descending tracts Flashcards
Key areas of the motor system - heirarchial organisation
Cerebral cortex -decision to move
Brain stem
Spinal cord
Parallel organisation of the motor system
Basal nuclei
Thalamus
Cerebellum
involved in coordinating, regulating and fine tuning
Generation of voluntary movement for eg throwing ball
Identify target/goal and locate it - VISUAL SYSTEM, retinotopic space
Determine limb trajectory ( body or hand centered system)
Calculate forces necessary to generate desired trajectory ( muscle based reference frame)
motor cortex
Cortical regions involved in movement plan control and initiate movement
primary, premotor, supplementary, cingulate
Motor area
Movement can be evoked by the LOWEST STIMULUS INTENSITY
- anatomical experiments
Primary motor cortex
location on the pre central gyrus
Somatotopic map
Neurones directly related to movement- specific parts f the body from spinal cord to cortex
Motor homunculus
Left side of brain controls
RIGHT SIDE OF BODY
Feedback control
Sensory info from voluntary movements are sent to the cerebrum and cerebellum
Error signal
Difference between desired and actual position
Feed forward control
Sensory info gives advanced info
- Anticipation of the required movement
- Enables movement to be direction to the target
Describe motor output from brain
HEIRARCHICAL SYSTEM
Target of movement identified by a pooling of sensory info in teh posterior parietal cortex combined with info from the primary sensory cortex
Info transmitted to the supplementary motor and pre motor areas( planning)
Primary motor cortex Commands transmitted(via descending pathways) to spinal cord and brain stem motor nuclei
Motor output - PARALLEL DISTRIBUTION NETWORK
Numerous motor areas are all bidirectionally connected
Each area contributes to several stages of planning and executing a movement
Each cortical area makes a significant contribution to descending pathways
Word to describe the motor descending pathway
TOPOGRAPHICALLY ORGANISED
2 TYPES OF NEURONES in the motor pathway
Upper motor neurone - cell body in primary motor cortex of the frontal lobe
lower body neurone-synapses on the lower motor neuron, which is in the ventral horn of the spinal cord and projects to the skeletal muscle in the periphery.
limb muscles - descending tract
Column extends for several segment
Lateral part of ventral horn
Distal part of limb, proximal muscles
Axial musculature - descending tract
Column/tract extend greater length of spinal cord
Medial part of ventral horn
Interneurones enable bilateral innervation ( postural support)
2 main groups of descending motor pathways
Dependent on location of tract
LATERAL
MEDIAL
LATERAL pathways
Control proximal distal muscles
Responsible for most voluntary movements of arms and legs
Lateral corticospinal tract and rubrospinal tract
MEDIAL pathways
Control anti gravity muscles
Control axial and postural muscles = posutre and balance
anterior corticospinal tract, tectospinal tract, vestibulospinal tracts, reticulospinal tracts
Corticospinal ( pyramindal ) tract
COntrols musles of distal limbs and trunk
FINE MOTOR MOVEMENT
Longest and largest CNS descedning tract
Motor cortex — spinal cord
Form medullary pyramids
Decussation at medullary spinal cord junction
lateral corticospinal tracts Function and route
Function:
Controls muscles of distal limbs, voluntary movements of arms and legs, fine movement of contralateral limbs
Route: Originates in cerebral cortex Upper motor neurones decussate in the medulla Runs in lateral tract in spinal cord Innervate lateral lower motor neurones
Anterior corticospinal tract
FUNCTION AND ROUTE
Function
- Controls trunk muscles
- Responsible for maintaining posture
Route - Originates in cerebral ortex Upper motor neurones DO NOT decussate in medulla Smaller than lateral pathway Runs in anterior tract in spinal cord Innervate medial lower motor neurones
Corticonuclear tract
Originate in motor cortex
Terminates in brain stem nuceli
Innervates cranial nerves - face, jaw and tongue movement
Most nuclei receive bilateral innervation from cortex EXCEPT - facial motor nucleus and hypoglossal nucleus
rubrospinal tract
Originates in red nucleus( brainstem)
Voluntary movement of upper limbs and shoulders
Vestibulospinal tract
Originates in vestibular nucelus
Controls muscles of neck, trunk adn some legs
Upright posture
Tectospinal tract
Originates in superior colliculus in midbrain
Info from eyes and visual cortex
Innervate contralateral motor neurones controlling head position
Reticulospinal tracts
Pontine
Medullary
Innervate interneurons affecting corticospinal tract
Where does reticulospinal tracts originate
Originates from reticular formation (pons and medulla)
Potine reticulospinal tract
Ipsilateral innervation of extensor motor neruones
Medullary reticulospinal tract
Bilateral innervation of flexor motor neurones
Innervate interneurons affecting corticospinal tract - reticulospinal tracts
Modulates voluntary movements, aid locomotion and posture, influences muscle tone
How can level of damage to motor pathways show differently
Dictates
Damage between upper and lower limb trunk - paraplegia
Tetraplegia - higher up spinal cord= upper motor neurons , loss of upper limb movement
effect of upper motor neuron damage
Damage in cortex/brain stem/spinal cord - any point
HIGHER LEVEL DAMAGE
Cortex involved with long term planning and execution - release
effects long term planning and execution
Different activity in brain stem, different patterns in lower motor neurones- incorrect, or may stop working all
Specific regions affected
Lower motor neuron damage
Damage to the alpha motor neurones that innervate skeletal muscle
Effects small groups of muscles (motor unit)
Upper motor neurone syndrome symptoms
Paralysis of movements Increased muscle tone Hyperactive stretch reflexes Extensor plantar reflex ( babinski sign) Reduction in superficial reflexes
Lower motor neurone syndrome symptoms
Paralysis of muscles
Hypotonia and atrophy of muscles
Fasciculations and fibrillations
Loss of stretch reflexes but superficial reflexes are maintained
Babinski reflex
When do reflex that makes toes go down
