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Cranial Nerves in vertebrates refer to those paired nerves of the peripheral nervous system. It connect the muscles and sense organs of the head and thoracic region directly with the brain.
- Cranial Nerves are responsible for sending information between the brain and parts of the body.
- The information is sent in the form of electrical signals.
- The predominant functions of the cranial nerves include motor and sensory activities.
- Some of the nerves conjointly perform both sensory functions.
- The nerves are numbered in Roman numerals from 1 – 12.
- The numbers of each nerve correspond to the position of these nerves in the brain.
- Cranial Nerves increase the tasting, smelling and hearing power of an individual.
Read More: Nervous System
Key Terms: Cranial Nerves, Brains, Nerves, Sensory Motor, Organs, Head, Neck, Nervous System, Spinal Bones
What are Cranial Nerves?
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Cranial nerves are responsible for carrying information from the brain to other parts of the body, particularly to the head and neck region. These nerves are paired and are present along both the sides of the body.
- Cranial Nerves are mainly responsible for facilitating functions such as vision, smell, muscular movement and hearing.
- They are mainly concerned with the regions of head, neck, and other facial regions of the body.
- These nerves arise directly from the brain in contrast to spinal nerves and exit through its foramina.
- Most of the cranial nerves originate in the brain stem.
- They pass through the muscles and sense organs of the head and neck.
- The nerves are part of the peripheral nervous system and central nervous system.
Cranial Nerves
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Types of Cranial Nerve
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Nervous System consists of twelve cranial nerves which are numbered using the Roman numerals. The detail about each nerves is provided:
| Cranial Nerves | Location of nerves | Type of nerves | Function of nerves |
|---|---|---|---|
| Olfactory | Cribriform plate | Sensory | Smell |
| Optic | Optic foramen | Sensory | Vision |
| Oculomotor | Superior orbital fissure | Motor | Eye movement |
| Trochlear | Superior orbital fissure | Motor | Eye movement |
| Trigeminal | Superior orbital fissure | Mixed | Facial sensation |
| Abducens | Superior orbital fissure | Motor | Eye movement |
| Facial | Internal auditory canal | Mixed | Facial expression |
| Vestibulocochlear nerve | Internal auditory canal | Sensory | Hearing and balance |
| Glossopharyngeal | Jugular foramen | Mixed | Oral sensation and taste |
| Vagus | Jugular foramen | Mixed | Vagus nerve |
| Accessory | Jugular foramen | Motor | Shoulder elevation and head-turning |
| Hypoglossal | Hypoglossal | Motor | Tongue movement |
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Functions of Cranial Nerves
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The function of cranial nerves are as follows:
Olfactory Nerves
This is the primary nerve that is responsible for the smell. Damage to this nerve may result in distortion of smell as well as taste.
Optic Nerves
The optic nerve II is responsible for vision. This nerve is responsible for transmitting visual information from the eyes to the brain and vice versa. Any damage to this nerve results in issues related to sight and vision.
Oculomotor Nerves
Oculomotor nerve is responsible for aiding the movement of the eyes in the body. Damage to this nerve leads to distortion in vision or double vision and even problems in the coordination of the eyes.
Read More: Neural Control and Coordination
Trochlear and Abducens Nerves
These nerves are also responsible for helping in eye movement. Damage to the Trochlear nerve might cause the inability to move the eyeball downwards, and damage to the abducens nerve might result in diplopia.
Trigeminal Nerves
This nerve helps in facial sensation and comprises three parts, namely ophthalmic, maxillary and mandibular.
Facial Nerves
This nerve is responsible for aiding facial expressions. Any damage to this nerve might cause the inability to move face parts on one or more sides.
Vestibulocochlear Nerves
Vestibulocochlear (auditory, vestibular nerve) is responsible for hearing and for maintaining balance. This helps the eyes to keep track of moving objects while your head is stable. Any damage to this nerve results in the sensation of spinning and dizziness. Furthermore, this nerve branches into the vestibular nerve and cochlear nerve.
Glossopharyngeal
This nerve is responsible for the oral sensations and the sense of taste. Any damage to this nerve may disable the sensation of taste.
