Lecture 10 Flashcards
What is the pathway of the pyramidal (corticospinal) tract? What is the origin of this tract?
Origin: Primary motor cortex, premotor cortex, and somatosensory cortex
Pathway: Site of origin -> internal capsule -> medullary pyramids -> cross 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; other fibers pass into caudate nucleus and putamen, to red nucleus, to reticular substance and vestibular nuclei; large number of fibers pass to pontine nuclei
Define the pyramidal system (what is it) and list the components
Definition: These are tracts that pass through the medullary pyramids; other motor pathways are extrapyramidal
Components: Corticospinal tract and corticobulbar tract
What is the pathway of the corticobulbar tract?
Upper motor neurons of the cranial nerves innervating the face, head, and neck; most fibers terminate in reticular formation near cranial nerve
Association Neurons: Leave reticular formation and synapse in cranial nerve nuclei; synapse with lower motor neurons
List the characteristics of the extrapyramidal system and its component tracts
Includes pathways that contribute to motor control but that are not part of the corticospinal system; includes descending motor tracts that do not pass through medullary pyramids or corticobulbar tracts
Components: rubrospinal, vestibulospinal, reticulospinal, and olivospinal tracts
What is the pathway of the rubrospinal tract? Include its level of decussation
Originates in red nucleus and decussates in midbrain; descends in lateral funiculus (column); function is closely related to cerebellar function; less important in human for motor control; responsible for large muscle movement and some fine motor of UE
Describe the characteristics of lesions associated with the rubrospinal tract
Lesions result in impairment of distal arm and hand movement, intention tremors (similar to cerebellar lesions), and may take over for injured corticospinal tract in some animals
What is the pathway of the vestibulospinal tract and what is its major input? What function is this tract primarily involved with?
Originates in vestibular nuclei and receives input from vestibular nerve (CN 8) about changes in head position with the goal of maintaining balance; descends in anterior funiculus, synapses with LMNs to extensor muscles (primarily involved in maintenance of upright posture)
What is thought to be the function of the reticulospinal tract?
Mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs; controls activity of both alpha and gamma motor neurons, mediates autonomic functions like circulatory system and breathing; can modulate pain information
List the reticular nuclei and their functions
Pontine Reticular Nuclei: fibers make up the pontine reticulospinal tract (anterior column); stimulatory effect on both extensors and flexors, but especially extensors (antigravity muscles)
Medullary Reticular Nuclei: Fibers make up the medullary reticulospinal tract (lateral column); inhibitory effect on both extensors and flexors, but especially extensors (antigravity muscles)
Describe the maculae of the utricle and saccule and indicate their planes of orientation and their associated functions
Utricle: macula is located on a horizontal plane and plays a role in determining orientation of head when head is upright
Saccule: macula is located in a vertical plane and signals head orientation when a person is lying down
Describe the structure of a macula and the function of the statoconia in relation to the hair cells
Macula of both utricle and saccule contains large numbers of embedded small calcium carbonate crystals (statoconia), contains thousands of hair cells which project cilia into the gelatinous layer; the weight of the statoconia bends cilia in the direction of gravitational 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 different directions causes 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, inertia of the fluid in one or more of the semicircular canals remains stationary while semicircular canal rotates with the head; fluid flows from the duct and through the ampulla and causes the cupula to bend to one side; hundreds of hair cells within each cupula detect this bending and send signals via the vestibular nerve
Describe the lateral corticospinal tract, inclduing its function
Made up of corticospinal fibers that have crossed in medulla; supply all levels of spinal cord
Adds speed and agility to conscious movements (especially movements of the hand) and provides a high degree of motor control (movement of individual fingers)
Describe the anterior corticospinal tract, including its function
Made up of uncrossed corticospinal fibers that cross near level of synapse with LMNs; supply neck and upper limbs
Adds speed and agility to conscious movements (especially movements of the hand) and provides a high degree of motor control (movement of individual fingers)
