Lecture 13 Flashcards
All senses require 3 common steps but what are they?
They require a physical stimulus
They all must transform the stimulus into nerve inpulses
- this occurs in the PNS
They all evoke a response to the signal in the form of perception or conscious experience of sensation
- this occurs in the CNS
Where does sensation begin?
With sensory receptors in the periphery
What do sensory receptors enable?
Sensory transduction, the conversion of energy from the environment into electrochemical signals
- sound/touch/light to electrical signals
What do many sensory receptors contain?
Ion channels and G-protein coupled receptors that are common to many bodily functions
How is specifity of sensory modalities achieved by?
The structure and position of the sensory receptor
What are sensory modalities?
Vision, smell, taste, touch, hearing, thermal senses, pain, balance, proprioception
How are receptors classified?
Modality: Chemo, thermo, mechano etc
Origin:
- exteroceptors: vision, hearing, touch, cutaneous pain
- interoceptors: internal organs, visceral pain, nausea, stretch
- proprioceptors: muscles, tendons, joints - position and movement
- nociceptors: high threshold mechano and thermoreceptors
Distribution:
- General senses (somesthetic): touch, pressure, stretch hot, cold, blood pressure/composition
- Special senses: Head, innervated by cranial nerves
What is the stimulus in taste receptors?
Chemical; e.g. Na in salt
How do membranes depolarize in taste receptors?
Graded response
What is the stimulus in olfactory receptors?
Chemical; an odorant
How are graded receptor potential within a receptor cilium caused?
Local changes in membrane permeability
What happens when large enough receptor potentials are generated?
Cause depolarization in the cell soma, triggering action potentials that travel along the olfactory nerve
Sensory receptors conveys four types of information:
Modality (quality)
Location
Intensity
Timing
How is modality determined?
By the type of energy transmitted by the stimulus and the receptor \s that are specialized to detect that energy
What is the labelled line code?
The receptor is selective for one type of stimulus energy
The axons of the receptor/associated afferent neuron acts as a modality specific line of communication
Axons from these neurons make connections with specific areas in the CNS
How is the labelled line code like a transducer?
e.g. initial receptor and where it’s located that sets the system
What does stimulating afferent neurons electrical lead to?
A perception of the associated sensation
What happens when the labelled line code is faulty?
Synesthesia
What happens in synesthesia?
“Rare variants in axonogenesis genes connect three families with sound-color synesthesia”
- New research in PNAS only 9 days ago has found genes that are likely to be responsible
“The name Catherine tastes like Chocolate cake.”
What does spatial arrangement of activated receptors provide?
Information about the stimulus
What is the receptive field in the somatic system?
The region of skin innervated by the terminals of the receptor neurons
What is the receptive field of a photoreceptor?
The region of the visual field projected onto that receptor
What does the spatial arrangement of receptors allow in the auditory system?
Frequency discrimination
- large stimuli will activate more neurons
e. g. a large object in the hand will activate receptive fields in many areas of the hand, whereas a small object will only activate a few receptive fields
What is stimulus intensity?
Intensity is the total amount of stimulus energy delivered to the receptor
What is the sensory threshold?
The lowest stimulus strength that can be detected
How is intensity determined?
The response amplitude of the receptor and thus the firing frequency of the afferent neurons
What does an increased neural response lead to?
Perception of a larger stimulus
How is onset timing is determined by?
When the stimulus energy is received by the receptor and causes it to fire
How is stimulus duration determined by?
Adaptation rates of receptors
What is adaptation?
In response to continuous stimuli; the firing rate of action potentials decrease
What do slowly adapting receptors (tonic receptors) respond to?
Respond to prolonged stimulation
Can tell duration of stimuli
What do Rapidly adapting receptors (phasic receptors) respond to?
The beginning and end of a stimulus
What is divergence?
Allows primary afferent neurons to signal to more than one relay neuron
What is convergence?
Ensures that relay neurons have larger receptive fields than primary afferent neurons
What are inhibitory neurons?
Ensures the signal in the most active neuron is propagated e.g. this enables contrast enhancement in the eye
