Brain & N eurorehabilitation Vol. 2, No. 2, September, 2009 정상삼킴과관련된신경생리학 가천의과학대학교의학전문대학원재활의학교실 이주강 Normal Swallowing Mechanism on Neurophysiogical Basis Ju Kang Lee, M.D., Ph.D. Department of Physical and Rehabilitation Medicine, Gachon University of Medicine and Science School of Medicine Swallowing, known scientifically as deglutition, is the process in the human or animal body that makes something pass from the mouth, to the pharynx, into the esophagus, with the shutting of the epiglottis. If this fails and the object goes through the trachea, then choking or pulmonary aspiration can occur. In the human body it is controlled by the swallowing reflex. The nose and pharynx serves as a pathway for air in breathing. During swallowing, the pharynx is isolated from the nasal cavity and lower airway by velopharyngeal and laryngeal closure during the pharyngeal swallow. Normal swallowing process is complex neuromuscular activities consisting of three phases, an oral, pharyngeal and esophageal phase. The oral phase is usually voluntary process and mainly controlled by the fronto-temporal cerebral cortex with contributions from the motor cortex and other cortical areas. The pharyngeal phase is controlled by swallowing center in the medulla and pons. It is initiated mainly by the receptors of the posterior upper pharyngeal wall and swallowing reflex occurred. The food bolus is advanced from the pharynx to the esophagus through sequential contraction of the constrictor muscles. During swallowing reflex, the respiratory center of the medulla is inhibited by swallowing center accompanied by velopharyngeal and laryngeal closure to prevent airway aspiration. The esophageal phase, which is passive process, started from relaxation of upper esophageal sphincter. The autonomic system network coordinates the smooth muscles of pharynx and esophagus sequentially pushes the bolus through the esophagus into the stomach. (Brain & NeuroRehabilitation 2009; 2: 98-102) Key Words: physiology, swallowing, swallowing phase 서론 삼킴이란음식혹은물질을구강으로받아들이고인두를통해식도로이동시키는과정을말하는데이과정중기도입구와코인두가닫혀질식이나기도흡인을방지하게된다. 정상삼킴은통상적으로음식물덩어리의위치에따라구강준비기 / 구강기, 인두기, 식도기의세과정으로나누어진부드럽게조화된일련의움직임으로이루어진다. 각각의과정은고유한기능을가지게되며이러한기능에이상이올때그에따른증상이생기게된다. 삼킴과정이흡인이나질식이없이일어나기위해서는호흡및저작기능과의조화가필요한데이러한동작들은뇌간에있는조화운동중추 (central pattern generator) 에의해조절 교신저자 : 이주강, 인천시남동구구월동 1198 406-760, 가천의과학대학교길병원재활의학과 Tel: 032-460-8427, Fax: 032-460-3722 E-mail: pmrdoc@gilhospital.com 되는정형화된형태로나타난다. 