Cranial Nerves

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  • Topic: Cranial nerves, Nervous system, Internal carotid artery
  • Pages : 10 (3664 words )
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  • Published : April 12, 2012
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Cranial Nerves

The human body is a unique and fascinating entity. There is not much notice taken of the features the human body is capable of. The brain is necessary to perform day-to-day actions, such as the ability to speak, and see amongst us. This brain is made up of simple mater (Pia mater, Arachnoid mater, Dura mater) and the cranial surface to protect the brain. We live our daily lives without acknowledging the importance of this organ, the brain, unless you’re a medical student of course! Despite that people go on with their daily activities using the human natural senses. Looking at the world through the eyes, watching for any danger around us; ears for hearing the sounds detecting something that may call for danger, the nose to smell the natural environment, touching and feeling surfaces to become familiar with the surrounding, and to taste the different foods that provide nourishment to stay healthy. All these senses are essential for survival, although what happens if one or more of these senses are taken away? Surviving the everyday world becomes just a little tougher and even impossible in other societies. The cranial nerves in the brain control these senses along with other bodily functions necessary to survive. There are 12 pairs of cranial nerves that emerge from the brain out of various foramina or fissures from the cranium. Each cranial nerve contains sensory or motor fibers or a combination of these fivers to carry impulses from the brain to the various locations allowing the individual to perform normal human functions.

The 12 pairs of cranial nerves (Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducent, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Spinal Accessory, and Hypoglossal) can carry one or more of the five functional components of the motor (efferent) or sensory (afferent) fibers. The motor (efferent) fibers can innervate voluntary (stratified) muscle or it can be involved in innervating glands and involuntary (smooth) muscle. There are 3 types of sensory (afferent) fibers. These fibers can convey sensation from the viscera, transmit general sensation, and transmit unique sensation. The somatic motor axons innervate the striated muscles in the orbit, tongue, external muscles of the neck, and muscles of the face. The motor fibers innervate glands and the involuntary smooth muscles such as viscera and blood vessels have visceral motor axons that make up the cranial outflow of the parasympathetic division of the autonomic nervous system. Sensory fibers that convey sensation from the viscera include visceral sensory fibers that transmit information from the carotid body and sinus, pharynx, larynx, trachea, bronchi, lungs, heart and gastrointestinal tract. Sensations of temperature, pressure and touch are sensed by the somatic sensory fibers that transmit general sensations from the skin and mucous membranes. Sensory fibers that transmit unique sensations use special sensory fibers to convey taste, smell, vision, hearing, and balance.

The cranial nerve pairs are numbered I-XII. The first cranial nerve is olfactory. The main function of cranial number one is to smell. Olfactory enters the cranium via the foramina in cribiform plate of the ethmoid bone. The nerve cell bodies of the olfactory nerve are located on the nasal septum and the medial wall of the superior nasal concha. These special sensory fibers enter into the olfactory bulb and synaps with the mitral cells in the olfactory bulb, which transmits impulses to the brain. There are also a few nerve dysfunctions that are associated with the olfactory nerve. These dysfunctions include Anosmia, loss of smell; hyposmia, decreased sense of smell; parosmia, prevision of the sense of smell; cocosmia, awareness of a disagreeable or offensive odor that does not exist. These nerve dysfunctions maybe caused due to injury to the neurofibrils, compression of the olfactory bulb by hemorrhage and edema or contusion and...
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