biology

Upper motor neuron

Upper motor neuron is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Upper motor neuron rather than just read about it. In short: Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles to contract or relax.

Key takeaways

Upper motor neuron belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Upper motor neuron to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Upper motor neuron from memory before moving on to harder problems.

Reference excerpt

Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles to contract or relax. UMNs represent the major origin point for voluntary somatic movement. Upper motor neurons represent the largest pyramidal cells in the motor regions of the cerebral cortex. The major cell type of the UMNs is the Betz cells residing in layer V of the primary motor cortex, located on the precentral gyrus in the posterior frontal lobe. The cell bodies of Betz cell neurons are the largest in the brain, approaching nearly 0.1 mm in diameter. The axons of the upper motor neurons project out of the precentral gyrus travelling through to the brainstem, where they will decussate (intersect) within the lower medulla oblongata to form the lateral corticospinal tract on each side of the spinal cord. The fibers that do not decussate will pass through the medulla and continue on to form the anterior corticospinal tracts. The upper motor neuron descends in the spinal cord to the level of the appropriate spinal nerve root. At this point, the upper motor neuron synapses with the lower motor neuron or interneurons within the ventral horn of the spinal cord, each of whose axons innervate a fiber of skeletal muscle. These neurons connect the brain to the appropriate level in the spinal cord, from which point nerve signals continue to the muscles by means of the lower motor neurons. The neurotransmitter glutamate transmits the nerve impulses from upper to lower motor neurons, where it is detected by glutamate receptors.

Pathways Upper motor neurons travel in several neural pathways through the central nervous system (CNS):

Lesions Any upper motor neuron lesion, also known as pyramidal insufficiency, occurs in the neural pathway above the anterior horn of the spinal cord. Such lesions can arise as a result of stroke, multiple sclerosis, spinal cord injury or other acquired brain injury. The resulting changes in muscle performance that can be wide and varied are described overall as upper motor neuron syndrome. Symptoms can include muscle weakness, decreased motor control including a loss of the ability to perform fine movements, increased vigor (and decreased threshold) of spinal reflexes including spasticity, clonus (involuntary, successive cycles of contraction/relaxation of a muscle), and an extensor plantar response known as the Babinski sign.

See also Lower motor neuron Upper motor neuron lesion Lower motor neuron lesion

References

External links "motoneuron" at Dorland's Medical Dictionary

Illustrations

Worked examples

Example 1 — a first encounter with Upper motor neuron

Start with the simplest possible case. Write down what Upper motor neuron claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Upper motor neuron before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Upper motor neuron ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Upper motor neuron

In research: Upper motor neuron appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Upper motor neuron in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Upper motor neuron is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cerebral palsy types, Efferent neurons, Motor system, so understanding it makes those chapters shorter.
In everyday life: Look for Upper motor neuron outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Upper motor neuron” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Upper motor neuron in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Upper motor neuron means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Upper motor neuron out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Upper motor neuron in simple terms?

Why does Upper motor neuron matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Upper motor neuron?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Upper motor neuron.