Podcast Beta
Questions and Answers
What is the arrangement of fibers in the internal capsule?
What percentage of fibers in the anterior or ventral CST remain uncrossed?
Where do the fibers of the lateral CST terminate?
What is the effect of lesions within the cerebral cortex above the pyramidal decussations?
Signup and view all the answers
What is the name of the tract that is formed by the crossing of fibers?
Signup and view all the answers
Which side of the motor strip controls the left half of the body?
Signup and view all the answers
What is the characteristic of the shorter tract in the CST system?
Signup and view all the answers
What is the result of a lower motor neuron lesion in the facial motor nucleus pathway?
Signup and view all the answers
Which of the following cranial nerves is purely sensory?
Signup and view all the answers
What is the location of the facial motor nucleus?
Signup and view all the answers
What is the result of an upper motor neuron lesion in the facial motor nucleus pathway?
Signup and view all the answers
What do the projection fibers from the basal nuclei ganglia terminate in?
Signup and view all the answers
What is the function of the corticoreticular fibers in the pons and medulla?
Signup and view all the answers
What is the characteristic of the innervations of the facial motor nucleus?
Signup and view all the answers
Where is the rubrospinal tract located?
Signup and view all the answers
What is the origin of the rubrospinal tract?
Signup and view all the answers
In which laminae does the rubrospinal tract terminate?
Signup and view all the answers
What is the function of the tectospinal and tectobulbar tracts?
Signup and view all the answers
What is the characteristic of the tract originating from the interstitial nucleus of Cajal?
Signup and view all the answers
Where does the tract originating from the interstitial nucleus of Cajal terminate?
Signup and view all the answers
What is the similarity in function between the tectospinal and tectobulbar tracts and the tract originating from the interstitial nucleus of Cajal?
Signup and view all the answers
Which nucleus is the origin of the medial vestibulospinal tract?
Signup and view all the answers
Where do the fibers of the medial vestibulospinal tract descend to?
Signup and view all the answers
Up to which level do the medial vestibulospinal tract fibers descend?
Signup and view all the answers
In which laminae do the medial vestibulospinal tract fibers terminate?
Signup and view all the answers
What type of afferents do the medial vestibulospinal tract receive?
Signup and view all the answers
What is the main function of the medial vestibulospinal tract?
Signup and view all the answers
Which motor neurons are excited by the medial vestibulospinal tract?
Signup and view all the answers
Which nucleus is associated with the Medial Vestibulospinal tract?
Signup and view all the answers
Where do the fibers of the Pontine Reticulospinal tract originate from?
Signup and view all the answers
What is the main function of the Vestibulospinal tract?
Signup and view all the answers
In which funiculus do the fibers of the Medial Vestibulospinal tract descend?
Signup and view all the answers
What is the effect of the Vestibulospinal tract on extensor motor neurons?
Signup and view all the answers
Which tract has a descending autonomic pathway?
Signup and view all the answers
In which spinal cord levels do the fibers of the Lateral Vestibulospinal tract terminate?
Signup and view all the answers
What is the origin of the Medullary Reticulospinal tract?
Signup and view all the answers
In which nucleus is the Reticulospinal tract associated?
Signup and view all the answers
What is the effect of the Reticulospinal tract on extensor motor neurons?
Signup and view all the answers
Study Notes
Internal Capsule
- Anterior limb: contains fibers controlling upper limbs
- Genu: contains fibers controlling lower extremities
- Posterior limb: contains fibers of the corticospinal tract (CST)
- CST fibers follow a somatotopic arrangement
Corticospinal Tract (CST)
- Divided into anterior (ventral) and lateral CST
- Anterior CST:
- Uncrossed fibers (10-15%)
- Eventually cross before terminating on anterior horn cells in cervical and upper thoracic spinal cord segments
- Shorter tract
- Lateral CST:
- Crossing of fibers (75-90%)
- Forms pyramidal decussations
- Terminates at the anterior gray column of all spinal cord segments
- Longer tract
- Pyramidal tract is a crossed tract:
- Right motor side controls left half of the body
- Left motor strip controls right half of the body
Lesions
- Upper motor neuron lesion (supranuclear lesion):
- Affects tract before facial nucleus
- Ventral portion innervates lower half, which will affect the facial nerve
- Results in paralysis on the contralateral lower half of the face
- Also called central facial paralysis
- Lower motor neuron lesion:
- Affects facial nucleus or facial nerve
- Lesion is on or after the dorsal and ventral portions of the facial motor nucleus
- Results in paralysis on the ipsilateral half of the face
- Also called peripheral facial paralysis (Bell's palsy)
Projections
- Fibers would pass through corona radiata and genu of the internal capsule and terminate in the brainstem
- Fibers project to:
- Motor nuclei of CN III, IV, V, VI, VII, IX, X, XI, XII (except CN I, II, and VIII)
- Parts of reticular formation in pons and medulla
- Sensory relay nuclei (nucleus gracilis, nucleus cuneatus, sensory trigeminal nuclei, and nucleus of the solitary fasciculus)
- Projections are bilateral, except for facial motor nucleus (CN VII) and hypoglossal nucleus (CN XII)
Pyramidal and Extrapyramidal Tracts
- Rubrospinal tract:
- Origin: red nucleus in the tegmentum of the midbrain
- Fibers cross immediately in the ventral tegmental decussation
- Descend down the brainstem to enter the lateral funiculus of the spinal cord
- Terminate on internuncial neurons in all spinal cord levels
- Interstitiospinal tract:
- Origin: interstitial nucleus of Cajal
- Uncrossed fibers
- Forms part of MLF
- Terminate in the anterior horn of upper cervical levels of the spinal cord
- Function: modulates reflex postural movements in response to visual and auditory stimuli
Vestibulospinal Tracts
- Medial vestibulospinal tract:
- Origin: medial vestibular nucleus
- Fibers are both crossed and uncrossed
- Descend in MLF and anterior funiculus of spinal cord
- Terminate on Rexed laminae VII and VIII
- Lateral vestibulospinal tract:
- Origin: lateral vestibular nucleus
- Fibers are both crossed and uncrossed
- Descend in MLF and anterior funiculus of spinal cord
- Terminate on Rexed laminae VII and VIII
- Function: for maintenance of upright posture, excites neck and back motor neurons
Reticulospinal Tracts
- Pontine (medial) reticulospinal tract:
- Origin: pons
- Fibers descend in anterior funiculus of spinal cord
- Terminate on Rexed laminae VII and VIII
- Function: facilitatory to extensor motor neurons
- Medullary (lateral) reticulospinal tract:
- Origin: medulla
- Fibers descend in lateral funiculus of spinal cord
- Terminate on Rexed laminae VII and VIII
- Function: inhibitory to extensor motor neurons
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
This quiz covers the internal capsule, its parts, and the pyramidal decussation. It discusses the organization of corticospinal tract (CST) fibers and their somatotopic arrangement. Test your knowledge of this critical brain region!