General somatic afferent
General
somatic afferent
General somatic afferent fibers convey impulses for exteroreceptors of
the skin (cutaneous sensation of pain, temperature, touch, vibration, or
pressure) & from proprioreceptors localized in the muscles, joints,
ligaments, or in the periosteum of bones via spinal nerves and some cranial
nerves.
Nerves contain general somatic afferent fibres
1. All the spinal nerves, except
occasionally the first cervical, and conduct impulses of pain, touch and temperature from the surface of the body through the dorsal
roots to the spinal cord and impulses of muscle sense, tendon sense and
joint sense from the deeper structures
2. Trigeminal nerve:
Ophthalmic nerve: general
somatic afferents fibre of this nerve supply to the upper face, skull, and eye:
·
Face: Upper eyelid and associated conjunctiva. Eyebrow,
forehead, scalp all the way to the lambdoid suture.
·
·
Skull: Roof of orbit, frontal, ethmoid, and possibly sphenoid
sinuses.
·
Eye: The eye itself (all the intraocular structures such as
cornea) and the lacrimal gland and sac.
·
Maxillary
nerve : general somatic afferents fibres of this nerve supply to the mid-face
and skull:
·
Face: Lower eyelid and associated conjunctiva. Cheek, upper lip.
·
Skull: Orbital floor, maxillary sinus, upper teeth, nasal
cavity, and palate, cheekbone.
Mandibular nerve : The sensory fibres associated with the mandibular branch
of CN V provide innervation to:
·
The facial skin in the
lower third of the face, including the chin and lower lip
·
Inferior row of teeth and
gingiva
·
The anterior two thirds of
the tongue
3. Facial nerve : The facial nerve
carries axons of type GSA, general somatic afferent, to skin of the posterior
ear.
4. Glossopharyngeal nerve: the
glossopharyngeal nerve transmits
general sensory information from inside of the tympanic membrane, skin of the
external ear, upper portion of the pharynx and general sensation from the
posterior one-third of the tongue.
5. Vagus nerve GSA axons carry pain, temperature, and touch
sensations from the posterior cranial fossa, posterior ear, external auditory meatus, pharynx, and posterior, and the external surface of the tympanic membrane
General somatic
afferent (sensory) nuclei
General somatic
afferent (sensory) nuclei related with spinal nerve
- Marginal zone (MZ, posterior
marginalis) – located at the tip of
the dorsal horn, and is important for relaying pain and temperature
sensation to the brain.
- Substantia gelatinosa (SG) – located at the top of the dorsal horn, the SG
is important for relaying pain, temperature and light touch sensation
to the brain.
- Nucleus proprius (NP) – located in the ‘neck’ of the dorsal horn, the
NP relays mechanical and temperature sensation to the brain.
General somatic
afferent (sensory) nuclei related with trigeminal, facial, glossopharyngeal
& vagus nerve
·
The
main or principal sensory nucleus of the trigeminal nerve: This
nucleus lies in the upper part of the pons, in the lateral part of the
reticular formation. It lies lateral to the motor nucleus of the trigeminal.
The superior sensory nucleus is mainly concerned in mediation of proprioceptive
impulses, touch and pressure.
·
The spinal nucleus of the trigeminal nerve: The
spinal nucleus is another sensory cranial nerve nucleus which extends from the
main nucleus (superior sensory nucleus) in the pons down into the medulla,
& into the upper two segments of the
spinal cord. The lower end of the spinal nucleus is continuous with the
substantia gelatinosa of the spinal cord. The spinal nucleus receives general
somatic sensations carried by the facial, glossopharyngeal and vagus
nerves. Functions of the spinal nucleus includes mediation of pain and
thermal sensibility. The spinal nucleus is divisible (cranio-caudally) into
three sub-nuclei, the oralis, interpolaris,
and caudalis.
· The mesencephalic nucleus of the trigeminal nerve: This is also called the mesencephalic nucleus of the trigeminal nerve. It extends cranially from the upper end of the main sensory nucleus in the pons into the midbrain. In the midbrain, the mesencephalic nucleus lies in the central grey matter lateral to the aqueduct. Functionally, this nucleus appears to be similar to sensory ganglia of the cranial nerves, and to the spinal ganglia, rather than to afferent nuclei. The processes (dendrites) of the neurons of this nucleus are believed to carry proprioceptive impulses from muscles of mastication, and possibly also from muscles of the eyeballs, face, tongue and teeth. The mesencephalic nucleus is the centre for jaw jerk.
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