pyramidals and extra - 2 Flashcards
RUBROSPINAL TRACT
function
The rubrospinal tract controls flexor muscles of upper limbs (i.e. it controls tone of flexor muscles, which are important for grasping) unilaterally (not bilaterally). Therefore, it is a flexor-biased tract. It complements the function of the lateral corticospinal tract. It receives afferent input from the motor cortex.
TECTOSPINAL TRACT pathway
The tectospinal tract originates in the superior colliculi (bypasses LGN), crosses over at midbrain tegmentum and descends to the anterior funiculus (column) of the spinal cord to terminate on motoneurons in the cervical spinal cord that innervate the neck muscles that are important for head movement.
TECTOSPINAL TRACT
it directs the visual axis to the source of a given sensory stimulus. The fibres that facilitate this head movement are located within the tectospinal tract
Functions of reticulospinal tract:
- is essential for initiation of locomotion as it gets input from the basal ganglia
- maintains upright body posture by innervating anti-gravity muscles (gets input from the vestibulospinal tract “to sense gravity”).
- Is primarily an extensor-biased tract.
- receives input from the motor cortex (pyramidal tract) concerning intended movement, and from tectospinal tract to stabilize the body during fast (reflexive) movements of the head
- receives input from the cerebellum concerning the actual sensory (prioprioceptive) input related to skeletal muscles.
reticulospinal motor behaviours
Briefly, the reticulospinal system is involved in two different kinds of motor behaviour: locomotion and postural control.
reticulospinal tract
Cell bodies of the neurons are located in the caudal pontine tegmentum and rostral medullary tegmentum reticular formation. These structures get afferent input from motor cortex, basal ganglia, cerebellum as well as tectospinal and vestibulospinal tracts. > Fibres of reticulospinal tract descend ipsilaterally and bilaterally to the anterior funiculus (medial motor system).
- hence is involved in anticipatory postural changes).
VESTIBULAR NUCLEI
Vestibular information is conveyed via the vestibular nerve to vestibular nuclei in the brainstem. Four vestibular nuclei are located in the pons and medulla (superior, inferior, lateral and medial).
The reflexes involving the vestibular system include the
(1) vestibulo-ocular reflex: helps maintain fixation of the eyes on an object during head movement (e.g. you can fixate your eyes and read even if your head moves);
(2) vestibulo-cervical reflex: stabilizes head position during movement
(3) vestibulospinal reflexes: maintains upright position and posture (maintains muscle tone in extensor muscles = anti-gravity muscles)
VESTIBULAR NUCLEI
(1) Medial vestibular nuclei: is concerned with vestibulo-ocular reflex via the medial longitudinal fasciculus, (MLF) and vestibulo-cervical reflex (via medial vestibulospinal tract).
(2) Lateral vestibular nuclei: gives rise to lateral vestibulospinal tract and is concerned with vestibulospinal reflex
VESTIBULAR NUCLEI location
The medial vestibular nuclei are located in the medulla; the lateral vestibular nuclei are situated at the junction between the pons and the medulla.
1) lateral vestibulospinal tract (LVST) from lateral vestibular nuclei:
- generates muscle tone (tonic active) in deep back & limb extensors (“antigravity„ muscles [refer to reticulospinal tract]) in response to gravity (to maintain stance & balance)
- responds to postural changes to compensate for tilts and movements of the body (uses input from the semicircular canals & visual system)
- hyperactivity of your lateral vestibulospinal tract (is involved in vestibulospinal reflex) - dizziness after spinning
- does not cross over, acts unilaterally and innervates all levels of the spinal cord
1) medial vestibulospinal tract (MVST) from medial vestibular nuclei:
- keeps the head upright & stabilizes head position during movement (uses input from semicircular canals)
- coordinate head movements with eye movements (uses input from the visual system)
- acts bilateral (partially crosses over) and is limited to cervical spinal cord segments.
- is involved in vestibulo-ocular and vestibulo-cervical reflexes
vestibular system
serves to regulate posture (keeps the centre of gravity between the feet) and to coordinate eye and head movements. The anatomical substrates of these functions are connections with the spinal cord (vestibulospinal reflex) and with the motor nuclei of the extraocular muscles (vestibulo-ocular reflex). Signals from the vestibular apparatus interact (i.e. they are connected reciprocally) with signals from other sensory systems (visual, auditory, and proprioceptive information from the cerebellum) in the vestibular nuclei.
Therefore, the output of neurons from the vestibular nuclei
(including vestibulospinal tract) is a summation of interactions of different sensory modalities that ultimately is employed to construct the vector (trajectory) representing the organism’s orientation to gravity.
all motor pathways
descend in spinal cord through the lateral or anterior funiculi. The posterior funiculus mainly contains ascending [sensory pathways] (dorsal column pathway). Most other ascending [sensory] pathways are located in the lateral funiculus (e.g. anterolateral spinothalamic tracts)