Vagus Nerves
This nerve monitors the level of oxygen and aids in feeling the sensation of heat or cold near the throat area. Any damage to this nerve results in the inability to swallow. Furthermore, any major damage to the vagus nerve might result in hypertension or high blood pressure and, subsequently, a heart attack.
Read More: Types, Nervous System, Neurons, Nerves Disorders
Accessory Nerves
This nerve, also known as nerve XI, arises from two roots, namely the cranial and spinal bones. This nerve aids in controlling the swallowing movements and additionally helps in the movement of the head as well as the shoulders.
Hypoglossal Nerves
This nerve facilitates the movement of the tongue and helps in activities such as swallowing, talking and so on.
Cranial Nerves
Read more: Sensory Perceptions
Damages to the Cranial Nerves
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The following are few kinds of damages which are commonly observed in case of cranial nerves:
Compression
The nerves may be compressed as a consequence of increased intracranial pressure, mass effect of intracerebral haemorrhage, or tumour that presses against the nerves and interferes with the transmission of impulses along the nerve.
- An increase in intracranial pressure may lead to impairment of the optic nerves (II).
- The consequence of compression of the surrounding veins and capillaries, thereby cause swelling of the eyeball (papilloedema).
Stroke
Occlusion of blood vessels that supply the nerves or their nuclei ( a condition known as ischemic stroke) may cause specific signs and symptoms relating to the damaged area. If there is a stroke of the midbrain, pons or medulla, there is a possibility that various cranial nerves may be damaged, thereby resulting in their dysfunction and thus resulting in symptoms of numerous different syndromes.
Inflammation
Inflammation of cranial nerves can occur as a consequence of infections, such those caused by viruses such as reactivated herpes simplex virus, or these infections can even occur spontaneously. For instance, Inflammation of the facial nerve (VII) may result in Bell's palsy.
Read More: Pons
Things to Remember
- Cranial nerves emerge from the central nervous system located above the level of the first vertebrae of the vertebral column.
- Each cranial nerve is present on both sides of the nervous system.
- It forms an integral part of the peripheral nervous system.
- Humans have twelve pairs of cranial nerves (I–XII), with the terminal nerve (0) more recently canonised.
- Nerves can be damaged by compression, inflammation and stroke.
Read More: Control and Coordination
Sample Questions
Ques. How many cranial nerves are present in the human body? [2 mark]
Ans. There are 12 pairs of cranial nerves situated in the human body. The olfactory nerve, optic nerve, facial nerve, oculomotor nerve, vagus nerve, hypoglossal, nerve, vestibulocochlear nerve, accessory nerve, trochlear nerve, glossopharyngeal nerve, trigeminal nerve and abducens nerve.
Ques. What is the function of the optic nerve and oculomotor nerve? [2 marks]
Ans. The optic nerve is responsible for relaying signals between the brain and the eyes and acts as the agent of vision. Thereby, enabling the eyes to see. The oculomotor nerve is situated at the Superior orbital fissure and is responsible for the eye movement.
Ques. How are cranial nerves different from spinal nerves? [2 marks]
Ans. The cranial nerves emerge directly from the brain as well as the brainstem. On the contrary, the spinal nerves emerge from the segments present in the spinal cord.
The cranial nerves transmit information between the brain and body. Whereas, the spinal nerves carry signals from the spinal cord to the body.
Ques. What is a spinal nerve? [1 mark]
Ans. A spinal nerve is a mixed nerve that is responsible for transmitting sensory, motor or autonomic signals between the spinal cord to the body. There are 31 pairs of spinal nerves present in the human body.
Ques. What happens if the vestibulocochlear nerve gets damaged? [1 mark]
Ans. In conditions wherein the vestibulocochlear nerve gets damaged, it results in dizziness and the sensation of spinning in the body.
Ques. What is the purpose of cranial nerves and accessory nerve in the human body? [2 marks]
Ans. The cranial nerves carry information from the brain to all parts of the body and thereby facilitates the sense of vision, smell, muscle movement and hearing. On the other hand, the accessory nerve is that cranial nerve which arises from the cranial and the spinal bones and is responsible for controlling the activity of swallowing as well as the movement of the head and shoulders of the body.
