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sensorimotor system - Coggle Diagram
sensorimotor system
the sensorimotor system is hierarchal organised and is divided into levels. the higher levels plan movements, and the lower levels execute these planned movements. highest level is association cortex, second is secondary motor cortex moving onto the primary motor cortex, brain stem motor nuclei going to the spinal motor cirtuits
the system also has functional segregation - each level is divided into sub-levels which perform different functions
the system has a parallel structure - signal flows across the levels through multiple paths , provides some robustness against damage.
dorsolateral prefrontal cortex: - DLPFC receives signals from PPC and sends information to primary and secondary motor cortices - DLPFC is involved in motor planning
- motor cortices executes movements
secondary motor cortex - receives input from the association and projects to the primary motor cortex
- further subdivided into
supplementary areas
- premotor areas
cingulate motor areas
- coordinates movement sequences and projects towards primary motor corticies
damage to secondary motor areas - brivnkman (1984) tested monkeys with premotor and supplementary motor lesions on a bimanual coordination tasks
- monkeys completed tasks in which they retrieved a piece of food wedged in the slot of a table
- results indicated difficulty coordinating both hands to extract food
- highlights the role of these regions in complex programming movements sequences
basal ganglia: structures - dorsal striatum - caudate - putamen - globus pallidus - plays a role in spontaneous self-initiated behaviours and habit learning - disorders of movements = parkinsons, huntingtons
parkinsons symptoms - rigidity, muscle tremors , slow movments and difficulty initiating physical and mental acitivty
immediate cause - gradual progressive death of neurons, especially in the substation nigra, which sense dopamine releasing axons to the caudate nucleus and putamen
huntingtons disease symptoms - motor symptoms usually begins with arm jerk, facial twitches , later tremors, this condition is mostly seen between ages 30 and 50, the condition is associated with damage to the cerebral regions and basal ganglia
the sensorimotor system dictates how we move, basic behaviours require complex biological mechanisms
the areas of the sensorimotor hierarchy
- sensorimotor association heirarchy
- secondary motor cortex
- primary motor cortex
motor output is guided by sensory input from from sensory systems such as the visual and vestibular systems . information or feedback from these are used to fine-tune bodies movements except fast movements (ballistic) as there is not enough time to update movements as its too quick.
e.g. case study patient G.O.
- loss of sensory input illustrates the importance feedback plays in movement production
- this patients motor power was unaffected, just couldn't feel anything
- reported the case G.O. who experiences loss of sensory input from limbs
- unable to perform a variety of everyday tasks - couldn't maintain a constant motor output
- shows role of sensory feedback
learning changes, the nature of the locus of sensorimotor control, learning changes the nature of movement e.g., dancers become aware of every step initially in a routine however after a while they will not think about every single step - execution becomes more automated with practise
areas of the sensorimotor hierarchy
- sensorimotor association cortex
- posterior parietal association cortex
- dorsolateral prefrontal association cortex
posterior parietal cortex - integrates information about body part location and external objects (where you are in regards to objects) which is necessary in initiating movement
- it receives information from other sensory areas such as visual cortex which allows us to locate position to our body
- outputs to motor cortex
damage to the PPC - apraxia - disorder of voluntary movement, difficulty completing actions out of context e.g. can brush hair teeth but at school couldnt do it
- problem only evidnet when instructed to perform an acrion
- usually a consequence of damage to the left posterior parietal cortex but systems often occur bilaterally
cerebellum and basal ganglia both have a role in movement coordination but are not part of sensorimotor hierarchy - both are important but neither part, through which signals descend through sensory motor hierarchy
- instead both structures interact with different levels of the hierarchy and thus coordinate and modulates its acitivities
cerebellum structures and functions - constitutes two hemispheres separated by the vermis
- surface area increased by fissures and folia
- constitutes 10% of brain mass >50% of its neurons
- recieves input from the primary and secondary motor cortex, brain stem nuclei and feedback from sensory systems - allowing coordinating movements
primary motor cortex, the primary motor cortex is located on the precentral gyrus, recieves input from the secondary motor cortex. just like primary somatosensory cortex the primary cortex also has a somatotropin organisation
cerebellar ataxia
- damage to cerebellum - using finger to reach from your nose repeatedly
- repeat this procedure with a moving target 9which could be the finger of a friend)
- movements become uncoordinated and less accurate following cerebellar damage = ataxia
- dysnegria - impaired joint movements and difficulty coordinating movements so movements broken down into single joint movement
- dysmetria- tendency to over or undershoot when moving
research evidence: - Ivry and keel 1989 - examined the role of the cerebellum in timing functions using 2 tasks - rhythmic tapping and perception task, patients with cerebellar damage demonstrated great variability in their performance on the tapping and made more errors when making perceptual discriminations of sound - Day et al (1989) participants made reaching movements to a visually presented target, cerebellar damage was associated with delayed movement onset, longer movement times and greater spatial variability - park et al (2009) evidence for increased cerebellar volume in basketball players, 2021 increased right cerebellar hemisphere volume in short-track speed skaters.