BIO2242 Lecture Notes - Lecture 12: Olfactory Bulb, Olfactory Epithelium, Cribriform Plate
Lecture 13 – Senses
Coordination
• Sensor → sensory input (received by brain) → integration (central nervous
system)→ motor output (peripheral nervous system) → effector
• The reflex
o Sensory perception from muscle passed to spinal column
o E.g. cockroaches – can move without a brain because connected to
spinal cord
How senses work
• Detectable information
o Light
o Chemicals
o Temperature
o Movement
• Transmit to CNS > sensation
• Sensory cell types:
o Neurons
▪ Short single dendrite
▪ Long branched dendrites
▪ Specialised epithelial cells
o Stimulus energy
▪ Mechanical – mechanoreceptor
▪ Chemical – chemoreceptor
▪ Light – photoreceptor
o Location
▪ Exteroreceptors (somatic)
▪ Enteroreceptors (visceral)
Stimulus Response
• Detection
o Selectivity
o Sensitivity
• Transduction
o Convert signal into something useful
o Converting one form of energy into another form
o Translate into language of the nervous system
▪ Chemical messengers
▪ Receptor potentials
▪ Nerve impulses (action potentials)
• Amplification
• Transmission
• Integration
• Response
Chemoreception
• Transduction of chemical binding energy
o Most widespread sense
o May operate on contact or over distance
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o Usually two systems
1. Taste (gustation)
• Contact chemoreception
• Often less sensitive than smell
• Epithelial receptor cells (not neurons)
• Different locations on the body:
o Taste buds in oral cavity (amniotes)
o Also on rest of the body in fish (e.g. barbels)
and aquatic amphibians
• Limited discrimination ability
o Five tastes: salty, sour, bitter, sweet and umami
o Receptor cells are differentially sensitive
o Taste buds can include different cell types
o Limited segregation of taste qualities on tongue
o Fifth taste – umami (glutamate and peptides)
2. Smell (olfaction)
• Chemoreception over distance
• Air or water borne odours
• Relatively small molecules dissolve in mucus
• Receptors on antennae, nasal cavity
• Ciliated neurones
• Specialised brain area
o Antennal lobe (insect)
▪ Sensilla
▪ Non motile cilia on sensory neurons →
area increased
▪ Increase sensitivity structure by
increasing number of hairs
o Olfactory bulb (vertebrate)
▪ Nasal cavity: human nose
▪ Olfactory epithelium
• Mucus
• Sensory neurons
• Cilia
▪ Axons pass through cribiform plate to
the olfactory bulb in brain
• Glomeruli are processing areas
• Plates allow us to increase area
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▪ Primary receptor cells
▪ Shortest cranial nerve
▪ Information directly to olfactory cortex
▪ E.g. dog
• Turbinates increase surface
o Olfactory epithelium
(OE)
o Breath humidity
regulation
• Increased sensitivity and
discrimination
o Range of different molecules
o Discrimination with many receptors
▪ Each molecule can bind to several different receptors
▪ Each receptor detects several odorants
▪ Mammals can differentiate ~10,000 different odours
▪ Single transduction mechanism
o Smell, taste or flavour?
▪ Distinction isn’t very large
▪ Humans: smell is important component of flavour
▪ Most fish have receptors on skin for waterborne chemicals
▪ Some invertebrates combine olfactory and gustatory neurons in
single organ
▪ Distinctions between taste and smell in vertebrates
• Distance, many qualities, centralised location (nose)
• Contact, only five qualities, diffuse location
Mechanoreception
• Receptors are ion channels
o Respond to physical motion of cell membrane
o Structure that transduces kinetic energy into chemical energy →
electric energy
o Changes membrane permeability to Na+ and K+
• Special structures for transfer of energy
• Includes: touch, vibration, pressure and pain
• Specialised systems
o Lateral line system
o Hearing – detect movement of air
o Equilibrium
o Echolocation
• Somatosensory (touch)
o Hairs to detect light movement → passed to CNS
o Gentle contact stimulates hair
• Proprioceptors
o Hair responds to sensation
o Responds to deformation of hair (stimulus) → produces signal to CNS
Movement and Balance
• Invertebrates
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Document Summary
Stimulus response: detection, selectivity, sensitivity, transduction, convert signal into something useful, converting one form of energy into another form, translate into language of the nervous system, chemical messengers, receptor potentials, nerve impulses (action potentials, amplification, transmission. Information directly to olfactory cortex: turbinates increase surface, olfactory epithelium (oe, breath humidity regulation. Mechanoreception: receptors are ion channels, respond to physical motion of cell membrane, structure that transduces kinetic energy into chemical energy electric energy, changes membrane permeability to na+ and k, special structures for transfer of energy, specialised systems. Invertebrates: statocysts: signals gravity, depends on which of hairs is deformed to affect animal"s gravity, moving structures around ciliated surface: provides information about orientation of animal, sac with heavy statoliths (intertia), marble like structure, receptor cells with cilia. Mechanoreception ii hearing: hearing conversion of some kind of mechanical energy into electrical signal, propagated sound waves (water/air, vibrating membranes respond to pressure oscillations, most invertebrates can"t hear, however, many sense substrate vibrations.
