Neurobiophysics: Excitability and Action Potentials

Flashcards covering the biophysics of neurons, membrane potentials, action potential generation and propagation, and synaptic transmission based on the lecture notes.

What is the primary function of neurons and the neural system in advanced organisms?

The transmission of data.

Approximately how many neurons and glial cells compose the nervous system?

Approximately $10^{12}$ neurons and glial cells that are $10-50$ times the number of neurons.

Which part of the neuron is typically a long extension that transmits signals to other cells at synapses?

The axon.

What is the name of the cone-shaped base of an axon?

The axon hillock.

What are the chemical messengers passed across a synapse by a synaptic terminal?

Neurotransmitters.

List the five physiological stimuli and their associated receptors mentioned in the transcript.

1. Hormones (acetylcholine receptors), 2. Heat (thermal receptors), 3. Mechanic (pacini bodies, hearing hair cells), 4. Chemical factors (taste sense receptors), 5. Electromagnetic rays (cones and rods in retina).

Which cells are considered excitable cells?

Neural cells, muscle cells, neurosecretory cells, and some endocrine, immune, and reproductive cells.

What is the typical range of the Resting Membrane Potential (MRP) for excitable cells like neural and muscle cells?

Between $-60mV$ and $-95mV$.

What are the three main origins of membrane potential mentioned?

a) Negative Donnan Potential of cytoplasm, b) Different permeabilities of $Na^{+}$, $K^{+}$ and $Cl^{-}$ (ion selectivity), c) Active transport mechanisms.

How many ions are moved by the Sodium-Potassium Pump, and in which direction?

$3Na^{+}$ are pumped outside the cell and $2K^{+}$ are pumped into the cell using energy from $ATP$.

Define the term 'Hyperpolarization'.

When the membrane potential becomes more negative than the Resting Membrane Potential (RMP).

What is 'Overshoot' in membrane potential terms?

When the membrane potential becomes positive.

What is the 'All-or-none' principle of action potentials?

The magnitude, size, amplitude, and velocity of an action potential are independent of the intensity of the stimulus, provided the stimulus is at or above the threshold point.

Contrast the Absolute Refractory Period and the Relative Refractory Period.

In the Absolute Refractory Period, it is impossible to evoke another action potential. In the Relative Refractory Period, a stronger than usual stimulus is required to evoke one.

What are the conduction speeds for very small demyelinated cells versus very thick myelinated cells?

Demyelinated: $0.25\,m/s$; Thick myelinated: $100\,m/s$.

How is a Biphasic Action Potential characterized during recording?

By a positive deflection followed by an isoelectronic pause and a negative deflection, recorded by placing both electrodes on the surface.

Which glial cells form the myelin sheath in the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)?

Oligodendrocytes in the CNS and Schwann cells in the PNS.

What is saltatory conduction?

The process in which action potentials in myelinated axons jump between the nodes of Ranvier.

How does the conduction velocity of an action potential relate to the axon radius in myelinated versus unmyelinated fibers?

In unmyelinated fibers, it increases approximately with the square root of the radius; in myelinated fibers, it increases directly with the radius.

Compare Electrical and Chemical synapses regarding directionality and speed.

Electrical synapses are bi-directional and faster; Chemical synapses are one-directional and slower.

What ion influx is required at the presynaptic terminal to trigger the release of neurotransmitters?

$Ca^{++}$ ions.

How does acidosis (low pH) and alkalosis (high pH) affect synaptic conduction?

Acidosis decreases neuron activity and synaptic conduction; Alkalosis increases excitability and synaptic conduction, potentially causing spontaneous discharges.

What is the effect of strychnine on neurons?

It suppresses some inhibitors, causing excitatory neurons to be so stimulated that tonic contractions occur from rapid repetitive discharges.

Which structural feature is typically found in dendrites but not in axons?

Nissl bodies.