신경계손상에의한다양한종류의삼킴곤란을진단하고치료하기위해서는정상삼킴에대한이해가필수적이므로정상삼킴을각과정별로나누어각과정의해부학적인움직임과신경생리학적기전을살펴보고자한다. 본론 1) 정상삼킴과정 (Normal swallowing process) (1) 구강준비기 / 구강기구강준비기는구강기에서가장앞부분을차지한다. 이시기는삼킬수있도록음식물을적당히작은덩어리로만들어혀위에놓게되는과정이며이러한과정이성공적으로일어나기위해서는입술이제대로닫히고혀의움직임이원활해야하며씹는과정을수행하는근육들의기능이유지되어야한다. 씹는것은음식덩어리를변화시킬뿐만아니라침분비를자극하기도하는데이러한현상이 98
이주강 : 정상삼킴과관련된신경생리학 없으면삼키기가어려워지고늦어지게된다. 구강기의분류는음식물의이동에따라입안으로음식물을받아들이는과정을 1기이동으로, 삼키기적당하게준비된음식물이인두로이동하는과정을 2기이동으로구분하게된다. 구강기에일어나는과정은음식물의물리적인형태에따라차이를나타내는데액체상태의음식물인경우씹는과정이필요없고유동식일경우도거의씹는과정을거치지않고음식덩어리를혀위에올려놓는동작이일어날수있다. 단단한음식물일경우는일단입술을통과해구강안에들어온후씹는과정을통해작은크기로잘리고부수어지고갈리며침과고루섞이게된다. 이때음식물이잇몸과경구개의감각수용기를자극하여 5번뇌신경을통해저작에관여하는뇌간의조화운동중추를자극하게되고이에따라턱을올리고내리는근육들의순차적인운동이일정한순서로일어나게되어결과적으로일정한주기를가지는턱의움직임과혀의회전운동을일으켜씹는과정을수행하게된다. 혀의회전운동은턱의움직임에맞 추어음식물을아래윗니의열려진사이로밀어넣는작용을하며볼에위치한근육들이동시에수축하여바깥쪽에서음식물을치아사이로밀어주는작용을한다. 이과정이일어나는동안침샘에서침이분출되어섞임으로써음식물을부드럽게해주고혀의미뢰 (taste bud) 를자극하게된다. 입안의감각수용기는지속적으로음식물의물리적인성상을감지하게되며씹혀진음식물이일단삼키기적당한상태로부드럽게준비되면삼키기적당한크기로혀위에적당히놓여지게되어음식물의 2기이동이시작된다. 이과정은혀의앞부분이치아바로뒤쪽경구개의가장앞부분에밀착되고이어서혀의옆부분이경구개의가장자리에밀착되어혀위에놓여진음식물덩어리를감싼상태에서연속적으로혀가앞부분부터뒷부분의순서로연동운동과비슷한형태의수축을일으켜혀와경구개사이의압력을높임으로서음식물덩어리를밀어내는동작과동시에구개인두쪽의빨아들이는동작에의해구개인두로음식물덩어리가이동하게되는과정이다. 이때삼 Fig. 1. Normal swallowing process. (A) Oral preparatory/oral phase (B) Pharyngeal phase (C) Esophageal phase. Fig. 2. Four sequential model and process model are illustrated in diagrams showing progression from left to right, and aligning the common elements of the two models. (A) In the conventional sequential model, the four stages have minimum overlap so that oral propulsive stage starts after oral preparatory stage is completed. (B) In the Process Model, food processing (in the oral cavity) and bolus aggregation (in the pharynx) can occur at the same time. After food is ingested into the mouth, it is carried to the post-canine teeth for mastication (stage I transport). The food is reduced in size by chewing and mixed with saliva until it is ready to swallow (Food Processing). A portion of the chewed food is propelled into the oropharynx (stage II transport, ST II), where the bolus gradually accumulates while food processing continues in the mouth. Subsequent stage II transport cycles bring additional food to the oropharynx, and the bolus gradually accumulates there. Arrows indicate stage II transport cycles. Pharyngeal and esophageal stages have essentially the same mechanisms in the two models (adapted from Matsuo 2009). 4 99
