Rapid, involuntary response to stimuli in which a specific stimulus results in a specific motor response.
An automatic, unlearned response that occurs without conscious effort.
A physiological reaction without any conscious thought involved, e.g. a knee jerk or a sneeze, which happens in response to a particular stimulus.
An involuntary, automatic movement in reaction to a particular event (stimulus) that triggers a response from the body’s nervous system, such as the knee-jerk that follows a sharp tap below the kneecap. Some such sensorimotor reactions are found only in newborns, generally disappearing in the first few months. Among these so-called primitive reflexes are the grasp reflex, tonic neck reflex, moro’s reflex (startle reflex), walking or stepping reflex, and rooting reflex. Physicians often use various reflexes as signs to indicate the health or illness of a patient, and the primitive reflexes are especially important in judging the early health and development of a baby. Absence or disturbance of one of these reflexes can indicate a problem in the nervous system; for example, Landau’s reflex can suggest possible cerebral palsy or mental retardation.
Involuntary function or movement of a part in response to a particular stimulus (e.g., the kneejerk or patellar reflex).
An involuntary movement or action due to a particular stimulus.
An automatic or involuntary activity brought about by relatively simple nervous circuits, without consciousness being necessarily involved. Thus a painful stimulus such as a pinprick will bring about the reflex of withdrawing the finger before the brain has had time to send a message to the muscles involved.
The nervous circuit involved in a reflex, being at its simplest a sensory nerve with a receptor, linked at a synapse in the brain or spinal cord with a motor nerve, which supplies a muscle or gland. In a simple reflex (such as the patellar reflex) only two neurons may be involved, but in other reflexes there may be several interneurons in the arc.
An involuntary response to a stimulus; an involuntary action. Reflexes are specific and predictable and are usually purposeful and adaptive. They depend on an intact neural pathway between the stimulation point and a responding organ (a muscle or gland). This pathway is called the reflex arc. In a simple reflex this includes a sensory receptor, afferent or sensory neuron, reflex center in the brain or spinal cord, one or more efferent neurons, and an effector organ (a muscle or gland). Most reflexes, however, are more complicated and include internuncial or associative neurons intercalated between afferent and efferent neurons.
An involuntary and almost immediate movement in response to a stimulus.
Automatic reaction to a stimulus that involves the movement of an impulse from a sensory receptor along the sensory nerve to the spinal cord. A responsive impulse is sent along a motor neuron to a muscle, causing a reaction (for example, the quick removal of the hand from a hot object). Reflexes do not have to be learned; they are automatic.
An involuntary response of the nervous system to a stimulus, such as the stretch reflex, which is elicited by tapping a tendon with a reflex hammer, resulting in a contraction. Increased, diminished, or absent reflexes can be indicative of neurologic damage, including MS, and are therefore tested as part of the standard neurologic exam.
A response that takes place involuntarily and consistently upon encountering a specific stimulus; a reflex is not under the conscious control of the individual.
In the most basic form of a reflex, a sensory nerve cell responds to a stimulus like heat or pressure, transmitting a signal along its nerve fiber to the central nervous system (which includes the brain and spinal cord). Within the central nervous system, another nerve cell gets activated, leading to the contraction of a muscle or an enhancement in the secretory function of a gland. The journey of the nerve signal from the initial sensation to the eventual response is termed a reflex arc.
Reflexes can be innate or learned. Certain innate reflexes are exclusive to infants, such as the grasp reflex triggered when an adult’s finger is placed in the palm of a baby. Innate reflexes encompass those regulating fundamental bodily processes, like the contraction of the bladder after it reaches a certain capacity. These inherent reflexes are governed by the autonomic nervous system.
Conditioned reflexes are developed through learning via a process termed conditioning. As an illustration, an individual might navigate a well-known route back home from work without needing to consciously deliberate about it.
A number of uncomplicated reflexes, including the knee-jerk reflex and the pupil’s constriction when exposed to light, are assessed during a physical examination. Alterations in these reflexes can suggest nervous system impairment. The evaluation of crucial reflexes overseen by the brainstem forms the foundation for diagnosing brain death.
An involuntary and automatic reaction to a stimulus.