The major functions of the nervous system are organized into separate longitudinal systems carrying information between the brain, spinal cord, nerves and muscles, The motor system is efferent, controlling movement of the muscles, the sensory system is afferent, carrying sensation from the body to the brain: the autonomic pathways are afferent and efferent, controlling automatic functions like blood flow, blood pressure, bladder and bowel functions, sweating, and many other bodily activities.
Corticofugal projections are descending systems for the selective control of lower sensory or motoneurons. The ventral posterior thalamus and other thalamic nuclei (corticothalamic) for selective attention to modality-specific processing. The dorsal column nuclei (gracile and cuneate nuclei)(corticobulbar) for feedback about limb position preparatory to new movement sequences. The reticular formation (corticoreticular) for attentional adjustments integrating expectation with sensory feedback. The spinal cord (corticospinal) for rapid, voluntary adjustments of skeletal muscle. The functions of corticofugal projections are feedback for error control, preparatory for the next series of postural and locomotor events, anticipation of and planning for future events, focusing attention on a particular modality or set of muscles
Receptive fields; definition. Center-surround organization reflects neural integration. There is a role of inhibition in the construction and modulation of receptive fields. Input from peripheral nerves defines the dermatome; the dermatome is made up of many receptive fields. Dermatomal organization is analogous to the cortical and spinal representation of muscle. Parallels in receptive field organization in the visual and auditory systems.
Parallel processing of touch, pressure, vibration and joint sensibility. The somatic sensory cortex contains representations of the body surface. Superimposed on these maps is a second layer of organization in which alternating cortical columns contain neurons turned preferentially to slowly or rapidly adapting mechanoreceptor populations; this means that a specific cortical column (and a particular neuron) specifies the modality, body surface position and speed of adaptation. Multiple maps of the body surface in the dorsal column nuclei, sensory thalamus and somatic sensory cortex are the physiological manifestation of parallel pathways. Why are there so many sensory and motor maps in the brain? The maps are not redundant or functionally duplicative, they are co-participants in serial processing, such as the projection of SI - SII.
AL (Anterolateral) System
- mediates pain, temperature sense
- cells of origin are mostly in the dorsal horn, not primary afferent
- cross in spinal cord, NOT medulla
- terminate in the brainstem, hypothalamus, thalamus, not just the thalamus
- project both contralateral and ipsilateral