Examination of Motor Nervous System

Practical medical physiology examination of motor nervous system
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9- Examination of Motor Nervous System
Introduction:
From the motor cortex, corticospinal (pyramidal) neurons pass down to
the brain stem. The majority of pyramidal tract (80%) crosses the midline
(contralateral side) at lower medulla oblongata and pass into the lateral
corticospinal tract of spinal cord. These fibers terminate on the anterior
horn then pass out of the cord through peripheral nerves to controlling the
muscles on the opposite side of the body. Other fibers (20%) pass in same
side of the body (ipsilateral) in ventral corticospinal tract of spinal cord
(figure 9-1).
The upper motor neurons (UMN) start from the motor cortex to
anterior horn of spinal cord, while lower motor neuron (LMN) is from the
anterior horns downwards.Practical medical physiology examination of motor nervous system
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Figure (9-1): Pathway of motor nervous system (Corticospinal Tract)
Examination of motor system include:
Aims
To test the integrity of motor nervous system (tone, power and reflexes)
and to detect the level of lesion if present whether upper or lower motor
neuron.
A- Inspection of muscles:
1- Inspect for wasting or atrophy:
A wasted or atrophic muscle is a muscle that has no bulk, the affected limb
appears emaciated, smaller than normal & there is no muscular lump and
always compare the affected side to normal side.
2- Inspection for hypertrophy:
A hypertrophied muscle is a muscle that is bulkier; the affected limb
appears bigger & full of muscle lump.
3- Inspection for tremor:
An involuntary, rhythmic, muscle contraction and relaxation involving to
and fro movements of one or more body parts (group of muscles). It is thePractical medical physiology examination of motor nervous system
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most common of all involuntary movements can affect the hands, arms,
head, and legs.
4- Fasciculation:
Fasciculation or "muscle twitch", is a small, local, involuntary muscle
contraction visible under the skin (bundle of muscle fibers within a single
motor unit).
5- Abnormal posture:
Posture is human position, abnormal posture occurs in many conditions.
B- Palpation of muscles:
1- Muscle tone:
It is resistance felt when a joint is moved passively through its range of
movement. In normal peoples who are relaxed there is elastic type of
resistance felt. The tone may be normal, increased (hypertonia) or
decreased (hypotonia). Hypertonia may be either plasticity or rigidity.
Hypotonia is feature of lower motor neuron lesion (LMN) lesion while
hypertonia is feature of upper motor neuron lesion (UMN). Clonus is
muscle contraction evoked by sudden stretch of muscle; sustained clonus is
indication of UMN.
- Ask the subject to relax, extend and flex knee and ankle joints passively to
detect clonus of lower limb joints.
2-Muscle Power:
Examine individual muscles group in both upper and lower limbs
alternately.
Ask the patient to undertake a movement. First assess whether he can
overcome gravity, e.g. instruct the patient ‘Lift your right leg off the bed’ to
test hip flexion. Then apply resistance to this movement testing across a
single joint, e.g. apply resistance to the thigh in hip flexion, not the lower
leg. Ask the patient to lift his arms above his head. Then assess each muscle
separately.Practical medical physiology examination of motor nervous system
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Biceps muscle: Ask subject to flex elbow joint then hold the wrist and resist
flexion (figure 9-2).
Figure 9-2:- Biceps Contraction
Quadriceps muscle: Ask the subject to lie on supine position, knee joint is
on 20o flexion then ask the subject to extend his knee against your power
(figure 9-3).
Figure 9-3:- quadriceps power
Power can be classified to different grades:
Grade 0: No muscle contraction visible.
Grade 1: Muscle contraction but no movement.
Grade 2: Joint movement with gravity.
Grade 3: Movement against the gravity.
Grade 4: Movement against gravity and the resistance is weaker than
normal.
