XI. GHI DIEN Cd
1. Nguyen tac ghi dien cd (electromyography = EMG)
Dtfa tren nguyen tac: moi neuron van dong ngoai vi chi phoi mot nhom cac sdi cd, tao nen mot ddn vi van dong. Khi cd hoat dong, do hien ttfpng k h i ctfc va tai ctfc se sinh ra stf thay doi ve dien.
I--- l- t ---1 1 0 0 y iV
Hinh 2.11: Nhtfng dang dien co chinh (theo Yu.S.Yusvic) Dang I: loai nhanh
Dang II: loai dien the rieng le dtfdc nhac lai co nhjp do Dang III: loai tirng "loat" dao dong nhanh, doi khi ket hdp vdi dao dong cham dien the thap xuat hien khi run cd.
Bang cach cam dien ctfc kim vao trong cd (hoac b&ng dien ctfc dat tren da) se giup danh gia chiic nang cua cac ddn vi van dong quanh dien ciic. Ta co the ghi lai nhiing thay doi dien cd. Sau khi da phong dai len nhieu lan roi chuyen thanh nhiing tin hieu quang hoc va am thanh, ta diidc nhiing ket qua co the nhin thay tren man huynh quang va tren phim anh hoac tren giay gh de nhan dinh so sanh.
2. Dien cd do binh thiidng (electromyogram)
a. Hinh anh dien cd do binh thiidng
Luc cd nghi, dien cd bieu hien yen lang dien: dien cd la mot diidng thang, tren loa cung khong thaiy tieng no nao phat ra.
Luc cd co nhe: chi co mot ddn vi van dong hoat dong, dien cd thay ro nhiing song ba pha le te de phan biet. Buchthal goi dien cd do nay la do thi gian ddn.
Luc cd co v ia : co them mot so" ddn vi hoat dong, dtfdng dang dien khong ro niia. Tren loa tieng no nghe thay cung day hdn, to hdn. Do nhieu dien the hdp lai nen bien do tang: Buchthal goi la loai dien cd do nay la do thi trung gian.
Luc cd co toi da: co them nhieu ddn vi van dong niia hoat dong. Cac song chong len nhau, bien do tang cao hdn, doi khi co dang hinh sin khong deu dan. Buchthal goi dien cd do nay la do thi giao thoa, cung con goi la nhip Piper.
Song 1 pha Song 2 pha Song 3 pha Song da pha
H inh 2.12: Song dien cd
b. Chi so dien ca do binh thiidng
- Bien do: thtfdng ttf 300 microvon (mcv) den 2 milivon. Thdi gian xung: trung binh ttf 3 den 6 miligiay, co the den 15,7miligiay. Co nhiing ddn vi van dong be nhtf d mat, d mat; Ddn vi van dong ldn nhtf d dui, d mong. Do dd thdi gian xung cua moi cd cd khac nhau. Thdi gian xung cdn tang dan theo tuoi. Ngtfdi gia tang gap hai l&n tre nho.
Dang xung: thtfdng gap nhat la song ba pha, nhtfng cung cd the la song hai pha, mot pha hay da pha. Cd binh thtfdng cd ty le song da pha dtfdi 10%. Ngtfdi ldn cd ty le song da pha nhieu hdn tre nho, hai yeu to lam xuat hien song da pha la stf kem dong bo cua dong dien d cac sdi cd cung trong mot ddn vi van dong va vi tri kim tiep xuc vdi hai ddn vi van dong canh nhau se ghi nhan dong thdi dien the cua hai dien trtfdng nay.
Hinh 2.13: a) Do thi gian ddn: cd tCr dau dui co nhe (kim Bronk, toe do quet 30cm/giay nhip 8 giay, dang 3 pha, bien do 800 microvon thdi gian 3 milligiay. b) Do thi trung gian: cd nhi dau canh tay co vi/a
(kim Bronk, toe do quyet 30cm/giay) nhip trung gian, dang binh thudng bien do 800 microvon, thdi gian 3 miligiay c) Do thi giao thoa:
cd mong nhd co toi da (kim Bronk, toe do quet 7cm/giay) nhip giao thoa, bien do 1,5 milivon.
- Tan so": tan so" do mot ddn vi van dong tit 4 - 12 chu ky/giay, tan so" do nhieu ddn vi van dong giao thoa, toi da, la 50 chu ky/giay.
Hinh 2.14: Dien cd do dudi ki'ch thi'ch day than kinh: m6i giay kich thich 5 lan (A); 10 lan (B); 25 lan (C); 50 lan (D).