Touch, Temperature and Pain Flashcards
How do structural constraints shape our evolution/human development?
Affect the nature of info we might take in and perceive/learn from
What is sensation?
Arriving info from senses
What is perception?
Conscious awareness of a sensation - info taken to brain, where processing takes place
What does stimulation occur through?
Tactile, auditory, visual and chemical sensation - specialised receptors for each sensation which transduce info
What are the mechanical senses?
- vestibular sensation
- Somatosensation
What is the vestibular system made up of?
Receptors in inner ear that respond to body position and movement/tilt of head
How is information in the vestibular system used?
It is used alongside other senses to perceive what is happening + aids balance (why inner ear infections cause dizziness and a loss of balance)
What 2 organs does the vestibular organ consist of?
Semicircular canals
Otolith organ
What are the semicircular canals?
3 canals filled with endolymph (fluid) with hair cells in it.
What does movement cause in the semicircular canals?
Endolymph moves against hair, bending it
Oriented on 3 planes - comparative stimulation gives brain info about movement of head
What does the otolith organ do?
Sends messages about our position in 3D space
What are otolith organs sensitive to?
acceleration, deceleration and direction changes
Where are the otolith organs?
Utricle (horizontal plane) and saccule (vertical plane) - different orientations
(similar to endolymph but are glutinous)
What happens in the otolith organ when the head is upright?
Equilibrium (everything in normal position)
What happens in the otolith when the head is bent forward?
Gravitational forces pull the membrane in the same direction (otolithic membrane sags) and stereocilia of hair cell bands stimulating organs (opposite when the head is bent back)
What make up the vestibulocochlear nerve?
Vestibular afferent fibres
Where are the vestibular nuclei located?
In medulla and pons (hindbrain)
What do the vestibular nuclei do?
Integrate vestibular info and somatic receptor info from cerebellum, nuceli of cranial nerves and the ventral posterior thalamus to vestibular area of primary sensory cortex (S1).
In the vestibular pathway, what is the cerebellum responsible for?
Balance/posture - sends corrective adjustments to motor cortex
In the vestibular pathway, what are the nuclei of cranial nerves responsible for?
Coordinating eye movement and to help equilibrium
In the vestibular pathway, what is the ventral posterior thalamus to vestibular area of S1 responsible for?
Conscious awareness of head position
What are the modalities of somatosensation?
Hapsis (fine touch/pressure)
Kinesthesis, vestibular (movement, position and spatial orientation/balance)
Proprioception (awareness of our body in space)
Temperature
Pain
What are the different varieties of receptors? (according to location of stimulus)
Interoceptors & Proprioceptors - stimuli inside body
Exteroceptors - stimuli outside of body eg. touch
How many different types of receptors are there and where?
20 (sensory neurons) in all parts of the body other than the brain (vary in density and sensitivity to stimuli)
What are the 2 types of skin?
Hairy and glabrous
What is glabrous skin?
Hairless (eg. palms) - sensitive (used to explore objects)
What are the functions of glabrous skin?
- protective
- prevents evaporation of bodily fluids
- provides direct contact with the world
How would you test the sensitivity of skin?
2 point sensitivity test - how close can the 2 points get with the ability to perceive both as separate sensations?
- weaker in hairy skin (2-5cm)
What is the epidermis?
Top layer of skin - contains cells that produce pigment and protect the immune system
What is the dermis?
Contains much of our nerve endings, oil and sweat glands, and hair follicles
what is subcutaneous tissue?
Fat, connective tissue and blood vessels
What are cutaneous receptors?
Found in dermis and epidermis
can be:
encapsulated (surrounded by a capsule)
Unencapsulated (includes free nerve endings)
What are free nerve endings?
Unencapsulated ends of dendrites
Most common in skin
not specialised (polymodal) - sensitive to painful stimuli, hot and cold and light touch
SLOW to adjust to a stimulus
What is an example of a specialised variety of a free nerve ending?
