C h a p t e r 3 4
Organization and Control of Neural Function
833
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.
Neurons of
input association
cell columns
GVIA
SVIA
GSIA
SSIA
Dorsal horn
Lateral gray horn
Dorsal
root ganglion
Spinal or
mixed nerve
GVA
SVA
GSA
SSA
GVE
SVE
GSE
Ventral root
Neurons of output
cell column
GVE
PE
GSE
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.
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)
CN III: Oculomotor
GVE
Iris sphincter
Ciliary muscle
Pupillary constriction
Accommodation
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
CNV:Trigeminal (V
3
)
mandibular division
SSA
GSA
PE
Lower jaw, muscles: mastication
Skin, mucosa, teeth, anterior
⅔
of tongue
Muscles: mastication
tensor tympani
tensor veli palatini
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 )
