touch, taste, smell, pheromones
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what are the three interacting somatosensory systems?
• the skin senses or exteroceptive system responds to external stimuli applied to the skin (e.g., touch and temperature) • the organic senses or interoceptive system provides information about conditions inside the body for regulating the internal milieu of the body (e.g., heart rate, breathing, hunger, bladder) • the kinesthetic or proprioceptive system monitors information about the position of the body, posture, and movement (e.g., the tension of the muscles inside the body)
what is the function of the somatosensory system?
provides information about touch, pressure, temperature, and pain on the surface of the skin AND inside the body.
what are the cutaneous senses?
pressure (touch): 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: can be caused by many different types of stimuli, but primarily tissue damage
how is called the outer layer of the skin?
epidermis
from where do cells of the epidermis get oxygen from?
the air
what is the dermis
it’s where most of the cutaneous receptors are located.
Immediately beneath the dermis is the..
hypothermis or subcutaneous
what is glabrous skin?
hairless skin
what is the main function of free nerve endings?
respond to temperature and pain
What are meissner’s corpuscles and where are they found?
they are only found in glabrous skin. they detect very light touch and localized edge contours (brail-like stimuli)
what are thermal receptors?
ion channels that are gated by temperature. Some are activated by heat; others are activated by coldness
Many cells that express thermal receptors also act as…?
nociceptors (neurons that detect pain)
what are thermal receptors?
ion channels that are gated by temperature or some by ligands
thermal receptors that are activated by ligands are found where?
all over the skin and mouth receptors.
why can’t some animals feel the heat of spicy chili peppers?
most species of birds have a modified form of the thermal receptor TRPV1. The bird version cannot bind capsaicin. This is why chickens readily eat spicy peppers. Note, this doesn’t significantly change the taste of their meat or eggs.
true or false: pain and temperature information is poorly localized.
true, we are not great at pinpointing precisely where these sensations occur on our body.
Describe the axons that carry pain and temperature information to the CNS.
unmyelinated or thinly myelinated.
where are receptors for pain and temperature located?
on free nerve ending in the skin
what are called pain-sensing neurons
nociceptors - “detectors of noxious stimuli”
what are high-threshold mechanoreceptors?
pressure receptors. these free nerve endings respond to intense pressure, like striking or pinching.
can nociceptor respond to heat?
yes, other types of nociceptors respond to extreme heat (or the presence of capsaicin from spicy chili peppers).
true or false: all somatosensory sensations enter the CNS via spinal nerves.
true
what are the 2 main pathways of somatosensory sensations?
spinothalamic tract and dorsal column
describe the spinothalamic tract
it carries poorly localized information (e.g., crude touch, temperature and pain). this pathway crosses the midline immediately after entering the spinal cord, just after the first synaptic connection. medulla - midbrain - ventral posterior nucleus of thalamus - primary somatosensory cortex