No Motor Pathways 1. Motor Pathways

Ⅱ. The Motor (descending) Pathways The motor pathways are concerned with motor function, and composed of upper motor neurons and lower motor neurons. The upper motor neurons are the efferent neurons from the cerebral cortex to the motor nuclei of cranial nerves and anterior horns of spinal cord. The lower motor neurons are the nerves in the motor nuclei of cranial nerves and the anterior horns of spinal cord. The cell bodies and axons of lower motor neurons serve as the final common pathway connecting motor impulses. The motor pathways are concerned with motor function, and composed of upper motor neurons and lower motor neurons. The upper motor neurons are the efferent neurons from the cerebral cortex to the motor nuclei of cranial nerves and anterior horns of spinal cord. The lower motor neurons are the nerves in the motor nuclei of cranial nerves and the anterior horns of spinal cord. The cell bodies and axons of lower motor neurons serve as the final common pathway connecting motor impulses. The motor pathways include pyramidal and extrapyramidal systems. The motor pathways include pyramidal and extrapyramidal systems.

Ⅰ ) The Pyramidal System It is concerned with the voluntary movement of the skeletal muscles and is composed of two orders of neurons, i.e. the upper and lower motor neurons. It is concerned with the voluntary movement of the skeletal muscles and is composed of two orders of neurons, i.e. the upper and lower motor neurons. The upper motor neurons are composed of the giant pyramidal cells (Betz cells) and other pyramidal cells of various sized which are located in the precentral gyrus and the anterior part of paracentral lobule and the pyramidal cells in the some areas of frontal, parietal lobes. The upper motor neurons are composed of the giant pyramidal cells (Betz cells) and other pyramidal cells of various sized which are located in the precentral gyrus and the anterior part of paracentral lobule and the pyramidal cells in the some areas of frontal, parietal lobes.

Their axons form the descending pyramidal tract, among which, the fibers ending in the cranial motor nuclei are designated as the corticonuclear tract and those terminating in the anterior horn of the spinal cord as corticospinal tract. Their axons form the descending pyramidal tract, among which, the fibers ending in the cranial motor nuclei are designated as the corticonuclear tract and those terminating in the anterior horn of the spinal cord as corticospinal tract. The lower motor neurons include the cranial motor cells of the brain stem and spinal motor cells of the spinal cord. The lower motor neurons include the cranial motor cells of the brain stem and spinal motor cells of the spinal cord.

1. The corticospinal tract The upper motor neurons are the pyramidal pyramidal cells in the superior and middle parts of the precentral gyrus and the anterior part of paracentral lobule. The upper motor neurons are the pyramidal pyramidal cells in the superior and middle parts of the precentral gyrus and the anterior part of paracentral lobule. The axons arising from these upper motor neurons form the corticospinal tract. The axons arising from these upper motor neurons form the corticospinal tract.

It traverses the posterior limb of internal capsule, the intermediate 3/5 of the crus cerebri, the basilar part of the pons, and the ventral part of the medulla oblongata. In the caudal part of the medulla oblongata the greater part (75-90%) of the tract crosses to the opposite side to form the pyramidal decussation and continues as the lateral corticospinal tract in the lateral funiculus of the spinal cord. The fibers of the lateral corticospinal tract terminate in the anterior gray horns of all the spinal segments controlling the movements of muscles of the limbs. It traverses the posterior limb of internal capsule, the intermediate 3/5 of the crus cerebri, the basilar part of the pons, and the ventral part of the medulla oblongata. In the caudal part of the medulla oblongata the greater part (75-90%) of the tract crosses to the opposite side to form the pyramidal decussation and continues as the lateral corticospinal tract in the lateral funiculus of the spinal cord. The fibers of the lateral corticospinal tract terminate in the anterior gray horns of all the spinal segments controlling the movements of muscles of the limbs.

The non-crossed fibers continue as the anterior corticospinal tract directly into the anterior funiculus of the same side and cross the median plane in the anterior white commissure and synapse, as do those of the lateral tract, directly or indirectly with the motor neurons of the anterior gray horn. The anterior corticospinal tract is generally believed to exist above the level of the mid-thoracic segments, controlling the muscles of trunk and limbs. A small part in the anterior corticospinal tract do not crosses to the opposite side, terminating in the ipilateral anterior horns of the spinal cord. These uncrossed fibers innervate the trunk muscles by way of the motor cells of the anterior gray horn. So that the trunk muscles are controlled by bilateral motor cortex of the hemisphere. The non-crossed fibers continue as the anterior corticospinal tract directly into the anterior funiculus of the same side and cross the median plane in the anterior white commissure and synapse, as do those of the lateral tract, directly or indirectly with the motor neurons of the anterior gray horn. The anterior corticospinal tract is generally believed to exist above the level of the mid-thoracic segments, controlling the muscles of trunk and limbs. A small part in the anterior corticospinal tract do not crosses to the opposite side, terminating in the ipilateral anterior horns of the spinal cord. These uncrossed fibers innervate the trunk muscles by way of the motor cells of the anterior gray horn. So that the trunk muscles are controlled by bilateral motor cortex of the hemisphere.

