Neural Communication: How Signals Travel To & From the Brain

The nervous system transmits information via electrical and chemical signals through specialized cells (neurons) and glial support cells.

Signal Flow: Sensory → CNS → Motor

1. Sensory Transduction: Receptors (mechanoreceptors, photoreceptors, etc.) convert stimuli → graded receptor potentials.
2. Action Potential Generation: If threshold reached, voltage-gated Na+ channels open → all-or-none action potential (AP) propagates along sensory neuron axon.
3. Central Transmission: AP reaches spinal cord/brainstem → synapses on interneurons or projection neurons.
4. Ascending Pathways: Specific tracts carry modalities:
   • Dorsal column-medial lemniscus: Fine touch, vibration, proprioception.
   • Spinothalamic: Pain, temperature, crude touch.
   • Spinocerebellar: Unconscious proprioception.
5. Thalamic Relay: Most sensory info (except olfaction) synapses in thalamus → projects to primary sensory cortex.
6. Cortical Processing: Perception, integration, decision-making in association cortices.
7. Motor Command: Upper motor neurons (cortex) → descending tracts (corticospinal, rubrospinal, etc.) → lower motor neurons (spinal cord/brainstem) → neuromuscular junction.
8. Effector Response: ACh release at NMJ → muscle contraction; glandular secretion.

Synaptic Communication

• Electrical synapses (gap junctions): Fast, bidirectional (rare in CNS).
• Chemical synapses: Neurotransmitter release (vesicular) → binds receptors → ionotropic (fast) or metabotropic (slow/modulatory) effects.
• Key neurotransmitters: Glutamate (excitatory), GABA/glycine (inhibitory), ACh, dopamine, serotonin, norepinephrine.

Integration & Plasticity

Convergence, divergence, temporal/spatial summation, and synaptic plasticity (LTP/LTD) allow learning, memory, and adaptation.

This intricate, high-speed network underlies every sensation, thought, and action.