It arises from the olfactory lobe of the forebrain and enters the mucous membrane of the nose. It carries sensory nerves and olfactory impulses to the brain.

OOO-TTA-FAG-VAH
I. Olfactory: It arises from the olfactory lobe of the forebrain and enters the mucous membrane of the nose. It carries sensory nerves and olfactory impulses to the brain.
II. Optic: The right and left optic nerves arise from the optic lobes of the midbrain to form an X-shaped optic chiasma. It carries sensory nerves and vision to the brain.
III. Oculomotor: arises from the cingulate region of the midbrain and innervates the rectus muscle of the eye and the inferior oblique muscle. It is the optic nerve. It controls eye muscle function.
IV. Trochlear: arises from the surface of the midbrain and inserts into the superior oblique muscle of the eye. It controls the circulation of the vagus nerve and the optic nerve.
V. Trigeminal: arises from the medulla oblongata and divides into three branches.
(i) Opthalmic: It is the smallest branch. It penetrates the skin of the front of the head, the upper axilla and the mucous membrane of the nose. It carries sensory nerves and sensations from the affected parts to the brain.
(ii) Ophthalmic: It penetrates the mucous membranes of the lower orbit, upper jaw and upper jaw. It carries sensory nerves and sensations from the affected parts to the brain.
(iii) Ophthalmic: It penetrates the skin of the lower jaw and lips. It is mixed nerves. It gives definition to the skin of the lower jaw and lips.
VI. Abducens: arises from the medulla oblongata and innervates the rectus muscle of the eye. They control the circulation of the vagus nerve and the optic nerve.
VII. Facial: It arises from the medulla oblongata and divides into two branches. It is mixed nerves.
(i) Palatine: It enters the roof of the mouth and receives taste. It is a sensory nerve.
(ii) Hyomandibular: It penetrates the eardrum, lower jaw and mucous membrane of the mouth. It controls the conduction of mixed nerves and muscles of taste and throat.
VIII. Auditory: arises from the medulla oblongata and enters the inner ear. It carries sensory nerves and sensations of hearing and balance to the brain.
IX. Glossopharyngeal: arises from the medulla oblongata and enters the tongue. It is mixed nerves. It helps in the circulation of taste, tongue and pharynx.
X. Glossopharyngeal: It arises from the medulla oblongata and divides into four branches. It is mixed nerves.
(i) Laryngeal: It enters the larynx.
(ii) Cardiac: It extends to the heart.
(iii) Gastric : Carries nerves in the stomach.
(iv) Pulmonary: Extends to the lungs.

Those nerves that carry nerve impulses from different parts of the body to the central nervous system and from the central nervous system to different parts of the body are called mixed nerves.

The nerves that carry the stimulus from the central nervous system to different parts of the body are called vagal nerves. It is composed of motor neurons. They are known as extrinsic, afferent, efferent nerves etc.

The nerves that carry stimuli from the peripheral parts of the body to the central nervous system are called sensory nerves. It is composed of sensory neurons. They are known as intrinsic, sensory, sensory, afferent nerves etc.

The carotid nerve can be divided into three types based on the nature of the function.
1. Sensory Nerves: The nerves that carry stimuli from the peripheral parts of the body to the central nervous system are called sensory nerves. It is composed of sensory neurons. They are known as intrinsic, sensory, sensory, afferent nerves etc.
2. Motor Nerve: The nerves that carry the stimulus from the central nervous system to different parts of the body are called vagal nerves. It is composed of motor neurons. They are known as extrinsic, afferent, efferent nerves etc.
3. Mixed nerve: Those nerves that carry nerve impulses from different parts of the body to the central nervous system and from the central nervous system to different parts of the body are called mixed nerves.

The structural and functional unit of a cell is called a nerve. All the peripheral nerves originating from the brain and spreading to different parts of the body through the carotid foramen are called carotid nerves. Humans have 12 pairs of carotid nerves (OOO-TTA-FAG-VAH). They are indicated by Roman numerals (I-XII).

The cavity of the medulla oblongata is called the fourth ventricle. One end is connected to the cerebral aqueduct and the other end to the central canal of the spinal cord.

The cavity of hypothalamus is called third ventricle. One end of it is connected to the 3rd ventricle.

The 1st and 2nd ventricles of the brain are collectively called the lateral ventricles. There are two cavities inside the cerebral hemispheres. These two cavities are called lateral ventricles. They are individually connected to the 3rd ventricle by the foramen of Monro or interventricular orifice.