Topic 4: NS - Sensory Input Flashcards
what can receptors be?
-dendrites on unipolar neurons
-individual cells which synapse to neurons (hair cells in the internal ear)
what occurs when a receptor is stimulated?
-the stimulus will cause the opening of gated ion channels (typically Na+)
on the receptor membrane
-a graded potential occurs on the membrane (stimulus becomes electrical)
-2 types of possible graded potentials depending on the receptor cell
what are the 2 possible graded potentials that can take place on a receptor cell membrane?
-generator potential
-receptor potential
what is a generator potential?
-graded potential that occurs on the dendrites of a first order sensory neuron
-directly generates an AP on the axon of the same neuron
what is a receptor potential?
-graded potential that occurs on a seperate cell from the sensory neuron
-causes the release of a neurotransmitter onto the dendrites of the sensory neuron
what is an example of a receptor potential?
-hair cell in the inner ear
-a receptor potential is created on the hair cell and causes the hair cell to release a neurotransmitter onto the associated sensory neuron
-an EPSP occurs on the dendrites of the sensory neuron
-the EPSP generates an AP on the axon of the sensory neuron
what are the 2 types of receptors?
-phasic receptors
-tonic receptors
how do phasic receptors respond? what are examples of phasic receptors?
-respond to stimulus change
-in the presence of a constant stimulus they show adaptation (decrease in sensitivity to the stimulus)
-ex: touch (mechanoreceptors in skin) and smell (olfactory receptors)
what is an example of how mechanoreceptors in your skin adapt to a stimulus?
-if you put a hat on the mechanoreceptors will detect the onset of this stimulus and there is a burst of APs (feeling the hat on your head)
-over time the receptors adapt to the feeling and the AP frequency to the CNS decreases (brain does not perceive the stimulus even though it is maintained at a constant strength)
-when you remove the hat, the receptors respond again to the change in pressure and there is another burst of APs
-this sensation fades as the receptors adapt to the lack of stimulus
what are examples of mechanoreceptors in the skin?
-pacinian/lamellated corpuscles
how do tonic receptors respond? what are examples of tonic receptors?
-in the presence of a constant stimulus there is no adaptation
-the frequency of APs going to the CNS remains constant
-provides continuous monitoring of sensory information (monitor presence and intensity of stimulus)
-have a protective function
-ex: proprioceptors (posture) and some nociceptors (pain)
how can the brain perceive different types of stimuli?
-mainly by the type of receptor (touch, light, etc)
-has synaptic connections to a part of the CNS that is concerned with that sense (always knows from where the stimulus is coming and what receptor)
what are 2 examples of how the brain can perceive types of stimulus?
-ex: if a meissner’s corpuscle (touch) is stimulated in the right index finger, it will impulse to the postcentral gyrus region for the right index finger
-ex: if there is mechanical pressure on your eyeball it is seen as light, so all signals received from the retina are perceived as light
how does the brain perceive stimuli of different strengths?
-mainly by the frequency of APs going to the CNS
-the stronger the stimulus the higher the AP frequency (vice versa)
-a stronger stimulus will also activate more receptors (ex: pressure + touch together)
what is the sensory ascending pathway?
-3 neurons in succession (1st, 2nd, 3rd order)
-ex: posterior (dorsal) column pathways for touch
-a generator potential caused by mechanical gates is created when a stimulus is sent to the dendrites of the 1st order neuron (meissners corpuscle, unipolar)
-AP results on the axon of the 1st order neuron (axons are located in the posterior column of the spinal cord)
-EPSP is created onto the 2nd order neuron (multipolar) and generates an AP that will then form another EPSP onto the 3rd order neuron (multipolar)
-the AP that then will generate on the 3rd order neuron goes to the postcentral gyrus
-postcentral gyrus = general sensory area/somatosensory cortex
-this area will identify the stimulus as touch and localize (where the stimulus occurred on the body)
-this information moves to association areas such as memory and others
-the information is then integrated and forms the response starting in the motor areas of the cortex
what is the pathway of the vision special sense?
-light enters the pupil and the image is focused on the retina (image gets reduced and inverted)
-light then stimulates a chemical reaction on rods and/or cones that produce a receptor potential
-the receptor potential on the rods or cones releases a neurotransmitter onto a bipolar neuron (no AP) which results in another graded potential that releases a neurotransmitter onto a ganglion cell (no AP)
-the ganglion cell has an EPSP which results in an AP
-this AP innervates the optic nerve (axons of ganglion cells)
-this travels to the optic tracts and finally enters the visual cortex of the occipital lobe
what is the pathway of the hearing special sense?
-hair cells in the cochlear duct are stimulated and generate a receptor potential and release a neurotransmitter onto the associated sensory neuron (no AP)
-an EPSP is generated onto the sensory neuron which results in an AP
-AP generates on the axon of the cochlear branch of the cranial nerve VIII (vestibulocochlear nerve)
-reaches the auditory cortex of the temporal lobe
how is equilibrium in balance and spatial orientation kept in the ear?
-hair cells in the semicircular ducts and saccule or utricle in the vestibule generate a receptor potential (no AP) and release a neurotransmitter onto the associated neuron
-an EPSP is generated and an AP results
-AP generates on the axon of the vestibular branch of cranial nerve VIII (vesibulocochlear nerve)
-the brainstem processes these signals and integrates them to the cerebellum and thalamus
-cerebellum coordinates muscle contraction
-the brain stem affects the eye muscles and other muscles of the neck and trunk for balance
