Posterior/Dorsal Columns (aka Dorsal column-lemniscal system)

• Fasciculus Cuneatus – cervical and thoracic regions Fasciculus Gracilis – lumbar and sacral regions
• Both tracts communicate information about:
• Spatial awareness: proprioception and kinesthesia
• Fine discriminative touch (localized)
• Vibration

 Spinothalamic Tracts (aka Spinal Lemniscus, Anterolateral System)

Lateral Spinothalamic Tract – primarily pain and temperature

Anterior Spinothalamic Tract – primarily diffuse or crude touch/pressure/light touch (global)

Spinocerebellar tracts

• Ventral/Anterior Spinocerebellar Tract – fibers cross twice – ipsilateral 
• Dorsal/Posterior Spinocerebellar Tract – fibers don’t cross – ipsilateral
• Allow for integration of proprioceptive impulses
• No 3rd order neuron

dorsal root ganglion of the spinal cord; collect info from the periphery and transmit to second order neurons

thalamus – which projects to the sensory cortex

 •Touch 

•Visual

 •Auditory

 •Taste

 •Smell

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GSA – General Somatic Afferent

Touch, pressure, vibration, pain, temperature, stretch, position sense

From Skin & Skeletal Muscles

GVA – General Visceral Afferent

Pressure, pain and sensation from visceral areas

From internal organs: (ANS) heart, lungs, stomach, pancreas, bladder

Sensory transduction

Ascending pathway

begins at the neuron’s entry to the CNS at the level of the spinal cord (dorsal root) and ends either in the sensory cortex or the cerebellum

close to the body, detect sensory information from the environment – touch, pressure, temperature, pain, vibration

2 types:

teleoreceptors

contact receptors

Interoceptors

Proprioceptors

Nociceptors

•detect painful or noxious stimuli

•(visceral pain)

Mechanoreceptors (Exteroceptors and Proprioceptors)

inner awareness of our limbs and movement

position of our body in relation to the environment

•Meissner’s corpuscles – 2-point discriminative touch

•Merkel’s discs – light pressure, discriminative touch

•Extrafusal Fibers

 •Intrafusal fibers

•Muscle spindles

 •Golgi tendon organs

ordinary skeletal muscles – majority of gross muscle

dispersed throughout/within gross muscle

receptors– groups of intrafusal fibers (2-12)

dorsal root ganglion of the spinal cord; collect info from the periphery and transmit to second order neurons

either the spinal cord or the brainstem; point of decussation before traveling to thalamus in opposite hemisphere

thalamus – which projects to the sensory cortex (except for the spinocerebellar tracts)

•Lateral Dorsal Column/Fasciculus Cuneatus

 •Both tracts communicate information about:

 •Spatial awareness:  proprioception and kinesthesia

 •Fine discriminative touch (localized)

 •Vibration

Anterior Spinothalamic Tract

primarily diffuse or crude touch/pressure/light touch (global) 

fibers cross twice – ipsilateral

Dorsal/Posterior Spinocerebellar Tract

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 •hole in the center of the iris that allows light to travel through the lens (convex) to the retina

•light sensitive tissue in the back of the eye; temporal and nasal fibers

rods

cones

 •more numerous (120 million) – grayscale

 •(6 or 7 million) – sensitive to color

 •overlap of what is seen by both eyes, allows for depth perception

 •central vision – rays through pupil converge on the macula – central part of retina

The left temporal fiber sees the nasal area of the right visual field and projects info ipsilaterally to the left side of the brain

The right nasal fiber sees the temporal area of the right visual field and projects info through the optic chiasm to the left side of the brain

dorsal visual stream

"where"

through the parietal lobe

Ventral visual stream

"what"

through the temporal lobe

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