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Electricity within the body

الكلية كلية طب حمورابي     القسم الكلية ذات القسم الواحد     المرحلة 1
أستاذ المادة نادية حسين صاحب طاهر       07/06/2018 00:36:28
Lecture:Electricity within the body
Objectives:
1. To get information about physical laws and their applications in medical physics.
2. Ability to; identify relevant properties and laws when dealing with tools in both and disease state.

A cross membrane of neuron an electrical potential (voltage) is present dueto presence of more negative ions in the inside of the membrane than outside.
Neuron to be polarized; the inside of the cell (60 - 90 mv) more negative than outside, (60-90 mv)= resting potential
If stimulation (heat, cold, light, sound) causes change in the action potential

The inside go positive to 50 mv. The action potential last few milliseconds, for most neuron and muscle.
The action potential last 150-300 msec for cardiac muscle. The membrane of some axons is covered with fatty insulating layer called myelin, has small non-insulating gabs called nodes of Ranvier.
The action potential decreases in the amplitude as it travels through myelinated segment just an electrical signal is attenuated when it passes through a cable.
The reduced signal then acts like stimulates at the next node of Ranvier (gab) to restore the action so its original size and shape. This process repeat along the axon. The action potential seems to jump from one node to the next, it travels by salutatory conduction.
Electrical signal from muscle electromyogram:
The record of potentials from muscles during movement is called Electromyogram. The conduction velocity of sensory nerve was measured its typical value are 40-60 m/sec.
The latency period for the response to stimulus 1 is 4sec longer than that for response to stimulus 2.

? t = 4 x 10?³ sec

? x = 0.25 m
V = ? x / ? t = 0.25 m / 4 x 10? ³ sec = 62.5 m / sec
This is the nerve conduction velocity.
Electrical signal from the heart (Electrocardiogram):
The electrical signals from SA nods or pacemaker initiates the depolarization of the nerve and muscles of both atria , causing
atria to contract and pump blood into ventricles.
The electrical signals then passes through atrioventricular (AV) node, which initiate depolarization of right and left ventricles,
causing them to contract and force blood to pulmonary and general circulation. The ventricle nerves and muscles then depolarized
and the sequence begins again.

The major electrical events of the normal heart cycle as:
The atrial depolarization which produce ( P wave )
The atrial depolarization which rarely seen and is unlabeled
The ventricular depolarization which produces ( QRS)
The ventricular depolarization which produces ( T wave )


المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .