Page 128 - untitled

AAAC56 21/5/05 10:56 AM Page 127
The head and neck are supplied by the first four spinal and the 12 cra-
nial nerves.
through the cribriform plate to synapse in the olfactory bulb of the
brain.
The spinal nerves the nasal mucosa. Their axons form the olfactory nerves which ascend
• II. The optic nerve (Fig. 56.1): the eye and optic nerve develop as an
• C1: supplies the small suboccipital muscles. Its anterior ramus joins the outgrowth of the embryonic brain and the nerve is therefore enveloped
hypoglossal nerve but leaves it later to form the descendens hypoglossi. in meninges. The cell bodies are in the retina and the axons pass back in
• C2: The posterior ramus forms the greater occipital nerve which is the optic nerve to the optic chiasma where the axons from the nasal
sensory to the scalp. halves of the retina cross over but those from the temporal side continue
• The posterior rami of C2, 3 and 4 provide muscular and sensory on the same side. They then form the optic tract on each side.
branches to the back. Their anterior rami provide muscular branches, • III. The oculomotor nerve (Fig. 56.2): arises from the brain just in
including the descendens cervicalis (see hypoglossal nerve). They also front of the pons, traverses the cavernous sinus and enters the orbit
supply sensory branches: the greater auricular, lesser occipital, an- through the superior orbital fissure. Supplies the levator palpebrae
terior cutaneous and the three supraclavicular nerves (Fig. 56.4). The superioris, superior, inferior and medial rectus muscles and the inferior
greater auricular supplies the skin in the parotid region, the only sens- oblique. It also carries parasympathetic fibres to the ciliary ganglion
ory supply to the face which is not derived from the trigeminal. The where the fibres synapse and then pass in the short ciliary nerves to the
others supply the skin of the neck and the upper part of the thorax. sphincter pupillae and the ciliary muscles (see Chapter 69).
• The remaining cervical nerves (C5–8) join the brachial plexus. • IV. The trochlear nerve (Fig. 56.3): arises from the dorsal surface
of the brain just behind the inferior colliculus, winds round the mid-
The cranial nerves (Figs 56.1–3) brain and enters the cavernous sinus. It enters the orbit through the
• I. The olfactory nerve: the cell bodies of the olfactory nerve are in superior orbital fissure and supplies the superior oblique.

Spinal nerves and cranial nerves I–IV 127