| internal anal sphincter | <anatomy> A smooth muscle ring, formed by an increase of the circular fibres of the rectum, situated at the upper end of the anal canal, internal to the outer voluntary external anal sphincter. This sphincter is maximally-contracted when the rectal ampulla is at rest -empty or relaxed to accommodate a distending faecal mass. It is inhibited with filling of the ampulla, increased distension and peristalsis. Synonym: musculus sphincter ani internus, internal sphincter muscle of anus. (05 Mar 2000) |
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| internal arcuate fibres | <anatomy> Fibres that arise in the cuneate and gracile nuclei, pass in a curving course across the midline of the medulla oblongata, and form the contralateral medial lemniscus. It also designates other fibres such as those of the olivocerebellar tract that arch through the substance of the medulla and form sensory decussation. Synonym: fibrae arcuatae internae. (05 Mar 2000) |
| internal attachment | A frictional or mechanically retained unit used in fixed or removable prosthodontics, consisting of closely fitting male and female parts, an attachment that may be rigid in function or may incorporate a movable stress control unit to reduce the torque on the abutment. Synonym: frictional attachment, internal attachment, key attachment, keyway attachment, parallel attachment, slotted attachment. (05 Mar 2000) |
| internal auditory artery | <anatomy, artery> Internal acoustic meatal branch. A branch of the basilar artery that enters the labyrinth through the internal acoustic meatus. Synonym: arteria labyrinthi, ramus meatus acustici interni, arteria auditiva interna, artery of labyrinth, internal auditory artery. (05 Mar 2000) |
| internal auditory canal | <anatomy> Abnormal if difference in diameter greater than 2 mm, schematic: 7 8-sv anterior posterior 8-c 8-iv, 7 facial nerve (VII), 8-c cochlear division of VIII, 8-sv superior vestibular division, 8-iv inferior vestibular division (12 Dec 1998) |
| internal auditory foramen | The inner opening of the internal acoustic meatus on the posterior surface of the petrous part of the temporal bone. Synonym: porus acusticus internus, internal acoustic foramen, internal acoustic pore, auditory pore, internal auditory foramen, orifice of internal acoustic meatus. (05 Mar 2000) |
| internal auditory meatus | internal acoustic meatus |
| internal auditory veins | One or more veins accompanying the labyrinthine artery; they drain the internal ear, pass out through the internal acoustic meatus, and empty into the transverse sinus or the inferior petrosal sinus. Synonym: venae labyrinthi, internal auditory veins. (05 Mar 2000) |
| internal axis of eye | <anatomy> That part of the optic axis from the midpoint of the posterior surface of the cornea to the anterior surface of the retina opposite the posterior pole. Synonym: axis bulbi internus. (05 Mar 2000) |
| internal base of skull | <anatomy> The interior aspect of the skull base on which the brain rests; the floor of the cranial cavity. See: base of skull. Synonym: basis cranii interna. (05 Mar 2000) |
| internal bias | Applied to the motile behaviour of crawling cells that, in the short term, show persistence and do not behave as true random walkers. Any intrinsic regulation of the random motile behaviour of the cell could be considered as internal bias. (18 Nov 1997) |
| internal branch of accessory nerve | <anatomy, nerve> Branch of the accessory nerve trunk which carries fibres from the cranial root and which unites with the vagus nerve in the jugular foramen. See: accessory nerve. Synonym: ramus internus nervi accessorii, internal ramus of accessory nerve. (05 Mar 2000) |
| internal branch of superior laryngeal nerve | <anatomy, nerve> Terminal branch of superior laryngeal nerve (with external branch) conveying sensory fibres to the supraglottic larynx. Synonym: ramus internus nervi laryngei superioris. (05 Mar 2000) |
| internal canthus | The angle formed by the union of the upper and lower eyelids medially. Synonym: angulus oculi medialis, angulus oculi nasalis, internal canthus, medial canthus. (05 Mar 2000) |
| internal capsule | <anatomy, neurology> A massive layer (8 to 10 mm thick) of white matter separating the caudate nucleus and thalamus (medial) from the more laterally situated lentiform nucleus (globus pallidus and putamen). It consists of 1) fibres ascending from the thalamus to the cerebral cortex that compose, among others, the visual, auditory, and somatic sensory radiations, and 2) fibres descending from the cerebral cortex to the thalamus, subthalamic region, midbrain, hindbrain, and spinal cord. The internal capsule is the major route by which the cerebral cortex is connected with the brainstem and spinal cord. Laterally and superiorly it is continuous with the corona radiata which forms a major part of the cerebral hemisphere's white matter; caudally and medially it continues, much reduced in size, as the crus cerebri which contains, among others, the pyramidal tract. On horizontal section it appears in the form of a V opening out laterally; the V's obtuse angle is called genu (knee). Its anterior and posterior limbs, respectively, the crus anterior and crus posterior. Synonym: capsula interna. (05 Mar 2000) |