The 12 cranial nerves are the abducent, accessory, facial, glossopharyngeal, hypoglossal, oculomotor, olfactory, optic, trigeminal, trochlear, vagus, and vestibulocochlear nerve. The cranial nerve functions are broken up into managing different aspects of your body’s daily tasks from chewing and biting to motor function, hearing, sense of smell, and vision.
The human brain has a number of different nerves running out of it and into the body, which serve to carry important signals to and from the brain. There are twelve cranial nerves in all, but what are their respective functions?
The brain has to have a complex system of nerves and connections with the rest of the body, in order to control the various parts of the body. There are twelve different nerves that run from the brain, out of the base of the skull, and down to the various regions of the body. The majority of these cranial nerves have both sensory and motor neurons, though some of them only have motor neurons.
The twelve different cranial nerves are:
- the abducent nerve
- the accessory nerve
- the facial nerve
- the glossopharyngeal nerve
- the hypoglossal nerve
- the oculomotor nerve
- the olfactory nerve
- the optic nerve
- the trigeminal nerve
- the trochlear nerve
- the vagus nerve
- the vestibulocochlear nerve
The Olfactory Nerve
The olfactory nerve is the first cranial nerve or CN1. The first cranial nerve contains sensory nerves relating to the sense of smell. The olfactory nerve has special olfactory receptor neurons located in the upper portion of the nasal cavity. The olfactory nerve is made out of bundled nerve fibers, and these fibers are stimulated by molecules in the air. The fibers transmit this signal to the olfactory bulb which then transmits the information to the brain.
The Optic Nerve
The optic nerve is a paired nerve, one for each side of the body, which is responsible for transmitting information on visual stimulus to the brain. The visual information that is collected by the various parts of the eye, like rods and cones, is carried via the optic nerve to the occipital lobe of the brain. The optic nerve is also responsible for facilitating the focusing of the eye on objects and constricting the pupil in response to light.
The Oculomotor Nerve
The third cranial nerve, the oculomotor nerve, is responsible for handling most of the motion of the eye. It also allows the eyelids to raise. The oculomotor nerve has general somatic efferent (GSE) axons that are responsible for handling the movement of various skeletal muscle groups around the eye like the superior rectus and the palpebrae superioris.
The Trochlear Nerve
The fourth cranial nerve is the trochlear nerve. The trochlear nerve only hs somatic motor components. The function of the trochlear nerve is to innervate the superior oblique muscle, which is in the region surrounding the eye. It allows for fine, precise movements of the eye when tracking objects.
The Trigeminal Nerve
The trigeminal nerve is divided into three different branches, making it the largest nerve out of all the cranial nerves. The trigeminal nerve is the primary sensory nerve in the face. Not only does it provide sensory information about the face, it also plays a pivotal role in allowing functions like chewing and biting.
The Abducens Nerve
Many nerves are involved in the operation of the eyeball due to how complex it is. This is also true of the abducens nerve. The abducens nerve, or the sixth cranial nerve, helps move the laterus rectus muscle of the eye. This means that it is involved in moving the gaze of the eye outward, away from the nose.
The Facial Nerve
The seventh cranial nerve is the facial nerve. The facial nerve, as the name implies, is concerned with the motion of the face. The facial nerve enables the wide variety of facial expressions humans have by innervating all the various muscles of the face, such as the procerus muscle and nasalis muscle. The facial nerve also carries a large amount of sensory information to the brain, including information regarding taste.
The Vestibulocochlear Nerve
The eighth cranial nerve, AKA the vestibulocochlear nerve, is responsible for bringing information about sound to the brain. The sensory cells of the ear sense information, which is then transported along the vestibulocochlear nerve. The vestibulocochlear nerve is a combination of the vestibular nerve, which carries information about balance, and the cochlear nerve which carries auditory information.
The Glossopharyngeal Nerve
The glossopharyngeal nerve is the ninth cranial nerve, and it has a number of different functions regarding the mouth, nose, and throat. The glossopharyngeal nerve receives information from the middle ear, the rear portion of the tongue, and the tonsils. It also receives sensory information from the carotid bodies and lets the pharyngeal plexus move.
The Vagus Nerve
The tenth cranial nerve is the vagus nerve. The vagus nerve runs down from the skull to the core of the body where it interfaces with the digestive tract, heart, and lungs through a number of different branches. The different branches make the vagus nerve the cranial nerve with the greatest distribution. The vagus nerve supplies almost every organ in the body with motor parasympathetic fibers. The vagus nerve controls a number of skeletal muscles including the palatoglossus muscle and the cricothyroid muscle.
The Accessory Nerve
The accessory nerve, sometimes called the spinal accessory cranial nerve, controls two muscles in the upper body. The accessory nerve is involved with the movement of the sternocleidomastoid muscle, which allows you to turn your head. The accessory nerve is also responsible for the motion of the trapezius muscle, which allows you to move and shrug your shoulders. The portion of the accessory nerve within the cranium gives motor control to the muscles of the pharynx and larynx.
The Hypoglossal Nerve
The twelfth and final cranial nerve, the hypoglossal nerve, is responsible for innervating the intrinsic and extrinsic tongue muscles. The nerve allows the muscles to move and protrude the tongue, though this nerve only has a motor function. The nerve allows you to make the vast array of tongue motions needed to eat, drink, speak, and clear the mouth of saliva.
Damage to any of the nerves can cause a number of different problems, such as facial paralysis or difficulty speaking. Without the cranial nerves, you wouldn’t be able to make the various motions you need to stay alive.
Summary Of The 12 Cranial Nerves
- Olfactory Nerve: Responsible for sense of smell
- Optic Nerve: Plays a role in vision
- Oculomotor Nerve: Controls movement of the eyeballs and eyelids
- Trochlear Nerve: Also involved in movement of the eye
- Trigeminal Nerve: Performs a wide variety of functions, including chewing and facial sensation.
- Abducent Nerve: Involved in eye movement
- Facial Nerve: Controls taste and facial expressions
- Vestibulocochlear Nerve: Responsible for hearing and balance
- Glossopharyngeal Nerve: Responsible for controlling saliva, taste, and swallowing
- Vagus Nerve: Plays a role in the motion of the lungs, throat, heart and digestive system
- Accessory Nerve: Moves the shoulders and neck
- Hypoglossal Nerve: Controls speech, tongue, and swallowing
Hopefully, this gave you a good sense of the cranial nerves and their functions within your body. Have any questions, feel free to leave them below and we’ll try to answer.