Weeks 10-12 Flashcards
Somatosensory system
Responds to the EXTERNAL environment. (E.g. touch, temp, pain)
Cerebrum, cerebellum, brainstem and spinal cord
Viscerosensory system
Responds to the internal environment
3 classes of somatosensory receptors
Tactile sensations (mechanoreceptors)
Thermal sensations (thermoreceptors)
Nociceptive (painful) sensations (mechanical, thermal and polymodal nociceptors)
Where are the meissner corpuscle and merkel’s disks located.
Epidermis
Meissner b/t dermal pupillae.
Merkels aligned with dermal pupillae.
Where are pacinian corpuscles located
Subcutaneous tissue.
Where are ruffini’s corpuscles located
Deep in the dermis (20% of skin receptors)
Meissner’s corpuscle
LOW FREQ VIBRATIONS.
Looping axonal terminals.
Merkel’s disks
SMALL FORMS AND SHAPES.
Dome structure
Pacinian corpuscle
HIGH FREQ VIBRATIONS.
Sensory axon surrounded by fluid filled capsule
Ruffini’s corpuscle
PRESSURE.
Nerve terminals and collagen fibrils.
Free nerve endings
NOXIOUS (HARMFUL)
Penetrate into epithelial cells
Stages of sensory transduction
1) Stimulus changes nerve ending.
2) Alters the membrane permeability of receptor membrane.
3) Produces receptors (generator) potential.
4) Triggers AP.
Out of mechanoreceptors, nociceptors and thermoreceptors which are fast and slow afferents
Mechanoreceptors are fast.
Nociceptors and thermoreceptors are slow due to small diameter.
Describe the 3 neurone chain in a mechanosensory pathway
1st order neurone: Primary afferent (into dorsal horn, spinal cord)
2nd order neurone: Central neurone (to thalamus)
3rd order neurone: Central neurone (to cortex)
Where is the primary somatosensory cortex located?
Post central gyrus
Where does the transduction of a painful stimulus occur
Free nerve endings of unmyelinated C fibres and thinly myelinated Ad fibres.
What do pain afferents release?
NT glutamate and vesicles containing the neuropeptide substance P
Where does the mechanosensory pathway cross over?
Decussates at the medulla.
Where does the pain pathway cross over?
Decussates at the dorsal horn.
Contralateral pathway
What structure is responsible for your blind spot?
Optic disc - where optic nerve axons leave the eye
What are the two types of photoreceptors and their role?
Convert light energy to neural activity.
Cone cells: Colour vision (large number in fovea)
Rod cells: Achromatic (without colour), more sensitive to light (periphery of retina)
What is the role of bipolar cells in the retina?
Create pathway from photoreceptors to ganglion cells.
Amacrine/horizontal cells
Indirect pathways (modulators)
Retinal ganglion cells
Axons leave the eye to form optic nerve
