SENSORY FIBERS OF TRIGEMINAL NERVE
Trigeminal nerve carries somatosensory information from face, teeth, periodontal tissues (tissues around teeth), oral cavity, nasal cavity, cranial dura mater and major part of scalp to sensory cortex. It also conveys proprioceptive impulses from the extrinsic muscles of the eyeball.
Origin
Sensory fibers of trigeminal nerve arise from the trigeminal ganglion
situated near temporal bone.
Peripheral
processes of neurons in this ganglion form three divisions of trigeminal nerve,
namely ophthalmic, mandibular and maxillary divisions. Cutaneous distribution of
the three divisions of trigeminal nerve. Central processes from neurons of
trigeminal ganglion enter pons in the form of sensory root.
Termination
After reaching the pons, fibers of sensory root divide into two groups, namely descending fibers and ascending fibers. Descending fibers terminate on primary sensory nucleus and spinal nucleus of trigeminal nerve. Primary sensory nucleus is situated in pons. Spinal nucleus of trigeminal nerve is situated below the primary sensory nucleus and extends up to the upper segments of spinal cord. Ascending fibers of sensory root terminate in the mesencephalic nucleus of trigeminal nerve, situated in brainstem above the level of primary sensory nucleus .
Central Connections
Majority
of fibers from the primary sensory nucleus and spinal nucleus of trigeminal
nerve ascend in the
form of
trigeminal lemniscus and terminate in ventral posteromedial nucleus of thalamus
in the opposite side. Remaining fibers from these two nuclei terminate on the
thalamic nucleus of same side. From thalamus, the fibers pass via superior thalamic
radiation and reach the somatosensory areas of cerebral cortex. Primary sensory
nucleus and spinal nucleus of trigeminal nerve relay the sensations of touch,
pressure, pain and temperature from the regions mentioned above. Fibers from
mesencephalic nucleus form the trigeminocerebellar tract that enters
spinocerebellum via the superior cerebellar peduncle of the same side. This nucleus
conveys proprioceptive impulses from facial muscles, muscles of mastication and
ocular muscles.
LEMNISCUS
Lemniscus
or fillet is the prominent bundle of sensory nerves in brain.
Lemniscus
is of four types:
1. Spinal lemniscus formed by
spinothalamic tracts in medulla oblongata
2. Lateral lemniscus formed by the
fibers carrying sensation of hearing from cochlear nuclei to inferior
colliculus
and medial geniculate body nucleus cuneatus and nucleus gracilis
4. Trigeminal lemniscus formed by fibers
from sensory nuclei of trigeminal nerve. This lemniscus carries general senses
from head, neck, face, mouth, eyeballs and ears.
APPLIED PHYSIOLOGY
Lesions or
other nervous disorders in sensory pathway affect the sensory functions of the
body.
SOMATOMOTOR SYSTEM
MOTOR ACTIVITIES OF
THE BODY
Motor
activities of the body depend upon different groups of tissues of the body.
Motor
activities are divided into two types:
1.
Activities of skeletal muscles, which are involved in posture and movement
2.
Activities of smooth muscles, cardiac muscles and other tissues, which are
involved in the functions of
various
visceral organs. Activities of skeletal muscles (voluntary functions) are
controlled by somatomotor system, which is constituted by the somatic motor
nerve fibers. Activities of tissues or visceral organs (involuntary functions) are
controlled by visceral or autonomic nervous system, which is constituted by the
sympathetic and parasympathetic systems
SOMATOMOTOR SYSTEM
Movements
of the body depend upon different groups of skeletal muscles. Various types of
movements or motor activities brought about by these muscles are:
1.
Execution of smooth, precise and accurate voluntary movements
2.
Coordination of movements responsible for skilled activities
3.
Coordination of movements responsible for the maintenance of posture and
equilibrium.
Voluntary
actions and postural movements are carried out by not only the simple
contraction and
relaxation
of skeletal muscles but also the adjustments of tone in these muscles. The execution, planning,
coordination and adjustments of movements of
the body are under the influence of different parts of
nervous system, which are together called motor system.
Sensory system of the body also plays a vital role
in the control of movements.
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