4.1 Sensation and Perception and 4.2 Chemical Senses

Sensation

detection of stimuli

Perception

interpretation of those stimuli

Sensory transduction

converting environmental stimuli into action potentials

Receptors

specialized cells that are able to detect environmental stimuli and perform sensory transduction

Olfaction

the ability to sense and perceive volatile chemicals that are suspended in the air

Nasal cavity

an empty, air-filled space just behind the front of the skull

Olfactory epithelium

odorants dissolve in the mucus-covered dorsal most portion of the nasal cavity

What three things can you find in the olfactory epithelium?

1. Olfactory receptor neurons

2. Supporting cells

3. Basal cells

Olfactory receptor neurons (ORNs)

bipolar sensory cells in the nasal cavity that detect airborne chemicals and convert them into electrical signals.

Cranial nerve 1 (olfactory nerve)

collectively the axons of the olfactory neurons make it up

Supporting cells

help dispose of dead and dying cells, metabolize pollutants and may also help to physically maintain the epithelium by producing mucus

Basal cells

function to replace the olfactory receptor neurons

Glomerulus

site of synaptic connectivity between the ORNs and the secondary neurons in the olfactory bulb, highly specialized clump of tissue

Mitral cells and tufted cells

project axons directly into the olfactory cortex

Granule cells

found within glomeruli, help refine synaptic processing of scent information using lateral inhibition

Periglomerular cells

send axonal projections into the glomeruli, help refine synaptic processing of scent information using lateral inhibition

Odorant receptor proteins

G-protein coupled receptor on the cilia of the olfactory receptor neurons

Population coding

activity of a population of cells must be measured to determine how an odorant ultimately alters neuronal signaling

Piriform Cortex

the main cortical input site for axonal projections from the olfactory bulb

amygdala

part of the brain that helps mediate complex emotional states

Entorhinal cortex

a small section of the medial temporal lobe, sends strong connections into the hippocampus, other than receiving and processing olfactory signals the EC is also involved in spatial navigational tasks

Orbitofrontal Cortex (OFC)

found behind the orbit, bony socket of the skull where the eyes sit. Function as an integration site for sensory inputs and also receives projections from visual and taste

Hyposmia

reduced ability to smell

Anosmia

complete loss of smell

Phantosmia

when a person perceives “phantom” scents/experiences an olfactory hallucination

Gustatory system

mediates sense of taste

papillae

surface of the tongue is covered in papillae which is small visible bumps, taste buds are located within the papillae

labeled line coding method

each cell and the related afferent taste axon only responds to one type of taste

cranial nerve VII (facial nerve)

front two thirds of the tongue is innervated by the facial nerve

cranial nerve IX (glossopharyngeal nerve)

back third of the tongue is innervated by this nerve

cranial nerve X (vagus nerve)

epiglottis and pharynx are innervated by this nerve

gustatory cortex

located deep in the lateral fissure in a region called the insulation