Special Senses

Sensation

This refers to conscious or subconscious awareness of changes in the external or internal environment

Perception

→ This refers to the conscious awareness and interpretation of sensation, primary function of the cerebral cortex

→ How our brain processes the information from the environment

General senses, Special senses

Two classes of sensory modalities

General senses

This sensory modality refers to both somatic senses and visceral senses

Somatic senses

→ These senses refer to tactile, pain, and proprioceptive sensations

→ "Of the body"

Visceral senses

These senses provide information about conditions within internal organs (hunger, pressure, temperature, etc.)

Special senses

This sensory modality includes the sensory modalities of smell, taste, vision, hearing, and equilibrium or balance

Sensory receptors

These are specialized cells or dendrites of a sensory neuron where the process of sensation begins

2 → 4 → 1 → 3

Arrange the process of sensation in order:

1) Generation of nerve impulses

2) Stimulation of the sensory receptor

3) Integration of sensory input

4) Transduction of the stimulus

Receptive field

→ This region is where stimulation activates receptor, leading to response

→ Unique to each type of receptor

Stimulation of the sensory receptor

Which step in the process of sensation is described:

→ An appropriate stimulus must occur within the sensory receptor's receptive field

→ If stimulus is too small or little, no impulse is produced

Transduction of the stimulus

Which step in the process of sensation is described:

Sensory receptors transduces (converts) energy in a stimulus into electrical signals called neural impulses (graded or action potential) and sent to brain

Selectivity

What characteristic is exhibited by each type of sensory receptor that can only transduce one kind of stimulus?

Generation of nerve impulses

Which step in the process of sensation is described:

Graded potential reaches threshold and triggers nerve impulses which propagates towards CNS

First-order neurons

During generation of nerve impulses, this refer to sensory neurons that conduct impulses from the PNS to the CNS

Integration of sensory input

Which step in the process of sensation is described:

→ Certain region of CNS receives and integrates the sensory nerve impulses

→ Sensations are caused by sensory impulses from parts of the body reaching a specific region of the cortex

Cerebral cortex

During integration of sensory input, where do conscious sensations or perceptions integrate into?

Free nerve endings of first-order sensory neurons

→ This classification of sensory receptors (based on microscopic structure) represents bare, not encapsulated dendrites

→ Lack any structural specializations that can be seen under a microscope

Free nerve endings of first-order sensory neurons

This classification of sensory receptors (based on microscopic structure) serves as receptors for pain, temp, tickle, itch, and some touch sensations

Encapsulated nerve endings of first-order sensory neurons

This classification of sensory receptors (based on microscopic structure) serves as receptor for other somatic and visceral sensations (e.g. pressure, vibration, and some touch sensations)

Dendrites enclosed in capsule (i.e. Pacinian corpuscle)

Separate cells that synapse with first-order sensory neurons

This classification of sensory receptors (based on microscopic structure) include hair cells (hearing and inner ear equilibrium), gustatory receptor cells (taste buds), and photoroceptors (retina/eye for vision)

Exteroceptors

→ This classification of sensory receptors (based on location and activating stimuli) is located at or near the external surface of the body

→ Sensitive to stimuli originating outside the body and provide info about the external environment

Special senses, pressure vibration, temperature, pain

These are sensations conveyed by exteroceptors

Interoceptors (Visceroceptors)

→ This classification of sensory receptors (based on location and activating stimuli) is located in blood vessels, visceral organs, muscles, and the NS

→ Monitor conditions in the internal environment

True

[True or False] Nerve impulses produced by interoceptors are not consciously perceived unless it is activated by a strong stimuli (i.e. pain or pressure)

Proprioceptors

→ This classification of sensory receptors (based on location and activating stimuli) is located in muscles, tendons, joints, and the inner ear

→ Provide information about body position, muscle length and tension, and the position and movement of joints

Muscle spindle

This type of proprioceptor senses changes in muscle length

Tendon organ

This type of proprioceptor senses force in muscle contraction

Mechanical energy (sound waves, pressure), Electromagnetic energy (light, heat), Chemical energy (glucose molecules)

Three most common types of stimuli

Mechanoreceptors

→ This classification of sensory receptors (based on stimuli detected) is sensitive to mechanical stimuli such as deformation, stretching, bending of cells

→ Monitor the stretching of blood vessels and internal organs, touch, pressure, vibration, proprioception, and hearing and equilibrium

