Sensory PhysiologyBio 219

Napa Valley CollegeDr. Adam Ross

Sensory Receptor

• Specialized receptor that detects a specific stimulus

• Transduces stimuli into a change in membrane potential• Signal then sent to brain or spine for response

• Signal causes changes in ionic conductance via opening of ion channels• Can be direct or indirect

Classes of Sensory Receptors

• Chemoreceptors• Specific chemicals, function in taste in olfaction, detecting pH and 02

• Mechanoreceptors• Touch, pressure, vibration, texture, stretch, movement

• Photoreceptors• Light

• Thermoreceptors• Hot and cold

• Nociceptors• Pain, noxious stimuli (chemical, mechanical, thermal)

Sensory Transduction

• Sensory receptors receive graded potentials in response to stimuli

• Sensory neurons convert graded potentials into Aps

• Stimulus → Sensory Receptor → Sensory Neuron → CNS

Receptive Field

• The area supplied or covered by a single sensory neuron• May or may not have sensors everywhere

• Neurons with smaller receptive fields give better sensitivity to stimulus• 2 point discrimination test

Transmission of Sensory Signals

• Afferent division of peripheral nervous system sends AP from sensory neuron to CNS• Somatic sensory

• Touch, temp, pain, proprioception

• Visceral sensory• Mechanical and chemical stimuli from internal organs

• Special senses• Vision, hearing, equilibrium, olfaction, taste

Sensory Pathways in CNS

• Ascending tracts in spinal cord• 1st order: from sensory receptor to spinal cord or brainstem

• 2nd order: from spinal cord or brainstem to thalamus

• 3rd order: from thalamus to cerebral cortex

• Also have cranial nerve sensory pathways

Sensory Areas of the Cerebral Cortex

• Somatosensory Cortex• Parietal lobs (postcentral gyrus)

• Visual Cortex• Occipital lobe

• Auditory Cortex• Temporal lobe

CNS Integration of Sensory Information

• Properties of stimulus:• Modality

• Location

• Intensity

• Duration

Modality• Indicated by:

• Specificity of the neurons and receptors being activated

• Specific neural pathway being activated in the CNS (specific areas of the brain)• Labeled line coding

Localization• Where is the stimulus being presented?

• Specific neural pathways connect receptive fields to specific parts of the brain• Sound localization uses differences in timing between left and right ears

• Lateral inhibition (see image)• Increases contrast between adjacent receptive fields

Intensity of Stimulus

• Number of receptors activated (spatial)

• Frequency of action potentials (temporal)

Duration of Stimulus

• Coded by duration of APs

Receptor Adaptation

• Decrease in response to a persistent stimulus over time• Tonic receptors: non, or slowly adapting (muscle spindle stretch receptors)

• Phasic receptors: rapidly adapting (olfactory receptors)

TRP Channels

• Transient Receptor Potential Channels• Rapidly adapting receptors

• Quickly inactivate after activation

• Involved in numerous cellular processes

TRP Channels

• Several classes of TRP Channels• TRPC

• Classical or canonical TRP channels• Membrane stretch

• TRPM• Melastatin

• Sensitive to Menthol and Eucalyptol

• TRPA• Ankyrin repeat

• Sensitive to mechanical stress and extreme cold

• TRPV• Vanilloid

• Sensitive to capsaicin and thermal pain

Thermosensation