Question

1. Where does the impulse of the plantar reflex go that is different from a muscle stretch reflex?( hint: tell me where the integrating centers for each is located)

2. What is the difference between a monosynaptic reflex and a polysynaptic reflex? Which one is faster?

3.Describle the Jendrassick's Maneuver. How does it work?

4. What are the two types of hearing loss and how can they be identified?

5. What is nystagmus? Why does it occur after the subject stops spinning?

  

Answer 1

1.The PR is elicited by stroking the lateral or outer border of the sole of the foot with the thumb nail or a blunt point like the end of the handle of the reflex hammer or the tip of a key. The stimulus is directed from the heel forwards towards the little toe, and on reaching the foot pad, directed transversely across the metatarsal pad from the little to the base of the great toe. The stimulus should stop short of the base of the toes because extending the stroke to the base of the toes produces unpredictable movements. Before eliciting the reflex, the patient should be instructed to relax and let his limb remain as floppy as possible. The * Professor, Department of Neurology, G. B. Pant Hospital, New Delhi - 110 002. Introduction The plantar reflex (PR) is one of the most important and well studied reflex in the body; and yet its elicitation and interpretation remains an art. It is basically a polysynaptic superficial reflex, designed to withdraw the stimulated part, i.e., the foot from a potentially dangerous stimulus. Anatomical considerations The reflex arc for the PR comprises of the afferent and efferent fibres in the tibial nerve and the L4-5 to S1-2 cord segments. The reflexogenic area is the first sacral dermatome, with the receptor nerve endings being located in the skin on the sole of the foot. The afferent fibres travel in the tibial nerve which is a branch of the sciatic nerve, to relay in the L4-5 to S1-2 cord segments. The efferent fibres from the spinal cord travel back in the sciatic nerve which divides into two large branches just proximal to the knee. Fibres supplying the toe flexors travel in the tibial nerve while those supplying the toe extensors travel in the peroneal nerve to reach the foot. Injury or transection of the tibial nerve therefore, would interrupt the afferent and efferent arcs of the normal plantar response, leaving the toe extensor muscles innervated. Interruption of the reflex arc can cause a diminution or absence of the reflex. Supraspinal influences from the cortex also influence and modify the spinal reflex or response. Impulse from the lumbosacral cord segments ascend up through the spinal cord and the brainstem to the parietal areas of the brain, which in turn has connections with the motor centres of the cortex. Efferent impulses from motor and premotor JIACM 2005; 6(3): 193-7 194 Journal, Indian Academy of Clinical Medicine Vol. 6, No. 3 July-September, 2005 leg should be positioned in such a way that the knee is straight or slightly flexed and the thigh externally rotated. It is important to distract the patient with conversation after warning him that the sole of the foot will be scratched. It is advisable to hold the patient’s ankle with one hand, to keep the foot in place and control the pressure of the plantar stroke. The stimulus should be firm, gentle and should cause neither pain nor tickle. A sharp stimulus is applied only if the initial stimulus fails to elicit a response. The response can be reinforced by rotation of the patient’s head to the opposite side. Following the stimulus, it is important to watch the big toe at the metatarsophalangeal joint and the remainder of the foot. The response usually occurs after the plantar stroke has moved a few centimeters along the sole to produce a spatial and temporal summation of the applied stimulus. Interpretation of the response The plantar response may be: 1. Normal flexor plantar response 2. Pathologic or abnormal extensor plantar response (Babinski’s sign) Normal flexor plantar response In normal people after infancy, there is a plantar flexion of the foot and toes along with adduction of the toes. The primary movement is a plantar flexion of the great toe at the metatarsophalangeal joint, even if the terminal joint appears to extend. The response is a fairly rapid one and may be accompanied at times by an associated flexion of the hip and knee on the stimulated side. Abnormal extensor plantar response (Babinski’s sign) Joseph Babinski, a French neurologist, first differentiated between a normal and a pathologic plantar response and described the Babinski sign in 1896. The Babinski’s sign is encountered in patients with pyramidal tract dysfunction and is characterised by a dorsiflexion or extension of the great toe with or without fanning or abduction of the other toes. The fully developed response is also accompanied by dorsiflexion of the ankle and flexion of the hip and knee joint and slight abduction of the thigh, leading to a withdrawal of the leg on plantar stimulation. The Babinski sign is always pathological. There is no such thing as a negative Babinski sign. The muscles taking part in a fully developed response include the extensor hallucis longus, tibialis anterior, extensor digitorum longus, hamstring group of muscles, and the tensor fasciae latae. The dorsiflexion of the toes may be the only visible effect, but the contraction of the thigh and leg muscles is always present and can be detected by palpation. Contraction of the tensor fasciae latae has been referred to as Brissaud’s reflex. The fully developed extensor plantar response forms part of the primitive ‘flexion reflex synergy’ of the lower limbs designed to withdraw the limb from a painful stimulus. This spinal defence reflex mechanism described by Sherrington, activates all the muscles involved in shortening the stimulated limb. It involves flexion of the hip and knee, dorsiflexion of the ankle and extension of the great toe. The ‘toe and foot extensors’ although named extensors by anatomists, are in fact flexor in a physiological sense, because their action is to shorten the limb and contract reflexly alongwith other flexor muscles. The physiologist looks on the Babinski sign as simply a part of the ‘primitive flexion reflex’. The Babinski sign may be a normal occurrence in the first year of life. In the infant, before myelination of the nervous system is complete and an upright stance has been achieved, the normal plantar response is extensor, due to a brisker ‘flexion synergy’ as part of the withdrawal response to pain. As the nervous system matures and the pyramidal tracts gain more control over spinal motor neurons, the ‘flexion synergy’ becomes less brisk and the toe ‘extensors’ are no longer a part of it. When the child assumes an upright posture, the plantar response becomes part of the postural reflex maintaining the tones of the foot and leg. At this time, the normal response to stimulation becomes a flexor movement of the toes and the ‘withdrawal extensor’ movement is suppressed by the influence of the pyramidal tract over the spinal reflex arc. The toe then goes down instead of up, as a result of a segmental reflex involving small foot muscles and the overlying skin.

