Exam 2: Cortical Microcircuitry & Cell Signaling

How are neurons arranged in the cortex?

Neurons are arranged in 6 layers of the cortex - lots of lateral connectivity in the uppermost layer (layer 1)

What type of neuron is the most abundant in the cortex?

Pyramidal cells - the primary building block; they are projection neurons (the output pathway for the cortex) and use glutamate (which means that they send out excitatory projections

What are pyramidal cells’ main structural and functional characteristics? (eg types of dendrites, its axons, its neurotransmitters)

They have:

• Apical dendrites - extending from the some (cell body) towards the upper cortical layers

• Basal dendrites - extending from the base of the soma 

• Most synaptic contacts are located on dendritic spines (the basis of neuroplasticity, which underlies learning and memory)

• Extensive axonal collaterals

• Neurotransmitter: glutamate

What other cells play an essential role in the cortex? What about capillaries/blood supply? Glia?

• GABA

• The brain is only about 2% of the body’s weight but consumes about 20% oxygen and 25% glucose. It is a real energy guzzler. Most of this energy is used by neurons to fire and maintain electrical polarization, etc. This energy is supplied by capillaries, which are intermingled with neurons and glial cells that provide essential support and nourishment.

What type of process is cell signaling? Why is it this type of process?

A neuron carries messages through an electrochemical process:

• Electrical processes in the neuron

• Chemical processes at the synapse 

  • This results in postsynaptic currents, which are recorded as EEG

What is the resting membrane potential?

around -70mV

What does it mean that the cell is polarized?

The inside of the cell has a greater negative potential than the outside: around -70mV → the cell is polarized

What ions predominate outside vs inside the cell?

• Outside: Na⁺ and Cl^-

• Inside: K⁺ and anions

What is a concentration gradient?

The difference in the concentration of a substance between two areas, causing a net movement of that substance from an area of higher concentration to an area of lower concentration

• The concentration gradient drives Na⁺ to flow into the cell and it drives K⁺ to flow out of the cell

What are ion channels, and what is their relative permeability?

• Ion channels are proteins in cell membranes that allow specific ions, like potassium and sodium, to pass through the membrane.

• Relative permeability refers to the membrane’s permeability to one type of ion compared to another. For example, a neuron’s membrane at rest is far more permeable to K⁺ than to Na⁺ because many potassium leak channels are open, while most sodium channels are closed.