The motor neurons whose axons terminate at neuromuscular junctions and which activate voluntary skeletal muscles contraction upon stimulation are the lower motor neurons. These are located in the anterior horns of the spinal cord grey matter and the motor cranial nerve nuclei.
The upper motor neurons are situated in the cerebral cortex, and their axons leave the cortex to control the lower motor neurons. These are distributed in the primary motor cortex, supplementary motor area, and premotor cortex.
The effect of lower motor neuron lesion is the weakness (ultimately paralysis) of affected muscles with marked wasting. The effects of upper motor neuron lesions are more variable, depending on the pathways affected. There can be a loss of dexterity, weakness, and spasticity.
Bulk and Nutrition of Muscles
- Expose the limbs and compare corresponding parts of both sides.
- To check for wasting use the bony points on the limbs to compare both sides using a measuring tape.
- For forearms measure the distance from the styloid process to a point at forearm where the muscle bulk is maximum and measure the circumference of forearm at that site. Repeat on the other side by measuring circumference at the same distance from the styloid process.
- For upper arms mark the midpoint between the acromion of scapula and olecranon of ulna (with elbow flexed at 90˚). Measure the circumference of the upper arm at that site on both sides.
- For legs measure the distance from medial malleolus to a point at calf where muscle bulk is maximum and measure the circumference of calf at that site. Repeat on the other side at the same distance.
- For thighs measure the distance from the lateral tibial condyle to a point at thigh where muscle bulk is maximum and measure the circumference of thigh at that site. Repeat on the other side at the same distance.
Wasting of muscle is a common sign of disease but does not always have a neurological basis as atrophy can also occur due to misuse but tends to be mild. Cachexia involves diffuse muscle wasting. Thyrotoxicosis can lead to diffuse muscle wasting eventually resulting in weakness. Many myopathic disorders can lead to muscle wasting in which the specific pattern of wasting is diagnostic.
When considering a neurological basis of wasting, peripheral nerve disease which affects motor neurons present with muscle wasting. Denervated muscles waste markedly indicating motor nerve terminal or axon loss. In mononeuropathies, the wasting only affects muscles supplied by the affected nerves range of pathologies of the spinal cord can also cause wasting, for example, poliomyelitis and syringomyelia.
Fasiculations can also be seen accompanying muscle wasting. These are involuntary contractions of a group of muscle fibers innervated by a single motor neuron. These appear as fine, flickering, irregular twitching movements that occur spontaneously. Widespread fasciculations are characteristic of amyotrophic lateral sclerosis and can also be seen in peripheral neuropathies and radiculopathies.
Tone of Muscles
The tone is defined as the resistance felt when a joint is moved passively.
- The patient should lie supine and should be relaxed and comfortable.
- First, grasp the patient’s forearm and shake it. Observe the movement of the wrist (this indicates the tone around the wrist). Compare both sides.
- Repeat the act in the lower limb by grasping the leg below the knee and moving it from side to side while supported on the bed. Observe the movements of the ankle. Compare both sides.
- Then carry out a full range of passive movements at wrist, elbow, hip, knee and ankle joints. At first rapidly and then slowly assessing the resistance encountered during these movements. Make sure the movements do not elicit any pain or are uncomfortable for the patient. Also be wary of degenerative diseases (especially in the elderly) that can lead to stiff movements.
The tone may either be increased, referred to as hypertonia, or decreased, referred to as hypotonia. Hypertonia will present as greater resistance to movement and hypotonia will present as decreased resistance to movement.
There are two types of hypertonia: spasticity and rigidity. In spasticity, the resistance increases with the speed of passive movements. Spastic hypertonia in the upper limbs affects flexor muscles more than extensor muscles. This may give rise to a characteristic posture of the limb which is flex at the elbow, wrist, and fingers. There will be more resistance to passive extension of these joints than to passive flexion. The resistance increases in proportion to the speed of stretch of affected muscles until it suddenly reduces. It resembles the opening or closure of a clasp knife and is also called clasp knife spasticity. It occurs in UMN lesions. Accordingly, detecting spasticity is best achieved by fairly fast and vigorous movements of the patient’s limbs to stretch the relevant muscles. In the leg, spasticity typically affects adductors and extensors more than flexors. With spinal cord lesions, the spasticity is often bilateral (a spastic paraparesis).
In rigidity, there is uniform increased resistance throughout the range of passive movements. This takes two forms: either an increase in muscle tone affecting the movement of any muscle groups (so-called lead pipe rigidity) or rigidity which is modified by tremor (so-called cogwheel rigidity, in which a high-frequency intermittency in the severity of the resistance to movement is felt and the movements are jerky). Cogwheel rigidity is best detected by slow rotatory movements of the wrist. This is usually seen in Parkinsonism.
