Week 2 Sensory Receptors, Sensory Pathways, Lesions Flashcards
Define stimulus transduction.
The process by which a sensory receptor converts the sensory stimulus into an electrical signal that is carried by sensory axons
What is a graded potential (aka generator potential or receptor potential)?
- changes in ion fluxes across the membrane in varying degrees (not all or none)
- an increase in magnitude of a receptor potential (stimulus energy) causes an increase in frequency of action potentials
Define adaptation or desensitization.
-decrease in frequency of action potentials in a sensory neuron despite maintenance of the stimulus at constant strength
What is the difference between rapidly adapting (phasic) receptors and slowly adapting (tonic) receptors?
- rapidly adapting: response quickly to onset of stimulus then decreases over time or may stop responding. important for indicating change in stimulus. E.g. putting on a sock, then forgetting it is on your feet
- slowly adapting: responses that maintain response to stimulus over time, e.g. receptors in joints/muscles that convey positional info, receptors that measure oxygen tension in blood
What are the 4 attributes coded for by a sensory stimulus?
- modality (what it is)
- touch, temperature, pain receptors - location (where it is)
- related to size of receptive fields of neurons - intensity
- conveyed via freq of action potentials - duration
How do receptive fields of neurons convey the degree of acuity of a particular sense?
- overlapping receptive fields give more precise location (e.g. if recorded by 3 neurons, stimulus is at the intersection of those receptive fields)
- size of receptive field: small on fingertips and large on back (less able to distinguish between two points close together) [2 point discrimination]
- lateral inhibition: ability of excited neuron to reduce activity of it neighbors and sharpen spatial profile of excitation
Where is neuron 1 and its axons for the DC/ML pathway?
Neuron 1 is in DRG
Its axons for C1-T5 are in Fasciculus cuneatus in spinal cord
Its axons for T6-S5 are in Fasciculus gracilis in the spinal cord
Where is neuron 2 and its axons for the DC/ML pathway? Where is neuron 3?
Neuron 2 is the Nucleus cuneatus and Nucleus gracilis in the lower medulla. Its axons take the ML pathway after decussation. Neuron 3 is VPL in the thalamus.
Where is neuron 1 and its axons for the STT pathway?
Neuron 1 is DRG
Its axons doesn’t have a name
Where is neuron 2 and its axons for the STT pathway? Where is neuron 3?
Neuron 2 is nucleus proprius in the dorsal horn where the axons of neuron 1 enter the spinal cord.
Axons of neuron decussate 1-2 segments above nucleus proprius through white commissure and follow STT tract to Neuron 3-VPL in thalamus
Where is neuron 1 and its axons for the TL (trigeminal lemniscus) pathway?
Neuron 1: trigeminal ganglion
Its axons aren’t named
Where is neuron 2 and its axons for the TL pathway? Where is neuron 3?
Neuron 2: Chief/main sensory nucleus of V in mid pons
The axons decussate in the mid pons and follow the TL pathway
Neuron 3: VPM in thalamus
Where is neuron 1 and its axons for the TTT (Trigeminal thalamic tract) pathway?
Neuron 1: trigeminal ganglion
The axons follow spinal tract of V in mid pons-descending to lower medulla
Where is neuron 2 and its axons for the TTT pathway? Where is neuron 3?
Neuron 2: Spinal nucleus of V
Axons follow TTT pathway, decussating in lower medulla and ascending to Neuron 3
Neuron 3: VPM in thalamus
What is the sensory pathway for taste?
Neuron 1: sensory ganglion of VII, IX, and X Neuron 1 axons: solitary tract Neuron 2: nucleus solitarius Neuron 2 axons central tegmental tract Neuron 3: insula, SS1 for tongue
