Exercises: The nervous system

Look at the image of the neuron. 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 organization, and explain your criterion: neuron, brain, nervous system, nervous tissue.

Explain which three main parts a neuron has and what the general function of each one is in the transmission of the nerve impulse.

Name the three organs that form the brain and state a characteristic function of each one.

Explain which bony structures protect the brain and the spinal cord, and why this protection is so important in the case of the nervous system.

State whether these statements are true or false and justify your answer: a) the spinal cord is protected by the vertebral column; b) nerves only carry information from the body towards the brain; c) the cerebellum is involved in coordinating movement and balance.

Explain the difference between a sensory nerve and a motor nerve, and give an example of the information each one carries.

In the image of the neuron, 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 system 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.

Explain the difference between the rapid responses coordinated directly by the spinal cord and the decisions made by the brain, and give an everyday example of each type.

When you raise your hand to ask a question in class, a voluntary response is set in motion. Describe the route the information follows: which part of the brain decides the movement, which structure coordinates it so that it is precise, where the order travels down, and what finally carries it out.

The medulla oblongata is not involved in conscious decisions, and yet an injury to it is fatal. Explain which automatic functions of the body it regulates and why it is considered vital.

Reaction time is the time that passes from when we perceive a stimulus until we respond. Explain why it increases when driving while sleepy or looking at a cell phone, relating it to the processing of information in the nervous system.

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

• Patient A: When the tendon is tapped, 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.

Two patients who have suffered damage to different parts of the brain arrive at the emergency room:

• Patient 1: Is unable to speak and has complete motor paralysis in their right arm and leg, but perfectly understands what they hear and maintains their balance.

• Patient 2: Speaks with complete fluency and has normal strength in all four limbs, but is unable to stand without falling and cannot coordinate simple movements, such as touching the tip of their nose with their finger.

1. a) Deduce in which cerebral hemisphere Patient 1's lesion is located and justify why the motor loss manifests specifically on the right side of the body.
2. b) Why do Patient 2's symptoms indicate that their damage is not in the motor cortex of the cerebrum? Justify what other structure of the brain is affected.

The human brain weighs approximately 1.4 kg and is suspended in cerebrospinal fluid inside the cranial cavity.

1. a) Using the principle of inertia and the anatomy of the meninges, explain what physically happens to the brain inside the skull when an athlete undergoes sudden deceleration or braking of the head ("whiplash effect"), and why this can cause a severe concussion even if there is no bone fracture.
2. b) A company designs a helmet with an undeformable steel outer shell and claims in its advertising: "Since the outer shell never deforms or breaks, the brain is 100% protected against any concussion." Scientifically refute this claim by explaining what type of protection the brain actually needs inside the helmet to reduce injuries.

A pedestrian is about to be hit by a vehicle and experiences two successive responses:

• Response 1 (at 0.15 seconds): Leaps onto the sidewalk, avoiding the impact.

• Response 2 (at 10 seconds): Their heart rate increases from 75 to 140 beats per minute, they begin to sweat profusely, and their hands tremble. This state lasts for nearly 10 minutes.

1. a) Identify which coordination system (nervous or endocrine) is primarily responsible for each of the two responses. Justify your assignment by relating the reaction time to the way the signal travels in each system.
2. b) Explain why Response 1 ceases the moment the body touches the sidewalk, whereas Response 2 takes several minutes to disappear even though the danger has already passed.