Motor cortex and reflexes Flashcards
What is the function of the cerebral cortex?
Voluntary movement and motor learning.
Sensory input provides constant feedback for adjustments. Involves the precentral gyrus / primary motor cortex
What type of control is in the two types of descending pathways?
Lateral = Voluntary Ventromedial = Unconscious brainstem control
What are the features of the motor system?
Hierarchy organisation
Feedback loops from sensory input
Somatotopic representation
What is somatotopic representation?
Allows the cortex to detect where the information is coming from so that the correct muscles contract.
Why is the cortex not needed for every movement?
The brainstem allows unconscious control due to motor memories e.g. walking
Where is a protective reflex produced?
Spinal cord as part of a closed loop e.g. limb withdrawal
How is a rhythmic motor pattern produced?
Uses combination of reflexes and voluntary e.g. chewing, breathing. Usually involuntary overrides
Where does the command for a voluntary purposeful movement originate?
Higher centres in an open loop for conscious control
Motorneuron activity is regulated by which types of inputs?
Sensory input to provide local feedback via dorsal roots.
Spinal interneurons to generate contraction or relaxation in the ventral horn.
UMN for initiation and control and input to interneurons.
Why can coordinated movements still occur even if the descending influences are severed?
Spinal cord circuits generate movement in isolation but is dependent on sensory input to induce the reflex. = central pattern generators
Which type of motor neurons do interneurons influence?
alpha motor neurons
What is the purpose of UMN descending input?
Sophisticated, adaptable patterns of voluntary movement superimposed on intrinsic circuit of the spinal cord
What are medial motorneurons used for?
POSTURE, locomotion and larger movements to control axial/trunk and proximal muscles (upto elbow and knee)
EXTENSORS
Involuntary and unconscious
What are the lateral motorneurons used for?
Fine motor and voluntary control over distal muscles (hands, feet, digits)
FLEXORS
Which descending tracts use the lateral motorneurons?
Corticospinal tract
Rubrospinal tract
Which descending tracts use the ventromedial motorneurons?
Reticulospinal tract
Vestibulospinal tract
Tectospinal tract
What is the pathway taken by the corticospinal tract?
Projects directly from motor cortex in areas 4 + 6 to later spinal motor neurons. Forms synapse with alpha motor neurons in ventral horn for control over distal muscles, particularly flexors.
What is the pathway taken by the rubrospinal tract?
Originates in the red nucleus of midbrain. The tract receives input from the motor cortex. For voluntary movement of distal muscles. The contralateral projections from the red nucleus run down the lateral column of the spinal cord.
What does a lesion in the lateral pathway result in?
Motor deficits in the voluntary movements causing them to be SLOWER. Posture unaffected.
What is severing of the lateral ascending pathways used for? What is its risk
To treat intractable pain, but it may damage the lateral descending pathway at the same time.
What compensates for a loss of corticospinal tract?
Rubrospinal can compensate for all but fine digit control. Shows plasticity as recruits cortical output via rubrospinal tract.
What are ventromedial pathways also known as?
Extra pyramidal tracts
Where do ventromedial pathways originate from and terminate?
Brain stem nuclei with contra and ipsilateral pathways. Terminate at medial alpha MNs.
What is the function of modulating spinal reflexes?
Allows for small adjustments to body position, balance and visual input
