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Sensory System Chp 10. Outline General considerations Somatic senses Smell and Taste Hearing and Equilibrium Vision. General properties. Stimulus transduction into APs CNS The type of receptor activated defines the type or modality of stimulation
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Sensory System Chp 10 Outline General considerations Somatic senses Smell and Taste Hearing and Equilibrium Vision
General properties • Stimulus transduction into APs CNS • The type of receptor activated defines the type or modality of stimulation • The receptors transform the stimuli into graded potentials need adequate stimulation to reach threshold
Somatic Mechanoreceptors: Touch, pressure, pain, equilibrium, hearing, proprioception Chemoreceptors: smell, taste Photoreceptors: vision Autonomic Baroreceptors: blood pressure Osmoreceptors: blood concentration Chemoreceptors: blood chemistry Types of receptors
Receptive field: a receptor covers a certain area CNS integration: the number of neurons assigned to afferent impulses varies General properties
Location: varies with the senses touch: topographical arrangements of the receptors define the body location Sounds: difference in time of arrival in the brain helps to localize a sound Lateral inhibition: Helps sharpened the location of a stimulation How are location, Intensity and duration coded?
How to code for intensity?The stronger the stimulus, the more frequent the APs
Tonic receptors They fire as long as the stimulus is present Phasic receptors: they fire only when the strength of the stimulus changes How to code for duration?2 ways: Tonic and phasic receptors
Receptors (touch, pain, pressure) send an APs through 1st sensory neuron (where is the body of this neuron?) Relay and crossing over in MO (2nd sensory neuron) Relay in thalamus before projection on the primary sensory cortex in parietal lobe. Associated sensory cortex helps give a meaning to the sensation Somatic senses
Many qualities to pain - superficial / deep - sharp / dull Several modes of control Abnormalities: - referred pain - phantom pain Pain
Conduction of pain • Sharp, superficial pains are conducted fast • Dull, visceral pains are conducted through slower axons
Perception of pain is modulated by past experiences Minor stimulations will be blocked; stronger one will be allowed to continue to the brain Gate control theory of pain other touch sensation can block pain APs from going to the brain Control of pain
Organ: the nose Receptors: Olfactory receptors (many different ones) Pathway: Olfactory receptors olfactory bulbs Olfactory nerve Olfactory cortex in lower frontal lobe (+ amygdala and hippocampus) Smell
Organ: Tongue (papilla) Receptors: taste buds (5 different ones: ?), specialized epithelial cells Pathway: receptors nerves (VII-IX-X) MO thalamus gustatory cortex (base of parietal lobes) Taste Figure 10-14 - Overview
Organ: the ear cochlea Receptors: Organ of Corti Pathway: Receptors cochlear nerve MO thalamus auditory cortex in temporal lobes Hearing
The louder the noice the more frequent will be the APs sent through the cochlear nerve How to code for sound intensity?
Two types: Linear acceleration and head position controlled by the maculas from the Utricle and Saccule Rotational equilibrium controlled by the Cristaes ampullaris from the semi-circular canals Equilibrium
The stereocilia are sensitive to pulling In upright position, one of the macula is firing, the other one is quiet In horizontal position, the firing pattern is reversed Head position and linear acceleration
Controlled by the 3 semi-circular canals They act as 3 spatial axes: X, Y, and Z The receptor, crista ampullaris, fired when its cilia are pulled (by movement) Rotational equilibrium
Organ: Eye Receptors: photoreceptors Pathway: Optic nerve Optic chiasmata thalamus (lateral geniculate nucleus) Visual areas of occipital lobe Vision
What are? • Glaucoma • Cataract • Retinal detachment