Cranial nerves in the context of Diplopia

A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as such (namely sight, smell, touch, taste, and hearing), many more are now recognized. Senses used by non-human organisms are even greater in variety and number. During sensation, sense organs collect various stimuli (such as a sound or smell) for transduction, meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of an organism's cognition, behavior and thought.

In organisms, a sensory organ consists of a group of interrelated sensory cells that respond to a specific type of physical stimulus. Via cranial and spinal nerves (nerves of the central and peripheral nervous systems that relay sensory information to and from the brain and body), the different types of sensory receptor cells (such as mechanoreceptors, photoreceptors, chemoreceptors, thermoreceptors) in sensory organs transduct sensory information from these organs towards the central nervous system, finally arriving at the sensory cortices in the brain, where sensory signals are processed and interpreted (perceived).

The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

The brainstem is very small, making up around only 2.6 percent of the brain's total weight. It has the critical roles of regulating heart and respiratory function, helping to control heart rate and breathing rate. It also provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. Ten pairs of cranial nerves come from the brainstem. Other roles include the regulation of the central nervous system and the body's sleep cycle. It is also of prime importance in the conveyance of motor and sensory pathways from the rest of the brain to the body, and from the body back to the brain. These pathways include the corticospinal tract (motor function), the dorsal column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception), and the spinothalamic tract (pain, temperature, itch, and crude touch).

Shingles, also known as herpes zoster or zona, is a viral disease characterized by a painful skin rash with blisters in a localized area. Typically the rash occurs in a single, wide mark either on the left or right side of the body or face. Two to four days before the rash occurs, there may be tingling or local pain in the area. Other common symptoms are fever, headache, and tiredness. The rash usually heals within two to four weeks, but some people develop ongoing nerve pain which can last for months or years, a condition called postherpetic neuralgia (PHN). In those with poor immune function the rash may occur widely. If the rash involves the eye, vision loss may occur.

Shingles is caused by the varicella zoster virus (VZV) that also causes chickenpox. In the case of chickenpox, also called varicella, the initial infection with the virus typically occurs during childhood or adolescence. Once the chickenpox has resolved, the virus can remain dormant (inactive) in human nerve cells (dorsal root ganglia or cranial nerves) for years or decades, after which it may reactivate and travel along nerve bodies to nerve endings in the skin, producing blisters. During an outbreak of shingles, exposure to the varicella virus found in shingles blisters can cause chickenpox in someone who has not yet had chickenpox, although that person will not suffer from shingles, at least on the first infection. How the virus remains dormant in nerve cells or subsequently re-activates is not well understood.

The vagus nerve, also known as the tenth cranial nerve (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibers and serves as a major pathway that connects the brain to various organs, including the heart, lungs, and digestive tract. As a key part of the parasympathetic nervous system, the vagus nerve helps regulate essential involuntary functions like heart rate, breathing, and digestion. By controlling these processes, the vagus nerve contributes to the body's "rest and digest" response, helping to calm the body after stress, lower heart rate, improve digestion, and maintain homeostasis.

There are two separate vagus nerves: the right vagus and the left vagus. In the neck, the right vagus nerve contains on average approximately 105,000 fibers, while the left vagus nerve has about 87,000 fibers, according to one source. Other sources report different figures, with around 25,000 fibers in the right vagus nerve and 23,000 fibers in the left.

In neuroanatomy, the trigeminal nerve (lit. triplet nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name (trigeminal, from Latin tri- 'three' and -geminus 'twin') derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V₁), the maxillary nerve (V₂), and the mandibular nerve (V₃). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.

The motor division of the trigeminal nerve derives from the basal plate of the embryonic pons, and the sensory division originates in the cranial neural crest. Sensory information from the face and body is processed by parallel pathways in the central nervous system.

A mixed nerve is any nerve that contains both sensory (afferent) and motor (efferent) nerve fibers. All 31 pairs of spinal nerves are mixed nerves. Four of the twelve cranial nerves – V, VII, IX and X are mixed nerves.

In neuroanatomy, the cranial nerve ganglia are ganglia of certain cranial nerves. They can be parasympathetic or sensory. All cranial nerve ganglia are bilateral.

Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear, sensory organ (cochlea and associated structures), or the vestibulocochlear nerve (cranial nerve VIII). SNHL accounts for about 90% of reported hearing loss. SNHL is usually permanent and can be mild, moderate, severe, profound, or total. However, if the loss happened suddenly, and very recently, Prednisone and other treatments may reverse the loss (See SSHL below). Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat.

Sensory hearing loss often occurs as a consequence of damaged or deficient cochlear hair cells. Hair cells may be abnormal at birth or damaged during the lifetime of an individual. There are both external causes of damage, including infection, and ototoxic drugs, as well as intrinsic causes, including genetic mutations. A common cause or exacerbating factor in SNHL is prolonged exposure to environmental noise, or noise-induced hearing loss. Exposure to a single very loud noise, such as a gunshot or bomb blast, can cause noise-induced hearing loss. Using headphones at high volume over time, or being in loud environments regularly, such as a loud workplace, sporting events, concerts, and using noisy machines, can also be a risk for noise-induced hearing loss.

Diplopia is the simultaneous perception of two images of a single object that may be displaced in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results from impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves (III, IV, and VI) that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

Diplopia can be one of the first signs of a systemic disease, particularly to a muscular or neurological process, and it may disrupt a person's balance, movement, or reading abilities.

A nerve root (Latin: radix nervi) is the initial segment of a nerve leaving the central nervous system. Nerve roots can be classified as:

• Cranial nerve roots: the initial or proximal segment of one of the twelve pairs of cranial nerves leaving the central nervous system from the brain stem or the highest levels of the spinal cord.
• Spinal nerve roots: the initial or proximal segment of one of the 31 pairs of spinal nerves leaving the central nervous system from the spinal cord. Each spinal nerve is a mixed nerve formed by the union of a sensory dorsal root and a motor ventral root, meaning that there are 62 dorsal/ventral root pairs, and therefore 124 nerve roots in total, each of which stems from a bundle of nerve rootlets (or root filaments).

Lower motor neurons (LMNs) are motor neurons located in either the anterior grey column, anterior nerve roots (spinal lower motor neurons) or the cranial nerve nuclei of the brainstem and cranial nerves with motor function (cranial nerve lower motor neurons). Many voluntary movements rely on spinal lower motor neurons, which innervate skeletal muscle fibers and act as a link between upper motor neurons and muscles. Cranial nerve lower motor neurons also control some voluntary movements of the eyes, face and tongue, and contribute to chewing, swallowing and vocalization. Damage to lower motor neurons often leads to hypotonia, hyporeflexia, flaccid paralysis as well as muscle atrophy and fasciculations.

The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain, the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

The brainstem is very small, making up around only 2.6 percent of the brain's total weight. It has the critical roles of regulating heart and respiratory function, helping to control heart rate and breathing rate. It also provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. Ten pairs of cranial nerves come from the brainstem. Other roles include the regulation of the central nervous system and the body's sleep cycle. It is also of prime importance in the conveyance of motor and sensory pathways from the rest of the brain to the body, and from the body back to the brain. These pathways include the corticospinal tract (motor function), the dorsal column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception), and the spinothalamic tract (pain, temperature, itch, and crude touch).