Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
10/7/2010
1
Sensory ReceptorsSensory ReceptorsSensory Receptors
(some basic properties) Sensory Receptors
(some basic properties)
Organs which receive information from outside or
Organs which receive information from outside or within the body and send it to the central nervous system for processing
within the body and send it to the central nervous system for processing
Activated by various forms of energy:
light heat
Activated by various forms of energy:
light heat
Sensory Receptors(some basic properties)
Sensory Receptors(some basic properties)
Specialised nerve ending
light, heat, mechanical chemical etc.
light, heat, mechanical chemical etc.
Sensory receptors are either specialized endings of afferent neurones or separate cells that signal to the afferent neuroneSensory receptors are either specialized endings of afferent neurones or separate cells that signal to the afferent neurone
Specialised cells
Definition of a Transducer or TransductionConversion of one form of energy (e.g. heat, pressure, chemical) into another form: e.g. electrical energy or depolarisation
Definition of a Transducer or TransductionConversion of one form of energy (e.g. heat, pressure, chemical) into another form: e.g. electrical energy or depolarisation
Sensory Receptors Are Transducers Sensory Receptors Are Transducers
The depolarisation occurring at the sensory terminal is a). Graded – Non-propagating, confined to terminalb). Called the Receptor Potential (R.P.)
The depolarisation occurring at the sensory terminal is a). Graded – Non-propagating, confined to terminalb). Called the Receptor Potential (R.P.)
The Receptor Potential:If large enough will evoke all or nothing action potentials that propagate along the nerve fibre
The Receptor Potential:If large enough will evoke all or nothing action potentials that propagate along the nerve fibre
Variable stimulusintensity
Produces graded receptor potentials
The Receptor PotentialThe Receptor Potential
Adequate stimulus
10mV
Produces variable patterns of
action potentialsin the CNS
More Stimulus = More Transmitter Released
Intensity of Stimulus is Linearly EncodedIntensity of Stimulus is Linearly Encoded
The number of action potentials generated by a pressure-sensitive sensory afferent neuron is directly proportional to the stimulus intensity.
The number of action potentials generated by a pressure-sensitive sensory afferent neuron is directly proportional to the stimulus intensity.
10/7/2010
2
Receptor Potential: more or less proportional to stimulus
Receptor Potential: more or less proportional to stimulus
stimulus receptor potentialstimulus receptor potential
adaptationmV
Adaptation to stimulus depends on receptor typeAdaptation to stimulus depends on receptor type
adaptation
Who can guess how a membraneof a neurone could react topressure or temperature by achange in membrane potential?
The offresponse
Adaptation: A Mechanism Preventing Sensory Information Overload
Adaptation: A Mechanism Preventing Sensory Information Overload
Skin:Paccinian
Corpuscles pressure/touch
Skin:Paccinian
Corpuscles pressure/touch
Different receptors vary in their speed of adaptation to stimuliDifferent receptors vary in their speed of adaptation to stimuli
Muscle:stretch
receptors
Muscle:stretch
receptors
Specific types of sensory receptors for different mechanosensory stimulationSpecific types of sensory receptors for different mechanosensory stimulation
Receptor SpecificityReceptor Specificity
Mechanoreceptors PhotoreceptorsPhotoreceptors ChemoreceptorsChemoreceptors
Receptors have a differential sensitivity to different energies or stimuliReceptors have a differential sensitivity to different energies or stimuli
nerve ending
A receptor is specific to one energy (or stimulus), because it is most sensitive to that energy. Other energies may
stimulate but only at high intensities.
A receptor is specific to one energy (or stimulus), because it is most sensitive to that energy. Other energies may
stimulate but only at high intensities.
Sensory afferent (A) has a more spatially limited receptive field than sensory afferent
Sensory afferent (A) has a more spatially limited receptive field than sensory afferent
Sensory Processing:spatial discrimination
Sensory Processing:spatial discrimination
neuron (B).neuron (B).
10/7/2010
3
Lips Back
Sensory Processing:spatial discrimination – the paired point test
Sensory Processing:spatial discrimination – the paired point test
Overlapping stimulation between neighboring receptive fields
id l i f ti
Overlapping stimulation between neighboring receptive fields
id l i f ti
Sensory Processing:spatial discrimination
Sensory Processing:spatial discrimination
provides general information about the location of a stimulus. provides general information about the location of a stimulus.
Stimulus A occurs in an area of greater nerve ending density
Stimulus A occurs in an area of greater nerve ending density
Sensory Processing:density of sensory afferent terminals
Sensory Processing:density of sensory afferent terminals
Stimulus A will generatea greater number of action potentials than stimulus B.
Stimulus A will generatea greater number of action potentials than stimulus B.
Sensory Processing:descending modulation from higher centres
Sensory Processing:descending modulation from higher centres
Painful Condition
Descending inputPainful Condition& Fight or Flight
Context and Sensory PerceptionContext and Sensory Perception
Monty Python & the Holy Grail
Sensory Processing: sensory discriminationSensory Processing: sensory discrimination
Provide background information about touch and temperature
Deliver information about location-specific changes in touch and temperature in the periphery.
10/7/2010
4
Convergence of sensory pathways is one of the reasons for “referred” pain from visceral organs
Sensory Modality Representation is Location Specific in the Cerebral Cortex
Sensory Modality Representation is Location Specific in the Cerebral Cortex
Fine discrimination is highly representedFine discrimination is highly represented
Sensory Representation is CortexSensory Representation is Cortex
cortical homunculus
Summary:
1. Sensory receptors allow our body to interact with the external environment2. Sensory receptors in internal organs are essential for homeostasis and
also alert the body in case of some anomaly3. Some receptors adapt fast, others slow and some – almost not at all.4. The intensity of the stimulus is encoded by the frequency of the action
potentials.5. Most receptors detect the stimulus via a subset of highly specialised ion
channels which open (Na+) or close (K+) to evoke depolarisation of the membrane of the sensory ending in response to the stimulus.
6. Information sent from the receptors is called AFFERENT information. In the CNS it is usual that several afferent neurones contact the same postsynaptic cell. This is the convergence, which is also a reason for referred pain.
7. The organs with the highest tactile sensitivity have the largest representations in the “sensory homunculus”