Week 9 - The brain and special senses Flashcards
Give examples of general senses
Temperature
Pain
Touch
Pressure
Vibration
Proprioception (body position)
What is Olfaction (smell) and describe the process
Provided by olfactory organs, consisting of olfactory epithelium and olfactory glands.
Process:
1. During inhalation, air swirls in nasal cavity
2. Lipid and water soluble chemicals diffuse into mucus before stimulating olfactory receptors.
3. Dissolved chemicals interact w receptors - oderant binding proteins on the cilia surface
4. Binding of oderants changes permeabilty of receptor membrane - action potential
5. Information is relayed to CNS where smell is interpreted. Between 10-20 million olfactory receptor cells are packed into approx 5cm squared
What are the olfactory pathways
Bundles of axons (CN I) penetrate cribform plate of ethmoid bone to reach olfactory bulb. Axons leaving each olfactory bulb travel along olfactory tract to olfactory cortex of cerebrum, the hypothalamus and portions of the limbic system
What are the taste/gustatory receptors
Located near superior surface of the tongue and adjacent pharynx and larynx. Taste recptors and specialised epithelial receptors form sensory structure - taste buds. Taste buds lie along the sides of epithelial projections - papillae.
What are the 3 types of papillae
Filiform - no taste buds
Fungiform - around 5 taste buds
Circumvallate - around 100 taste buds
each taste bud contains slender sensory receptors - gustatory cells - plus supporting cells. Each cell extends slender microvilli into surrounding fluids through a taste pore
What are the taste mechanisms
Dissolved chemicals contacting taste hairs stimulate a change in the membrane potential of the taste cell
Resulting in an action potential in the sensory neuron
What are the taste pathways
Sensory fibres of the different nerves
synapse within a nucleus in the medulla
oblongata
Axons of the postsynaptic neurons synapse
in the thalamus
Give a summary of the anatomy of the eye
Eye is virtually spherical with a diameter of approx. 24mm.
Located in the orbit along with: extrinsic eye muscles, lacrimal gland, cranial nerves, blood vessels and fat.
Describe the mechanisms of vision
Light enters the eye and is refracted at the cornea and lens. Refraction is the alteration, or bending, of light when it travels from one medium to another. Greatest refraction occurs at cornea.
Light is absorbed at retina by photoreceptors (rods and cones). Each eye contains approx. 100 mill rods and 5 mil cones. Cones predominate in central vision, rods predominate in the periphery
Describe the process of seeing
Light interacts with light-sensitive molecules (photopigments) in the photoreceptors. Photopigments consist of rhodopsin, made of opsin and retinal. In the presence of light, rhodopsin splits, altering the flow of electrical current.
describe the visual pathways
Two optic nerves (CN II) reach diancephalon 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 thalamus relay visual info to reflex centres in brain stem as well as to the visual cortex of the cerebrum.
Summarise hearing
Provided by the iner ear, a receptor complex located in the temporal bone of skull. The receptors, or hair cells, are simple mechanoreceptors.
Describe anatomy of Middle ear
Air filled cavity.
Separated from ear canal by tympanic membrane
Contains auditory ossicles: Malleus, Incus and Stapes.
Describe anatomy of Inner ear
Receptors lie within the membranous labyrinth which contains two fluids: endolymph and perilymph.
The Bony cochlea contains the cochlear duct. Cochlear duct is sandwiched between pair of perilymph filled chambers. Bony labyrinth walls are dense bone everywhere except 2 places:
Round window (base of tympanic duct)
Oval window (base of vestibular duct)
Describe the organ of corti
Hair cells of cochlear duct located in organ of corti. Sits above basilar membrane. Stereocilia of hair cells in contact with tectorial membrane.
