The thicker the skin is, the more sensitive it is for touch, and it's usually found on human fingertips and lips.
A two-point discrimination test can be used to demonstrate the relative density of pressure receptors.
In this demonstration, two sharp points, such as two thumbtacks, are brought into contact with the subject's skin, though not hard enough to cause pain or break the skin.
If the subject feels one point or two points, he or she reports it.
The two points are both in the receptive field of a single sensoryreceptor if the two points are felt as one point.
If two points are felt as two different points, they are in the same sensory field.
The points could be moved closer and retested until the subject reported feeling only one point, and the size of the receptive field of a single receptor could be estimated from that distance.
There are different types of thermoreceptors on some free nerve endings that can be activated by different temperatures.
Warmth and cold information from the face travels through one of the cranial nerves to the brain.
You know from experience that a tolerably cold or hot stimulus can quickly progress to a much more intense one that is no longer enjoyable.
The same pathways that carry pain sensations are also where temperature sensations are conducted.
There are true sources of injury that cause pain, such as contact with a heat source that causes a thermal burn or contact with a corrosive chemical.
Pain can be caused by harmless stimuli that mimic the action of damaging stimuli, such as contact with capsaicins, the compounds that cause peppers to taste hot and which are used in self-defense pepper sprays.
The same calcium channels that are activated by warm receptors are also open by the capsaicin.
Pain does not start until it is communicated to the brain, which is where the perception of nociception begins.
The brain has several nociceptive pathways.
The neural signal undergoes final processing in the primary somatosensory cort and most axons carry nociceptive information into the brain.
Stimuli can cause a fight-or-flight response in the sympathetic branch of the sensory system.
There is a video that shows the five phases of nociceptive pain.
An animal can sense the presence of food or other animals in the environment through smell.
Animals have a sense of taste.
Different tasting foods have different qualities.
For survival in lean times, sweet-tasting substances tend to be high in calories.
It is important for the body to retain water and for cells to function if there is a lack of salty foods.
The smell and taste come from the environment.
Humans have sweet, sour, bitter, salty, and umami tastes.
The first four tastes are not explained.
The taste of savoriness is due to the taste of L-glutamate.
Monosodium glutamate is often used in cooking to improve the taste of certain foods.
savory substances are high in calories.
Molecules are in the air that we breathe.
There is no smell if a substance does not release its smell into the air.
If a human or other animal does not have areceptor that recognizes a specific molecule, that molecule has no smell.
Humans have about 350 olfactory subtypes that work in various combinations to allow us to sense thousands of odors.
Compare that to mice, which have about 1,300 olfactory receptor types, and they probably sense odors more.
Both odors and tastes have something in common.
Humans work together to create the perception of taste and smell.
A person's perception of flavor is reduced if he or she has a lot of congestion in his or her nose.
Remember that sensory cells are part of the brain.
There are hundreds of different olfactory types that respond to different odors.
rabbits have about 100 million, most dogs have about 1 billion, and bloodhounds have about 4 billion.
Bloodhounds are many times larger than humans and the overall size of the olfactory epithelium is different between species.
Each neuron has a single dendrite buried in the olfactory epithelium, which extends from this dendrite to 5 to 20 hair-like cilia.
The differences in the amino acid chains of the cilia's sensoryreceptor make it sensitive to different odors.
Each sensory neuron has a single type ofreceptor on its cilia that is specialized to detect specific odors.
The sensory neuron associated with the receptor is stimulated when an odorant is binding with it.
Other sensations are relayed through the thalamus, whereas olfactory stimulation only reaches the cerebral cortex.
The olfactory system in the human is made up of two parts: the olfactory epithelium and the olfactory bulb.
Pheromonal signals can have a profound effect on animals, but they are not perceived in the same way as other odors.
There are different types of pheromones, which can be released in urine or glandular secretions.
Some of the attractants to potential mates, others to potential competitors of the same sex, and still others play roles in mother-infant attachment.
The timing of puberty and reproductive cycles can be influenced by some pheromones.
Over evolutionary time, the importance of pheromones in human behavior has become less important than it was in nonhuman species.
Many animals have a tubular, fluid-filled, olfactory organ located next to the nose.
It is connected to the nose by a duct.
The VNO is where the pheromone molecule among them bind with the specialized pheromone receptors.
Pheromonal signals are sent to a different neural structure that projects directly to the amygdala, which is a brain center important in emotional reactions, such as fear.
There are areas of the hypothalamus that are important to reproductive behavior.
Some scientists think that the VNO is a vestigial system in humans, even though there is a similar structure located near the human nose, and others think that it may be a functional system that contributes to menstrual cycles in women living in close proximity.
The curling of the upper lip is caused by the flehmen response in this tiger.
Detection of a taste is similar to detection of an odor because both taste and smell rely on the same molecule.
The taste bud is the primary organ of taste.
There are several distinct strands of hair.
Filiform papillae, which are located across the tongue, provide a sense of touch that helps the tongue move substances and doesn't have taste cells.
The anterior portion of the tongue contains one to eight taste buds, which can be used for pressure and temperature.
There are up to 250 taste buds in the large circumvallate papillae.
In addition to those two types of papillae, there are also other types that areleaf-like, as seen in the Figure 36.10 micrograph.
The circumvallate papillae are in the shape of an inverted "V" at the back of the tongue.
There are about 250 taste buds in each of the papillae.
Every 10 to 14 days, the taste bud's taste cells are replaced.
Outside of the middle area of the filiform papillae, the tastants'receptor is located across the outer portion and front of the tongue.
tastants can enter taste pores in the tongue.
Humans have five primary tastes, and each taste has a corresponding type of receptor.
Like olfaction, each receptor is specific to its stimulation.
Different mechanisms reflect the composition of the tastant toduction of the five tastes.
The salty tastant gives the Na+) that enters the taste neurons.
The sour tastants are acids.
The binding of an acid or other sour-tasting molecule causes a change in the ion channel and increases hydrogen ion concentrations in the taste neurons.
There are sweet, bitter, and umami tastants.
These tastants are exciting the specialized neurons associated with them.
Tasting abilities and sense of smell change with age.
The senses decline by age 50 in humans.
An elderly person may find the same food to be bland and unappetizing as a child.
This animation shows how the sense of taste works.
The olfactory signals travel from the thalamus to the olfactory cortex.