Synapses and Sensory Receptors Flashcards
electrical synapse
current flows directly from cell to cell; less common
chemical synapse
most common
- AP reaches terminals of presynaptic cell
- presynaptic cell releases neurotransmitters into synaptic cleft (~20 nm wide)
- response in post synaptic cell
signaling across a chemical synapse
presynaptic cell cell synthesizes NT and stores them in synaptic vesicles
when AP reaches synaptic terminal
- VG Ca2+ channels open -> Ca2+ enters
- some synaptic vesicles fuse with PM
- NT released into synaptic cleft
acetylcholine
muscle stimulation and memory learning
glutatmate
AA, important in brain
dopamine
level in brain affects mood
endorphins
pain regulation
post synaptic potentials
change in membrane potential of post synaptic cells
-triggered by ligand-gated ion channel
ligand
something that binds
what the types of post synaptic potentials?
- excitatory (EPSP) - depolarizes
- inhibitory (IPSP) - hyperpolarizes
summation of post synaptic potentials
- addition of all excitatory and inhibitory signals
- often 100s of synaptic terminals on one dendrite or cell body
- many signals (some excitatory, some inhibitory)
temporal summation
2+ signals arrive at the SAME synapse (E1) in rapid succession -> 2nd arrives before MP resets
spatial summation
2+ signals arrive at same time, at DIFFERENT synapses (E1 and E2), on the same post synaptic neuron
EPSP and IPSP interactions
- axon hillock - neuron’s intergration site
- MP at AH = summed effect of all: inhibitory IPSPs and excitatory EPSPs
- if this sum = threshold -> AP
neuronal plasticity
capacity fro the NS to be remodeled
-synaptic connection b/w neurons are modified -> response to use or lack of use
brain remodeling
- during development, neurons form more synapses than needed
- throughout life, synapses are constantly remodeled
what is neuronal plasticity critical to?
memory and learning
hippocampus
forms temporary links with LTM -> esssential for acquiring memories (into STM), but not for maintaining them (in LTM)
LTM
info stored in cerebral cortex
-temporary links replaced by permanent connections
LTP
lasting increase in strength of synaptic transmissions
-fundamental process of memory storage and learning
LTP in presynaptic neuron
- 2 conditions must be met to establish LTP
1. high-frequency series of APs
2. those APs arrive at terminal when post synaptic neurons is already depolarized from another stimulus
why does LTP require context?
strengthens synapse only when its activity coincides with another synapse
LTP in post synaptic neuron`
- 2 types of receptors: NDMA receptors and AMPA receptors
- both are ligand-gated ion channel; open when something specific binds to it - here, the ligand = NT glutamate
before LTP
- NMDA receptors are already embedded in membrane
- AP in presynaptic neuron -> glutamate released into synapse
- glutamate (ligand) opens NMDA receptors
- but its BLOCKED by Mg2+ -> no membrane depolarization
establishing LTP
at same time:
- depolarization from one synapse -> Mg2+ released from NMDA receptor
- glutamate released into a different synapse -> Glutamate (ligand) opens NMDA receptors -> Na+, Ca2+ flow in (not a lot, but some)
- influx of Ca2+ causes stored AMPA receptors to be embedded in membrane
- similar to up-regulation in endocrine system
exhibiting LTP
- AP in presynaptic neuron -> glutamate released into synpase
- glutamate opens AMPA receptors -> influx of Na+ -> depolarization
- depolarization removed Mg2+ from NMDA receptor -> influx of more Na+ and Ca2+ -> depolarization reaches threshold -> AP
sensory pathways
- senses provide info about surroundings and body
- info processed by CNS -> appropriate response
types of sensory receptors
characterized by type of stimulus
- chemoreceptors: stimulus = specific molecules
- mechanoreceptors: stimulus = physical change from touch, motion, sound
what are the receptors for our senses
- taste - chemoreceptor in tongue
- smell - chemoreceptor in nose
- touch - mechanoreceptor in skin
- hearing - mechanoreceptor in ears (hair cells)
- vision - photoreceptors in retinas
what are the four basic steps of sensory processing
- sensory reception
- sensory transduction
- transmission
- perception
sensory reception
sensory detects change; often sense organ - receptors and associated cells -e.g. eyes
sensory transduction
E of stimulus is converted (transduced)
- receptor potential: change in MP of receptor cell
- stronger stimulus -> greater change
transmission
- sensory info travels as AP: receptor -> afferent neuron -> brain
- unstimulated receptor - at RP
- stimulated receptor - depolarized -> triggers AP
- larger receptor potential -> more frequent APs
perception
- brain processes info
- exists only in brain ( if a tree falls …)
taste and smell in terrestrial animals
- taste - chemoreceptors detect tastants
- smell - chemoreceptors detect odorants
taste and smell in aquatic animals
taste and smell, no distinction in water
integration of taste and smell
- neuronal pathway independent
- but flavor complexity mostly due to smell; mouth and nasal passages connected -> chewing releases odorants
gustation
- sense of taste
- 1 papilla on the tongue contains many taste buds
- 1 taste bud contains many taste cells (sensory receptor cells)
tastants and taste cells
each taste bud contains taste cells to detect all 5 tastant types (sweet, salty, sour, bitter, umami)
taste cell receptors
taste cells with G protein-coupled receptors
- sweet - one receptor type
- umami - one receptor type
- bitter - 30 receptor types
taste cells with ion channels opened by tastants directly
- sour - similar to capsaicin and other thermoreceptors
- salty - sodium channels
taste sensory reception
tastants enter taste pore, bind to receptor for that tastant
taste sensory transduction
- if tastant is sweet, bitter or umami, binding activates G-protein coupled receptor (GPCR)
- if tastant is sour or salty, binding opens channels directly
taste transmission
open ion channels -> depolarization in taste cell -> AP -> signal to afferent neurons -> signal to brain
perception
- brains integrates APs into taste perception
- perception is unique to individual
olfaction
- sense of smell
- biggest difference from gustation: sensory cells in the nose are ALSO the afferent neurons
olfactory receptor cells
- sensory cells/neurons
- line upper nasal cavity
- odorants bind to cilia in nasal cavity
- send APs along axon to olfactory bulb in the brain
odorants
- each odorant is structurally distinct (Humans can distinguish 1000s of different odorants)
- each olfactory receptor cell responds to one specific odorants (always via GPCR); each odorant stimulates a distinct part of olfactory bulb
odorant sensory reception
odorants bind to receptor on cilia of olfactory receptor cells
odorant sensory transduction
same as tastants (sweet, bitter and umami), but this time instead of tastants, its odorants
odorant transmission
depolarization in olfactory receptor cell/afferent neuron -> APs conducted along its axon -> signal to brain
odorant perception
- brain integrates signals -> smell perception
- interprets type, location, intensity of smell
