For example, the name of the olfactory nerve is cranial nerve I, and it is responsible for vision. Except for olfactory, optic, and vestibulocochlear nerves, all other cranial nerves are mixed nerves, where they consist of both sensory and motor fibres.
Olfactory, optic, and vestibulocochlear nerves consist only a sensory fibre; hence they pick only the stimuli and bring to the brain. Nerves that are originating from the spinal cord are spinal nerves. There are 31 pairs of spinal nerves that are named in relation to their location on the spinal cord. All of them are mixed nerves so that each nerve consists of both ventral motor and dorsal root sensory components. These nerves mainly carry nerve impulse to and from the spinal cord to all parts of the body.
Spinal nerves either go directly to a particular body segment or form a network with adjacent spinal nerves and veins called a plexus. There are four main spinal nerve plexus is present in the body, namely; cervical plexus, brachial plexus, lumber plexus, and sacral plexus.
Cranial nerves and spinal nerves are two types of nerves of the peripheral nervous system. The key difference between cranial and spinal nerves is that the cranial nerves come from the brain while the spinal nerves come from the spinal cord.
Another difference between cranial and spinal nerves is that there are 12 cranial nerve pairs while there are 31 spinal nerve pairs in mammals.
In addition, we can also identify a difference between cranial and spinal nerves based on their functions. Spinal Nerves: Spinal nerves are distributed in the skin, sweat glands, mucosa, blood vessels, joints, and skeletal muscles. Spinal Nerves: All spinal nerves are composed of both sensory and motor neurons. Cranial Nerves: Cranial nerves are involved in vision, sense of the smell, hearing, sense of taste, and eye movements. Spinal Nerves: Spinal nerves are involved in movement, sensation, and sweat secretion.
Cranial Nerves: Cranial nerves form dorsal and ventral roots. Spinal Nerves: Spinal nerves do not form dorsal and ventral roots. Cranial and spinal nerves are the two components of the peripheral nervous system.
Both types of nerves are involved in connecting the internal organs and muscles to the central nervous system to coordinate the functions of the body.
Cranial nerves arise from the brain and are distributed in the brain, neck, and facial areas. In contrast, spinal nerves arise from the spinal cord and are distributed in the rest of the body.
Therefore, the main difference between cranial and spinal nerves is in their paths. The spinal nerves play the major role in reflex actions and the spinal cord saves us from the dangerous stimuli through its reflex actions. The Cranial Nerves and Spinal Nerves are the parts of the peripheral nervous system. It consists of the nerves arising from brain and spinal cord. The vestibular nerve travels from the vestibular system of the inner ear.
The vestibular ganglion houses the cell bodies of the bipolar neurons and extends processes to five sensory organs. Three of these are the cristae, located in the ampullae of the semicircular canals.
Hair cells of the cristae activate afferent receptors in response to rotational acceleration. The other two sensory organs supplied by the vestibular neurons are the maculae of the saccule and utricle.
Hair cells of the maculae activate afferent receptors in response to linear acceleration. The vestibulocochlear nerve has axons that carry the modalities of hearing and equilibrium.
Damage to the vestibulocochlear nerve may cause hearing loss, vertigo, a false sense of motion, loss of equilibrium in dark places, nystagmus, motion sickness, and gaze-evoked tinnitus. A benign primary intracranial tumor of vestibulocochlear nerve is called a vestibular schwannoma also called acoustic neuroma. The glossopharyngeal nerve cranial nerve IX serves many distinct functions, including providing sensory innervation to various head and neck structures.
The glossopharyngeal nerve is the ninth of 12 pairs of cranial nerves. It exits the brainstem out from the sides of the upper medulla, just rostral closer to the nose to the vagus nerve.
Glossopharyngeal nerve : Image of head structures including the glossopharyngeal 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. There are a number of functions of the glossopharyngeal nerve. It controls muscles in the oral cavity and upper throat, as well as part of the sense of taste and the production of saliva.
Along with taste, the glossopharyngeal nerve relays general sensations from the pharyngeal walls. The various functions of the glossopharyngeal nerve are that:. The vagus nerve cranial nerve X is responsible for parasympathetic output to the heart and visceral organs.
The vagus nerve, also known as the pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves. Upon leaving the medulla between the medullary pyramid and the inferior cerebellar peduncle, it extends through the jugular foramen, then passes into the carotid sheath between the internal carotid artery and the internal jugular vein below the head, to the neck, chest and abdomen, where it contributes to the innervation of the viscera.
Vagus nerve : Diagram demonstrating the course of the vagus nerve. The vagus nerve supplies motor parasympathetic fibers to all the organs, except the suprarenal adrenal glands, from the neck down to the second segment of the transverse colon. The vagus also controls a few skeletal muscles, most notably:. This means that the vagus nerve is responsible for such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech via the recurrent laryngeal nerve , swallowing, and keeping the larynx open for breathing via action of the posterior cricoarytenoid muscle, the only abductor of the vocal folds.
