Bio Psy week three

Non-neuronal structures of the brain 

• Meninges 

• Ventricles 

• Blood-brain barrier (BBB)

Connectivity underlies function

Input and output can underlie what the brain area is doing

Record a brain area’s actions

Brain imaging: structural v. functional

Ablation studies

Humans: case studies

animals: lesions studies

Human brain imaging - structural imaging

Computed Tomography (CT Scan)

Magnetic Resonance Imaging (MRI)

Human brain imaging - functional imaging (Both techniques measure changes in regional blood flow)

Positron emission tomography (PET Scan)

Functional MRI (fMRI)

Patient HM: removed hippocampus

Henry Molaison

Suffered from debilitating seizures

Studies in rodents: Lesioned hippocampus

Lesions via electrolytic damage or chemical ablation, then observe behavior

Lesions to the rat hippocampus cause loss in spatial navigation ability when put into a maze

Electrical signal is an action potential

1. Nerve impulse 

2. Electrical component of how neurons communicate with each other 

3. Occurs because neuronal membrane is excitable 

Chemical signal is neurotransmission 

Chemicals cross the synapse (the space between neurons)

Nerves/neurons are like

telephone wires

Action potential

nerve impulse

Potential

separation of electrical charge across the membrane

Resting membrane potential

neurons are quiet

Understanding the membrane potential

Action potential = neurons are active and talking

Membrane potential

separation of electrical change across the membrane

Neural communication: Membrane potential

3 important players 

1. Ions 

2. Phospholipid Bilayer 

3. Proteins 

Atoms consist of

Electrons (negatively charged)

Protons (positively charged)

Neutrons (uncharged )

Ions

atoms or molecules where the total number of electrons is not equal to the total number of protons

Ions can be

positively charged or negatively charged

Ions provide

the electrical charge of membrane potential

Ions exist in

both the cytosol (inside the cell) and extracellular fluid (outside of teh cell)

Important ions

1. K+

2. Na+

3. CI-

4. Ca 2+

Phospholipid bilayer makes up the cell membrane

1. Has two layers 

2. Each layer has a polar head and a nonpolar tail 

3. The polar head prevents water and ions from moving between the extracellular fluid and cytosol 

Proteins allow ions to

cross the cell membrane

Ion channels

Can be selective for a specific ion

Does not require energy for ions to move between the cytosol and extracellular space

Ion pumps

Also selective for specific ions

Require energy in the form of ATP

Leak channels

These channels are constantly open

Allow for ions to “leak” through the cell membrane

Voltage-gated channels

These channels only open if there is enough change in membrane potential

Na+ and K+ channels are essential to the membrane potential

1. Na+ leak channels 

2. K+ leak channels 

3. Voltage-gated Na+ channels 

4. Voltage-gated K+ channels 

Membrane potential: Two important forces to move ions across the membrane

Diffusion

Electrostatic force

Diffusion

Particles move from areas of high concentration to low concentration

Movement of particles down their concentration (high -> low) does not require energy

Remember

The phospholipid bilayer of the cell membrane is impermeable to ions

Ions move from

high -> low concentration 

Ion channels make

the membrane permeable

Electrostatic force

1. Opposite charges attract, as charges repel 

2. Electrical charge (movement of ions) 

3. Membrane must be permeable 

Resting membrane potential 

• The difference in electrical charge/ voltage across the cell membrane when a neuron is at rest 

• Neuron is quiet

The resting membrane potential is negative 

The resting membrane potential ~ -65 mV

1. This means the cell is about 65 mV more negative inside the neuron compared to outside

Why is the concentration of Na+ higher outside of the neuron and K+ higher inside of the neuron

Beacuase of the Na+/K+pump

The sodium-potassium (Na+/K+) Pump

Exchanges 3 Na+ ions for 2 K+ions 

1. Na+ is moved out 

2. K+ is moved in 

Exchanges 3 Na+ ions for 2 K+ ions:

Na+ is moved out and K+ is moved in

The sodium-potassium (Na+/K+) pump goes against

their concentration gradient: requires energy = ATP

Energetically costly

Consumes 70% if total ATP used by the brain

The sodium-potassium (Na+/K+) pump maintains

uneven charge across the neuronal membrane

The resting Membrane Potential

• Membrane potential (Vm)= voltage across the neuronal membrane 

• Membrane is polarized because electrical charge is unevenly distributed across the membrane 

The inside of the resting Membrane Potential

The inside will always be negative compared to the outside

Changes in the membrane potential

Sudden increase or decrease in the membrane potential due to the movement of ions across the cell membrane

Depolarization: Enhances the ability for the neurons to fire

voltage increases, less polarization: Inside the cell becomes more positive.

Membrane hyperpolarization

voltage decreases, more polarization: Inside the cell becomes more negative. Working its way to rest

Any time ions move, it creates

a current that creates cells. Goes towards the ion and then rest goes into a deporization a influx of positive

Graded potentials (defin)

Potential= difference in voltage across the cell membrane

Graded potentials

• Adding more and more positive charge to the inside of the cell -> larger and larger depolarizations

• Not all depolarizations result in an action potential  

• If you inject positive into the neuron, you expect the outside to become more depolarizing. Based on how many ions you injected.

An action potential is produced 

• If enough depolarization occurs that the membrane potential exceeds a threshold, an action potential will be produced: Threshold is -50 mV

• Because you crossed a depolarization threshold, which creates an action potential 

Potassium is the Ion that is

most expressed/ more dense in the neuron

At rest, Na+ ions will want to

flow into the cell (because they are going to flow down and obey the laws of diffusion)

At rest, K+ ions will want to flow

Out of the cell ( due to diffusion force)

(The action potential) A nerve impulse; when the neuron is “talking”

the electrical component

Electrical communication that travels down the axon of a neuron

Electrical communication = ions moving in and out of the neuron

When this neuron gets stimulated

then the sodium starts filling up the neuron, including the dendrites, which gets it excited. Changing the inside to the outside so that the axon hillock recognizes that it’s becoming positive enough for an action potential, “making it talk”

Properties of an action potential

• Electrical communication that travels down the axon of a neuron 

• Maintains its size as it travels down the axon 

• All-or-nothing response 

• All action potentials are similar in size and duration 

• Intensity is dictated by frequency and pattern