Neurophysiology: from cells to networks

Give a brief description of neurons:

Primary function is communication. The most active cells in the body. Prone to apoptosis.

Briefly describe the function of Glia:

Support functions and immune regulation

Give a more detailed description of neurons:

The basic unit of structure and function in the nervous system. Cells that conduct impulses. Process information. Sense environmental changes. Communicate changes to other neurons. Command body response. High energy usage, constant need to glucose and oxygen.

What are the three main sections of a neuron?

1. cell body - contain nucleus and cellular activity

2. axons - single extension of the neurons providing output.

3. Dendrites - branch like extensions that receive messages from other neurons.

What are the four main factors that can be used to divide neurons?

Function, location, cell morphology, neurotransmitter

What is the general function of motor neurons?

Carry impulses away from the brain and spinal cord

What is the general function of sensory neurons?

Carry impulses from inside/outside the body to the brain/spinal cord

What is the general function of relay neurons?

Process incoming impulses and pass them on to motor neurons.

What is the function of the neuronal membrane?

Separates intracellular fluid from extracellular fluid. Allows some substances to cross while restricting others.

Briefly describe how the neuronal membrane is highly selective:

They are not freely permeable to most ions. Ion movement depends of specific ion channels and membrane properties.

Briefly describe channel proteins:

Span the membrane, contain a central pore, provide a hydrophilic pathway through the hydrophobic core, allow specific ions to cross the membrane.

Briefly describe the ion selectivity of channel proteins:

Selectivity depends on channel size and the charge lining the pore. It is critical for controlling neuronal excitability.

Briefly describe the excitability of a ligand gated ion channel:

Channel is closed at rest, ligand bind to receptor site opening the ion channel. This creates a hydrophilic pore through the membrane. Ions move down their electrochemical gradients. Na+/Ca2+ enters and K+ exits. Ion movement changes membrane potential and converts chemical signal to electrical response.

Briefly describe the excitability of mechanically gated ion channels:

Channel closed at rest. Opens in response to mechanical deformation. Mechanical force causes conformational change in the channel protein. The rest is the same as a ligand gated ion channel.

Briefly describe the excitability of leakage ion channels:

Channels are not gated by stimuli. Randomly open and close at rest. Allow continuous passive ion movement, ions move down their concentration gradients. Most are permeable to K+. Net K+ efflux dominates. Establish and maintain resting membrane potential. Membrane potential is stable but never static.

How is resting membrane potential measured?

Measured using two electrodes - reference electrode in extracellular fluid and recording microelectrode inside the neuron. The voltmeter measures the electrical difference.

What is the resting membrane potential?

-77 mV

What is threshold membrane potential?

-55mV

Where do action potentials start?

At the axon hillock due to the high proportion of voltage-gated Na+ and K+ channels there. This high proportion of voltage-gated Na+ and K+ channels continues down the axon to the terminal.

What is the relationship between axon diameter and ion flow?

The larger the diameter, the more ions flow through them.

What is the role of myelin?

Speeds-up the conduction of an action potential down the axon.

Is the conduction of the action potential between two nodes active or passive?

Passive

What are the two types of synapse?

Electrical and Chemical

What are electrical synapses held together by?

Gap junctions

Briefly describe the movement of ions across a gap junction in an electrical synapse:

Ions and small molecules pass directly across the membrane. Transmission at an electrical synapse is fast, bidirectional and fail-safe.

What does EPSP mean?

Excitatory postsynaptic potential

How do do EPSP’s lead to the firing of an action potential?

They have to be summed together to bring a neuron to firing threshold. Actively across space and time is additive.

What are the five locations for electrodes for an EEG?

Pre-frontal (Fp), Frontal (F), Parietal (P), Occipital (O) and Temporal (T)

What is an EEG?

An EEG rhythm is a combination of local field potentials

What is a LFP?

A measure of the underlying ionic environment, and therefore activity.