Peter's Physiology 3 - Somatosensory System (1) Flashcards by Sophia White

What type of sensations is the somatosensory system not concerned with?

Visual
Auditory
Gustatory
Olfactory
Vestibular sense of equilibrium

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What sensory modalities does the somatosensory system deal with?

Mechanosensation (touch, pressure and vibration)
Proprioception (joint and muscle position sense)
Thermosensation (temperature)
Nociception (pain)
Pruriception (itch)

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How are primary sensory afferent fibres able to generate different sensations when they all transit impulses along their axons using the same physiological principles?

They connect to unique neurones in the CNS which are capable of decoding similar nerve signals in different ways (i.e. primary sensory afferent fibres confer modality by their site of termination in the CNS - labeled line principle)

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4 classes of somatic sensation?

Exteroceptive sensations
Proprioceptive sensations
Visceral sensations
Deep sensations

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What are exteroceptive sensations?

Cutaneous senses from the surface of the skin

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What are proprioceptive sensations?

sensations concerning posture and movement (sensors in muscle and tendons and joints)

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What are visceral sensations?

Sensations specifically from the internal organs

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What are deep sensations?

Sensations from fasciae, muscles and bone

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How does a stimulus elicit a depolarisation receptor (or generator) potential?

Stimulus opens cation selective on channels in nerve terminal

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What is the amplitude of the generator potential proportional to?

Stimulus intesnity

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What does local current flow in a sensory neurone terminal due to a stimulus trigger?

“All or none” action potentials at a frequency proportional to the amplitude of the receptor potential

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What is muscle spindle?

A sensory structure in skeletal muscle activated by stretch

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What is the name for sensory receptors which are activated by variable stimuli?

Polymodal

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What is the name for the principle type of adequate stimulus that is traduced into an electrical signal by a primary afferent neurone?

Modality

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What is the physiological receptors for touch, pressure and vibration primary afferent neurones?

Skin mechanoreceptors

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What are the physiological receptors for proprioception?

Joint and muscle mechanoreceptors

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What is the stimulus for proprioceptive primary afferent neurones?

Mechanical forces acting on joints and muscles

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What are the physiological receptors for pain?

High threshold mechanoreceptors (aka mechanical nociceptors)
Thermal nociceptors
Chemical nociceptors
Polymodal nociceptors

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What are the stimuli for pain primary afferent neurones?

Strong mechanical force on skin, viscera

Heat on skin, mucous membranes and viscera

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What is the stimuli for itch sensation?

Irritant (e.g. chemical) on skin, or mucous membranes

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What is the physiological receptor for itch sensation?

Itch receptors

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What kind of stimuli do low threshold units respond to?

Low intensity i.e. non-damaging and non-painful

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What sensations do low threshold mechanoreceptors mediate?

Touch, vibration, pressure

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What sensations do low threshold thermoreceptors mediate?

Cold, cool, indifferent, warm and hot

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What is another name for high threshold units?

Nociceptors

Describe the intensity of stimuli that high threshold units respond to?

High (Noxious, potentially damaging) but not (normally) low, intensity stimuli

Is information from high threshold units allows perceived as painful?

No, they are subject to both spinal segmental and supra spinal influences that "gate" input to second order neurones

What is another name for high threshold mechanoreceptors? | What do these respond to?

Mechanical nociceptors | High intensity mechanical stimuli

What do thermal nociceptors respond to?

Extreme degrees of heat (>45 degrees C) to cold (< 10-15 degrees C)

What do chemical nociceptors respond to?

Substances in tissue (as found in inflammation) e.g. prostaglandins, bradykinin, serotonin, histamine, K+, H+ and ATP

What is the name for the feature of primary sensory neurones that determines whether they change their firing rate only in response to a stimulus of changing intensity?

Adaption

What type of adaptive neurone response provides continuous information to CNS while terminal deformed?

Slowly adapting (SA) tonic/ static response

What type of information do slowly adapting tonic/ static response neurones give? Examples?

Information about position, degree of stretch, or force | E.g. Stretch receptors

What type of adaptive neurone response detects changes in stimulus strength with the number of impulses proportional to the rate of change of stimulus?

Rapidly adapting (RA) phasic/ dynamic response

Examples of location of rapidly adapting (RA) phasic/ dynamic response neurones?

Some muscle spindle afferents | Hair follicle afferents

What type of adaptive neurone response responds only to very fast movement, such as rapid vibration?

Very rapidly adapting (very RA) very phasic/ dynamic response

Example of structure that displays a very rapidly acting (very RA) very phasic/ dynamic response?

Pacinian corpuscle

What is the nomenclature used to describe primary sensory afferents leaving the skin with a diameter of 13-20 micro metres?

A alpha

What is the nomenclature used to describe primary sensory afferents leaving the skin with a diameter of 6-12 micro metres?

A beta

What is the nomenclature used to describe primary sensory afferents leaving the skin with a diameter of 1-5 micro metres?

A delta

What is the nomenclature used to describe primary sensory afferents leaving the skin with a diameter of 0.2-1.5 micro metres? Does this type of fibre have myelination?

C | No

As you go from group A alpha to group C primary sensory afferents, how does the conduction velocity differ/

Decreases

What sensory receptor do type A alpha primary sensory afferents function as?

Proprioceptors of skeletal muscle

What sensory receptor do type A beta primary sensory afferents function as?

Mechanoreceptors of skin

What sensory receptor do type A delta primary sensory afferents function as?

Pain, temperature

What sensory receptor do type C primary sensory afferents function as?

Temperature, pain, itch

What is the receptive field of an afferent neurone?

The region that when stimulated with an adequate stimulus causes a response in that neurone

Does receptive field vary a lot over the body surface?

Yes (evidenced by wide differences in 2 point discrimination)

Do regions with the highest discriminative capacity have the smallest or largest receptive fields?

Smallest

Where in the skin are Meissner's corpuscles found abundantly?

In areas where 2 point discrimination is highest

What are Merkel's discs often grouped in?

Iggo domes

What is the difference between the distribution of Meissner's corpuscles and Merkel's discs?

Meissner's corpuscles aren't present in hair skin where as Merkel's discs are present in moderate numbers in hairy skin

Where are krause end bulbs found?

At the border of dry skin and mucous membrnaes

Where are Ruffini endings found?

Within dermis and also joint capsules

Where are Pacinian corpuscles located?

Within dermis and fascia

Fibre group, adaptability and type of sensation for Meissner's Corpuscle?

A beta Rapidly acting Stroking, flutter

Fibre group, adaptability and type of sensation for merkel disk receptor?

A beta Slowly adapting Pressure, texture

Fibre group, adaptability and type of sensation for pacinian corpuscle?

A beta Very rapidly adapting Vibration

Fibre group, adaptability and type of sensation for Ruffini ending?

A beta Slowly adapting Skin strethc

Fibre group and type of sensation for hair (G) - guard (long)?

A beta | Stroking, flutter

Fibre group and type of sensation for hair (D) - down (short)?

A delta | Light stroking

Fibre group and type of sensation for C mechanoreceptor?

C | Stroking, social and erotic touch

What is the name for the 10 laminae the spinal cord is divided into?

Laminae of Rexed

Which laminae do the nociceptors terminate in? | Fibre class?

Laminae I and II | A delta/ C

Which laminae do the LTMs terminate in? | Fibre class?

Laminae III to VI | A beta

Which laminae do the proprioceptors terminate in? | Fibre class?

Laminae VII to IX | A alpha

Peter's Physiology 3 - Somatosensory System (1) Flashcards

(66 cards)