What are sensory receptors?
Sensory receptors are nerve endings with specialised non-neural structures
What do sensory receptors do?
Sensory receptors are transducers that convert different forms of energy into frequency of action potentials, informing the CNS about the internal and external environment
What is sensory modality?
Sensory modality is the stimulis type activating a receptor
What is an adequete stimulis?
An adequete stimulis is the type of energy to which a receptor normally responds
What can you say about sensory receptors being activated by many stimuli?
Sensory receptors are highly sensitive to one kind of stimuli, but may be activated by another
What are some different types of receptors?
Some different types of receptors are:
Mechanoreceptors (mechanical stimuli like touch)
Proprioreceptors (informations about position in space)
Thermoreceptors (cold and warmth)
Chemoreceptors (chemical change)
Photoreceptors (responds to the wavelength of light)
What does sensory receptor transduction involve?
Sensory receptor transduction involves ion channels opening and closing, adequete stimuli generates a graded potential
What is membrane deformation?
Membrane deformation is adequete stimuli in mechanoreceptors and proprioreceptors
What does membrane deformation activate?
Membrane deformation activates stretch sensitive ion channels, causing a local graded potential
What happens when the graded potential reaches threshold?
When the graded potential reaches threshold an action potential is fired
What is frequency coding of stimulis intensity?
This means a larger stimuli produces a larger graded potential which produces higher frequency of action potentials fired
What does the number of receptors activated in an area reflect?
The number of receptors activated in an area reflects the stimulis intensity
What are some contrasts in the action potentials of some mechanoreceptors?
In some mechanoreceptors if the stimuli persists then action potentials are constantly fired
In others, action potentials are only fired when something changes
What is adaptation?
Adaptation is when some mechanoreceptors adapt to a maintained stimulus and only signal change
What are the two different kinds of adapting receptors?
The two different kinds of adapting receptors are:
Rapidly/moderately adapting receptors (fire AP at change)
Slowly adapting receptors (constantly fires AP)
Why do nocioreceptors not adapt?
Nocioreceptors do not adapt because they are free nerve endings
What is the pacinian corpuscle and how does it work?
The pacinian corpuscle is a mechanoreceptor:
- Mechanical stimuli deforms capsule
- Stretches nerve endings and opens ion gated channel
- Na+ influx causes graded potential
- Action potential generated and fired
What does rapid adaption occur?
Rapid adaption occurs because the fluid redistributes in the capsule and removes mechnical stress from the nerve ending
How do nerve endings respond without a capsule?
Without a capsule, bare nerve endings have no adaptation and fire constant action potentials
What are receptive fields?
Receptive fields are somatic sensory neurons activated by stimuli in a specific area
What posseses receptive fields?
Sensory receptors posses receptive fields
What does our ability to determine two points on the skin depends on?
Our ability to determine two points on the skin depends on:
Receptive field size
What is our ability to determine two points on the skin tested by?
The two point discrimination test
What is neuronal convergence?
Neuronal convergence is when multiple pre-synaptic neurons input a smaller number of post synaptic neurons
What do sensory neurons with neighbouring receptive fields show?
Neighbouring neurons with receptive fields show neuronal convergence
What does neuronal convergence allow?
Neuronal convergence allows sub threshold stimuli to summate at the secondary neuron to generate an action potential
What leads to an insensitive area?
Neuronal convergence and a large receptive field leads to an insensitive area
What is an example of a sensitive and insensitive area?
The lips are sensitive
The back is insensitive
What is acutiy?
Acuity is the ability to locate a stimulis on the skin and differentiate it from another closeby
When does high acuinty occur?
High acuinity happens when lots of signals from an area goes to the brain, low acuinity happens when less go
What is lateral inhibition?
Lateral inhibition is when information from a neuron from a sensory receptor at the end of a stimuli is inhibited by information from the centre
What does lateral inhibition allow us to do?
Lateral inhibition allows us to precisely locate stimulis
What is tonic level of firing?
Tonic level of firing is a base level of nerve impulses firing when nothing is going on