This explains why a person may cough when tickled on the ear such as when trying to remove ear wax with a cotton swab. Afferent vagus nerve fibers that innervate the pharynx and back of the throat are responsible for the gag reflex. In addition, 5-HT3 receptor-mediated afferent vagus stimulation in the gut due to gastroenteritis and other insults is a cause of vomiting.
Parasympathetic innervation of the heart is partially controlled by the vagus nerve and is shared by the thoracic ganglia. This occurs commonly in cases of viral gastroenteritis, acute cholecystitis, or in response to stimuli such as the Valsalva maneuver or pain. Excessive activation of the vagal nerve during emotional stress can also cause vasovagal syncope due to a sudden drop in cardiac output, causing cerebral hypoperfusion.
The accessory nerve cranial nerve XI controls the sternocleidomastoid and trapezius muscles of the shoulder and neck. It begins in the central nervous system CNS and exits the cranium through a foramen. Unlike the other 11 cranial nerves, the accessory nerve begins outside the skull. In fact, most of the fibers of the nerve originate in neurons situated in the upper spinal cord.
The accessory nerve : Upon exiting the skull via the jugular foramen, the spinal accessory nerve pierces the sternocleidomastoid muscle before terminating on the trapezius muscle. The fibers that make up the accessory nerve enter the skull through the foramen magnum and proceed to exit the jugular foramen with cranial nerves IX and X.
Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull. Traditional descriptions of the accessory nerve divide it into two components: a spinal component and a cranial component. However, more modern characterizations of the nerve regard the cranial component as separate and part of the vagus nerve.
Therefore, in contemporary discussions of the accessory nerve, it is common to disregard the cranial component when referencing the accessory nerve and assume reference to the spinal accessory nerve. The accessory nerve provides motor innervation from the CNS to the sternocleidomastoid and trapezius muscles of the neck.
The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle has several actions on the scapula, including shoulder elevation and adduction of the scapula.
During neurological examinations, the function of the spinal accessory nerve is often measured by testing the range of motion and strength of the aforementioned muscles.
Limited range of motion or diminished muscle strength often indicates injury of the accessory nerve. Patients with spinal accessory nerve palsy may exhibit signs of lower motor neuron disease, such as atrophy and fasciculations of both the sternocleidomastoid and trapezius muscles. The hypoglossal nerve is the twelfth cranial nerve XII and innervates all extrinsic and intrinsic muscles of the tongue, except for the palatoglossus.
The hypoglossal nerve emerges from the medulla oblongata in the preolivary sulcus where it separates the olive olivary body and the pyramid medullary pyramid. It goes on to traverse the hypoglossal canal and, upon emerging, it branches and merges with a branch from the anterior ramus of C1. It passes behind the vagus nerve and between the internal carotid artery and internal jugular vein which lies on the carotid sheath.
After passing deep to the posterior belly of the digastric muscle it proceeds to the submandibular region to enter the tongue. Hypoglossal nerve : Schematic image of the hypoglossal nerve and the structures it innervates.
The hypoglossal nerve controls tongue movements of speech, food manipulation, and swallowing. It supplies motor fibers to all of the muscles of the tongue, with the exception of the palatoglossus muscle, which is innervated by the vagus nerve cranial nerve X or, according to some classifications, by fibers from the glossopharyngeal nerve cranial nerve IX that hitchhike within the vagus.
Proper function of the hypoglossal nerve is important for executing the tongue movements associated with speech. Many languages require specific and sometimes unusual uses of the nerve to create unique speech sounds, which may contribute to the difficulties some adults encounter when learning a new language.
Several corticonuclear-originating fibers supply innervation and aid in the unconscious movements required upon engaging in speech and articulation. Progressive bulbar palsy is a neuromuscular atrophy associated with the combined lesions of the hypoglossal nucleus and the nucleus ambiguous, upon atrophy of the motor nerves of the pons and medulla. This condition causes dysfunctional tongue movements that lead to speech and chewing impairments and swallowing difficulties.
Tongue muscle atrophy may also occur. Privacy Policy. Skip to main content. Peripheral Nervous System. Search for:. Cranial Nerves. Brief Overview of Cranial Nerves The peripheral nervous system has 12 pairs of cranial nerves that control much of the motor and sensory functions of the head and neck. Learning Objectives Describe the function of the cranial nerves. Key Takeaways Key Points The cranial nerves serve functions such as smell, sight, eye movement, and feeling in the face.
The cranial nerves also control balance, hearing, and swallowing. The twelve cranial nerves, in order from I to XII are: olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharengeal nerve, vagus nerve, spinal accessory nerve, and hypoglossal nerve.
0コメント