Sensory Receptors Flashcards
What are the five basic types of sensory receptor?
Mechanoreceptors Thermoreceptors Nociceptors (pain receptors) Electromagnetic receptors (rods and cones) Chemoreceptor
What do mechanoreceptors do?
detect mechanical compression / stretching of the receptor or tissue
What do thermoreceptors do?
detect changes in temperature (cold and warmth receptors)
What do nociceptors (pain receptors) do? (I’ll give you three guesses)
detect physical or chemical damage of tissues
What do electromagnetic receptors (rods and cones) do?
detect light on retina of eye
What do chemoreceptors do?
Transduces a chemical substance (endogenous or induced) to generate a biological signal
e.g., taste, smell, arterial oxygen level, osmolality, blood carbon dioxide
What category of receptor provide the tactile senses of the skin (epidermis and dermis)?
cutaneous mechanoreceptors
What types of cutaneous mechanoreceptors are there in the skin?
Free nerve endings
Expanded tip endings
- Merkel’s discs
Spray endings
Ruffini’s endings
Encapsulated endings
- Meissner’s corpuscles
Hair end-organsWhat types of cutaneous mechanoreceptors are there in the deep tissue that provide deep tissue senses?
Free nerve endings
Expanded tip endings
Spray endings
- Ruffini’s endings
Encapsulated endings
- Pacinian corpuscles
Muscle endings
- Muscle spindles
- Golgi tendon organsWhat two corpuscles act as touch receptors?
Pacini’s corpuscle
Meissner’s corpuscle
Describe Pacini’s corpuscle
- Pacini’s corpuscle
- largest mechanoreceptor - 2mm long
- Onion like encapsulation of nerve endings
- Found in deep layers of dermis
- Detects high frequency (40-500Hz) vibration
- Aβ fibres - glabrous & hairy skin
- Rapidly adapting due to a slick viscous fluid between the layers
- Has a low activation threshold i.e. is sensitive
Describe Meissner’s corpuscle
- Encapsulated nerve endings similar to Pacini’s but much smaller
- Stacks of discs interspersed with nerve branch endings
- Found between dermal papillae
- detects touch, flutter & low frequency vibration (2-40Hz)
- Aβ fibres - glabrous skin types
- Rapidly adapting - low activation threshold (sensitive)
What receptors act as pressure/touch receptors?
Merkel disks
Hair follicles
Describe Merkel discs
- Non-encapsulated nerve endings
- Consist of a specialised epithelial cell + nerve fibre
- Found just under the skin surface in for example the finger tips – good discrimination - detects static touch and light pressure
- Aβ fibres - all skin types
- Slowly adapting - low activation threshold (sensitive)
- Work with Meissner’s corpuscles to help determine texture
Describe hair follicles
- Embedded in skin – innervated by nerve ending wrapped around its follicle
- detect muscular movements of the hair (erector muscle) and external displacements of hair
Name a stretch receptor?
The Ruffini corpuscle
Describe the Ruffini corpuscle
- Encapsulated nerve ending
- Nerve ending weave between collagen fibres which activate the nerve when they are pulled longitudinally
- responds to skin stretch and is located in the deeper layers of the skin as well as tendons and ligaments
- Aβ fibres - all skin types but especially abundant in hands and fingers as well as soles of feet
- Slowly adapting - low threshold activation (sensitive)
What are muscle spindles?
Main proprioceptors that provide information about the state of musculature
Where do muscle spindles lie?
Muscle spindles lie within muscles in parallel with skeletal muscle fibres
Particularly numerous in fine motor control muscles (e.g. eyes, hands)
What are muscle spindles innervated by?
by y(gamma)-motoneurons (efferents) and group Ia and II afferent fibres
What is the difference between afferent and efferent neurons?
Afferent neurons are sensory neurons that carry nerve impulses from sensory stimuli towards the central nervous system and brain, while efferent neurons are motor neurons that carry neural impulses away from the central nervous system and towards muscles to cause movement
Afferent - sensory
Efferent - motor
What do the afferents and efferents do in muscle spindles
Afferents respond to muscle stretch while y(gamma)-efferent activity regulates the sensitivity of the spindle
What are Golgi tendon organs?
Main proprioceptors that provide information about the state of musculature
Respond to degree of tension within the muscle
Group Ib afferent fibres relay information to CNS (particularly spinal cord and cerebellum)
Where are Golgi tendon organs found?
Golgi tendon organs lie within tendons in series with contractile fibres
What is the difference between a generator potential and a receptor potential?
Generator potential refers to potential caused by a stimulus to a NERVE ENDING
Receptor potential refers to potential caused by stimulus to a RECEPTOR CELL
What does a generator potential do?
Generates action potentials in a sensory neuron
What does a receptor potential do?
Affects amount of neurotransmitter released by receptor cell onto sensory neuron
Discuss receptor potential generation in a pacini corpuscle?
