Special Senses 12.1 Olfaction

Special senses: sensations Sensations: conscious or subconscious awareness of changes in the internal or external environment 4 conditions must be satisfied in order for a sensation to occur Stimulus(change in environment) has to activate sensory receptors Sensory receptors convert the stimulus to an electrical signal which produces a nerve impulse Nerve impulse is conducted to the brain Region of the brain must receive and integrate the impulse into a sensation Adaptation: decrease in strength of sensation during a prolonged stimulus

Special senses: Olfaction Olfaction: sense of smell Chemoreceptors: detect chemicals in the mouth (taste) and nose (smell) Nose contains 10-100 million receptors for the sense smell in the Olfactory Epithelium Nerve impulses for smell and taste propagate(travel to) the limbic system Because of this smell and taste can evoke memories or emotional responses

Special senses: Olfaction Structure of the Olfactory Epithelium occupies the upper portion of the nasal cavity consist of a 3 different cells olfactory receptors, supporting cells and basal stem cells

Special senses: Olfaction Structure of the Olfactory Epithelium Continued Olfactory Receptors: first- order neurons of the olfactory pathway Olfactory hairs project off the receptors Respond to inhaled chemicals These chemicals are known as Odorants

Special senses: Olfaction Structure of the Olfactory Epithelium Continued Basal Stem Cells: continually undergo cell division to produce new olfactory receptors Olfactory receptors only last for a month before they are replaced Olfactory Glands: produce mucus that acts as a solvent for inhaled odorants

Special senses: Olfaction Stimulation of Olfactory Receptors There are hundreds of primary odors Our ability to recognize 10,000 different odors depends on the patterns of activity in the brain Brain activity arises from the activation of different olfactory receptors When stimulated by an odorant olfactory receptors produce an electrical signal that triggers nerve impulses

Special senses: Olfaction Olfactory Pathway On each side of the nose there are 40 unmyelinated axons of olfactory receptors Axons form the right and left olfactory (I) nerve Both olfactory nerves terminate in an area on the brain called the olfactory bulbs

Special senses: Olfaction Olfactory Pathway Continued Axons coming off the olfactory bulb neuron form the olfactory tract Olfactory tract projects to the primary olfactory area Where conscious awareness of smell begins Other olfactory tract axons project to the limbic system Accounts for emotional and memory evoked responses from smell

Check for understanding 1 Detect chemicals in the nose and mouth System which accounts for emotional responses or memories from food or smell Fill in the olfactory pathway starting at the axons of the olfactory receptors, _________, olfactory bulbs, ________, primary olfactory area First- order neurons of the olfactory pathway Chemicals olfactory hairs respond to Decrease in strength of sensation during a prolonged stimulus

Special Senses 12.2 Gustation

Special senses: Gustation Gustation: sense of taste Chemoreceptors: detect chemicals in the mouth (taste) and nose (smell) Nerve impulses for smell and taste propagate(travel to) the limbic system Because of this smell and taste can evoke memories or emotional responses Only 5 primary taste can be distinguished Sour, sweet, bitter, salty, umami

Special senses: Gustation Gustation: sense of taste Olfaction is more sensitive than gustation Food can stimulate the olfactory system thousands of times more strongly than the gustatory system When you have a cold or stuffy nose and you can’t taste your food it’s the olfactory system that is blocked NOT the gustatory system

Special senses: Gustation Structure of Taste Buds Receptors for taste are located in the taste buds 10,000 taste buds are located on the tongue There are also taste buds on the roof of the mouth and throat Taste buds are located in papillae Elevations found on the tongue 3 types Circumvallate/Vallate papillae Fungiform papillae Filifrom papillae

Special senses: Gustation Structure of Taste Buds Continued Circumvallate/vallate papillae Form an inverted V-shaped row at the back of the tongue Fungiform papillae Mushroom-shaped elevations scattered over the entire tongue Filifrom papillae Found over the entire surface of the tongue Contain touch receptors but no taste receptors

Special senses: Gustation Structure of Taste Buds Continued Each taste bud contains 3 different epithelial cells Supporting cells: surround gustatory cells Gustatory Receptor Cells: Contain a single gustatory hair that projects to the external surface through the gustatory pore Basal Stem Cells: produce supporting cells WHICH BECOME gustatory receptor cells

Special senses: Gustation Stimulation of Gustatory Receptors Tastants: chemicals which stimulate gustatory receptor cells Tastant is dissolved in saliva then it enters the taste pore Dissolved tastant makes contact with the gustatory hairs Gustatory receptor cell releases a neurotransmitter Neurotransmitter binds to dendrites of the first-order sensory neuron

Special senses: Gustation Stimulation of Gustatory Receptors Continued Individual gustatory receptor cells respond to more than one of the five primary taste Some individual gustatory cells respond more strongly to some tastants than other Different taste arise from activation of different groups of taste neurons Adaptation to a specific taste can occur in 1 to 5 minutes of continuous stimulation

Special senses: Gustation The Gustatory Pathway Facial nerve(VII), Glossopharyngeal nerve(IX), Vagus nerve(X) all contain axons of first-order gustatory neurons that innervate the taste buds From the taste buds nerve impulses travel along the cranial nerves to the medulla oblongata From the medulla oblongata some axons go to the limbic system (Accounts for emotional and memory evoked responses from taste) and some axons go to the thalamus Taste signals go from the thalamus to the primary gustatory area Primary gustatory area gives rise to the conscious perception of taste

Check for understanding 2 Contains the receptors for taste Release a neurotransmitter which then triggers the sensory neuron Area which gives rise to the conscious perception of taste Mushroom-shaped elevations scattered over the entire tongue Chemicals which stimulate gustatory receptor cells Contain touch receptors but no taste receptors Where taste buds on the tongue are located