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Explores the specialized anatomy of neurons and the electrochemical basis of signal transmission.
Imagine a message traveling at 270 miles per hour through a biological wire thinner than a human hair. How does your body generate electricity from just salt and water to make you think, move, and feel?
The neuron is the functional unit of the nervous system, designed for rapid communication. It consists of three primary regions. Dendrites are the branched extensions that act as 'antennae,' receiving chemical signals from other neurons. These signals converge in the Soma (cell body), which contains the nucleus and integrates incoming information. If the signal is strong enough, it is transmitted down the Axon, a long, slender projection that carries the electrical impulse away from the cell body toward the Axon Terminals. To increase the speed of these impulses, many axons are insulated by a Myelin Sheath, a fatty layer that prevents 'leaks' of electrical charge.
Quick Check
Which specific part of the neuron is responsible for integrating incoming signals to determine if an impulse should be sent?
Answer
The Soma (or cell body).
Even when a neuron is not firing, it is electrically active. This 'ready state' is called the Resting Membrane Potential, typically measured at . This negative charge inside the cell is maintained by ion gradients. The Sodium-Potassium Pump (-ATPase) actively transports ions against their concentration gradients, moving ions out of the cell for every ions moved in. Because more positive charge is pumped out than in, and because 'leaks' out through passive channels more easily than leaks in, the interior remains negative relative to the exterior.
To understand why the cell becomes negative, look at the ratio of the pump's activity: 1. The pump moves Sodium ions () to the extracellular fluid. 2. The pump moves Potassium ions () to the intracellular fluid. 3. Net change per cycle: ion lost from the inside. 4. Result: The inside of the cell becomes increasingly negative compared to the outside.
Quick Check
If a metabolic poison stopped all ATP production in a neuron, what would happen to the resting membrane potential?
Answer
The resting membrane potential would gradually disappear (move toward ) because the pump requires ATP to maintain the gradient.
Neurons do not work alone; they are outnumbered by Glial Cells (glia), which provide essential support. In the Central Nervous System (CNS), Oligodendrocytes wrap axons in myelin, while Schwann Cells perform this same task in the Peripheral Nervous System (PNS). Astrocytes are star-shaped cells that anchor neurons to blood supplies and regulate the chemical environment. Finally, Microglia act as the brain's immune system, patrolling for pathogens and cellular debris. Without these 'helper' cells, neurons would be unable to maintain homeostasis or transmit signals efficiently.
Consider the pathology of Multiple Sclerosis (MS), where the immune system attacks the myelin sheath in the CNS. 1. Normal state: Myelin allows for Saltatory Conduction, where the signal 'jumps' between gaps called Nodes of Ranvier. 2. Diseased state: As myelin is destroyed, the electrical resistance of the axon membrane decreases. 3. Result: The electrical current leaks out of the axon, causing the signal to slow down or dissipate entirely before reaching the terminal, leading to loss of motor control and sensory issues.
What is the primary ratio of ions moved by the Sodium-Potassium pump?
Which glial cell is responsible for forming the blood-brain barrier and supporting neurons structurally?
In the Central Nervous System, the myelin sheath is produced by Schwann cells.
Review Tomorrow
In 24 hours, try to sketch a neuron from memory and explain why the inside of the cell is negative () without looking at your notes.
Practice Activity
Research the difference between 'continuous conduction' and 'saltatory conduction' to see how myelin changes the physics of the action potential.