Week 19 Flashcards
What is the ora serrata
The ora serrata is the serrated junction between the choroid and ciliary body.
marks the transition from the simple, non-photosensitive area of the ciliary body to the complex, multi-layered, photosensitive region of the retina.
Differences between Rods and Cones?
Rods:
- Around the retina, not in the fovea
- Monochromatic
- Contain rhodopsin
- Low acuity
- High sensitivity
Cones:
- Highest concentration in the fovea
- Trichromatic (red, green, and blue detecting cones)
- High acuity
- Low sensitivity
How do rods function in darkness?
- Rhodopsin consists of cis-retinal and opsin
- Na⁺ enters channels on the outer segment of the rod
- Gets pumped out of the inner segment
- More Na⁺ in than out → rod depolarises
- Releases glutamate (inhibitory neurotransmitter)
- Inhibits bipolar neuron
- No impulse in optic nerve
How do Rods function in low light intensity?
- Rhodopsin is bleached
-Na⁺ enters channels on the outer segment of rod
- Is pumped out of inner segment
- More Na⁺ out than in → rod hyperpolarises
- No neurotransmitter (glutamate) released
- Bipolar neuron depolarises → depolarises ganglion cell
- Impulse in axon of optic nerve
- Light hits rhodopsin and converts cis-retinal to trans-retinal
What does Glutamate do?
It is inhibitory and stops the bipolar neuron from depolarising
What is Critical Flicker Fusion Frequency (CFF)?
The ability of an eye to fuse signals to give a constant image
What happens during accommodation for close objects?
- Increased convexity of the lens
- Suspensory ligament inserts peripherally into lens
- At rest: ligament keeps lens flat
- During accommodation:
- Parasympathetic neurons contract ciliary muscles
- This relaxes ligament tension
- Lens becomes thick
What happens during disaccommodation for distant objects
Ciliary muscles relax
Suspensory ligaments become tense
Pulls lens thin
Focus is on distant object
How does frequency detection change along the cochlear?
Basilar membrane inside cochlea, membrane changes in stiffness and width from base to apex
Base is narrow and stiff(High frequency) , apex is wide and flexible (Low frequency)
What are the features of the basilar membrane and hair cells?
Basilar membrane has hair cells in rows:
- Inner hair cells: 1 row
- Outer hair cells: 3 rows
- Outer hair cells have stereocilia embedded in the tectorial membrane – control amplitude of sound
- Inner hair cells have stereocilia with tip links
How does the Organ of Corti transduce sound?
Stereocilia bend toward the tall edge of bundle
Tip links (fibres) are connected to gated channels
Sound vibrations cause endolymph movement
Tension in tip links opens trap doors
K⁺ moves in and depolarises cell
Voltage-gated Ca²⁺ channels open
Ca²⁺ influx triggers glutamate release via exocytosis
Action potential is generated in cochlear branch of vestibulocochlear nerve
Impulse sent to brain – we can hear
Has hair cells with stereocilia
What is olfaction and where does odour detection occur?
Olfaction is the sensation of smell from detection of aerosols in the environment
Occurs at top of the nasal cavity
Odour molecules reach olafactory epithelium from nose and via the mouth
How does the body detect smell?
- Odour molecules dissolve in a mucus layer over the olfactory epithelium (necessary for detection)
- Olfactory epithelium contains millions of receptor cells
- Each receptor cell has a single dendrite and cilia
- Odorant binds to cilia → causes depolarisation
- Action potential travels along axon to olfactory bulb
- Axons synapse with mitral and tufted relay neurons in olfactory bulb
- Depolarisation travels along olfactory tract to olfactory cortex
How is smell processed in the brain?
Olfactory bulb signals are transmitted to the olfactory cortex for processing
Where are taste receptors located and how do they vary?
Tongue has papillae that contain taste buds
Taste buds are arranged in different areas but all respond to all tastes
Some areas are more sensitive to specific tastes
How do taste buds work?
- Found in walls of papillae
- Each taste bud has 50–150 taste receptor cells
- Gustatory hairs protrude from the top
- Hairs contact taste molecules in a fluid-filled funnel
- Ion channels open → cell depolarises → releases neurotransmitter
- Sensory neurons depolarise → impulse travels to gustatory cortex
- Taste is determined by interaction between gustatory and olfactory input
