Whereas
imaging technology, like magnetic resonance imaging (MRI) or computed
tomography (CT) scanning, could localize the injury as well, nothing more
complicated than a cotton-tipped applicator can localize the damage. That may
be all that is available on the scene when moving the victim requires crucial
decisions be made. The sensory and motor exams assess function related to the
spinal cord and the nerves connected to it. Sensory functions are associated
with the dorsal regions of the spinal cord, whereas motor function is
associated with the ventral side. Localizing damage to the spinal cord is
related to assessments of the peripheral projections mapped to dermatomes.
Sensory tests address the various submodalities of the somatic senses: touch,
temperature, vibration, pain, and proprioception. Results of the subtests can
point to trauma in the spinal cord gray matter, white matter, or even in
connections to the cerebral cortex. Motor tests focus on the function of the
muscles and the connections of the descending motor pathway. Muscle tone and
strength are tested for upper and lower extremities. Input to the muscles comes
from the descending cortical input of upper motor neurons and the direct
innervation of lower motor neurons. Reflexes can either be based on deep
stimulation of tendons or superficial stimulation of the skin. The presence of
reflexive contractions helps to differentiate motor disorders between the upper
and lower motor neurons.
The specific signs associated with Nooflex motor disorders can
establish the difference further, based on the type of paralysis, the state of
muscle tone, and specific indicators such as pronator drift or the Babinski
sign. The role of the cerebellum is a subject of debate. There is an obvious
connection to motor function based on the clinical implications of cerebellar
damage. There is also strong evidence of the cerebellar role in procedural
memory. The two are not incompatible; in fact, procedural memory is motor
memory, such as learning to ride a bicycle. Significant work has been performed
to describe the connections within the cerebellum that result in learning. A
model for this learning is classical conditioning, as shown by the famous dogs
from the physiologist Ivan Pavlov’s work. This classical conditioning, which
can be related to motor learning, fits with the neural connections of the
cerebellum. The cerebellum is 10 percent of the mass of the brain and has
varied functions that all point to a role in the motor system. The cerebellum
is located in apposition to the dorsal surface of the brain stem, centered on
the pons. The name of the pons is derived from its connection to the
cerebellum. The word means “bridge” and refers to the thick bundle of
myelinated axons that form a bulge on its ventral surface. Those fibers are
axons that project from the gray matter of the pons into the contralateral
cerebellar cortex. These fibers make up the middle cerebellar peduncle (MCP)
and are the major physical connection of the cerebellum to the brain stem
([link]). Two other white matter bundles connect the cerebellum to the other
regions of the brain stem. The superior cerebellar peduncle is the connection
of the cerebellum to the midbrain and forebrain.
The inferior cerebellar
peduncle is the connection to the medulla. The connections to the cerebellum
are the three cerebellar peduncles, which are close to each other. The ICP
arises from the medulla—specifically from the inferior olive, which is visible
as a bulge on the ventral surface of the brain stem. The MCP is the ventral
surface of the pons. The SCP projects into the midbrain. These connections can
also be broadly described by their functions. The ICP conveys sensory input to
the cerebellum, partially from the spinocerebellar tract, but also through
fibers of the inferior olive. The MCP is part of the cortico-ponto-cerebellar
pathway that connects the cerebral cortex with the cerebellum and
preferentially targets the lateral regions of the cerebellum. It includes a
copy of the motor commands sent from the precentral gyrus through the
corticospinal tract, arising from collateral branches that synapse in the gray
matter of the pons, along with input from other regions such as the visual cortex.
The SCP is the major output of the cerebellum, divided between the red nucleus
in the midbrain and the thalamus, which will return cerebellar processing to
the motor cortex. These connections describe a circuit that compares motor
commands and sensory feedback to generate a new output. These comparisons make
it possible to coordinate movements. If the cerebral cortex sends a motor
command to initiate walking, that command is copied by the pons and sent into
the cerebellum through the MCP. Sensory feedback in the form of proprioception
from the spinal cord, as well as vestibular sensations from the inner ear,
enters through the ICP. If you take a step and begin to slip on the floor
because it is wet, the output from the cerebellum—through the SCP—can correct
for that and keep you balanced and moving.
