Afferent nerve
(noun)
Carries nerve impulses from sensory receptors or sense organs toward the central nervous system.
Examples of Afferent nerve in the following topics:
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Classification of Nerves
- Nerves are primarily classified based on their direction of travel to or from the CNS, but they are also subclassified by other nerve characteristics.
- Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from mechanoreceptors in skin.
- Mixed nerves contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same nerve bundle.
- Cranial nerves innervate parts of the head and connect directly to the brain.
- Cranial nerves are typically assigned Roman numerals from 0 to 12.
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Vagus (X) Nerve
- The vagus nerve (cranial nerve X) is responsible for parasympathetic output to the heart and visceral organs.
- The vagus nerve, also known as the pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves.
- Eighty to 90% of the nerve fibers in the vagus nerve are afferent (sensory) nerves that communicate the state of the viscera to the brain.
- The vagus nerve includes axons that emerge from or converge onto four nuclei of the medulla.
- Afferent vagus nerve fibers that innervate the pharynx and back of the throat are responsible for the gag reflex.
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The Peripheral Nervous System (PNS)
- Both divisions work without conscious effort and have similar nerve pathways, but they generally have opposite effects on target tissues.
- Afferent fibers, or nerves that receive information from external stimuli, carry sensory information through pathways that connect the skin and skeletal muscles to the CNS for processing.
- The information is then sent back via efferent nerves, or nerves that carry instructions from the CNS, back through the somatic system.
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Classification of Neurons
- Afferent neurons convey information from tissues and organs into the central nervous system (e.g. sensory neurons).
- Afferent and efferent also refer generally to neurons that bring information to or send information from a brain region.
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General Organization of the Somatosensory System
- The cell body of the primary neuron is housed in the dorsal root ganglion of a spinal nerve or, if sensation is in the head or neck, the ganglia of the trigeminal or cranial nerves.
- Spinal cord: Afferent pathways in the spinal cord serve to pass information from the periphery and the rest of the body to the brain.
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Trochlear (IV) Nerve
- The trochlear nerve (cranial nerve IV) is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye.
- The trochlear nerve (cranial nerve IV) is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye.
- The trochlear nerve is unique among the cranial nerves in several respects.
- Other than the optic nerve (cranial nerve II), it is the only cranial nerve that decussates (crosses to the other side) before innervating its target.
- Lesions of all other cranial nuclei affect the ipsilateral side (except of course the optic nerve, cranial nerve II, which innervates both eyes).
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Accessory (XI) Nerve
- The accessory nerve (cranial nerve XI) controls the muscles of the shoulder and neck.
- The accessory nerve (cranial nerve XI) controls the sternocleidomastoid and trapezius muscles of the shoulder and neck.
- Unlike the other 11 cranial nerves, the accessory nerve begins outside the skull.
- Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull.
- However, more modern characterizations of the nerve regard the cranial component as separate and part of the vagus nerve.
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Brief Overview of Cranial Nerves
- Cranial nerves are the nerves that emerge directly from the brain (including the brainstem).
- The terminal nerves, olfactory nerves (I) and optic nerves (II) emerge from the cerebrum or forebrain, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.
- The optic nerve (II): This nerve carries visual information from the retina of the eye to the brain.
- The abducens nerve (VI): A motor nerve that innervates the lateral rectus muscle of the eye, which controls lateral movement.
- The hypoglossal nerve (XII): This nerve controls the tongue movements of speech, food manipulation, and swallowing.
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Olfactory (I) Nerve
- The olfactory nerve, or cranial nerve I, is the first of 12 cranial nerves and is responsible for the sense of smell.
- The olfactory nerve, or cranial nerve I, is the first of the 12 cranial nerves.
- The olfactory nerve is the shortest of the 12 cranial nerves and only one of two cranial nerves (the other being the optic nerve) that do not join with the brainstem.
- The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity.
- The olfactory nerves consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the cribriform plate of the ethmoid bone.
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Oculomotor (III) Nerve
- The oculomoter nerve (cranial nerve III) controls eye movement, such as constriction of the pupil and open eyelids.
- The oculomotor nerve is the third paired cranial nerve.
- Cranial nerves IV and VI also participate in control of eye movement.
- Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve, while the nasociliary nerve is placed between its two rami (the superior and inferior branch of oculomotor nerve).
- Image of cranial nerves showing the position of the oculomotor nerve.