Term
T or F
Descending pathways consist of axons (mostly myelinated) arising from neuronal cell bodies in supraspinal structures (cortex and brainstem) that synapse on neurons in the gray mater of the spinal cord. |
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Definition
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| The descending motor pathways work directly (monosynaptically, the minority) and indirectly (through interneurons, the majority) on what neurons of the ventral horn of the spinal cord? |
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| On alpha and gamma motor neurons. Also acting on alpha and gamma motor neurons are the segmental inputs from cutaneous afferents, muscle spindles and tendon organs. |
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| The descending pathways may be ________ to some motor neurons and ________ to other motor neurons (depending upon spatial and temporal summation of thousands of inputs from inhibitory and excitatory interneurons that synapse with the motor neurons). |
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| Include alpha and gamma motor neurons (and their axons) which innervate extrafusal muscle (alpha) and intrafusal muscle (of the spindle, gamma), respectively. Lower motor neurons also include the cranial nerve neurons (and their axons) that innervate muscles of the face (facial expression), muscles of mastication, tongue, etc. |
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| Include the descending motor pathways described below. The term "pyramidal system" basically refers to the corticospinal tract; named because the corticospinal tract passes through and forms the pyramids of the medulla. The term "extrapyramidal system" is an old-fashioned term that is still used sometimes. It refers to several other descending pathways (e.g., rubrospinal tract, reticulospinal tract, vestibulospinal tract). The extrapyramidal system also includes the motor contribution of the basal ganglia. Corticospinal tract neurons and axons are upper motor neurons for spinal cord (lower) ventral horn motor neurons. Corticobulbar neurons and axons are the upper motor neurons for many of the cranial nerves and nuclei with motor function (these cranial nerves and nuclei are also considered lower motor neurons). |
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| the corticospinal tract; named because the corticospinal tract passes through and forms the pyramids of the medulla |
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| Refers to several other descending pathways (e.g., rubrospinal tract, reticulospinal tract, vestibulospinal tract). The extrapyramidal system also includes the motor contribution of the basal ganglia. |
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| Corticospinal tract neurons and axons are... |
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Definition
| Upper motor neurons for spinal cord (lower) ventral horn motor neurons. |
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| Corticobulbar neurons and axons are... |
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Definition
| the upper motor neurons for many of the cranial nerves and nuclei with motor function (these cranial nerves and nuclei are also considered lower motor neurons). |
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Definition
1. The largest and clinically most important descending motor tract, also known as the pyramidal tract.
2. Fibers consist of upper motor neurons whose cell bodies lie mostly in the primary motor cortex (pre-central gyrus, area 4, primarily from the body regions of the homunculus) and area 6. Their axons descend through the corona radiata, become tightly packed in the internal capsule, descend through the cerebral peduncles of the midbrain, continue through the pons, to the medulla where 85-90% of the fibers cross (decussate) in the pyramids of the medulla.
3. The crossed fibers continue to descend to all levels of the spinal cord as the lateral corticospinal tract in the lateral funiculus, medial to the dorsal spinocerebellar tract.
4. Only 3-5% of the lateral corticospinal tract fibers have monosynaptic input to motor neurons. The vast majority work through interneurons to activate alpha (and gamma) motor neurons of lamina IX, to achieve fine, manipulative movements.
5. The 10-15% of uncrossed corticospinal tract fibers descend in the anterior funiculus as the anterior corticospinal tract (some of which cross back at the segmental level at which they terminate onto interneurons that synapse with alpha and gamma motor neurons).
6. The lateral corticospinal tract is universally regarded as the descending pathway most concerned with voluntary, discrete, skilled movements (e.g., piano playing, typing, playing Nintendo).
7. The anterior corticospinal tract projects mainly to the cervical and upper thoracic spinal cord and controls bilateral axial musculature |
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| known as the pyramidal tract... |
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Definition
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| The lateral corticospinal tract is universally regarded as... |
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| the descending pathway most concerned with voluntary, discrete, skilled movements (e.g., piano playing, typing, playing Nintendo). |
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| The anterior corticospinal tract projects mainly to... |
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Definition
| the cervical and upper thoracic spinal cord and controls bilateral axial musculature |
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Definition
1. Fibers arise from neurons in the face region of motor cortex; descend through corona radiata, internal capsule.
2. Project to and synapse with motor nuclei of cranial nerves in the brainstem. Cranial nerves: III (oculomotor; Eye movment), IV (trochlear; eye movement), V (trigeminal; muscles of mastication), VI (abducens; eye movement), VII (facial; muscles of facial expression), IX (glossopharyngeal; swallowing), X (vagus; swallowing and speech), XI (accessory; sternomastoid & trapezius muscles) and XII (hypoglossal; tongue movements).
