Lecture 13 - Somatic Sensation Flashcards
where is the primary afferent neuron present in?
present in the spinal cord
where does the primary afferent neuron synapse on?
synapses on the secondary neurons in the CNS
where is the cell body of the primary afferent neuron?
its cell body is located in the dorsal root ganglion
where are the dorsal root ganglion part?
considered to be part of the central process
what makes up the axons in the PNS in terms of processes?
both the central process and the peripheral make up the axons in the PNS
what is the receptive field at the end of the primary afferent neuron composed of?
composed of sensory endings of an axon that contains sensory receptors
what is a receptive field?
an area of the skin that a particular axon is responsible for
what are the two pathways in the spinal cord used to relay somatic sensation?
anterolateral pathway
dorsal column pathway
what is the anterolateral pathway?
begins directly after entering the dorsal root ganglion through the dorsal root in the spinal cord. The anterolateral fibres pass to the front of the spinal cord and cross to the other side up to the nucleus within the brainstem
what information does the anterolateral pathway carry?
carries poorly resided stimuli that doesn’t need to be precisely located at the body surface
what is examples of the stimuli the anterolateral pathway detects?
includes pain and temperature as they are general sensations from wider areas of the body
what is the dorsal column pathway?
enters at the dorsal root and stays at the dorsal side at the back of the spinal cord. It goes up on the same side it comes in and then crosses over at a higher level
what is the dorsal column pathway for?
it is for fine touch and proprioception
what is the reticular activating system (RAS)?
alerts that something is happening in the environment acting as an alert system
- for integrated/expected vs actual outcomes and proprioception
where does the reticular activating system branch into to?
branches into the brainstem
what do sensory receptors of the skin convert?
sensory receptors of the skin convert physical stimuli into AP’s in the primary sensory neuron by transduction
what is transduction?
transduction is the conversion of energy from one form to another
what are proprioreceptors?
skin mechanoreceptors that measure the position of limbs though muscle spindles, Golgi tendon organs and joint capsules
what are touch receptors?
mechanoreceptors that are sensitive to mechanical deformation
what are nociceptors for pain?
receptors that respond to extreme mechanical temperatures and/or chemical stimuli
what are hair receptors?
receptors that detect airflow past the body surface
what is a pacinian corpuscle?
a skin touch receptor that detects pressure and vibration and associated with myelinated fibres for precise detection
what are the 4 ways sensory information is coded?
modality
intensity
location
duration
what is modality?
the specificity of receptors
e.g specific for touch or temp
what is intensity in terms of sensory information?
the frequency of AP’s in each axon or the number of axons activated
what is location in terms of sensory information?
the mapping of receptive fields of individual primary afferents to specific corticol locations
why does location of sensory information vary?
varies due to somatotopic representation in the somatosensory cortex
what is duration in terms of sensory information?
detects movement and changing pressure
how do rapidly adapting receptors respond?
respond briefly even if the stimulus is sustained
how do slowly adapting receptors respond?
can signal the true duration of a stimulus as they fire though-out the whole duration of a stimulus
what are the two skin receptors that allow us to distinguish the direction skin is being stretched?
ruffini’s endings and pacinian corpuscles
what is lateral inhibition?
a fundamental mechanism to increase the accuracy of sensory information
what is lateral inhibition mediated by?
mediated by inhibitory interneurons
when is lateral inhibition used?
used wherever an accurate location of a stimulus is required or where a pattern of input needs to be discriminated
e.g vision, smell etc
what does lateral inhibition result in?
results in centre-surround inhibition
what is the relationship between somatic sensation and lateral inhibition?
in somatic sensation lateral inhibition is a localised sensation to a restricted area of the skin