Hair follicle receptor
What are the 4 primary tactile mechanoreceptors in the skin?
- Pacinian corpuscles
- Ruffini’s corpuscles
- Merkel’s disks
- Meissner’s corpuscles
What are pacinian corpuscles and where are they found?
Specific capsule involved in pressure detection - important for detecting deep touch and vibration
Rapidly adapting
Involves both superficial and deep layers and hair
What are pacinian corpuscles also known as?
Lamellar corpuscles (lamellar = thin layer structure)
What are Ruffini’s corpuscles also known as?
Ruffini’s ending
What are Ruffini’s corpuscles and where are they found?
Sensitive to stretching and sustained deep touch
- found in dermis and subcutaneous tissue in both hairy and glabrous skin
Slow adapting
what are Merkel’s Disks and where are they found?
Merkel cells + nerve endings
Unencapsulated
Found in epidermis and deeper in glabrous and hairy skin
Slow adapting (tonic) receptors - sustained light touch
What are Meissner’s corpuscles also known as?
Tactile corpuscles
What are meissner’s corpuscles and where are they found?
Encapsulated, found high within dermis particularly in glabrous skin and finger pads
Rapidly adapting and sensitive to light touch
- sensitive to shape and textural changes in exploratory and discriminatory touch
What is discriminative touch?
Stimuli from skin and body tissue
What is discriminative touch facilitated by?
Specialised touch receptors with different structures
Only surface of sensory dendrite or includes other tissue
What are hair receptors and how do they work?
Dendrite attached to hair on skin
Object moves across skin, hairs move, sending a nerve impulse - detect direction as there are specialised receptors for each direction eg. leftwards
What are touch receptors? (hapsis)
receptors on skin that detect vibration and pressure (hapsis)
What is affective touch?
Low threshold receptors in hairy skin (afferent C fibre family)
- slower touch system
- includes pleasant touch, pain, temperature and itch
Important in many forms of social communication
What do nociceptors detect?
pain and temperature
What do thermoreceptors detect and how are they separated?
Temperature
Separate for hot and cold
What temperature do the end-bulbs of Krause detect?
Cold - found in specialised regions
What temperature do Ruffini’s corpuscles detect?
Warmth
What is proprioception?
awareness of the relative position of parts of the body and movement of the body - i.e. the sense of awareness of where limbs are
What are proprioceptors?
Encapsulated nerve endings which are sensitive to stretch of muscles/tendons and joint movement
Which fibres are fastest?
Proprioceptors
What would someone living without proprioception experience?
A lack of awareness of where their limbs are in relation to their body
Would struggle to move without concentrating on the action
What is kinesthesis?
Sensation of muscles, tendons and joints moving - allows coordinated movement
How is kinesthesis different to proprioception?
Kinesthesia focuses on bodily movements and motion (behavioural) whilst proprioception focuses on awareness of these movements and behaviours (cognitive)
In kinesthesis, what detect the movement of muscles, tendons and joints?
Specialised receptors
How is pain defined?
“an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” (IASP)
What are the 2 types of pain?
Chronic (long term)
Acute (short term)
What is one positive aspect of pain?
Has adaptive value - usually trying to tell you something
What do those without nociceptors experience?
Deformity through failure to adjust posture + acute injuries due to failure to avoid harmful situations
When would peptides and other chemicals be released by cells?
When cells are damaged/irritated
What is the process of cells releasing peptides and other chemicals?
irritation in surrounding tissue –> stimulate chemical release
Excites free nerve endings that function as nociceptors (triggers action potentials along dorsal root ganglion) –> stimulates blood flow and pain fibres (why we experience pain, redness and swelling)
Pain fibres release neurotransmitters and neuromodulators in spinal cord (dorsal horn) - info travels up to thalamus
Which other sense contributes to pain sensation?
