Rapid,
alternating movements are tested for the upper and lower extremities. The
patient is asked to touch each finger to their thumb, or to pat the palm of one
hand on the back of the other, and then flip that hand over and alternate
back-and-forth. To test similar function in the lower extremities, the patient
touches their heel to their shin near the knee and slides it down toward the
ankle, and then back again, repetitively. Rapid, alternating movements are part
of speech as well. A patient is asked to repeat the nonsense consonants
“lah-kah-pah” to alternate movements of the tongue, lips, and palate. All of
these rapid alternations require planning from the cerebrocerebellum to
coordinate movement commands that control the coordination. Posture and Gait
Gait can either be considered a separate part of the neurological exam or a
subtest of the coordination exam that addresses walking and balance. Testing
posture and gait addresses functions of the spinocerebellum and the vestibulocerebellum
because both are part of these activities. A subtest called station begins with
the patient standing in a normal position to check for the placement of the
feet and balance. The patient is asked to hop on one foot to assess the ability
to maintain balance and posture during movement. Though the station subtest
appears to be similar to the Romberg test, the difference is that the patient’s
eyes are open during station.
The Romberg test has the patient stand still with
the Nooflex eyes closed. Any changes in posture would be the result of proprioceptive
deficits, and the patient is able to recover when they open their eyes.
Subtests of walking begin with having the patient walk normally for a distance
away from the examiner, and then turn and return to the starting position. The
examiner watches for abnormal placement of the feet and the movement of the
arms relative to the movement. The patient is then asked to walk with a few
different variations. Tandem gait is when the patient places the heel of one foot
against the toe of the other foot and walks in a straight line in that manner.
Walking only on the heels or only on the toes will test additional aspects of
balance. Ataxia A movement disorder of the cerebellum is referred to as ataxia.
It presents as a loss of coordination in voluntary movements. Ataxia can also
refer to sensory deficits that cause balance problems, primarily in
proprioception and equilibrium. When the problem is observed in movement, it is
ascribed to cerebellar damage. Sensory and vestibular ataxia would likely also
present with problems in gait and station. Ataxia is often the result of
exposure to exogenous substances, focal lesions, or a genetic disorder. Focal
lesions include strokes affecting the cerebellar arteries, tumors that may
impinge on the cerebellum, trauma to the back of the head and neck, or MS.
Alcohol intoxication or drugs such as ketamine cause ataxia, but it is often
reversible. Mercury in fish can cause ataxia as well. Hereditary conditions can
lead to degeneration of the cerebellum or spinal cord, as well as malformation
of the brain, or the abnormal accumulation of copper seen in Wilson’s disease.
The examiner would look for issues with balance, which coordinates
proprioceptive, vestibular, and visual information in the cerebellum. To test
the ability of a subject to maintain balance, asking them to stand or hop on
one foot can be more demanding. The examiner may also push the subject to see
if they can maintain balance. An abnormal finding in the test of station is if
the feet are placed far apart. Why would a wide stance suggest problems with
cerebellar function? The Field Sobriety Test The neurological exam has been
described as a clinical tool throughout this chapter. It is also useful in
other ways. A variation of the coordination exam is the Field Sobriety Test
(FST) used to assess whether drivers are under the influence of alcohol. The
cerebellum is crucial for coordinated movements such as keeping balance while
walking, or moving appendicular musculature on the basis of proprioceptive
feedback. The cerebellum is also very sensitive to ethanol, the particular type
of alcohol found in beer, wine, and liquor. Walking in a straight line involves
comparing the motor command from the primary motor cortex to the proprioceptive
and vestibular sensory feedback, as well as following the visual guide of the
white line on the side of the road. When the cerebellum is compromised by
alcohol, the cerebellum cannot coordinate these movements effectively, and
maintaining balance becomes difficult. Another common aspect of the FST is to
have the driver extend their arms out wide and touch their fingertip to their
nose, usually with their eyes closed. The point of this is to remove the visual
feedback for the movement and force the driver to rely just on proprioceptive
information about the movement and position of their fingertip relative to
their nose.