3. Most of these projections are crossed. Those to the facial nucleus are bilateral. |
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| Corticobulbar Tracts project to and synapse with motor nuclei of cranial nerves in the brainstem. Cranial nerves: |
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Definition
| : III (oculomotor; Eye movment), IV (trochlear; eye movement), V (trigeminal; muscles of mastication), VI (abducens; eye movement), VII (facial; muscles of facial expression), IX (glossopharyngeal; swallowing), X (vagus; swallowing and speech), XI (accessory; sternomastoid & trapezius muscles) and XII (hypoglossal; tongue movements). |
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| Most of the corticobulbar tracts are crossed or uncrossed? |
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Definition
| Crossed and those to the facial nucleus are bilateral. |
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Definition
1. Cells bodies are in the red nucleus in the midbrain. All fibers cross to the opposite side in the ventral tegmentum of the midbrain as they exit the red nucleus.
2. Rubrospinal tract fibers are just anterior to the lateral corticospinal tract in the lateral funiculus of the spinal cord.
3. Fibers terminate at all spinal levels, but most terminate in the cervical segments. Rubrospinal fibers synapse onto interneurons that then excite or inhibit spinal motor neurons.
4. The red nucleus receives input from both the cerebral cortex and the cerebellum.
5. The rubrospinal tract and, more importantly in humans, the reticulospinal tracts (described below), are alternate routes for achieving voluntary movement.
6. In humans the rubrospinal tract is relatively small. It is thought to function in control of skilled dexterous movements of the upper extremity. Redundant tract. |
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| All fibers in the Rubrospinal Tract cross or uncross? |
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Definition
| Cross to the opposite side in the ventral tegmentum of the midbrain as they exit the red nucleus. |
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| Rubrospinal tract fibers are just ______ to the lateral corticospinal tract in the lateral funiculus of the spinal cord? |
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| humans the rubrospinal tract is relatively small. It is thought to function in control of... |
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Definition
| skilled dexterous movements of the upper extremity. Redundant tract. |
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Definition
The two large brainstem reticular formation regions in the pons and in the medulla give rise to the pontine (medial) reticulospinal tract and the medullary (lateral) reticulospinal tract, respectively.
1. Medullary (lateral) reticulospinal tract
A. The medullary (lateral) reticulospinal tract descends both crossed and uncrossed in the anterior funiculus of the spinal cord to all spinal levels.
B. This pathway acts primarily on gamma but also on alpha motor neurons.
C. In general, the lateral reticulospinal tract is thought to inhibit lower extremity extensors and facilitate flexors, reducing muscle tone in the lower extremities.
2. Pontine (medial) reticulospinal tract
A. Descends mostly uncrossed in the anterior funiculus of the spinal cord to all spinal levels.
B. This pathway facilitates lower extremity extensor (alpha and gamma) motor neurons, increasing muscle tone, especially to musculature of the lower extremity. |
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Term
| The two large brainstem reticular formation regions in the pons and in the medulla give rise to... |
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Definition
| the pontine (medial) reticulospinal tract and the medullary (lateral) reticulospinal tract, respectively. |
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| Medullary (lateral) reticulospinal tract |
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Definition
A. The medullary (lateral) reticulospinal tract descends both crossed and uncrossed in the anterior funiculus of the spinal cord to all spinal levels.
B. This pathway acts primarily on gamma but also on alpha motor neurons.
C. In general, the lateral reticulospinal tract is thought to inhibit lower extremity extensors and facilitate flexors, reducing muscle tone in the lower extremities. |
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| Pontine (medial) reticulospinal tract |
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Definition
A. Descends mostly uncrossed in the anterior funiculus of the spinal cord to all spinal levels.
B. This pathway facilitates lower extremity extensor (alpha and gamma) motor neurons, increasing muscle tone, especially to musculature of the lower extremity. |
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Term
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Definition
, a lateral vestibulospinal tract (LVST) and a medial vestibulospinal tract (MVST). These arise as the descending output from two of the four vestibular nuclei in the floor of the fourth ventricle of the pons and medulla. Inputs to the vestibular nuclei include the vestibular component of cranial nerve VIII (vestibulocochlear) and the cerebellum. The vestibulospinal pathways are sometimes called postural pathways. Activity of the LVST and MVST is important in support of the body against gravity and for the maintenance of upright posture.
