The Reflex Arc
Reflex arcs The nerve pathway followed by a reflex action is called a reflex arc. For example, a simple reflex arc happens if we accidentally touch something hot. Receptor in the skin detects a. Reflex arc, neurological and sensory mechanism that controls a reflex, an immediate response to a particular stimulus. The primary components of the reflex arc are the sensory neurons (or receptors) that receive stimulation and in turn connect to other nerve cells that activate muscle cells (or effectors), which perform the reflex action.
A reflex arc defines the pathway by which a reflex travels—from the stimulus to sensory neuron to motor neuron to reflex muscle movement. A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.
When a person accidentally touches a hot object, they automatically jerk their hand away without thinking. A reflex does not require any thought input. The path taken by the nerve impulses in a reflex is called a reflex arc. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord.
This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs. Most reflex arcs involve only three neurons.
The stimulus, such as a needle stick, stimulates the pain receptors of the skin, which initiate an impulse in a sensory neuron.
This travels to the spinal cord where it passes, by means of a synapse, to a connecting neuron called the relay neuron situated in the spinal cord. The relay neuron in turn makes a synapse with one or more motor neurons that transmit the impulse to the muscles of the limb causing them to contract and pull away from the sharp object. Reflexes do not require involvement of the brain, although in some cases the brain can prevent reflex action.
Reflex arc : The path taken by the nerve impulses in a reflex is called a reflex arc. This is shown here in response to a pin in the paw of an animal, but it is equally adaptable to any situation and animal including humans. There are two types of reflex arcs:the autonomic reflex arc, affecting inner organs, and the somatic reflex arc, affecting muscles. When a reflex arc consists of only two neurons, one sensory neuron, and one motor neuron, it is defined as monosynaptic.
Monosynaptic refers to the presence of a single chemical synapse. In the case of peripheral muscle reflexes patellar reflex, achilles reflexbrief stimulation to the muscle spindle results in the contraction of the agonist or effector muscle. By contrast, in polysynaptic reflex arcs, one or more interneurons connect afferent sensory and efferent motor signals. For example, the withdrawal reflex nociceptive or flexor withdrawal reflex is a spinal reflex intended to protect the body from damaging stimuli.
It causes the stimulation of sensory, association, and motor neurons. Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex. The stretch reflex myotatic reflex is a muscle contraction in response to stretching within the muscle. This reflex has the shortest latency of all spinal reflexes. It is a monosynaptic reflex that provides automatic regulation of skeletal muscle length. When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases.
This increases alpha motor neuron activity, causing the muscle fibers to contract and thus resist the stretching. A secondary set of neurons also causes the opposing muscle to relax. The reflex functions to maintain the muscle at a constant length. The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system. The tendon reflex operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn.
Although the tendon reflex is less sensitive than the stretch reflex, it can override the stretch reflex when tension is great, making you drop a very heavy weight, for example. Like the stretch reflex, the tendon reflex is ipsilateral.
The sensory receptors for this reflex are called Golgi tendon receptors, and lie within a tendon near its junction with a muscle. In contrast to muscle spindles, which are sensitive to changes in muscle length, tendon organs detect and respond to changes in muscle tension that are caused what to do about dry heaves a passive stretch or muscular contraction.
Jendrassik maneuver : The Jendrassik maneuver is a medical maneuver wherein the patient flexes both sets of fingers into a hook-like form and interlocks those sets of fingers together note the hands of the patient in the chair.
This maneuver is used often when testing the patellar reflex, as it forces the patient to concentrate on the interlocking of the fingers and prevents conscious inhibition or influence of the reflex.
The crossed extensor reflex is a withdrawal reflex. The reflex occurs when the flexors in the withdrawing limb contract and the extensors relax, while in the other limb, the opposite occurs. An example of this is when a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body. The crossed extensor reflex is contralateral, meaning the reflex occurs on the opposite side of the body from the stimulus.
To produce this reflex, branches of the afferent nerve fibers cross from the stimulated side of the body to the contralateral side of the spinal cord. There, they synapse with interneurons, which in turn, excite or inhibit alpha motor neurons to the muscles of the contralateral limb. The withdrawal reflex nociceptive or flexor withdrawal reflex is a spinal reflex intended to protect the body from damaging stimuli. It is polysynaptic, and causes the stimulation of sensory, association, and motor neurons.
When a person touches a hot object and withdraws his hand from it without thinking about it, the heat stimulates temperature and danger how to find the range math in the skin, triggering a sensory impulse that travels to the central explain what occurs during the reflex arc system.