With eyes open, the corrections to the movement of the arm might be
so small as to be hard to see, but proprioceptive feedback is not as immediate
and broader movements of the arm will probably be needed, particularly if the
cerebellum is affected by alcohol. Reciting the alphabet backwards is not
always a component of the FST, but its relationship to neurological function is
interesting. There is a cognitive aspect to remembering how the alphabet goes
and how to recite it backwards. That is actually a variation of the mental
status subtest of repeating the months backwards. However, the cerebellum is
important because speech production is a coordinated activity. The speech rapid
alternating movement subtest is specifically using the consonant changes of
“lah-kah-pah” to assess coordinated movements of the lips, tongue, pharynx, and
palate. But the entire alphabet, especially in the nonrehearsed backwards
order, pushes this type of coordinated movement quite far. It is related to the
reason that speech becomes slurred when a person is intoxicated. The cerebellum
is an important part of motor function in the nervous system. It apparently plays
a role in procedural learning, which would include motor skills such as riding
a bike or throwing a football. The basis for these roles is likely to be tied
into the role the cerebellum plays as a comparator for voluntary movement. The
motor commands from the cerebral hemispheres travel along the corticospinal
pathway, which passes through the pons.
Collateral branches of these fibers
synapse on neurons in the pons, which then project into the cerebellar cortex
through the middle cerebellar peduncles. Ascending sensory feedback, entering
through the inferior cerebellar peduncles, provides information about motor
performance. The cerebellar cortex compares the command to the actual
performance and can adjust the descending input to compensate for any mismatch.
The output from deep cerebellar nuclei projects through the superior cerebellar
peduncles to initiate descending signals from the red nucleus to the spinal
cord. The primary role of the cerebellum in relation to the spinal cord is
through the spinocerebellum; it controls posture and gait with significant
input from the vestibular system. Deficits in cerebellar function result in
ataxias, or a specific kind of movement disorder. The root cause of the ataxia
may be the sensory input—either the proprioceptive input from the spinal cord
or the equilibrium input from the vestibular system, or direct damage to the
cerebellum by stroke, trauma, hereditary factors, or toxins. Communication is a
process in which a sender transmits signals to one or more receivers to control
and coordinate actions. In the human body, two major organ systems participate
in relatively “long distance” communication: the nervous system and the
endocrine system. Together, these two systems are primarily responsible for
maintaining homeostasis in the body. The nervous system uses two types of
intercellular communication—electrical and chemical signaling—either by the
direct action of an electrical potential, or in the latter case, through the
action of chemical neurotransmitters such as serotonin or norepinephrine.
Neurotransmitters act locally and rapidly. When an electrical signal in the
form of an action potential arrives at the synaptic terminal, they diffuse
across the synaptic cleft (the gap between a sending neuron and a receiving
neuron or muscle cell). Once the neurotransmitters interact (bind) with
receptors on the receiving (post-synaptic) cell, the receptor stimulation is
transduced into a response such as continued electrical signaling or
modification of cellular response. The target cell responds within milliseconds
of receiving the chemical “message”; this response then ceases very quickly
once the neural signaling ends. In this way, neural communication enables body
functions that involve quick, brief actions, such as movement, sensation, and
cognition.In contrast, the endocrine system uses just one method of
communication: chemical signaling. These signals are sent by the endocrine
organs, which secrete chemicals—the hormone—into the extracellular fluid.
Hormones are transported primarily via the bloodstream throughout the body,
where they bind to receptors on target cells, inducing a characteristic
response. As a result, endocrine signaling requires more time than neural
signaling to prompt a response in target cells, though the precise amount of
time varies with different hormones. For example, the hormones released when
you are confronted with a dangerous or frightening situation, called the
fight-or-flight response, occur by the release of adrenal hormones—epinephrine and
norepinephrine—within seconds. In contrast, it may take up to 48 hours for
target cells to respond to certain reproductive hormones.
In addition,
endocrine signaling is typically less specific than neural signaling. The same
hormone may play a role in a variety of different physiological processes
depending on the target cells involved. For example, the hormone oxytocin
promotes uterine contractions in women in labor. It is also important in
breastfeeding, and may be involved in the sexual response and in feelings of
emotional attachment in both males and females. In general, the nervous system
involves quick responses to rapid changes in the external environment, and the
endocrine system is usually slower acting—taking care of the internal
environment of the body, maintaining homeostasis, and controlling reproduction
([link]). So how does the fight-or-flight response that was mentioned earlier
happen so quickly if hormones are usually slower acting?
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