Accessory Nerve

XI. Spinal accessory nerve. Trapezius and sternomastoid muscles Test power of shrugging shoulders and turning the head to one side against resistance. 

RNS (at 3 Hz with square-wave pulses 0.3 ms in duration) of the facial nerve to the orbicularis oculi and orbicularis nasalis, accessory nerve to the trapezius, and median nerve to the abductor pollicis brevis muscles can be studied. Hand-held bipolar electrodes and adhesive surface electrodes are used for stimulation and recording, respectively. Routine nerve conduction studies (NCS) of all four limbs, including the VII nerve, can also be performed. 

Somatic motor fibers are carried in three cranial nerves to the muscles of the eye, the occulo-motor (III), trochlear (IV), and abducens (VI), and in one to the tongue, hypoglossal (XII). Branchial motor fibers are carried by the trigeminal (V) to the temporalis and masseter muscles, by the facial (VII) to the muscles of expression of the face, by the glossopharyngeal (IX) and vagus (X) to the muscles of the pharynx and larynx, and the accessory nerve (XI) to the sternocleidomastoid and trapezius. 

By the spinal accessory nerve which is formed by the spinal roots (upper 5 cervical ventral roots) they ascend through the foremen magnus, to exit through the jugular foremen, after joining the cranial roots. 

The two heads merge together and the muscle end over the mastoid process. Before the muscle end, it is pierced by the spinal accessory nerve. 

Spinal Portion of Accessory Nerve and Twigs from C3, C4. 

Following the sequence of clinical neurological examination there can be disturbances of lower cranial nerves difficulty in swallowing, nasal speech, atrophy and weakness of muscles innervated by the accessory nerve. Upper cervical nerves can be involved in a series syndromes of neck pain. This however is only occasionally encountered in transoral surgery. 

Muscle contraction is initiated by a signal from a motor nerve. This triggers an action potential, which is propagated along the muscle plasma membrane to the T-tubule system and the sarcotubular reticulum, where a sudden large electrically excited release of Ca " into the cytosol occurs. Accessory proteins closely associated with actin (troponins T, I, and C) together with tropomyosin mediate the Ca -dependent motor command within the sarcomere. Other accessory proteins (titin, nebulin, myomesin, etc.) serve to provide the myofibril with both stability... 

Both primitive and advanced forms have been examined for vomeronasal excitation. The turtle VN nerve was the subject of EOG recordings elicited by small organic molecules and by specific signal compounds (Tucker, 1963 Hatanaka, 1987). The simple arrangement of the chelonian accessory area (Fig. 2.8) allows air or liquid delivery hence the preferred odourant vehicle varies with habitat across the aquatic or terrestrial turtles, and the land tortoises (Chap. 1 and Halpem, 1992). 

Burton P.R. (1990). Vomeronasal and olfactory nerves of adult and larval bullfrogs II. Axon terminations and synaptic contracts in the accessory olfactory bulb. J Comp Neurol 292, 624-637. 

MacCotter R.E. (1912). The connection of the vomeronasal nerves with the accessory olfactory bulb in the Opossum and other mammals. Anat Rec 6, 299-318. 

Mori K., Imamura K., Fujita K. and Obata K. (1987). Projections of two subclasses of vomeronasal nerve fibers to the accessory olfactory bulb in the rabbit. Neuroscience 20, 259-278. 

Since in the normal state both nicotine and curari abolish the effect of nerve stimulation, but do not prevent contraction from being obtained by direct stimulation of the muscle or by a further adequate injection of nicotine, it may be inferred that neither the poison nor the nervous impulse acts directly on the contractile substance of the muscle but on some accessory substance. 

The vomeronasal system, also known as the accessory olfactory system, consists of chemoreceptors, organized into the VNO, the vomeronasal nerve, its terminal, the accessory olfactory bulb, and more central pathways. First described by Jacobson in 1811, the VNO has been studied intensely. We now know how stimuli reach it and what behaviors it mediates. The VNO occurs in amphibians, reptiles, and mammals. Among mammals, it is best developed in marsupials and monotremes. In birds it only appears during embryogenesis. The VNO and its function are best known for squamate reptiles, particularly snakes, and rodents and ungulates among the mammals. 

The VNO is extremely important in mediating endocrine responses to primer pheromones. Puberty acceleration in female rats by male urine odors can be prevented by electrolytic damage to the vomeronasal nerve. Also, effects of male urine odor such as shortening of the estrus cycle (see Ch. 8) can be eliminated by section of the vomeronasal nerve, or bilateral electrocoagulation of the accessory olfactory bulb (Sanchez-Criado, 1982). In rats, the odor of males stimulates ovulation in females, an effect that is lost if the VNO is extirpated (Johns etal., 1978). Female prairie voles, M. ochrogaster, respond to odors from males with reproductive activation. Surgical removal of the VNO from adult females impedes this reproductive activation by the stud male. The weights of the uterus and the ovaries of these females were lower than those of normal or sham-operated individuals. However, the females without a VNO were still able to locate food by chemical cues (Lepri and Wysocki, 1987). 

Nerve transection experiments have shown that normal estrus cyclicity and behavioral estrus in mice relies on sensory input through the main olfactory bulbs and does not require the accessory olfactory system (Rajendren and Dominic, 1986). 

---