Brain& NeuroRehabilitation:2009; 2: 98~102 킴동작의시작과함께숨을멈추는아주중요한동작이일어나게되는데만약숨을멈추기전에구강기의음식물덩어리가인두로흘러들어가게되면흡인이일어날수있다 (Fig. 1A). 상기에기술한고전적인삼킴과정모델에비해주로고형식을삼킬때구강기의과정을세분한새로운모델 (Process model) 이 Palmer 등에의해제시되었다 (Fig. 2). 1-4 새로운모델은구강기과정을세단계로나누었는데입으로받아들여진음식물이앞니에서부터어금니까지이동하는과정인 1기이동 (stage I transport) 단계와다음으로씹는과정을통해음식물덩어리를삼킬수있게잘게부수는 처리 (Processing) 단계, 그다음목구멍 (fauces) 을통해음식물덩어리가구개인두부의혀위로이동하는 2 기이동 (stage II transport) 단계로구성된다. 이단계들은고형식의경우연속적으로일어나게되며또한각단계가따로구분되어일어나지않고 처리 단계가진행되면서동시에 2기이동이일어나고이러한단계들이주기적으로반목되며음식물들이후두개곡에점차로모이게되면인두기삼킴으로연결되게된다. 2 이모델에의하면고형식의경우음식물의크기, 양, 성상에따라씹는과정과 2기이동이서로유기적으로연계되어동시에반복적으로진행되며점차적으로후두개곡에적당량의음식물덩어리가모이면인두기삼킴이일어나게된다. 이과정은대략 2초에서 10초간의시간이소요된다. (2) 인두기구강에서인두로음식물이이동해오면적절한감각신호가뇌간의조화운동중추를자극하게되어삼킴반사를일으키게된다. 인두기는후두의흡인방지기전이제대로작동하지않을경우기도흡인이일어날수있으므로특히중요한시기이며대개 1초정도소요된다. 음식물의기도침투와흡인을방지하기위해서는후두개가후두입구로덮이는것, 성대가닫히는것, 후두가전상방으로상승하는것등의몇가지기전이작용한다. 인두기에일어나는동작의순서와작용하는근육을보면, 비강인두가닫혀 (levator veli palatini, tensor veli palatini, palatophatyngeus) 비강으로의음식물역류를방지하게되고, 이어서성문이닫히며 (thyroarytenoid, lateral cricoarytenoid, aryepiglottic, oblique arytenoid), 인두길이가짧아지고후두가상승하게되고 (mylohyoid, geniohyoid, anterior digastric, stylohyoid, stylopharyngeus, salpingpharyngeus, thyrohyoid) 음식물덩어리가밀려들어오게되며 (posterior tongue, hyoglossus, styloglossus) 이어서인두에서아래로내려보내게된다 (superior, middle, inferior pharyngeal constrictors). 상부식도괄약근은후두상승이정점에달했을때가장크게열 리게되며바로직전에평소에는긴장성수축을유지하고있던하부인두조임근 (cricopharyngeus, thyropharyngeus) 이이완하게된다. 음식물이혀뒷부분과연구개의밀어내는작용으로구강인두로들어오게되면입천장올림근 (levator veli palatini) 이연구개를상승시키고입천장인두근 (palatopharyngeus) 등의수축이일어나연구개가상부인두의후벽에밀착하여비강쪽을막아음식물이역류되는것을방지하고동시에호흡이멈추게된다. 이어턱밑근육군 (submandibular muscles) 이수축하여인두가전상방으로이동하여혀뿌리의아래로상승하게되고반지인두근이이완하고인두의상승에따라반지인두근의앞쪽벽이당겨져서상부식도괄약근이열리게되며인두의직경이증가하게되어음식물을받아들이고인두조임근의연동운동형태의수축이일어나서음식물을상부식도괄약근을통과하여식도로밀어낸다. 이때혀가음식물을밀어주는동작과인두조임근의작용이중요하며이시간은약 0.6초가소요된다. 이러한작용이느리거나약하면후두가음식물에노출되는위험도가증가한다 (Fig. 1B). 인두는삼킴동작시에음식물이지나가는통로이자동시에호흡시에는공기가지나가는통로이다. 삼킴동작이일어난후음식물이인두의후두개곡이나배꼴동에남으면정상적인경우반복된삼킴동작을통하여완전히제거되지만그렇지않는경우기관지내로흘러들어갈수있다. 반지인두근과인두식도괄약근은상부식도괄약근 (upper esophageal sphincter) 으로작용하는데음식물이남을수있는원인으로작용할수있다. 반지인두근은다른인두조임근들과는달리평소에지속적인수축을유지하여식도로부터의역류를막아주는역할을하고있다가삼킴반사시에이완하고인두가상승함에따라앞쪽벽이당겨져서열림으로써음식물을인두에서식도로통과할수있게한다. 인두조임근의근력약화가있는경우인두에의한음식물을밀어내는압력이작아져음식물이식도로통과하지않을수있다. 또한인두의운동부조화가있는경우삼킴반사시에상부식도괄약근이이완하지않을수있다. 두경우모두인두에음식물이남게되어삼킴후의흡인이나타날수있다. (3) 식도기식도기는삼킴과정의가장마지막부분으로대개 6 10초간의긴시간동안지속된다. 식도를이루는근육의연동운동과중력에의해음식물이식도를통과하게되어식도하부에도달하게되면평소에지속적인수축으로닫혀있던하부식도괄약근이이완되어열려서음식물이위장으로들어가게된다 (Fig. 1C). 이시기의문제는인두기부위의증상으로호소하는경우가많아진단이어려울수있다. 100
