Motor pathways
Next, we’ll trace the path that movement-related information takes from the cortex to the muscles it activates.
1) Start with this video about the corticospinal tract, the main pathway for voluntary movement:
2) Then, read this article:
History of Neuroscience - Corticospinal Tract
3) Watch this video about the neuromuscular junction, which is where the nervous system interacts with muscles:
4) Finally, answer these questions to test your understanding:
1. Most of the neurons that enter the corticospinal tract originate in the:
- A. basal ganglia
- B. cerebellum
- C. motor cortex
- D. thalamus
Show Answer
Correct answer: C
Most corticospinal tract neurons originate in the motor cortex. Their axons descend through the brainstem and spinal cord to influence motor neurons involved in movement.
2. Where do most of the fibers in the corticospinal tract decussate (i.e., cross to the other side of the nervous system)?
- A. in the medulla
- B. in the pons
- C. in the midbrain
- D. in the spinal cord
Show Answer
Correct answer: A
The upper motor neurons of the corticospinal tract leave the motor cortex and descend to the brainstem, continuing down into the medulla where the fibers form two bundles, known as the pyramids. At the base of the pyramids, about 90% of the fibers in the corticospinal tract decussate, or cross to the other side of the brainstem in a bundle called the pyramidal decussation.
3. After a car accident, a patient suffers substantial damage to the right side of the cervical spinal cord. Her corticospinal tract fibers on the right are severely damaged. What motor deficit would you expect to see?
- A. weakness or paralysis on the right side of the body below the damage
- B. weakness or paralysis on the right side of the body above the damage
- C. weakness or paralysis on the left side of the body below the damage
- D. weakness or paralysis on the left side of the body above the damage
Show Answer
Correct answer: A
Damage to the right corticospinal tract in the spinal cord causes weakness or paralysis on the same side (ipsilateral) of the body below the lesion/damage.
4. At the neuromuscular junction (where a neuron communicates with a muscle to cause muscle contraction), what is the neurotransmitter that is released to cause muscles to contract?
- A. dopamine
- B. glutamate
- C. serotonin
- D. acetylcholine
Show Answer
Correct answer: D
Neurons primarily release the neurotransmitter acetylcholine to cause contraction of skeletal muscle. Acetylcholine then binds to receptors in the muscle membrane to cause muscle contraction.
5. What enzyme is found at the neuromuscular junction and is responsible for breaking down acetylcholine?
- A. choline acetyltransferase
- B. monoamine oxidase
- C. catechol-O-methyltransferase
- D. acetylcholinesterase
Show Answer
Correct answer: D
The enzyme acetylcholinesterase is present at the neuromuscular junction; it breaks down acetylcholine and in the process terminates its effects on the muscle fiber, thus ending the communication between the motor neuron and the muscle fiber.