Hypotonia or flaccidity is characterized by absence or loss of tone and occurs in LMN lesions, lesions of sensory pathways, early stages of neuronal or spinal stroke and cerebellar dysfunction.
Power of Muscles
Due to the variation of power in individuals, it is important to compare both sides to detect weakness. The following grading method is used to classify the degree of weakness in the muscle group.
|Grade 0||No movement|
|Grade 1||Barest flicker of movement of the muscle, though not enough to move the structure to which it’s attached.|
|Grade 2||The voluntary movement which is not sufficient to overcome the force of gravity. For example, the patient would be able to slide their hand across a table but not lift it from the surface.|
|Grade 3||Voluntary movement capable of overcoming gravity, but not any applied resistance. For example, the patient could raise their hand off a table, but not if any additional resistance were applied.|
|Grade 4||Voluntary movement capable of overcoming “some” resistance|
|Grade 5||Normal strength|
Small Muscles of the Hand
Abductor pollicis brevis: Ask the patient to abduct the thumb at a right angle to the palm against resistance.
Opponens pollicis: Ask the patient to touch the little finger with the thumb and then try to separate them with your index finger.
Adductor pollicis brevis: Ask the patient to adduct the thumb towards the palmar surface of the index finger against resistance.
Lumbricals: Ask the patient to flex the metacarpophalangeal joints and extend the interphalangeal joints against resistance.
Interossei: To test dorsal interossei ask the patient to spread their fingers against resistance. To test the palmar interossei, ask the patient to hold a card between the two fingers as you try to pull from the fingers.
Flexors of Fingers
Ask the patient to make a fist, squeezing their hand around two of your fingers. If the grip is normal, you will not be able to pull your fingers out. Test each hand separately.
Extensors of Fingers
Ask the patient to open their fist against resistance.
Extensors of the Wrist
Ask the patient to grip something firmly in their hands. Paralysis of the extensors of the wrist leads to wrist drop so that can be checked for.
Ask the patient to flex their elbow against resistance while their arm is midway between supination and pronation.
Ask the patient to flex their elbow against resistance while the arm is fully supinated.
Ask the patient to straighten the flexed forearm against resistance.
Supraspinatus and Deltoid
Ask the patient to abduct the arm against resistance; the first 30˚ of abduction is carried out by supraspinatus and the next 60˚ by the deltoid.
Ask the patient to push against the wall; if serratus anterior is paralyzed, there is winging of the scapula. The patient would also be unable to elevate their arm above the right angle.
Ask the patient to stretch out their arms in front of them and then clasp their hands together against resistance.
Dorsiflexion of the Toes
Ask the patient to move the toes upwards against resistance.
Dorsiflexion of the Foot
Ask the patient to move their foot upwards against resistance.
Plantar Flexion of the Toes
Ask the patient to move their toes downwards against resistance.
Plantar Flexion of the Foot
Ask the patient to move their foot downwards against resistance.
Extensors of the Knee
Bend the patient’s knee and ask the patient to straighten it against resistance.
Flexors of the Knee
Raise the patient’s leg up from the bed. Support their thigh with your left hand and hold their ankle with your right hand. Then ask the patient to bend their knee against resistance.
Extensors of the Hip
Place your right hand on the Achilles tendon. Lift the patient’s leg up while their knee is fully extended and ask the patient to push it down against resistance.
Flexors of the Hip
Place your right hand on the patient’s knee. Ask the patient to bend their leg at the hip against resistance.
Adductors of the Thigh
Place your right hand on the medial side of the patient’s leg. Ask the patient to bring abducted limbs toward their midline against resistance.
Abductors of the Thigh
Place your right hand on the lateral side of the patient’s leg. Place the patient’s legs together and ask them to separate them against resistance.
It should be made sure that both sides are tested, and a comparison of strengths is made. A comparison of strength can also be made when comparing the upper and lower limbs or when comparing proximal and distal muscle groups.
Reflexes can broadly be categorized as deep (tendon) reflexes and superficial reflexes.
