Sensory Physiology Flashcards
What are the 4 major groups of receptors?
Chemoreceptors
Mechanoreceptors
Thermoreceptors
Photoreceptors
What is another name for primary and secondary sensory neurons?
1st and 2nd order neurons
What are the 4 properties of a stimulus?
- Modality
- Location
- Intensity
- Duration
What are the classes of somatosensory nerve fibres?
AB- large, myelinated
Ad- small, myelinated
C- small, unmyelinated
What is AB fibres associated with?
Mechanical stimuli
Whay is Ad fibres associated with?
Cold
Fast pain
Mechanical stimuli
What are C fibres associated with?
Heat
Cold
Slow pain
Mechanical stimuli
What are the mechanoreceptive fibres and how do they transmit sensory information?
Aa and AB
Project straight up through ipsilateral dorsal column
Synapse in cuneate and gracile nuclei
2nd order fibres decussate in brainstem and project to reticular formation, thalamus an dcortex
What are the thermoreceptive and nociceptive fibres and how do they transmit sensory information?
Ad and C
Synapse in dorsal horn
2nd order fibres cross over midline in spinal cord
Project up through lateral spinothalamic tract to reticular formation, thalamus and cortex
What is the gate control theory of pain modulation?
AB fibres activate inhibitory interneurons
Descending pathways also activate inhibitory interneurons
Inhibitory interneurones release endorphins that inhibit transmitter release from Ad and C fibres
What is hyperalgesia?
Increased perception of pain
What are the type of peripheral sensitization?
Hyperalgesia- exaggerated response to stimuli
Allodynia- decreased threshold for nociceptor response
What are the types of central sensitization?
- Wind up- winding up response of activated synapses
- Classical- opening up of silent synapses
- Long term potentiation- involves activated synapses primarily for very intense stimuli
What are the 3 types of pain?
- Nociceptive
- Neuropathic
- Nociplastic
What is nociceptive pain?
Nociceptors respond to noxious stimuli
Localised at site of injury
Resolves when damaged tissue heals
What is neuropathic pain?
Pain caused by lesion/disease of somatosensory nervous system
Pain in neurological territory of affected structure
Chronic
What is nociplastic pain?
Arises from altered nociception with no clear evidence of tissue/somatosensory damage
Stimulus independent
No injury, inflammation of neuronal damage
Serves no protective or adaptive function
Where is the vestibular system?
Inner ear
What is the vestibular system composed of?
Membranous labyrinths: A series of fluid filled labyrinths embedded in temporal bone
- Otolith organs
- Semi-circular canals
What are the 2 otolith organs?
Utricle
Saccule
What fills the vestibular apparatus?
Endolymph secreted by epithelial cells
What do the semi-circular canals monitor?
Rotational acceleration
Posterior canal- tilt of head left or right
Horizontal canal- rotation of head left or right (‘no’)
Superior canal- rotation of head front and back (‘yes’)
What is at the base of each canal?
Ampulla- enlarged chamber containing a crista
What is a crista?
Sensory structure that consists of hair cells and a gelatinous mass, the cupula
Hair cell cilia are embedded in the cupula
How is rotation sensed in the semi-circular canals?
- If the skull is rotated the endolymph at first does not move because of its inertia.
- However the ampullae moves instantly because it is embedded in the skull.
- Inertia of endolymph produces drag which bends cupula and embedded cilia in the opposite direction to movement
- If rotation continues, the endolymph catches up and rotates at the same speed, removing the shearing forces, but this takes several seconds
- Sudden stop will cause endolymph to continue to move due to momentum creating a sense of movement and dizziness
What are the 2 types of hair cilia?
Kinocilium- single, very large
Stereocilia- smaller
What do the otolith organs sense?
Linear acceleration and head position
What is the sensory structure of the otolith organs?
Maculae
Consists of hair cells which protrude into a gelatinous mass called the otolith membrane
Embedded in the otolith membrane are calcium carbonate and protein particles called otoliths
How do otolith organs sense linear acceleration and head position?
If gravity or acceleration causes the otoliths to slide forwards or back, the otolith membrane slides with them, bending the hair cell cilia and setting off a signal
What do the maculae of the utricle sense?
Horizontal orientation
Forward acceleration or deceleration,
Head tilt
What do the maculae of the saccule sense?
Vertical orientation when head is erect
Sensitive to vertical forces
What are the vestibular system reflexes?
- Tonic labyrinthine reflexes- keep axis of head in a constant relationship with the rest of the body
- Dynamic righting reflexes - rapid postural adjustments to stop you falling when you trip
- Vestibulo-ocular reflexes- strong association is evident between vestibular apparatus, visual apparatus and postural control
What are the clinical associations with the vestibular system?
Motion sickness: nausea, vomiting, low BP, dizziness, sweating, pallor
Labyringitis: ANS symptoms, vertigo
Meniere’s disease: vertigo, nausea, nystagmus, tinnitus
