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Brainstem’s involvement in motor process
The brainstem’s function in motor processing:
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It mediates motor (and sensation) control of the head, neck and face across the cranial nerves.
Specialized neurons in brainstem mediate parasympathetic reflexes, such increased peristaltis of the
gut, and constriction of the pupils.
The brainstem contains ascending and descending pathways that carry motor (and sensory)
information to other divisions of the central nervous system.
The input-output properties of motor neurons are modified by input from the brain stem.
The discharge rate of motor neurons depends on the magnitude of the depolarization generated by
excitatory inputs and the intrinsic membrane propereties of the motor neurons in spinal cord. These
properties can be profoundly modified by input from monoaminergic neurons in the brainstem.
Part of brainstem with role in motor process:
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Neuronal groups in medulla participate in control of neck and facial muscles
The ventral portion of the pons contains the pontine nuclei, groups of neurons that relay
information about movement (and sensation too) from the cerebral cortex to the cerebellum.
Noradrenergic cell groups in the pons send extensive projections to motor neurons.
This modulatory input facilitates excitatory inputs to motor neurons by acting on beta and alfa1
adrenergic receptors.
Sum of these effects is to facilitate motor neuron responses in steretypic and repetitive behaviors
such as thythmic chewing,swimming or locomotion.
Nuclei in midbrain provide important linkages between components of the motor system,
particularly the cerebellum, basal ganglia, and cerebral hemipheres.
Cranial nerves:
Cranial nerves from III. to XII. arise from the brainstem, III, IV,VI,XI,XII are motor, the others are mixed
nerves.
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The occular motor nerves (III.,IV.,VI.) control movements of the eyes
The spinal accessory nerve (XI.) is purely motor and originates from motor neurons in the upper
cervical spinal cord. It innervates the trapesius and sternocleidomatoid muscles on the same side of
the body.
The hypoglossal nerve (XII.) is also purely motor, innervating the muscles of the tongue.
Nuclei of brainstem:
Cranial nerve nuclei are organized in rostrocaudal coumns like laminae of the spinal cord.The
brainstem’s nuclei are divided into general nuclei, wich serve functions similar to those of laminea, and
special nuclei, which serve functions unique to the head.
The nuclei on each side are organized in six rostrocaudal columns, three of sensory nuclei and three of
motor nuclei.
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General visceral motor column:
It contains preganglionic neurons that control eye movements and parasymphatetic preganglionic
neurons that innervate multiple regions of parasymphatetic system.
Special Visceral Motor Column
TheseI nuclei innervates muscles of mastication,facial expression, larynx pharynx.