8. Sensory Processing 2 Flashcards
Define conduction
Afferent pathway
Define transduction
CNS integration and information processing
Describe sensory projections
Ascend from the spinal cord into the brain through the brainstem
They travel through the thalamus, which acts as a relay processing station of signals to other brain regions
Describe olfactory pathways
From the nose project to the primary olfactory cortex
Describe vestibular pathways
Also project to cerebellum - important for motor control & equilibrium
Which are the most common receptors in the body?
Touch receptors
What are the two layers of the skin?
The epidermis (thin outer layer) and the dermis (thick inner layer)
How many receptors are there across the dermis and hypodermis?
4
What are the 3 components of the skin?
Glabrous skin
Hairy skin
Sweat glands
Describe the features of glabrous skin
Smooth, thick skin on palms and soles of our feet
Epidermis = 1.5mm
Dermis = 1-2mm
Describe the features of hairy skin
Thick skin populated with hair follicles
Epidermis = 0.1mm
Dermis = 1-2mm
Describe the features of sweat glands
Eccrine - secrete saline
Sebaceous - secrete complex cell cytoplasm
Describe the features of vibration (Pacinian Corpuscle) (RF’s, Response)
Large receptive fields
Fast adapting
Describe the features of touch (Meissner’s corpuscle) (RF’s, Response)
Small receptive fields
Fast adapting
Describe the features of touch (Merkel Cells) (RFs, Response)
Small receptive fields
Slow adapting
Describe the features of stretch (Reffini’s ending) (RFs, Response)
Large receptive fields
Slow adapting
RFS all us to have good ___ ___ of where the stimulus is applied on the skin
Spatial resolution
The smaller the RF the higher/lower the resolution?
Higher
The higher density of RF the higher/lower the resolution?
Higher
Which test is used to test spatial acuity?
‘Two-point discrimination test’
How does the signal transfer to the brain?
Innervation via spinal nerves
What are the dorsal horn and the ventral horn responsible for in terms of bell-magendie law?
Dorsal horn = Afferent sensory info
Ventral horn = Efferent motor signals
What is dermatome?
An area of skin that is mainly supplied by a spinal nerve
How many dermatomes are there?
30
Tactile signals are sent through the spinal cord via what and to where?
Via the dorsal column pathway to the primary somatosensory cortex in the brain
What is the tactile pathway?
Dorsal column - thalamus - primary somatosensory cortex (S1) - secondary somatosensory cortex (S2) - other brain areas
Define pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What are nociceptors?
Free nerve endings that respond to stimuli that can cause tissue damage or when tissue damage has taken place
Small diameter afferent neurons do what?
Respond to acute painful stimuli & superficial in the dermis (we have many covering the skin’s surface)
Nociceptors respond to what type of stimuli?
Noxious (painful)
Where are nociceptors found?
Skin, muscle, joints and some visceral tissues
What are the 3 key features of nociceptors?
- Some are specific to one type of stimulus (mechanical or thermal)
- But most are polymodal - not a high level specificity as some respond to both mechanical and thermal
- The number and size of the receptive fields served by each fibre may be small or large
What are the 2 types of fibres for the two types of pain?
A(delta) and C fiber
What do A(delta) fibers transmit and what are the characteristics?
Sharp, prickly pain
Thin, myelinated, fast
What do C fibrers transmit and what are the characteristics?
Dull, aching pain
Thin, unmyelinated, slow
Describe which fibre is active first when it comes to pain?
A(delta) fiber is first as it is sharp but it tends to fade quickly and is then followed by C fibre pain
Pain signals travel through which tract to the brain and run parallel to somatosensory pathways?
Spino-thalamic tract
What is the pain pathway?
Afferent to spinal cord laminae I & II - Cross midline to contralateral anterolateral column - Thalamus - Primary somatosensory cortex (S1) - Secondary somatosensory cortex (S2) - Anterior Cingulate Cortex, Insula, Amygdala
What controls the emotional response of pain?
