PCB 4843 Exam 3 Bales FSU

Function of the olfactory receptor neuron (ORN) (olfactory epithelium cell type)

Detect odor, cilia extend into mucus

Function of Bowman’s glands (olfactory epithelium cell type)

Make mucus that traps odorants and protects against viruses

Function of supporting cells (olfactory epithelium cell type)

Contain enzymes that break down harmful chemicals

Function of basal cells (olfactory epithelium cell type)

Stem cells that regenerate ORNs

Olfactory Transduction

1. Odorant binds GPCR

2. G_olf activated

3. Adenylyl cyclase activated

4. cAMP produced

5. cAMP opens cyclic nucleotide-gated cation channels (Na+ and Ca2+ depolarize cell)

6. Ca2+ opens Ca2+ activated Cl- channels (amplification)

True or False: Each ORN expresses only one receptor type

True

Where do odors generate a receptor potential?

In the cilia → action potential triggered
Puffing odor onto cell body does NOT produce strong response

What is the population code?

One odorant activates many receptors at different affinities
Odor identity = combination of activated receptors

Explain labeled line coding

Many, very specific sensors (requires immensely large number of highly specific receptors)

Population coding

Roughly labeled lines, large numbers of broadly tuned neurons

Which taste cells release serotonin and which release ATP?

Serotonin = Sour

ATP = sweet/bitter/umami/SALT

Salt transduction mechanism

1. Na+ enters through ENaC channel

2. Na+ depolarizes membrane and activates voltage-gated sodium channels

3. Na+ enters and generates action potential

4. Action potential opens ATP-permeable channels and releases ATP

Two sour transduction mechanisms

1. Protons can block/close K+ channel (net depolarization by decreasing K+ permeability)

2. wwDirect passage through a proton channel which has a net depolarizing effect on the cell

Bitter/sweet/umami transduction

1. Tastant binds to GPCR

2. Activated Phosphlipase C

3. Increases IP3 synthesis

4. Triggers Ca2+ release

5. Na+ enters

6. Voltage-gated Na+ channels open → action potential

7. CALHM1/3 channel opens → ATP diffuses

NKCC

Active transporter that moves sodium, potassium, and chloride in the same direction (Na, K, Cl Co-transporter)

How is odor information encoded in the olfactory bulb across a population of glomeruli?

• Each glomerulus reflects the input from one olfactory receptor type

• Odorants evoke activity in distinct spatial patterns of glomeruli

Which GPCR combination functions as sweet tastants receptor for mammals?

T1R2 + T1R3

Which cranial nerve provides primary taste innervation to the anterior two-thirds of the tongue?

Facial nerve (CN VII)

Which tastants bind to T1R1 and T1R3?

L-amino acids (like glutamate)

Where does olfactory sensory transduction physically take place within olfactory receptors neurons?

Across cilia surface

What expression pattern governs the distribution of odorant receptor proteins across mature olfactory receptor neurons?

One receptor type per neuron

Each individual mature ORN = 1 functional odorant receptor gene from one allele (One neuron, one receptor)

Where do the unmyelinated axons of olfactory receptor neurons expressing the same receptor gene converge?

Axons of all ORNs expressing the same specific odorant receptor converge onto two symmetric glomeruli in each olfactory bulb

Which cell types are the main output neurons of olfactory bulbs in mammals?

Mitral and tufted cells

True or False: Primary olfactory information bypasses an obligatory thalamic relay to reach the cerebral cortex

True. Olfactory bulbs projection neurons project directly to primary olfactory cortex without synapsing in the thalamus

How does odor representation in the primary olfactory cortex differ from that in the olfactory bulb?

It discards spatial order for dispersed overlap
Piriform cortex lacks chemo topic map; individual cortical pyramidal neurons receive diffuse, overlapping inputs from multiple glomeruli

What functional role does temporal coding play during odor identification in olfactory bulb circuits?

Locking action potentials to respiratory cycles
Mitral cell spike timing is locked to specific phases of the respiratory cycle

Hairy vs. glabrous skin

Hairy = lower receptor density, larger receptive field

Mechanoreceptor cell types

Meissner’s corpuscle, Merkel’s disk, Ruffini’s ending, Pacinian corpuscle

How is mechanical force converted into a neural signal in sensory afferents?

