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Nervous System, Neuron Structure, and Neurotransmission (Vocabulary)

Dendrites, Axon, and Synapses

  • Dendrites: branch-like structures that receive information from other neurons.
  • Axon: conducts information away from the dendrites toward the terminal.
  • Terminal button: the end of the axon where signals are released.
  • Synapse: the gap between the terminal of one neuron and the next neuron; neurotransmission crosses this gap.
  • Signal flow: dendrite → cell body → axon → terminal → synapse → next neuron.

Resting and Action Potentials

  • Resting potential: neuron at rest with balanced ions; no message to send.
  • Upon stimulation, positive ions flood in, creating a charge that triggers firing.
  • Action potential: the neuron's all-or-none electrical impulse that travels down the axon.
  • All-or-none: once threshold is reached, the signal fires fully; no partial signals.
  • Refractory period: after firing, the neuron briefly rests before firing again.

Neurotransmitters, Drugs, and Receptors

  • Neurotransmitters: chemical messengers released at the synapse; regulate mood, sleep, hunger, pain, emotions.
  • Drugs can mimic or block neurotransmitters, altering signaling.
  • Example: opioids mimic dopamine-like effects, producing high; withdrawal can cause severe crashes due to depleted natural dopamine.
  • Lock-and-key: neurotransmitters fit specific receptors; imbalance (too much or too little) can lead to dysfunction or disorders.

Hormones vs Neurotransmitters

  • Neurotransmitters: released in the brain to regulate brain/body function.
  • Hormones: released into the bloodstream to affect organs; still part of the signaling system though often slower-acting than neurotransmitters.
  • Stress hormones (e.g., cortisol, adrenaline) respond to danger signals and regulate body-wide arousal.

Nervous System Organization

  • Central Nervous System (CNS): brain and spinal cord; backbone of control and coordination.
  • Peripheral Nervous System (PNS): all nerves outside the CNS; links CNS to the body.
  • Autonomic vs Somatic (two parts of the PNS):
    • Autonomic: automatic, involuntary control of internal organs (digestion, heart rate, etc.).
    • Somatic: voluntary control of skeletal muscles and conscious sensing.

Autonomic: Sympathetic and Parasympathetic

  • Sympathetic: arousal - prepares body for danger (fight-or-flight); increases heart rate, redirects energy, etc.
  • Parasympathetic: calms body back to baseline (rest-and-digest); conserves energy.
  • In stress, sympathetic arousal can become prolonged and harmful; parasympathetic helps restore balance.

Fight-or-Flight and Stress Response

  • Fight-or-flight: automatic arousal in response to imminent danger; involves many autonomic processes.
  • Prolonged arousal can be detrimental to health; understanding balance is important in stress-related contexts.

Neuroplasticity and Learning

  • Neurons: you are born with most neurons, but learning strengthens connections between neurons.
  • Neural connections (synapses) grow with experience (language, skills, etc.), improving communication efficiency.
  • Not about creating many new neurons in adulthood, but about forming and strengthening neural networks.

quick recap (keys to remember)

  • Dendrite, Axon, Terminal, Synapse – basic signal path.
  • Resting potential vs Action potential; all-or-none firing; refractory period.
  • Neurotransmitters: chemical messengers; drugs can mimic/block; receptor-specific effects.
  • CNS vs PNS; Autonomic vs Somatic; Sympathetic vs Parasympathetic.
  • Fight-or-flight as a key autonomic response; stress implications.
  • Learning relies on neural connectivity and plasticity, not just neuron quantity.