The Neuron: Biological Bases

Neuron

  • Neuron: Nerve cell; building block of the nervous system.
  • Glial Cells (Glia): Support, nourish, and protect neurons; play a role in learning, thinking, and memory.

Neural Firing Process

  • Resting Potential: Neuron is NOT firing; negative charge with potassium ions inside, sodium ions outside (Polarization).
  • Polarization: Sodium outside, potassium inside at resting potential (Homeostasis).
  • Threshold: Stimulation level required to trigger a neural impulse.
  • Action Potential: Neural impulse; brief electrical charge traveling down an axon. Speed ranges from 2 to over 200 miles per hour.
  • Depolarization: Change in electrical charge; gates open, sodium ions flood in. Potassium ions rush out.
  • Refractory Period: Period after firing where neuron resets and cannot fire again.
  • All or None Response: Neuron either fires fully or not at all.

Communication Between Nerve Cells

  • Synapse: Junction between axon tip of sending neuron and dendrite/cell body of receiving neuron.
  • Synaptic Gap/Cleft: Tiny gap at the synapse.
  • Neurotransmitters: Chemical messengers crossing synaptic gaps.
  • Action potentials stimulate neurotransmitter release.
  • Neurotransmitters bind to receptor sites on the receiving neuron.
  • Excess neurotransmitters undergo Reuptake, drift away, or are broken down by enzymes.

Neurotransmitters and Their Influence

  • Agonists: Mimic neurotransmitter activity.
  • Antagonists: Block neurotransmitter activity.
  • Excitatory Neurotransmitters: Increase information flow (e.g., Glutamate).
  • Inhibitory Neurotransmitters: Decrease information flow (e.g., GABA).

Key Neurotransmitters and Functions

  • Dopamine: Influences movement, learning, attention, and emotion.
  • Norepinephrine: Controls alertness and arousal.
  • Epinephrine (Adrenaline): Released in response to stress; involved in fight-or-flight response.
  • Glutamate: Excitatory neurotransmitter; involved in memory.
  • Serotonin: Affects mood, hunger, sleep, and arousal. SSRIs increase synaptic levels.
  • GABA: Inhibitory neurotransmitter; reduces anxiety and tension.

Neurotransmitter Imbalances

  • Serotonin: Too little linked to depression.
  • GABA: Too little linked to seizures, tremors, insomnia, epilepsy.
  • Norepinephrine: Too little linked to depressed mood, lack of energy.
  • Acetylcholine (Ach): Deterioration linked to Alzheimer’s disease.
  • Glutamate: Overstimulation linked to migraines or seizures.
  • Endorphins: Oversupply from opiate drugs can suppress natural supply.
  • Dopamine: Imbalances linked to schizophrenia and Parkinson’s disease.