Lecture 11: Spinal Cord and Brainstem Control of Motor Function II Flashcards by Tyler Turner

Which reflex is responsible for polysynaptic excitation of contralateral extensors?

A.) stretch reflex (myotactic)
B.) Golgi tendon reflex (inverse myotactic)
C.) Flexor withdrawal reflex
D.) Subliminal occlusion reflex

C.) Flexor withdrawal reflex

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Definition of pyramidal system

These are tracts that pass through the medullary pyramidals. (other motor pathways are extrapyramidal)

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Components of pyramidal system

Corticospinal tract
Corticobulbar tract

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upper motor neurons of the pyramidal system orginate in the _____. ______% decussate in pyramids and form the lateral corticospinal tracts

motor cortices
75-85%

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75-85% of upper motor neurons decussate in the pyramids and form the lateral corticospinal tracts. The remainder decussate

near synapse with lower motor neurons. And form anterior corticospinal tracts

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Most upper motor neurons synapse with association neurons in _____

spinal cord central gray

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Upper motor neurons are classified according to where they synapse in the ventral horn

medial activation system
- Innervate postural and girdle muscles
Lateral activation system
- Associated with distally located muscles used for fine movements
Nonspecific activating system
- Facilitate local reflex arcs

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Lateral corticospinal tract

made up of corticospinal fibers that have crossed in medulla
supply all levels of spinal cord

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Anterior corticospinal tract

made up of uncrosssed corticospinal fibers that cross near level of synapse with LMNs
Supply neck and upper limbs

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origin of the corticospinal tract

Primary motor cortex
Premotor cortex
Somatosensory area

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The corticospinal tract is referred to as the

pyramidal tract

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What is the pathway of the Corticospinal tract

site of origin –> internal capsule –> medullary pyramids –> X in lower medulla (most fibers) –> lateral columns of spinal cord (lateral corticospinal tract)
some fibers do not cross but continue down ipsilaterally in ventral corticospinal tract

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Giant pyramidal (Betz) cells are located in

motor cortex

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Giant pyramidal (Betz) cells transmit at ___ m/sec

70 m/sec

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Giant pyramidal (Betz) cells make up about __% (_____) of fibers in the corticospinal tract

3% (34,000)

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Giant pyramidal (Betz) cells sends ___ back to cortex

collaterals

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other fibers (not giant pyramidal (Betz) cells) from the cortex in Corticospinal tract pass into _____ and ____. Pass to ____, Pass to ____ and ______. And a large number of fibers pass to ____

caudate and putamen red nucleus
Reticular substance and vestibular nuclei
pontine nuclei

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Functions of Corticospinal Tract

Adds speed and agility to conscious movements
- Especially movements of hand
Provides a high degree of motor control: (i.e. movement of individual fingers)

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Symptoms of Corticospinal Tract Lesions

Reduced Muscle Tone
Clumsiness
Weakness
Not complete paralysis
(note: complete paralysis results if both pyramidal and extrapyramidal systems are involved )

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Complete paralysis results if

both pyramidal and extrapyramidal systems are involved

The Corticobulbar Tract innervates the

head

most fibers of the corticobulbar tract terminate in

reticular formation near cranial nerve nuclei

association neurons of corticobulbar tract leave reticular formation and synapse in _____ and with

cranial nerve nuclei, lower motor neurons

Fibers from primary motor cortex (corticorubral pathway) and branches from corticospinal tract synapse in ______ of red nucleus

magnocellular portion

Large neurons from magnocellular region red nuclues give rise to ____ which decussates in lower brain stem

Rubrospinal tract

Magnocellular region has a ______ representation of all the muscles of the body

somatotopic

Stimulation of Red nucleus results in

Stimulation of flexors Inhibition of extensors (antigravitiy muscles)

The extrapyramidal system includes pathways that

contribute to motor control but that are not part of the corticospinal system

extrapyramidal system includes descending motor tracts that do not pass through ______ or \_\_\_\_\_

medullary pyramids or corticobulbar tracts

Extrapyramidal system includes

* Rubrospinal tracts * Vestibulospinal tracts * Reticulospinal tracts

Rubrospinal tract originates in \_\_\_\_\_\_

red nucleus

Rubrospinal tract decussates in \_\_\_

midbrain

Rubrospinal tract descends in \_\_\_\_\_\_

lateral funiculus (column)

Rubrospinal tract function is closely related to

cerebral function

Lesions of Rubrospinal tract result in

Impairment of distal arm and hand movement Intention tremors (similar to cerebellar lesions)

Vestibulospinal Tract originates in

Vestibular nuclei

The vestibulospinal tract receives major input form

vestibular nerve (CN VIII)

The Vestibular Nuclei descends in \_\_\_\_\_

Anterior funiculus (column)

Vestibulospinal tract synapses with ____ to \_\_\_\_\_

LMNs to extensor muscles

The Vestibulospinal tract is primarily involved in

maintenance of upright posture

The Reticulospinal tract originates in various regions of

reticular formation

The Reticulospinal Tract descends in

anterior portion of lateral funiculus (column)

What is the function of Reticulospinal tract

Thought to mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs

Describe the maculae of the utricle and saccule and indicate their planes of orientation and their associated functions

* Urticle * Macula * Located on a **horizontal plane** * Plays a role in determining orientation of head when head is upright * Saccule * Macula * Located in a **verticle plane** * signals head orientation when person is lying down

Describe the structure of a macula and the function of the statoconia in relation to the hair cells

* The macula is covered by a gelatinous layer * Contains large number of embedded small calcium carbonate crystals (**statoconia**) * Contains thousands of hair cells which project cilia into the gelatnous layer * The weight of the statoconia bends cilia in the direction of gravitional pull

Explain how hair cells in the macula become depolarized and hyperpolarized

* Bending of stereocilia towards kinocilium opens hundreds of cation channels causing receptor membrane depolarization and excitation * Bending of cilia in opposite direction closes channels and hyperpolarizes receptor membrane * Hair cells are oriented such that bending the head in differents cause different groups of hair cells to depolarize

Explain how semicircular canals are able to detect motion of the head in three dimensional space

* When head begins to rotate in any direction, intertia of the fluid in one or more of the semicircular canals remains stationary while semicircular canal rotates with the head * When head is bent forward 30° * Lateral ducts are horizontal * anterior ducts are in vertical planes projecting forward and 45° outward * Posterior ducts are in vertical planes projecting backward and 45° outward

Trace the connections of the vestibular nerves to the vestibular nuclei, fastigial nuclei, red nuclei, and spinal cord