Neuroscience Basics Quiz

Electricity Within the Body

• Physical phenomena involving electricity and magnetism have been observed since ancient times
• Electricity plays an important role in medicine
• Two aspects of electricity and magnetism in medicine:
  • Electrical and magnetic effects generated inside the body
  • Applications of electricity and magnetism to the surface of the body
• Electricity generated inside the body controls and operates nerves, muscles, and organs
• The nervous system is crucial for all body functions
• The brain receives internal and external signals and makes a proper response
• The nervous system is divided into two parts:
  • Central nervous system (consists of the brain, spinal cord, and peripheral nerves)
    • Afferent nerves transmit sensory information to the brain or spinal cord
    • Efferent nerves transmit information from the brain or spinal cord to muscles and glands
  • Autonomic nervous system (controls internal organs such as the heart, intestines, and glands)
    • Control of the autonomic nervous system is involuntary

The Neuron

• The basic structural unit of the nervous system
• Specialized for reception, interpretation, and transmission of electrical signals or messages
• Consists of:
  • Dendrites: Short, branched, unmyelinated parts that receive electrical signals from other neurons
  • Soma (cell body): Contains the nucleus and associated intracellular structures; receives signals from dendrites
  • Axon (nerve fiber): Carries electrical messages away from the cell body (approximately 1 meter long)
  • Axon terminals: Transmit messages to muscles, glands, or other neurons
  • Synapses: Basic units of communication in the brain; chemical neurotransmitters are released, binding to receptors on the second cell, initiating electrical and biochemical signals

Electrical Potentials of Nerves

• A human body is made of multiple cells composed of different chemical substances (e.g., sodium, potassium, calcium, chloride)
• Cell membranes separate cells from their environment (intracellular and extracellular)
• Intracellular environment is rich in potassium ions, while the extracellular environment has many sodium and chloride ions
• This creates a potential difference (biopotential) between the two environments
• Biopotential can be measured using electrodes, amplified, and monitored to study organ function (e.g., heart, brain, eye, muscles)
• Two types of biopotential:
  • Resting potential: The inside of the cell is typically 60-90 mV more negative than the outside
  • Action potential: A large momentary change in the resting potential that propagates along the axon, the main method of signal transmission

Electrical Signals from Muscles (EMG)

• Electromyogram (EMG) is the recording of muscle potentials during movement
• A muscle consists of many motor units
• Each motor unit comprises a single branching neuron from the spinal cord and 25-2000 connected muscle fibers (cells)
• Muscle action is initiated by action potentials
• Single muscle cells are usually not monitored in EMG examinations due to difficulties in isolating a single fiber
• EMG electrodes measure the electrical activity of multiple fibers
  • Surface electrodes on the skin measure the activity of many motor units
  • Concentric needle electrodes inserted under the skin measure single motor unit activity

Electrical Signals from the Brain (EEG)

• Electroencephalogram (EEG) measures very weak complex electrical signals from brain cortex neurons
• Electrodes on the scalp measure the brain's electrical activity
• Reference electrodes are typically attached to the ear
• EEG signals are low amplitude (approximately 50µV)
• External electrical signals often cause interference in EEG signal processing
• EEG is used to diagnose diseases
• Asymmetrical activity is often an indicator of brain disease
• Recording of neural signals from the brain is called electroencephalogram (EEG)

Action of EMG

• Action potential appears in EMG after a latency period between stimulation and response
• EMGs of symmetrical muscles are compared to detect nerve damage, which can affect action potential and latency periods
• Velocity of action potential in motor nerves can decrease due to nerve damage

Electrical Signals from the Eye (ERG and EOG)

• Electroretinogram (ERG) measures potential changes in the retina when exposed to light
  • One electrode is in a contact lens over the cornea, and the other is on the ear or forehead
  • ERGs can be used to detect retinal inflammation
• Electrooculogram (EOG) measures potential changes due to eye movement
  • Two electrodes are placed near the eye
  • EOG provides information about eye orientation, angular velocity, and angular acceleration

Electrical Signals from the Heart (ECG)

• Electrocardiogram (ECG) is a graphical representation of the heart's electrical activity
• The electrical system controls all heart events
• The Sinoatrial (SA) node is the heart's pacemaker.
• Atrioventricular (AV) node is located on the interatrial septum.
• The His-Purkinje system is located along the walls of the ventricles
• Cardiac cycle has two phases:
  • Systole: Ventricular contraction and pumping of blood
  • Diastole: Relaxation of the atria and ventricles, and filling with blood

Additional Notes

• ECG can diagnose cardiac problems such as arrhythmias, heart attacks, and fibrillation.
• Normal heart rate ranges between 60-100 beats/minute.
• Heart rate can increase or decrease depending on the body's needs for oxygen and other function.