Dominic Stone
Reflexes are involuntary and nearly instantaneous movements in response to a stimulus. They are the body's intrinsic stimulus-response systems for maintaining homeostasis. Reflexes are protective in nature and help to safeguard the body from harmful stimuli. For example, when you touch a hot stove, a reflex causes you to immediately remove your hand before the message of pain reaches your brain. There are many types of reflexes, including superficial reflexes, which are elicited by stroking the skin or mucous membranes, and deep tendon reflexes, which are commonly tested by doctors to ensure the nervous system is functioning properly. Muscle reflexes, such as the H-reflex, are also studied extensively and are useful in clinical neurology for diagnosing various diseases.
| Characteristics | Values |
|---|---|
| Definition | Reflexes are involuntary and nearly instantaneous movements in response to a stimulus. |
| Involvement of brain | Reflexes are automatic responses to a stimulus that do not require conscious thought as they occur through a reflex arc. |
| Types | Reflexes can be superficial, deep tendon, or visceral. |
| Examples | Patellar reflex, Achilles reflex, flexor reflex, stretch reflex, and autogenic inhibition reflex. |
| Function | Reflexes help protect the body and maintain homeostasis. |
| Clinical significance | Reflexes are important in neurological examinations to localize lesions within the nervous system and diagnose various diseases, including cranial neuropathies, focal lesions, and movement disorders. |
| Techniques | Techniques such as the Jendrassik manoeuvre can be used to augment hypoactive reflexes. |
Explore related products
What You'll Learn
Monosynaptic reflexes
A monosynaptic reflex is a reflex arc that facilitates direct communication between sensory and motor neurons innervating the muscle. This reflex is sometimes called the muscle stretch reflex or deep tendon reflex. When the muscle is subjected to a stretch stimulus, sensory impulses are transmitted from the muscle spindle through Ia afferent fibres to the dorsal root of the spinal cord. The monosynaptic stretch reflex circuit is a unique model system for studying neuronal circuit development. The reflex circuit comprises two distinct functional units: a sensory unit and an effector unit.
The sensory unit relays information about the length of a muscle to the CNS. It is composed of relatively few, stretch-sensitive, muscle-embedded mechanoreceptors, known as muscle spindles, and specific subpopulations of proprioceptive neurons (Ia afferents) that innervate the muscle spindles peripherally. These make excitatory monosynaptic connections to α-motoneurons in the spinal cord. The effector unit controls muscle contraction and its activity is regulated by inputs from the peripheral sensory system, the spinal cord, and higher brain centres.
The tendon tap reflex (or T-reflex) and the H-reflex are two versions of the monosynaptic reflex. Muscle contractions produced by the monosynaptic reflex occur after the shortest possible delay, which is mostly due to the conduction time along the afferent (sensory) and efferent (motor) axons. Typical delays (latencies) of monosynaptic reflexes in the human arm and leg muscles are in the range of 20–40 ms.
Muscle Response to Stimulus: Understanding the Science
You may want to see also
Explore related products
![Recherches Sur L'Exhibition Des Muscles Et Du ReFlexe Patellaire : TheSe PreSenteE a La Faculte De MeDecine De L'Universite De GeneVe Pour Obtenir Le Grade De Docteur 1910 [Leather Bound]](https://m.media-amazon.com/images/I/617DLHXyzlL._AC_UY218_.jpg)
Stretch reflex
The stretch reflex, also known as the myotatic reflex, is a neural reflex involving a receptor and effector neurone. It is responsible for muscle contraction in response to stretching stimuli and plays a crucial role in maintaining posture and muscle tone. The stretch reflex is considered the simplest of all central reflexes as it consists of only two nerve cells: a receptor and an effector neurone. However, its apparent simplicity can be deceptive due to the various influences that can alter its sensitivity in health and disease.
The stretch reflex is accomplished through several structures in the muscle, including muscle spindles. These spindles contain intrafusal muscle fibres that lie parallel to the muscle fibres and sense changes in length and velocity. When a muscle is stretched, the muscle spindle is also stretched, increasing the rate of neural firing of muscle spindle afferents. This increase in nerve activity triggers a contraction in the muscle, causing it to resist the stretching.
The stretch reflex can be either phasic or tonic. A phasic stretch reflex involves a synchronous motor neuron discharge caused by brief stimulation of muscle spindles or their afferent nerve pathways. An example of a phasic stretch reflex is the tendon jerk. On the other hand, a tonic stretch reflex is characterised by a prolonged asynchronous discharge of motor neurons, resulting in sustained muscle contraction for the maintenance or alteration of posture.
The stretch reflex is often tested as part of a neurological examination, particularly in cases of injury to the central nervous system. The patellar reflex, or knee jerk, is a commonly tested example of the stretch reflex. During this test, the clinician strikes the tendon of the relaxed muscle, expecting a contraction in response. This response is then rated by the clinician.
The stretch reflex is a crucial mechanism for maintaining muscle length and posture, and its sensitivity can be influenced by various factors, including mental concentration, anticipation, and physical activity. Understanding the stretch reflex has provided valuable insights into the physiology of synaptic transmission in the peripheral nervous system.
