Descartes and Galvani: Neural Information Flow & Electrical Activity in Neuroscience

What three questions did René Descartes ask regarding information flow in the nervous system?

1. How do our nerves detect a sensory stimulus and inform the brain? 2. How does the brain decide what response to make? 3. How does the brain command muscle to move?

What did Descartes suggest about the flow of information in the nervous system?

He suggested that fluid flowing through nerve tubes carries information to the mind, which then orders the brain to allow muscle movements in response to stimuli.

Who was Luigi Galvani and what was his contribution to understanding electrical activity in the nervous system?

Luigi Galvani was an Italian physician and physicist who discovered that electrical stimulation could produce behavior, demonstrating this with muscular contractions in a dead frog.

What is 'animal electricity' as described by Galvani?

'Animal electricity' refers to the concept that electrical stimulation can produce muscle contractions and behavior.

How do negatively charged electrons behave in an electrical field?

Negatively charged electrons are attracted to the positive pole because opposite charges attract.

What is electrical potential and how is it measured?

Electrical potential is the amount of work energy needed per unit of electric charge to move a charge from a reference point to a specific point, measured in volts (V).

What role do ions play in biological tissue?

Biological tissue contains electrically charged ions, and the flow of these ions in and out of cells creates electrical currents that can be measured.

What are the three methods to measure electrical activity in the human body?

1. Electrocardiogram (ECG or EKG) for heart activity. 2. Electroencephalogram (EEG) for brain activity. 3. Galvanic skin response (GSR) for skin conductance.

How does information travel through a neuron?

Information travels through the axon of a neuron by the flow of electrically charged ions, which creates an electrical current.

What did Hodgkin and Huxley use to measure a neuron's electrical activity?

They used an oscilloscope to visualize and measure electrical signals in neurons.

What is the composition of extracellular and intracellular fluid in relation to ions?

Extracellular fluid has a higher concentration of sodium (Na+) and chloride ions (Cl-), while intracellular fluid has more protein anions (-) and potassium ions (K+).

What is the membrane potential?

The membrane potential is the difference in electrical charge between the inside and outside of a neuron, with the inside being negatively charged compared to the outside.

What is the resting potential of a neuron?

The resting potential is around -70 mV, with more protein anions and potassium ions inside the cell and more sodium and chloride ions outside.

How is the resting potential maintained in neurons?

Resting potential is maintained by ungated potassium channels allowing K+ to exit the cell and closed sodium channels.

What is the function of the Na+/K+ pump?

The Na+/K+ pump moves 3 Na+ ions out of the cell and 2 K+ ions into the cell, maintaining a negative charge inside the cell and requiring significant energy.

What are graded potentials in neuronal membranes?

Graded potentials occur when the neuronal membrane is rarely at resting potential, as neurons are almost always receiving synaptic inputs.

What is the significance of ion channels and pumps in neuronal communication?

Ion channels and pumps facilitate the movement of ions in and out of cells, crucial for generating electrical currents and neuronal signaling.

What are cations and anions in the context of neuronal function?

Cations are positively charged ions (e.g., K+, Na+), while anions are negatively charged ions (e.g., Cl-, protein molecules), both playing vital roles in electrical activity.

What is the role of the phospholipid bilayer in neuronal membranes?

The phospholipid bilayer prevents uncontrolled diffusion of ions, maintaining the necessary ion concentration gradients for neuronal function.

What is the difference between concentration gradient and voltage gradient?

A concentration gradient allows substances to diffuse from high to low concentration, while a voltage gradient allows current flow due to differences in charge.

What is a graded potential?

A local, temporary change in a neuron's membrane potential, triggered by a stimulus that opens or closes gated ion channels.

Where do graded potentials typically occur?

In the membrane of the soma and dendrites.

What happens during depolarization?

The membrane potential becomes more positive, usually due to the inward flow of sodium ions.

What occurs during hyperpolarization?

The membrane potential becomes more negative, usually due to the inward flow of chloride ions or outward flow of potassium ions.

What does 'neuron firing' refer to?

Sending an electrical message down the axon to communicate with other neurons.

What is the threshold potential for triggering an action potential?

Approximately -50 to -55 mV.

What is an action potential?

A rapid electrical impulse that travels down the axon, lasting approximately 1 millisecond.

What initiates an action potential?

The opening of Na+ voltage-gated channels when the membrane potential reaches the threshold.

What occurs at the peak of an action potential?

The membrane potential typically reaches around +40 mV, Na+ channels close, and K+ channels remain open.

What is repolarization?

The process by which a neuron's membrane potential returns to a negative value after depolarization.

What is the absolute refractory period?

A phase during which stimulation will not result in another depolarization because Na+ channels are inactive.

What is the relative refractory period?

A later phase of the action potential where a stronger stimulus could produce another action potential.

What does the all-or-none law state regarding action potentials?

An action potential either occurs fully or does not occur at all.

What is saltatory conduction?

The process by which action potentials jump from one Node of Ranvier to the next, allowing for faster signal transmission.

Why does the action potential only travel in one direction?

Refractory periods prevent the action potential from reversing direction and traveling back toward the soma.

What are excitatory postsynaptic potentials (EPSPs)?

Changes that depolarize the cell, making it more likely to reach threshold, typically due to the influx of Na+.

What are inhibitory postsynaptic potentials (IPSPs)?

Changes that hyperpolarize the cell, making it less likely to reach threshold, typically due to the efflux of K+ or influx of Cl-.

What is temporal summation?

A process where multiple postsynaptic potentials occur at the same synapse in rapid succession, adding their effects over time.

What is spatial summation?

The process by which multiple postsynaptic potentials from different synapses on the same postsynaptic neuron are combined.

What is the role of the axon hillock in neuron firing?

It is the specific point where the summation of postsynaptic potentials occurs, determining whether an action potential is triggered.

What factors determine neural integration?

Type of synaptic input (EPSP or IPSP) and size of postsynaptic potentials (temporal and spatial summation).

What is the significance of the myelin sheath?

It acts as an insulator, reducing ion leakage across the membrane and facilitating faster signal transmission.

What is the typical duration of an action potential?

Approximately 1 millisecond.

How does the action potential maintain its strength along the axon?

It does not decrease in strength as it travels; it always reaches the same size (~100 mV change).

What happens to Na+ channels during the depolarization phase?

They open, allowing Na+ to rush into the cell, following its concentration and voltage gradients.

What is the role of voltage-gated potassium channels during an action potential?

They open after Na+ channels, allowing K+ to leave the cell, contributing to repolarization.