Brain and Special Senses Flashcards
special senses
smell (olfaction)
taste (gustation)
vision
hearing
balance (equilibrium)
receptors are concentrated within special structure- sense organs
senses
sensory information is picked up by sensory receptors- simple ones are dendrites of sensory neurons
branching tips- free nerve endings
sensory info arrives at the CNS in the form of action potentials
arriving info is called sensation and conscious awareness of this is a perception
1% of information reaches conscious awareness
general senses
temperature
pain
touch
pressure
vibration
proprioception ( body position)
receptors for these are located throughout the body
smell- olfaction
provided by olfactory organs
located in nasal cavity in either side of nasal septum- inferior to cribifrom plate of ethmoid bone
organs consists of olfactory epithelium and glands
process of olfaction
1- when you breathe in, air swirls within nasal cavity
2-air reaches olfactory organs and lipid and water soluble chemicals diffuse into the mucus before stimulating olfactory receptors
glands secrete mucus
(mucus protect receptors + dissolve lipid and water soluble chemicals)
cillia attaches to each receptor cell and extends to surrounding mucus
3- dissolved chemicals interact with receptors- oderant binding proteins (AP)- on cillia surfaces
odorants- chemicals that stimulate olfactory receptors
4- binding of odorents changes permeability of receptor membrane leading to action potentials
5-information is relayed to CNS
10-20 million olfactory receptor cells in area of 5cm2
olfactory pathways
bundles of axons penetrate cribifrom plate of ethmoid bone to reach olfactory bulb
axons leaving each olfactory bulb travel along olfactory tract to olfactory cortex of cerbrum, hypothalamus and portions of limbic system (temporal lobe)
taste (gustatory)
tongue- sensory organ
receptors are located over superior surface of tongue -adjacent to pharynx and larynx
taste receptors and specialised epithelial cells form sensory structures called taste buds
taste buds
taste buds lie along side of epithelial projection- papillae
each taste bud contains slender sensory receptors- gustatory cells- plus supporting cells
each gustatory cell extends slender microvilli into surrounding fluids through taste pore
taste sensations
sweet, salt, sour, bitter
umami and water
taste mechanisms
dissolved chemicals contacting taste hairs stimulate a change in the membrane potential of the taste cell
resulting in action potential in sensory neuron
monitored by 3 cranial nerves- facial, vagus and glossopharyngeal
taste pathways
sensory fibres of the different nerves synapse within a nucleus in the medulla oblongata
axons of postsynaptic neurons synapse in the thalamus
travel to gustatory cortex in temporal lobe
vision- eye anatomy
eye is virtually spherical
eyes are located in the orbit of the skull
mechanisms of vision
light enters eye and is refracted at the cornea and lens
refraction- alteration or bending of light when it travels from one medium to another
light is absorbed at retina by photoreceptors (rods and cones)
cones- central vision (fovea) - colour
rods- periphery of retina - presence of light
process of seeing
light interacts with light sensitive molecules- photopigments- in photorecptors
pigments- rhodopsin= retinal + opsin
in presence of light; rhodopsin splits altering flow of electric current
visual pathways
two optic nerves reach the diencephalon at the optic chiasm
half of the nerve fibres from each eye cross over to reach the thalamus on the opposite side of the brain
nuclei in the thalamus relay visual info to reflex centres in the brain stem aswell as visual cortex of cerebrum
hearing
senses of hearing and equilibrium (balance) are provided by the inner ear- receptor complex in temporal bone
receptor mechanism for both of these senses is the same
simple mechanoreceptors
ear anatomy
external ear, middle ear and inner ear
middle ear- air filled cavity- separated from ear canal by tympanic membrane
contains auditory ossicles- malleus, incus and stapes (small bones)
inner ear-receptors for hearing and balance in bony cochlear- in membranous labyrinth (tubes) containing fluid- endolymph (cochlear duct) and perilymph
cochlear duct is sandwiched between a pair of perilymph filled chambers
hair cells of cochlear duct located in organ of corti- where receptors are found- sits above basilar membrane (look at process)
movement of hair cells= AP
process of hearing
1-sound waves arrive at tympanic membrane
2-movement of tympanic membrane causes displacement of auditory ossicles
3-movement of the stapes at the oval window establishes pressure waves in perilymph of vestibular duct
4-pressure waves distort basilar membrane on their way to the round window of tympanic duct
5-vibration of basilar membrane causes vibration of hair cells against tectoral membrane
6-information about the region and intensity of stimulation is relayed to CNS over the cochlear branch of cranial nerve 8
auditory pathways
sensory neruons located in spiral ganglion monitor cochlear hair cells
afferent fibres form cochlear branch of vestibucochlear nerve
auditory complex of temporal lobe
equilibrium
equilibrium sensations provided by hair cells of vestirbular apparatus:
semi circular canals- rotational movements
otoliths- accelerations
semi circular canals
fluid filled chambers- central one formed of endolymph
rotation causes movement of fluid in SCC, fluid presses against cupula and causes movement of hair cells which generates action potential
otoliths
contain receptors in gelatnious material
movement of fluid is detected by hair cells
trigger action potential
utricle- horizontal linear accelerations
saccule- vertical linear accelerations/ gravity
equilibrium pathways
sensory neuron monitor hair cells of otoliths and SCC
afferent fibres form vestibular branch of vestibulocochlear nerve
fibres synapse on neurons in vestibular nuclei
roles of vestibular nuclei
integrate sensory information arriving from each side of the head
relay information to cerebellum
relay information to cerebral cortex
send commands to motor nuclei in brain stem and spinal cord (to skeletal muscles)