The red nucleus sends new motor
commands to the spinal cord through the rubrospinal tract. The cerebellum is
divided into regions that are based on the particular functions and connections
involved. The midline regions of the cerebellum, the vermis and flocculonodular
lobe, are involved in comparing visual information, equilibrium, and
proprioceptive feedback to maintain balance and coordinate movements such as
walking, or gait, through the descending output of the red nucleus ([link]).
The lateral hemispheres are primarily concerned with planning motor functions
through frontal lobe inputs that are returned through the thalamic projections
back to the premotor and motor cortices. Processing in the midline regions
targets movements of the axial musculature, whereas the lateral regions target
movements of the appendicular musculature. The vermis is referred to as the
spinocerebellum because it primarily receives input from the dorsal columns and
spinocerebellar pathways. The flocculonodular lobe is referred to as the
vestibulocerebellum because of the vestibular projection into that region.
Finally, the lateral cerebellum is referred to as the cerebrocerebellum,
reflecting the significant input from the cerebral cortex through the
cortico-ponto-cerebellar pathway. Major Regions of the Cerebellum The left
panel of this figure shows the midsagittal section of the cerebellum, and the
right panel shows the superior view. In both panels, the major parts are
labeled. The cerebellum can be divided into two basic regions: the midline and
the hemispheres. The midline is composed of the vermis and the flocculonodular
lobe, and the hemispheres are the lateral regions. Coordination and Alternating
Movement Testing for cerebellar function is the basis of the coordination exam.
The subtests target appendicular musculature, controlling the limbs, and axial
musculature for posture and gait. The assessment of cerebellar function will
depend on the normal functioning of other systems addressed in previous
sections of the neurological exam. Motor control from the cerebrum, as well as
sensory input from somatic, visual, and vestibular senses, are important to
cerebellar function. The subtests that address appendicular musculature, and therefore
the lateral regions of the cerebellum, begin with a check for tremor. The
patient extends their arms in front of them and holds the position. The
examiner watches for the presence of tremors that would not be present if the
muscles are relaxed. By pushing down on the arms in this position, the examiner
can check for the rebound response, which is when the arms are automatically
brought back to the extended position. The extension of the arms is an ongoing
motor process, and the tap or push on the arms presents a change in the
proprioceptive feedback. The cerebellum compares the cerebral motor command
with the proprioceptive feedback and adjusts the descending input to correct.
The red nucleus would send an additional signal to the LMN for the arm to increase
contraction momentarily to overcome the change and regain the original
position. The check reflex depends on cerebellar input to keep increased
contraction from continuing after the removal of resistance. The patient flexes
the elbow against resistance from the examiner to extend the elbow. When the
examiner releases the arm, the patient should be able to stop the increased
contraction and keep the arm from moving.
A similar response would be seen if
you try to pick up a coffee mug that you believe to be full but turns out to be
empty. Without checking the contraction, the mug would be thrown from the
overexertion of the muscles expecting to lift a heavier object. Several
subtests of the cerebellum assess the ability to alternate movements, or switch
between muscle groups that may be antagonistic to each other. In the
finger-to-nose test, the patient touches their finger to the examiner’s finger
and then to their nose, and then back to the examiner’s finger, and back to the
nose. The examiner moves the target finger to assess a range of movements. A
similar test for the lower extremities has the patient touch their toe to a
moving target, such as the examiner’s finger. Both of these tests involve
flexion and extension around a joint—the elbow or the knee and the shoulder or
hip—as well as movements of the wrist and ankle. The patient must switch
between the opposing muscles, like the biceps and triceps brachii, to move
their finger from the target to their nose. Coordinating these movements
involves the motor cortex communicating with the cerebellum through the pons
and feedback through the thalamus to plan the movements.
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