Thermoreceptors

→ This classification of sensory receptors (based on stimuli detected) detects changes in temperature

Nociceptors (noci - harmful)

This classification of sensory receptors (based on stimuli detected) responds to painful stimuli from physical or chemical damage to tissue

Photoreceptors

This classification of sensory receptors (based on stimuli detected) detects light that strikes the retina (eye)

Chemoreceptors

This classification of sensory receptors (based on stimuli detected) detects chemicals in the mouth (taste), nose (smell), and body fluids

Osmoreceptors

This classification of sensory receptors (based on stimuli detected) detects the osmotic pressure of body fluids

Olfactory epithelium

→ Occupies the superior part of the nasal cavity, covering the inferior surface of the cribriform plate and extending along the superior nasal conchae

→ Where the olfactory receptors are located

Olfactory sensory neurons, Supporting epithelial cells, Basal epithelial cells

Three types of cells in the olfactory epithelium

Olfaction

What is the sense of smell?

10 to 100 million

How many olfactory receptors does the nose contain in the olfactory epithelium?

Olfactory hairs

→ These are cilia that project from the dendrite, protective, support signal transmission

→ Part of the olfactory receptor that respond to inhaled chemicals

Olfactory sensory neurons

→ These are bipolar neurons with an exposed, knob-shaped dendrite and an axon projecting through the cribriform plate

→ Live for only about two months before they are replaced

Olfactory cilia

→ This extends from the dendrite of an olfactory sensory neuron

→ Site of olfactory transduction that help in the detection of odorants

False (non-motile)

[True or False] Olfactory cilia are motile

Olfactory receptor proteins

→ These are found within the plasma membranes of the olfactory cilia

→ Proteins that detect inhaled chemicals

Odorants

→ This refers to inhaled chemicals detected by olfactory sensory neurons

→ Chemicals that bind to and stimulate the olfactory sensory neurons in the olfactory cilia

Supporting epithelial cells

→ This refers to columnar epithelial cells of the mucous membrane lining of the nose

→ Provides physical support, nourishment, electrical insulation for olfactory sensory neurons, helps detoxify chemicals that come into contact with the olfactory epithelium

Basal epithelial cells

→ These are stem cells (non-differentiated) located between the bases of supporting epithelial cells

→ Continually undergo cell division to produce new olfactory sensory neurons

Bowman's glands

Another name for olfactory glands

Olfactory glands

These produce mucus which are brought to the surface of the epithelium through ducts

3 → 1 → 2 → 4

Arrange the olfactory transduction pathway in order:

1) G protein activates adenylyl cyclase → produces secondary messenger, cyclic adenosine monophosphate (cAMP)

2) cAMP opens a cation channel → allows Na⁺ and Ca²⁺ to enter cytosol → depolarizing receptor potential forms in the membrane of the sensory neuron

3) Odorant binds to olfactory sensory neuron protein in olfactory cilium → stimulates G protein (membrane protein)

4) Depolarization reaches threshold → nerve impulse is generated along axon of sensory neuron

False (low threshold, few molecules of certain substances need to be present in air to be perceived as odor)

[True or False] Olfaction has a high threshold

True

[True or False] Olfactory sensory neurons adapt by approx. 50% in the first second or so after stimulation, but adapt very slowly thereafter

Adaptability

This phenomenon refers to decrease in sensitivity (occurs rapidly) to strong odors which occurs about a minute after exposure?

Olfactory (I) nerves

These are bundles of olfactory sensory neurons present on each side of the nose

Olfactory bulbs containing glomeruli

This refers to parts of the brain where olfactory nerves extend towards

Mitral Cells

These are second order neurons of the olfactory pathway where axons of olfactory receptor cells converge

Axons of mitral cells

What forms the olfactory tract?

Olfactory cortex of the temporal lobe

Where do some axons project to cause conscious awareness of smell?

Hyposmia

→ This refers to reduced ability to smell, affects half over 65 and 75% of those over 80

→ Caused by neurological changes (Alzheimer's, Parkinson's, antihistamines, analgesics, steroids, smoking)

Gustatory

What is the sense of taste?

Salty, sweet, sour, bitter, umami

What are the five primary tastes?

Taste buds

Where are taste receptors located?

