Unit 17: The Nervous and Endocrine Systems
How electrical nerve signals and chemical hormones each carry messages across your body, on very different timescales.
7 topics · 22 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
The Structure of a Neuron
- How it worksHow do dendrites receive signals while the axon carries a signal away to the next cell?
- Common mistakeWhy isn't a single neuron long enough to stretch from your brain to your toe on its own?
- Going furtherWhat happens to signal speed when a myelin sheath wraps around an axon?
Your turn1 of 2
Most cells in the body are roughly round or cube-shaped, but a neuron has a distinct cell body, a long thin axon, and many branching dendrites. Why does a neuron have this specialized shape instead of just being round like most cells?How a Nerve Impulse Travels
- How it worksHow does a wave of sodium and potassium ions crossing the membrane create an action potential?
- Worked exampleFind the direction of net ion flow when a neuron's membrane depolarizes from negative 70 millivolts toward positive 30 millivolts.
- Common mistakeWhy doesn't an action potential get weaker as it travels down a long axon?
Your turn1 of 2
A myelinated axon conducts a nerve signal at a speed of about 90 meters per second. About how long, in seconds, would it take a signal to travel 1.08 meters down that axon?Synapses and Neurotransmitters
- How it worksHow do neurotransmitters cross the synaptic gap and bind to receptors on the next neuron?
- Common mistakeWhy isn't a synapse a physical point where two neurons' membranes actually touch?
- Going furtherWhat happens to signal transmission when a drug blocks neurotransmitter receptors at a synapse?
Your turn1 of 2
An electrical signal travels quickly down one neuron's axon, but that same signal has to convert into a chemical signal to actually cross into the next neuron rather than continuing as electricity. Why does an electrical signal have to become a chemical signal to reach the next neuron?The Brain and Spinal Cord
- How it worksHow do the cerebrum, cerebellum, and brainstem each handle a different set of the body's functions?
- How it worksHow does the spinal cord relay signals between the brain and the rest of the body?
- Common mistakeWhy isn't it true that humans only use ten percent of their brain?
Your turn1 of 2
A stroke or injury affecting one small, specific region of the brain can wipe out a person's ability to speak while leaving their ability to understand language, move their limbs, or remember faces completely intact. Why does damage to one small brain region sometimes wipe out just one specific ability?The Reflex Arc
- How it worksWalk me through how a reflex arc sends a signal straight to the spinal cord and back without waiting for the brain.
- Going furtherHow does bypassing the brain in a reflex arc make the response faster than an ordinary voluntary reaction?
- Common mistakeWhy doesn't a reflex mean the brain is completely uninvolved in the sensation?
Your turn1 of 2
Your hand jerks away from a hot stove within a fraction of a second, well before you consciously feel or register the pain of the burn. Why does your hand jerk away before you consciously register the pain?Hormones and the Endocrine System
- How it worksHow does a hormone find and bind only to cells that have the matching receptor for it?
- Common mistakeWhy doesn't every cell in the body respond to every hormone circulating in the blood?
- Ties togetherHow does the endocrine system's chemical signaling compare in speed to the nervous system's electrical signaling?
Your turn1 of 2
A hormone released into the bloodstream travels throughout the entire body, past essentially every organ and tissue, yet it typically only produces a noticeable effect on a small subset of them. Why can a gland release a chemical into your bloodstream that only affects certain distant organs and not others?How the Pancreas Regulates Blood Sugar
- How it worksHow does insulin signal cells to absorb glucose and lower blood sugar after a meal?
- How it worksHow does glucagon signal the liver to release stored glucose when blood sugar drops too low?
- Common mistakeWhy doesn't type 1 diabetes mean a person's body produces too much insulin instead of too little?
- Ties togetherHow does insulin and glucagon's push and pull form a negative feedback loop around blood sugar?
Your turn1 of 2
After a meal, insulin helps lower blood glucose by about 2.94 milligrams per deciliter for every minute it acts. Over 42 minutes, how much would blood glucose be expected to drop, assuming this rate holds steady?