general sensory systems Flashcards
what is a sensory system
sensory system: receives information from the environment through receptors at the periphery and transmits the information to the CNS
sensory systems encode four basic attributes of a stimulus, these are modality, intensity, duration and location, each of these attributes can be correlated quantitatively with a sensation
what are sensory modalities
sensory modalitites: vision, hearing, touch, taste, smell, balance, proprioception
what are sense organs
structures that mediate sensory modalities
describe sensory receptors
sensory receptors are specialised cells found within sensory organs, that transduce physical information about a stimulus into a neural signal
types of sensory receptors: chemoreceptors; taste, smell, pCO2/ pO2
mechanorecptors; hearing, balance, touch, proprioception
thermoreceptors: touch
photoreceptors: vision
nociceptors: touch and pain
where do different sensory neurones have their cell bodies
olfactory neurones and visual neurones have their primary neuronal cell bodies in the periphery, they are part of the olfactory and optic nerves respectively, they neurones themselves perform transduction of stimuli
somatosensory and visceral neurones have their cell bodies in the sensory root ganglion, they project to the viscery and cuteanous cells and muscle (muscle spindle, golgi tendon organs, muscle etc.), they are part of spinal sensory nerves and the trigeminal nerve, the nerves themselves also perform signal transduction
there are also somatosensory neurones that have their cell bodies in the CNS that control jaw muscle and teeth, they are part of the trigeminal nerve as well and also perform their own signal transduction
neurones that control auditory-vestibular system have cell bodies in periphery, are part of cranial nerve 8 and do not perform their own signal transduction, there are 10^5 of them in man
taste neurones have cell body in sensory root, they are part of cranial nerves 7,9 and 10, do not perform their own signal transduction, 10^5 of them
there are also somatosensory neurones with cell bodies in sensory root ganglion that are involved in cutaneous activity as well as touch corpuscles, they are part of spinal sensory nerves as well as the trigeminal nerve, they do not perform their own signal transduction 2x10^4 of these
how do sensory receptors perform signal transduction
energy of stimuli causes a change in the membrane potential of the sensory receptor aka the receptor potential
receptor potential propagates electronically, is restricted to the sensory receptor’s cell membrane, is a graded potential
what is the receptor potential controlled by
receptor potential is controlled by; transduction process generates a change in conductance, opening and closing of ion channels (transduction channels) which together contribute to a change in membrane potential
the intensity of a stimulus determines the amplitude of the receptor potential
the amplitude of the receptor potential determines the frequency of action potentials (firing rate or frequency coding)
what is effect of receptor adaptation
adaptation also occurs, so that for a given stimulus of uniform strength the frequency of action potentials fired will decrease over time
over time for a given stimulus the amplitude of the receptor potential in a receptor cell will decline, which causes decline in frequency of APs in a sensory neurone
useful because of wide range of intensities that sensory systems can signal
slow or non adapting: is caused by signal prolonged stimuli or tonic signals
rapid adaptation occurs in brief signal changes or phasic signals
often a result of desensitisation of ion channels underlying transduction, can also be due to transmission properties at the synapse
what sensory receptor allows for balance
in the mammalian vestibular system sense of balance is encoded via the ampulla, which detects rotational acceleration, linear acceleration and gravity
describe the structure of the ampulla
there is a membranous labyrinth on the top, much like an epithelium, underneath is the endolymp which contains the cupula which is like the cell body of the receptors, at the base of the cupula there are hair cells projecting from supporting cells underneath the cupula, the supporting cells and the hair cells together are called crista, sensory nerves innervate the hair cells
the ampullas are located in the semi circular canals, accelaration causes the endolymph to move within these which causes the hairs to move, exciting the sensory nerve endings
how do stereocillia of ampulla convey information
the ends of the hairs (stereocilia) are connected via tip links, the stretching of these tip links opens non selective cation channels causing influx of positive current and so increasing the receptor potential
stereocillia are in bundles with staggered size (smallest cilia on one side and largest on the other)
pushing the stereocilia bundle towards to largest one causes tip links to stretch which opens transduction channels and depolarises the cell
pushing the stereocilia bundle away from largest steroeocilia causes compression of tip links which closes transduction channels and hyperpolarises cell
describe efferent modulation
muscle spindle: gamma efferents in muscle spindles reset the length of the intrafusal muscle fibres
hair cells: in auditory system the efferent modulation is via a special type of hair cell
