Sensory Pathways Flashcards
WHAT ARE SENSORY MODALITIES?
A MODALITY IS A TYPE OF STIMULUS
Speed of transduction, size of fibre, and state of myelination of fibre, and modality conducted of Abeta fibres?
Very fast transduction fibres- large and myelinated transmit mechanical stimulation e.g. brush
Speed of transduction, size of fibre, and state of myelination of fibre, and modality conducted of Adelta fibres?
Fast transduction (less fast and smaller than Abeta)- myelinated transmit pain/temperature
Speed of transduction, size of fibre, and state of myelination of fibre, and modality conducted of C fibres?
C Slow transduction, small and no myelination transmit slower achey pain, temperature, itch
Nerve endings of thermoreceptors?
Free nerve ending
Nerve endings of nociceptors?
Free nerve ending
Nerve endings of mechanoreceptors?
Nerve endings enclosed in connective tissue capsules
Nerve endings of auditory hair cells?
Special hair receptor cells
Nerve endings enclosed in connective tissue capsules are which type of receptor?
Mechanoreceptors
Free nerve endings are which type of receptor?
Nociceptors and thermoreceptors
- Somatosensory receptors are X that convert energy from the environment into neuronal action potentials
transducers
- The ABSOLUTE THRESHOLD of somatosensory receptors is the …
Level of stimulus (strength) that produces a positive response of detection 50% of the time
Thermoreceptors have what kinda nerve ending
Free nerve endings with high thermal sensitivity
Thermoreceptors have what kinda channels (2)
- 4 heat-activated TRP channels: TRPV1-4 - 2 cold-activated TRP channels: TRPM8 TRPA1
What are the heat activated TRP channels
TRPV1-4
What are the cold activated TRP channels
TRPM8
TRPA1
What are the 4 mechanoreceptors
Meissners corpuscle, Merkel cells, Pacinian corpuscle and Ruffini endings
What type of touch stimulates Meissners corpuscle
Fine, discriminative touch
What type of touch stimulates Merkel cells
Light touch and superficial pressure
What type of touch stimulates Pacinian corpuscles
Detects deep pressure, vibration and tickling
What type of touch stimulates Ruffini endings
Continuous pressure or touch and stretch
Fine, discriminative touch stimulates what receptor
Meissners corpuscle
Light touch and superficial pressure stimulates what receptor
Merkel cells
deep pressure, vibration and tickling stimulates what receptor
Pacinian corpuscles
Continuous pressure or touch and stretch stimulates what receptor
Ruffini endings
How can mechanoreceptors be specific to types of touch
Through adaptation speed (fast and quick) and type of stimulus (continuous vs change)
How do tonic receptors work in adaptation
- Tonic receptors detect continuous stimulus strength
- These do not adapt or adapt very slowly
- Continue to transmit impulses to the brain as long as the stimulus is present
- Keeps the brain constantly informed of the status of the body
- E.G. MERKEL CELLS- slowly adapt allowing for fine touch perception
How do phasic receptors work in adaptation
- Detect a change in stimulus strength
- Adapt quickly
- Train of action potentials transmitted at start (when pressure excited the receptor), and then at end (when pressure is released)
- Also called “movement receptors” or “rate receptors”
- E.G. PACINIAN RECEPTOR
What is the RECEPTIVE FIELD in sensation
THE RECEPTIVE FIELD IS THE REGION ON THE SKIN WHICH CAUSES ACTIVATION OF A SINGLE SENSORY NEURON WHEN ITSELF ACTIVATED
What does a small receptive field detect
- Small receptive fields allow precise perception and detection of fine detail
What does a large receptive field detect
- Large receptive fields allow detection of changes over a wider area
What is TWO POINT DISCRIMINATION and what is this related to
Minimum distance at which two points are perceived as separate
- Related to size of the receptive field
Adelta fibres mediate what type of pain
sharp, intense or first pain
What are the two types of Adult fibre and what do they detect
- TYPE 1: A-MECHANOHEAT RECEPTORS Noxious mechanical and thermal stimuli
- TYPE 2: A-MECHANORECEPTORS Noxious mechanical stimuli
C fibres mediate what type of pain
mediate dull, persistent or second pain:
What stimuli do C fibres respond to
- Respond to thermal, mechanical and chemical stimuli(chemical stimuli = inflammatory mediators, PG, BK) - (polymodal)
Myelination of C fibres?