In addition to the descending outputs from the vestibular nuclei (i.e., the LVST and MVST), there is also an ascending output by way of the ascending portion of the medial longitudinal fasciculus (MLF) to motor nuclei of cranial nerves III (oculomotor), IV (trochlear), and VI (abducens), for coordination of eye and head movements in the vestibuloocular reflex (to be discussed in the lecture on the vestibular system). |
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| Lateral Vestibulospinal Tract |
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Definition
A. Arises from cell bodies in the lateral vestibular nucleus (also called Deiter's nucleus). The pathway descends uncrossed in the anterior funiculus.
B. The LVST neurons terminate at all levels of the spinal cord where they act via interneurons to facilitate extensor alpha and gamma motor neurons of the lower extremities and flexors of the upper extremities. These muscle groups are antigravity muscles and the LVST is the primary antigravity pathway. |
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| Medial Vestibulospinal Tract |
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Definition
Arises from the medial vestibular nucleus. Descends in the descending portion of the MLF to terminate primarily on motor neurons in the cervical and upper thoracic levels.
B. The primary function of the MVST is to inhibit upper extremity extensors and facilitate flexors (i.e., antigravity muscles). |
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Term
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Definition
1. Arises from cell bodies in the superior colliculus of the midbrain tectum. All fibers cross in the tegmentum of the midbrain and enter the descending portion of the MLF, running along with the medial vestibulospinal tract in the upper cervical spinal cord.
2. Most fibers terminate in the upper four cervical segments of the spinal cord on interneurons that have input to motor neurons to neck musculature.
3. The function of the tectospinal tract is to mediate reflex postural movements of the head and neck in response to novel visual stimuli.
This is the pathway that turns your head to orient to visual stimuli. Has gotten ppl into troubled! |
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| Is the spinal cord segmented? |
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Definition
Yes.
A. For the motor system, this means that axons of descending pathways terminate (synapse) on neurons (interneurons and ventral horn motoneurons) at different spinal cord levels (i.e. C1, C2, C3, etc.).
B. The ventral horn motoneurons at each spinal level then project their axons out through the ventral root and become part of the spinal root and peripheral nerves innervating a particular muscle. |
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| Can limb muscles be supplied by several ventral roots? |
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| Most of the larger muscles, especially limb muscles are supplied by several ventral roots (i.e the biceps is innervated by spinal cord levels C5-C6). This means that the ventral horn motoneurons that send axons to synapse on the biceps muscles are located at C5 and C6. In addition the segmental muscular nerve supplies overlap as do dermatomes (i.e. The biceps is innervated by C5 & C6 and the triceps is innervated by C6, C7, & C8) |
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| Paresis (partial paralysis or weakness) occurs if... |
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Definition
| only one or two ventral roots are damaged. |
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| all roots innervating a particular muscle are destroyed. [Paralysis can also occur when upper motor neurons (e.g., corticospinal tract neurons) are damaged as in stroke]. |
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| The diaphragm is innervated by... |
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| C3, C4, and C5. Spinal cord lesions above the C3 level denervate the diaphragm and leave the patient ventilator-dependent. |
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| Most spinal cord lesions will affect control of bladder and bowel since... |
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Definition
| these are innervated by very low spinal cord segments (S2, S3, and S4). |
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Term
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Definition
| 12-20 microns, 15-120 velocity, Innervates extrafusal skeletal muscle fibers (i.e., the motor unit); heavily myelinated |
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Term
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Definition
| 2-10 microns, 10-45 velocity, Innervates intrafusal muscle fibers of muscle spindle; myelinated |
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Term
autonomic pre-ganglionic
(B motor) |
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Definition
~3 microns, 3-15 velocity, pre-ganglionic autonomic fibers; lightly
myelinated |
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autonomic post-ganglionic
(C motor) |
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Definition
| ~1 microns, 2 velocity, post-ganglionic autonomic fibers; unmyelinated |
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