Lecture 6 Flashcards
What is a sensory modality ? What are they in modern physiology ?
complex of sensations.
5 classical sensory performances + warmth/cold, pain, joint position and position in space
what is the difference between special and somatic senses ? What are the 5 types of receptors ?
Special senses have specific sensors for them (and not somatic senses).
Chemoreceptors, mechanoreceptors (baroreceptors, osmoreceptors, …) , photoreceptors, thermoreceptors, nociceptors
what is proprioception ?
awareness of body movement and position in space, muscle and joint sensory receptors either unconscious or conscious
2 types of sensory receptor cells
1) primary sensory cell : neuron with either free nerve endings or enclosed nerve endings
2) secondary sensory cell : sepcialized cell + synapse to a sensory neuron
what is a receptive field ? difference between large and small fields ?
It is the area from which a sensory receptor (and its corresponding neuron) can detect a stimulus.
Large field -> convergence to one secondary neuron -> no two-point discrimination, less precise.
Small field -> each primary neuron connects to a secondary neuron -> two-point discrimination, more sensitive
what is lateral inhibition ?
It enhances contrast : pathway closest to the stimulus inhibits the neighbors (inhibitary interneurons)
How are sitmulus intensity and duration encoded ?
Longer or stronger stimuli release more neurotransmitter -> the FREQUENCY of action potentials increase (not the amplitude)
two types of receptor adaptation
1) tonic receptors : maintain firing as long as stimulus is present
2) phasic receptors : once stimulus reaches steady intensity, the phasic receptors turn of
where do sensory pathways go in the brain ?
First to the thalamus, which selects and relays info to the cortical centers (auditory cortex, visual, …)
Exception : olfactory pathways go directly to olfactory cortex
Which pathways cross where ?
Touch, vibration, proprioception : cross in the medulla
Pain, T, coarse touch : cross in the spinal cord
Difference between fast and slow pain
Fast (warning) : sharp and localized, rapidly transmitted to CNS (A_delta fibers)
Slow (information) : duller / more diffuse, small unmyelinated C fibers
Concept of referred pain
Pain in internal organs is sensed on the surface of the body.
Because nociceptors from several locations converge on a single ascending tract in spinal cord (can’t differentiate)
5 sensory receptors in skin
Free nerve endings
Meissner’s corpuscules
Pacinian corpuscules
Ruffini corpuscules
Merkel receptors
describe the olfactory pathway
olfactory epithelium -> olfactory sensory neurons -> synapse in olfactory bulb with secondary neurons -> olfactory cortex
How is the lifetime of olfactory neurons ?
They live only about 2 months -> replaced by new neurons who have to find their way to bulb