The sensory neuron then synapses with interneurons that connect to motor neurons. Some of these send motor impulses to the flexors to allow withdrawal. Some motor neurons send inhibitory impulses to the extensors so flexion is not inhibited—this is referred to as reciprocal innervation. Although this is a reflex, there are two interesting aspects to it:. Golgi tendon organ : The Golgi tendon organ, responsible for the Golgi tendon reflex, is diagrammed with its typical position in a muscle leftneuronal connections in spinal cord middlehow to do fancy writing styles expanded schematic right.
The tendon organ is a stretch receptor that signals the amount of force on the muscle and protects the muscle from excessively heavy loads by causing the muscle to relax and drop the load.
Reflex arcs that contain only two neurons, a sensory and a motor neuron, are considered monosynaptic. Examples of monosynaptic reflex arcs in humans include the patellar reflex and the Achilles reflex.
Most reflex arcs are polysynaptic, meaning multiple interneurons also called relay neurons interface between the sensory and motor neurons in the reflex pathway. Key Terms motor neuron : A neuron located in the central nervous system that projects its axon outside the CNS and directly or indirectly control muscles.
There are two types of reflex arcs: autonomic reflex arc affecting inner organs and what do triglycerides do in the body reflex arc affecting muscles.
Spinal Reflexes Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex. Learning Objectives Distinguish between the types of spinal reflexes. Key Takeaways Key Points The stretch reflex is a monosynaptic reflex that regulates muscle length through neuronal stimulation at the muscle spindle.
The alpha motor neurons resist stretching by causing contraction, and the gamma motor neurons control the sensitivity of the reflex.
The stretch and Golgi tendon reflexes work in tandem to control muscle length and tension. Both are examples of ipsilateral reflexes, meaning the reflex occurs on the same side of the body as the stimulus. The crossed extensor reflex is a contralateral reflex that allows the body to compensate on one side for a stimulus on the other.
The withdrawal reflex and the more-specific pain withdrawal reflex involve withdrawal in response to a stimulus or pain. When pain receptors, called nociceptors, are stimulated, reciprocal innervations stimulate the flexors to withdraw and inhibit the extensors to ensure they are unable to prevent flexion and withdrawal.
Key Terms golgi tendon reflex : A normal component of the reflex arc of the peripheral nervous system. In this reflex, a skeletal muscle contraction causes the agonist muscle to simultaneously lengthen and relax. This reflex is also called the inverse myotatic reflex because it is the inverse of the stretch reflex.
Although muscle tension is increasing during the contraction, the alpha motor neurons in the spinal cord that supply the muscle are inhibited. However, antagonistic muscles are activated. They innervate the extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction.
Alpha motor neurons are distinct from what happened 27 years ago today motor neurons that innervate the intrafusal muscle fibers of muscle spindles. Licenses and Attributions.
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How does the nervous system help us respond? - OCR 21C
Reflex Arcs •In a knee-jerk reflex arc the sensory neuron directly connects to the motor neuron in the spinal cord. This is called a simple reflex arc. • Follow the sensory neuron from the spindle (receptor) to where it connects with the motor neuron in the spinal cord. The reflex arc is a pathway along which the information about the stimulus is carried to the spinal cord and the information regarding the response is carried to the effector organ. A reflex arc consists of the following components. Jan 21, · A person experiences a reflex arc when they cough on food that is stuck in their throat. A reflex arc is a nerve pathway in the body of humans and some animals that connects certain muscle groups to others, without involving the brain. These sorts of pathways primarily control involuntary movements in response to some sort of stimulus.
Reflex arc , neurological and sensory mechanism that controls a reflex , an immediate response to a particular stimulus. The primary components of the reflex arc are the sensory neurons or receptors that receive stimulation and in turn connect to other nerve cells that activate muscle cells or effectors , which perform the reflex action.
The simplest arrangement of a reflex arc consists of the receptor, an interneuron or adjustor , and an effector ; together, these units form a functional group. Sensory cells carry input from the receptor afferent impulses to a central interneuron, which makes contact with a motor neuron. The motor neuron carries efferent impulses to the effector, which produces the response. Three types of neurons are involved in this reflex arc, but a two-neuron arc, in which the receptor makes contact directly with the motor neuron, also occurs.
In a two-neuron arc, simple reflexes are prompt, short-lived, and automatic and involve only a part of the body. Examples of simple reflexes are the contraction of a muscle in response to stretching, the blink of the eye when the cornea is touched, and salivation at the sight of food.
Reflexes of these types are usually involved in maintaining homeostasis. Reflex arc. Additional Info. More About Contributors Article History. Home Science Biology Reflex arc physiology. Print Cite verified Cite. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.
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