9th to 12th Cranial Nerve Examination | Clinical Lab | Physiology

The 12 cranial nerves are pairs of nerves that bypass the spinal cord and originate directly from the brain and brainstem, classified as sensory (carrying information into the brain), motor (sending signals out to control muscles), or mixed (containing both types). They include: Olfactory (smell, sensory), Optic (vision, sensory), Oculomotor (eye movement, motor), Trochlear (eye rotation, motor), Trigeminal (facial sensation and chewing, mixed), Abducens (outward eye movement, motor), Facial (facial expressions and tongue sensation, mixed), Vestibulocochlear (hearing and balance, sensory), Glossopharyngeal (swallowing and tongue sensation, mixed), Vagus (wandering nerve controlling heart, lungs, and digestion, mixed), Accessory (shoulder and head movements, motor), and Hypoglossal (tongue movements, motor). An easy acronym to remember them is 'O to touch and feel a very good Velvet' (Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal).

The glossopharyngeal nerve (IX) is a mixed nerve carrying sensory information from the carotid sinus, carotid body, posterior one-third of the tongue, tonsils, oropharynx, external auditory meatus, and tympanic membrane, while providing parasympathetic innervation to the parotid gland and motor innervation to the stylopharyngeus muscle. The vagus nerve (X) is the longest cranial nerve, providing sensory innervation to the heart, lungs, palate, pharynx, larynx, trachea, bronchi, and external ear, carrying taste from the epiglottis and pharynx, and providing parasympathetic innervation to thoracic and intestinal organs (stimulating digestion and energy storage). It also provides motor innervation to palatoglossus, soft palate, pharyngeal, and laryngeal muscles. The accessory nerve (XI) provides motor innervation to the sternocleidomastoid and trapezius muscles, originating from the spinal cord and exiting through the jugular foramen.

This segment tests cranial nerves IX (glossopharyngeal), X (vagus), XI (accessory), and XII (hypoglossal). Pharyngeal function is assessed through sniffing and nostril touch to evaluate the gag reflex. Accessory nerve function is tested through shoulder shrugging, raising shoulders, rolling shoulders, and moving arms downward. Hypoglossal nerve function is evaluated by having the patient stick their tongue out and move it to each cheek. These tests assess the motor and sensory functions of the glossopharyngeal, vagus, accessory, and hypoglossal nerves, which control swallowing, tongue movements, and shoulder/neck muscles.

Cranial nerves are 12 pairs (24 total) of nerves that connect the brain to the head, neck, and trunk, classified into three types: sensory (carrying messages to the brain), motor (carrying messages from the brain), and mixed (performing both functions). The 12 cranial nerves are: Olfactory (I, sensory), Optic (II, sensory), Oculomotor (III, motor), Trochlear (IV, motor), Trigeminal (V, mixed), Abducens (VI, motor), Facial (VII, mixed), Vestibulocochlear (VIII, sensory), Glossopharyngeal (IX, mixed), Vagus (X, mixed), Accessory (XI, motor), and Hypoglossal (XII, motor).

The nervous system is divided into the Central Nervous System (brain and spinal cord) and Peripheral Nervous System (nerves). Nerves are classified anatomically into cranial nerves (12 pairs connected to the brain) and spinal nerves (31 pairs connected to the spinal cord). Functionally, nerves are categorized as sensory (carry information to CNS), motor (carry commands from CNS), or mixed (both). Cranial nerves include olfactory (I, sensory), optic (II, sensory), oculomotor (III, motor), trochlear (IV, motor), trigeminal (V, mixed), abducens (VI, motor), facial (VII, mixed), vestibulocochlear (VIII, sensory), glossopharyngeal (IX, mixed), vagus (X, mixed), accessory (XI, motor), and hypoglossal (XII, motor). All spinal nerves are mixed nerves. The peripheral nervous system further divides into somatic (controls skeletal muscles) and autonomic (controls internal organs) systems, with the autonomic system having sympathetic (emergency response) and parasympathetic (rest and digest) divisions.

The oral cavity is divided into vestibulum oris (outer space between teeth and cheeks) and cavitas oris (inner space containing the tongue). The retromolar area behind the molars serves as a passageway for feeding tubes. The pharynx consists of three parts: nasopharynx (behind nasal cavity), oropharynx (behind oral cavity), and laryngopharynx (behind larynx). The lips have a pink appearance due to thin skin with rich capillary networks and meet at the commissures. The buccinator muscle is the 'smiling muscle' in the cheek. The parotid gland is the largest salivary gland, located near the ear, with its duct opening at the second molar level. The palate consists of hard palate (anterior two-thirds, supported by maxilla and palatine bones) and soft palate (posterior one-third with uvula). The tongue consists of root, body, and apex, divided by the terminal sulcus. It has four papillae types: filiform (mechanical function), fungiform, circumvallate, and foliate (taste buds). Taste buds are more numerous in infants than adults. Tongue muscles are intrinsic (within tongue) and extrinsic (genioglossus, hyoglossus, styloglossus, palatoglossus). The hypoglossal nerve (CN XII) innervates tongue muscles.

