Uploaded July 2023 | Updated September 2026, 1 week ago
In this video, I cover the basics of the action potential beginning with an explanation of membrane potential and how it sets the stage for the action potential. Then, I describe how an action potential is generated and how it ends. I cover the propagation of an action potential down the axon and the role myelin plays in this process. Finally, I discuss the absolute and relative refractory periods and what they mean for repeated action potential firing.
Key points:
00:00 Introduction
0:17 Membrane potential
4:18 Action potential
7:20 Propagation down the axon and role of myelin
8:51 Absolute and relative refractory periods
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📚Your Brain, Explained: What Neuroscience Reveals About Your Brain and its Quirks: amazon.com/Your-Brain-Explained-Neuroscience-Reveals/dp/1473696569
📚Bizarre: The Most Peculiar Cases of Human Behavior and What They Tell Us About How the Brain Works: amazon.com/Bizarre-Peculiar-Cases-Human-Behavior/dp/139980121X
REFERENCES:
Bean BP, Koester JD. 2021. Propagated Signaling: The Action Potential. In: Kandel ER, Koester JD, Mack SH, Siegelbaum SA, eds. Principles of Neural Science, 6th ed. New York: McGraw-Hill.
Koester JD, Siegelbaum SA. 2021. Membrane Potential and the Passive Electrical Properties of the Neuron. In: Kandel ER, Koester JD, Mack SH, Siegelbaum SA, eds. Principles of Neural Science, 6th ed. New York: McGraw-Hill.
Pinel JPJ. 2014. Biopsychology. 9th ed. New York: Pearson.
In this video, I cover the basics of the action potential beginning with an explanation of membrane potential and how it sets the stage for the action potential. Then, I describe how an action potential is generated and how it ends. I cover the propagation of an action potential down the axon and the role myelin plays in this process. Finally, I discuss the absolute and relative refractory periods and what they mean for repeated action potential firing.
Key points:
00:00 Introduction
0:17 Membrane potential
4:18 Action potential
7:20 Propagation down the axon and role of myelin
8:51 Absolute and relative refractory periods
đź§ Take your learning further with my free, self-paced Introduction to Neuroscience course featuring my videos, articles, and hundreds of quiz questions: neuroscientificallychallenged.com/course
If you're looking for accessible and entertaining ways to learn more about the brain, check out my books:
📚Your Brain, Explained: What Neuroscience Reveals About Your Brain and its Quirks: amazon.com/Your-Brain-Explained-Neuroscience-Reveals/dp/1473696569
📚Bizarre: The Most Peculiar Cases of Human Behavior and What They Tell Us About How the Brain Works: amazon.com/Bizarre-Peculiar-Cases-Human-Behavior/dp/139980121X
REFERENCES:
Bean BP, Koester JD. 2021. Propagated Signaling: The Action Potential. In: Kandel ER, Koester JD, Mack SH, Siegelbaum SA, eds. Principles of Neural Science, 6th ed. New York: McGraw-Hill.
Koester JD, Siegelbaum SA. 2021. Membrane Potential and the Passive Electrical Properties of the Neuron. In: Kandel ER, Koester JD, Mack SH, Siegelbaum SA, eds. Principles of Neural Science, 6th ed. New York: McGraw-Hill.
Pinel JPJ. 2014. Biopsychology. 9th ed. New York: Pearson.


![2-Minute Neuroscience: Motor Neurons
In this video, I discuss upper and lower motor neurons as well as the syndromes (i.e., upper and lower motor neuron syndrome) that occur when a motor neuron is damaged.
đź§ Take your learning further with my free, self-paced Introduction to Neuroscience course featuring my videos, articles, and hundreds of quiz questions: https://neuroscientificallychallenged.com/course
If youre looking for accessible and entertaining ways to learn more about the brain, check out my books:
📚Your Brain, Explained: What Neuroscience Reveals About Your Brain and its Quirks: https://www.amazon.com/Your-Brain-Explained-Neuroscience-Reveals/dp/1473696569/
📚Bizarre: The Most Peculiar Cases of Human Behavior and What They Tell Us About How the Brain Works: https://www.amazon.com/Bizarre-Peculiar-Cases-Human-Behavior/dp/139980121X/
TRANSCRIPT:
A motor neuron is a type of neuron that carries information from the brain or spinal cord and is involved in regulating activity in muscles or glands. There are two types of motor neurons: upper motor neurons and lower motor neurons, which interact with one another to cause movement and other responses.
