Lecture 18: Synapses & Sensory Receptors

2 types of synaptic transmissions

Chemincal, Electrial

Electrical transmission

• fast

• connected to pre/post-synapses via junctions

• transmits a signal directly

• less common

• allow ion flow

Chemical transmission

• slower compared to electrical

• signals transmitted via the synaptic vesicle (pre)

• makes neurotransmitter (pre)

• VG Ca2+ channels (pre)

• NT binds to specific receptors in PM (post membrane)

• Ligand-gated channels (post)

What are NT reduced by

• Reuptake from the presynaptic neuron

• Enzymatic decay

• Diffusions

Types of changes in post-synaptic potential

Inhibitory ISPS (hyperpolaraztion)

Excitatory EPSP (depolarization)

depolarization

increases chance of AP

EPSP makes more +

Hyperpolarization

lowers changes of AP

IPSP, makes more -

Long Term Potenetion (LTP)

• Long-lasting

• greater synaptic strength

• activity-dependent

Short term memory (STM)

• 7+/ 2

• thrown away if not used

• 15-30secs

• prefrontal cortex+ hippocampus

LTM

• sleep consolidation

• “Last forever”

• LTP

• Cerebal cortex+ hippocampus

What does LTP cause

more NT

More Ampa receptors

Synapse

junction btw synaptic terminal and another neuron

Synaptic cleft

The small gap between the presynaptic and postsynaptic neuron.

What triggers neurotransmitter release?

Calcium (Ca²⁺) entering the presynaptic terminal

Main excitatory neurotransmitter in the brain

Glutamate

AMPA receptor

A glutamate receptor that allows sodium to enter and causes fast excitation, triggered by Ca2+

Front: NMDA receptor

: A glutamate receptor involved in learning that allows calcium to enter.

What blocks NMDA receptors at rest?

Mg

What is required for NMDA receptors to open?

Glutamate binding and strong depolarization (CA2+ influx).

Why is calcium entry important?

It triggers long-term changes at the synapse.

What causes LTP?

Repeated stimulation and calcium entry through NMDA receptors.

One synaptic change during LTP

More AMPA receptors are added to the postsynaptic membrane

Sensory receptor

A cell that detects stimuli and converts them into electrical signals.

Sensory transduction

The conversion of a physical stimulus into a neural signal.

Sensory adaptation

A decrease in receptor response over time to a constant stimulus.

Mechanoreceptors

Receptors that respond to touch, pressure, or stretch.

Chemoreceptors

Receptors that respond to chemical stimuli.

Photoreceptors

Receptors that respond to light.

Thermoreceptors

Receptors that respond to temperature.

Key difference between AMPA and NMDA

AMPA is fast and lets in sodium; NMDA controls learning and lets in calcium.

Big picture of sensory pathway

stimulus → CNS → Response

Sensory reception

where stm is deteced detected

Transmission

sensory info travels via sensory neuron

Pathway of sensory

stim → sensory reception → Transduction → transmission → perception → response

What triggers an AP in the SN

receptor potential

2 types of photoreceptors

rods (strongly photosensitive, no color)

cones (less photosensitive, color)

Sensory reception of eyes

Corena → Aqueous humor → Lens → iris → pupil → viterous huomor → retina → Fovea → optic never

Retinal processing

rods and conn → bipolar cells → ganglion cells → optic nerve

Corena

Transparent

Aqueous humor

clear fluid

Lens

foucs light on retina and fovea Focus

Iris

Regulation the entry of the eye

pupil

opening

Vitreous humor

clear gel

Retina

lines back wall

Fovea

sharp ccentral vision

optic nerve

cranial nerve. Visual infro from retina to brain