Grade 5: Normal power.Practical medical physiology examination of motor nervous system
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3-Muscle Reflexes:
A reflex is an involuntary event that we cannot control it. It requires reflex
arc that consist; 1-receptor, 2-afferent limb (sensory fiber), 3- CNS center,
4-efferent limb (motor fiber) and 5-effector organ (muscle or gland). To
initiate a reflex we need a stimulus.
Reflexes can be classified into:
1- Deep reflexes, 2- Superficial reflexes
Objective:
To test the integrity of the different component of the reflex arc.
Materials:
1- Subjects.
2- Neurological hammer.
Procedures:
1-Deep reflexes: Such as knee jerk, ankle jerk, and biceps jerk etc. They are
monosynaptic reflexes. They depend on muscle stretch receptors. When
tendon of the muscle is blow with a soft rubber hammer, suddenly
stretching the muscle, afferent impulses from sensory endings of muscle
spindles.
a- Knee jerk: (L 2, 3, 4)
Ask subject to put tested knee upon the opposite knee, then tap quadriceps
tendon by patellar hammer causing extension of knee (figure 9-4a).
b- The ankle jerk: (S 1, 2)
Ask the subject to slight flex ankle joint (Dorsiflexion of foot), tap the
Achilles tendon by tendon hammer, calf muscle quick contracts (figure 9-
4b).
c- Triceps jerk: (C 6, 7)
Ask subject to slight flex elbow, tap the triceps tendon just above
olecranon. Triceps muscle quick contracts.
d- Biceps jerk: (C 5, 6)
Ask the subject to slight extend elbow and place forearm in semi-pronated
position. The examiner places his thumb on the biceps tendon and stroke it
with tendon hammer, biceps muscle quick contracts.Practical medical physiology examination of motor nervous system
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AFigure 9-5: reflexes (a) knee jerk (b) ankle jerk.
2- Superficial reflexes
Such as planter reflex, abdominal reflex, cremasteric reflex etc. These
reflexes are polysynaptic reflexes. They elicited in response to cutaneous
stimuli, not dependent on muscle stretch receptors.
a- Planter reflex:
The lateral outer edge sole of the foot is gently stimulated by a key from
the heel toward the little toe then medially. The response is planter flexion
and adduction of toes particularly the big toe. Abnormal response
(dorsiflexion of the big toe and fanning the other toes) called Babiniski sign.
Children under two years of age exhibit this sign because of an incomplete
development of the nervous system. Presence of this sign after this age
refers to UMN lesion (figure 9-6).Practical medical physiology examination of motor nervous system
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Figure 9-6 babiniski sign
b- Abdominal reflex: (T7– 12)
Ask subject to lie supine with abdomen uncovered, a thin wooden stick or
end of tendon hammer is dragged quickly from the loin towards the
midline. Contractions underlying abdominal muscles follow the stimulus.
This reflex is absent in UMN lesion above their spinal levels and difficult to
elicit in obese and woman with multiple pregnancies. An anxious subject
will brisk this reflex as well as brisk tendon reflex.
c- Cremasteric reflex: (L 1 – 2)
Stroke the skin of the upper inner thigh causes testicle move upward.
Table 1 shows the differences between lower and upper motor neuron
lesion.
Lower motor neuron lesion Upper motor neuron lesion
Affect fibers above anterior horn
cells
Affect fibers from anterior horn
(spinal cord) to muscles
1-
Decrease control of active
movement.
Muscle weakness, wasting,
fasciculation
2-
Hypertonia, clonus is often
present.
3- Hypotonia
Hypereflexia and absent
abdominal reflex
4- Hyporeflexia or areflexia
5- Reduced muscle power Reduced power of muscles.
6- Babiniski sign is absent Babiniski sign is present.Practical medical physiology examination of motor nervous system
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Some motor defects terms (patterns):
1- Paresis: Partial muscle weakness.
2- Plegia: Complete muscle weakness.
3- Monoplegia: Involvement single limb.
4- Hemiplegia: Involvement of one half of body.
5- Paraplegia: Involvement of both legs.
6- quadriplegia: weakness of 4 limbs.