How do stretch receptors work

Physical changes in these proteins increase ion flow across the membrane, and can generate a graded potential in the sensory neurons. Stimuli in the environment activate specialized receptors or receptor cells in the peripheral nervous system. Different types of stimuli are sensed by different types of receptors. Receptor cells can be classified into types on the basis of three different criteria: cell type, position, and function.

Receptors can be classified structurally on the basis of cell type and their position in relation to stimuli they sense. They can also be classified functionally on the basis of the transduction of stimuli, or how the mechanical stimulus, light, or chemical changed the cell membrane potential. The cells that interpret information about the environment can be either 1 a neuron that has a free nerve ending dendrites embedded in tissue that would receive a sensation; 2 a neuron that has an encapsulated ending in which the dendrites are encapsulated in connective tissue that enhances their sensitivity; or 3 a specialized receptor cell , which has distinct structural components that interpret a specific type of stimulus Figure The pain and temperature receptors in the dermis of the skin are examples of neurons that have free nerve endings.

Also located in the dermis of the skin are lamellated and tactile corpuscles, neurons with encapsulated nerve endings that respond to pressure and touch. The cells in the retina that respond to light stimuli are an example of a specialized receptor cell, a photoreceptor.

Graded potentials in free and encapsulated nerve endings are called generator potentials. When strong enough to reach threshold they can directly trigger an action potential along the axon of the sensory neuron. Action potentials triggered by receptor cells, however, are indirect.

Graded potentials in receptor cells are called receptor potentials. These graded potentials cause neurotransmitter to be released onto a sensory neuron causing a graded post-synaptic potential. If this graded post-synaptic potential is strong enough to reach threshold it will trigger an action potential along the axon of the sensory neuron. Another way that receptors can be classified is based on their location relative to the stimuli.

An exteroceptor is a receptor that is located near a stimulus in the external environment, such as the somatosensory receptors that are located in the skin.

An interoceptor is one that interprets stimuli from internal organs and tissues, such as the receptors that sense the increase in blood pressure in the aorta or carotid sinus. Finally, a proprioceptor is a receptor located near a moving part of the body, such as a muscle or joint capsule, that interprets the positions of the tissues as they move.

A third classification of receptors is by how the receptor transduces stimuli into membrane potential changes. Stimuli are of three general types. Some stimuli are ions and macromolecules that affect transmembrane receptor proteins by binding or by directly diffusing across the cell membrane. Some stimuli are physical variations in the environment that affect receptor cell membrane potentials.

Other stimuli include the electromagnetic radiation from visible light. For humans, the only electromagnetic energy that is perceived by our eyes is visible light. Some other organisms have receptors that humans lack, such as the heat sensors of snakes, the ultraviolet light sensors of bees, or magnetic receptors in migratory birds.

Receptor cells can be further categorized on the basis of the type of stimuli they transduce. Chemical stimuli can be detected by a chemoreceptors that detect chemical stimuli, such as a chemicals that lead to the sense of smell. Osmoreceptors respond to solute concentrations of body fluids. Pain is primarily a chemical and sometimes mechanical sense that interprets the presence of chemicals from tissue damage, or intense mechanical stimuli, through a nociceptor.

Physical stimuli, such as pressure and vibration, as well as the sensation of sound and body position balance , are interpreted through a mechanoreceptor. Another physical stimulus that has its own type of receptor is temperature, which is sensed through a thermoreceptor that is either sensitive to temperatures above heat or below cold normal body temperature. Ask anyone what the senses are, and they are likely to list the five major senses—taste, smell, touch, hearing, and sight.

However, these are not all of the senses. The most obvious omission from this list is balance. Also, what is referred to simply as touch can be further subdivided into pressure, vibration, stretch, and hair-follicle position, on the basis of the type of mechanoreceptors that perceive these touch sensations.

Other overlooked senses include temperature perception by thermoreceptors and pain perception by nociceptors. Within the realm of physiology, senses can be classified as either general or special. A general sense is one that is distributed throughout the body and has receptor cells within the structures of other organs. Mechanoreceptors in the skin, muscles, or the walls of blood vessels are examples of this type. General senses often contribute to the sense of touch, as described above, or to proprioception body position and kinesthesia body movement , or to a visceral sense , which is most important to autonomic functions.

A special sense discussed in Chapter 15 is one that has a specific organ devoted to it, namely the eye, inner ear, tongue, or nose. Each of the senses is referred to as a sensory modality. Modality refers to the way that information is encoded into a perception. The main sensory modalities can be described on the basis of how each stimulus is transduced and perceived.

The chemical senses include taste and smell. The general sense that is usually referred to as touch includes chemical sensation in the form of nociception, or pain.

Pressure, vibration, muscle stretch, and the movement of hair by an external stimulus, are all sensed by mechanoreceptors and perceived as touch or proprioception.

Hearing and balance are also sensed by mechanoreceptors. Finally, vision involves the activation of photoreceptors. Listing all the different sensory modalities, which can number as many as 17, involves separating the five major senses into more specific categories, or submodalities , of the larger sense.