이주강 : 정상삼킴과관련된신경생리학 2) 삼킴과정의신경기전 (1) 삼킴에관여하는조화운동중추와신경망삼킴과정의신경학적구성은상당히복잡하다. 간단하게요약하면중추와말초의감각신호와삼킴중추들과그에이어지는운동신경및근육들로구성된다. 구강기의삼킴과정은음식을받아들이고씹고구개인두로보내는과정이며대부분의식적인신경과정이다. 따라서음식의냄새, 맛, 모양등에의해영향받은뇌의전전두엽과일차운동영역, 변연계 (limbic system) 및측두엽의신경망이동원된다. 인두기의삼킴반사에관여하는뇌간의중추는뇌간후방부에고립로핵 (nucleus tractus solitarius) 및그주변부와전방부에는의문핵 (nucleus ambigus) 주변부에위치하고그주위에있는그물형성체 (reticular formation) 가관여되어있다. 양측의신경군들은서로밀접하게많은연결을하고있어서한측만으로인두및식도의삼킴과정을나타나게할수있다. 뇌간의삼킴중추에영향을주는대뇌피질부위는중심전피질 (precentral cortex) 에연접한전외측의피질부가알려져있으며이부위를자극하면삼킴이일어나고때로는씹는동작도연관되어일어난다. 5-7 그외에도실험적으로적어도네군데의전두엽부위가자극에 의해삼킴동작이유발되는것으로알려져있다. 8 피질및피질하전달로의정확한역할은알려져있지않으나능동적인삼킴과정의유발이나조절또는삼킴반사의역치를조절하는데에관여한다. 전외측피질에서시작된신경로는내섬유막 (internal capsule) 을통해내려와피질연수로 (corticobulbar tract) 를통해상부연수로연결된다. 7,9 뇌간에서는교뇌 (pons) 부터연수의하부까지에걸쳐여러신경핵군들이관여되어있는데감각신경의신호를받아들이고여러연접을거쳐서구강및인두와식도의근육을움직이는운동신경신호를보내게된다 (Fig. 3). 9-12 인두와식도의프로그램된연속적인삼킴반사운동은연수상부의기능이없는상태에서도일어나며하부연수의중추에서담당하는것으로알려져있다. 삼킴을조절하는신경핵들과말초신경은서로복잡한연결을통해작용한다. 인두기의삼킴동작에작용하는뇌간의운동신경핵은삼차신경운동핵, 안면신경운동핵, 미주신경의고립로핵, 설하신경핵과제 1 3 경수운동신경원이고운동신경들은제 5, 7, 9, 10, 11, 12 뇌신경이다. 제 5 뇌신경은턱목뿔근 (mylohyoid muscle), 입천장긴장근 (tensor veli palatini muscle), 이복근 (digastric muscle) 을지배하고제 7 뇌신경은깃목뿔근 (stylohyoid muscle) 과이 Fig. 3. A schematic diagram of the lateral cortex and the dorsal view of the brain stem indicating that sensory input eliciting pharyngeal and esophageal swallowing is primarily carried by sensory fibers in the vagus (Xth) and golossopharyngeal (IXth) nerves. These fibers synapse in one of the sensory nuclei of the brain stem, the nucleus of the tractus solitaries, and simultaneously, send fibers more rostrally. The diagram suggests that a long brain stemcortical reflex arc interacts with the brain stem to control pharyngeal and esophageal phases of swallowing. The oral state appears to involove a different pathway in which the trigeminal sensory nuclei are involoved (adapted from Miller 1997). 12 101
