unit 5a

Question 1

orderant molecule

Answer 1

any substance capable of stimulating the sense of smell by binding to an olfactory receptor; -
substance must be volatile (able to vaporize)

Question 2

olfactory epithelium (AKA olfactory neuroepithelium)

Answer 2

a sheet of cells that contains the olfactory receptors & lines the upper part of nasal passages

Epithelium is covered by mucous layer thru which orderings must be absorbed before activating the olfactory receptors

Question 3

Olfactory receptors (AKA odorant receptors)

Answer 3

Are expressed in the dendrites of the olfactory receptor neurons & are responsible for the detection of odorant molecules

-Rather than binding only 1 specific odorant, olfactory receptors can bind to a range of odorant molecules w/ different degrees of activation & conversely, a single ordorant molecule may bind to a number of olfactory receptors w/ varying affinities.

Question 4

Olfactory receptor neurons (AKA olfactory receptor cells or Olfactory sensory neurons )

Answer 4

bipolar nuerons w/ dendrites facing nasal cavity (in the olfactory epithelium) & axons that pass thru openings in the cribriform plate (bone) to synapse in the olfactory bulb

Located along the dendrites & lie across the olfactory epithelium w/in the MUCUS LAYER.

Make up the ‘olfactory nerve’- the 1st cranial nerve & are only ~3 structures in the brain that have been found to undergo continuing neurogenesis in adult mammals

Question 5

Olfactory nerve

Answer 5

the 1st CRANIAL NERVE (CN 1) is actually many small nerve fascicles of the olfactory receptor neurons

• Unique among cranial nerves b/c its capable of some regeneration if damaged

Question 6

Cribriform plate

Answer 6

section of bone that separates nasal civility f/ brain

Contains many small holes thru which olfactory receptor neurons project axons

CLINICAL SIGNIFICANCE:
1. fractured cribriform plate can result in leaking of CSF into nose & loss sense of smell
2. Tiny holes of cribriform plate can become the entry pt for pathogenic amoeba
- this amoeba destroys olfactory bulb & adjacent inferior surface of frontal lobe of brain before spreading fatally to the rest of the brain & CSF

Question 7

trigeminal sense

Answer 7

sensation of touch, pain, pressure, temperate in the mouth, eye, & nasal cavity by the trigeminal nerve (5th cranial nerve: CN V)

~70% of odorants co-activate both the olfactory nerve & the trigeminal nerve

EX: hot chili peppers

Question 8

Olfactory bulb

Answer 8

multi-layered structure located on ventral surface of brain
- receives inputs f/ olfactory receptor neurons & sends output → cortex via mitral cell axons

Olfactory-receptor neuron axons that form synapses in olfactory bulb glomeruli are also capable of reiteration following regrowth of an olfactory receptor neuron in the olfactory epithelium

Neural circuitry here may play role in the identification of odor type & concentration

Question 9

Olfactory glomerulus

Answer 9

spherical structure located in the olfactory bulb where synapses form b/t axon terminals of the olfactory nerve & the dendrites of mitral cells

Each glomerulus receives inout f/ olfactory receptor neurons expressing only 1 type of olfactory receptor

• the glomerular activation patterns w/in the olfactory bulb are thought to represent the odor being detected
  → specifically, the glomeruli layer represents a spatial odor map organized by chemical structure of the brain

Question 10

Mitral cells

Answer 10

neurons located in the olfactory bulb that receive inputs f/ the olfactory receptor neurons w/in the glomeruli
- along w/ inputs f/ modulatory cells
- & then project axons to several cortical areas including the olfactory tubercle & priform cortex & regions in the limbic system, (part of cortex involved in emotions & memory)

May encode odor concentration in timing of firing

Question 11

Olfactory tract

Answer 11

bundle of axons including those from the mitral cells that connects the olfactory bulb to several target regions in the brain (olfactory tubercle & piriform cortex & regions in the limbic system)

Question 12

Olfactory tubercles & piriform cortex

Answer 12

ventral regions that are considered ‘PRIMARY’ OLFACTORY CORTEX
- definition not clear as other senses
→ olfactory info does NOT pass thru thalamus before reaching these cortical regions

Both regions are involved in identification of odor type & concentraion

Question 13

Orbitofrontal cortex for olfaction

Answer 13

ventral region of frontal lobes that is locate just above the orbits of eyes

Contains SECONDARY OLFACTORY CORTEX (among other functions; taste) which is involved in odor identification & determining the REWARD VALUE (ex: pleasantness) of an odor

Question 14

limbic system

Answer 14

includes several interconnected regions in the medial temporal lobe (amygdala, entorhinal cortex) that play important roles in processing emotion & memory

One func: higher-order olfactory processing - tying odors to emotion & memory

Question 15

Sniffing

Answer 15

key for olfactory perception;
- odor localization
- odor identification
- olfactory attention

Question 16

Anosmia

Answer 16

lack of ability to smell; assoc. w/ trauma to olfactory neurons projecting thru cribriform plate bone

Damage to 1 olfactory bulb can cause unilateral anosmia, which is only noticeable if nostrils are tested separately

Question 17

Hyposmia

Answer 17

decreased ability to smell
- often assoc. w/ clogged nasal sinuses or nerve damage f/ trauma-infection

Question 18

Dysosmia

Answer 18

things smell differently than they should’ often assoc. w/ hormonal changes like pregnancy, w/ clogged sinuses as seen in colds, or nerve damage f/ trauma-infection

Question 19

Hyperosmia

Answer 19

abnormally acute sense of smell

• often assoc. w/ hormonal changes like pregnancy

Question 20

Phantosmia

Answer 20

‘hallucinated smell’ often unpleasant
- common seen as an aura (early symptom) of seizure in temporal lobe epilepsy