nerve histology Flashcards
describe the cell body of a neuron
prominent nucleosome with a large euchromatic nucleus. rich in rER and sER. many mitochondria and lysosomes.
what are the nissl bodies
aggregations of endoplasmic reticulum and ribosomes in the soma
what region of the neuron is free of nissl bodies
the axon hillock
what are the presynaptic boutons
terminal swellings of the axon - where it synapses to the post ganglionic cell
what cells make the macroglia
astrocytes and the oligodendrocytes
describe the astrocytes role
converting glucose to glycogen, maintaining and regulating synapses and they help in forming the blood brain barrier. One astrocyte can enwrap several somata, and make connections with many synapses.
what are the microglial cells
these are antigen presenting cells within the CNS
how is the myelin sheath formed
The myelin sheath is a tight spiral wrapping of the schwann cell or oligodendrocyte. It goes from outside to inside and it will esentially wrap itself around the axon so many times until a thick insulating membrane is formed or many small layers, like an onion. This insulates the axon when its conducting AP and increases the speed and efficiency of nerve conduction. It is just consecutive layers.
When the myelin sheath is formed the nucleus of the cell is however always on the periphery.
what do unmyelinated axons look like
unmyelinated axons will also interact with the schwann cell or oligodendrocyte, but the cell more holds the axons rather than envelope them. one cell can envelope many axons but the cell nucleus will be in the middle of the big group of axons it envelopes.
describe the dorsal root ganglion
Neurons here are the afferent unipolar neurons. Has the central soma and the two peripheral processes. The neuronal soma here is centrally placed in the dorsal root ganglion. They are also surrounded by a sheath of satellite glial cells which provide structural and metabolic support to the neurons. These can be myelinated or unmyelinated. All the cells in the ganglia are within a highly vascular CT that is continuous with the endoneurium
describe the parasympathetic chain ganglia
Contain multipolar neuronal somata and some dendritic fields which synapse to these neural somata. The neuons here receive many synapses from preganglionic axons. Some of these axons will pass through without synapsing however. Satellite glia cells are smaller and fewer in number and irregularly placed * Neuron cells are widely spaced since separated by dendrites and axons. So on histology we don’t see that nice central nucleus surrounded by the satellite cells for support.
whats the free nerve ending make up and function
Free nerve endings: these are the most common receptor in skin.
These are mostly unmyelinated small diameter fibres.
Usually small swellings at distal ends = sensory terminals. TSensory terminals have receptors that can respond to various painful, thermal and chemical stimuli. The free nerve endings mainly respond to temperature, pain some movement and pressure, some itch in response to histamine.
Some of these nerve endings wrap around hair follicles acting as touch receptors for hair displacement.
what are the merkel discs
Free nerve endings within the deepest layer of the epidermis. These are tactile discs as they are associated with large disc shaped (merkel) cells. Communication between the tactile cell and the nerve ending is possibly by serotonin.
These have small receptive fields soi are involved in fine two point touch discrimination.
They are sensitive to fine touch and light pressure, and can respond to texture shape and edges of objects.
what are the meisseners corpuscles
Located in the papillary of the dermis. Are especially common in hairless skin.
Branch sensory termional which is associated with adapted schwan cells, which is then ensheathed in a capsule. Shwann cell doesn’t make myelin when wrapped around.
They are encapsulated by schwann cells and then a thin oval of fibrous connective tissue. When these capsules are deformed an action potential is made due to entry of Na+. As they are deformed they thus respond to delicate touch, light pressure and low frequency vibrations.
what are the pacinian corpuscles
These are more deeply in the dermis and hypodermis.
They are made by a single dendrite being surrounded by concentric layers of collagen. Between this collagen is gelatenous interstitial fluid. The collagen is made by fibroblasts.
These respond mainly to deep pressure, when defromed the opening of Na+ channels makes an AP.
Rapidly adapt, so they dectect deep pressure and vibration quickly and only for short time. Helpful for running fingers over things to feel surface material.
When outer layer is deformed pressure wave goes through the fluid and to the dendrite causing AP.