An individual sensory modality represents the sensation of a specific type of stimulus. For example, the general sense of touch, which is known as somatosensation , can be separated into light pressure, deep pressure, vibration, itch, pain, temperature, or hair movement. In this chapter we will discuss the general senses which include pain, temperature, touch, pressure, vibration and proprioception.

We will discuss the special senses, which include smell, taste, vision, hearing and the vestibular system, in chapter Somatosensation is considered a general sense, as opposed to the submodalities discussed in this section.

Conscious movement comes from impulses in the brain travelling down the spinal cord, over this loop, and then back to the brain for processing. The stretch reflex skips the brain portion of the trip and follows the simple loop from muscle to spinal cord and back, making it a very rapid sequence. The diagram to the right shows how nerve impulses triggered by the stretch reflex travel between the spinal column and the muscles. The gamma efferent cells in the loop work to keep the muscles ready for the stretch reflex, even when inhibited or contracted.

This is important because if the muscle is working against a load and shortening during contraction and an additional load is added, the muscle recognizes the stretch immediately and can compensate with a stronger contraction. This also protects the inhibited antagonist muscles from being injured from excessive stretching. Stretch reflex anatomy pictures used from The Anatomy of Stretching.

Walker Important : The length of time that a stretch is held for has nothing to do with whether the stretch reflex is activated or not.

The stretch reflex in the calf muscle for example is triggered within 3 hundredths of a second, so any claim that a particular type of stretching can somehow bypass or outsmart the stretch reflex is nothing more than fantasy. The stretch reflex is activated or caused by a stretch in the muscle spindle. When the stretch impulse is received a rapid sequence of events follows. The motor neuron is activated and the stretched muscles, and its supporting muscles, are contracted while its antagonist muscles are inhibited relaxed.

The stretch reflex can be activated by external forces such as a load placed on the muscle or internal forces the motor neurons being stimulated from within.

An example of the former is a person holding an empty tray in their outstretched arm and then having a plate of food set on it. The stretch reflex would kick in to keep the tray at the same height and balanced. An example of the latter would be the shivering of a cold muscle.

Any abrupt, forceful stretch on the muscle causes the stretch reflex to fire, in a healthy person. Delays in or absence of the stretch reflex are signs of possible neurological or neuromuscular compromise.

Avoiding the Stretch Reflex Many people have never learnt how to stretch properly. Maybe you have done this yourself: You watch other people stretch in the gym and try to imitate what you see. But who is to say that the person you are watching is doing it right? Here are some of the most common mistakes made while stretching:. So, to avoid the stretch reflex and potential damage to your muscles and joints, avoid pain.

Never push yourself beyond what is comfortable. Only stretch to the point where you can feel tension in your muscles. This way, you will avoid injury and get the maximum benefits from your stretching. While the recommendations on this page are a good place to start, you'll get a lot more benefit when you add the right stretches to your training program.

You'll get clear photographs and 44 video demonstrations of unique stretches for every major muscle groups in your body. And the Handbook will show you, step-by-step, how to perform each stretch correctly and safely.

Plus, you'll also learn the 7 critical rules for safe stretching; the benefits of flexibility; and how to stretch properly. Amazon author page has listed his books on five Best-Seller lists. Google cites over , references to him and his work on the internet.

And satisfied customers from countries have sent 1,'s of verified customer reviews. If you want to know about stretching, flexibility or sports injury management, Brad Walker is the go-to-guy. Disclaimer : The health and fitness information presented on this website is intended as an educational resource and is not intended as a substitute for proper medical advice. Please consult your physician or physical therapist before performing any of the exercises described on this website, particularly if you are pregnant, elderly or have any chronic or recurring muscle or joint pain.

Click here to get it now! Understanding the Stretch Reflex or Myotatic Reflex. What is the Stretch Reflex and how can you use it to improve your flexibility? What is the Stretch Reflex? The stretch reflex is designed as a protective mechanism , to prevent strain and tear injuries to the muscles and tendons.

When the muscle spindle is excited an impulse is immediately received to contract the muscle, thereby protecting it from being pulled forcefully or stretched beyond a normal range of motion. Examples of the Stretch Reflex in action The stretch reflex is very important in posture. Important : The length of time that a stretch is held for has nothing to do with whether the stretch reflex is activated or not. What Activates the Stretch Reflex?

Here are some of the most common mistakes made while stretching: Bouncing. Many people have the mistaken impression that they should bounce to get a good stretch. Bouncing will not help you and could do more damage as you try to push too far beyond the stretch reflex.

Every move you make should be smooth and gentle. Lean into the stretch gradually, push to the point of mild tension and hold. Each time going a little further, but never forcing it. Not holding the stretch long enough. If you do not hold the stretch long enough, you may fall into the habit of bouncing or rushing through your stretch workout. Hold your stretch position for at least 15 to 20 seconds and up to 60 seconds for even better results before moving back to your original position.

Pushing the stretch too hard. Stretching takes patience and finesse. Each move needs to be fluid and gentle. Do not throw your body into a stretch or try to rush through your routine. Take your time and relax. Forgetting form and function. Think about your sport or activity. Which muscles will you be using? A routine for a marathon runner will be very different from a routine for an hour of lifting weights.