Sensory Receptors Flashcards
5 Types of sensory receptor:
Mechanoreceptors
Thermoreceptors
Nociceptors (pain receptors)
Electromagnetic receptors (rods and cones)
Chemoreceptors
Cutaneous mechanoreceptors - where are they found?
Skin tactile senses - epidermis and dermis
Deep tissue senses
Skin tactile senses:
Free nerve endings
Expanded tip endings - Merkel’s disks
Spray endings
Ruffini’s endings
Encapsulated endings - Meissner’s corpuscles
Hair end-organs
Deep tissue senses:
Free nerve endings
Expanded tip endings
Spray endings- Ruffini’s endings
Encapsulated endings - Pacinian corpuscles
Muscle endings - Muscle spindles + Golgi tendon organs
What are the touch receptors?
Pacini’s corpuscle
Meissner’s corpuscle
Pacini’s corpuscle:
Largest mechanoreceptors
Onion of encapsulated NE
Detects high frequency vibration
Rapidly adapting
Low activation threshold- sensitive
Meissner’s corpuscle:
Encapsulated NE - smaller than Pacini’s
Stacks of discs
Detects touch, flutter and low frequency vibration
Rapidly adapting
Low activation threshold - sensitive
What are the pressure/touch receptors?
Merkel disks
Hair follicles
Merkel disks:
Non-encapsulated NE
Detects static touch and light pressure
Slowly adapting
Low activation threshold - sensitive
Work with Meissner’s corpuscles to help determine texture
Hair follicles:
Embedded in skin
NE wrapped around follicle
Detects muscular movements of hair and external displacements of hair
What is the stretch receptor?
Ruffini corpuscle
Ruffini corpuscle:
Encapsulated NE - weave between collagen fibres
Responds to skin stretch
Slowly adapting
Low threshold activation - sensitive
Muscle spindles:
Provide info about state of musculature
Within muscles in parallel with skeletal muscle fibres
Innervated by efferents and group Ia and II afferent
Efferents - sensitivity
Afferent - stretch
Golgi tendon organs:
Provide info about state of musculature
Within tendons in series with contractile fibres
Respond to degree of tension
Group Ib afferent fibres relay info to CNS
Generator potential:
Potential caused by stimulus to NE
Generates AP in sensory neuron
Receptor potential:
Potential caused by stimulus to receptor cell
Affects amount of neurotransmitter released by receptor cell onto sensory neuron
Receptor potential generation in Pacini’s Corpuscle: Myelination
Tip of NE is myelinated
Receptor potential generation in Pacini’s Corpuscle: central fibre
Compression on outside deforms central fibre
Receptor potential generation in Pacini’s Corpuscle: receptor potential
Induces current that spreads down nerve fibre
Reaches 1st node of Ranvier
Receptor potential generation in Pacini’s Corpuscle: 1st Node of Ranvier
Current depolarises fibre membrane
APs spread to CNS
What must happen for APs to fire?
Receptor potential above theshold
What happens when receptor potential increases even more above theshold?
Greater AP frequency
What is AP frequency in sensory nerve directly related to?
Stimulus size
Slowly adapting sensory receptors:
Slow decline in action potentials firing - retain frequency
Rapidly adapting sensory receptors:
Rapid decline in APs firing
Frequency is high but stops
What is localisation of stimulus determined by?
Size of individual nerve
Density of sensory units
Amount of overlap in nearby receptive fields
Receptive fields of sensory mechanoreceptors:
Pacini’s corpuscles - broad field
Meissner’s corpuscle + Merkel disks - very small fields
What do small receptive fields allow?
High spatial resolution
Why is lateral inhibition important?
To enable localisation of stimulus
Neural pathways in somatosensory system:
Dorsal column
First-order neurons
Second-order neurons
Third-order neurons
peripheral receptors
Where does sensory information go to?
Passes through thalamus to primary sensory cortex
