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The human body has over 600 muscles that help us move, breathe, and survive. These muscles are made of thousands of small fibres woven together, allowing them to stretch and press together to facilitate movement. Our muscles are controlled by our nervous system, which includes the cranial nerves. These are a set of 12 paired nerves that originate in the brain and are responsible for various functions, such as vision, taste, smell, hearing, and facial expressions. Certain cranial nerves, like the oculomotor nerve (CN III), trochlear nerve (CN IV), and abducens nerve (CN VI), are specifically involved in controlling eye movements. For instance, the trochlear nerve enables us to look down and towards or away from our nose by innervating the superior oblique muscle.
| Characteristics | Values |
|---|---|
| Number of cranial nerves | 12 |
| Function | Help you see, taste, smell, hear, feel sensations, make facial expressions, blink your eyes, move your tongue and neck |
| Type of movement | Voluntary and involuntary |
| Nerves controlling eye movement | Trochlear nerve (CN IV), Oculomotor nerve (CN III), Abducens nerve (CN VI) |
| Nerve controlling tongue movement | Hypoglossal nerve (CN XII) |
| Nerve controlling swallowing | Glossopharyngeal nerve (CN IX) |
| Nerve controlling shoulder and neck movement | Accessory nerve or spinal accessory nerve (CN XI) |
| Condition caused by damage to the trochlear nerve | Fourth nerve palsy or trochlear nerve palsy |
| Condition caused by damage to the oculomotor nerve | Third nerve palsy or oculomotor palsy |
| Condition caused by damage to the abducens nerve | Sixth nerve palsy or abducens nerve palsy |
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What You'll Learn
- The glossopharyngeal nerve (CN IX) controls muscles for swallowing
- The oculomotor nerve (CN III) controls the levator palpebrae superioris muscle, which lifts the eyelid
- The trochlear nerve (CN IV) controls the superior oblique muscle, allowing you to look down and towards your nose
- The abducens nerve (CN VI) controls eye movement
- The hypoglossal nerve (CN XII) controls tongue movement
The glossopharyngeal nerve (CN IX) controls muscles for swallowing
The glossopharyngeal nerve, also known as CN IX, is the ninth of twelve cranial nerves. These nerves start in the brainstem and connect to organs, muscles, and other structures in the mouth and throat. The glossopharyngeal nerve has three types of fibres: motor, parasympathetic, and sensory. The motor fibres enable muscle movement, the parasympathetic fibres help tissues and organs rest when not in use, and the sensory fibres provide sensation, allowing you to detect taste, touch, and temperature.
The glossopharyngeal nerve controls muscles for swallowing. It innervates the stylopharyngeus muscle of the pharynx, which acts to shorten and widen the pharynx and elevate the larynx during swallowing. This nerve also provides parasympathetic innervation to the parotid gland, which decreases saliva production when you finish eating.
The glossopharyngeal nerve is clinically relevant in glossopharyngeal neuralgia, a condition characterised by oropharyngeal pain triggered by mandibular actions such as swallowing, chewing, coughing, and yawning. This condition can cause fear of future attacks, making eating difficult. Another condition related to the glossopharyngeal nerve is glossopharyngeal nerve palsy, which can be caused by an injury or medical condition affecting CN IX nerve functioning. This condition may result in partial or full paralysis of the nerve.
The glossopharyngeal nerve also has other important functions. It provides taste sensations to the back third of the tongue and carries sensory information from the carotid sinus and body. Additionally, it plays a role in regulating blood pressure and saliva production. Overall, the glossopharyngeal nerve is a crucial component of the cranial nerve system, facilitating various functions related to swallowing, taste, and other sensory processes.
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The oculomotor nerve (CN III) controls the levator palpebrae superioris muscle, which lifts the eyelid
The oculomotor nerve, or CN III, is one of 12 cranial nerves that stem from the brain. It has two main functions: somatic motor and visceral motor or parasympathetic. The somatic motor function is controlled by the oculomotor nucleus, while the visceral motor function is controlled by the accessory oculomotor nucleus, or Edinger-Westphal nucleus. Both of these nuclei are located in the midbrain.
The oculomotor nerve controls the levator palpebrae superioris muscle, which lifts the eyelid. This muscle is located in the orbit and elevates the upper eyelid. It originates from the inferior surface of the lesser wing of the sphenoid bone, just above the optic foramen. The levator palpebrae superioris muscle receives motor innervation from the superior division of the oculomotor nerve.
Damage to the levator palpebrae superioris muscle or its innervation can cause ptosis, or drooping of the eyelid. This occurs when the eyelid is unable to oppose the force of gravity without stimulation from the oculomotor nerve. Ptosis can also be caused by damage to the adjoining superior tarsal muscle or its sympathetic innervation, as seen in Horner's syndrome.
Oculomotor nerve palsy, or third nerve palsy, is a condition resulting from damage to the oculomotor nerve. Clinical features of CN III injury include ptosis, a "down and out" position of the eye at rest, and a dilated pupil. This condition typically causes one of the eyes to stay positioned as though looking down and out to the side.
