PSY2061 Chapter Notes - Chapter 8: Anterior Grey Column, Midbrain Tectum, Withdrawal Reflex
5 Jun 2018
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PSY2061 – Week 6 – Readings – The Control of Action
• three principles of sensorimotor function
•
o hierarchically organised
o
▪ levels of a hierarchy - from the association cortex - highest
levels (president) - to the muscles - lowest levels - workers
▪ advantage - the higher levels of the hierarchy are left free to
perform more complex functions
▪ parallel hierarchical system - system in which signals flow
between levels over multiple paths
▪ characterised by functional segregation
▪ each level tends to be composed of different units - neural
structures or departments - each of which perform a
different function
▪ information mainly flows down
o motor output is guided by sensory output
o
▪ the eyes, the organs of balance, and the receptors in skin,
muscles and joints all monitor the body’s responses and
they feed their information back into sensorimotor circuits
▪ this sensory feedback plays an important role in directing
the continuation of the responses that produced it
o learning changes the nature and locus of sensorimotor control
o
▪ During the initial stages of motor learning, each individual
response is performed under conscious control; then, after
much practice, individual responses become organised into
continuous integrated sequences of action that flow
smoothly and are adjusted by sensory feedback with out
conscious regulation.
• general model of sensorimotor system function
• sensorimotor association cortex
•
o association cortex is at the top of the sensorimotor hierarchy
o there are two major areas of association cortex
o
▪ the posterior parietal association cortex
▪
▪ plays an important role in integrating information
regarding the ordinal positions of the parts of the
body that are to be moved and the positions of an
external objects with which the body is going to
interact
▪ directs behaviour by providing spatial information
▪ directs attention
▪ most of the output goes to areas of motor cortex
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find more resources at oneclass.com
▪ contains a mosaic of small areas, each specialise for
guiding particular movements of eyes, head, arms or
hands
▪ damage can produce a variety of deficits
▪
▪ including deficits in the reception and
memory of spatial relationships
▪ in accurate reaching and grasping
▪ in the control of eye movement
▪ in attention
▪ apraxia
▪
▪ a disorder of voluntary movement that
is not attributable to a simple motor
deficit or to any deficit in
comprehension or motivation
▪ difficulty making specific movements
when requested to do so - particularly
when the movements are out of
context
▪ can often readily perform the same
movements under natural conditions
when they are not thinking about what
they are doing
▪ contralateral neglect
▪
▪ disturbance of a patient’s ability to
respond to stimuli on the side of the
body opposite to the side of a brain
lesion in the absence of simple sensory
or motor deficits
▪ often behave as if the left side of their
world doesn’t exist
▪ fail to realise they have a problem
▪ left of their own bodies - egocentric
left
▪ many patients tend not to respond to
the left sides of objects, regardless of if
the objects are in their visual fields
▪
▪ object-based contralateral
neglect
▪ the dorsolateral prefrontal association cortex
▪
▪ receives projections from the posterior parietal
cortex
▪ sends projections to areas of secondary motor
cortex, to primary motor cortex and to the frontal
eye field
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find more resources at oneclass.com
• secondary motor cortex
•
o areas of secondary motor cortex are those that receive much of
their input from the association cortex
o supplementary motor area - wraps over the top of the frontal lobe
and extends down its medial surface into the longitudinal fissure
o premotor cortex - runs in a strip from the supplementary motor
area to the lateral fissure
o identifying areas of secondary motor cortex
o
▪ at least eight areas - with their own subdivisions
▪ three different supplementary motor areas (SMA, preSMA,
and supple mentary eye field), two premotor areas (dorsal
and ventral), and three small areas—the cingulate motor
areas—in the cortex of the cingulate gyrus.
▪ to qualify as secondary motor cortex - an area must be
appropriately connected with association and secondary
motor areas
• mirror neurons
•
o neurons that fire when an individual performs a particular goal-
directed hand movement or when they observe the same goal-
directed hand movement by another
o provide a possible mechanism for social cognition -knowledge of
perceptions, ideas and intentions of others
o
▪ these neurons respond to the understanding of the purpose
of an action - not a superficial characteristics of the action
itself
• primary motor cortex
•
o located in the pre central gyrus of the frontal lobe
o major point of convergence of cortical sensorimotor signals
o major point of departure of sensorimotor signals from the cerebral
cortex
o conventional view of primary motor cortex function
o
▪ primary motor cortex is organised soma topically
▪
▪ according to the map of the body
▪ the somatopic layout of the human primary motor
cortex is commonly referred to as the motor
homunculus
▪ most of the primary motor cortex is dedicated to
controlling parts of the body that are capable of
intricate movements such as the hands
▪ many primary motor cortex neurons are tuned to
movement in a particular direction
find more resources at oneclass.com
find more resources at oneclass.com
