PILOEREKTION (Latin pilus of hair + erection; synonym pilomotor reflex) — reduction of voloskovy muscles of skin (the muscles raising hair) under the influence of local or reflex irritation. The item is one of vegetative components of emotional reactions. The size and P.'s character are used as diagnostic indicators at a number of diseases.
The Voloskovy muscle (m. arrector pili) is presented by a layer longwise of the oriented smooth muscle cells connecting an outside cover of a bottom of a hair sack, or a bag of a hair with a papillary layer skin (cm.). The muscle is constantly tense at an obtuse angle in relation to skin. Reduction of a muscle leads to straightening of a hair that is externally shown in the form of a so-called goosellesh. Strong reduction of a voloskovy muscle can squeeze a sebaceous gland and empty it. Are innervated a hair-kovye of a muscle by branches of sympathetic nerves (nn. pilomotorii). The beginning pilomotor, or the volosko-Vyya, nerve fibrils take in nervous cells of side horns of a spinal cord. From here as a part of ventral spinal roots through white connecting branches (rr. communicantes albi) they get to nodes of a sympathetic boundary trunk. Shoots of cells of sympathetic nodes through gray connecting branches (rr. communicantes grisei) join spinal nerves as a part of which they reach further these or those segments of skin. P.'s regulation is not limited to the level of the corresponding segments of a spinal cord. The cerebral cortex, and also the separate centers of a hypothalamus and striate body exercise the central control of pilomotor reactions.
Distinguish two types of P.: local and reflex (true). Local P. has local character and is shown, e.g., after shaped irritation of skin only in the place of influence. It arises in 2 — 3 sec. after influence and lasts for 20 — 30 sec. Reflex P. covers big sites of a body surface, develops in 1 — 2 sec. after irritation and only several seconds last. Reflex P. can be cerebral and spinal. Cerebral P. is caused by mechanical irritation of skin of a back surface of a neck, it extends from top to down and can occupy all party of the same name. The centers of a hypothalamus, a spinal cord and nodes of a sympathetic trunk take part in its implementation. At damages of a spinal cord (a tumor, a myelitis, a prelum) cerebral P. extends only to the level of damage of a spinal cord. Spinal P. is caused by mechanical or thermal irritation of foot; the goosellesh appears on the party of irritation and extends from below up. Spinal P. arises only at the damages of a spinal cord breaking bonds between a head and spinal cord. Defeat of peripheral departments of century of N of page leads to P.'s loss in the corresponding body parts.
The research P. gives the chance of topical diagnosis patol, process in a spinal cord. Determination of size and P.'s character is carried out in reference conditions of the environment by the dosed mechanical irritation or by means of the dosed electric stimulation with photoregistration of sites P. Size P. fluctuates at healthy people depending on a condition of c. N of page, features of endocrine regulation, regulation of body temperature, time of day; To the Item it is most strongly expressed in the morning.
Bibliography: Rosin Ya. A. Fiziologiya of the autonomic nervous system, page 190, M., 1965; Burn J. H. The autonomic nervous system, Oxford, 1971.
P. S. Orlov.