The lower motor neurons are the large multipolar cells of the anterior gray horn. The lower motor neurons are the large multipolar cells of the anterior gray horn. They give rise to the motor fibers that leave the spinal cord through the anterior roots to be distributed by way of the spinal nerves to the skeletal muscles. They give rise to the motor fibers that leave the spinal cord through the anterior roots to be distributed by way of the spinal nerves to the skeletal muscles. Because of the inhibitory functions of the upper motor neurons to the lower ones, there are different clinical signs in the cases of damage to the upper or lower motor neurons Because of the inhibitory functions of the upper motor neurons to the lower ones, there are different clinical signs in the cases of damage to the upper or lower motor neurons

2. The corticonuclear tract The upper motor neurons are the giant pyramidal and certain other smaller pyramidal neurons in the inferior part of the precentral gyrus. The upper motor neurons are the giant pyramidal and certain other smaller pyramidal neurons in the inferior part of the precentral gyrus. The axons arising from these upper motor neurons form the corticonuclear tract. The axons arising from these upper motor neurons form the corticonuclear tract.

In the course of descending through the genu of internal capsule and the brain stem, it give rise to the collaterals of the bilateral oculomotor, trochlear, trigeminal motor, ambiguous, accessory nuclei and superior part of the facial nucleus, and to the contralateral hypoglossal nucleus and the inferior part of the facial nucleus. So, the hypoglossal nucleus and inferior part of the facial nucleus receive the fibers only from the contralateral corticonuclear tract. In the course of descending through the genu of internal capsule and the brain stem, it give rise to the collaterals of the bilateral oculomotor, trochlear, trigeminal motor, ambiguous, accessory nuclei and superior part of the facial nucleus, and to the contralateral hypoglossal nucleus and the inferior part of the facial nucleus. So, the hypoglossal nucleus and inferior part of the facial nucleus receive the fibers only from the contralateral corticonuclear tract.

The lower neurons are the cells in the above cranial motor nuclei. The lower neurons are the cells in the above cranial motor nuclei. The lower neurons give rise to axons joining the corresponding cranial nerves that control the movements of the innervated skeletal muscles. The lower neurons give rise to axons joining the corresponding cranial nerves that control the movements of the innervated skeletal muscles. Because the inferior part of the facial nucleus and hypoglossal nucleus receive fibers just from the contralateral corticonuclear tract, the injury of the unilateral corticonuclear tract can usually cause paralysis of the contralateral glossal muscles and facial muscles below the palpebral fissure. This is designated as supranuclear paralysis. Because the inferior part of the facial nucleus and hypoglossal nucleus receive fibers just from the contralateral corticonuclear tract, the injury of the unilateral corticonuclear tract can usually cause paralysis of the contralateral glossal muscles and facial muscles below the palpebral fissure. This is designated as supranuclear paralysis.

Paralysis of the unilateral facial muscles caused by an injury of the homolateral facial nerve is termed as infranuclear paralysis. Paralysis of the unilateral facial muscles caused by an injury of the homolateral facial nerve is termed as infranuclear paralysis. Form 1. The comparison of expressions after injury to the upper and lower motor neurons Form 1. The comparison of expressions after injury to the upper and lower motor neurons

Upper motor neurons (suppranuclear paralysis) Lower motor neurons (infranuclear paralysis) Injured sites ① Pyramidal cell body (Precentral gyrus and the paracentral lobule) ② Pyramidal tract (Corticonuclear tract Corticospinal tract) ① Cranial motor nuclei, Motor neurons of the anterior gray horn. ② Cranial nerves, Spinal nerves Spinal nerves Paralytic characteristic Hard paralysis Spasmoparalysis Central paralysis Soft paralysis Flaccid paralysis Peripheral paralysis Muscular tonicity IncreasingDecreasing Deep reflex Hyperfunction Decreasing or disappear Superficial reflex Decreasing or disappear Pathological reflexes Existence (+) (Babinski sign) Nonentity (-) Muscular atrophy Not have (-) Have (+)

Ⅱ ) The Extrapyramidal System It is a common name for the descending pathways regulating and controlling the voluntary movements except the pyramidal system. It is a common name for the descending pathways regulating and controlling the voluntary movements except the pyramidal system. Functions: Functions: The main functions of the extrapyramidal system in man are to regulate the tonicity of the muscles, coordinate the muscular activities, maintain the normal body posture and produce habitual and rhythmic movements. For example, riding and running are initiated in the beginning by the pyramidal system, but are controlled by the extrapyramidal system when the motions later become habitual and rhythmic. The main functions of the extrapyramidal system in man are to regulate the tonicity of the muscles, coordinate the muscular activities, maintain the normal body posture and produce habitual and rhythmic movements. For example, riding and running are initiated in the beginning by the pyramidal system, but are controlled by the extrapyramidal system when the motions later become habitual and rhythmic.

