Exercises: The nervous system

Look at the image of the neurone. State which number points to the dendrites and which points to the axon, and explain the difference between the function of the former and the latter in the transmission of the nerve impulse.

Name the two main divisions of the nervous system and list at least two organs that form part of each of them.

Order the following structures of the nervous system from highest to lowest level of organisation, and explain your criterion: neurone, brain, nervous system, nervous tissue.

In the image of the neurone, a sheath covering sections of the axon is shown. Name it, explain its function, and reason why a disease that destroys it, such as multiple sclerosis, causes movement and sensory problems.

Describe the pathway of information in a simple voluntary movement, such as writing your name on paper: which nervous center gives the order, where the impulse travels, and which types of neurons are involved.

Explain what a reflex action is and how it differs from a voluntary action. Give an example of each and state which part of the nervous system mainly coordinates each type of response.

In a neurology consultation, the patellar reflex (tap on the tendon below the kneecap) and tactile sensitivity are examined in three patients, obtaining these results:

• Patient A: Upon receiving the tap on the tendon, extends their leg automatically as normal, but states that they did not feel the touch or the tap.

• Patient B: Feels the tap completely clearly, but the leg does not move reflexively (although they can extend it if the doctor voluntarily asks them to do so).

• Patient C: Feels nothing and the leg does not move at any point either.

1. a) Based on the elements that make up a reflex arc (receptor, sensory neuron, spinal cord, motor neuron, and effector) and its connection to the brain, reasonably deduce at what point in the nervous circuit the alteration may be located for each of the three patients.
2. b) Why does a healthy person pull their foot back from a prick before becoming conscious of the pain?

A motorcyclist has an accident and loses sensation and movement in his legs, but keeps those in his arms intact. Based on your knowledge of the spinal cord, reason in which part of the spinal column the injury probably occurred and why only the lower limbs were affected.

Analyze how two different toxins act on the neuromuscular synapse (the junction between the motor neuron and muscle fibers):

• Substance X (curare): Binds to the neurotransmitter receptors on the muscle cell and blocks them, preventing the neurotransmitter from interacting with them.

• Substance Y (nerve gas): Destroys the enzyme that breaks down the neurotransmitter after its release, causing it to remain indefinitely in the synaptic cleft.

1. a) Predict what will happen to the muscles of a person exposed to substance X and to those of a person exposed to substance Y (will the muscles remain flaccid and paralyzed, or in permanent contraction and spasm?). Justify your answer based on how chemical synapses work.
2. b) Although they act through completely opposite mechanisms on the muscle, explain why both substances cause death by asphyxiation if they affect the respiratory muscles.