Lecture #14 Flashcards
what are the two main parts of the sensory system?
thalamus and the somatosensory cortex
what is the somatosensory cortex responsible for?
the elaboration of the sensory inputs
describe pseudopolar unipolar neurons:
ex: in the finger there are the terminal regions of these cells whereas the cell bodies are in the dorsal route ganglia which are flanking the spinal cord → cytoplasmic bundles are directly connected to the axons allowing the electrical signal arising from the periphery to travel to the spinal cord
what is one way you can activate some areas of the thalamus allowing the brain to discriminate the position of incoming stimuli?
some of the long axons cross the midline and some of them cannot
what type of signal is created by mechanoreceptors?
located in the periphery and enter in contact with the stimulations - an analogical signal is transformed into an electrical signal formed by trains of action potentials
the signal then traces to pseudo-polar cells up to the dorsal nuclei of the spinal cord and to the thalamus
what is the second relias important in?
contacts the somatosensory cortex and is involved in the elaboration of information
helps to build a representation of the external environment
which of the two original philosophical theories about how the brain creates images is probably more correct?
Kant - the brain has an innate ability to elaborate images
how to mechanoreceptors in the skin work?
specialized cells under the skin that can sense a variation in pressure and transform this input in trains of action potentials that propagate it to the dorsal root ganglia
what do the specific mechanoreceptors in muscles, tendons, and joints sense?
proprioreception: to understand the position of a limb or allow you to move it in a specific way
why are the cells n charge of perception called pseudo polar?
they are directly connected to a structure very similar to an axon → signals travel directly from the periphery to the spinal cord
according to Webb, what does the difference between two stimuli depend on?
the intensity of the strength = there is a linear relationship
ΔS=k x S
what formula is used today for the difference in two stimuli?
I=k x (S-S(0))^n
n depends on the sensory pathway involved (pressure = 1 for example)
what is the sensory threshold?
under a certain intensity, a subject cannot sense a sound - if this threshold starts to drift to the right then there is an issue with the hearing system
what is reaction time elicited by?
strong stimuli that are shorter than the ones elicited by weak stimuli
describe a parallel analysis:
try to find a blue cross among red crosses → if you increase the number of items in a picture or if you reduce the number of items you need to look for, the reaction time does not change because in this case the brain is doing a parallel search
describe a serial analysis:
if asked to find a blue cross among a bunch of blue dashes - objects need to be analyzed one by one to find the right one
which is faster for our brains to perform, a parallel analysis or a serial analysis?
parallel analysis
what happens when pressure is applied to your finger?
there is an alteration of the cell membrane of this specific receptor and sensors that are closed in resting conditions
these sensors can sense the membrane stretching, and when this stretch occurs ion channels start to open → these channels are specific for sodium so therefore you will have a sodium infiltration under the cell membrane
causes a depolarization of the cell membrane making the membrane potential drift from the resting potential
a strong stimulus will cross the critical threshold and you will generate an action potential
what are the stretch receptors called?
Pacini cells
what is the equation used to describer the firing rate of our sensory cells?
u= n(sp)T / T
in essence, what are colors?
different frequencies of electromagnetic waves
in essence, what is music?
vibrations
in essence, what are scents?
different chemicals in the air
what are mechanoreceptors?
located under the skin and in muscles and tendons → sense vibrations, light touch, and movement
what are the function of chemoreceptors?
sense and manage inputs from olfaction, pain, and visceral sensations
what are the function of thermoreceptors?
monitors blood temperature in the hypothalamus and are responsible for whether we feel hot or cold
what is the tuning curve important for?
the visual sensation
what are the four receptors we have the sense light?
rod, blue cone, green cone, and red cone
what is the threshold of activation?
a certain wavelength in which the cones are activated at minimal energy
describe how our brain can distinguish different colors:
if you activate the retina at 564 nm you can perfectly activate the red cone allowing you to see yellow
if you activate the retinal at 520 nm you are activating the red cone, but at the same time the green cone and only this combination will allow you to see that shade of green
describe the process of events that occur if you stick your hand under hot water:
- sensory receptors under the skin are activated
- action potential runs through the dorsal route ganglionic neurons
- enters the spinal cord where there is a specific second neuron that receives the synapsis and sends it along the very long axon
- in this case the axon crosses the midline and travels to the thalamus
- axon makes contact with the thalamic neurons that will send another signal to the somatosensory cortex and the activation of the first motor neuron
- motor neurons have very long axons that cross the midline at the level of the cervical tract and enter the spinal cord to make contact with the second motor neuron connected to the muscles
what is the average time for a sensory reaction like this?
100-200 ms
describe how slowly adapting receptors work:
they start to fire in response to stimulation - the intensity of the firing is higher at the beginning, and the frequency is proportional to the intensity of stimulation
if stimulation is kept constant, there is a slight reduction in frequency, but the sensory cells are still firing
describe rapidly adaptive receptors:
they start to fire at the beginning when there is a variation of stimuli, but then when the stimuli becomes constant, they stop firing and only result when the stimulation is removed
what size of axons are the proprioreceptor cells of muscles and tendons characterized by?
big axons → their conduction is very fast
what is the speed of conduction of the smaller receptors that sense vibrations, light tough, and pressure (smaller axon diameter and smaller conduction velocity)?
45-50 m/s
what is the conduction speed of pain and temperature sensors (very small caliber fibers)
send action potentials with very slow speeds → 5-30 m/s