Membrane stretch or tether deformation opens cation channels, causing depolarizing sodium and calcium influx

Where do primary afferent axons carry information from and to?

From somatic receptors through dorsal root ganglia

What are the types of axons from the skin and which sensory receptors do they deal with?

A alpha mediates proprioception

A beta mediates touch perception

C mediate temperature, pain, itch

What are dermatomes?

Skin segments innervated by the dorsal root of a single spinal segment
- 1 dermatome:1 spinal segment

Contrast slowly adapting and rapidly adapting afferent responses in touch

Slowly adapting afferents keep firing during sustained pressure
Rapidly adapting afferents go silent during constant pressure and fire at onset/offset

Higher order somatic areas (1,2, 3a, 5/7)

1 = texture, 2 = shape, 3a = body position, 5/7 = object perception

Astereognosia

Can’t recognize object by touch, though vision works

Hemispatial neglect

Fails to perceive stimuli on one side of the body or of objects generally

Which mechanoreceptor is rapidly adapting and possesses a small, well-defined receptive field in glabrous skin?

Meissner corpuscle

Which mechanoreceptor is most sensitive to high-frequency mechanical vibrations between 200 and 300 Hz

Pacinian corpuscle

What happens to the physiological adaptation rate of a Pacinian corpuscle if its multilayered capsule is stripped away?

It adapts slowly to sustained mechanical displacement
(Normally absorbs steady forces to enforce rapid adaptation, stripping it leave the bare neurite behaving like a slowly adapting receptor)

Which peripheral axon group transmits discriminative touch and vibratory sensations from the skin?

A-beta fibers

Which mechanoreceptor is slowly adapting, located deep in the dermis, and responds selectively to lateral skin stretch?

Ruffini endings

Which cranial nerve carries tactile mechanosensory signals from the face, teeth, and anterior two-thirds of the tongue into the brainstem?

Trigeminal nerve (CN V)

After death, muscles become stiff (rigor mortis) as ATP runs out. Based on the sliding-filament model, why?

Myosin heads cannot detach from actin without ATP binding

As an odorant's concentration rises, how can the neural code change?

Additional lower-affinity receptors join the activated population, changing the code

Where are nociceptors expressed?

In branching, unmyelinated free nerve endings

Hyperalgesia

Reduced threshold for pain following tissue damage

What substances do damaged tissues release that trigger inflammation and modulate nociceptor responsiveness?

Bradykinin: directly depolarizes nociceptors
Prostoglandins: increase sensitivity of nociceptors to painful stimuli
Substance P + GPCR: causes swelling of capillaries, triggers histamine release from mast cells → depolarizes nociceptors

Which gene mediates heat nociception?

TRPV1

What activated TRPV1?

Temp >43°C
Capsaicin
Protons (Anaerobic metabolism results in buildup of lactic acid which builds up H+ in extracellular fluid)

What are the other candidate receptors that detect nociceptive stimuli?

TRPA1 and ASIC3

What are the nociceptive cell-specific voltage-gated Na+ and K+ channels

Nav1.7 and Nav1.8

Which two axons carry nociceptor signals?

A-delta and C fibers

Does nociception enter the brain more slowly or quickly than touch?

More slowly

Referred pain

Referred pain is pain you feel in a part of your body that is different from its actual source or site of injury

Which nociceptive pathway is analogous to dorsal-column medial-lemniscus pathway for somatic touch?

Spinothalamic pathway

How do the touch and pain pathways differ in the senses they carry?

Touch: Fine touch, vibration, position sense
Pain: pain, Temp, crude touchH

How do the touch and pain pathways differ in their fiber types?

Touch: A-beta fibers
Pain: A-delta (fast pain) and C (slow pain) fibers

How do the touch and pain receptors differ in the places they deccusate?

Touch: medulla (lower brainstorm)
Pain: Spinal cord

How do touch and pain receptors differ in spinal ascent?

Touch: Ipsilaterally first
Pain: Contralaterally immediately

gate theory of pain

Mechanical stimulation could activate interneurons that inhibit the spinothalamic tract
Concurrent activation of somatic and nociceptive neuron leads to reduced nociceptor response

Which endogenous chemicals bind to opioid receptors in the PAG?

Endorphins, enkephalins, and dynorphins