Brain& NeuroRehabilitation:2009; 2: 98~102 복근의뒤쪽을, 제 9 뇌신경은깃인두근 (stylophryngeus muscle) 을, 제 10 뇌신경은입천장올림근, 입천장인두근 (palatophatyngeus muscle), salpingopharyngeus, 방패모뿔근 (thyroarytenoid muscle), 인두수축근, 반지인두근 (cricophryngeus muscle), 인두의근육들및식도의횡문근을, 제 12 뇌신경은방패목뿔근 (thyrohyoid muscle) 과혀목뿔근 (geniohyoid) 을지배하고제 11 뇌신경은미주신경을통해운동분지를내고있다. 이러한운동신경활동과더불어삼킴과정에따른다양한감각되먹임 (sensory feedback) 이존재한다. (2) 삼킴을유발하는감각자극삼킴은턱의움직임, 혀의상승에의해촉진되며인두의접촉, 압력및액체가주입되는감각에의해시작된다. 이러한감각은제 5, 7, 9, 10 뇌신경을통해연수및교뇌와피질까지전달된다. 삼킴을유발하기위한효과적인감각자극은진동이단순한압박보다효과적이고정적인자극보다동적인자극이, 또복합적으로여러뇌신경이자극받는것이효과적으로알려져있으며특히상후두신경 (superior laryngeal nerve) 의자극이가장효과적이다. 그외진동이나압박같은기계적자극다음으로삼킴중추를활성화시키는자극은화학적감각 ( 미각 ), 온도감각등의순이며기계적감각과더불어중요하게작용한다. 결론 삼킴은음식물을입으로받아들여인두와식도를통해위장으로보내는과정을말한다. 음식이지나는통로인구강, 인두는삼킴이일어나지않을때에는호흡의통로로작용한다. 삼킴과정은구강기에는대부분의식적으로조절되며음식물을받아들이고씹고목뒤로보내는과정이다. 이후이어지는인두기는거의반사적인과정으로조절이되며비강과성문이닫히고혀의뒷부분과인두의조임근들의조화로운반사동작에의해기도로의흡인이없이음식물을식도로통과시키게된다. 이러한삼킴반사에관 여하는조화운동중추는뇌교 (pons) 와연수에있다. 식도기에는상부식도괄약근을통과한음식물이비교적느린속도의연동운동에의하여위장까지이동되게되며식도벽에위치한자율신경계의조절을받는다. 참고문헌 1) Hiiemae K, Heath MR, Heath G, Kazazoglu E, Murray J, Sapper D, Hamblett K. Natural bites, food consistency and feeding behaviour in man. Arch Oral Biol. 1996;41:175-189 2) Hiiemae KM, Palmer JB. Food transport and bolus formation during complete feeding sequences on foods of different initial consistency. Dysphagia. 1999;14:31-42 3) Palmer JB, Rudin NJ, Lara G, Crompton AW. Coordination of mastication and swallowing. Dysphagia. 1992;7:187-200 4) Matsuo K, Palmer JB. Coordination of mastication, swallowing and breathing. Japanese Dental Science Review. 2009;45: 31-40 5) Miller AJ, Bowman JP. Precentral cortical modulation of mastication and swallowing. J Dent Res. 1977;56:1154 6) van der Bilt A, Engelen L, Pereira LJ, van der Glas HW, Abbink JH. Oral physiology and mastication. Physiol Behav. 2006;89:22-27 7) Sumi T. Activity in single hypoglossal fibers during cortically induced swallowing and chewing in rabbits. Pflugers Arch. 1970;314:329-346 8) Martin RE, Sessle BJ. The role of the cerebral cortex in swallowing. Dysphagia. 1993;8:195-202 9) Amri M, Car A, Jean A. Medullary control of the pontine swallowing neurones in sheep. Exp Brain Res. 1984;55: 105-110 10) Car A, Amri M. [Pontine deglutition neurons in sheep. I. Activity and localization]. Exp Brain Res. 1982;48:345-354 11) Car A, Amri M. Activity of neurons located in the region of the hypoglossal motor nucleus during swallowing in sheep. Exp Brain Res. 1987;69:175-182 12) Miller AJ, Bieger D, Conklin JL. Functional controls of deglutition. In: Perlman AL, Schulze-Delrieu K, eds. Deglutition and its disorders anatomy, physiology, clinical diagnosis, and management. San Diego, London: Singular publishing group Inc.; 1997:43-97 102