Deep (Tendon) Reflexes
The deep (tendon) reflexes are monosynaptic stretch reflexes. They are tested through the use of a clinical hammer. Striking the clinical hammer against the tendon of the muscle elicits a sudden stretch impulse which can be observed as a contraction of the muscle. Abnormally brisk tendon reflexes indicate an upper motor neuron disorder, whereas an absence of tendon reflexes indicate disorders of sensory afferents from muscle spindles or LMN damage. As in neuropathy, motor neuron disease, poliomyelitis and tabes dorsalis (it is possible for the sensory or motor component of the reflex arc to be affected in the absence of a tendon reflex). The following table shows the deep tendon reflexes which are assessed:
|Reflex||Nerve||Nerve root(s)||Technique||Clinical Correlation|
|Biceps jerk||Musculocutaneous||C5, C6||Flex the patient’s elbow at a right angle and place their forearm in a semipronated position. Place the thumb or index of your left hand over the tendon of the biceps in the cubital fossa and strike it with the hammer. Observe the contraction of the biceps tendon.||Reduced or absent in radiculopathy or focal cord pathology at C5-C6 cord level|
|Supinator jerk||Radial||C5, C6||This involves the brachioradialis muscle. Flex the patient’s forearm at the elbow and place it in a semipronated position. Bend their hand slightly towards the ulnar side. Strike the tendon of the brachioradialis, proximal to the styloid process of the radius. Observe the contraction.||Mainly of interest when it is inverted*|
|Triceps jerk||Radial||C6, C7||Place the patient’s forearm on their abdomen, and the elbow is flexed at the right angle. Strike the tendon of the triceps above the olecranon. Observe the contraction.||Reduced or absent in high radial nerve lesion, radiculopathy or focal cord pathology of the C6-C7 level.|
|Knee-jerk||Femoral||L3, L4||The patient should be lying supine. Flex their knee and support it with your left hand. Feel for the tendon of the quadriceps and strike it between the patella and tibial tuberosity with the hammer. Observe the contraction of the quadriceps.||Reduced in radiculopathy, lumbar plexopathy or femoral neuropathy.|
|Ankle jerk||Tibial branch of sciatic||S1||The patient should be lying supine. Flex their leg gently and place it in an externally rotated position. Place your left hand on the sole and dorsiflex it. Strike the Achilles tendon with the hammer. Observe the contraction of the calf muscles.||Absence may be the only sign other than restricted straight leg raising in S1 radiculopathy due to L5/S1 disc prolapse.|
*if a tendon jerk being elicited is absent or diminished, but there is the contraction of muscles innervated from an adjoining spinal segment, this is called inversion of that reflex. It indicates combined spinal cord and root pathology and has a precise localizing value. The inversion of biceps or brachioradialis jerk would occur if the jerk is absent or diminished, but there is flexion of the fingers.
The following precautions should be taken when eliciting the tendon jerks:
- The patient should be relaxed and comfortable.
- The muscle being tested should be visible so there should be enough exposure of the muscle.
- The flexible shaft of the hammer should be held from its end and let the heavy end of the hammer fall on the tendon to be tested.
- It is important to strike the tendon and not the muscle.
- Compare the tendon jerks of both sides.
- If the reflex is absent, elicit it again after reinforcement. For reflexes of the lower limb ask the patient to clench their hands or hook the fingers of both hands together and then pull them away from each other without disengaging. For reflexes of the upper limb, ask the patient to clench their teeth.
- If clonus is present, there are regular oscillations of the foot due to contraction and relaxation of the muscles.
Superficial reflexes are polysynaptic reflexes and include the following reflexes:
Plantar Reflex (S1)
The patient should lie supine with legs extended. Scratch the outer edge of the sole with some blunt object like a key, starting from the heel towards the little toe and then medially across the metatarsals. Stop as soon as the first movement of the toe occurs. The normal response is the plantar flexion of the great toe along with the flexion and adduction of the other toes. This is referred to as the negative Babinski’s sign. If there is dorsiflexion of the great toe along with fanning out of the other toes, it is referred to as the positive Babinski’s sign. A positive Babinski’s sign is present in UMN lesion, hypoglycemia, deep coma, post-epileptic fit and also in infants.
Abdominal Reflex (T8-T12)
The patient should be lying in a supine position with a low pillow supporting the head. Draw a pin from the lateral part of the abdomen towards the midline on either side. It should be below and parallel to the costal margins for upper abdominal reflexes and above and parallel to the inguinal ligaments for lower abdominal reflexes. There should be a brisk contraction of the muscles of the stimulated area and movement of the umbilicus towards that side. Abdominal reflex is absent in UMN lesion above their segmental level or if there is LMN lesion of the concerned spinal nerves.
Cremasteric Reflex (L1, L2)
Scratch the inner aspect of the upper part of the thigh. This should result in the elevation of the testes in male patients. This reflex is absent in UMN lesion.
Anal Reflex (S3, S4)
Scratch the skin near the anal margin with a sharp object. This should result in the contraction of the anal sphincter.
Corneal/conjunctival reflexes have already been described.
Coordination of Movements
Coordination of movements refers the performance of purposeful movements carried out smoothly by different groups of muscles. For this to occur, the motor, sensory and cerebellar systems need to be intact. Loss of coordination is called ataxia which is of two types: sensory and cerebellar. There are several tests which can be done to assess coordination. Sensory ataxia is due to the loss of sense of position. Hence the coordination tests become worse when the patient closes their eyes. Otherwise, sensory ataxia is compensated through vision. In cerebellar ataxia, the closure of eyes has no effect at all.
