Movements
of the tongue, soft palate, or superior pharynx can be observed directly while
the patient swallows, while the gag reflex is elicited, or while the patient
says repetitive consonant sounds. The motor control of the gag reflex is
largely controlled by fibers in the vagus nerve and constitutes a test of that
nerve because the parasympathetic functions of that nerve are involved in
visceral regulation, such as regulating the heartbeat and digestion. Movement
of the head and neck using the sternocleidomastoid and trapezius muscles is
controlled by the accessory nerve. Flexing of the neck and strength testing of
those muscles reviews the function of that nerve. also available. The patient
is asked to indicate whether one or two stimuli are present while keeping their
eyes closed. The examiner will switch between using the two points and a single
point as the stimulus. Failure to recognize two points may be an indication of
a dorsal column pathway deficit.
Similar to two-point discrimination, but
assessing laterality of perception, is double simultaneous stimulation. Two
stimuli, such as the cotton tips of two applicators, are touched to the same
position on both sides of the body. If one side is not perceived, this may
indicate damage to the contralateral posterior parietal lobe. Because there is
one of each pathway on either side of the spinal cord, they are not likely to
interact. If none of the other subtests suggest particular deficits with the
pathways, the deficit is likely to be in the cortex where conscious perception
is based. The mental status exam contains subtests that assess other functions
that are primarily localized to the parietal cortex, such as stereognosis and
graphesthesia. A final subtest of sensory perception that concentrates on the
sense of proprioception is known as the Romberg test. The patient is asked to
stand straight with feet together.
Once the patient has achieved their balance
in that position, they are asked to close their eyes. Without visual feedback
that the body is in a vertical orientation relative to the surrounding
environment, the patient must rely on the proprioceptive stimuli of joint and
muscle position, as well as information from the inner ear, to maintain
balance. This test can indicate deficits in dorsal column pathway
proprioception, as well as problems with proprioceptive projections to the
cerebellum through the spinocerebellar tract. representing a Watch this video
to see a quick demonstration of two-point discrimination. Touching a
specialized caliper to the surface of the skin will measure the distance
between two points that are perceived as distinct stimuli versus a single
stimulus. The patient keeps their eyes closed while the examiner switches
between using both points of the caliper or just one. The patient then must
indicate whether one or two stimuli are in contact with the skin. Why is the
distance between the caliper points closer on the fingertips as opposed to the
palm of the hand? And what do you think the distance would be on the arm, or
the shoulder? Muscle Strength and Voluntary Movement The skeletomotor system is
largely based on the simple, two-cell projection from the precentral gyrus of
the frontal lobe to the skeletal muscles.
The corticospinal tract represents
the neurons that send output from the primary motor cortex. These fibers travel
through the deep white matter of the cerebrum, then through the midbrain and
pons, into the medulla where most of them decussate, and finally through the
spinal cord white matter in the lateral (crossed fibers) or anterior (uncrossed
fibers) columns. These fibers synapse on motor neurons in the ventral horn. The
ventral horn motor neurons then project to skeletal muscle and cause
contraction. These two cells are termed the upper motor neuron (UMN) and the
lower motor neuron (LMN). Voluntary movements require these two cells to be
active. The motor exam tests the function of these neurons and the muscles they
control. First, the muscles are inspected and palpated for signs of structural
irregularities. Movement disorders may be the result of changes to the muscle
tissue, such as scarring, and these possibilities need to be ruled out before
testing function. Along with this inspection, muscle tone is assessed by moving
the muscles through a passive range of motion. The arm is moved at the elbow
and wrist, and the leg is moved at the knee and ankle. Skeletal muscle should
have a resting tension representing a slight contraction of the fibers.
The
lack of muscle tone, known as hypotonicity or flaccidity, may indicate that the
LMN is not conducting action potentials that will keep a basal level of
acetylcholine in the neuromuscular junction. If muscle tone is present, muscle
strength is tested by having the patient contract muscles against resistance.
The examiner will ask the patient to lift the arm, for example, while the
examiner is pushing down on it. This is done for both limbs, including
shrugging the shoulders. Lateral differences in strength—being able to push
against resistance with the right arm but not the left—would indicate a deficit
in one corticospinal tract versus the other. An overall loss of strength,
without laterality, could indicate a global problem with the motor system.
Diseases that result in UMN lesions include cerebral palsy or MS, or it may be
the result of a stroke. A sign of UMN lesion is a negative result in the
subtest for pronator drift. The patient is asked to extend both arms in front
of the body with the palms facing up. While keeping the eyes closed, if the
patient unconsciously allows one or the other arm to slowly relax, toward the
pronated position, this could indicate a failure of the motor system to
maintain the supinated position.
Reflexes Reflexes combine the spinal sensory
and motor components with a sensory input that directly generates a motor
response. The reflexes that are tested in the neurological exam are classified
into two groups. A deep tendon reflex is commonly known as a stretch reflex,
and is elicited by a strong tap to a tendon, such as in the knee-jerk reflex. A
superficial reflex is elicited through gentle stimulation of the skin and
causes contraction of the associated muscles. For the arm, the common reflexes
to test are of the biceps, brachioradialis, triceps, and flexors for the
digits. For the leg, the knee-jerk reflex of the quadriceps is common, as is
the ankle reflex for the gastrocnemius and soleus. The tendon at the insertion
for each of these muscles is struck with a rubber mallet. The muscle is quickly
stretched, resulting in activation of the muscle spindle that sends a signal
into the Inteligen In the context of the neurological exam, reflexes indicate
that the LMN is functioning properly. The most common superficial reflex in the
neurological exam is the plantar reflex that tests for the Babinski sign on the
basis of the extension or flexion of the toes at the plantar surface of the
foot. The plantar reflex is commonly tested in newborn infants to establish the
presence of neuromuscular function. To elicit this reflex, an examiner brushes
a stimulus, usually the examiner’s fingertip, along the plantar surface of the
infant’s foot.
An infant would present a positive Babinski sign, meaning the
foot dorsiflexes and the toes extend and splay out. As a person learns to walk,
the plantar reflex changes to cause curling of the toes and a moderate plantar
flexion.
