Question

Describe representative examples of cranial reflexes that produce somatic responses or visceral responses to specific stimuli.

Answer 1

Olfactory Nerves (I)
-Primary function: Special sensory (smell)
- Olfactory Epithelium

Visceral Response:  During breathing air molecules attach to the olfactory mucosa and stimulate the olfactory receptors of cranial nerve I and electrical activity is transduced into the olfactory bulb. Olfactory bulb cells then transmit electrical activity to other parts of the central nervous system via the olfactory tract which helps us to smell the surroundings.

Optic Nerves (II)
-Primary function: Special sensory (vision)
-Retina of eye
Somatic Response:  Light strikes the rod and cone cells and electrical impulses are transduced and transmitted to the bipolar cells. The bipolar cells, in turn, transmit electrical activity to the central nervous system through the optic nerve which helps to see different colors.

Oculomotor Nerves (III)
-Primary function: Motor (eye movements)
-Intrinsic eye muscles

Somatic motor function

These nerve axons will arise from the oculomotor nucleus and innervate skeletal muscles associated with the eye. There are seven extrinsic eye muscles (muscles that lay outside of the eye itself) that move the superior eyelid and the eyeball. Five of them are innervated by the oculomotor nerve.

Visceral motor function

The visceral motor axons of the oculomotor nerve are part of the autonomic nervous system, specifically the parasympathetic division. They will arise from the Edinger-Westphal nucleus and innervate two separate intrinsic muscles within the eye. These will constrict the pupil and cause accommodation of the lens of the eye respectively.

The Trochlear Nerves (IV)
-Primary function: Motor (eye movements)
-Superior oblique muscle

somatic Response: a motor nerve that innervates only a single muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea.

The Trigeminal Nerves (V)
-Primary function: Mixed (sensory and motor) to face
-Jaw

somatic Response: The trigeminal nerve is a nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name derives from the fact that each of the two nerves has three major branches: the ophthalmic nerve, the maxillary nerve, and the mandibular nerve. The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory functions. Adding to the complexity of this nerve is the fact that autonomic nerve fibers as well as special sensory fibers are contained within it.

The Abducens Nerves (VI)
-Primary function: Motor (eye movements)
-Lateral Rectus Muscle

Somatic function:

The abducens nerve provides innervation to the lateral rectus muscle – one of the extraocular muscles. The lateral rectus originates from the lateral part of the common tendinous ring and attaches to the anterolateral aspect of the sclera. It acts to abduct the eyeball (i.e. to rotate the gaze away from the midline).

The Facial Nerves (VII)
-Primary function: Mixed (sensory and motor) to face
-Tongue and glands

Visceral Response: It emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue. The nerves typically travel from the pons through the facial canal in the temporal bone and exit the skull at the stylomastoid foramen. It arises from the brainstem from an area posterior to the cranial nerve VI and anterior to cranial nerve VIII which can have facial responses on our face

The Vestibulocochlear Nerves (VIII)
-Primary function: Sensory: Balance, equilibrium, and hearing.
-Cochlea and Vestibule

Somatic response: The vestibulocochlear nerve originates in the pontomedullary region. It provides special somatic afferent fibers for hearing and balance. The cochlea transmits sound waves to mechanical ossicle movements to electrochemical action potentials. The vestibular apparatus detects changes in head motion.

The Glossopharyngeal Nerves (IX)
-Primary function: Mixed (sensory and motor) to head and neck
-Tongue, Pharyngeal muscles and salivary gland
Visceral response: Known as the ninth cranial nerve, is a mixed nerve that carries afferent sensory and efferent motor information. It exits the brainstem out from the sides of the upper medulla, just anterior to the vagus nerve. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, while the sensory division originates from the cranial neural crest.

The Vagus Nerves (X)
-Primary function: Mixed (sensory and motor) Widely distributed in thorax and abdomen
-Pharynx, external acoustic meatus, auricle, pharyngeal muscle

Visceral response: It interfaces with the parasympathetic control of the heart, lungs, and digestive tract. The vagus nerves are normally referred to in the singular. It is the longest nerve of the autonomic nervous system in the human body. The ending part of the vagus nerve is known as the nucleus ambiguous which produces a stimulus for the thorax and abdomen which is helpful for motor and sensory.

The Accessory Nerves (XI)
-Primary function: Motor to muscles of the neck and upper back
-Skeletal muscles of palate, pharynx, and larynx, sternocleidomastoid and trapezius

Somatic response: the cranial nerve that supplies the sternocleidomastoid and trapezius muscles. It is considered as the eleventh of twelve pairs of cranial nerves, or simply cranial nerve XI, as part of it was formerly believed to originate in the brain. The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle, connecting to the scapula, acts to shrug the shoulder.

The Hypoglossal Nerves (XII)
-Primary function: Motor (tongue movements)
-Tongue musculature

Somatic response:  This innervates all the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus which is innervated by the vagus nerve. It is a nerve with a solely motor function. The nerve arises from the hypoglossal nucleus in the medulla as a number of small rootlets, passes through the hypoglossal canal and down through the neck, and eventually passes up again over the tongue muscles it supplies into the tongue.