4800 Exam 2 Pathways

CNS

integrates info from and responds to external/internal environment

PNS

conveys info from external/internal environment to CNS and from CNS to external/internal environment

gray matter

function

white matter

pathway

white matter pathways

link functional areas of CNS and PNS together

association pathways

role: link functional gray matter areas within same hemisphere

examples: arcuate fasciculus, inferior occipitofrontal fascicsulus, and frontal aslant tract

arcuate fasciculus

association pathway

links frontal and temporal lobes in same hemisphere

complemented by parallel pathways called superior longitudinal fasciculus

together, these white matter pathways are often referred to as the “dorsal pathway”

superior longitudinal fasciculus

parallel pathway that complements the arcuate fasciculus association pathway

dorsal pathway

comprised of arcuate fasciculus and superior longitudinal fasciculus

role is to link speech and language areas that facilitate production of speech sounds and language comprehension

inferior occipitofrontal fasciculus

association pathway

links areas ranging from occipital to temporal and frontal lobes in same hemisphere

complemented by uncinate fasciculus

together, these white matter pathways are often referred to as the “ventral pathway”

uncinate fasciculus

parallel pathway that complements inferior occipitofrontal fasciculus association pathway

ventral pathway

comprised of inferior occipitofrontal fasciculus and uncinate fasciculus

role is to link functional areas association with language comprehension and production of speech content

frontal aslant tract

association pathway

links premotor cortex with inferior frontal gyrus

integrates speech sound with speech content planning

commissural pathways

role: link homologous areas between left and right hemispheres

example: corpcorpus callosum

corpus callosum

commissural pathway

massive pathway that interconnects both hemispheres

integrates homologous areas of both hemispheres:

• integrates sentence motor plan prepared by left hemisphere (Broca’s area) with prosodic motor plan prepared by right hemisphere (Broca’s homologue)

  • integrates comprehension of spoken content of left hemisphere (Wernicke’s area) with comprehension of speech prosody of homologous area of right hemisphere

projection pathways

“vertical” pathways that interconnect NS

descending “vertical” projection pathways link cortex with brainstem and spinal cord

ascending “vertical” projection pathways connect body sense info with thalamus and cerebral cortex

corticospinal tract

descending projection pathway (motor functions)

links cortical areas (UMN) with motor neurons of spinal cord (LMN)

consists of UMN axons from neuron cell bodies located in primary motor and premotor cortex, as well as small % of axons from primary somatosensory cortex

these UMN axons leave their cortical areas to go to spinal cord

at spinal cord, they synapse with LMNs of spinal cord, known as spinal cord motor neurons

these neurons synapse with various muscles “neck down” — including muscles of respiration for speech production

has contralateral connectionsb

contralateral connections

motor plans from right hemisphere conveyed to left side of body and vice versa

corticospinal tract

corticobulbar tract

descending projection pathway (motor functions)

links cortical motor areas (UMN) with cranial motor neurons of brainstem (LMN)

consists of UMN axons from neuron cell bodies located in primary motor and premotor cortex, as well as small percent of axons from primary somatosensory cortex

these axons leave their cortical areas and go to brainstem, where they synapse with LMNs of brainstem, known as cranial nerves with motor functions

these nerves synapse with muscles of speech production for phonatory and articulatory systems — or “neck up”

most axons have bilateral connections with cranial nerves with motor function

dorsal column-medial lemniscus

ascending projection pathway (sensory)

conveys info for touch and proprioception related to body from “neck down”

contralateral connections

info conveyed to thalamus before ending journey in primary somatosensory cortex

provides important info to primary somatosensory cortex about muscle and joint movements related to respiration for speech

spinothalamic tract

ascending projection pathway (sensory)

provides info about pain and temperature from “neck down”

nociceptors and thermoreceptors

these sensations are contralateral and they travel to thalamus first, then to primary somatosensory cortex for conscious processing

nociceptors

sensory neurons that convey body pain or tissue damage

spinothalamic tract

thermoreceptors

sensory neurons that convey temperature sensations

spinothalamic tract