The oral cavity is divided into the oral cavity proper (the space within the teeth) and the oral vestibule (the space between the teeth and lips/cheeks); it contains key structures including the palate (hard palate formed by the maxilla and palatine bones, and soft palate), teeth (20 primary replaced by 32 permanent), salivary glands (parotid, submandibular, and sublingual), and the tongue, which together serve digestive, respiratory, and speech functions; the oral cavity connects to the pharynx through the oropharyngeal isthmus and is innervated by cranial nerves including the trigeminal nerve (sensory), facial nerve (parasympathetic motor and taste), glossopharyngeal nerve (parotid gland), and hypoglossal nerve (tongue muscles).

The pharynx divides into nasopharynx (behind nose), oropharynx (behind mouth), and laryngopharynx (behind larynx), each containing three sequential constrictor muscles. The larynx contains two major cartilages (thyroid and cricoid) and two minor cartilages (epiglottis and arytenoids). Two muscles have two bellies: digastric (anterior belly by V3 mandibular nerve, posterior belly by facial nerve CN VII) and omohyoid (both bellies by ansa cervicalis). The facial nerve's terminal branches follow TO ZANZIBAR IN A MOTOR CAR: temporal, zygomatic, buccal, marginal mandibular, and cervical branches, all motor. The sternocleidomastoid originates from manubrium sterni and medial clavicle, inserts into mastoid process and superior nuchal line, is innervated by CN XI, and enables head turning and shoulder shrugging. The scalene muscles (anterior, medius, posterior) originate from cervical transverse processes and insert onto first and second ribs; scalenus anterior (C4-C7) elevates first rib during inspiration; scalenus medius (largest) is innervated by all cervical nerves; scalenus posterior (C4-C6) fixes second rib.

This video provides a comprehensive anatomical demonstration of the tongue, pharynx, and larynx, presenting detailed visual and verbal explanations of these interconnected structures of the head and neck region for educational purposes.

The oral cavity is bounded superiorly by the hard and soft palate, inferiorly by the tongue base, and opens posteriorly into the oropharynx. The pharynx has three portions: nasopharynx (bounded by pharyngeal walls, skull base, and soft palate), oropharynx (bounded by pharyngeal walls and epiglottis), and hypopharynx (bounded by pharyngeal walls and extending to the cricoid cartilage). The velopharyngeal portion prevents reflux into the nasopharynx. The pharynx contains longitudinal muscles (stylopharyngeus, salpingopharyngeus, palatopharyngeus) and constrictor muscles (superior, middle, inferior). The larynx is a hollow, muscular structure with cartilaginous framework (cricoid, thyroid, epiglottis) suspended from the hyoid bone. It contains intrinsic muscles for phonation and divides into vestibular, ventricular, and infraglottic cavities.

Checking a patient's gag reflex before giving medications is important to prevent choking or aspiration. The medication aid uses a tongue depressor and gently stimulates the back of the throat. If the patient moves or shows discomfort, they have a gag reflex. If there is no movement and the patient appears unconcerned, this may indicate a weak or absent gag reflex, which could mean the patient cannot protect their airway safely.

Safe swallowing requires proper function of cranial nerves 9 (glossopharyngeal) and 10 (vagus). Brain injury, stroke, or neurodegenerative diseases affecting these nerves increase aspiration pneumonia risk. The gag reflex (protective against choking) involves sensory input via cranial nerve 9 and motor output via cranial nerve 10. Absence of gag reflex doesn't always indicate pathology. Testing soft palate elevation bilaterally assesses vagus nerve function.

The gag reflex test involves the patient extending their tongue while the examiner touches the posterior tongue with a tongue depressor. The patient should experience a gagging sensation. This tests the glossopharyngeal nerve (afferent limb) and vagus nerve (efferent limb).

The gag reflex tests cranial nerves IX (sensory) and X (motor). To test it, use a tongue depressor to compress the tongue and stimulate the posterior pharyngeal wall with a cotton applicator. A positive gag reflex shows contraction of the pharyngeal muscles. Absent gag reflex indicates brainstem damage (medullary lesion).

The gag reflex is tested by stimulating the posterior pharyngeal wall with a tongue depressor. A normal response is a gagging sensation and contraction of the pharyngeal muscles. This reflex is mediated by the glossopharyngeal nerve (CN IX) and protects the airway from foreign objects.