Lecture one reading – Introduction.
Dopamine is not an effective treatment for Parkinson’s Disease (PD) because it doesn’t readily penetrate the blood-brain barrier.
L-Dopa (the chemical precursor of dopamine) readily penetrates the blood-brain barrier and is converted into dopamine once inside the brain.
One key to understanding neural function is the membrane potential, the difference in electrical charge between the inside and the outside of the cell.
Recording the membrane potential
To record a neurons membrane potential: position the tip of one electrode inside the neuron; the tip of the other in the extracellular fluid. – the intracellular electrodes are called microelectrodes.
The resting membrane potential
A neurons resting potential = -70mV.
This indicates that the potential inside the resting neuron is about 70mv less than outside the neuron.
In its resting state, a neuron is said to be polarized.
The Ionic Basis of the Resting Potential
The resting potential results from the ratio of negative to positive charges is greater inside the neuron than outside.
This unequal distribution of charges occurs due to the interaction of 4 factors:
2 factors that act to distribute ions equally throughout the intracellular and extracellular fluids and 2 of the neural membrane that counteract these homogenizing effects.
1. Random motion – the ions In the neural tissue are in constant random motion, and particles in random motion tend to get evenly distributed because they are more likely to move down their conc. gradients than up them.
2. The second factor that promotes the even distribution of ions is electrostatic pressure. Any accumulation of charges, positive or negative, in one area tends to be dispersed by the repulsion among the like charges in the vicinity and the attraction of opposite charges concentrated elsewhere.
Despite these homogenizing effects of random movement and electrostatic pressure, no...