Electricity within the body
Across membrane of neuron an electrical potential (voltage) due to presence of more negative ions on the inside of the membrane than outside.
Neuron is to be polarized, the inside of the cell is 60-90 mV more negative than out side and this represent the resting potential. if stimulation heat, cold, light, sound cause change in action potential
Fig a : resting potential of axon= - 80mV
+ + + + + - - - - + + + + + + + + + + + + +
- - - - ++ - - - - - - - - - - - - - -
- - - - ++ -- - - - - - - -- - - - - -
+ + + +- - - - - + + + + + + + + + + + + + +
b . depolarized a. polarized
inside go positive to 50 mV. The action potential last few m sec for most neuron and muscles, and last 150-300 m sec for cardiac muscle. The membrane of some axons is covered with fatty insulating layer called myelin has small uninsulated gaps called nodes of ranvier.
The action potential decreases in amplitude as it travels through myelinated segment just on electrical signal is attenuated when it passes through a cable . the reduced signal then acts like a stimulates at the next node of ranvier (gap) to restore the action so its original size and shape, this process repeats a long the axon. The action potential seems to jumb from one anode to the next , it travels by salutatory conduction.
Electrical signals from muscles …Electromyogram.
The record of the potentials from muscles during movement is called Electromyogram . the conduction velocity of sensory nerves was measured its typical value are 40-60 m/sec
……Stimulus1 … 0.25 m …stimulus 2
Last figure is a method of measuring the motor nerve conduction velocity. The latency period for the response to stimulus 1 is 4 sec longer than that for response to stimulus 2.
... t = 4*10-3
X= 0.25 m difference in distance
V=x/t = 62.5 m/sec = the nerve conduction velocity.
Electrical signals from the heart electrocardiogram :
The electrical signals from SA node (sinoaterial) or pacemaker initiate 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 aterioventricle AV anode, which initiates depolarization of right and left ventricles causing them to contract and force blood to pulmonary and general circulations. The ventricle nerves and muscles then repolarized and the sequence begins again. The major electrical events of the normal heart cycle as:
1. the atrial depolarization, which produce (p) wave
2. the atrial repolarization, which is rarely seen and is unlabeled .
3. the ventricular depolarization which produces (QRS).
4. the ventricular repolarization which produces (T) wave.
e
lectrical signal from the brain : electroencephalogram
the recording of brain signals is called (EEG). The frequencies of EEG signals depend on mental activity.
For example: relaxed person has EEG signals pf 8-13 Hz or ? waves more alert person has above 13 Hz or ? waves.
Application of EEG :
1. EEG useful in diagnosis of epilepsy
2. in confirming brain tumors, since electrical activity is reduced in the region of tumor.
3. used as monitor in surgery when ECG can not use also useful for indicating the anesthesia level of the patient.
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 .