Lecture 10 Flashcards
What is the defining characteristic for the pyramidal tracts?
They pass through the medullary pyramid
All other motor tracts are considered to be extrapyramidal
Of the 3 subdivisions of the pyramidal system (lateral corticospinal, Anterior corticospinal, and Corticobulbar tracts) state what they supply and what the tract is composed of.
Lateral corticospinal tract: supplies all levels of the spinal cord
Made up of corticospinal fibers that have crossed in the medulla
Anterior corticospinal tract: supplies the neck and upper limbs
Made up of uncrossed corticospinal fibers that cross near level of synapse with LMNs
The corticobulbar tract:
Most of it’s fibers terminate in the reticular formation near the cranial nerve nuclei
composed of motor neurons of the cranial nerves, innervating the head, face, and neck
State the 2 main functions of the corticospinal tracts
The corticospinal tracts function to:
Add speed/agility to conscious movements
Provide a high degree of motor control
The following are all functions of what?
Relays info from the motor cortex to the cerebellum
Has projections to the contralateral spinal cord via the rubrospinal tract or ipsilater inferior olive
Stimulation of this structure results in:
Stimulation of flexors
Inhibition of extensors (antigravity muscles)
The Red nucleus
Describe the relationship of the magnocellular region to the rubrospinal tract and the skeletal muscles.
Fibers from the primary motor cortex (corticorubral pathway) and branches from the corticospinal tract synapse in the magnocellular region of the red nucleus
Large neurons from the magnocellular region of the red nucleus give rise to the rubrospinal tract which decussates in the lower brain stem
Trace the corticorubrospinal pathway.
From the motor cortex to the red nucleus
once the path passes through the red nucleus, it is considered the rubrospinal tract
State the 4 tracts that are all components of the extrapyramidal system
Rubrospinal tracts
Vestibulospinal tracts
Reticulospinal tracts
Olivospinal tracts
Generally describe the extrapyramidal system as it pertains to the systems they are a part of and what they contribute to.
The extrapyramidal system includes pathways that contribute to motor control but ARE NOT part of the corticospinal system
This includes descending motor tracts that do not pass through the medullary pyramids or corticobulbar tracts
For the rubrospinal tract, state where it originates, decussates, and descends
Originates in the red nucleus
Decussates in the midbrain
Descends in the lateral funiculus (column)
State 2 common symptoms that occur with lesions to the rubrospinal tract
Impairment of distal arm and hand movement
Intention tremors (similar to cerebellar lesions)
For the Vestibulospinal tract, state where it originates, descends, and what is synapses with. Also state it’s main goal
Originates in the vestibular nuclei (receives major input from the vestibular nerve (CNVIII) about changes in head position) with the goal of maintaining balance
Descends in the anterior funiculus (column)
Synapses with LMNs to extensor muscles (primarily involved in maintenance of upright posture)
Main goal: maintaining balance
What is thought to be the function of the reticulospinal tract?
It is thought to mediate larger movements of the trunk and limbs that do not require balance or fine movements of the upper limbs
For the maculae of the utricle and saccule, indicate their plane of orientation and their associated functions.
Maculae of the utricle are located on a horizontal plane and play a role in determining the orientation of the head when the head is UPRIGHT
Maculae of the saccule are located on a vertical plane and play a role in determine the orientation of the head then a person is LYING DOWN
Explain how hair cells in the macula become depolarized and hyperpolarized.
Bending of the stereocilia towards the kinocilium open hundreds of cation channels, causing receptor membrane depolarization and excitation
Bending of the cilia in the opposite direction of the kinocilium closes the cation channels and hyperpolarizes the receptor membrane
Explain how semicircular canals are able to detect motion of the head in three dimensional space.
When the head begins to rotate in any direction, a portion of the fluid in one or more of the semicircular canals remains stationary while the other portion rotates with the movement of the head
Fluid flows from the duct, through the ampulla, and causes the cupula to bend to one side, which bends hair cells in the cupula that then create a signal via the vestibular nerve