Ques. Which cranial nerve is responsible for taste and eye movement? [2 marks]
Ans. The glossopharyngeal nerve is responsible for sensation of taste occurring via the tongue. Four cranial nerves are responsible for controlling eye movement. These cranial nerves are abducen, oculomotor, trochlear and the optic nerve.
Ques. What is a neuron? [2 marks]
Ans. A neuron is the basic building block of the nervous system. Neurons are responsible for transmitting information throughout the body and are responsible for communicating that information in both chemical as well as electrical forms.
Ques. What are the two mnemonics phrases that can be used to remember the phrase for cranial nerve? (2 marks)
Ans. The two mnemonics phrases that can be used to remember the phrase for cranial nerve are as follows:
- Oh Once One Takes The Anatomy Final, Very Good Vacations Are Heavenly
- Oh, Oh, Oh, To Touch And Feel Very Good Velvet, Are Heavenly.
Ques. Name the different type of cranial nerves with their location and type? (3 marks)
Ans. The different type of cranial nerves with their location and type are as follows:
| Cranial Nerves | Location of nerves | Type of nerves |
|---|---|---|
| Olfactory | Cribriform plate | Sensory |
| Optic | Optic foramen | Sensory |
| Oculomotor | Superior orbital fissure | Motor |
| Trochlear | Superior orbital fissure | Motor |
| Trigeminal | Superior orbital fissure | Mixed |
| Abducens | Superior orbital fissure | Motor |
| Facial | Internal auditory canal | Mixed |
| Vestibulocochlear nerve | Internal auditory canal | Sensory |
| Glossopharyngeal | Jugular foramen | Mixed |
| Vagus | Jugular foramen | Mixed |
| Accessory | Jugular foramen | Motor |
| Hypoglossal | Hypoglossal | Motor |
Ques. Explain the cranial nerve? (4 marks)
Ans. Cranial nerves are considered to be a part of the peripheral nervous system, although olfactory and optic nerves are considered to be part of the Central nervous system. Majority of the cranial nerves belong to the somatic system.
- In the body, some of the cranial nerves are responsible for sensory and motor functions as they contain only sensory fibres and motor fibres whereas others are mixed nerves because they include both sensory and motor fibres.
- Only cranial nerves I and II are entirely sensory and are responsible for the human sense of smell and vision (optic nerve II). However, the rest of the cranial nerves contain both the afferent as well as the efferent fibres and are thus referred to as mixed cranial nerves.
- However, the vagus nerve also has branches to most of the internal organs present in the body and thus forms a part of the autonomic nervous system.
Ques. What kind of damages are caused to the cranial nerve? [3 marks]
Ans. The kind of damages caused to the cranial nerves are as follows:
- Compression: Compression is a kind of damage which is caused by the increased intracranial pressur and mass effect of intracerebral haemorrhage. It also includes the tumour that effects the nerves and interferes with the transmission of impulses.
- Stroke: Stroke effects the blood vessels that supply the nerves or their nuclei which are relating to the damaged area. The cranial nerves get severely damaged when medulla, pons and midbrain are damaged.
- Inflammation: Infections, for example viruses like reactivated herpes simplex virus or these infections can be spontaneous, may cause inflammation of the cranial nerves.
Ques. What is the function of the facial nerve and vagus nerve? [2 marks]
Ans. The facila nerve is a mixed type of nerve that is responsible for aiding facial expressions. Any damage to this nerve might cause the inability to move face parts on one or more sides. On the other hand vagus nerve is used to monitors the level of oxygen and aids in feeling the sensation of heat or cold near the throat area.
Ques. How many types of nerves are sensory, and how many types of nerves are mixed nerves? [1 mark]
Ans. There are three types of sensory nerves present in the cranial nerves. In addition to it, four types of mixed nerve are found in the cranial nerve.
Ques. What is the function of Accessory nerve and Hypoglossal nerve? [2 marks]
Ans. Accessory nerve is a type of nerve that aids in controlling the swallowing movements and additionally helps in the movement of the head as well as the shoulders. On the other hand, hypoglossal nerve is a nerve that facilitates the movement of the tongue and helps in activities such as swallowing, and talking.
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