Neruo 4.2 Descending Tracts and UMNs Flashcards
In what part of th ebrain do most muscle movements originate?
pre central gyrus
What parts of the spinal cord are considered parasympathetic and sympathetic?
parasympathetic - craniosacral
Sympathetic - Thoracolumbar
Explain the distinction between pyramidal and extra-pyramidal UMN. What tracts does each contain?
Pyramidal - consists of corticospinal (begins in cerebral cortex and terminates in spine) and corticobulbar tracts which are both responsible for voluntary movement of body and fascial muscles respectively. Directly innervates motor neurons
Extra-pyramidal - Modulate motor activity without directly innervating motor neurons. Involved in reflexes, locomotion, complex movement and postural control. Consists of vestibulospinal, reticulospinal, rubrospinal, and tectospinal tracts.
Which side of the brain controls skeletal muscle movement son the left side of the body and vice versa?
right side and vice versa
What does the corticospinal tract convey?
Axial and limb motor control
Where does the corticospinal tract begin?
pre central gyrus
Which neurons innervate the axial muscles and the limb muscles
Describe the pathway of the 1st order neurons of the corticospinal tract
Leaves nuclei and cortex by descending through internal capsule and into medulla through brainstem where:
- 75-90% decussate AKA decussation of pyramids and runs through the lateral corticospinal tract (goes on to innervate limbs) and once they reach their intended spinal level they synapse with a neuron on the anterior horn of grey matter
- 10-25% dont decussate and run through the anterior corticospinal tract (innervate axial muscles). However, once the anterior corticospinal tract nerves reach their intended spinal level they decussate through the anterior white commissure and synapse with neuron in anterior horn of grey matter
What is a UMN lesion of corticospinal tract?
A lesion in the 1st order neurons of the corticospinal tract
What is the pathway of the 2nd order neurones of the corticospinal tract? What can these neurones be described as?
Project from anterior horn nuclei to the limb and axial muscles AKA LMN
Describe the pathway of the corticobulbar tract
Starts in cerebral cortex and descrends through internal capsule to brainstem where they decussate. terminate on contralateral cranial nerve motor nuclei in midbrain, pons, and medulla
What muscles does the corticobulbar tract control?
facial expression, extra-ocular muscles
What is the function of the vestibulospinal tract? Where does it arise from? Does it decussate?
Balance and posture
Does not decussate
Arises from vestibular nucleus
What is the function of the reticulospinal tract?
Helps with extensor spinal reflexes
What is the function of the rubrospinal tract? Does it decussate? Describe its pathway
Arises from red nucleus and decussates in midbrain and descends the spinal cord
Function is to facilitate flexor motoneurones and inhibit extensor motoneurones
What is the function and pathway of the tectospinal tract?
Function - aids in directing head movements
Neurons arise from tectum of brainstem and decussate within brainstem. Terminate in the upper cervical segments
What tract inhibits the reticulospinal tract and what would occur if inhibition was released?
corticospinal tract inhibits
Release from inhibition would result in upposed extension of head and limbs
What would occur if the vestibulospinal tract was damaged?
loss of righting reflex, ataxia of gait, postural instability
Give the strict definition of a reflex
An automatic, unlearned, repeatable response to a specific stimulus that does not require the brain to be intact
Why is it important to distinguish between a voluntary and a reflex movement?
Both use different and separate neural circuits. Reflex movements can be achieved with a brain that is not intact and thus does not tell us much about the functionality of the brain
What is a monosynaptic stretch reflex and a muscle stretch reflex?
Muscle stretch reflex is an umbrella term that covers all the versions of the reflex circuits
The monosynaptic stretch reflex is the simplest muscle stretch reflex, containing only one synapse between afferent and efferent neurone
Explain how some relaxed healthy individuals are found to be areflexic
Severity of constant descending inhibition is variable in time.
