Trigeminal nerve
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The trigeminal nerve is the fifth (V) cranial nerve, and carries sensory information from most of the face, as well as motor supply to the muscles of mastication (the muscles enabling chewing), tensor tympani (in the ear) and other muscles in the floor of the mouth.
It is named trigeminal because it splits into three nerves - the ophthalmic nerve (V1), the maxillary nerve (V2) and the mandibular nerve (V3).
The ophthamlmic, maxillary, and mandibular branches leave through various holes in the skull: the superior orbital fissure, foramen rotundum and foramen ovale respectively.
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Sensory innervation
It is the major cutaneous sensory nerve of the head, and is responsible for sensation over most of the skin on your head.
Motor innervation
It also supplies motor fibres to temporalis muscle, lateral pterygoid muscle, medial pterygoid muscle, masseter muscle (the four main muscles involved in mastication), tensor veli palatini, mylohyoid muscle and the tensor tympani muscle.
Testing the trigeminal nerve
As the trigeminal nerve contains both sensory and motor fibres, and also branches into different regions, these should be tested separately and on both sides of the face.
To test the sensation, the skin is touched lightly (for instance with cotton wool) and also tested for pain (such as the sharpness of a pin prick). This is done on the three regions: forehead, cheeks and chin, as well as around the nose and mouth.
The corneal reflex is dependent on the trigeminal nerve sensing touching the eye, (as well as the facial nerve for the motor response). This can be done with a wisp of cotton wool, and approaching from the side (so the person being investigated doesn't blink at the sight approaching). The corneal reflex elicits a blink with both eyes, and feels very uncomfortable for the patient.
To test the motor pathways are functional, the temporalis and masseter muscles may be felt. The temporalis can be felt contracting at the temples (just lateral to the eyes) when a person is chewing (or clenching and unclenching their teeth). Masseter can be felt just above the angle of the jaw in the same movement.
The strength of the jaw muscles can be tested by holding a person's jaw closed and telling them to open it, (tests the pterygoids), and opening the jaw and getting them to close it (tests the masseters). The jaw muscles are normally quite strong, and there should be little difficulty overcoming pressure from a hand.
If there is unilateral to the motor root of the trigeminal nerve, the jaw will tend to deviate towards the paralysed side.
The jaw jerk reflex will be very brisk if there is any upper motor neuron damage above the pons.
Trigeminal nerve nuclei
The sensory trigeminal nerve nucleus is the largest of the cranial nerve nuclei, and extends through the whole of the brainstem, midbrain to medulla.
The nucleus is divided into three parts, from rostral to caudal (top to bottom in humans), the mesencephalic nucleus, the chief or pontine nucleus and the spinal nucleus.
The mesencephalic nucleus is involved with proprioception, that is the feeling of position of the muscles.
The pontine nucleus receives information about discrimative sensation and light touch.
The spinal nucleus does light touch, pain and temperature. Pain from other cranial nerves also enters the spinal nucleus. The facial, glossopharyngeal and vagus nerves all carry pain from their areas to this part of the trigeminal nucleus.
Conditions involving the trigeminal nerve
- Trigeminal neuralgia is an example of a disorder of the trigeminal nerve where the sufferer suffers pain in the territory of the trigeminal nerve innervation.
- Cluster headaches are an intense type of headache involving the trigeminal nerve.
Branches
Named branches of the trigeminal nerve: (important branches in bold)
Ophthalmic nerve (V1)
Maxillary nerve (V2)
- zygomaticotemporal nerve
- zygomaticofacial nerve
- infraorbital nerve
- superior alveolar nerves
- Pterygopalatine ganglion
Mandibular nerve (V3)