2. When a reflex arc in an animal consists of only one sensory neuron and one motor neuron, it is defined as monosynaptic, referring to the presence of a single chemical synapse. In the case of peripheral muscle reflexes (patellar reflex, achilles reflex), brief stimulation to the muscle spindleresults in contraction of the agonist or effector muscle. By contrast, in polysynaptic reflex pathways, one or more interneurons connect afferent (sensory) and efferent (motor) signals. All but the most simple reflexes are polysynaptic, allowing processing or inhibition of polysynaptic reflexes within the brain.

3.

The Jendrassik maneuver is a medical maneuver wherein the patient clenches the teeth, flexes both sets of fingers into a hook-like form, and interlocks those sets of fingers together. The tendon below the patient's knee is then hit with a reflex hammer to elicit the patellar reflex. The elicited response is compared with the reflex result of the same action when the maneuver is not in use. Often a larger reflex response will be observed when the patient is occupied with the maneuver, as the maneuver may prevent the patient from consciously inhibiting or influencing his or her response to the hammer. This effect was first observed in the late 19th century by Hungarian physician Ernő Jendrassik, whom it was named after.

This maneuver is particularly useful in that even if the patient is aware that the interlocking of fingers is just a distraction in order to elicit a larger reflex response, it still functions properly.

The maneuver can also be used to distract patients when performing other tests or procedures and any suitable distraction may be used; for example when looking for Romberg's sign.

4.

Types of hearing loss

Below is a brief explanation of each of the three basic types of hearing loss: 1) sensorineural, 2) conductive, and 3) mixed.

