Flashcards in Spinal Cord, Brainstem, Cortex Control Of Motor Function II Deck (46):
Where do upper motor neurons in the pyramidal system decussate?
17 - 85% decussate in pyramids and form the lateral corticospinal tract.
The remainder decussate near synapses with lower motor neurons and form anterior corticospinal tracts.
What does the medial activation system innervate?
Postural and girdle muscles
What is the function of the lateral activation system?
Associated with distally located muscles used for fine movements.
What is the function of the non-specific activating system?
It facilitates local reflex arcs.
What does the lateral corticospinal tract supply?
All levels of the spinal cord
What does the anterior corticospinal tract supply?
The neck and upper limbs
What comprises the lateral corticospinal tract?
Corticospinal fibers that have crossed in the medulla.
What comprises the anterior corticospinal tract?
Uncrossed corticospinal fibers that cross near the level of synapse with LMNs.
What is the origin of the corticospinal tract?
Primary motor cortex
What is the pathway of the corticospinal tract?
Site of origin
Decussates in lower medulla
Lateral columns of spinal cord.
Where are giant pyramidal (Betz) cells located?
In the motor cortex.
They send collaterals back to the cortex.
Where do other fibers (not giant pyramidal) cells pass?
Into caudate nucleus and putamen
Reticular substance and vestibular nuclei
What are functions of the corticospinal tract?
Adds speed and agility to conscious movements (especially to the hand)
Provides a high degree of motor control (i.e. Movement of individuals fingers).
What occurs when there is a lesion to the corticospinal tract?
Reduced muscle tone
Not complete paralysis (complete paralysis results if both pyramidal and extrapyramidal systems are involved).
What does the corticobulbar tract innervate?
Most fibers terminate in reticular formation near cranial nerve nuclei.
Where are association neurons found?
They leave the reticular formation and synapse in cranial nerve nuclei.
They then synapse with lower motor neurons.
Fibers from the primary motor cortex and the corticospinal tract synapse in the magnocellular portion of the:
What does stimulation of the red nucleus result in?
Stimulation of flexors
Inhibition of extensors
What is the extrapyramidal system?
A system that includes pathways that contribute to motor control, but are not part of the corticospinal system.
It includes descending motor tracts that do not pass through medullary pyramids or corticobulbar tracts.
What tracts are included in the extrapyramidal system?
Where does the rubrospinal tract originate and decussate?
Originate in the red nucleus
Decussates in the midbrain
What occurs where there is a lesion to the rubrospinal tract?
Impairment of distal arm and hand movement
Intention tremors (similar to cerebellar lesions)
Where does the vestibulospinal tract originate?
In the vestibular nuclei. It receives major input from vestibular nerve (CN VIII).
Where dos the vestibulospinal tract descend and synapse?
It descends in the anterior funiculus.
It synapses with LMNs to extensor muscles, which are involved in maintaenance of upright posture.
Where does the reticulospinal tract originate?
In regions of the reticular formation.
It descends in the anterior portion of the lateral funiculus.
What is the function of the reticulospinal tract?
It mediates larger movements of trunk and limbs that do not require balance or fine movements of upper limbs.
What do fibers of the pontine reticular nuclei make up?
The pontine reticulospinal tract.
What effect do pontine reticular nuclei have on extensors and flexors?
They have a stimulatory effect on both extensors and flexors.
Fibers of the medullary reticular nuclei make up what tract?
Medullary reticulospinal tract.
What effect does the medullary reticular nuclei have on extensors and flexors?
An inhibitory effect.
What is the vestibular apparatus?
A membranous labyrinth consisting of three semicircular canals and vestibule.
What is a vestibule composed of?
Utricle and saccule.
What types of lymph are found in ducts?
Endolymph and perilymph.
Ducts are filled with endolymph and surrounded by perilymph.
What is the function of the utricle and saccule?
The detect angular (semicircular canals) and linear (utricle and saccule) acceeleration of the head.
They are also involved in reflex adjustments of the head, eyes and postural muscles
The utricle and saccule each contain a macula, which contains what?
What is the function of the utricle?
It plays a role in determining orientation of the head when the head is upright.
What is the function of the saccule?
It signals head orientation when a person is lying down.
What occurs as the stereocilia bend towards the kinocilium?
It opens hundreds of cation channels causing membrane depolarizaiton and excitation.
What occurs when the sterocilia beds away fromt he kinocilium?
Channels are closed and the receptor membrane is hyperpolarized.
Whent the head begins to rotate in any direction, inertia of the fluid in one or more of the semicricular canals remains stationary while semicircular canal rotates with the head.
As fluid flows from the duct and through the ampulla, this causes the cupula to bend to one side. What then occurs?
Hundreds of hair cells within each cupula detect the bending and send signals via the vestibular nerve.
What occurs when the head is bend 30 degrees?
Lateral ducts are horizontal
Anterior ducts are in vertical planes projecting foward and 45 degrees outward.
Posterior ducts are in vertical planes projecting backward and 45 degrees outward.
What is an ampulla?
An enlargement at one end of each semicircular canal duct.
It is filled with endolymph.
What is a crista ampullaris?
A small crest within each ampulla
What is a cupula?
A loose mass of gelatinous tissue on top of the crista.