BGYB30 Chapter 10 textbook notes

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18 Feb 2011
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MAMMILIAN PHYSIOLOGY
Chapter 10 Sensory Physiology
Special Senses:Include vision, hearing, smell, taste, equilibrium
Somatic Senses:include touch, temperature, pH, itch, proprioception (the awareness of
body
movement and position in space mediated by sensory receptors in
muscles and joints)
General Properties of Sensory Stimulation
All sensory pathways begin with a physical stimulus that acts on a receptor. The receptor
acts as a transducer and converts the stimulus to an intracellular signal. If it is above the
threshold, it is transferred to the CNS where it is integrated either consciously or
unconsciously
Sensory receptors vary in complexity. The most basic, simplest receptor is the neuron with
naked (free) nerve endings (i.e. somatosensory receptors). In the complex ones, the nerve
endings are encased in connective tissue
The most complex type of sensory receptor is that of the special senses. All of them except
for smell use non-neuronal receptor cells that synapse onto secondary neurons (smell goes
straight to the brain through one of the cranial nerves)
When activated, they release neurotransmitters that initiate action potentials that send
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information to the brain
Non-neuronal accessory structures are very important to help receptors. I.e. the cornea of
the eyes help focus light for photoreceptors; the hairs on ones arm help sense movement of
air close to skin. These attributes enhance information gathering
Receptors are divided into 4 major groups:
1.Chemoreceptors:respond to chemical ligands that bond to receptors. I.e. taste,
smell
2.Mechanoreceptors:Respond to various types of mechanical energy. I.e.
pressure, vibrations,
acceleration, sound (i.e. hearing)
3.Thermoreceptors:Respond to temperature
4.Photoreceptors:Respond to light
Transduction
The first step of converting physical stimuli into an electrical one is transduction
(conversion of stimulus energy into information that can be processed by the nervous
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system)
Adequate Stimulus:Each type of receptor has a particular form of energy it is most
responsive to (Thermoreceptors heat; Mechanoreceptors pressure)
Although receptors may have adequate stimuli, they are also responsive to different forms
of stimuli, given it has enough intensity. (I.e. photoreceptors are sensitive to light but if you
punch someone in the eye, they will see stars (mechanoreceptors)
The threshold the amount of stimulus required to activate a receptor is much lower for
their specific adequate stimuli
Usually the physical stimulus causes the opening or closing of ion channels in the receptor
membrane. Opening causes an influx of Na or other cations causing depolarization whereas
closing it or an influx of K causes hyperpolarisation
The change in sensory receptor membrane potential is called graded potential or receptor
potential. In some cells, this causes an action potential to the nervous system. In other cells,
it causes the release of neurotransmitters which alters electrical activity in associated
neurons
Receptive Fields
Somatic sensory receptors and visual neurons are activated if stimuli fall within a certain
physical area called a receptive field
Each receptive field has a primary neuron which relays electrical info to the secondary
neuron located in the CNS
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Document Summary

Somatic senses: body include touch, temperature, ph, itch, proprioception (the awareness of movement and position in space mediated by sensory receptors in muscles and joints) All sensory pathways begin with a physical stimulus that acts on a receptor. The receptor acts as a transducer and converts the stimulus to an intracellular signal. If it is above the threshold, it is transferred to the cns where it is integrated either consciously or unconsciously. The most basic, simplest receptor is the neuron with naked (free) nerve endings (i. e. somatosensory receptors). In the complex ones, the nerve endings are encased in connective tissue. The most complex type of sensory receptor is that of the special senses. All of them except for smell use non-neuronal receptor cells that synapse onto secondary neurons (smell goes straight to the brain through one of the cranial nerves) When activated, they release neurotransmitters that initiate action potentials that send www. notesolution. com information to the brain.

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