on caudal forearm and lateral 
5th digit.  transection of median nerve causes no change in gait, and 
sensory fibers still work on lat 5th digit. transection of ulnar nerve 
only also doesn't change gait.
when both ulnar and median nerves are severed, sensation is lost, and 
there is a slight sinking of carpus and fetlock due to loss of muscle 
tone.

lumbosacral plexus: formed by ventral branches of last four lumbar and 
first three sacral nerves. various named nerves of hindlimb arise here.

obturator nerve is purely a motor nerve. courses down shaft of ilium, 
vulnerable to injury during parturition. Goes through obturator foramen 
and supplies adductor muscles of thigh. obturaor nerve paralysis causes 
limb to slide laterally when dog walks on smooth surface.

femoral nerve functionally key nerve. supplies part of iliopsoas, and is 
sole innervation to extensors of stifle. the saphenous branch is sensory 
to medial side of thigh stifle leg and paw. In femoral nerve paralysis, 
sensation to those areas is lost, and animal cannot extend or fix stifle 
to bear wt. animal must hop, basically. paralyzed leg cannot bear wt.

peroneal nerve is terminal branch of sciatic. supplies flexors of hock 
and extensors of digits, and is sensory to lateral hock and dorsal paw. 
paralysis causes knuckling over to dorsal aspect of paw, and straightened 
hock. peroneal nerve is superficial as it crosses lateral side of stifle 
and is vulnerable to injury.

tibial nerve is second of two terminal branches of scitatic. supplies 
motor to extensors of hock and flexors of digits. sensory to plantar side 
of hind paw. transection produces anesthesia in that region, and motor 
paralysis produces flexion of hock and overextension of digits. injecting 
irritants into caudal thigh can affect tibial and peroneal nerves.

sciatic nerve is vulnerable to pressure injury w/in pelvis. brances into 
peroneal and tibial as noted above. sciatic supplies caudal thigh muscles 
which extend hip and flex thigh. sensory to caudal and lateral leg. 
transection produces anesthesia below stifle except medially. all flexors 
below stifle are lost, only extensors are functional. leg can bear wt if 
cut, because femoral nerve fixes stifle. dog walks on fixed stifle 
w/knuckled paw.

----end film----

what can go wrong in peripheral nervous system? 

injuries. animals sometimes get limbs caught in something,and when they 
pull away, they tear nerve roots out of spinal cord. nerve root avulsion 
causes loss of all nerves from brachial or lumbosacral plexus. if this 
happens, muscles atrophy quite quickly. limb loses cutaneous sensation, 
and becomes non wt bearing. limb is flaccid, paralyzed, anesthetic, and 
nonfunctional. this happens with HBC dogs a lot. partial nerve loss can 
preserve function, but the whole plexus is a Bad Thing.

if examining hind limb, and you want to check femoral nerve, which toes 
do you pinch? the medial toes. the lateral toes would demonstrate sciatic 
nerve competence.

showed us EMG. animals won't tolerate this test so must be anesthetized. 
denervated muscles will show abnormal activity.

anesthetized animal shows "electrical silence" while denervated muscle 
will show wild peaks, indicating polarizing/depolarizing activity which 
shouldn't be happening in an anesthetized animal.


realize that post plexus peripheral nerves are axons. myelinated nerve 
fibers. generally mixed nerves, containing ventral and dorsal root 
fibers. cell bodies live in CNS.

motor neurons in ventral horns of grey matter of cord. sensory cell 
bodies are OUTSIDE of the cords. in root avulsions, tear out often comes 
between sensory cell body and cord. animal still loses sensory 
capability, but sensory nerve cell body stays alive. so, conduction 
velocity tests on sensory nerve can be misleading. need to look at 
clinical signs. now, if motor nerve conducts, you know something.