08 | Touch, Taste, Movement Flashcards
__% of taste is smell
75
Taste cells do not have ___. They form ___ with afferent nerve in the taste bud.
- axons
2. chemical synapses
Nerves involved in taste
- VII (facial)
- IX (glossopharyngeal)
- X (vagus)
How many taste buds on tongue?
5000
How many taste receptors per taste bud?
100
Which taste modalities use ion channels? G-proteins?
- salty, sour, bitter
2. sweet, bitter, umami
Signalling: salt
Na flow down conc. gradient through Na channels
Signalling: sour
- inward H flow through salt channels
2. Block K channels
Bitter compound =
quinine
Signalling: bitter (ion)
Block K channel
Signalling: sweet, bitter, umami
Gustductin
- PLC pathway
- activate cAMP
what experiment demonstrated that fat could be a 6th taste modality?
CD36 (FA transporter) found with Gustductin on taste bud
What NT is associated with taste receptors?
ATP
Which nerve is responsible for signalling spicy?
V -> activate pain pathways
Capsaicin receptor is a __ sensitive channel
Ca
What are the 2 types of touch receptors?
- Temperature (but no extremes)
2. Mechanoreceptors
What are the 4 capsular structures of touch receptors?
- Merkel’s disk
- Pacinian corpuscle
- Ruffini’s corpuscle
- Meissner’s corpuscle
Where are the most sensitive mechanoreceptors located?
in the ear (hair cells)
What NT does Merkel’s disk use?
Glutamate
What does Merkel’s disk sense?
pressure, position, shape
What does Pacinian corpuscle sense?
vibrations
What does Ruffini’s corpuscle sense?
stretch
What does Meissner’s corpuscle sense?
Initial contract, motion
Where can Ruffini’s corpuscles be found?
Base of fingernails, tissue around joints and ligaments, palms
define: polymodality (and what does it apply to?)
Responds to multiple modalities (free nerve endings)
Cell body of touch receptors are located in…
dorsal root ganglion
What are the 2 branches of touch receptors?
- central branch (dorsal root -> spinal cord)
2. peripheral branch (nerve terminal -> brain)
Velocity of signal propagation depends on…
- diameter of nerve
2. myelination
Fiber type for light touch. Velocity?
A-β (60 m/s)
Fiber type for 1st pain (sting, prickle). Velocity?
A-δ (2-10 m/s)
Fiber type for 2nd pain (burn, ache). Velocity?
C (0.2-2 m/s, unmyelinated)
Which nerve fibre is responsible for the jerk reflex (e.g. pull hand away from stove)
A-δ
What are the 2 ascending touch pathways?
- dorsal column-medial lemniscal
2. spinothalamic tract
Difference between the 2 ascending touch pathways?
- dorsal column makes synapse in the medulla, spino does not
- spino crosses to contralateral side in spinal cord, dorsal column crosses in medulla
- dorsal column senses sensations, spino senses temp and pain
Similarities between the 2 ascending touch pathways?
- both make synapse at thalamus
- both end at primary somatosensory cortex
- both have 3 orders or neurons
Which sections in the cortex are the primary somatosensory cortex? Where is it located?
1, 2, 3a, 3b
@ anterior parietal lobe
What is another name for the primary somatosensory cortex?
postcentral gyrus
Which section in the cortex is the secondary somatosensory cortex?
5
Touch plasticity
e.g. area devoted to left fingertips in the postcentral gyrus can increase with practice (violin)
Each muscle fiber adds __% to tension
5
Why are small motoneurons less powerful than larger motoneurons?
Small ones innervate only a few muscle fibers, but large ones innervate more.
What is the size principle? Why?
Small motoneurons recruited first, followed by large.
Smaller have larger input resistance, and therefore have bigger changes in voltage (easier to reach threshold with the same input current).
Motor cortex is also known as…
precentral gyrus
Role of basal ganglia in regulating movement
- Regulate posture
- counteract tremor
- maintain steady muscle contraction
Dorsal striatum is made up of…
caudate nucleus + putamen
Ventral striatum is made up of
NAc
DS release…
GABA, NO
Symptoms of Parkinson’s
- Tremor at rest
- Rigidity
- Akinesia/bradykinesia
Parkinson’s ultimately results in what effect on the cortex? What is the pathway?
Decreased
Less DS activity -> less GP inhibition -> more inhibition on thalamus -> less cortical stimulation
What causes Parkinson’s (in the brain)?
degeneration of SN DA neurons
What kind of disease is Huntington’s?
autosomal dominant
Symptoms of Huntington’s
- cognitive issues
- lack of coordination
- spontaneous, disruptive movements
- dementia
At what age does Huntington’s show up?
late 20s to early 30s
What is the cause of Huntington’s (in the brain)?
Degeneration of DS GABA neurons -> less inhibition of extra movements
