6.1 afferent pathways

1st order neurons involved in the CNS

• collect & transmit sensory information to the CNS.

The INTEGRATION of sensory information occurs in

various structures within the CNS

Structures involved in the integration of sensory information 

• Tracts

• Medulla oblongata

• Brainstem

• Thalamus

• Sensory Cortex

• Cerebellum

Cerebellum

• receives proprioceptive input for coordination

 Sensory Cortex corresponds to

• primary & association cortex

Thalamus

• sensory information, except olfactory, is classified here & directed to the corresponding sensory cortex.

Brainstem

• (cranial nerve nuclei)

Tracts

• Ascending tracts → posterior/dorsal & lateral spinal cord tracts.

Initial processing of the sensory information 

• encoded by the 3rd order neuron (thalamic)

Initial processing of the sensory information encoded by the 3rd order neuron (thalamic)

• Primary sensory areas (Primary somatosensory cortex, visual, auditory, insular cortex & olfactory bulbs)

Interpretation of sensory information

• Association areas adjacent to primary sensory areas (auditory, visual and somatosensory)

Three unimodal sensory association areas are typically identified:

• auditory

• visual

• somatosensory

Olfactory pathways

• projects through olfactory bulb to the olfactory cortex

Thalamus after receiving sensory information

• modifies & relays information to cortical centers

Equilibrium pathways

• projects primarily to the cerebellum

-Primary somatosensory map (S1)

• primary somatosensory cortex is responsible for receiving the bulk of somatosensory inputs, including touch,

temperature, vibration, pressure, & pain.

secondary somatosensory cortex

• integrates bilateral sensory input; involved in tactile learning, object recognition by touch, & sensory memory.

Pathway

• Primary somatosensory cortex

• Secondary somatosensory cortex

• Projection to areas such as the amygdala or the hippocampus (tactile learning and memory)

After an amputation, there is reorganization of the somatosensory cortex

→ The area to which the information from finger 3 arrived, two months later receives information from areas 2 and 4.

Sensory information is transformed into (during the phase of integration)

• perception

Often the perceived stimulus is different from the actual stimulus: (example)

• The photoreceptors in the eye receive energy waves of different wavelengths that we perceive as different colors.

The telencephalon is capable of

• filling in the information missing, in order to complete a picture, or can translate a two-dimensional drawing into a three-dimensional shape