Unmyelinated
Myelination of Adelta fibres?
Myelinated
Cell bodies of primary afferent neurones are located in … (body and face (for face think nerve innervation))
dorsal root ganglia (body) and trigeminal ganglia (face)
- Dorsal horn of the spinal cord is Organised into:
Rexed Laminae (I-VII)
- Innocuous mechanical stimuli (Aalpha and Abeta fibres) terminate in lamina X-Y of the dorsal horn
III-VI
- Pain and temperature (Adelta and C fibres) terminate in lamina X-Y of the dorsal horn
I-II (referred to as the superficial dorsal horn)
- X is the main excitatory neurotransmitter of the dorsal horn
Glutamate
What is lateral inhibition in the dorsal horn performed by
- Interneurons that connect between different laminae and between adjacent peripheral inputs
Lateral inhibition prevents…
overlap of receptive fields
What is the GATE CONTROL THEORY and what is this due to
A dull achey pain response in the dorsal horn can be modulated by activating an Abeta fibre e.g. rubbing on a painful area can reduce pain
Due to lateral inhibition
THE DORSAL COLUMN SYSTEM transmits what modality
Innocuous mechanical stimuli - fine discriminative touch and vibration
- Information is conveyed from lower limbs and body (below T6) ipsilaterally along the X fasciculus
GRACILE
- Information is conveyed from upper limbs (above T6) ipsilaterally along the X fasciculus
CUNEATE
Fibres of the dorsal column/cuneate and gracile fasciculus?
Aalpha and Abeta
1st ORDER NEURONS of the dorsal column pathway TERMINATE IN THE X in their respective nucleus
MEDULLA dorsal column
2nd ORDER NEURONS of the dorsal column pathway DECUSSATE IN THE X
Caudal MEDULLA
What tract do second order neurons of the dorsal column pathway follow to where
CONTRALATERAL MEDIAL LEMNISCUS TRACT from the medulla to the thalamus
Where do the 2nd order neurons of the dorsal column pathway terminate (SPECIFIC NUCLEUS)
VENTRAL POSTERIOR LATERAL NUCLEUS of the thalamus (VPL)
Where do the 3nd order neurons of the dorsal column pathway project from and to
- 3rd order neurons from the VPL nucleus project to the somatosensory cortex
Where is there a somatotopic representation of the body in the afferent dorsal column pathway
Somatosensory cortex
Where is there a topographic representation of the body in the afferent dorsal column pathway
In the cuneate and gracilis nuclei in the medulla and the ventral posterior lateral nucleus in the thalamus
What are the 2 pathways in THE SPINOTHALAMIC (ANTEROLATERAL) PATHWAY and what are their modalities
lateral pathway (pain and temp.) and anterior pathway (crude touch)
Where do the 1st order neurons of the the spinothalamic (anterolateral) pathway terminate
- primary afferent (1st order) axons terminate upon entering the spinal cord
Where do the 2nd order neurons of the the spinothalamic (anterolateral) pathway project from and to
From spinal cord to terminate in the ventral posterior lateral nucleus of the thalamus
Where do the 3rd order neurons of the the spinothalamic (anterolateral) pathway project from and to
- 3rd order neurons from the VPL project to the somatosensory cortex
Where do the 2nd order neurons of the the spinothalamic (anterolateral) pathway decussate
Immediately after synapsing upon entry to the spinal cord
What is the spinoreticular system (pain from X to X in X and then to X)
Pain transmitted through a pathway from the spinal cord, to the parabrachial area in the brainstem, and then to the limbic system
Parts of the brain involved in pain reception? (4)
Cortex
Amygdala
Cerebellum
Brainstem
