Lecture 3: Peripheral and Central Afferent Pathways

mechanoreceptors

specialized cells that project to an afferent neuron or are actually part of the afferent neuron itself

factors affecting speed of signal transduction

- insulation around the axon
- diameter of the axon

A-delta fibers

fast pain fibers

C fibers

slow pain fibers

A-beta fibers

- cutaneous mechanoreceptors
- static muscle spindles
- joint receptors

A-alpha fibers

-dynamic muscle spindles
- golgi tendon organs

divergence

- the same input separates/disperses to multiple locations
- axon branches out

convergence

- multiple inputs project to a common location
- common in association areas

topographic

ordered projection of a sensory surface, like the retina or the skin, within nuclei in the central nervous system

ipsilateral

belonging to or occuring from the same side of the body

contralateral

belonging to or occuring on the opposite side of the body

geniculostriate visual system

- primary visual pathway
- 90% of fibers

tectopulvinar visual system

- secondary visual pathway
- 10% of fibers

visual field

part of the visual environment that can be detected by both eyes

hemifield

the left or right half of the visual field

optic chiasm

- point at which optic nerve fibers cross in the brain
- information from the contralateral visual field cross

right thalamus/V1

represents the left hemifield

left thalamus/V1

represents the right hemifield

monocular hemianopia

the complete loss of vision in one eye due to damage of the ipsilateral optic nerve

optic tract

the bundle of nerves relaying visual information from the optic chiasm to the LGN thalamic nucleus

dorsal stream visual areas

- relate the visual information to the body
- vision for action

ventral stream visual area

- emphasize object recognition and classification
- vision for perception

prosopagnosia

- a disorder characterized by the inability to recognize faces
- damage to the ventral stream

vestibular nuclei

relay vestibular signals to the cerebellum, cortex and brainstem nuclei that send efferent signals to the eye muscles

vestibular nerve projects to

- ipsilateral vestibular nuclei
- ipsilateral cerebellum

dorsal horn

entry point of somatosensory nerves into the spinal cord

dorsal root ganglion

cell bodies of sensory neurons

fibers in the posterior column

convey fine touch, vibration and proprioceptive afferent information

third order neuron

axon projects from the thalamic nuclei to the primary somatosensory cortex

second order neuron

axon that crosses the body midline in the medulla and projects to the thalamic nucleus

first order neuron

axon that projects form the receptor to the medulla

anterior spinothalamic tract

- the more anterior-medial part of the spinothalamic tract
- crude, poorly localized, information about touch

lateral spinothalamic tract

- the more lateral part of the spinothalamic pathway
- information about noxious stimuli and temperature

dorsal spinocerebellar tract (DSCT)

- projects to the inferior peduncle of the cerebellum
- proprioceptive information from the lower limbs
- spindle fibers via Ia afferent neurons

rostral spinalcerebellar tract (RSCT)

- projects to the inferior peduncle of the cerebellum
- proprioceptive information from the upper limbs

ventral spinocerebellar tract (VSCT)

- projects to the superior cerebellar penducle
- proprioceptive information from the lower limbs
- golgi tendon organs via Ib afferent neurons

peduncle

thick stock or bundle of axons