ZOO 2090 Lecture Notes - Lecture 20: Lingual Papilla, Olfactory Epithelium, Nasal Placode
1 May 2018
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ZOO2090 – Sense Organs
Function: perceive and integrate sensation, and initiate action
Components:
• A sensory receptor is usually composed of the dendrites of a neuron and can include
tissue that amplifies stimulus
• The receptor is a transducer that transforms a stimulus into an electrical impulse that
spreads to cell body and along axon to other neurons (usually in CNS)
Chemoreception:
1. Olfactory organs
• Ectodermal origin
• Olfactory epithelium located in the nasal pit or respiratory passage are responsible
• Filaments serve to increase SA
• Olfaction used for discrimination of chemicals in the environment
• Fish:
o Admit water to nasal pit
o Lamellae made of olfactory epithelium and support tissue
• Air breathing vertebrates:
o Add mucous cells (dissolves particle and washes away old samples)
• Size and complexity of the nasal chamber is increased in tetrapods:
o Mammals have most complex turbinate to increase surface size
o Highly sensitive: mammals can distinguish 10,000 odors (human:1000-4000)
2. Taste (gustatory)
• Detects similar molecules as olfactory
• General structure is similar to olfactory but differs in:
o Endodermal origin
o Less sensitive
o Receptor cells aggregate into taste buds; don’t have axons but receive afferent
fibers from the CNS
o Taste buds are exposed, worn and replaced
• Triple sensory innervation of the tongue:
o Vagus nerve vallate papillae
o Glossopharyngeal nerve
o Facial nerve foliate and fungiform papillae
o Each papilla has taste buds with microvilli
• The distribution of taste buds varies across major groups:
o Fish: mouth, pharynx, heads and other body parts
o Amphibians: tongue, pharynx and skin
o Reptiles/Birds: pharynx (poor sense of taste)
o Mammals: mouth and pharynx
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