So the skeletal muscular movements are controlled by the cortex of the hemisphere by way of the pyramidal and extrapyramidal systems to produce coordinated, precise motions. The two systems have the coordinated and dependent functions with each other. So the skeletal muscular movements are controlled by the cortex of the hemisphere by way of the pyramidal and extrapyramidal systems to produce coordinated, precise motions. The two systems have the coordinated and dependent functions with each other.

Structures of the extrapyramidal system are very complicated including cerebral cortex (somatic motor area and somatic sensory area), corpus striatum, dorsal thalamus, subthalamic nucleus, tectum of midbrain, red nucleus, substantia nigra, pontine nucleus, vestibular nucleus, cerebellum, reticular formation of brain stem, and their fibrous connections. Structures of the extrapyramidal system are very complicated including cerebral cortex (somatic motor area and somatic sensory area), corpus striatum, dorsal thalamus, subthalamic nucleus, tectum of midbrain, red nucleus, substantia nigra, pontine nucleus, vestibular nucleus, cerebellum, reticular formation of brain stem, and their fibrous connections.

1. The cortex-neostriatum-thalamus-cortical circuit 1. The cortex-neostriatum-thalamus-cortical circuit The somatic motor and sensory areas in the cerebral cortex The somatic motor and sensory areas in the cerebral cortex ↓ (corticotriatum fibers) ↓ (corticotriatum fibers) neorstriatum neorstriatum ↓ (striatopallidal fibers) ↓ (striatopallidal fibers) globus pallidus globus pallidus ↓ (globus pallidothalamus fibers) ↓ (globus pallidothalamus fibers) ventral anterior nucleus and ventral lateral nucleus ventral anterior nucleus and ventral lateral nucleus ↓ dorsal thalamus dorsal thalamus ↓ (internal capsule) ↓ (internal capsule) the somatic motor area in the cerebral cortex. the somatic motor area in the cerebral cortex.

2. The neostriatum-substantia nigra circuit 2. The neostriatum-substantia nigra circuit The caudate nucleus and putamen → substantia nigra → caudate nucleus and putamen. The caudate nucleus and putamen → substantia nigra → caudate nucleus and putamen. Recent researches indicate that the cause of Parkinsonism is degeneration of the substantia nigra and reduction of dopamine in the corpus striatum. Lesions of the substantia nigra and globus pallidus cause Parkinsonism which manifests muscular stiffness and a coarse tremor, especially involving the more distal extremities. Recent researches indicate that the cause of Parkinsonism is degeneration of the substantia nigra and reduction of dopamine in the corpus striatum. Lesions of the substantia nigra and globus pallidus cause Parkinsonism which manifests muscular stiffness and a coarse tremor, especially involving the more distal extremities.

3. The cortex-pons-cerebellum-cortical circuit 3. The cortex-pons-cerebellum-cortical circuit The frontal, parietal, occipital, and temporal lobes in the cerebral cortex. (corticopontine fibers: frontopontine, parietopontine, occippitopontine and temporopontine tracts) ↓ pontine nuclei (pontocerebellar tract) pontine nuclei (pontocerebellar tract) ↓ cerebellar cortex cerebellar cortex ↓ dentate nucleus dentate nucleus (crossing) ↓ ↓ (crossing) (crossing) ↓ ↓ (crossing) (superior cerebellar peduncle) ↓ ↓ (middle cerebellar peduncle) (superior cerebellar peduncle) ↓ ↓ (middle cerebellar peduncle) red nucleus dorsal thalamus red nucleus dorsal thalamus (corssing) ↙ (ventral anterior and lateral nuclei) (corssing) ↙ (ventral anterior and lateral nuclei) (rubrospinal tract) ↙ ↘ (rubrospinal tract) ↙ ↘ motor cells in the anterior horn somatic motor area in cerebral cortex motor cells in the anterior horn somatic motor area in cerebral cortex

In the extrapyramidal system, cerebellum plays an important part in the coordination and regulation of large movement complexes including posture and equilibrium adjustments In the extrapyramidal system, cerebellum plays an important part in the coordination and regulation of large movement complexes including posture and equilibrium adjustments Injury of the route, at any levels, causes the loss of the above functions. Injury of the route, at any levels, causes the loss of the above functions.