Taste & smell Flashcards
How many nerves does the peripheral nervous system have?
43 pairs
12 pairs of cranial nerves
31 pairs of spinal nerves
What type of process is sensation?
Cognitive
What are the tastes that can be detected?
- Salty
- Sour
- Sweet
- Bitter
- Umami
- Fat
Where is the taste sensation detected?
Main organ - tongue
Also in palate, pharynx and epiglottis
What type of receptors are taste receptors?
Chemoreceptors
What is the olfactory sense?
Smell
Where are taste buds found?
Mainly in papillae Soft palette Inner surface of cheeks Pharynx Epiglottis of larynx
What is the mechanism for sour taste receptor transduction?
- H+ is the sour stimulant
- The K+ channel is inhibited blocking K+ efflux and increases the K+ in the cell
- This causes depolarisation which causes the calcium channels to open
- Calcium influx triggers the exocytosis of the neurotransmitters from their synaptic vesicles
- Neurotransmitters travel to gustatory afferent axon
What is the mechanism for salt taste transduction?
- Na+ enters the taste cell through a sodium sensitive channel
- Depolarisation of the membrane occurs which causes the calcium voltage gated channels to open
- Influx of calcium into the cytoplasm triggers exocytosis of the neurotransmitters out of the cell to the gustatory afferent axon
What is the mechanism for sweet taste receptor transduction?
- Sugar binds to GPCR activating the G-protein
- The alpha-subunit dissociates and binds and activates adenylyl cyclase
- Activated adenylyl cyclase causes the conversion of ATP to cAMP (secondary messenger)
- The cAMP activates protein kinases which inhibit K+ channels causing depolarisation
- Calcium voltage-gated channel open
- Calcium influx leads to exocytosis of neurotransmitters to gustatory afferent axon
What is the mechanism for bitter taste receptor transduction?
- Bitter substance binds to bitterness receptor
- Activates the bound g-protein, alpha subunit which dissociates and activates phospholipase C
- Activated PLC activates the hydrolysis of PIP2 to IP3 which binds to the endoplasmic reticulum and causes the ligand-gated channel for calcium to open and calcium is released from stores in the intracellular endoplasmic reticulum
- Increase in intracellular Ca2+ triggers the release of neurotransmitters via exocytosis
What is the mechanism of olfactory signal transduction?
- Odorant binds to receptor on cillia on the olfactory epithelium located at the roof of the nose. These receptors are GPCR, the binding of the odourant cause the G-protein to activate.
- The activation of the G-protein the activates adenylate cyclase which can now synthesise the conversion of ATP to cAMP
- cAMP binds to specific ion channels causing them to open
- Ca2+ and Na+ channel open and there is influx of these molecules
- Opening of the Ca2+ activated Cl- channel to open causing the efflux of Cl-
- This causes depolarisation of the receptor cell membrane which creates an action potential which send the impulse along the olfactory fibres to the olfactory bulb which send the signal to the brain
The axons of the olfactory receptor cells synapse in the brain structures known as olfactory bulbs. Axons from olfactory receptor cells that share a common receptor specificity synapse together on certain olfactory bulb neurons, so that specific odorant receptor cells activate only certain olfactory bulb neurons allowing the brain to determine which receptors have been activated
What is ansomia?
How can it be causesd?
Loss of smell
Inflammation of the nasal mucosa prevents odorous substances from reaching olfactory area of the nose prevent olfactory signal transduction, or less.
What are the 3 stages of swallowing?
Oral, pharyngeal and oesophageal
What is the mechanism of swallowing
Oral phase
- Voluntary muscles of the tongue and cheek push food bolus backward towards the pharynx - this under neural control of cerebral cortex
Pharyngeal phase
- Autonomic control of swallowing centre located in lower pons and medulla oblongata of the brainstem
- Reflex arc stimulates muscles of the pharynx which are coordinated by the mechanoreceptors that signal the swallowing centre in the medulla. The involuntary contraction of these muscles pushes the bolus down the oesophagus
- During this the soft palate rises to block the nasopharynx to prevent nasal regurgitation.
- The epiglottis covers the glottis to prevent food from entering the trachea
- The tongue and pharyngeal folds block the food coming back into the mouth
- Respiration is inhibited
Oesophageal stage
- Presence of bolus in pharynx stimulates wave of peristalsis that propel the bolus through the oesophagus to the stomach
- Before the waves the lower oesophageal sphincter relaxes to allow food into the stomach
What does the lower oesophageal sphincter do?
Prevents reflux of gastric acid into the oesophagus
How is the oesophagus adapted and designed for swallowing?
It is lubricated with mucus which assists the passage of the bolus during peristaltic contraction of the muscular wall
What type of activity of swallowing?
Voluntary and involuntary reflex activity
What is dysphagia?
Inability to swallow
Malfunction of cranial nerves involved in swallowing can lead to dysphagia
Difficulty can lead to food going the wrong way, e.g. nasal regurgitation or food entering the trachea
What are the muscles involved in the oesophagus during swallowing?
Skeletal muscle - located in the upper third
Smooth muscle - located in bottom 2 thirds forming lower oesophageal sphincter
Describe the action of the cranial nerves and muscles during swallowing
- Efferent activity in somatic nerves is sent from the swallowing centre in the medulla oblongata to the skeletal muscles
- Efferent activity in the autonomic nerves is sent from the swallowing centre in the medulla oblongata to the smooth muscles
- Receptors in the oesophageal wall send information along afferent fibres to the swallowing centre which can change efferent activity. e.g. stimulate secondary peristalsis
