Sensory Receptors Flashcards by Cormac Mathieson

What are the five basic types of sensory receptor?

Mechanoreceptors
Thermoreceptors 
Nociceptors (pain receptors) 
Electromagnetic receptors (rods and cones) 
Chemoreceptor

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What do mechanoreceptors do?

detect mechanical compression / stretching of the receptor or tissue

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What do thermoreceptors do?

detect changes in temperature (cold and warmth receptors)

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What do nociceptors (pain receptors) do? (I’ll give you three guesses)

detect physical or chemical damage of tissues

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What do electromagnetic receptors (rods and cones) do?

detect light on retina of eye

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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

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What category of receptor provide the tactile senses of the skin (epidermis and dermis)?

cutaneous mechanoreceptors

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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-organs

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What 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 organs

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What two corpuscles act as touch receptors?

Pacini’s corpuscle

Meissner’s corpuscle

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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

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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)

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What receptors act as pressure/touch receptors?

Merkel disks

Hair follicles

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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

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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

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Name a stretch receptor?

The Ruffini corpuscle

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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)

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What are muscle spindles?

Main proprioceptors that provide information about the state of musculature

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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)

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What are muscle spindles innervated by?

by y(gamma)-motoneurons (efferents) and group Ia and II afferent fibres

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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

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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

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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)

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Where are Golgi tendon organs found?

Golgi tendon organs lie within tendons in series with contractile fibres

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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 _F_o_r_A_p_e_B_r_a_i_n 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

Sensory Receptors Flashcards

(63 cards)