Descending Neural Pathways Flashcards
what does the body need to do a purposeful movement
- goal or purpose
- activation of relevant movement
- feedback of movement
- refinement/correction of movement
- cessation on completion
where is the motor cortex located and what are its sub areas
- anterior to central cortical sulcus
- primary motor area
- premotor area
- supplementary area
primary motor cortex
topographical representations mapped by electrical stimulation of motor cortex areas
- more than half the primary motor cortex controls hands and muscles of speech
- excitation of a single umn usually excites a specific movement not one specific muscle
PATTERNS
Premotor area
similar topographical regions to primary motor cortex
nerve signals give more complex patterns of movement
supplemental motor area
contractions elected are often bilateral
usually functions together with premotor area
- gives background movement onto which promotor and primary motor cortex and finer control
rehearsal - planning - action
corticopspinal tract
transmission of signals from motor cortex to muscles
- carriers signals direct from cortex to spinal cord
- cortex to pyramids of medulla to (majority) cross in lower medulla and then go on to the lateral corticospinal tracts and mainly terminate on interneurones
ONES THAT DO NOT CROSS PASS IPSILATERALLY IN VENTRAL CORTICOSPINAL TRACTS
conscious movement - lateral pathways
principally controlled by the cerebral cortex via two corticospinal tracts
general control of voluntary movement
mainly associated with control of distal muscles
unconscious movement - ventromedial pathways
principally controlled in the brainstem
control of posture and rhythmic movements associated with locomotion
control axial and proximal muscles
extra pyramidal tracts
reticulospinal tracts - posture, locomotion and autonomic function
vestibulespinal tracts - balance and posture
rubrpspinal tract - red nucleus, influences by cerebellum and reticular nuclei, excitatory flexors
tectospinal tract - head and neck moevemtns for visual tracking
control of motor functions by the brains stem
- extension of the spinal cord upward into the cranial cavity
- control of respiration, CV system
- Partial control GI function
- Control of many stereotyped body movements, equilibrium, eye, movements
serves as a way station for command signs;s for higher neural centres
posture
position of the body and its parts relative to each other. is a compromise between balance and movement
how do we maintain balance
posture is adjusted predominantly by involuntary movement driven both predictively (postural set - preparing) and reactively (compensation - falling)
- is controlled and driven by the brainstem and is where the postural set is governed
what are the sensory inputs to postural control
muscle proprioceptors (detect changes in muscle length and tension)
sense of balance derived from movements fo the head relative to the earths gravitational field (vestibular apparatus)
visual inputs (detecting movements in visual field representing movement of the body
INTEGRATED IN THE BRAINSTEM
reticular nuclei
- pontine (in pons)
- medullary (in medulla)
Mainly function antagonistically to each other
vestibular nuclei
every other place in the brainstem
the pontine reticular system
- they transmit excitatory signals down into the cord via PONTINE RETICULOSPINAL TRACTS in the ANTERIOR column of the spinal cord
- fibres terminate on MEDIAL ANTERIOR motor neurones that excite axial muscles that support the body against gravity
- high degree of natural excitability
- when unopposed by medullary reticular system It produces powerful excitation of antigravity muscles throughout the body
medullary reticular system
nuclei transmit inhibitory signals to same antigravity anterior motor neurone via MEDULLARY RETICULOSPINAL TRACT in LATERAL column of the cord
- meduallty reticular nuclei receive strong input collaterals from:
1. corticospinal tract
2. rubospinal tract
3. other more pathways
active medullary reticular inhibitory system to counterbalance excitatory signals from pontine reticular systems therefore under normal conditions body muscles are not abnormally tense
vestibular nuclei
function in association with pontine reticular nuclei to control antigravity muscles
• Transmit strong excitatory signals to antigravity muscles via lateral and medial vestibulospinal tracts in the anterior columns of the spinal cord.
– Without vestibular nuclei support, the pontine reticular system would lose much of its excitation of the axial antigravity muscles.
• Specific role of vestibular nuclei is to selectively control the excitatory signals to the different antigravity muscles to maintain equilibrium in response to signals from the vestibular apparatus.
Upper motor neurons (UMNs)
- Found in the cortex and brainstem nuclei
- Restricted to the CNS and do not contact muscle
- Executive function for lower motor neurons (LMNs) and circuits controlling LMNs
Lower motor neurons (LMNs)
- Foundinthebrainstemandspinalcord
- Not restricted to the CNS and contact muscle to stimulate
- Motorfunctiontomuscles
Upper motor neuron lesions
Relatively common as these axons are very long (therefore vulnerable).
• Signs of lesions are presented as positive or negative signs
• Negative is a loss of function,
• Positive is the appearance of an abnormal response.
• Extensor Planter reflex (Babinski sign) is an example of a positive
sign seen following corticospinal lesions.
Corticospinal lesions give rise to Upper motor neurone syndrome
Lower motor neuron lesions
• Lower motor neurons are the motor neurons whose cell axons leave the CNS and innervate muscle.
– Muscle paralysis
– Reduced motor tone
– Reduced stretch reflex
– Fasciculation
– Atrophy
upper:
– there is no atrophy or fasciculation
– but muscle tone increase often leading to painful spasticity
• Hypertonia is thought to be caused by hyperexcitable spindle neurons which induce over reactive stretch responses
Anterior spinal cord syndrome
- Hyperextension injury
* Infarction of anterior spinal artery
Posterior Spinal cord Syndrome
- Penetration injury
* Posterior spinal artery occlusion • Multiple sclerosis
Central Spinal cord syndrome
- Hyperextension
* Cord compression
Brown-Sequard Syndrome
• Penetrating trauma
