Responses and reflexes

Our body reacts and emits different types of responses, depending on the stimulus.

The Human Body Chapter 5: Peripheral Nervous System Peripheral Nervous System Somatic nervous system Spinal nerves Cranial nerves Autonomous nervous system Peripheral Nervous System Diseases What you must know Láminas bilingües para imprimir / Bilingual laminae to print

Imágenes In the image, we see how triceps reflexes are tested. When receiving a painful stimulus, the pupil dilates (the cutaneous-pupillary reflex). LÁMINAS Three types of Responses Reflex arc Painful reflex.

In the peripheral nervous system (PNS), a series of responses when faced with determined stimuli are developed, and there are different types (see the three responses infography). In the somatic nervous system, the responses can be a reflex act (see reflex arc infography) or a voluntary act. The reflex act is that which develops when the response is elaborated in the spinal cord and in order to achieve this, a sensory nerve carries a nerve impulse to the spinal cord and from there is transmitted to an association neuron, which passes it on to a motor neuron that stimulates the movement of a muscle fiber. It is a very quick and unconscious response before situations of danger that need immediate action, like for example, when we feel a prick or excessive heat on our hand. The pain sensation reaches the brain after the reaction movement takes place (see painful reflex infography). The voluntary act is produced when the response is elaborated in the brain. Its nerve coordination implies that a sensory neuron connects with a neuron from the spinal cord and this one, with a neuron that goes up to the brain. Several association neurons are involved here, which allow a response nerve impulse to be emitted that descends down the spinal cord, and, it reaches the muscle through a motor neuron. In this case, there is consciousness of the decided response before it is executed. As we have seen, the responses of the autonomous nervous system (ANS) have to do with the control of involuntary and visceral functions. In the case of the sympathetic division, these responses are quick and arise in dangerous situations, for example, an increase in heart rate, dilation of the bronchi to ease the entrance of oxygen, increase in sweating, vasoconstriction of the arteries, dilation of the pupils to allow the entry of more light, etc..

Reflexes that involve cranial peripheral nerves

Next, we list the names of some of the reflexes that have a protective function:
- Photomotor reflex: It is the contraction of the pupil (miosis) in response to a luminous stimulus.
- Cutaneous-Pupillary Reflex: the perception of a painful stimulus generates mydriasis, that is, the dilation of the pupil.
- Visual Corporal Reflexes: They include the exploratory movements of the eyes and the head when reading, the automatic movement of the eyes, the head and the neck reacting to a visual stimulus, and the closing of the eyelids when faced with an eventual dangerous situation.
- Cough Reflex: it is a reflex caused by an irritation of the larynx, the trachea or the bronchi.

Testing reflexes

When the tendon located under the patella (kneecap) is hit lightly with a rubber hammer, it makes the leg stretch. This reflex, known as the patellar reflex or knee-jerk, provides information on the state of the sensitive nerve, its connection with the spinal cord and the motor nerve that issues from the spinal cord towards the leg muscles. If the leg doesn't move or is hyperactive, it could mean that there is some damage in the spine. Other reflexes that are preventively tested are the Babinski reflex, that consists in stimulating the lateral side of the sole of the foot with a round object. Normally, the fingers of the foot curve downwards; but if, contrary to that, they extend and open like a fan, it could be a symptom that there is an anomaly in the brain or in the motor nerves that run from the brain to the spinal cord.

PALABRAS CLAVE

• Responses
• Reflexes
• Nerves
• "Photomotor reflex"
• "Cutaneous-Pupillary Reflex"
• "Visual Corporal Reflexes"
• "Cough Reflex"

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