BIOL 2312 Chapter 44.1-44.3: Chapter 44.1- 44.3 Sensory Systems

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Exteroceptors- sense external environmental stimuli
Does this as evolutionary run off-- most of the external
receptors evolved in water before land.
Mammalian hearing converts airborne stimulus into a waterborne
one
Electrical organs in fish
Cannot function in the air and thus not found in terrestrial
animals
Vertebrate sensory systems that function well in water:
Infrared heat detectors
Does not work well in water
Terrestrial sensory systems that work well for land
Muscle length
Muscle tension
Limb positon
Pain
Blood chemistry
Blood volume and pressure
Body temperature
Interceptors: detect body stimuli
Sensory receptors detect both external and internal stimuli.
Receptors groups into 3 categories:
44.1- Overview of Sensory Receptors:
Touch, hearing and balance
Pressure.
Mechanoreceptors: mechanical force
Smell and taste
Chemoreceptors: chemicals/ chemical changes
Sight (photoreceptors)
Electromagnetic: light, heat, energy.
React to bending and stretching of the sensory neuron in
response to changes in temperature, or chemicals in the
extracellular fluid.
Free nerve endings: the simplest sensory receptors
1.) stimulation: a physical stimulus impinges on a sensory neuron
or an associated but separate receptor.
2.) Transduction: the stimulus energy is transformed into graded
potentials in the dendrites of the sensory neuron.
3.) Transmission: Action Potentials develop in the axon of the
sensory neuron and are conducted to the CNS along an afferent
nerve pathway.
We perceive not with our brains, but with our sense organs.
4.) interpretation: brain creates a sensory perception from the
electrochemical events produced by afferent stimulation
Sensory information is conveyed in a 4 step process:
Receptors categorized by the type of stimulus that best stimulates dendrites:
Chapter 44.1- 44.3: Sensory Systems
Monday, January 30, 2017
7:14 PM
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We perceive not with our brains, but with our sense organs.
THUS, sensory stimuli are transduced into receptor potentials
which can trigger sensory neuron action potentials that are
conducted to the brain.
The sensory stimulus produces a depolarization of the receptor
cell, this I similar to EPSP
Larger stimulus, larger potential
Receptor potential is graded potential
Decrease in size depending on distance from the source.
Depolarization occurring in a sensory receptor is a receptor
potential.
Increase depolarization of graded potential---> increase
frequency of action potential.
Log relationship between stimulus intensity and action
potential frequency.
Allows CNS to interpret the strength of a sensory stimulus
based on frequency of incoming signals
If receptor potential is great enough, then action potential.
Sensory transduction involves gated ion channels:
Respond to internal and external environment.
Pain
Heat
Cold
Touch
Pressure
Respond to:
Good examples of specialization of receptor structure and
function.
Skin receptors: interoceptor, (cutaneous)
Can be sensitive to noxious substances and tissue damage.
Specialized nociceptors exist, but hyper stimulated sensory
receptors can also produce perception of pain in brain
Consist of free nerve endings throughout body-- esp near
surface
Extremes in temperature
Hard impact
Chemicals in CSF
Nociceptors can respond to:
Can be sensitive but also can respond to damage before it
occurs… in some
Nociceptors: receptors that transmit impulses perceived as pain
Pain receptors alert the Body to damage or potential damage:
Found in noiceceptors
For noxious stimulus
Stimulated by temperature to produce inward flow of cations
(Na Ca)---> depolarizing--->sensory neuron fires---> release of
glutamate---> EPSP in neurons of spinal cord---> pain
Transient receptor potential (TRP):
Transient receptor potential ion channels:
44.2- Mechanoreceptors: touch and pressure:
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Stimulated by temperature to produce inward flow of cations
(Na Ca)---> depolarizing--->sensory neuron fires---> release of
glutamate---> EPSP in neurons of spinal cord---> pain
response
Some only respond to harmful temps
Other to milder temps
The degree of response to temperature change also
varies
This means we can feel hot and cold and have the
associated pain responses of extremes.
Have both hot and cold:
Respond to capsacin and heat.
This is why we feel the way we do when eating spicy
foods
Hot TRP channels:
Responds to methanol-- feels "cold"
Cold responsive TRP channel:
Analgesic response (methanol in cough drops)
Chemical stimulation of TRP channels reduce the body's pain
response by desensitizing the sensory neuron.
Naked dendritic endings of sensory neurons that are
temperature sensitive.
Contain TRP ion channels that respond to hot and cold
Skin has 2 populations of thermoreceptors
Located right below epidermis
3 to 4 times more numerous than warm receptors
Cold receptors stimulated by cold, inhib by warm
Located deeper in dermis
Warm is stimulated by rise in heat and inhibited by the cold
Thermoreceptors are also in the hypothalamus and monitor the
temperature of the circulating blood to keep track to body's
internal core temperature--- alter metabolism to keep things on
tract
Thermoreceptors detect change sin heat energy:
Merkel cells: tonic receptors, near surface of skin. Sensitive
to touch pressure and duration
Meissner corpuscle: phasic receptors sensitive to fine touch,
concentrated in hairless skin.
Ruffini corpuscle: tonic receptors located near surface of
skin. Sensitive to touch pressure and duration.
Pacinian corpuscle: pressure sensitive phasic receptor deep
below skin in subcutaneous tissue.
Localized cutaneous stimuli very precisely.
Pasic (intermittently activated)
Tonic (continuously activated)
Phasic
Hair follicle receptors:
Phasic
On surfaces without hair
Meissner receptors:
Morphologically specialized receptors in face and fingertips
Different receptors detect touch depending on intensity
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