Peripheral Nerves to Locate in the Cat
This dissection should be done in three phases. Make a full page illustration for each phase showing each region: the cuts made, the locations of the italicized features, and the nerves listed.
OPENING THE ABDOMEN: Pinch the ventral abdominal wall to produce a transverse fold. Snip with heavy scissors along the linea alba so that you nick the wall longitudinally. (Alternatively, use the cut made during latex injection.) Carefully insert the blunt end of the scissors into the nick and lift thesuperficial layer of abdominal muscles away from the underlying organs. Snip down to the pubis. Extend the cut up to the sternum, again taking care not to damage the underlying organs. Make two transverse cuts in the abdominal wall on each side 1) just inferior to the ribs, and 2) at the pubis (don’t cut vas deferens). Reflect the two abdominal flaps exposing the underlying organs.
OPENING THE THORAX: Slip the blunt end of the heavy scissors under the xiphoid process, lift and cut through the sternum all the way to the jugular notch. Keep the angle of the blunt tip shallow to avoid underlying organs. Insert the finger into the thorax just above the diaphragm, feel for the point of attachment just inferior to the ribs. Make lateral cuts to free it from the lower rib cage. Spread the thoracic walls. You need to crack some ribs at the vertebral column to get a good view. Note the mediastinum (the space between the lungs) contains the heart, its pericardium, the great vessels, the trachea and the thymus. Preserve connections of the vessels of the thorax for the cardiovascular lab studied next quarter.
NECK: Extend the cut up to the chin. Neck muscles adhere tightly to underlying organs. Cut and reflect the superficial muscles to expose the larynx. Along the sides, push (with some force) the outer wall of the neck to separate the superficial from the deep neck muscles (probe deeply) but do not sever the nerves. Cut the muscles just below the mandible so that you can turn out the flaps.
I. NERVES OF THE NECK AND THORAX AND THE CERVICAL PLEXUS
vagus: Find the common carotid arteries on either side of the trachea. (Here we have lifted both the R and L common carotids). The vagus nerves are attached to the carotid arteries. (See Gilbert, p 62 & 65)
cervical nerves: Find the longus capitis muscle deep behind the common carotid. It is just lateral to the cervical vertebral column. Emerging from under the longus capitis, you should see several cervical nerves emerging laterally.They form the delicate cervical plexus. (Gilbert, p. 67 & 95)
Here is a labeled view of the nerves ant features of the neck.
phrenic: There are R & L phrenic nerves, easily seen at diaphragm, attached to vena cava on R, in pleural folds on L. (p 69) They emerge from the fifth and sixth cervical nerves.
The right phrenic is attached to the inferior vena cava (upper image)
The left phrenic nerve is enfolded in the pleural folds which are attached to the diaphragm
chain ganglia: Gently push thoracic contents to R side so that you can see the descending aorta along the center of the rear abdominal wall. Note the intercostal arteries which branch off it. The thin sympathetic chain ganglia lie on top of the intercostal arteries but under the parietal pleura on either side of the vertebral column. (Gilbert, p. 69)
Here is a labeled version of the thoracic cavity with chain ganglia.
II. NERVES OF THE ARM AND THE BRACHIAL PLEXUS (Gilbert, p. 62 & 95)
If not already dissected, cut and reflect the pectoralis major, pectoralis minor, the epitrochlearis and the deltoid complex. (Do not cut underlying features.)
brachial plexus:Lies outside the rib cage below where the subclavian vein branches into the axillary and subscapular veins. (Pectoral muscles must be cut and reflected to see the brachial plexus) The brachial plexus produces the following major nerves of the arm (p. 95):
If the epitrochlearis is not already cut and reflected, do so now to see the following nerves of the arm:
radial: This is the largest nerve emerging from brachial plexus, soon plunges below biceps brachii about half way down the arm.
Here is a labeled image showing radial, ulnar and median nerves.
ulnar: This is the medial-most of the three nerves, plunges below the surface near the olecranon. You know of this nerve because when you hit it on your elbow, you call it your “funny bone.”
median: This is the smallest of the three nerves, lies between ulnar and radial nerves, follows the brachial artery into the forearm.
III. NERVES OF THE LEG AND THE SACRAL PLEXUS (Gilbert, p.98 & 99)
If not already dissected, cut and reflect the biceps femoris to reveal:
sciatic: The largest nerve in the body, it descends the latero-posterior thigh under the biceps femoris, branches to form several nerves of the leg. Note the muscular branch of the sciatic coming off at the L of the view.
Here is a labeled view of the sciatic nerve, sacral plexus, tibial and peroneal nerves.
Tibial: The larger of the branches of the sciatic, plunges between the heads of the gastrocnemius, supplies lower leg.
peroneal: The smaller branch of the sciatic, branches laterally to supply the “side of the shin.”
sacral plexus: Follow the sciatic nerve upward with a probe. Lift the muscles above it and cut the muscles which overlie it (the gluteal muscles and the piriformis). Note several component nerves. (p. 99)
The second illustration is labeled.
CLOSING UP: As always, when you have finished for the day, replace the internal organs in their proper locations, close the cat, wrap in its skin, place in the plastic bag, press out the air, seal with three turns of a large rubber band and return to the box with number to right. Wash your desk top with warm soapy water. Wash your instruments well, dry them, replace the kit in the storage box. Check the sinks and the floor around your desk to be sure they are thoroughly clean.
NERVE ENDINGS ON THE PERIPHERAL NERVOUS SYSTEM
Of the nerve endings in the perpheral nervous system, the most highly developed are those which detect pressure and vibration in an organ, the Pacinian corpuscles. We will be looking a sections of pancreas which display these features.
Slide 10: Vater-Pacini corpuscles, pancreas, H-eosin (H 1688)
Pacinian Corpuscles (MF 9 th: page 229 and 147) at 100x:
connective tissue capsule
central cavity with numerous lamellae (with flattened nuclei)
Here is a labeled view of Pacinian corpuscles.