Special senses Flashcards
Special senses
- Part of sensory division of PNS (alongside somatic senses)
- Receptors which mediate the special senses are located in specialised organs in the head
- Special senses signals interpreted by specialised areas of the brain
Vision
Cones:
- Colour and detail
- Concentrated at the fovea
- 3 types; red, green, blue
Rods:
- Vision in dim light
- One type
- Rhodopsin (needs vitamin A)
Detailed image is created at the fovea as this is where there is the highest conc of cones
Near response (looking at close object):
- Parasympathetic
- Ciliary muscles contract; suspensory ligaments slacken
- Lens thickens
- Eyeballs converge
- Pupils constrict (circular contraction, radial relaxation)
- Constriction is necessary when looking at close object because if light were to hit the thinner, weaker parts of the lens at the periphery, lens may not be strong enough to focus those light rays onto the fovea
- Results in edge effects (blurring around the edge of images)
- Blocks out light hitting thin part of lens around edge
Looking at distant object:
- Sympathetic
- Ciliary muscles relax; suspensory ligaments pulled taut
- Lens pulled thin
- Pupils dilate (circular relaxation, radial contraction)
Part of brain that controls innervation of ciliary, circular and radial muscles: midbrain
Taste
5 basic tastes:
- Bitter
- Sour
- Salty
- Sweet
- Umami
- Other aspects to taste: temperature, texture and smell
- Taste buds are located on the tongue
- Each bud has taste cells which have microvilli (taste hairs; receptors for taste molecules) which project into pores on the tongue surface
- The area of the brain which receives signals from these cells to generate the conscious sensation of taste is the gustatory cortex of the frontal lobe
Smell
- Olfactory receptor cells - detect odours
- These are modified dendrites of neurones; cilia
- For a substance to be smelt, it must be volatile
- When substance reaches hair cells in the olfactory epithelium of the nasal cavity, they interact with cilia, causing the cilia to send a signal to olfactory cortex of temporal lobe
- Olfactory signals travelling to hippocampus; smells can evoke powerful memories
- Olfactory signals travelling to amygdala; emotional responses
Hearing
Cochlea
- Scala vestibuli
- Cochlear duct
- Scala tympani
Organ of Corti
- Sits on basilar membrane between cochlear duct and scala tympani
- Hair cells with stereocilia projecting off their surface
- Each hair cell communicates with fibres of the cochlear nerve (carries info to auditory cortex in temporal lobe)
- Vibrations created by sound are transmitted to the inner ear via malleus, incus and stapes
- Stapes makes contact with the oval window, disturbing the membranes of the cochlea
- When the basilar membrane is vibrated, the stereocilia of the hair cells are sheared back and forth against elastic tectorial membrane
- Mechano-sensitive ion channels in hair cells open allowing entrance of K+ (endolymph has high concentration of K+)
- Depolarisation of hair cell –> AP
Ossicular conduction pathway:
- Sound waves enter ear via external auditory canal
- Sound waves strike tympanic membrane (ear drum)
- Ear drum vibrates, causing vibration of malleus, incus and stapes bones etc…
- 3 little bones ensure that there is no degradation in the vibrations created by sound
Bone conduction pathway:
- Bones around inner ear are vibrated and vibrations are transferred to cochlea
- Useful in certain forms of deafness: conductive deafness (problem with the transfer of vibrations from outer ear to cochlea)
Sound discrimination:
Louder sound = higher frequency of APs generated by hair cells
Pitch; hair cells in different locations within cochlea respond to sounds of different frequencies
Low pitch = far from oval window
High pitch = near oval window
Balance
- Maintaining body position and centre of gravity
- Providing a stable background against which voluntary skeletal muscle movements can occur
Static balance: senses position of head when body is stationary
- Stereocilia of hair cells in the macula are embedded in gelatinous material
- Otoliths (calcium carbonate crystals) make gelatinous material heavy
- When head is tipped forward, gelatinous material sags and pulls on stereocilia of hair cells
- When stereocilia are flexed, ion channels open and hair cells are excited etc…
Dynamic balance: detects direction of body movements
- Semi-circular canals are on 3 different planes
- All fluid filled and contain crista ampullaris
- If the head is rotating, the semi-circular canals and crista ampullaris are also rotating; the fluid within the semi-circular canals (endolymph) has a bit of inertia
- Due to the inertia, the crista ampullaris is dragged through the fluid and so the hair cells are bent, resulting in the opening of mechano-sensitive ion channels, allowing positive ions to enter and so depolarisation occurs
Cerebellum receives info from proprioceptors and vestibular apparatus:
eg. proprioceptors send signals that muscles and joints are not in the right position (muscles are stretched etc); vestibular apparatus sends signals that body position/head tilt is not correct either
When cerebellum receives these signals that are in conflict with the planned movement, it feeds back to the pre-motor cortex in order to make necessary adjustments