Sensorineural Hearing Loss

The vast majority of people with hearing loss have sensorineural hearing loss (pronounced sen(t)sərēˈn(y)o͝orəl). This occurs when there is a problem with the sensory (hair cells) and/or neural structures (nerves) in the inner ear (cochlea). Most often, sensorineural hearing loss involves damage to the tiny hair cells that are activated by sound waves to vibrate and release chemical messengers that stimulate the auditory nerve. The auditory nerve is made up of many nerve fibers that then carry signals to the brain that are interpreted as sound. While sensorineural hearing loss usually involves damage to the tiny hair cells, it also can result from damage to the auditory nerve.

A sensorineural hearing loss reduces the intensity of sound. But a sensorineural hearing loss also can distort what is heard—even when the sounds are loud enough. That is why people with sensorineural hearing loss often struggle to hear words clearly—particularly certain spoken consonant sounds and when in noisy environments.

Most sensorineural hearing loss cannot be reversed with medical treatment and is typically described as an irreversible, permanent condition. Nevertheless, research into a cure continues.

The good news is that once any underlying medical conditions have been ruled out or addressed, most people with sensorineural hearing loss can benefit from hearing aids.

Ninety-one percent of people who purchased hearing aids in the last year say they’re satisfied, in fact. And 90 percent say they’d recommend getting hearing aids to family members and friends.

Some of the potential causes of sensorineural hearing loss include:

• Exposure to loud noise
• Aging
• Medicines that damage the ear (ototoxic)
• Illnesses, such as meningitis, measles and certain autoimmune disorders, among others
• Genetics—that is, hearing loss runs in the family
• Trauma to the head
• Structural malformation of the inner ear

Conductive Hearing Loss

Conductive hearing loss is mechanical in nature. That means that something—a physical condition or disease—is stopping sound from being conducted from the outer or middle ear to the inner ear, where nerves are stimulated to carry sound to the brain.

Often, the cause of conductive hearing loss can be identified and treated. Medical treatment of conductive hearing loss often allows for partial or complete improvement in hearing. Then, hearing aids are usually helpful in compensating for any remaining hearing loss.

Potential causes of conductive hearing loss include:

• Wax buildup
• Fluid in the middle ear due to colds or allergies
• Fluid in the middle ear due to poor eustachian tube function (The eustachian tube drains fluid from the middle ear and ventilates it to regulate air pressure there.)
• Ear infection
• A foreign object lodged in the ear
• A ruptured eardrum (also called a perforated eardrum or a tympanic membrane perforation), which means there is a tear in the membrane that separates the outer ear from the middle ear
• Structural malformation of parts of the ear
• Trauma to the ear
• In rare cases, tumors

Mixed Hearing Loss

A mixed hearing loss means there is a sensorineural hearing loss along with a conductive hearing loss component. In addition to some irreversible hearing loss caused by a problem with the inner ear, there also is an issue with the outer or middle ear, which makes the hearing loss worse. But it may be possible to successfully treat the conductive hearing loss, as explained above. Following treatment, the individual also may benefit from hearing aids to help manage the remaining sensorineural hearing loss.

5.

Nystagmus is a condition of involuntary (or voluntary, in rare cases) eye movement, acquired in infancy or later in life, that may result in reduced or limited vision. Due to the involuntary movement of the eye, it has been called "dancing eyes".

In a normal condition, while the head rotates about any axis, distant visual images are sustained by rotating eyes in the opposite direction on the respective axis.The semicircular canals in the vestibule sense angular acceleration. These send signals to the nuclei for eye movement in the brain. From here, a signal is relayed to the extraocular muscles to allow one’s gaze to fixate on one object as the head moves. Nystagmus also occurs when the semicircular canals are being stimulated (e.g. by means of the caloric test, or by disease) while the head is not in motion. The direction of ocular movement is related to the semicircular canal that is being stimulated.

There are two key forms of nystagmus: pathological and physiological, with variations within each type. Nystagmus may be caused by congenital disorders, acquired or central nervous systemdisorders, toxicity, pharmaceutical drugs, alcohol, or rotational movement. Previously considered untreatable, in recent years several pharmaceutical drugs have been identified for treatment of nystagmus. Nystagmus is also occasionally associated with vertigo.