L04: Sensory Sytem (somatosensory) Flashcards
What is the primary sensory i.e first order neurone also known as
Primary afferent
Where is the cell body of the first order neurone found
In the dorsal root ganglia
Where does the axon of the first order neurone innervate
Receptive field
What happens to the first order neurone when it enter the spinal cord
- Splits into 3 : above, below, same spinal level
- Terminates to 2nd order neurone
Where does the second order neurone take the information to
Thalamus
At the thalamus what happens to the second order neurone
Terminates to give 3rd order neurone
Are sensory neurones excitatory or inhibitory
Excitatory
What is the common neurotransmitter that sensory neurones release
Glutamate
How do we classify axons in the primary afferents
Depending on myelination
What are the axons from the skin
A beta
A delta
C
What happens to the axon as you go from a beta to c fibre
The axon becomes more unmyelinated
What does a beta axons pick up from the skin
Mechanoreceptors
What does a gamma axons pick up from the skin
Pain
Temperature
What does c axon pick up from the skin
Temperature
Pain
Itch
Where does a each axon innervate within its dermatome
Receptive field
What is a dermatome
Area of skin innervated by as single spinal root
What is an adequate stimulus
The right stimulus which depends on the nerve ending
For a signal to be transducer what has to be reached
Threshold
What are the ion channels on the nerve endings called
Transduction channels
What happens to the tranduction channels which open upon suffice to energy stimulus
Open
What happens when the transduction channels open
Positive ions enter to cause depolarisation
What is a a graded receptor potential
The size of stimulus that determines the size of action potential e.g large stimulus= large potential
When is a signal only sent
When they reach a threshold
What is the firing rate of the action potential dependent on
Stimulus strength
What are the 2 types of adapting sensory receptors
1) slow or non adapting receptor
2) fast adapting receptors
What happens in a slow or non adapting receptor
Firing is continuous when stimulus is present
When is a slow or non adapting stimulus important
When maintaining information about a stimulus is valuable e.g amount of stretch or pain
What is the fast adapting receptor
When there is a change in stimulus there is a high rate of firing but firing decreases if the stimulus is maintained
When is the fast adapting receptor important
When the stimulus is no longer important e.g (tactile touch) getting dressed in the morning and not being able to feel you clothes on you later on
What does a slow adapting receptor detect
Strength of stimulus
What does a fast adapting receptor decked
How fast the stimulus is changing
What are the 3 types of sensory receptors found in the skin
Mechanoreceptors
Thermoreceptors
Nociceptors
What does mechanoreceptors detect
Touch
Pressure
Vibration
What does thermoreceptors detect
Hot and cold
What does thermoreceptors not detect
The Temperature
Where is temperature processed
At the brain
What does nociceptors detect
Noxious stimulation
What are the 2 main layers of the skin
Epidermis
Dermis
What is the most superficial layer
epidermis
What is the most deep layer
Dermis
What are the fibres of mechanoreceptors
A beta fibres
What is the structure of mechanoreceptors
Has an apparatus that is comprised of specialised cells
What are the 4 types of mechanoreceptors
Merkels receptors
Meissners corpuscle
Ruffins corpuscle
Pacinian corpuscle
Which mechanoreceptors are Lund in the superficial layer of the skin
Merkels receptors
Meissners corpuscle
What are the mechanoreceptors found in the deeper layers of the skin
Ruffini’s corpuscle
Pacinian corpuscle
What type of receptors are merkels receptor
Slow adapting
Which cells does the merkel receptor innervate in the skin
Keratocyte
What does merkel receptors detect
Skin indentation e.g allows Braille reading
What type of receptors are meissners corpuscle
Rapidly adapting sensory receptors
What does meissners corpuscle detect
Light touch vibration e.g putting clothes on
What does Ruffini’s corpuscle respond to
Lateral movement
Stretching
Deep touch
What type of receptors are pacinian corpuscle
Rapidly adapting receptor
What is the stimulus of pacinian corpuscle
Deep touch e.g poking
High frequency vibration
How does the pacinian corpus fire ap
When it is squashed it becomes deformed
What type of receptors are hair follicle receptors
Rapidly adapting receptors
What does the hair follicle receptor detect
Light touch
What are the cutaneous thermoreceptors like in their structure
With bare nerve endings
Does not have a specialised apparatus like the mechanoreceptors
What type of receptors are cutaneous thermoreceptors
Slow adapting receptors
What is the 2 stimulus for thermoreceptors
Cold
Hot
Where is temperature determined
In the brain
What type of channels does thermoreceptors have
Transient receptor potential (a family of receptors)
What type of channel is a transient receptors channel
Non specific cation channel
What does a non-specific cation channel mean
They allow any cations in
Name an example of a cold transient receptor potential channel
TRPM8
Name an example of a warm transient receptor potential channel
TRPV3/4
What type of fibres are cold receptors on
C and a delta fibres
What type of fibres are warm receptors on
C fibres
What is paradoxical cold perception
When cold receptors become excited by high temperature
What does cutaneous nociceptors detect
Pain
What is the structure of nociceptors
Bare nerve endings
What is the threshold of nociceptors
High
What are the 2 types of nociceptors
High threshold mechanoreceptors
Polymodal nociceptors
What does high threshold mechanoreceptors detect
Localised pricking pain
What fibres are the high threshold mechanoreceptors found at
A delta fibre
What is the stimulus for polymodal nociceptors
Mechanical stimulus Damaging heat (above 46) Noxious chemicals
What fibres are polymodal nociceptors found at
C fibres
What does propioception detect
Mechanical status
What are propioceptors
Sensory receptors from skeletal muscle
What are the fibres/axons of prioceptors
Group 1 (axons from muscle) that are thickly myelinated
What are the 2 propiceptors found in the body
Muscle spindles
Golgi tendon organ
What does muscle spindles detect
Length and acceleration
What type of fibres does muscle spindles contain
Intrafusal fibres
What are the group of axons that muscle spindle fibres contain
Group 1a
How does muscle spindle fibres become activated
When the fibres are stretched
What does golgi tendon organ detect
Muscle tension
What type of axons is golgi tendon organ innervated by
Group 1b afferents
What are the 2 main ascending tracts
Dorsal column
Spinothalamic tract
What fibres/axons does the dorsal column contain
A beta fibre
What fibre/axon does the spinothalamic pathway contain
A delta and c fibres
What type of sensory information does the dorsal column send to the Brian
Touch
Vibration
2 point discrimination
Propioception
What type of information does the spinothalamic tract send to the brain
Pain
Temperature