Hapsis –> location and type
What is gate theory (Malzack & Wall, 1965)
can inhibit pain through pain gates
Where are the pain gates according to gate theory (Malzack & Wall, 1965)?
Spinal cord
Brain stem
Cortex
According to gate theory (Malzack & Wall, 1965) how would you inhibit pain in the spinal cord?
Epidural
According to gate theory (Malzack & Wall, 1965) how would you inhibit pain in the brainstem?
Electrical stimulation
According to gate theory (Malzack & Wall, 1965) how would you inhibit pain in the cortex?
distraction
What type of function does thermoregulation have? (Arancibia et al., 1996; Mogenson, 1977)
Homeostatic function
How does thermoregulation operate?
Through automatic response of hypothalamus (with preoptic regions - contains temperature-sensitive neurons) and behavioural responses such as stamping feet to stay warm
How does the hypothalamus aid thermoregulation?
Contains temperature sensitive neurons - integrates info with input from skin receptors - releases pituitary hormones to regulate energy, metabolism and heat production
How does the body respond to an increase in heat?
Rate of metabolic activity decreases
Blood vessels dilate to transfer heat to body surface
Sweat production and evaporation increase - triggers thirst and panting
How does the body respond to cold?
Increases secretion of thyroid hormones
Increases discharge of sympathetic nervous system - shivering, piloerection (erection or bristling of hairs due to the involuntary contraction of small muscles at the base of hair follicles), blood vessels constrict to reduce heat loss
How do senses change as we age?
Vaguely - they decrease in quality (full tactile ability when young, tactile defect when old)
Altered detection, reduced sensory conduction, abnormal efferent response
What are the 2 receptor specialisations?
Rapidly adapting receptors - beginning and end of touch (produce bursts of action potential) and slowly adapting receptors - as stimulus is occurring
What are rapidly adapting receptors involved in + examples?
Detecting discriminate touch (Meissner’s corpuscles) and fluttering (Pacinian corpuscles)
What are slowly adapting receptors involved in + examples?
Light pressure (eg. Merkel’s receptors and hair receptors)
Firmer pressure (eg. Ruffini’s corpuscles - vibration due to stretching)
What is the pathway to the brain?
Receptors carry somatosensory info to cell body of neuron just outside spinal cord - neuron contains a single long dendrite with only the tip responsible to sensory stimuli - each segment of spinal cord has one dorsal root per side with many dorsal-root ganglion neurons each responsible for one stimuli type
What is the pathway to the brain (from spinal cord) in haptic-proprioception?
Axons for haptic-proprioception located in dorsal portion of spinal cord. Synapse at base of brain in dorsal-column nuclei - cross to other side of brain stem through medial lemniscus in medulla - synapse in ventrolateral thalamus sends axons to somatosensory and motor cortex
What is the pathway to the brain (from spinal cord) in nociception?
Nociceptor synapse in dorsal (top) part of grey matter in spinal cord. Axon sent to ventral (bottom) part of spinal cord + some to somatosensory cortex and insular and anterior part of cingulate cortex
What do lesions in the somatosensory cortex cause?
Impaired somatic sensatons
Where is the primary somatosensory cortex?
In postcentral gyrus
What does the posterior parietal cortex do?
Informs attended spatial aspects of touch
What is a homunculus?
A somatosensory map of the body - the more emphasised senses are made larger on the body eg. larger hands, lips and tongue as they are more sensitive
What are type A fibres?
Large, well-myelinated axons - faster for rapid response. eg. Haptic and proprioception
What are type C tibres?
Smaller axons with littel or no myelination - sensation occurs for a long time so no need for rapid response eg. nociception
What is the general pathway for touch and pain?
Somatosensory receptors –> Spinal column –> thalamus –> somatosensory cortex
What is the difference between the pathway of fine touch and nociceptive info?
Fine touch info ascends spinal cord ipsilaterally via dorsal column medial lemniscal pathway whereas nociceptive info ascends contralaterally via spinothalamic pathways
