Transcript 1838048b95a03c1

Deep Tendon Reflex
•The
reflex arc
•Myotatic Reflex
Introduction…
The spinal cord mediates local spinal
reflexes.
 The spinal reflexes consist of involuntary
responses to appropriate stimuli
transmitted to the spinal cord.
 They depends on the integrity of the
reflex arc.


Reflexes can be :
◦ Monosynaptic reflex : e.g., knee jerk reflex.
◦ Multisynaptic reflex: e.g., withdrawal reflex
The Reflex Arc of Monosynaptic reflex

Consist of:
◦ A receptor organ: Muscle spindle.
◦ Sensory (afferent) fibers of the spinal nerves:
carry sensory impulses from sensory receptors
to the spinal cord.
◦ Motor (efferent) fibers of the spinal nerves:
that activate muscles.
◦ The effector organ: the muscle.
Within the spinal cord; the afferent fibers
affect the efferent fibers either directly or
indirectly via interneurons.
 When the reflex arc involves only one
synapse, this is referred to as
monosynaptic reflex arc.

The deep tendon reflexes
The best example of these reflexes is the
stretch (myotatic) reflex.
 The stretch reflex consist of involuntary
muscular contraction in response to
stretching of muscle tendon.

Mechanism of the myotatic reflex
Tapping of a muscle tendon leads to
elongation (stretching) of the fibers of
that muscle.
 This leads to stimulation of muscle
spindles within the muscle.
 The muscle spindles are sensory
receptors present within the skeletal
muscles.

The sensory (afferents) fibers of the
spinal nerves carry the sensory impulses
from the muscle spindles to the spinal
cord.
 In the spinal cord, the sensory fibers
stimulate the motor neurons that send
their motor fibers (efferents) to the
muscle causing its contraction.

Important stretch reflexes and their
spinal segments
Stretch reflex
Spinal segment
Biceps reflex
C5,6
Brachioradialis reflex
C5,6
Triceps reflex
C6,7
Patellar reflex (Knee jerk)
L3,4
Achilles tendon reflex (Ankle jerk)
S1,2
Importance of a stretch reflex
A protective measure to prevent tearing.
 Important in posture: because a slight lean
to either side causes a stretch in the
spinal, hip and leg muscles to the other
side , which is quickly countered by the
stretch reflex

Clinical applications of the stretch
reflex

Physicians use the knee jerk and other
muscle jerks to determine the sensitivity
of the stretch reflexes and to assess the
degree of facilitations of the spinal cord
centers.
When large numbers of facilitatory
impulses are being transmitted from the
upper regions of the central nervous
system into the cord, the muscle jerks are
greatly exacerbated.
 On the other hand, if the facilitatory
impulses are depressed or abrogated, the
muscle jerks are considerably weakened
or absent.

Hyperreflexia Vs. Hyporeflexia
Stretch reflexes increase in case of lesions
in the pyramidal and extrapyramidal spinal
motor tracts.
 The reflexes decrease or disappear
(areflexia) in case of reflex arc lesions.

Stretch reflex and
Jendrassik
maneuver
Patient flexes both sets of fingers into a hook-like
form and interlocks fingers together.