The different types of neural reflexes are all rapid, automatic responses to stimuli PDF

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The different types of neural reflexes are all rapid, automatic responses to stimuli...

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The different types of neural reflexes are all rapid, automatic responses to stimuli Conditions inside or outside the body can change quickly and unexpectedly. Reflexes, which are rapid and automatic responses to specific stimuli, preserve homeostasis by making quick adjustments in the function of organs or organ systems. The response shows little variability: Each time a particular reflex is activated, it normally produces the same motor response. In Chapter 1, we introduced the basic functional components involved in all types of homeostatic regulation: a receptor, a control center (or integration center), and an effector. p. 19 Here we consider neural reflexes, in which sensory fibers deliver information from peripheral receptors to an integration center in the CNS, and motor fibers carry motor commands to peripheral effectors. This includes the events that happen when a reflex is triggered, as well as the types of neural reflexes. In Chapter 18, we examine a neuroendocrine response reflex, in which hormones in the bloodstream carry the commands to peripheral tissues and organs. The Reflex Arc The route followed by nerve impulses to produce a reflex is called a reflex arc. Spotlight Figure 13–14a diagrams the five steps in a simple neural reflex. 1) Arrival of a Stimulus and Activation of a Receptor. Reflex arcs begin with activation of a receptor, which may be a specialized cell or the dendrites of a sensory neuron. Receptors are sensitive to physical or chemical changes in the body or to changes in the external environment. We introduced the general categories of sensory receptors in Chapter 12. p. 395 If you lean on a tack, for example, pain receptors in the palm of your hand are activated. These receptors, the dendrites of sensory neurons, respond to stimuli that cause or accompany tissue damage. (We discuss the link between receptor stimulation and sensory neuron activation further in Chapter 15.) 2) Activation of a Sensory Neuron. When the dendrites are stretched, this causes a graded depolarization that leads to the formation and propagation of action potentials along the axons of the sensory neurons. This information reaches the spinal cord by way of a posterior root. In our example, 1 and 2 involve the same cell. However, the two steps may involve different. The stretch reflex is an example of a monosynaptic reflex. Because there is only one synapse, there is little delay between sensory input and motor output. These

reflexes control the most rapid motor responses of the nervous system. A stretch reflex provides automatic regulation of skeletal muscle length. The patellar reflex is an example of a stretch reflex. The stimulus is a tap on the patellar tendon that stretches receptors within the quadriceps femoris. The response is a brief contraction of those muscles, which produces a noticeable kick....