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Chapter 5

PSYB65H3 Chapter Notes - Chapter 5: Coprolalia, Thalamus, Palilalia

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Ted Petit

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Chapter 5: The Sensorimotor System
Somatosensory Receptors
Much of the somatosensory information that we receive about the world comes from sensory receptors in the
oVariety of different sensory receptors present in the skin
Three types of somatic information
oNociception – sensations of pain and temperature
oHapsis – sensations of fine touch and pressure
oProprioception – awareness of the body and its position in space
oRegardless of function, most of the sensory receptors in the skin are mechanoreceptors which
react to distortion such as bending or stretching
Most are axons that have mechanosensitive ion channels on them
Axons that contain these ion channels are primary afferent axons that enter the spinal
cord through the dorsal roots
Cell bodies of the primary afferent axons reside in the dorsal root ganglia of the spinal
Spinal cord is organized into dorsal and ventral root ganglia
oDorsal root ganglia are somatosensory
oVentral root ganglia are motor
o30 pairs of spinal nerves, each of which is made up of dorsal and ventral roots that exit the spinal
cord through a notch in the vertebrae of the spine
Spinal segments can be divided into four groups on the basis of where the nerves

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oEach of the 30 dorsal roots of the spinal cord innervates different areas of the skin called
oWhen a dorsal root is cut, spinal cord can no longer obtain information from that nerve
oNot all sensation from that dermatome is lost
Extensive overlap between dermatomes
To lose complete sensation in one dermatome, must cut three dorsal roots
One serving the dermatome and the dorsal roots above and below it
Somatosensory Pathways in the Brain
Two main pathways named for their position in the spinal cord and the connections made:
oDorsal spinothalamic tract
Responsible for transmitting information about proprioception and hapsis
Enters spinal cord through the dorsal root ganglion and synapses ipsilaterally in the
dorsal column nuclei of the spinal cord
Axons of the medial lemniscus synapse in the ventrolateral thalamus (sends projections to
both the motor and somatosensory cortex)
oVentral spinothalamic tract
Nociceptive information travels separately
Enters the spinal cord through the dorsal root ganglion and ascends the spinal cord
In the brainstem, these axons join the medial lemniscus and ascend to the ventrolateral
Some of these neurons send projections to the somatosensory cortex
oAlthough somatosensory information for hapsis and nociception is transmitted separately, because
they send information through the same pathways to the same destinations, damage to the
brainstem or thalamus results in equal loss of both hapsis and nociception
Damage to the spinal cord results in a loss of sensorimotor function below the site of
If spinal cord is not completely transected (cut through), nociception is lost of the side of
the body contralateral to the injury, and hapsis is lost for the side of the body ipsilateral to
the injury
Association Cortex

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Posterior Parietal Association Cortex
Active whenever brain is interacting with space or with spatial information
Plays important role in determining both the original position of the body and objects around the body in
Receives input from a variety of sensory systems, including proprioception, hapsis, and vision
oUsing this information, PPAC is responsible for creating mental picture of the boy in space
oBrodmann’s area 5 receives inputs from primary somatosensory cortical areas
oBA3, BA1, BA2, and BA7 receive higher-order visual information
oDamage to these areas of the parietal lobes tend to have difficulties with spatial relations
Also tend to have disturbances of body image
Fail to recognize parts of their body as belonging to themselves
Involved in processing of spatial relations of both the body and objects surrounding the body
oCritical role in the production of accurate movements
oExtensive interconnections between the posterior parietal association cortex and the dorsolateral
prefrontal association cortex allow this information to guide movements
Has extensive reciprocal connections with areas that are lower in motor hierarchy
oEg. Secondary and primary motor cortex
Dorsolateral Prefrontal Cortex
Involved with the decision to execute voluntary movements
Actively directs lower areas in the motor hierarchy
Assessing the likely outcome of planned movements
Secondary Motor Cortex
Include the supplementary motor area, premotor cortex, and the cingulate motor areas
Regardless of the specific site, all areas of the secondary motor area are reciprocally connected to one another
Secondary motor cortex sends direct projections to brainstem nuclei
Electrical stimulation of any of these areas results in complex motor movements
oAll play a role in voluntary motor production
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