Descending Tracts Flashcards
Give a general statement about the pyramidal tracts.
Originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face
Give a general statement about the extra-pyramidal tracts.
Originate in the brain stem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
All the neurones of the descending motor system are classed as what?
Upper motor neurones
The Pyramidal tracts are split in two. Name them and what they supply.
Corticospinal tracts - supplies the musculature of the body
Corticobulbar tracts - supplies the musculature of the head and neck
From what areas does the corticosinal tract get input from?
Primary motor cortex
Premotor cortex
Supplementary motor area
Somatosensory area
What area doe the neurones of the corticospinal tract descend through? Why is this clinically significant?
Internal capsule
Particularly suscetible to copression from haemorrrhagic bleeds known as a “capsular stroke”. This could cause a lesion of th descending tracts.
After the internal capsule, where do the neurones of the corticospinal tract course?
Through the crus cerebri of the midbrain, pons and into the medulla.
What happens to the tract at the most inferior part of the medulla?
It splits in 2;
lateral corticospinal tract
anterior corticospinal tract
Do the fibres from the anterior or lateral corticospinal tracts decussate?
Lateral
The anterior corticospinal tract terminates where?
Ventral horn of cervical and upper throacic segmental levels
The lateral corticospinal tract terminates where?
Ventral horn at all segmental levels
The corticoulbar tract start and finish where?
Arise from the lateral aspect of the primary motor cortex, pass thorugh into the brain stem and terminate/synapse on the motor nuclei of the cranial nerves. LMN carry the motor signals to the muscles of the face and neck
Do the majority of corticobulbar fibres innervate the motor neurones bilaterally or unilaterally?
Bilaterally
What are the exceptions to the corticobulbar tract terminating bilaterally and terminate contralaterally?
Facial nerve (CNVII) Hypoglossal nerve (CNXII)
How many extra-pyramidal tracts are there? Name them.
4 Vestibulospinal Reticulospinal Rubrospinal Tectospinal
Where do the medial and lateral vestibulospinal tracts arise from?
vestibular nuclei
Do the vestibulospinal tracts remain ipsilateral when conveying this information to the spinal cord or do they decussate?
Remain ipsilateral
What are the functions of the medial andlateral vestiulospinal tracs?
Control balance and posture by innervating the “anti-gravity” muscles (flexors of the arm and extensors of the leg), via LMNs.
What is the function of the medial reticulospinal tract? Where does it arise from?
Arises from the pons. It facilitates voluntary movements, and increases muscle tone.
Where does the lateral reticulospinal tract arise from and what is its function?
Arises from the medulla. It inhibits voluntary movements, and reduces muscle tone.
The rubrospinal tracts arise from where?
The red nucleus (a midbrain structure)
What is the course of the rubrospinal tracts?
As fibres emerge from the red nucleus, they decussate (cross over to the other side of the CNS), and descend into the spinal cord. Thus, they have a contralateral innervation.
What is the function of the rubrospinal tracts?
Thought to play a role in the fine control of hand movements
The tectospinal tracts begin where?
Superior colliculus of the midbrain
What is the course of the tectospinal tract?
The neurones then quickly decussate after arising fromthe superior colliculi, and enter the spinal cord. They terminate at the cervical levels of the spinal cord.
What is the function of the tectospinal tracts?
Coordinates movements of the head in relation to visual stimuli.
What are the cardinal signs of an UMN lesion?
Hypertonia – an increased muscle tone
Hyperreflexia – increased muscle reflexes
Clonus – involuntary, rhythmic muscle contractions
Babinski sign – extension of the hallux in response to blunt stimulation of the sole of the foot
Muscle weakness
