15.4-15.5

corticospinal pathway

-Carry voluntary somatic motor commands to provide voluntary control over skeletal muscles -Sometimes called the pyramidal system -Because the upper motor neuron is a Pyramidal cell -Begins at pyramidal cells of primary motor cortex -Axons descend into brainstem and spinal cord -Synapse on lower motor neurons that control skeletal muscles

upper motor neuron

-Cell body lies in a CNS processing center -Synapses on the lower motor neuron -Activity in upper motor neuron may facilitate or inhibit lower motor neuron

sensory homunculus

-Functional map of the primary sensory cortex -Distortions are because: Area of sensory cortex devoted to a particular body region are Proportional to density of sensory neurons Not proportional to the size of the body part

motor homunculus

-It is a functional map of the primary motor cortex -Corresponds with specific regions of the body -Size of homunculus indicates the degree of fine motor control available -Hands, face, & tongue appear large -Trunk is relatively small -Proportions similar to sensory homunculus

solitary nucleus

-Large nucleus in the medulla oblongata -Major processing and sorting center for visceral sensory information -Extensive connections with cardiovascular centers, respiratory centers and reticular formation

somatic nervous system

-Somatic Motor Portion of the Efferent Division -Motor neurons and pathways that control the contractions of skeletal muscles

Visceral sensory pathways

-Visceral sensory information is collected by interoceptors monitoring visceral tissues & organs -Located primarily within the thoracic and abdominopelvic cavities -Interoceptors include nociceptors, thermoreceptors, tactile receptors, baroreceptors chemoreceptors -Not as numerous as exteroceptors & proprioceptors in somatic tissues

Somatic motor pathways

-carries somatic motor commands from motor centers in the brain to skeletal muscle -always involve at least two motor neurons: upper motor neuron & lower motor neuron

lower motor neuron

-cell body lies in a nucleus of the brainstem or spinal cord -only the axon extends outside CNS -innervates a single motor unit in a skeletal muscle -triggers a contraction in the innervate muscle -destruction of or damage to a lower motor neuron eliminates voluntary and reflex control over innervates motor unit

Visceral sensory pathways

-cranial nerves V, VII, IX, & X -carry visceral sensory information form mouth, palate, pharynx, larynx, trachea, esophagus

Sensory information

-most somatic sensory info -is relayed to the thalamus for processing -only a small fraction (about 1%) of the arriving info -is projected to the cerebral cortex and reaches our awareness

Abnormalities in spinothalamic pathways can cause

-painful sensations that are perceived in a location where they were not produced (phantom limb syndrome) -referred pain- strong visceral sensations arriving at the spinal cord can stimulate interneurons that are part of spinothalamicpathway, causing visceral pain to manifest as pain from another area (heart attain is felt in the left arm)

Separate pathways carry

-somatic sensory info -somatic visceral sensation

3 major somatic sensory pathways

-spinothalamic pathway -posterior column pathway -spinocerebellar pathway

Posterior column pathway

Carries sensations of highly localized ("fine) touch, pressure, vibration and proprioception

Somatic sensory pathways

Carry sensory information from the skin & muscles of the body wall, head, neck, & limbs to the CNS

Spinocerebellar pathway

Cerebellum receives proprioceptive information about position of skeletal muscles, tendons, and joints

Conscious & subconscious motor commands

Control skeletal muscles by traveling over three integrated motor pathways -corticospinal pathway -medial pathway -lateral pathway

lateral pathway

Helps control distal limb muscles that perform more precise movements

medial pathway

Helps control gross movements of trunk and proximal limb muscles

spinothalamic pathway

Provides conscious sensations of poorly localized ("crude") touch & pressure, pain, and temperature

Other pathways carry subconscious somatic motor commands

Provides subconscious adjustments to skeletal muscles