Spinal MS. DOROTHY  These consist of three elements: • sensory neurones • connector neurones in the • lower motor neurones. REFLEXES

 A action is an immediate motor response to a sensory stimulus. results from a impulse passing over a reflex arc is called a reflex ; it is a predictable response to a stimulus.  It may or may not be conscious. Many connector and motor neurones may be stimulated by afferent impulses from a small area of skin, e.g. the pain impulses initiated by touching a very hot surface with the finger are transmitted to the spinal cord by sensory  Usually the term is used to mean only involuntary responses rather than those directly willed; that is, involving cerebral cortex activity.  If the centre of a reflex arc is in the brain, the response it mediates is called a cranial reflex.  If the centre of a reflex arc is in the spinal cord, the response is called a spinal reflex

 . These stimulate many connector and lower motor neurones in the cord which results in the contraction of many skeletal muscles of the hand, arm and shoulder, and the removal of the finger.  Reflex action takes place very quickly, in fact, the motor response may have occurred simultaneously with the perception of the pain in the cerebrum. Reflexes of this type are invariably protective but they can on occasion be inhibited. For example, if it is a precious plate that is very hot when lifted every effort will be made to overcome the pain to prevent dropping it!

TYPES OF REFLEXES OF CLINICAL IMPORTANCE

 The following reflexes are frequently tested: 1. knee jerk 2. ankle jerk 3. Babinski reflex 4. 5. KNEE JERK REFLEX

 It is an example of a ( it is also called deep tendon reflexes).It is also known as the  It is an extension of the lower leg in response to tapping of the patellar tendon. The tap stretches the tendon and its muscles, the quadriceps femoris, and thereby stimulates muscle spindles (receptors) in the muscle and initiates conduction over the following two-neuron reflex arc:

 Tapping the patellar tendon elicits the knee jerk (L 2,3,4), a stretch reflex of the quadriceps femoris muscle, because the tap on the tendon stretches the muscle. A similar contraction is observed if the quadriceps is stretched manually. When a skeletal muscle with an intact nerve supply is stretched suddenly, it contracts. This response is called the stretch reflex. It is a type of monosynaptic reflex.  The knee jerk reflex is an example of a deep (DTR) in a neurological exam and is graded on the following scale:  0 (absent),  1+ (hypoactive),  2+ (brisk, normal),  3+ (hyperactive without clonus),  4+ (hyperactive with mild clonus), and  5+ (hyperactive with sustained clonus).

 Absence of the knee jerk can signify an abnormality anywhere within the reflex arc, including the muscle spindle, the Ia afferent nerve fibers, or the motor neurons to the quadriceps muscle. In general the afferent loop is much more critical for reflex function than the efferent loop, so that unless the muscle is almost paralysed, loss of reflexes suggests a sensory nerve or root lesion rather than a motor nerve lesion.  The most common cause is a from such things as diabetes, alcoholism, and toxins.

 Increased tendon reflex activity suggests increased excitability of the anterior horn cells in the spinal segment of the stretched muscle due to loss of descending inhibition with a UMN( upper motor neurone) or corticospinal tract lesion. Brisk reflexes alone, however, are not necessarily pathological and usually result from anxiety.

 In hypothyroidism both the contraction and the relaxation phases of the tendon reflex may be prolonged, resulting in 'hung-up' reflexes.  In cerebellar ataxia the reflexes may be 'pendular': there are oscillatory limb movements after the initial reflex associated with 'loose' tone

 The knee jerk can be classified in various ways as follows: • As a spinal cord reflex—because the center of the reflex arc lies in the spinal cord gray matter • As a segmental reflex—because impulses that mediate it enter and leave the same segment of the cord  • As an ipsilateral reflex—because the impulses that mediate it come from and go to the same side of the body  • As a stretch reflex or myotatic reflex— because of the kind of stimulation used to evoke it

 As an extensor reflex—because it is produced by extensors of the lower leg • As a tendon reflex—because tapping of a tendon is the stimulus that elicits it • As a deep reflex—because of the deep location of the receptors stimulated to produce this reflex

 Ankle jerk reflex, or Achilles reflex, is an extension (plantar flexion) of the foot in response to tapping of the Achilles tendon.  As with the knee jerk, it is a tendon reflex and a deep reflex mediated by two neuron spinal arcs.  The centers for the ankle jerk lie in the first and second sacral segments of the cord.  The ankle jerk reflex, also known as the Achilles Reflex, occurs when the Achilles tendon is tapped while the foot is dorsi-flexed. A positive result would be the jerking of the foot towards its plantar surface. Being a deep tendon reflex, it is monosynaptic. It is also a stretch reflex. These are monosynaptic spinal segmental reflexes. When they are intact, integrity of the following is confirmed: cutaneous innervation, motor supply, and cortical input to the corresponding spinal segment.  The Achilles reflex checks if the S1 and S2[3] nerve roots are intact and could be indicative of pathology. It is classically delayed in hypothyroidism. This reflex is usually absent in disk herniations at the L5—S1 level. A reduction in the ankle jerk reflex may also be indicative of peripheral neuropathy.