WK 9 – Olfaction, Gustation & Motor Pathways

Question-and-answer flashcards covering key concepts in olfaction, gustation, and motor pathways from Week 9 lecture notes.

What are the two main survival functions of the sense of smell?

Identifying substances that should be consumed and detecting harmful or dangerous substances to avoid.

Roughly what percentage of detectable odours are judged as pleasant?

About 20 %.

List four behavioural roles of pheromones.

Reproductive behaviour, individual identification, territory marking, and signalling aggression or submission.

Where are olfactory receptor neurons located?

In the olfactory epithelium at the top of the nasal cavity.

Which sensory system reaches cortex without a thalamic relay?

The olfactory system.

To which three major brain regions does the olfactory bulb project, and what aspect of smell does each mediate?

Frontal cortex (conscious perception), hypothalamus & amygdala (emotional aspects), hippocampus (memory aspects).

Name the three cell types found in the olfactory epithelium.

Olfactory receptor cells, supporting cells, and basal cells.

How frequently are olfactory receptor neurons replaced?

Every 4–8 weeks.

Approximate number of olfactory receptors: dogs versus humans.

Dogs ~1 billion; humans ~10 million.

How many functional olfactory receptor gene types do humans possess?

About 350.

Which cranial nerve is formed by the axons of olfactory receptor neurons?

Cranial Nerve I (olfactory nerve).

Loss of smell due to olfactory nerve damage is called what?

Anosmia.

Through which bone do olfactory axons pass to reach the olfactory bulb?

The cribriform plate of the ethmoid bone.

What are the two principal output neurons of the olfactory bulb?

Mitral cells and tufted cells.

How is the olfactory tract divided and where does each division project?

Medial stria → septal area; lateral stria → parahippocampal gyrus/temporal lobe.

Which cortical area is key for conscious olfactory discrimination?

Orbitofrontal olfactory area.

At what life stage is smell identification ability highest?

Early adulthood.

Give three common causes of olfactory dysfunction.

Colds or sinus infection; head injury; age-related neurodegenerative disease (also radiation, genetics, pregnancy).

Which three cranial nerves carry taste sensation?

VII (facial), IX (glossopharyngeal), and X (vagus).

Match tongue regions to their taste cranial nerves.

Anterior 2/3 – CN VII; posterior 1/3 – CN IX; epiglottis & pharynx – CN X.

Name the five basic taste qualities.

Sweet, sour, salty, bitter, umami.

What type of receptors detect sweet, bitter, and umami tastes?

G-protein-coupled (metabotropic) receptors.

Which two tastes depolarise taste cells through ionotropic channels?

Salty and sour.

What transmitter is released by taste cells for salty and sour stimuli?

Serotonin.

What transmitter is released by taste cells for bitter, sweet, and umami stimuli?

ATP.

Typical number of taste buds in an adult human?

Approximately 2,000–5,000.

Identify the three papillae types that contain taste buds.

Fungiform, foliate, and circumvallate (circumballate) papillae.

Which papillae are most numerous yet lack taste buds?

Filiform papillae.

What is the average lifespan of a taste receptor cell?

About 10–14 days.

List the three subtypes of taste receptor cells and the tastes they detect.

Type I – salty/support; Type II – sweet, bitter, umami; Type III – sour.

Describe the central gustatory pathway.

Gustatory afferents → solitary nucleus (medulla) → VPM thalamus → primary gustatory cortex (insula/post-central gyrus).

Are taste pathways mainly ipsilateral or contralateral?

Primarily ipsilateral.

Which cortical region integrates taste with other sensory inputs to create flavour?

Orbitofrontal cortex.

Differentiate somatic versus visceral motor activity.

Somatic controls skeletal muscle, voluntary movement; visceral controls smooth/cardiac muscle and glands.

Where are upper motor neurons (UMN) and lower motor neurons (LMN) located?

UMN in motor cortex; LMN in brainstem (head/neck) or spinal cord (body).

Which motor neurons innervate extrafusal muscle fibres?

Alpha motor neurons.

Which motor neurons innervate intrafusal fibres of muscle spindles?

Gamma motor neurons.

Which receptors initiate the monosynaptic stretch reflex?

Muscle spindles.

Which receptors and interneurons create disynaptic inhibition of antagonists?

Golgi tendon organs via inhibitory interneurons.

What is the role of Renshaw cells?

Inhibitory interneurons that limit alpha motor neuron activity to prevent over-activity.

Name the two pyramidal motor tracts.

Corticospinal and corticobulbar tracts.

Where do corticospinal fibres decussate?

At the pyramidal decussation in the medulla.

What percentage of corticospinal fibres form the lateral versus anterior tract?

About 80–90 % lateral (crossed); 10–20 % anterior (uncrossed until spinal level).

Which cranial nerves receive fibres from the corticobulbar tract?

Motor nuclei of CN V, VII, X, XI, and XII.

Is a lesion of the lateral corticospinal tract above or below the decussation ipsilateral or contralateral?

Below the decussation it causes ipsilateral deficits; above it causes contralateral deficits.

Give three hallmark signs of an upper motor neuron lesion.

Spasticity/increased tone, hyperreflexia, and clonus (with minimal atrophy, no fasciculations).

Give three hallmark signs of a lower motor neuron lesion.

Flaccid weakness, severe atrophy, and fasciculations (with decreased tone and hypo/areflexia).

Define spastic paralysis.

Paralysis with hypertonia and exaggerated reflexes due to an upper motor neuron lesion.

Which arterial branch most commonly supplies the internal capsule (corticospinal fibres)?

Branches of the middle cerebral artery.

Besides head trauma, name another cause of anosmia.

Lesions at the base of the frontal lobe such as a meningioma (also viral infections, etc.).