Phan trung tam gom co tuy song va toan bo phan nao. Tuy song n im trong xoang cot xuong song, va nao bo n&m trong hop so.
Trong lviong trung binh cua phan nao d tuoi 18 den 50 thuong chung 1350gr den 1400 gr. Binh thuomg nao ciia phai nu nhe hom cua nam gidri chting 10-12%.
Cac loai dong vat neu tinh theo trong luong ciia bo nao luon luon nho hon nao nguOi. Neu tinh theo trong luong co the giua dong vat va nguOi thi nao nguOi co tr<?ng luong Ion hon, rieng nao voi thi co trong luong Ion binh quan toi 4000 - 4200gr. Khi nguOi Ion tU 49 tuoi trd len thi trong luong nao se giam dan.
Ban cau dai nao la mot cau tao bao gom niia ben trai va nua ben phai (nao) noi lien nhau nho mot cau noi Ion goi la the trai.
Trong ban cau dai nao cac te bao than kinh nam xung quanh ben ngoai va tao thanh mot lop xep rong noi lai, co be day khoang 2-4mm goi la vo nao. Trong vo nao co den khoang 14-15 ty te bao. Con nguOi ta gia bat dau tu dai nao, khi tuoi cao te bao bi suy giam, ve so luong nang luc, tri nho manh hay yeu deu phu thuoc chii yeu vao mang luOi hoat dong cua cac te bao nao. Mat ban cau dai nao co rat nhieu thuy va nhieu ranh . Theo cac cong trinh
nghien cuu cua Paplop 6 nguoi co khoang 2/3 so te bao than kinh cua vo nao nam d bo thanh va day ciia cac ranh.
Ban cau dai nao
1. Ranh; 2. Thuy
Tat ca cac he than kinh deu duoc cau tao boi nhung te bao than kinh va cac nhanh nho hem cua chung tiep theo. Neu c l t nao ciia nguoi ra chung ta thay co chat xam va chat tr in g n&m chong cheo lan nhau tao thanh m ot lop. Chat xam chinh la than ciia te bao than kinh, chat t r in g
la cac true va cac nhanh cua chung. Cac true va nhanh ciia te bao than kinh con goi la cac son than kinh no duoc noi lien voi nhau. Te bao than kinh cung vOi true va cac nhanh ciia no goi la neuron, neuron la don vi hinh thai co ban ciia he than kinh, he than kinh trung uong la mot bo phan tong hop cac neuron. Than ciia te bao nho chi bang mot phan van milimet va chung ta muon thay duoc no phai qua kinh hien vi. He thong than kinh ciia ngiroi gom co trung tam va ngoai bien . Phan ngoai bien duoc
cau tao rat it te bao va rat nhieu day than kinh, tire la nhanh cau true ciia cac te bao duoc huong di khap den cac co quan ciia co the. Cac day than kinh con duoc chia ra nhieu loai la cac day than kinh ly tam va cac day than kinh huong tam. Di theo cac day than kinh ly tam thi cac kich thich hay cac xung dong than kinh duo’c truyen tu he than kinh trung uong den cac co quan hoat dong nhu cac co bap. cac tuyen. tim. gan. than va cac co quan noi tang khac: nguoc lai di theo cac day than kinh huong tam thi cac kich thich ben ngoai nhu da. tac co quan va cac mo cua co the lai duoc dan truyen den he than kinh trung uong. Tom lai, than kinh co chtic phan chi phoi tat ca cac hoat dong cua co the, dieu hoa va phoi hop cac hoat dong ciia tung bo phan thanh mot khoi thong nhat trong co the lam cho co the thich nghi voi the giOi ben ngoai.
He than kinh nguoi