Lecture 13 Sensory Physiology Flashcards
List the modalities of the sensory system (5 main and others)
Vision, hearing, taste, smell, touch
Vestibular (balance), Proprioception, Somatosensory modalities (pain, temperature, itch)
The purpose of the sensory systems
Detect and convey information about external (light, sound, smell, touch) and internal (pH, body position, O2, CO2) environments
Being aware of events and environments
Bees
Describe some sensory system in bees
Describe how bees find the right flower to pollinate or get nectar
vision, odour, hearing, mechanoreceptor and electrical sense -> navigation, find food and home, social structure
- Bumblebee hair moves when detects small electric fields -> neurons fire AP depend on movement degree (greater movement, great AP) -> info used by bee to find the right flower.
Sensory system pathway
What is needed for a signal result in an action?
“She Can Try Processing Actively”
- Signal- physical stimulus that give info of surroundings
- Collection of signal
- Transduction - stimulus into nerve signal
- Processing - by brain
- Action generation as a results
2 important points to remember when neural coding of information is sent to brain centres
- Cranial nerves: how info from sensory neurons in head enters the CNS.
Spinal nerves: how info from sensory neurons below head enters spinal cord and passes through brain - All senses go through relay system (thalamus) in brain except smell which goes straight to the olfactory bulb and cortex
- Brain centres
- Sensory disorders
- Vestibular cortex (balance), somatosensory cortex (pain, temperature), gustatory cortex (taste), visual cortex, olfactory cortex, auditory cortex
- Anosmia (loss of smell), ageusia (loss of taste)
4 basic sensory system attributes of a stimulus
“MILT”
- Modality - type/class of stimulus
- Intensity - severity/amount measure of stimulus
- Location - Position of stimulus in space
- Timing - stimulus onset, duration and offset (how long the stimulus lasted)
Modality
What is important in terms of receptors?
What are the 4 class of receptors in humans? “MCTP”
Receptor specificity. They are specialised receptors where each responds to a narrow stimuli range.
Mechanoreceptors, Chemoreceptors, Thermoreceptors, Photoreceptors
What are two things that needed in modality?
Transduction and receptor potential
Transduction: transformation of signal into electrical energy( impulse) by sensory receptors
Which leads to an electrical response or change in membrane potential known as receptor potential
Modality
Two transduction mechanisms with examples
How do they vary
Direct transduction (skeletal muscle mechanoreceptors)
Indirect by 2nd messenger systems [GPCR] (olfactory epithelium chemoreceptors)
Vary based on physical stimulus
Modality
Describe mechanical transduction using the mechanoreceptors in the skeletal muscles as an example
Characteristics
- Sense physical deformation of their residing tissue
- Mechanical stimulation -> cytoskeletal strands (tether the stretch sensitive ion channels) stretch, pulling on the ion channels, opening them
- Influx of Na+ and Ca2+ ions, leading to depolarisation of receptor neuron.
Fibres stretch, channels open, receptor potential change. More pressure applied, channel opens more often
Greater stretch, higher receptor potential amplitude
Modality
Describe transduction via 2nd messengers using chemoreceptors in the olfactory epithelium as an example.
- Chemoreceptors detects odorant which binds to the ordorant receptor (GPCR), inducing conformational change.
- G proteins (α, β, γ) dissociate & α subunit binds to adenylate cyclase
- ATP is converted to cAMP which binds to the Na+/Ca2+ channel, allowing those ions to flow in, depolarising the neuron.
location
Why is the spatial arrangement of receptors important?
What is the receptive field?
- Provide info of stimulus location source on body
Enable object size and shape discrimination.
Enable fine detail resolution of stimulus or environment. - The area in which a stimulus activates a neuron by inducing action potentials
Characteristics of the spatial arrangement of receptors in receptive field (example : touch receptors)
- A patch of skin - contain overlapping receptive fields - increase change of ‘recognising’ stimulus
Small receptive fields (finger tips - immediate reaction) - allow high resolution of fine detail
Large the receptive field, harde to localise a stimulus. (Palms)
Receptor density
Defines the resolution of a stimulus
Is not uniform
Could be localise to give higher definition
Eye example: more receptors - finer detail & more resolution
