Neural Messages

Neural Communication Overview

Axonal Conduction

  • Action Potential: Electrical signal due to movement of ions (+) in/out of axon.

    • Lasts <2 ms.

    • Fastest can travel length of a football field in 1 sec.

  • Resting State: Inside axon is more negative (-70mV) than outside due to negative proteins (P-).

Steps of Action Potential

  1. Threshold Reached: More excitatory than inhibitory signals; threshold at -55mV.

  2. Depolarization: Na+ gates open, Na+ enters; inside becomes +40mV.

  3. Repolarization: K+ gates open, K+ exits; inside becomes more negative.

  4. Hyperpolarization: K+ gates open too long; inside is super negative.

  • Refractory Period: Neuron cannot fire again until it returns to -70mV.

Synaptic Transmission

  • Average neuron forms ~1,000 synapses; dynamic changes support learning.

Process Steps

  1. Trigger: Electrical signal reaches axon end, causes neurotransmitter release into synaptic space.

  2. Binding: Neurotransmitters bind to receptors on postsynaptic neuron; may generate action potential if threshold (-55mV) is reached.

  3. Types of Signals:

    • Excitatory Signals: Promote depolarization (allow + ions in).

    • Inhibitory Signals: Cause hyperpolarization (allow - ions out).

  4. Reuptake: After binding, neurotransmitters are either degraded or reabsorbed for recycling in the presynaptic neuron.

Neural Communication Overview

  • The brain communicates through electrical signals (action potentials) moving along neurons and chemical signals (neurotransmitters) between neurons.

Axonal Conduction (Electrical Signal)

  • Action Potential: A brief electrical impulse caused by ions moving in and out of the axon.

    • It's like a fast wave, lasting less than 2 milliseconds.

  • Resting State: When not firing, the inside of the axon is negatively charged (-70mV) compared to the outside.

Steps of Action Potential

  1. Trigger: If enough positive signals accumulate, the neuron reaches a "threshold" (-55mV) and decides to fire.

  2. Depolarization: Sodium (Na+) ions rush into the axon, making the inside briefly positive (+40mV).

  3. Repolarization: Potassium (K+) ions rush out, bringing the inside back to a negative state.

  4. Hyperpolarization: Sometimes, K+ gates stay open a bit too long, making the inside even more negative than the resting state.

  • Refractory Period: After firing, there's a short period where the neuron can't fire again until it resets to its resting state.

Synaptic Transmission (Chemical Signal)

  • Neurons connect at junctions called synapses, where they send chemical messages (neurotransmitters).

Process Steps

  1. Release: When an electrical signal reaches the end of a neuron, it releases neurotransmitters into the tiny gap (synaptic space).

  2. Binding: These neurotransmitters then bind to specific receptors on the next neuron.

    • If enough excitatory neurotransmitters bind, they can trigger a new action potential in the next neuron.

  3. Types of Signals:

    • Excitatory Signals: Encourage the next neuron to fire by making it more positive.

    • Inhibitory Signals: Discourage the next neuron from firing by making it more negative.

  4. Cleanup: After doing their job, neurotransmitters are either broken down or reabsorbed by the original neuron for reuse.