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The trochlear nerve (CN IV) controls the superior oblique muscle, allowing you to look down and towards your nose
The trochlear nerve, also known as the cranial nerve 4 or CN IV, is a motor nerve that controls the movement of the superior oblique muscle, allowing you to look down and towards or away from your nose. It is one of 12 sets of cranial nerves that send signals from the brain to muscles that control eye movement.
The trochlear nerve gets its name from the Latin word "trochleae," which means "pulley." A pulley is a device that helps lift and lower an object, aptly describing the function of the nerve in controlling the superior oblique muscle. This muscle is connected to the eye near the top of it and goes through a sling of connective tissue that acts as a pulley.
The trochlear nerve is the smallest of the cranial nerves, but it has the longest intracranial course as it is the only nerve to have a dorsal exit from the brainstem. It originates in the midbrain and extends laterally and anteriorly to the superior oblique muscle. The trochlear nerve is a somatic efferent (motor) nerve and, along with the oculomotor (CN III) and abducens (CN VI) nuclei, is responsible for eye movement.
Damage to the trochlear nerve can result in issues with eye movement and vision. Common signs of trochlear nerve damage, often called fourth nerve palsy or trochlear nerve palsy, include double vision (diplopia), tilting the head to compensate for eye movement or vision challenges, facial asymmetry (midfacial hypoplasia), and misalignment of the eyes (strabismus). The trochlear nerve's long path through the head makes it vulnerable to injury, especially from head trauma.
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The abducens nerve (CN VI) controls eye movement
The abducens nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a nerve present in humans and other animals that controls eye movement. It is a somatic efferent nerve. The abducens nerve controls the movement of a single muscle, the lateral rectus muscle of the eye, which is responsible for outward gaze. This nerve has the second longest path of travel for a nerve within the brain, after the vagus nerve.
The abducens nerve allows you to move your eyes to the left and right. You have an abducens nerve for both eyes, which moves your right eye to the right and your left eye to the left. This nerve also works with the medial rectus muscle to make both eyes move to the left and right at the same time. CN VI has an important job of moving your eye and helping you see the world around you. For example, if you hear a bird chirp from a tree to your right, your abducens nerve tells your outer eye muscle to move your eyes to the right so you can look at the bird.
The abducens nerve is a very small nerve in your head, just behind your eyes. The nucleus of the abducens nerve (abducens nucleus) is the command center of this nerve. It tells the nerve what to do. While this nerve reaches from the brainstem to the eye socket, you can find the nucleus in the pons, which is in the upper back portion of the brain. The pons sit below the midbrain and above the medulla oblongata, which is right above the spinal cord.
Damage to the abducens nerve can cause abducens nerve palsy, or sixth nerve palsy, which weakens the lateral rectus muscle and leads to muscle paralysis. This can occur due to diabetes, high blood pressure, head injuries, stroke, or many other causes. It is important to see a healthcare provider right away to determine the cause. Nerve damage is common because this nerve stretches from the back to the front of the brain.
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The hypoglossal nerve (CN XII) controls tongue movement
The hypoglossal nerve, also known as cranial nerve 12 (CN XII), is a motor nerve that controls the tongue's movement. It is one of 12 paired cranial nerves that stem from the brain. These nerves send electrical signals between the brain and different parts of the head, face, neck and torso.
The hypoglossal nerve is responsible for the movement of the tongue, which is essential for speaking, eating and swallowing. It controls the genioglossus, hyoglossus, styloglossus and intrinsic muscles of the tongue. These muscles enable the tongue to change shape, move forward, backward, up and down, and from side to side. The nerve also supplies movements, including clearing the mouth of saliva and other involuntary activities.
The nerve originates from the medulla and travels through the neck, eventually passing over the tongue muscles it supplies and into the tongue. It branches out, ending at the base and underside of the tongue. The hypoglossal nerve is at high risk of injury during carotid endarterectomy. Damage to the nerve can cause paralysis and atrophy of the tongue muscles, affecting the tongue's movement and appearance.
The nerve can be clinically implicated in the treatment of obstructive sleep apnea. Hypoglossal nerve stimulation can relieve tongue base obstruction during sleep by stimulating the tongue to protrude during inhalation. This procedure involves placing an electrical stimulator lead around branches of the hypoglossal nerve.
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Frequently asked questions
The trochlear nerve controls the superior oblique muscle, which is connected to the eye near the top of it.
The superior oblique muscle allows you to look down and towards or away from your nose.
Damage to the trochlear nerve will likely affect your eye movement and vision. Common signs of damage include double vision (diplopia), tilting your head to compensate for eye movement or vision challenges, facial asymmetry, and misalignment of the eyes (strabismus).
Trochlear nerve palsy can be caused by microvascular disease, tumours, increased intracranial pressure, Lyme disease, meningioma, Guillain-Barre Syndrome, Herpes zoster, and Cavernous Sinus Syndrome.
The oculomotor nerve (CN III) and the abducens nerve (CN VI) also control eye movement.