Muscle Tearing: Signs, Symptoms, and Recovery
You may want to see also
Explore related products
$17.01 $19.95
Superficial reflexes
The abdominal reflex is stimulated by stroking around the abdomen, which helps in determining the level of CNS lesion. The normal response is the contraction of the abdominal muscles, causing the umbilicus to move toward the area being stroked.
The cremasteric reflex is a superficial reflex found in human males. It is elicited when the inner part of the thigh is stroked, causing the cremaster muscle to contract and pull up the ipsilateral testicle toward the inguinal canal. The cremasteric reflex is most commonly performed in the evaluation of acute scrotal pain and the assessment of testicular torsion. The female counterpart of the cremasteric reflex is the Geigel reflex, which involves the contraction of muscle fibers along the upper part of the Poupart or inguinal ligament.
The corneal reflex is elicited by gentle stroking of the cornea with a cotton swab. This reflex helps determine damage to either the trigeminal nerve (V) or facial nerve (VII), which will disrupt the corneal blink circuit.
The plantar response is another type of superficial reflex, and it is evaluated by the Babinski, Chaddock, and Oppenheim reflexes. The normal reflex response is flexion of the great toe, while an abnormal response is slower and consists of extension of the great toe with fanning of the other toes and often knee and hip flexion. This abnormal response indicates spinal disinhibition due to an upper motor neuron lesion.
Muscle Man: What It Means and How to Become One
You may want to see also
Explore related products
Autogenic inhibition reflex
The autogenic inhibition reflex, also known as the autogenic inhibition (AI) reflex, is a protective mechanism that prevents muscles from tearing by reducing muscle tension. It is a sudden relaxation of a muscle in response to excess tension. This automatic lengthening reflex is controlled by the central nervous system and regulated by proprioceptors in the muscles and tendons, primarily the Golgi tendon organs (GTOs). GTOs are stretch receptors that signal the amount of force exerted by a muscle.
When a muscle is placed under tension, the GTO is stimulated, and nerve impulses travel along the sensory fibre Ib into the spinal cord. Within the spinal cord, the sensory fibre Ib synapses with and activates an inhibitory interneuron via glutamate. This inhibitory interneuron then releases the neurotransmitter glycine, which inhibits the α motor neuron. As a result, fewer nerve impulses are generated in the α motor neuron, leading to muscle relaxation.
The autogenic inhibition reflex plays a crucial role in motor control, especially in maintaining balance and posture. It helps to distribute the workload evenly across all muscle fibres, ensuring that no single group of fibres bears a disproportionate amount of the load. By inhibiting the contraction of overactive muscle fibres, the reflex encourages the activation of less active fibres, resulting in a more efficient and synchronised muscle function.
The autogenic inhibition reflex is a significant factor in preventing muscle damage. It acts as a feedback mechanism, controlling muscle contraction and causing muscle relaxation before the tension becomes high enough to rupture the tendon. This protective function was previously believed to be the sole role of GTOs. However, recent evidence suggests that GTOs have a more extensive role in signalling muscle tension and controlling muscle forces for fine activities.
Neck Muscle Imbalance: Is Yours Symmetrical?
You may want to see also
Explore related products
$24.53 $29.99
Flexor reflex
A reflex is an involuntary and nearly instantaneous movement in response to a stimulus. The reflex is an automatic response to a stimulus that does not require conscious thought as it occurs through a reflex arc. One such reflex is the flexor reflex.
The flexor reflex is initiated by cutaneous receptors and pain receptors in the skin or deep tissues. It involves the entire limb and is a protective withdrawal reflex. An example of this reflex is pulling your hand back from a hot object. The flexor reflex is also known as the withdrawal reflex, which is the automatic withdrawal of the potentially affected body part from the stimulus.
The flexor reflex is crucial for survival. It is a polysynaptic reflex, meaning it contains multiple interneurons (also called relay neurons) that interface between the sensory and motor neurons in the reflex pathway. The flexor reflex in the lower limb is a polysynaptic pathway traversing the spinal cord from the second lumbar to the first sacral segment. This is because all are required for the innervation of the flexor synergy to retract the leg from an offending source of irritation.
The flexor reflex also incorporates a crossed extension reflex, which is essential for maintaining balance. This is when the stimulated leg is raised from the ground, and the other leg extends to support the body weight. Without this coordination of the two legs, the shift in body mass would cause a loss of balance.
Muscle Recovery: Healing Injured Muscles
You may want to see also
Frequently asked questions
A reflex is an involuntary and nearly instantaneous movement in response to a stimulus. The reflex is an automatic response to a stimulus that does not require conscious thought as it occurs through a reflex arc.
Some examples of reflexes include the patellar reflex (knee-jerk reflex), the Achilles reflex, blinking when something flies towards the eyes, raising your arm if a ball is thrown your way, coughing, and sneezing.
Reflexes help to protect the body from harm. For example, if you touch a hot stove, a reflex causes you to immediately remove your hand before you feel pain. Reflexes are also important for maintaining balance.
Reflexes can be tested through a reflex exam, which is fundamental to the neurological exam. This may include tapping the patient's knee to test the patellar reflex or performing superficial reflexes by stroking the skin or mucous membranes.
