BIOS 286: Exam III

Retinofugal projections

Retinofugal projections

Neural projections coming out of the retina starting with the optic nerve

Optic chiasm

Crossing of some information from the nasal retinae to the opposite side of the brain

Decussation

Partial crossing of information

LGN

Lateral geniculate nucleus

Locations of axonal termination

LGN, hypothalamus, pretectum, and superior colliculus

Olfaction

Sense of smell

Gustation

Sense of taste

Olfactory epithelium

Area in nasal cavity of olfactory receptor neurons

Odorant receptors

GPCRs with different detection thresholds

OE

Olfactory epithelium

Olfactory epithelium cells

1. Olfactory receptor neurons

2. Basal cells

3. Supporting cells

Basal cells

Give rise to ORNs

Supporting cells

Metabolic support for the OE

Cilium

Thin protrusions from dendrites of ORNs, contains odorant receptors

ORNs

Olfactory receptor neurons

Cribriform plate

Bony structure with openings for axons of ORNs to pass through

How many odorant receptor genes are there per receptor cell?

One

Can a ligand activate multiple receptors?

Yes, affinity overlap

Signal transduction in ONs

1. Odorants bind to GCPRs, activates adenylyl cyclase

2. Adenylyl cyclase activates cAMP

3. cAMP binds cation channels

4. Na+ and Ca2+ enter

5. Membrane depolarizes

Are membrane potential changes graded due to odorants?

Yes

Olfactory bulb

Extension of the brain above the olfactory epithelium, processes olfactory information

Olfactory nerve

Formed from all axons from the ORNs, layered structure

Glomerulus

Cluster of axons from mitral cells, sends information to olfactory bulb, only receives input from ORNs that express the same ORGs

Are inputs from ORNs excitatory or inhibitory?

Excitatory

Mitral cells

Send their dendrite to only one glomerulus, do not interact with each other

Limbic system

Amygdala and hippocampus

Hippocampus

Memory processing, learning

Amygdala

Attention, fear, aggression

Thalamus

Sensory perception, sleep, memory, cognition

OFC

Orbitofrontal cortex

Orbitofrontal cortex

First point of convergence, origin of flavor

Olfactory bulb targets

1. Piriform cortex

2. Olfactory tubercle

3. Amygdala

4. Entorhinal cortex

Odor fatigue

Prolonged exposure to an odor causes less recognition

Odor fatigue pathway 1

1. Ca2+ enters

2. Ca2+ binds to receptor

3. cAMP affinity is reduced

Odor fatigue pathway 2

1. Ca2+ enters

2. Ca2+ activates CaMK

3. CaMK reduces adenylyl cyclase activity

4. cAMP is not produced

Anosmia

Inability to smell

Synaptic plasticity

Synapse strength can be altered

LTP

Long term potentiation

LTD

Long term depression

Long term potentiation

Synapses are strengthened by increased activity

Long term depression

Synapses are weakened by decrease in activity

EC

Entorhinal cortex

Entorhinal cortex

Major input to the hippocampus from the temporal, orbital, and amygdala

NMDARs

Requires 2 events: glutamate must bind and the cell membrane must depolarize so the Mg2+ ion can be ejected, permeable to Ca2+

Tetanus

Brief burst of strong stimulation

AMPARs

Normal glutamate binding receptor, glutamate will bind even if Mg2+ is not ejected.

LTP activation requirements

1. Glutamate must bind to AMPARs

2. Na+ ions flow in

3. Membrane is depolarized enough to eject Mg2+ from NMDRs

4. NMDARs enter, Ca2+ flow in

LTP early phase

More AMPA receptors are inserted into the membrane, does not require new protein synthesis, lasts a few hours

LTP late phase

Requires new protein synthesis and new signaling pathways, lasts 24+ hours

PKC

Protein kinase C

Protein kinase C

Activated by Ca2+

AMPA phosphorylation

Enhances activity, strengthens postsynaptic response

Dendritic spine morphogenesis

New growth of dendritic spines due to LTP, increases connectivity between axons and dendrites

Input specific

Only synapses that receive strong inputs will be strengthened

Bidirectionality

Synapses can receive inputs to be enhanced or weakened

LTP vs LTD

Depends on amount of Ca2+ that flows into the synapse

LTD pathway

1. Low frequency stimulus leads to depolarization

2. Ca2+ enters, Mg2+ is NOT ejected

3. Protein phosphatases are activated by Ca2+

4. Dephosphorylation of AMPARs

5. Less membrane depolarization

LTP pathway

1. High frequency stimulus leads to depolarization

2. Ca2+ enters, Mg2+ is ejected

3. Protein kinases are activated by Ca2+

4. Phosphorylation of AMPARs

5. Increased membrane depolarization

Learning

Acquisition of new information

Memory

Retention of information

Habituation

Decrease in strength of a behavioral response due to repeated mild stimulus

Sensitization

Increase in strength of a behavioral response due to a strong stimulus

Declarative memory

Facts and events, conscious recollection of explicit memories

Nondeclarative memory

Skills that are hard to put into words

Consolidation

Transformation of short term memory into long term memory

Working memory

Retention of information through repetition, but only lasts a short time

Medial temporal lobe

Forms declarative memories

Flow of sensory information

Cortical association areas → parahippocampal areas → hippocampus → cortical areas

Retrograde amnesia

Loss of memories BEFORE onset

Anterograde amnesia

Inability to form new memories AFTER onset

Visual information pathway

Retina → optic nerve → optic chiasm → optic tract → LGN → primary visual cortex (V1)