Tip unmyelinated – nerve fibre myelinated before leaving corpuscle
Compression anywhere on outside of corpuscle elongates, indents/deforms central fibre
Receptor potential induces local current flow (Na+ current) which spreads along nerve fibre
At 1st node of Ranvier local current flow depolarizes fiber membrane at this node, which sets off action potentials to CNS
Discuss the relationships between receptor potential and action potential generation
When receptor potential (from receptor) rises above threshold in nerve fiber - action potentials fire
Amplitude of receptor potential increases rapidly at first then less rapidly at high stimulus strength
The more receptor potential rises above threshold level, the greater the action potential frequency
APs generated in a sensory nerve at a frequency directly related to stimulus size
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Receptor potential go up
Action potential happen more often
Should be calculable
What happens to the generator potentials of sensory receptors that adapt more rapidly?
Their generator potential adapts more quickly too: Impulses per second will rapidly decrease after initial stimulus
What cutaneous mechanoreceptor would respond to a light brush?
Hair follicles
What cutaneous mechanoreceptor would respond to dynamic deformation?
Meissner corpsucle
What cutaneous mechanoreceptor would respond to vibration?
Pacinian corpsucle
What cutaneous mechanoreceptor would respond to indentation depth?
Merkel cell - neurite complex
What cutaneous mechanoreceptor would respond to stretch?
Ruffini corpsucle
What cutaneous mechanoreceptor would respond to touch?
C - fibre LTM (Low threshold mechanoreceptors)
What cutaneous mechanoreceptor would respond to injurious forces?
Mechano-nociceptor
Polymodal nociceptor
What are slowly adapting receptors that detect continuous stimulus strength called?
Tonic receptors
What are rapidly adapting receptors that detect continuous stimulus strength called?
Rate receptors/movement receptors/phasic receptors
What is the precision of localisation of a particular stimulus is determined by?
Size of individual nerve fibre receptive field
Density of sensory units
Amount of overlap in nearby receptive fields
What is receptive field distribution?
Different sensory modalities used by brain to describe World around us
Why is receptive field distribution important?
Quality of information relates directly to ability to comprehend them
Higher the resolution, higher the number of modalities for a given situation, the better the understanding
____
Sometimes we gotta know all about shit
Give an example of two cutaneous mechanoreceptors with different receptive field distribution?
Pacini’s corpuscles and Meissner’s corpuscles are both sensitive, but have different receptive field sizes
- Pacini corpuscles have broad receptive field - Meissner’s corpuscles and Merkel’s disks are very small
What is the benefit of a small receptive field distribution?
Small receptive fields allow high spatial resolution
What does two point discrimination describe?
minimum distance at which two points can be perceived as distinct
What is two point discrimination a result of?
receptive field size and receptor density in area
what does two point discrimination not represent?
sensitivity to stimulus
What is lateral inhibition?
Information from afferent neurons whose receptors are at edge of a stimulus are strongly inhibited compared to information from the stimulus’ centre
What does lateral inhibition aid?
Aids in enabling localisation of stimulus
What is the dorsal column–medial lemniscus pathway?
A sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints.
Where is the dorsal column?
Dorsal column (Fasciculus gracilis) exists at all levels of the spinal cord
What are the three groupings of neurons present in the dorsal column–medial lemniscus pathway?
first-order neurons (neuron I)
second-order neurons (neuron II)
third-order neurons (neuron III)
What are the first order neurons (neuron I)the dorsal column/medial lemniscus?
Sensory neurons located in the dorsal root ganglia represented from lower (T6-S5) and upper limbs (C1-T5)
What are the second order neurons (neuron II)the dorsal column/medial lemniscus?
Second-order neurons (neuron II) in the nucleus gracilis and cuneatus cross in the midline to form the medial lemniscus (and so make contact with neuron I), ascends through medulla, pons & midbrain to thalamus
What are the third order neurons (neuron III) in the dorsal column/medial lemniscus?
Axons of third-order neurons (neuron III) in thalamus travel in the internal capsule and terminate in the somatosensory cerebral cortex
Where do second order neurons (neuron II) terminate in the dorsal column/medial lemniscus?
Terminates in the contralateral ventral posterolateral nucleus of the thalamus
What do first order neurons form in the direct spinothalamic tract?
dorsal root ganglion cells (neuron I) synapse with neurons of nucleus proprius
How do the second order neurons ascend the spine in the direct spinothalamic tract?
Second-order neurons (neuron II) cross via the anterior white commissure & enter contralateral white matter
Ascend in spinothalamic tract
Where are the third order neurons (neuron III) in the direct spinothalamic tract?
Third-order neurons (neuron III) located in the ventral posterolateral nucleus of the thalamus
Axons of third-order neurons project to primary sensory cortex
How does the somatosensory cortex receive sensory information?
Sensory information passes through the thalamus to the primary sensory cortex
Where is the somatosensory cortex located?
In a strip posterior to the post central sulcus of the brain
How is sensory information projected in the somatosensory cortex?
in a topographical manner to this area
How is the somatosensory cortex organised?
Areas of higher discrimination/senses having a larger proportion of the space
