Neuro

What ions are in higher concentration extracellularly vs. intracellularly at rest?

• Extracellularly: Na+

• Intracellularly: K+; negatively charged organic molecules (proteins)

-Be able to define depolarization, Repolarization, Hyperpolarization

• Depolarization: Potential difference reduced (becomes more positive)

• Repolarization: Return to resting membrane potential (becomes more negative)

• Hyperpolarization: More negative than resting membrane potential

-What causes an action potential

• Stimulus (signal from another neuron) causes the Na+ channels to open; If enough sodium enters so that the cell becomes negative, an action potential will start.

• An AP is like flipping a switch—once they are triggered it’s all or nothing and travels along the neuron to send a signal.

-Absolute vs. Relative refractory period

• Absolute refractory period: The axon membrane is incapable of producing another action potential

• Relative refractory period:

▪ VG ion channel shape alters at the molecular level

▪ VG K+ channels are open

▪ Axon membrane can produce another action potential, but it requires stronger stimulus

- What is Saltatory conduction?

• Fast rate of conduction (leaping from node to node)

• **signals travel faster down myelinated axons because of saltatory conduction

-Electrical vs. Chemical synapses

• Electrical synapse:

▪ Direct flow of ions through gap junctions

▪ No delay; very fast

▪ Usually bidirectional

▪ Found in places requiring rapid communication such as the heart and some brain regions.

• Chemical synapse:

▪ Electrical signals trigger the release of neurotransmitters into the synaptic cleft (gap between cells); neurotransmitters bind to receptors on the next cell and create new signals.

▪ Slower than electrical synapses because of the time needed to release and bind the neurotransmitters

▪ Unidirectional

▪ Found mostly in the neuron-neuron communication of the brain, spinal cord and neuromuscular junctions

-EPSP vs IPSP

• EPSP (Excitatory postsynaptic potential): “Turnt man”

▪ Small depolarization causes the membrane potential to become less negative to excite the neuron and bring it closer to firing an AP

▪ Ex. Neurotransmitters: Glutamate, acetylcholine, norepinephrine, epinephrine

• IPSP (Inhibitory postsynaptic potential): “chill guy”

▪ Small hyperpolarization causes the membrane potential to become more negative to inhibit the neuron and reduce the chance of an AP

▪ Ex. Neurotransmitter: GABA