Taste buds

This is an oval body consisting of supporting

epithelial cells, gustatory epithelial cells, and basal epithelial cells

Salty

This primary taste is characterized by presence of Na⁺ in food

Sour

This primary taste is produced by H⁺ released from acids

Sweet

This primary taste is elicited by sugars and artificial sweeteners

BItter

This primary taste is composed of a variety of substances such as caffeine, morphine, and quinine

Umami

This primary taste is elicit by amino acids present in food ("meaty", "savory")

Gustatory microvilli (gustatory hairs)

Single, long microvillus that project from each gustatory epithelial (receptor) cell to the external surface through the taste pore (an opening in the taste bud)

Basal epithelial cells

Stem cells found at the periphery of the taste bud near the connective tissue layer, producing supporting cells, which develops into gustatory receptor cells (~10 days life span)

Supporting epithelial cells, Gustatory epithelial cells

Basal epithelial cells mature into two types of cells, which are?

Lingual Papillae

These refer to taste buds found in the elevations of the tongue

Decreases

As one grows older, the number of taste buds increase or decrease?

Vallate papillae (Circumvallate papillae), Fungiform papillae, Foliate papillae

Three types of lingual papillae that contain taste buds

Vallate papillae (Circumvallate papillae)

This type of lingual papillae forms an inverted V-shaped row at the back of the tongue

100-300 taste buds

Each vallate papillae contains how many taste buds?

Fungiform Papillae

This type of lingual papillae are mushroom-shaped elevations scattered over the entire surface of the tongue

About 5 taste buds

Each fungiform papillae contains how many taste buds?

Foliate papillae

→ This type of lingual papillae is located in small trenches on the lateral margins of the tongue

→ Most taste buds degenerate in early childhood

Filiform papillae

→ This type of lingual papillae contains no taste buds

→ Pointed, threadlike structures that contain tactile receptors

Tastants

→ These refer to chemicals that stimulate gustatory epithelial cells

→ Dissolved in saliva and make contact with gustatory microvilli

Depolarizing receptor potential

What stimulates exocytosis of synaptic vesicles from the gustatory epithelial cell?

neurotransmitters, nerve impulses

The liberated __________ trigger graded potentials that produce __________ in the first-order sensory neurons that eventually synapse with gustatory receptor cells

G proteins, IP₃

Tastants stimulating sweet, bitter and umami rather bind to receptors on the plasma membrane that are linked to __________ which produce the second messenger __________

False (only one type)

[True or False] Each gustatory epithelial cell responds to multiple types of tastants

Bitter

Which primary taste has the lowest threshold?

Sweet = Salty > Sour > Bitter

Arrange the thresholds of primary tastes in order: Sour, Bitter, Sweet, Salty

1 to 5 minutes

Duration of continuous stimulation to achieve complete adaptation to a specific taste

Taste receptors, Olfactory receptors, Neurons of the gustatory pathway in the CNS

Adaptation to taste occurs due to changes in?

Taste Aversion

→ This type of adaptation is characterized by a strong link between taste and pleasant or unpleasant emotions in which humans and animals quickly learn to avoid a food if it upsets the digestive system

→ Used for longer survival

Supporting cells

These cells surround about 50 gustatory receptor cells in each taste bud

saliva

Step 1 of gustatory pathway: Tastant is dissolved in _____

gustatory hairs

Step 2 of gustatory pathway: Transduction in the plasma membrane of __________

receptor potential

Step 3 of gustatory pathway: Transduction in gustatory hairs cause __________

Exocytosis

Step 4 of gustatory pathway: Involves __________ of synaptic vesicles

Neurotransmitters

Step 5 & 6 of gustatory pathway: __________ trigger a nerve impulse in the first-order sensory neuron

gustatory nucleus

Step 7 of gustatory pathway: From gustatory epithelial cells in the taste buds, nerve impulses propagate along cranial nerves to the __________ in the medulla oblongata

limbic system, hypothalamus, thalamus

Step 8 of gustatory pathway: From the medulla, some axons carrying taste signals project to the __________ and the __________ others to the __________

gustatory cortex, taste, taste perceptions

Step 9 of gustatory pathway: Taste signals that project from the thalamus to the __________ in the insula of the cerebrum, causing the conscious perception of _____ and discrimination of __________

Facial (VII) nerve, Glossopharyngeal (IX) nerve, Vagus (X) Nerve

What are the three cranial nerves that contain axons of the first-order gustatory neurons which innervate the taste buds