Anterior cingulate cortex, ínsula and amygdala
What are the two central mechanisms for pain?
Sensory discriminative and emotionally aversive
Describe the features of sensory discriminative mechanisms for pain
Low level sensory processing of pain
Somatosensory cortex
Mediate perception of location, intensity, and ‘quality’ of painful stimuli
Describe the features of emotional aversive mechanisms for pain
Mediate perception of fear, anxiety, and unpleasantness of painful stimuli
High level cognitive processing
This means that there is not one single area but an entire pain matrix
What is the purpose of the vestibular system?
Stabilisation of the head in space
Define gyroscopic stabilisation
Spinning wheel or disc in which the axis of rotation is free to assume any orientation by itself
Where is the vestibular system located?
Inside the inner ear
What are the two organs that comprise the vestibular system?
Semicircular canals - head angular acceleration
Otoliths - head linear acceleration gravity
Vestibular organs lie on which bone?
The temporal bone
Semicircular canals sense what?
Sense head rotations (angular acceleration)
Semicircular canals are filled with liquid, what is it called?
Endolymph
The rotation of the head causes the liquid to move in what direction?
Opposite to the rotation
When the liquid moves, what happens?
It bends the jelly-like cupola, causes embedded vestibular hair cells to bend and fire APs
The liquid works in a push/pull way which results in what?
Balances the organisation of the two organs
Brain gets information in a highly synchronised way
Super fast in sending info to the brain (25m/s)
What do otoliths sense?
Linear acceleration & gravity
What does linear acceleration (e.g. tilting the head) cause?
The crystals to pull the gelatinous substance downward, bending hair cell stereocilia and causing depolarisation
Moving the hair cells allows the brain to know what?
That the head has moved in function of the gravitational acceleration
The otoliths consist of hair cells embedded in a jelly-like substance, covered with what?
Heavy calcium carbonate crystals (which balance on the hair cells)
Which is the longest hair?
Kinocillium
Vestibular signals travel through the what to the brain?
Medial Longitudinal fasciculus
Outline the vestibular pathway
Vestibular nerve - brainstem - (cerebellum) - thalamus - vestibular areas
Outline the vestibular brain areas
Somatosensory cortex, premotor cortex, anterior insular, posterior parietal cortex, temporo-parietal junction, hippocampus
What are the 3 vestibular-driven reflexes?
Vestibular-ocular
Vestibular-collic
Vestibular-spinal
What does the vestibular-ocular reflex do?
Keeps the eyes still in space when the head moves
What does the vestibular-collie reflex do?
Keeps the head still in space (or on a level plan when you walk)
What does the vestibular-spinal reflex do?
Adjusts posture for rapid changes in body position
In VOR the semicircular canals measure what?
Rotation of the head and provide a signal for the oculomotor nuclei of the brainstem, which innervate the eye muscles
Smell and taste involve what type receptor?
Chemoreceptors
Chemoreceptors respond to what?
Chemicals in aqueous solutions
Where are smell receptors located?
In the root of the nasal cavity
What is the lifespan of cilia?
30-60 days
Each olfactory receptor only has one type of …
Receptor protein
What are the 4 stages of smell receptors?
- Odorants bind with receptors
- Olfactory receptor cells are activated and send APs
- Signals are relayed in glomeruli
- Signals travel to brain
How many odour molecules can the brain analyse
~400
How many odours can we recognise?
Over 1 trillion
Where do signals from the olfactory nerve travel travel to?
The pyriform cortex
What do neurons in the pyriform cortex respond to?
Odours
Define taste buds
Receptors with hairs covered
What is the lifespan of taste buds?
7-10 days
What are the 5 basic tastes?
- Sweet
- Sour
- Salty
- Bitter
- Savoury
What is the taste pathway?
Signals from the taste receptors - medulla - thalamus - gustatory cortex (in insular)
