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Cranial nerves are the nerves that emerge directly from the brain, of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck, including the special senses of vision, taste, smell, and hearing.
The sense of balance or equilibrioception is the perception of balance and spatial orientation. It helps prevent humans and nonhuman animals from falling over when standing or moving. Equilibrioception is the result of a number of sensory systems working together; the eyes, the inner ears, and the body's sense of where it is in space (proprioception) ideally need to be intact.
Tears are a clear liquid secreted by the lacrimal glands found in the eyes of all land mammals. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. The different types of tears—basal, reflex, and emotional—vary significantly in composition.
The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocular muscles responsible for outward gaze. It is a somatic efferent nerve.
Articles related to anatomy include:
The brainstem is the stalk-like part of the brain that connects the forebrain 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.
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. All Anura, and some reptiles, birds, and sharks have full nictitating membranes; in many mammals, a small, vestigial portion of the nictitating membrane remains in the corner of the eye. Some mammals, such as cats, beavers, polar bears, seals and aardvarks, have full nictitating membranes. Often called a third eyelid or haw, it may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia.
The vestibulo-ocular reflex (VOR) is a reflex that acts to stabilize gaze during head movement, with eye movement due to activation of the vestibular system, it is also known as the Cervico-ocular reflex. The reflex acts to stabilize images on the retinas of the eye during head movement. Gaze is held steadily on a location by producing eye movements in the direction opposite that of head movement. For example, when the head moves to the right, the eyes move to the left, meaning the image a person sees stays the same even though the head has turned. Since slight head movement is present all the time, VOR is necessary for stabilizing vision: people with an impaired reflex find it difficult to read using print, because the eyes do not stabilise during small head tremors, and also because damage to reflex can cause nystagmus.
Eyeblink conditioning (EBC) is a form of classical conditioning that has been used extensively to study neural structures and mechanisms that underlie learning and memory. The procedure is relatively simple and usually consists of pairing an auditory or visual stimulus with an eyeblink-eliciting unconditioned stimulus (US). Naïve organisms initially produce a reflexive, unconditioned response (UR) that follows US onset. After many CS-US pairings, an association is formed such that a learned blink, or conditioned response (CR), occurs and precedes US onset. The magnitude of learning is generally gauged by the percentage of all paired CS-US trials that result in a CR. Under optimal conditions, well-trained animals produce a high percentage of CRs. The conditions necessary for, and the physiological mechanisms that govern, eyeblink CR learning have been studied across many mammalian species, including mice, rats, guinea pigs, rabbits, ferrets, cats, and humans. Historically, rabbits have been the most popular research subjects.
The medial longitudinal fasciculus (MLF) is a prominent bundle of nerve fibres which pass within the ventral/anterior portion of periaqueductal gray of the mesencephalon (midbrain). It contains the interstitial nucleus of Cajal, responsible for oculomotor control, head posture, and vertical eye movement.
The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain. Three distinct, primarily inhibitory, cellular groups are located interspersed within these fibers, and are thus named the nuclei of the lateral lemniscus.
In neuroanatomy, the pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in mediating behavioral responses to acute changes in ambient light such as the pupillary light reflex, the optokinetic reflex, and temporary changes to the circadian rhythm. In addition to the pretectum's role in the visual system, the anterior pretectal nucleus has been found to mediate somatosensory and nociceptive information.
The Edinger–Westphal nucleus is one of two nuclei of the oculomotor nerve and is located in the midbrain. It receives afferents from both pretectal nuclei. It contains parasympathetic pre-ganglionic neuron cell bodies that synapse in the ciliary ganglion. It contributes the autonomic, parasympathetic component to the oculomotor nerve, ultimately providing innervation to the iris sphincter muscle and ciliary muscle to mediate the pupillary light reflex and accommodation, respectively.
The abducens nucleus is the originating nucleus from which the abducens nerve (VI) emerges—a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the caudal portion of the pons near the midline, medial to the sulcus limitans.
The facial motor nucleus is a collection of neurons in the brainstem that belong to the facial nerve. These lower motor neurons innervate the muscles of facial expression and the stapedius.
The accessory facial motor nucleus is a small cluster of neurons dorsal to the facial motor nucleus in the pontine tegmentum. It has been reported for the human, rat, and mouse.
Serotonergic cell groups refer to collections of neurons in the central nervous system that have been demonstrated by histochemical fluorescence to contain the neurotransmitter serotonin (5-hydroxytryptamine). Since they are for the most part localized to classical brainstem nuclei, particularly the raphe nuclei, they are more often referred to by the names of those nuclei than by the B1-9 nomenclature. These cells appear to be common across most mammals and have two main regions in which they develop; one forms in the mesencephlon and the rostral pons and the other in the medulla oblongata and the caudal pons.
Perihypoglossal nuclei are three prominent groups of neurons in the caudal medulla oblongata near the hypoglossal nucleus: the nucleus prepositus hypoglossi, intercalated nucleus, and sublingual nucleus. They are involved in controlling eye movements: they send their principal projections to the three cranial nerve nuclei controlling extrinsic eye muscles via the medial longitudinal fasciculus.
Salomon Zender Langer is an Argentinian pharmacologist whose family had fled from Poland to Argentina in the early 1930s and were thus saved from the Holocaust during the Second World War.
References
- ↑ Swanson LW (1998). Brain Maps: Structure of the Rat Brain (2nd Revised ed.). Amsterdam: Elsevier Science. OCLC 640898561.
- ↑ Marek GJ, McMaster SE, Gormezano I, Harvey JA (1984). "The role of the accessory abducens nucleus in the rabbit nictitating membrane response". Brain Res. 299 (2): 215–29. doi:10.1016/0006-8993(84)90703-0. PMID 6733447. S2CID 26319541.
- ↑ Crosby EC, Humphrey T, Lauer EW (1962). Correlative Anatomy of the Nervous System . New York: MacMillan. OCLC 557246.
