PSY/IPN1023 Body and Behavior
TASK 5 – SENSORY AND MOTOR AREAS + PATHWAYS
PART I – SENSORY AREAS AND PATHWAYS
Principles of sensory system organization
The primary sensory cortex of a system is the area of sensory cortex that receives most of its
input directly from the thalamic relay nuclei of that system. The secondary sensory cortex
of a system comprises the areas of the sensory cortex that receive most of their input from the
primary sensory cortex of that system or from other areas of secondary sensory cortex of the
same system. Association cortex is any area of cortex that receives input from more than one
sensory system; most input comes via areas of secondary sensory cortex. The interactions
among these three types of sensory cortex and among other sensory structures are
characterized by three major principles; hierarchical organization, functional segregation,
and parallel processing.
Hierarchical organization
Sensory systems are characterized by hierarchical organization. Sensory structures are
organized on the basis of the specificity and complexity of their function. As one moves
through a sensory system from receptors, to thalamic nuclei, to primary sensory cortex, to
secondary sensory cortex, to association cortex, one finds neurons that respond optimally to
stimuli of greater specificity and complexity. Each level of a sensory hierarchy receives
most of its input from lower levels and adds another layer of analysis before passing it on up
the hierarchy. The hierarchical organization is apparent from a comparison of the effects of
damage to various levels: The higher the level of damage, the more specific and complex the
deficit.
Sensation is the process of detecting the presence of stimuli, and perception is the higher-
order process of integrating, recognizing and interpreting complete patterns of sensations.
Functional segregation
It was once assumed that the primary, secondary, and association areas of a sensory system
were each functionally homogeneous. Actually, the sensory system is characterized by
functional segregation. It is now known that each of the three levels (primary, secondary,
association) has distinct functions.
Parallel processing
In a serial system, information flows among the components over just one pathway, like a
string through a strand of beads. Evidence now suggests that sensory systems are parallel
systems in which information flows through the components over multiple pathways.
Parallel systems feature parallel processing - the simultaneous analysis of a signal in different
ways by the multiple parallel pathways of a neural network.
There appear to be two fundamentally different kinds of parallel streams of analysis in our
sensory systems: one capable of influencing our behavior without our conscious awareness
and one that influences our behavior by engaging our conscious awareness.
, PSY/IPN1023 Body and Behavior
Somatosensory system
Sensations from our body are referred to as somatosensations. The somatosensory system
consists of three separate but interacting systems;
1) Exteroceptive system; external stimuli applied to the skin.
2) Proprioceptive system; monitors information about the position of the body.
3) Interoceptive system; provides general information about conditions within the body.
There are many kinds of receptors in the skin. The
simplest cutaneous receptors are the free nerve
endings (neuron endings with no specialized
structures on them), which are particularly sensitive
to temperature change and pain. The largest and
deepest cutaneous receptors are the onion like
Pacinian corpuscles; because they adapt rapidly,
they respond to sudden displacements of the skin but
not to constant pressure. In contrast, Merkel’s disks
and Ruffini endings both adapt slowly and respond
to gradual skin indentation and skin stretch,
respectively.
The structure and physiology of each type of somatosensory receptor seems to be specialized
for a different function. However, in general, the various receptors tend to function in the
same way; stimuli applied to the skin deform or change the chemistry of the receptor, and this
in turn changes the permeability of the receptor cell membrane to various ions.
Each tactile sensation appears to be produced by the interaction of multiple receptor
mechanisms, and each receptor mechanism appears to contribute to multiple sensations.
TASK 5 – SENSORY AND MOTOR AREAS + PATHWAYS
PART I – SENSORY AREAS AND PATHWAYS
Principles of sensory system organization
The primary sensory cortex of a system is the area of sensory cortex that receives most of its
input directly from the thalamic relay nuclei of that system. The secondary sensory cortex
of a system comprises the areas of the sensory cortex that receive most of their input from the
primary sensory cortex of that system or from other areas of secondary sensory cortex of the
same system. Association cortex is any area of cortex that receives input from more than one
sensory system; most input comes via areas of secondary sensory cortex. The interactions
among these three types of sensory cortex and among other sensory structures are
characterized by three major principles; hierarchical organization, functional segregation,
and parallel processing.
Hierarchical organization
Sensory systems are characterized by hierarchical organization. Sensory structures are
organized on the basis of the specificity and complexity of their function. As one moves
through a sensory system from receptors, to thalamic nuclei, to primary sensory cortex, to
secondary sensory cortex, to association cortex, one finds neurons that respond optimally to
stimuli of greater specificity and complexity. Each level of a sensory hierarchy receives
most of its input from lower levels and adds another layer of analysis before passing it on up
the hierarchy. The hierarchical organization is apparent from a comparison of the effects of
damage to various levels: The higher the level of damage, the more specific and complex the
deficit.
Sensation is the process of detecting the presence of stimuli, and perception is the higher-
order process of integrating, recognizing and interpreting complete patterns of sensations.
Functional segregation
It was once assumed that the primary, secondary, and association areas of a sensory system
were each functionally homogeneous. Actually, the sensory system is characterized by
functional segregation. It is now known that each of the three levels (primary, secondary,
association) has distinct functions.
Parallel processing
In a serial system, information flows among the components over just one pathway, like a
string through a strand of beads. Evidence now suggests that sensory systems are parallel
systems in which information flows through the components over multiple pathways.
Parallel systems feature parallel processing - the simultaneous analysis of a signal in different
ways by the multiple parallel pathways of a neural network.
There appear to be two fundamentally different kinds of parallel streams of analysis in our
sensory systems: one capable of influencing our behavior without our conscious awareness
and one that influences our behavior by engaging our conscious awareness.
, PSY/IPN1023 Body and Behavior
Somatosensory system
Sensations from our body are referred to as somatosensations. The somatosensory system
consists of three separate but interacting systems;
1) Exteroceptive system; external stimuli applied to the skin.
2) Proprioceptive system; monitors information about the position of the body.
3) Interoceptive system; provides general information about conditions within the body.
There are many kinds of receptors in the skin. The
simplest cutaneous receptors are the free nerve
endings (neuron endings with no specialized
structures on them), which are particularly sensitive
to temperature change and pain. The largest and
deepest cutaneous receptors are the onion like
Pacinian corpuscles; because they adapt rapidly,
they respond to sudden displacements of the skin but
not to constant pressure. In contrast, Merkel’s disks
and Ruffini endings both adapt slowly and respond
to gradual skin indentation and skin stretch,
respectively.
The structure and physiology of each type of somatosensory receptor seems to be specialized
for a different function. However, in general, the various receptors tend to function in the
same way; stimuli applied to the skin deform or change the chemistry of the receptor, and this
in turn changes the permeability of the receptor cell membrane to various ions.
Each tactile sensation appears to be produced by the interaction of multiple receptor
mechanisms, and each receptor mechanism appears to contribute to multiple sensations.
