descending pathways Flashcards
what is a ‘tract’ in the brain?
a large number of axons travelling in parallel within the CNS
what is a pathway?
the route taken along tracts by either a sensory signal or a motor signal - can cross tracts or travel along just a portion of them
what is a system in the brain?
this is the name usually given to a complex group of tracts found in a particular portion of the spinal cord or a group of tracts serving a similar function
where do UMNs arise from (upper motor neurones)?
found in the cortex and brainstem nuclei, restricted to the CNS (can have a control over other UMNs or LMNs)
where do you find lower motor neurones?
arise from the spinal cord/braainstem and synapse on muscles to stimulate contraction
what type of movements are controlled by descending VENTROMEDIAL pathways?
involuntary (e.g. posture, balance, muscle tone, head orientation and breathing)
whereabouts in the brain is POSTURE mediated?
in the brainstem
which sensory inputs are integrated in the brainstem and used to adjust balance to maintain posture in the VESTIBULOSPINAL PATHWAY (3)?
muscle proprioceptions - information from muscle spindles which give information about muscle length and tension)
- balance from the vestibular apparatus in the ear
- visual inputs (detection of movements in visual field representing movement of the body
which part of the brainstem is information collected in?
the reticulum
which are of the brainstem is the vestibular nucleus found in and what type of motor neurones are found in here?
the medulla - upper motor neurones
what information is given to the vestibular nucleus?
information from the vestibular apparatus of the inner ear about balance
where do all of the venture medial pathways originate?
brainstem (primarily the reticulum)
which ventromedial pathway is balance involved in?
the vestibulospinal pathway
what are the two pathways of the vestibulospinal system?
lateral and medial
what is the principle effect of the lateral vestibulospinal pathway?
to facilitate extensor motor neurones and relax antagonist muscles
also activates gamma motor neurones which causes enhanced muscle kindle mediates stretch reflexes to increase the tone in antigravity muscles
what is the principle effect of the medial vestibulospinal pathway?
controls head and eye movements usually in response to a moving target - head and eye movements remain fixed despite movements of the rest of the body. medial pathway links with lateral which receives information from the vestibular apparatus.
what does the reticulospinal pathway control?
co-ordinates movement and posture by receiving information from many different sources
where does the reticulospinal pathway receive sensory information from?
- vestibular nuclei
- comical areas for voluntary movement
- proprioception, vision etc
what are the main effects of the reticulospinal pathway?
coordinates truncal and proximal muscle activity to orientate body towards or away from a stimulus
also affects muscle tone in response to planned motor activity and overall coordinated distal and proximal muscle activity
where is the primary motor cortex located?
just anterior to the central sulcus on the frontal lobe
how can you tell if an area of the body is under finer motor control?
takes up a larger area in the primary motor cortex
what are the two devisions of the corticobulbar tract?
tract in the brainstem to facial and cranial muscles and influence over unconscious motor output (i.e. override reflexes to make yourself fall over)
what are the two divisions of the corticospinal tract?
the lateral contralateral tract and the anterior ipsilateral tract
what percentage of motor output is controlled by the lateral contralateral tract?
90-95%
what is the purpose of the anterior ipsilateral tract?
to contract antagonist muscles on the opposite side of the body to carry out movements (provides postural compensation for movements contra laterally)
where does the anterior ipsilateral tract terminate?
L2
how does each tract innervate at the segment?
anterior ipsilateral - bilaterally
lateral contralateral - unilaterally
Somatotopic organisation to alpha motor neurons in the ventral horn of the spinal cord - are flexor motor neurons more anterior/posterior?
more posterior than extensors
Somatotopic organisation to alpha motor neurons in the ventral horn of the spinal cord - are more distal muscles more lateral/medial?
lateral
what can a positive babinski response indicate?
corticospinal lesions - upper motor neurone syndrome
what are signs of a lower motor neurone lesion
muscle paralysis reduced motor tone reduced stretch reflex fasciculation atrophy
what are signs of an upper motor neurone lesion?
no atrophy or fasciculation but muscle tone often increase leading to painful spasticity
