Authors: Campbell, William W.
Title: Pocket Guide and Toolkit to DeJong’s Neurologic Examination, 1st Edition
Copyright ©2008 Lippincott Williams & Wilkins
> Table of Contents > Section G – The Reflexes > Chapter 27 – Introduction to the Reflexes
Chapter 27
Introduction to the Reflexes
The reflex examination is
important for several reasons. Reflex changes may be the earliest and
most subtle indication of a disturbance in neurologic function. The
testing of reflexes is the most objective part of the neurologic
examination. Reflexes are under voluntary control to a lesser extent
than most other parts of the neurologic examination, and reflex
abnormalities are difficult to simulate. They are not as dependent on
the attention, cooperation, or intelligence of the patient, and can be
evaluated in patients who cannot or will not cooperate with other parts
of the examination. In such circumstances, the integrity of the motor
and sensory systems can sometimes be appraised more adequately by the
reflex examination than by other means. Although the reflex examination
is an essential component, it is only one part of the neurologic
examination, and must be evaluated in the context of the other findings.
important for several reasons. Reflex changes may be the earliest and
most subtle indication of a disturbance in neurologic function. The
testing of reflexes is the most objective part of the neurologic
examination. Reflexes are under voluntary control to a lesser extent
than most other parts of the neurologic examination, and reflex
abnormalities are difficult to simulate. They are not as dependent on
the attention, cooperation, or intelligence of the patient, and can be
evaluated in patients who cannot or will not cooperate with other parts
of the examination. In such circumstances, the integrity of the motor
and sensory systems can sometimes be appraised more adequately by the
reflex examination than by other means. Although the reflex examination
is an essential component, it is only one part of the neurologic
examination, and must be evaluated in the context of the other findings.
A reflex is an involuntary response to a sensory
stimulus. Afferent impulses arising in a sensory organ produce a
response in an effector organ. There are segmental and suprasegmental
components. The segmental component is a local reflex center in the
spinal cord or brainstem and its afferent and efferent connections. The
suprasegmental component is made up of the descending central pathways
that control, modulate, and regulate the segmental activity. Disease of
the suprasegmental pathways may increase the activity of some reflexes,
decrease the activity of others, and cause reflexes to appear that are
not normally seen. A reflex response may be motor, sensory, or
autonomic.
stimulus. Afferent impulses arising in a sensory organ produce a
response in an effector organ. There are segmental and suprasegmental
components. The segmental component is a local reflex center in the
spinal cord or brainstem and its afferent and efferent connections. The
suprasegmental component is made up of the descending central pathways
that control, modulate, and regulate the segmental activity. Disease of
the suprasegmental pathways may increase the activity of some reflexes,
decrease the activity of others, and cause reflexes to appear that are
not normally seen. A reflex response may be motor, sensory, or
autonomic.
The stimulus is received by the receptor, which may be a
sensory ending in the skin, mucous membranes, muscle, tendon, or
periosteum, or, in special types of reflexes, in the retina, cochlea,
vestibular apparatus, olfactory mucosa, gustatory bulbs, or viscera.
Receptor stimulation initiates an impulse that travels along the
afferent pathway to the central nervous system (CNS), where there
sensory ending in the skin, mucous membranes, muscle, tendon, or
periosteum, or, in special types of reflexes, in the retina, cochlea,
vestibular apparatus, olfactory mucosa, gustatory bulbs, or viscera.
Receptor stimulation initiates an impulse that travels along the
afferent pathway to the central nervous system (CNS), where there
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is
a synapse in a reflex center that activates the cell body of the
efferent neuron. The efferent neuron transmits the impulse to the
effector: the cell, muscle, gland, or blood vessel that then responds.
A disturbance in function of part of the reflex arc—the receptor,
afferent limb, reflex center, efferent limb, or effector apparatus—will
disrupt the reflex arc, causing a decrease or loss of the reflex.
Most reflexes investigated clinically are more complex
than the primitive reflex response just described. Complex reflexes
involve connections between various segments on the same and opposite
sides of the spinal cord, brainstem, and brain. The more complex the
reflex, the greater the number of associated neurons and mechanisms
involved. Stronger stimuli cause the excitation of a greater number of
neurons: the phenomenon of irradiation.
than the primitive reflex response just described. Complex reflexes
involve connections between various segments on the same and opposite
sides of the spinal cord, brainstem, and brain. The more complex the
reflex, the greater the number of associated neurons and mechanisms
involved. Stronger stimuli cause the excitation of a greater number of
neurons: the phenomenon of irradiation.
Reflex activity is essential to normal functioning.
Nociceptive reflexes help avoid injurious stimuli. Reflex activity is
important in maintaining the body in its daily environment, in
sustaining an upright position, in standing and walking, and in moving
the extremities. It is an integral part of the response to visual,
gustatory, auditory, and vestibular stimulation; and it is important in
visceral functions.
Nociceptive reflexes help avoid injurious stimuli. Reflex activity is
important in maintaining the body in its daily environment, in
sustaining an upright position, in standing and walking, and in moving
the extremities. It is an integral part of the response to visual,
gustatory, auditory, and vestibular stimulation; and it is important in
visceral functions.
Reflexes have been named in various ways: according to
the site of elicitation, the body part stimulated, the muscles
involved, the part of the body that responds, the ensuing movements,
the joint acted on, or the nerve involved. Many carry the names of one
or more individuals who are said to have first described them. Hundreds
of reflexes have been identified. Since many are not clinically
important and it is impractical to test all the reflexes routinely,
only those more important for clinical diagnosis will be described. The
majority of these are muscle responses. Reflex abnormalities due to
disease involving the descending motor pathways are often clinically
referred to as upper motor neuron, corticospinal or pyramidal signs,
but the abnormalities likely result from dysfunction of related motor
pathways rather than the corticospinal tract proper.
the site of elicitation, the body part stimulated, the muscles
involved, the part of the body that responds, the ensuing movements,
the joint acted on, or the nerve involved. Many carry the names of one
or more individuals who are said to have first described them. Hundreds
of reflexes have been identified. Since many are not clinically
important and it is impractical to test all the reflexes routinely,
only those more important for clinical diagnosis will be described. The
majority of these are muscle responses. Reflex abnormalities due to
disease involving the descending motor pathways are often clinically
referred to as upper motor neuron, corticospinal or pyramidal signs,
but the abnormalities likely result from dysfunction of related motor
pathways rather than the corticospinal tract proper.