- Ask the patient to touch the tip of their nose and your finger alternately with their index finger. This has to be done rapidly and repeatedly.
- Your finger should be kept at a distance that makes the patient extend their full arm to reach it.
- The test should be performed with the patient’s eyes being open.
- Each arm should be tested separately.
- To further increase the sensitivity of the test, you can keep changing the position of your arm.
- In order to check for sensory ataxia make the patient close their eyes and then touch the tip of their nose.
A normal person will be able to perform these tasks seamlessly. If there is a problem with coordination, it will result in overshooting.
- Ask the patient to extend and abduct their arms fully and then bring the tips of their index fingers together after making a wide circle. This should first be done with eyes opened and then with eyes closed.
- Another test for coordination is to ask the patient to make circles in the air at first with eyes open and then with eyes closed.
A normal person will be able to perform these tasks seamlessly. If there is a problem with coordination, it will result in overshooting.
- The patient should be lying down.
- Ask the patient to place their heel on their opposite knee and slide it downwards along the shin to the ankle.
- Then lift their heel, make a semicircle and place it again on their knee and repeat the movement.
- Repeat with the other heel doing the same movements on the opposite knee.
The movements will be clumsy and jerky in loss of coordination.
- Ask the patient to walk along a straight line so that the heel of one foot comes directly in contact with the toes of the other foot.
- The rear foot is then advanced so that its heel is then placed in front of the foot which was previously the front foot.
A patient with cerebellar dysfunction is unable to do so and tends to fall towards the diseased side.
This helps to differentiate between sensory and cerebellar ataxia. Ask the patient to stand with their feet close together. A patient with sensory ataxia is steady when eyes are open and becomes unsteady when they close their eyes. A patient with cerebellar ataxia will be equally unsteady with eyes open or closed.
These are rhythmic, involuntary movements resulting in alternating contractions and relaxation of groups of muscles. To check for tremors ask the patient to outstretch their arms and abduct their fingers. If the tremors are still not obvious but are suspected, place a piece of paper on the dorsum of the hand and observe its movements. There are different causes of tremors, and they all present with different types of tremors.
Anxiety: the tremors are fine and become obvious only when the arms are outstretched, and fingers are spread. Hands will be cold and sweaty.
Thyrotoxicosis: tremors are similar to those of anxiety, but hands are sweaty and warm.
Essential familial tremors: tremors are coarse and present during rest and activity.
Senile tremors: these are similar to essential familial tremors but only occur in old age.
Parkinsonian tremors: these are slow and coarse and are pill-rolling movements. They disappear during voluntary work and sleep.
Intention tremors: ask the patient to hold an object. The tremors will occur during voluntary work but disappear at rest. These are the features of cerebellar dysfunction.
Flapping tremors: ask the patient to outstretch arms and dorsiflex hands at wrists. Jerky movements of the hands occur due to flexion and extension of the wrists and fingers. Flapping tremors can be caused by the respiratory, renal, hepatic or cardiac failure.
Tics or Habit Spasms
These are repetitive and stereotyped movements with the same movement being repeated again and again.
These are semi-purpose movements which look like fragments of normal movements but are repeated in a disorderly manner. These occur in Huntington’s chorea and rheumatic fever (Sydenham’s chorea).
These are slow writhing movements which primarily affect the distal parts of the limbs.
These are the sudden shock like contractions that involve one or more muscles or a whole limb. These are usually features of epilepsy.
There are sudden, violent, throwing movements of the limbs on one side. They occur due to the lesion in the contralateral subthalamic nucleus.
These are similar to the athetoid movements but involve the proximal parts of the limbs or trunk. These are also called torsion spasms. Spasmodic torticollis (in which repetitive rotatory movement of the head and neck to on side occurs) and dystonia musculorum deformans are examples of torsion spasms.
The patient doesn’t lift his/her feet off the ground completely so that the toes remain in contact with the ground. Legs swing outward and forward in a circular fashion. This is seen in UMN paraplegia. In hemiplegic gait, only one leg is affected.
High Stepping Gait
Patients lift their feet high to clear the toes from the ground and then return it with a loud slapping noise. This is seen in patients with bilateral foot drop as a result of the weakness of the extensors of the feet, as in polyneuropathy.
Patients walk on a broad base in a reeling manner. This occurs in the cerebellar lesion.
The body sways from side to side as each step is taken. It occurs in proximal muscular weakness, as in myopathies. It also occurs in congenital dislocation of hip joints.
A patient with Parkinsonism bends forward with flexion at the hips and knees. Arms are flexed at the elbows and adducted at the shoulder. There are no associated movements during walking. The patient makes rapid shuffling movements with their feet dragging against the floor.