Nervous System 2 - Sensory Input Flashcards
Lec 8 & 9
Within the afferent nervous system, how is sensory stimuli interpreted?
stimuli are detected by receptors that only respond to a spec stimulus ie temp receptors only respond to temp stim.
What can receptors be?
dendrites on unipolar neurons or individual cells which synapse to neurons (receptor cells).
What happens when a receptor is stimulated?
- stimulus causes opening of gated channels (usu Na) on receptor cell memb. 2. a GP occurs on the receptor memb (stim becomes electrical).
What are the two types of GPs that can happen on a receptor membrane?
- generator potential; occurs on dendrites of a first order sensory neuron and directly generates an AP on the axon of that same neuron. 2. receptor potential; receptor cell is separate form the sensory neuron. so, the receptor pot happens on the receptor cell which causes the release of nt onto the dendrites of the sensory neuron, then causing a PSP.
What are the types of receptors?
Phasic and tonic receptors.
What are phasic receptors?
receptors that respond to stimulus change. so if theres a constant stimulus they adapt to it usu by decreasing sensitivity. so an AP happens right when stim happens and then again when it turns off. ex. putting a hat on; mechanoreceptors detect the onset of stim and initially theres a burst of APs. over time the receptors adapt and the AP freq to the CNS decreases. when the hat is removed the receptors respond again to the change in pressure and theres a burst of APs
What are tonic receptors?
in the presence of a constant stim, the freq of APs remains relatively constant (no adaptation). continuous monitoring of sensory info and have a protective fxn. ie. proprioceptors and some nociceptors. monitor presence and intensity of stim.
How does the brain perceive diff types of stimuli?
mainly by the type of receptor stimulated. so when there are axons activated by receptors, there are synaptic connections to part of the CNS concerned with that sense. so spec signals from receptors go to spec parts of the CNS. so the brain always knows ‘whos’ calling (type of receptor) and from where (location).
How does the brain perceive stimuli of different strengths?
mainly by frequency of APs (number/time) going to CNS. the stronger the stim, the higher the AP freq. a stronger stim also activates more receptors.
What are the 3 neurons in succession in the sensory ascending pathways?
1st order, 2nd order, 3rd order. 1st order axon on the spinal cord receives signal from 1st order dendrites w/in receptors, 2nd order in medulla receive signal from 1st order, 3rd order in thalamus receive signal from 2nd order.
What is the sensory (afferent) pathway for vision?
- light enters the pupil and image is focused on retina (image reduced and inverted) 2. light stimulates a chemical rxn on rods and/or cones that produces a receptor potential. 3. nt releases and goes to bipolar neuron, causing a GP (no AP). 4. nt released and goes to ganglion cell where an EPSP happens, leading to an AP. 5. signal goes down optic nerve 6. signal goes to optic tracts. 7. signal goes to visual cortex of occipital lobe.
What is the sensory (afferent) pathway for hearing?
- hair cells in cochlear duct stimulated, leads to receptor potential. 2. release of nt onto associated neuron, causes EPSP, and then AP. 3. AP on axon of cochlear branch of cranial nerve VIII. 4. signal goes to auditory cortex in the temporal lobe.
What is the sensory (afferent) pathway for equilibrium?
- hair cells in semicircular ducts and saccule or utricle in vestibule stimulated, leads to receptor potential. 2. nt release onto associated neuron, causes EPSP leading to an AP. 3. AP on axon of vestibular branch of cranial nerve VIII. 4. signal goes to either cerebellum (coordinates mm contraction), thalamus, or brain stem (eye mms, mms of neck and trunk for balance).
