Touch , Taste,Smell, Pheromones

Sensomatory system

Provides information about touch, pressure, temperature, and pain on the surface of the skin and inside the body

Three interacting somatosensory systems

• the skin (exteroceptive system)

• Organic senses (interoceptive system)

• Kinesthetic (proprioceptive system)

Skin senses

Respond to external stimuli applied to the skin (touch and temperature)

Organic senses

Provides information about conditions inside the body for regulating the internal milieu of the body (heart rate, breathing)

Kinesthetic

Monitors information of the body, posture, and movement ( the tension of the muscles inside the body)

Cutaneous senses

• part of the exteroceptive system

• Endowed several types of stimuli: pressure, vibrations, temperature, pain

Pressure

Caused by mechanical deformation of the skin

Vibrations

Occur when we move our fingers across a rough surface

Temperature

Produced by objects that heat or cool the skin

Pain

Primarily caused by tissue damages, but can be caused by many different types of stimuli

Epidermis

• The outer layer of the skin

• Here, cells get oxygen from the air

Dermis

• middle layer

• Where most of the cutaneous receptors are located

Hypodermic

Located beneath the dermis

Glamorous skin

Hairless skin (palm of hands and feet)

Free nerve endings

Respond to temperature and pain

Meissner's corpuscles

• Only found in glabrous skin

• Detect very light touch and localized edge contours (brain-like stimuli)

Pacinian corpuscles

Respond to skin vibrations

Ruffini corpuscles

Sensitive to stretch and the kinesthetic sense of finger position and movement

Merkel's disks

Respond to local skin indentations ( simple touch)

Thermal receptors

• Ion channels gated by temperature

• Some are activated by heat and others by coldness

• May cells that express this also act as nociceptors (neurons that detect pain)

Thermal receptors activated by ligands

Found all over our skin and mouth

Temperature information

Like touch, it is processed in the somatosensory cortex

Location of pain receptors

Free nerve endings of the skin

Nociceptors

Pain sensing neurons

High threshold mechanoreceptors

A type of nociceptor where the free nerve endings respond to intense pressure, like striking or pinching

2 pathways where somatosensory sensations enter the CNS

The spinthalamic tract and the dorsal column

Spinothalamic tract

• Carries poorly localized information (crude touch, temperature, pain)

• This pathway crosses the midline immediately after entering the spinal cord, just after the first synaptic connection

The dorsal column

• Carries highly localized information ( fine touch)

• This pathway ascends ipsilaterally before first synapsing in the medulla

Somatosensory sensations

When different sites of primary somatosensory cortex are electrically stimulated

Tactile agnosia

Having trouble identifying objects by touch alone, but can draw these objects without looking

Phantom limb

The persistent feeding of a body part after it has been amputated or removed

Cause of phantom limb sensations

• Confusion in the somatosensory cortices ( primary and association)

• The brain gets confusing signals from the cut nerves ( sensory, motor, proprioceptive) and has difficulty interpreting them

Taste buds

• Little grooves in the tongue

• Each contains 20 to 150 receptor cells

Why taste cause continually regenerate and are replaced every 10 days

They are exposed to an hostile environment

Taste receptor cells

• Small cells clustered in taste buds

• Do not have axons or action potentials

• Release sultanate receptors in a graded fashion depending on their membrane potential

Six categories of taste receptors

Sweetness, umami, bitterness, saltiness, sourness, fat

Sweetness

• Detected by a single metabotropic receptor that is activated by sugar

• Some birds and the entire cat family cannot taste this

Umami ( savoy)

• Detected by a single metabotropic receptor that is activated by glutamate

Bitterness

• Detected by 50 different metabotropic receptors. Each one evolved to detect a different bitter molecules.

Saltiness

Detected by a single ion channel that is highly permeable to Na+ ions

Sourness

• Detected by a single in channel that is permeable to H+ ions

• Taste cells that detect this are responsible for the sensation of carbonation and the taste of astringency

Tat

Several metabotropic receptors and fatty acid transporters are thought to contribute to our taste of fat

Olfactory system

Specialized for identifying specific molecules called odorants

Odorants

• Volatile substances that have molecular weight between 15 and 300

• Most are lipid soluble and organic in origin; however, many substances that meet these criteria have no odor

Olfactory epithelium

• Responsible for our taste of smell

• Sits underneath the skull

Olfactory receptors

• Each olfactory cell expresses one type.

• They have axons

• Synapse in glomeruli,in the olfactory bulb

Glomerulus

• Each one of these processes information from just one type of olfactory receptor cell

• Each of these process a different color

Olfactory information steps

It goes directly to the primary olfactory cortex in the temporal lobe and the amygdala

Pheromones

• Molecules released by one animal to signal something to another member of the same species

• Behavioural responses to these are largely innate

what pheromones are used for

• Attract or repel other members of the same species

• Signal attractiveness and sexual receptivity

• Mark a path to follow

• Signal a danger

Vomeronasal organ and accessory olfactory bulb

Where the transduction and processing of pheromones occurs in mammals

Vomeronasal receptors

• Detect pheromones

• Humans, apes, and birds do not have these

Lee-Boot-Effect

When female mice are housed together (without any male urine present) their estrous cycles slow down and eventually stop

Whitten effect

Phéromones in thé urine of male mice can trigger synchronous estrus cycles in groups of female mice

Vandenbergh effect

Early onset of puberty seen in females animals that are house with males

Bruce effect

The tendency for female rodents to terminate their pregnancy following exposure to the scent of an unfamiliar male