sensory pathways Flashcards
(40 cards)
give examples of Somatosensory modalities and what receptors they are sensed by
Touch inc. light touch, pressure, vibration – sensed by mechanoreceptors
Proprioception inc. joint position, muscle length, muscle tension – sensed by mechanoreceptors
Temperature – sensed by thermoreceptors
Pain – sensed by nociceptors
how are neurones specialised for these modalities
Individual axons of sensory nerves have modified terminals
what are 3 classes of sensory neurones
Aβ-fibres: innocuous mechanical stimulation
C-fibers: noxious mechanical, thermal and chemical stimulation
Aδ-fibres: noxious mechanical and thermal stimulation
order sensory neurones from fastest to slowest
Aβ-fibres, Aδ-fibres, C-fibers
define sensory receptors
sensory receptors are transducers that convert energy from the environment into neuronal action potentials
how do thermoreceptors work
have free nerve endings and Transient receptor potential (TRP) ion channels
4 heat activated TRPs and and 2 cold activated
name 4 mechanoreceptors and what they detect
Meissner’s Corpuscle - Fine discriminative touch, low frequency vibration
Merkel cells - Light touch and superficial pressure
Pacinian Corpuscle - Detects deep pressure, high frequency vibration and tickling
Ruffini endings - Continuous pressure or touch and stretch
what is tonic receptor (give example)
Tonic receptors
Detect continuous stimulus strength
Continue to transmit impulses to the brain as long the stimulus is present
Keeps the brain constantly informed of the status of the body
example (Merkel)
What is phasic receptor (give example)
Detect a change in stimulus strength
Transmit an impulse at the start and the end of the stimulus
e.g. when a change is taking place
example (pacinian)
what is the stimulation threshold
the point of intensity at which the person can just detect the presence of a stimulus 50% of the time (absolute threshold) - The weakest detectable stimulus
what is Stimulus intensity discrimination
a more intense stimulus increases NT released and hence increases freq of AP’s AND increases the number of separate receptors activated – amplitude REMAINs the same
define receptive field
’The receptive field is the region on the skin which causes activation of a single sensory neuron when activated’ - can overlap
define Lateral inhibition
activation of 1 neural unit – inhibits activation of other units
Occurs at interneurons in the dorsal horn of spinal cord – this increases the precision in localization of the stimulus
(prevents overlap of receptive fields)
define 2 point discrimination
ability to detect that 2 stimuli are distinct from each other – the minimum distance required between 2 stimuli in order to perceive them as separate
what is gate theory
non painful stimulation can inhibit primary afferent inputs of pain before they are transmitted to brain – neuronal dysfunction can cause depolarization in response to non-painful stimuli
what is the difference between small and large receptive fields
Small receptive fields allow for the detection of fine detail over a small area. Precise perception
Large receptive fields allow the cell to detect changes over a wider area (less precise perception)
The fingers have many densely packed mechanoreceptors with small receptive fields
what does dorsal column pathway detect
Innocuous mechanical stimuli
Fine discriminative touch
Vibration
what is the difference between upper and lower limb innocuous sensation
Information conveyed from lower limbs and body (below T6) travel ipsilaterally along the gracile tract
Information conveyed from upper limbs and body (above T6) travel ipsilaterally along the cuneate tract
Path of 1° neurones – DC-ML pathway
Cell bodies of 1° neurones are in the dorsal root ganglia
1° neurones transmit information from the sensory receptors, ascend ipsilaterally up the spinal cord to the medulla.
Neurones from the upper limb synapse ascend in the cuneate fasciculus
Neurones from the lower limb ascend in the gracile fasciculus
Path of 2°/3° neurones – DC-ML pathway
1° neurones from the cuneate and gracile fasciculi synapse with 2° neurones in the cuneate and gracile nuclei.
The 2° will decussate across the medulla and synapse with 3° neurones in the contralateral thalamus (VPL)
3° neurones will ascend to the somatosensory cortex
what specific nucleus of the thalamus do secondary neurones terminate in and describe it
The axons of the second order neurons terminate in the ventral posterior lateral nucleus of the thalamus (VPL).
There is a topographic representation of the body in the VPL
where are lower extremities represented in the VPL
Laterally
what tracts can the spinothalamic pathway be divided into
anterior and lateral
what do different tracts of the spinothalamic pathway detect
Pain and temperature sensations ascend within the lateral spinothalamic tract
Crude touch ascends within the anterior spinothalamic tract
