General sensation Flashcards
Name some types of sensory receptors?
Mechanoreceptors
Chemoreceptors
Thermorecepors
Nociceptors
What do chemoreceptors detect?
pH
What do nocireceptors respond to?
Damaging stimuli
Pain when it enters brain
What receptors have free endings?
Nociceptors and cold receptors
What is the receptive field?
Respond to stimulus over a specific area
What is Meissner corpuscles?
consist of a cutaneous nerve ending responsible for transmitting the sensations of fine, discriminative touch and vibration
A-D
A = meissners corpuscle
B = merkles corpuscle
C = pacinian corpuscle
D = ruffini corpuscles
What does meissners corpuscle detect?
Light touch
What does merkels corpuscle detect?
Touch
What does pacinian corpuscle detect?
Deep pressure
What does ruffini corpuscle detect?
Warmth
What is a pharmacological receptor?
Ach receptor
Protein in the posterior-synaptic membrane
What is a physiological receptor?
Whole Sensory terminal
What does the size of the receptor potential encode?
Intensity of stimulus
E.g. bigger pressure then bigger potential
What encodes the intensity of stimulus through AP?
Frequency of firing of AP
What does the location of the receptive field tell us?
Location - Which bit if the skin the stimulus came from
Modality - e.g. mechano receptor
Intensity - number of AP Being fired tells you how strong the stimulus was
What is axon hillock called in efferent neurones?
Trigger zone
A = small receptive field
B = large receptive field
What areas have a small receptive field?
Finger tips and mouth
What areas have a high receptive field?
Back
Sparse receptive field
What makes your fingers more sensitive?
Acuity
What determines acuity?
Density if innervation and size of receptive field
The small receptive field neurones! Fingers have small and will activate more than 1 neurone compared to 1 (e.g. back)
What 3 receptors mediate cutaneous sensation?
Abeta
Adelta
C
What do the alpha-beta fibres conduct?
Large myelinated
Touch,
Reassure
Vibration
What do the alpha-delta fibres conduct?
Small myelinated
Cold
Fast pain
Pressure
What are the small myelinated Afferent fibres?
Alpha-delta
What do the C fibres conduct?
Unmyelinated fibres
Warmth
Slow pain
What are the unmyelinated Afferent fibres?
C fibres
What primary Afferent fibres mediate proprioception?
Aalpha
Abeta
What are the 2 modes of sensory transmission?
- Mechanoreceptive Abeta fibres
Ipsilateral - Thermoreceptive and Nociceptors fibres (A-delta and C)
Contralateral
Where do the mechanoreceptive fibres synapse?
Cuneate and gracile nuclei
When do the mechanoreceptive fibres cross over the midline?
The 2nd order neurones cross over the midline in the brain stem and project to reticular formation, thalamus to cortex
Where do the thermoreceptive and Nociceptive fibres synapse?
Dorsal horn
What tract do the thermoceptive and nociceptove fibres project up?
Condrolateral spinothalmic tract to reticular for,action to thalamus to cortex
What does damage to Dorsal columns cause?
Causes loss of touch, vibration, proprioception below lesion on Ipsilateral side
What does damage to anterolateral quadrant cause?
Causes loss of Nociception and temperature sensation below lesion on condralateral side
Where is the ultimate termination for sensory information?
Somatosensory cortex of the post central gyrus
What areas have a higher representation in the somatosensory cortex?
Finger tips
Density of receptors at each location
What is the sensory homunculus?
Brains view of the body
Can you stimulate sensations along the pathway?
Yes, e.g. funny bone stimulates AP from many neurones
What does this show?
Sensory homunculus
What are the levels of processing of sensory innervation?
Adaptation
Convergence
Lateral inhibition
Perception
What are 2 types of adaptation?
Rapidly adapting
Slowly adapting
What is the rapidly adapting neurone?
After stimulus it stops and gets used to it
What is an example of a rapid adaptation?
Hat on head
What is neural convergence (processing)?
Several sensory neurones will synapse on to the same secondary order neurone and it’ll go to cortex
What are the pros of convergence?
Saves on neurones
What are the disadvantages of convergence?
Reduces acuity
Underlies referral sensation (e.g. heart attack feel pain in shoulder and arm)
What are types of convergence?
Specific ascending pathways (same receptor Mechano for example)
Nonspecific (could be a mix of touch and temp…)
What is lateral inhibition in processing if sensory information?
Activation of a sensory input causes synaptic inhibition of its neighbours
What is the advantage of lateral inhibition?
Gives better definition boundaries
Cleans up sensory information
Why don’t all stimulus enter the brain?
Descending inhibitor controls
What are the 2 types of inhibition shown here?
Pre synaptic and post synaptic
What receptor does analgesia inhibit?
Nociceptive
What are the 2 separate forms of inhibition?
Segmental controls
Descending controls
What does the segmental controls revolve around?
Gate control theory of pain
What inhibits the Adelta and C fibres? (Segmental control)
Mechanoreceptive fibres going up the dorsal column
The Alpha/beta fibres via the axon collateral
Where do the descending inhibits controls come from?
Peri-acqueduct grey matter (PAG)
