L14 sensory pathways 2 Flashcards
What are the 4 steps in the somatosensory pathway?
- Activation of sensory receptor
- Transmission of sensory input to the spinal chord via peripheral nerves (1st order neuron).
- Transmission of signal via ascending pathway through the thalamus (2nd order neuron) to primary sensory cortex (3rd order neuron).
- Processing of sensory signals in primary sensory cortex (detection, size, frequency etc.) –conscious perception.
What is the lateral line?
- A line evolved in aquatic vertebrates (e.g. fish)
- Has cupula sticking out, open to the water
- Cupulas have sense hairs inside, sense vibrations and pressure changes in water.
What are the functions of the
a) external ear ?
b) middle ear?
c) inner ear?
a) hearing
b) hearing
c) 1. hearing (cochlea)
2. Head position (utricle + saccule) } vestibular
+ head movement (semi circular canals) } system
What does the vestibular system sense?
Head position
Head movement
Which range can we hear?
from 20Hz to 20,000 Hz (cycles per second)
What are the steps in the ear in hearing?
- Sound waves collected by auricle, conducted through
2, Sound waves vibrate the tympanic membrane - Vibration is transmitted through the ossicles
- Vibration on oval window causes fluid in cochlea to vibrate
- Vibrations stimulate the spiral organ (sensory receptor) which triggers APs in the vestibular cochlear nerve.
How does sound cause channels to open in the ear to spread the signal?
1.- Fluid movement in the cochlea causes stereocilia to move
2.- TRPA 1 channels in the stereocilia open.
3.- K+ enters through TRPA1 and depolarises cell.
4.- Causes neurotransmitter release.
(inner hair cells don’t fire action potentials themselves)
Where does information from the cochlea travel to?
- The primary auditory cortex in the temporal lobe.
- Here there’s a tonotopic organisation of information processing.
In the vestibular system what do these structures sense? a) Otolith organs?
b) Semi-circular canals?
a) Force of gravity and tilt of head
b) Head rotation
What in semi-circular canals senses head rotation?
There are ampullae at the base of each semi-circular canal.
Inside ampullae there’s crista ampullaris with endolymph and hair cells. This lags behind canal rotation due to inertia and bends the cupula.
(see diagram)
How do the otolith organs sense gravity?
- It has a gelatinous cap embedded with otolith crystals (CaCO3).
- Gravity pulls on the dense otoliths —deforms the cap and bends the hair cells.
- Bent hair cells –AP sent.
What are papillae?
Projections all over the tongue with 1- 1,000s of tastebuds
What does each taste bud contain?
~ 50 taste cells
Taste cells have hair-like processes covered in receptors. Taste cells aren’t neurones but can fire APs.
What are the 5 taste qualities?
Bitter- avoid poisons (class 1 GPCRS)
Sweet- Sugar + Carbohydrate } class III GPRCRs Umami - L-amino-acids }
Salty - NA+
Sour - acids/ H+
What are taste cells sensitive to?
More than one ‘tastant’ particularly in high concs. but some show preferences.
