Task 1 Flashcards
Corticospinal/pyramidal tract
- Originates in the neocortex, 2/3 of axons from motor cortex
- Axons from the cortex pass through the internal capsule, through the base of the cerebral peduncle in the midbrain, through the pons, and collect to form a tract at the base of the medulla.
- The axons terminate in the dorsolateral region of the ventral horns and intermediate gray matter.
- There, motor neurons and interneurons are located,
which control the distal muscles (particularly the flexors, say arms and fingers)
Rubrospinal tract
- Originates in the red nucleus, axons decussate in the pons, and join those in the corticospinal tract in the lateral column of the spinal cord.
- Also contributes to arms, hands and finger movements
Vestibulospinal tracts
- Originate in the vestibular nuclei of the medulla, which relay sensory information from the vestibular labyrinth in the inner ear
1. One component controls cervical spinal circuits guiding head movement
2. Another goes to the lumbar spinal cord and controls posture
Reticulospinal tracts
Pontine (medial) reticulospinal tract
Enhances the antigravity reflexes of the spinal cord, by facilitating the extensors of the lower limbs.
**Medullary (lateral) reticulospinal tract **-
Has the opposite effect - it liberates the antigravity muscles from reflex control.
Motor cortex
Definition
A region of the frontal lobe, including area 4 and 6
Primary Motor cortex
Definition
Also called M1 or motor strip, consists of the area 4 anterior to the central sulcus
Area 6
Definition
Includes the premotor areas (PMA) laterally and the Supplementary motor area (SMA) medially
Hierachical classification of Motor Systems
As explained in Bear et al.
- High: Includes the association areas of the neocortex and the basal ganglia and is responsible for strategy
- Middle: Includes the Motor cortex and the cerebellum and is responsible for tactics
- Low: Includes brainstem and spinal cord and is responsible for execution
Function of the Primary motor cortex
- M1 contains a crude somatotopic representation, in which different regions represent different body parts.
- Recordings from M1 neurons show that a burst of activity occurs immediately before and during a voluntary movement, and that
this activity encodes 2 aspects of the movement: force and direction
Coding of movement in the Primary Motor Cortex
- Much of M1 is active for every movement.
- The activity of each cell represents a single ‘vote’ for a particular direction of movement.
- The direction of movement is determined by averaging of the votes registered by each cell in the population (vector)
- It has been suggested that neurons should not be seen as static representational devices (e.g. with a fixed directional tuning), but as coding many different features depending on time and context.
Nonprimary motor areas
As explained in Chouinard et al.
- All areas in the frontal lobe that can influence motor output at the level of both M1 and spinal cord.
- This includes the PMA & SMA, and the cingulate motor areas
Dorsal premotor area (PMd)
- PMd can direct movements based on sensory information.
- PMd receives a combination of somatosensory and visual information for the visual guidance of arm movement trajectories from the medial intraparietal (MIP) area in the superior parietal lobule.
- Patients with frontal lobe damage, including portions of the premotor cortex, have difficulties in learning associations that involve motor stimuli
Ventral premotor area (PMv)
- PMv has an important role in the control of hand movements required for the manipulation of objects
- Grasping objects requires a transformation from the visual representation of the object’s geometry to the motor commands acting on the hand muscles.
- This relies on a parieto-frontal circuit composed of connections between the anterior intraparietal (AIP) area and PMv
- Also includes mirror neurons
Paresis
Weakness after partial damage to lower parts of the motor system
Areflexia
An absence of spinal reflexes
