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Module 1: Introduction to Neurophysiology

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Understanding the structure and function at the neuronal level of the central nervous system is the basis for understanding scalp recorded EEG and Event-Related Potentials.

Neurons have three parts:

• The nerve cell body, also termed the Perikaryon, is the cytoplasm surrounding the nucleus.
• Output: Axon or nerve fibres are present in most neurons. They transmit signals to target neurons.
• Input: Dendrites extend from the nerve cell body in complex patterns to receive contacts from other neurons. They have multiple protrusions or dendrite spines. Spines can also occur on axons.

The Nerve Cell Membrane is important for Electro-physiology.
1. Made up of Phospholipids.
2. Each unit has a hydrophilic head end and a hydrophilic tail.
3. Studded in the cell are protein structures or ionic channels.
4. There is a 60mV voltage across the cell membrane generated by the differing compositions of the ECF and ICF and the semi-permeability of the membrane.

The exchange of information between neurons takes place through two types of synapses: Chemical synapses and Electrical synapses. Chemical synapses make up the majority of synapses in the CNS.

• Type 1 synapses are asymmetrical and have variably shaped vesicles. Excitatory.
• Type 2 are symmetric and have clear round vesicles. Inhibitory.
• Information is transmitted via Action Potentials to the pre-synaptic terminal. This causes the synaptic vesicle to fuse with the cell membrane and release its neurotransmitter.
• The neurotransmitter binds to the post-synaptic membrane and causes the post-synaptic membrane to fire Action Potentials.

The Human Brain consists of all structures which are intra-cranial, that is, within the skull.

The Cerebrum:
• The frontal lobe: High-level processing, motor control, thinking, reasoning.
• The parietal lobe: Process and integrate sensory information.
• The occipital lobe: Visual processing.
• The temporal lobe: Language and speech production, memory, emotion processing.

The Cerebellum

Contains 50% of all of the cells in the brain. Balance, motor activities, walking, standing, and coordination of voluntary movement. It also coordinates muscular activity and speech and eye movements.

The Spinal Chord:
• The midbrain: Has two dorsal elevations, the superior and inferior colliculi. The upper layer of the superior colliculus receives visual signals from the eye. The lower layers process signals from other brain areas. The inferior colliculus is the auditory equivalent of the superior colliculus. It does signal integration, frequency recognition, and pitch discrimination.
• The pons: It is involved in the control of breathing, communication between different brain areas, sensation such as hearing, taste and balance.
• The medulla oblongata: It is the brain centre for respiration and circulation, it regulates breathing, heart and blood vessel function, digestion, sneezing, swallowing and vomiting.

Micro and Nanotechnology is used to fabricate the electrodes used in neuroinstrumentation technology.

There are two types of electrodes that are used for measuring or acquiring an EEG signal, wet electrodes, and dry electrodes. Wet electrodes require a gel to be used before they are placed on the scalp. Dry electrodes do not require a gel for making a contact to the scalp.

The – system of EEG Placement.

An internationally recognized method that allows EEG electrode placement to be standardised.

Ensures inter-electrode spacing is equal.

Electrode placements are proportional to skull size and shape.

Covers all brain regions, electrodes are numbered: F(frontal lobe), T (temporal lobe), P (Parietal lobe), O (Occipital lobe).

Numbering system for electrodes are: Odd=left side, Even= right side, Z=mid-line.