Nervous System
Motor Speech Disorders
- Nervous System
- Neuron - The neuron is the basic functional unit of
the nervous system. Neural transmission is a function basic to
the nervous system, and the neuron with its processes serves as
a basic conductive unit of the nervous system. Most of the
neurons conduct neural impulses to other neurons
- Basic components (Figure 3.30)
- Soma - cell body
- Dendrites - receives neural stimuli, shorter and
more numerous projections of the nerve cell
- Axons - conducts nerve impulses away from the
neuron to other parts, longer single fiber
- Synapse - is a juncture point at which electrical
impulses are transmitted from nerve to muscle, gland, or
another neuron.
- Myelin - is composed of Schwann cells., which
enhances rapid transmission of electrical impulse along the
nerve fiber. On the average, a myelinated transmission along
fiber is roughly 50 times as fast as one along an
unmyelinated fiber.
- Central Nervous System (CNS, Figure 3.32 in Text)- the
brain and spinal cord make up the CNS.
- Cerebral Cortex - Motor Cortex -The motor impulses
generated at the cortical level are relatively crude, but they
become integrated and coordinated as they pass through the
subcortical structures. This motor area is responsible for the
motor gestures that account for all of our voluntary movements.
- Apraxia results from involvement of the third frontal
convolution (unilateral left hemisphere), Broca's area.
There is a possibility of apraxia following more posterior,
probably parietal lesions. More importantly, lesions that
result in apraxia, like lesions that result in aphasia, are
not discrete and create a situation where apraxia and
aphasia coexist.
- Pyramidal System (Upper Motor Neurons, see Figure 2
below)- voluntary movement of the muscles of speech in
controlled primarily by the pyramidal system. It is the major
voluntary pathway for all movement. It is made up of the
corticospinal tract, and corticobulbar tract.
- Subcortical Structures - Basal Ganglia - The
principal structures for motor integration, responsible for
smooth, coordinated movement, are the basal ganglia, and
cerebellum.
- Brainstem - appear as series of structure that seem
to be upward extension of the spinal cord. Serves as the
connection between spinal cord and cerebrum. Origin of cranial
nerves. Nuclei of cranial nerves located in this region.
- Cerebellum- means little brain, it appears to be
important in coordinating extremely rapid and precise movement
needed for normal articulation of speech.
- Peripheral Nervous System
- The Cranial and Spinal Nerves for Speech and Hearing
(Figure 3.36) - The nuclei and axons of the cranial
and spinal nerves are termed lower motor neurons. or the final
common pathway. If they are destroyed, the muscles they serve
will be totally paralyzed and flaccid because no neural impulse
can access it . If this flaccidity involves the speech
mechanism, a form of dysarthria results. Neural signals
traveling the neural pathways make connections to the cranial
nerves, whose origins are in the pons or medulla. There are 12
cranial nerves, several of which are important for speech and
hearing. Cranial nerves arise from the brain and, with only one
exception, distribute their fibers to the head and neck. These
nerve transmit sensory and motor impulses, only sensory
impulses, or only motor impulses. Sensory-afferent: impulses
toward the brain. Motor-efferent: impulses away from the brain.
- Cranial Nerve V - Trigeminal - Sensory and motor;
controls the muscles of mastication.
- Cranial Nerve VII- Facial -Sensory and motor;
controls the muscles of mastication, including the
lips.
- Cranial Nerve VIII -Auditory -Sensory: serves the
sense of hearing.
- Cranial Nerve IX - Glossopharyngeal -Sensory and
motor; contributes to pharyngeal movement. Bilateral
innervation - single muscle not bilateral symmetry.
- Cranial Nerve X - Vagus -Sensory and motor;
contributes to movements of the pharynx and larynx and
serves a sensory function for pharynx, larynx, trachea,
bronchi, and lungs. Bilateral.
- Cranial Nerve XI - Spinal Accessory -Motor;
controls the movements of the muscles of the neck, thus
indirectly influencing the position of the larynx. Controls
turning of head & shrugging shoulders.
- Cranial Nerve XII - Hypoglossal -Motor; controls
the tongue movements. Bilateral except cells serving
genioglossus muscle; which receives only contralateral
fibers (Love, 127).
- Spinal Nerves are composed of nerves that extend
from the CNS. The Cranial Nerves subserve the head and neck,
and the spinal nerves innervate the rest of the body. The
spinal nerves and the extensions, called the peripheral
nerves, along with their branches, are one part of what is
called the PNS.
- The Neuromotor Control of Speech
- Upper Motor Neurons (see Figure 2 below)- all of the
neurons of the corticospinal and corticobulbar tracts are known
as upper motor neurons. Upper motor neurons care contained
within the brain, brainstem and spinal cord.
- UMN Paralysis - damage to corticospinal/corticobulbar
tract will produce spastic paralysis.
- Lower Motor Neurons (see Figure 2 below) - are
neurons that send motor axons into the peripheral nerves
-cranial and spinal nerves. There are second order neurons.
- LMN Paralysis - If a lesion is in a cranial or spinal
nerve, neural impulses will not be transmitted to the
muscles. This is called denervation. The result is flaccid
paralysis.
- Basal ganglia (Figure 3.32) - in conjunction with
the cerebellum , smooth out and coordinate all voluntary body
movements.
- Disorders of basal ganglia result in rigidity, jerky and
purposeless movements. Dyskinesias - refers to involuntary
movement disorders.
- Cerebellar System (Figure 3.32) - The principal
structures for motor integration, responsible for smooth,
coordinated movement, are the basal ganglia, and cerebellum.
- Cerebellar disorders result in awkwardness in gait, poor
coordination of intended movements, which is called
Ataxia.
