Anatomy and Cell Biology 3309 Lecture Notes - Lecture 3: Lamellar Corpuscle, Sciatic Nerve, Dermis
22 May 2018
School
Department
Professor
Histology 3309
Peripheral Nerves
The Nerve
- Ex: sciatic nerve
o One of biggest nerves in PNS
o Contains several thousand fibers (axons)
o Mixed nerve – has axons of both sensory and motor neurones
▪ afferent and efferent information is both conveyed
o has both myelinated and non-myelinated axons
- both the presynaptic terminals and the sensory receptors are neurons
PNS (ANS/SNS)
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Sensory Receptors
- there are 4 different types + free nerve endings
- the meissner corpuscle and the merkel disks are at the border of the dermis and the epidermis
- Meissner corpuscles
o free nerve ending with cell processes and nerve endings that coil around some
supporting cells that are encapsulated
o The entire capsule is embedded in the dermal papilla that reaches into epidermis
o Sensitive to light touch bc so close to surface
o Ability to adapt very rapidly to touch – so its mostly the changes in touch that they feel
o Abundant in fingers, hands, and lips
o This receptor is what blind people use to read braille
o If there is an ongoing touch, this receptor will stop responding
- Merkel disc
o Part of epidermis
o In close vicinity to a nerve ending
o Very sensitive
o Not rapidly adapting (keep firing if there is an ongoing touch)
o Sometimes can form tumors
- Pacinian corpuscle
o Free nerve ending that lie within a structure that is made of many diff layers of
connective tissue (made of 80% water – so kind of gelatinous)
o If there a slow indent on the skin, the neuron within the Pacinian corpuscle does not
respond bc the gelatinous layers slide against each other and absorb the stimulus
o Responds to fast indentations (vibrations)
o Lie deep within dermis – so not as sensitive to Meissner or merkel disc
- Ruffini corpuscle
o Free nerve ending embedded in spindle like connective tissue capsule
o Very abundant around fingernail
o Stretch receptors within the skin
o Important for grip adjustment – when something is slipping through our fingers, this
allows us to adjust our grip strength
▪ Ex: adjusting grip strength when picking up a glass that is full or empty
o Very slowly or no adapting – don’t inactivate
- Free nerve endings
o Nothing specialized around them
o Very sensitive
o Our pain/temp receptors
- Mixture of location, what kind of connective structure
they are associated with and what ion channels that
are expressed in the dendrites determine whether
they are fast/slow adapting, how sensitive they are
and to what kinds of stimuli
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Free Nerve Endings
- Nissl stain of epidermis
- Branching dendrite of sensory neuron embedded in dermis
- Has no specialized connective tissue that is connected to the free nerve endings
Pacinian Corpuscles
- Can see diff layers of gelatinous connective tissue
- Middle is nerve ending
Meissner Corpuscles
- Located at dermal papilla (fingerlike projections of dermis into epidermis)
- Free nerve endings are in red (dendrites of sensory neuron) which is embedded in flattened like
supporting cells that form the capsule
- Merkel discs would be at the base of the epidermis – there are specialized cells surrounding the
base of the epidermis which are innervated by sensory dendrite/neuron
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Document Summary
Sensory receptors there are 4 different types + free nerve endings the meissner corpuscle and the merkel disks are at the border of the dermis and the epidermis. If there is an ongoing touch, this receptor will stop responding. In close vicinity to a nerve ending: part of epidermis, very sensitive, not rapidly adapting (keep firing if there is an ongoing touch, sometimes can form tumors. Ruffini corpuscle: responds to fast indentations (vibrations, free nerve ending that lie within a structure that is made of many diff layers of. Free nerve endings: nothing specialized around them, very sensitive, our pain/temp receptors. Mixture of location, what kind of connective structure they are associated with and what ion channels that are expressed in the dendrites determine whether they are fast/slow adapting, how sensitive they are and to what kinds of stimuli. Branching dendrite of sensory neuron embedded in dermis. Has no specialized connective tissue that is connected to the free nerve endings.
