Porth's Essentials of Pathophysiology, 4e

833

Organization and Control of Neural Function

C h a p t e r 3 4

GVIA SVIA GSIA SSIA

Neurons of input association cell columns

Dorsal horn

Lateral gray horn

FIGURE 34-8. (A) Cell columns of the central nervous system.The cell columns in the dorsal horn contain input association (IA) neurons for the general visceral afferent (GVA), special visceral afferent (SVA), special sensory afferent (SSA), and general somatic afferent (GSA) neurons with cell bodies in the dorsal root ganglion.The cell columns in the ventral horn contain the general visceral efferent (GVE), pharyngeal efferent (PE), and general somite efferent (GSE) neurons and their output association (OA) neurons.

Dorsal root ganglion

Spinal or mixed nerve

GVE

PE

GVA SVA GSA SSA

GSE

Neurons of output cell column

GVE SVE GSE

Ventral root

Special visceral afferent (SVA) neurons innervate spe- cialized gut-related visceral receptors, such as the taste buds and receptors of the olfactory mucosa. They com- municate with neurons involved in salivation, chewing, swallowing, and sensations of taste (i.e., gustation) and smell (i.e., olfaction). General somatic afferent (GSA) neurons innervate the skin and other somatic structures, responding to stimuli such as those that produce pressure or pain. General visceral afferent (GVA) fibers innervate visceral structures such as the gastrointestinal tract, urinary

bladder, and heart and great vessels; they communicate with neurons that send information to the forebrain regarding visceral sensations such as stomach fullness and bladder pressure. Ventral Horn Cell Columns. The ventral horn contains three longitudinal cell columns: the general visceral effer- ent, general somatic efferent, and pharyngeal efferent (see Fig. 34-8). The efferent neurons for the ventral horn cell columns originate in brain centers (motor cortex and ANS centers) that control skeletal muscle and visceral function.

TABLE 34-1 The Segmental Nerves andTheir Components Segment and Nerve Component Innervation

Function

1. Forebrain

CN I: Olfactory

SVA

Receptors in olfactory mucosa

Reflexes, olfaction (smell)

2. CN II: Optic

Optic nerve and retina (part of brain system, not a peripheral nerve)

3. Midbrain

CNV:Trigeminal (V 1 ) ophthalmic division

SSA GSA

Muscles of the upper face: forehead, upper lid Skin, subcutaneous tissue; conjunctiva; frontal/ethmoid sinuses

Facial expression, proprioception Somesthesia Reflexes (blink) Pupillary constriction Accommodation

CN III: Oculomotor

GVE

Iris sphincter Ciliary muscle

GSE

Extrinsic eye muscles

Eye movement, lid movement

4. Pons

CNV:Trigeminal (V 2 ) maxillary division

SSA

Muscles: facial expression

Proprioception Reflexes (sneeze), somesthesia

GSA

Skin, oral mucosa, upper teeth, hard palate, maxillary sinus Lower jaw, muscles: mastication Skin, mucosa, teeth, anterior ⅔ of tongue Muscles: mastication tensor tympani tensor veli palatini

CNV:Trigeminal (V 3 ) mandibular division

SSA GSA PE

Proprioception, jaw jerk Reflexes, somesthesia Mastication: speech Protects ear from loud sounds Tenses soft palate

CN IV:Trochlear

GSE

Extrinsic eye muscle

Moves eye down and in

(Continued )