Upper motor neurons originate in multiple areas of the brain and brainstem and carry information about desired movements or other responses in descending tracts like the corticobulbar and corticospinal tracts. Upper motor neurons descend to various levels of the brainstem and spinal cord and form connections with lower motor neurons. Lower motor neurons then influence the activity of muscles or glands. There are three broad categories of lower motor neurons: somatic motor neurons, which extend to skeletal muscle to control movement and muscle tone; special visceral or branchial motor neurons, which supply muscles in the head and neck; and general visceral motor neurons, which are involved in the autonomic nervous system. Somatic motor neurons can be further subdivided into alpha, beta, and gamma motor neurons depending on the type of muscle fiber they supply.
The consequences of upper and lower motor neuron damage are distinct. Symptoms of upper motor neuron damage, which are collectively called upper motor neuron syndrome, can include weakness or paralysis, spasticity, increased muscle tone, over-responsive reflexes, and a positive Babinski sign, which occurs when the bottom of the foot is stroked and instead of the toes curling down the big toe extends up and the other toes fan out. Lower motor neuron damage leads to a collection of symptoms known as lower motor neuron syndrome, which may involve weakness or paralysis, decreased or absent muscle tone, decreased or absent reflexes, involuntary muscle twitches, and muscle atrophy.
REFERENCES:
Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, Mooney RD, Platt ML, White LE, eds. Neuroscience. 6th ed. New York. Sinauer Associates; 2018.
Zayia LC, Tadi P. Neuroanatomy, Motor Neuron. [Updated 2020 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554616/ 2-Minute Neuroscience: Motor Neurons](https://i.ytimg.com/vi/WKBREYS9C9g/mqdefault.jpg)

![2-Minute Neuroscience: Aphasia
Aphasia is a language disorder caused by damage to areas of the brain involved in producing or understanding language. In this video, I discuss several of the most common aphasia syndromes: Brocas aphasia, Wernickes aphasia, conduction aphasia, and global aphasia.
đź§ Take your learning further with my free, self-paced Introduction to Neuroscience course featuring my videos, articles, and hundreds of quiz questions: https://neuroscientificallychallenged.com/course
If youre looking for accessible and entertaining ways to learn more about the brain, check out my books:
📚Your Brain, Explained: What Neuroscience Reveals About Your Brain and its Quirks: https://www.amazon.com/dp/1473696569/
📚Bizarre: The Most Peculiar Cases of Human Behavior and What They Tell Us About How the Brain Works: https://www.amazon.com/dp/139980121X/
TRANSCRIPT
Aphasia is a language disorder caused by damage to areas of the brain involved in producing or understanding language. It most often occurs after stroke, especially when the language-dominant cerebral hemisphere is affected, which for most people is the left cerebral hemisphere. Aphasia can affect language comprehension, speaking, reading, and writing. The symptoms depend on where the damage occurs, and different patterns of impairment are often described as aphasia syndromes. In this video, I will cover several of the most common aphasia syndromes. While these syndromes are useful clinical descriptions, real patients don’t always fit neatly into one of these categories.
Broca’s aphasia is associated with damage to the frontal lobe, often in or near Broca’s area. People with Broca’s aphasia typically understand language relatively well, but they have difficulty producing language. Their speech is often slow, effortful, and limited to single words or short phrases.
Wernicke’s aphasia is typically linked to damage in the temporal lobe, often involving Wernicke’s area. In this syndrome, speech production remains fluent, but it may contain incorrect, confusing, or nonsensical words and phrases. People with Wernicke’s aphasia also often have difficulty understanding language.
Conduction aphasia is characterized by relatively fluent speech and fairly good comprehension, with a particular difficulty repeating words or phrases. It has classically been associated with damage to pathways connecting frontal and temporal language regions, especially a pathway called the arcuate fasciculus, although actual lesions can involve nearby language regions as well.
Global aphasia results from extensive damage to language areas in the dominant-hemisphere language network. It is linked to severe impairments in both speech production and language comprehension.
REFERENCES
Clark DG, Cummings JL. Aphasia. In: Brandt T, Caplan LR, Dichgans J, Diener HC, Kennard C, editors. Neurological Disorders. 2nd ed. San Diego (CA): Academic Press; 2003. p. 265-275. doi:10.1016/B978-012125831-3/50220-3.
National Institute on Deafness and Other Communication Disorders (NIDCD). Aphasia [Internet]. Bethesda (MD): National Institute on Deafness and Other Communication Disorders. Available from: https://www.nidcd.nih.gov/health/aphasia
Sheppard SM, Sebastian R. Diagnosing and managing post-stroke aphasia. Expert Rev Neurother. 2021 Feb;21(2):221-234. doi: 10.1080/14737175.2020.1855976. Epub 2020 Dec 10. PMID: 33231117; PMCID: PMC7880889.
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