Sensory Systems in Mammals and Dogs

Five Basic Senses: Hearing, sight, touch, smell, and taste.
General Mechanism:
- Receptors: Detect stimuli from the external environment.
- Transmission: Neural pathways transmit signals to the brain.
- Response: The brain processes the information, leading to a response.
Cranial Nerves: Most sensory information is conveyed to the brain via cranial nerves.
- Example: Taste buds on the tongue (receptors) send information to the brain via a cranial nerve.

Mechanism: Conversion of air vibrations into perceived sound.
- Pinna: Focuses sound waves into the ear canal.
- Tympanic Membrane: Amplifies sound waves through vibration.
- Ear Bones: Further amplify sound waves into the middle ear.
- Cochlea: Located in the inner ear; contains hair cells (receptors) that transmit sound information to the brain.
Process within the Cochlea:
- Vibrations cause the basilar membrane to move, moving hair cells against the tectorial membrane.
- Hair cell movement sends signals to the brain, which interprets the signals as sound.

Mechanism: Conversion of light wavelengths into perceived sight.
- Cornea: Protective outer coating of the eye.
- Pupil: Hole created by the iris, which gives the eye its color.
- Lens: Focuses light, with its shape adjusted by muscles.
- Retina: Contains photoreceptors (rods and cones).
Photoreceptors:
- Rods: Perceive changes in brightness and dimness of light.
- Cones: Respond to color.
Transmission:
- Light passes through retinal cells to reach photoreceptors.
- Photoreceptors send signals through neurons that synapse on horizontal and ganglion cells.
- Signals are transmitted to the brain via cranial nerve two (optic nerve).

Receptors: Various types of receptors for different types of touch.
- Free Nerve Endings: Respond to pain, heat, or cold.
- Tactile Nerve Endings: Respond to vibrations and light touch.
Transmission:
- Receptors throughout the body respond to changes in their environment (touch, pain, temperature) and transmit the information to the brain.
- Head: Mostly through cranial nerve number five (trigeminal nerve).
- Body: Through different nerves, generally conveyed through the spinal cord.

Mechanism: Detection of chemical cues dissolved in saliva.
- Taste Buds: Located throughout the oral cavity and throat.
- Taste Cells: Located inside taste buds, with a taste pore at the top.
Process:
- Chemicals (e.g., salt, sugar) dissolve in the mouth and enter the taste pore, interacting with taste receptor cells.
- Signals are transmitted to the brain.
Five Tastes: Salty, sweet, umami, bitter, and sour.
- Positive Cues: Sweet (glucose for energy), umami (protein taste), and small amounts of salt (sodium).
- Negative Cues: Large amounts of salt, bitter (associated with toxins), and sour (associated with spoiled food).
Transmission:
- Front Two-Thirds of Tongue: Cranial nerve seven.
- Back of Tongue: Cranial nerve nine.
- Throat: Cranial nerve 10.
Perigemmal Fibers: Associated with pain and temperature perception, possibly related to the perception of spicy and sour tastes.

Mechanism: Detection of chemical cues (odorants) in the air.
- Olfactory Receptors: Located in the nasal cavity, bind to odorants and send signals to the brain.
Main Olfactory Epithelium: Extensions from the olfactory bulb (cranial nerve number one) in the upper nasal cavity.
Fast Response Time: Direct connection between receptors and the cranial nerve.
Vomeronasal Organ: Specific to nonhuman mammals; associated with pheromones (reproductive and territorial responses).
Olfactory Bulb: Where olfactory fibers and receptors originate.
- Other cranial nerves: II (optic), V (trigeminal), VII, IX, X (taste-related), and Vestibulocochlear (VIII).

Vibrissae (Whiskers): Rich source of touch information.
Research Methods:
- Behavioral Research: Training dogs to choose between stimuli.
  - Forced choice: Rewarding correct choices.
  - Go/no-go: Rewarding responses (or lack thereof) to stimuli to determine sensory range.
- Evoked Potentials: Measuring electrical stimulus sent by nerves to the brain.
- Anatomic Research: Examining sensory organs to understand their structure and function.
Breed Variation: Differences in ear shape, nose shape (brachycephalic vs. dolichocephalic), and eye orientation affect sensory abilities.

Excellent Hearing: Can detect noises beyond the human range.
Ear Shape and Orientation: Affects hearing ability.
Ear Canal: Dogs have vertical and horizontal ear canals.
Frequency Range: Dogs have a higher frequency hearing range than humans (silent dog whistles).
Hair Cells: Dogs have more hair cells than humans, allowing for a larger range of frequency detection.
Breed Comparison: Bloodhounds (floppy ears) vs. Basenjis hearing differences.

Dichromatic Vision: Can see two types of colors (blue and yellow).
Color Blindness: Equivalent to red-green color blindness in humans.
Toys: Yellow is a good color.
Luminosity: Brightness perception is about half that of humans.
Focus on Movement: Eyes are designed to see movement, especially in low-light conditions.
Crepuscular: See best at dawn and dusk.
Retina: Fewer cones and more rods compared to humans.
Scotopic: High sensitivity to light with low color sensitivity.
Tapetum Lucidum: Membrane behind the retina that reflects light back to the rods and cones, enhancing vision in low light.
Breed Variation: Eye diameter and head shape (brachycephalic vs. dolichocephalic) affect sight ability. Eye placement on the side of their head gives a wider field of vision.

Mechanoreceptors: Cover the body.
Vibrissae (Whiskers): Provide information about the environment.
Facial Nerve: Movement of the whisker transmits movement to the blood sinus (pool of blood) and also increases the ability of nerve fibers to pick up on change of touch.

Most Developed Sense: Extensive olfactory system.
Natural Uses: Finding a mate, food, marking territory.
Human Uses: Locating prey, detecting drugs and bombs, finding people.
Olfactory Epithelium: Comparison (Humans have 10 squared centimeters vs. Pekingese, Dachshunds (have quite a bit), and Germans Shepherds (Up to 170 squared centimeters).
Olfactory Receptors: Bred ability to smell, structure, and organization of brain.
Dolicophalic Dogs: Have the extension of their nose out.

Pheromonal Cues: Reproductive and territorial cues.
Amygdala/Limbic System: Direct connection leads to fast emotional responses.

Functional MRI (fMRI): Study on brain responses to odorants in awake vs. anesthetized dogs.
Higher-Order Brain Structures: Activated in awake dogs only.

Nociceptive System** Respond to stimulus, pain or irritation itching. Free Nerve Endings will cause reactions.