Nervous Flashcards
What is the peripheral nervous system?
All nervous tissue outside CNS e.g. nerves, ganglia, nerve endings etc
What do efferent and afferent nerves do?
Efferent: conduct signals away from CNS to effector
Afferent: sensory receptors conducting to CNS
What are the basic features of a neuron?
Dendrites, cell body, axon and terminal arbors (axon terminal)
What is the function of dendrites
Multiple long processes which receive stimuli from other cells (receive many synapses)
Transmit signals to cell body
What are the components of cell body of neurone?
Nucleus, mitochondria, ribosomes, RER and neurofilaments (intermediate filament)
What are axons, what are the parts?
Axon hillock: from cell body as pyrimidal shaped region where axon projects
Axoplasm surrounded by plasma membrane (can be myelinated or unmyelinated)
Conduct impulses away from neurone’s cell body
Axon terminals: neurotransmitters in vesicles beneath terminal membrane
How are neurones both structurally and functionally polar?
Structural polarity: one domain specialised to receive signals, the other sends
Functional polarity: unidirectional impulse propagation
What are the cytoskeletal structures supporting neurones?
Microtubules: transport
Neurofilaments: maintaining axonal structure
Microfilaments: changes in cell shape + scaffold for signal transduction)
How can cytoskeleton of nerve be identified?
Immunocytochemistry
Actin (microfilament): red
Tubulin (microtubules): green
Describe what is anterograde transport, what it does and the structures that facilitate it?
From cell body to axon terminal
Mediated by molecular motor (enzyme) kinesin which walks along microtubules
e.g. GF, organelle and neurotransmitters (made in cell body)
Describe retrograde transport, direction, what facilitates it?
Axon terminal to cell body
Mediated by dyenin
e.g. endocytosis products in endosome
Describe the arrangements of nerve fibres and the connective tissue around them
Endoneurium: surround axons/schwann cells (made by schwann cells)
Perineurium: around fascicles
Epineurium: envelops bundles of fascicles (outermost layer of nerve) - nerve trunk
What is the name of bundles of nerve fibres?
Fascicles
What surrounds fascicles?
Perineurium
What neurones are unipolar, why?
Sensory neurones, cell body in the middle
What are synapses?
Specialised cell junctions between axons and dendrites of other cells.
Describe how myelination occurs
Schwann cells wrap membrane around axon, membranes of cell merge forming myelin
How many schwann cells needed to produce myelin for one node?
1
What do terms mesaaxon, lamella of myelin and major dense line refer to?
Each turn of myelin forms lamella of myelin
Mesaxon = 2 plasma membranes of Schwann cells meeting
Edge to edge contact between layers = major dense line
What are gaps in myelination called?
Nodes of Ranvier
What sort of substance is myelin?
Phospholipid protein substance
What are functions of myelination?
Support and nutrition for neurone
Fast axonal conduction (rapid propagation as clustered channels at nodes of Ranvier)
Provide insulation and reduce electrical capacitance
What are ganglia?
Clusters of cell bodies and glial cells in PNS
Describe structure of non myelinated axons
Non myelinated axons bury themselves in Schwann cell cytoplasm (so still have covering of Schwann cell)
One schwann cell associated with several axons
True of false, neurones are always associated with schwann cells?
True
What happens in Guillian Barre syndrome?
Antibodies to glycosphingolipids -myelination so can cause death from respiratory paralysis
What do oligodendrocytes do?
Wrap myelin around several axons at once, associated with CNS
What are 3 different types of ganglia?
Dorsal root ganglia - contain cell bodies of sensory neurone
Cranial nerve ganglia - cell body of cranial nerve neurone
Autonomic ganglia: cell bodies of autonomic nerves
Where are parasympathetic ganglia found?
Within the organ they innervate, supported by surrounding stroma of organ (minimal glia to support)
Describe ganglia of ENS
Small ganglia of Auerbach’s or Meissner’s plexus that lies within wall of oesophagus, stomach, intestines etc
How does ENS communicate via CNS?
Through parasympathetic (via vagus) and sympathetic ganglia
Describe nerve endings for autonomic nerves
No post synaptic terminal signed, neurotransmitters released form varicosities at varying distances form effector cells
Describe structure of sensory nerves
Bundles of afferent fibres from sensory receptors in PNS ( have different endings)
How are autonomic ganglia different from sensory ganglia?
Cell bodies dispersed
Fewer satellite cells present
Numerous axons (unmyelinated)
Neurones are multipolar
What are satellite cells?
Glial cells that cover the surface of nerve cell bodies in sensory, sympathetic, and parasympathetic ganglia.
What is the role of satellite cells?
Supply nutrients to the surrounding neurons a
Structural function - act as protective, cushioning cells.
Express a variety of receptors that allow for a range of interactions with neuroactive chemicals.
Which ganglia have the most satellite cells?
Dorsal root ganglia
What are the different types of sensory nerve endings?
Meissner corpuscle (dermis)
Ruffini endings (dermis)
Merkel discs (epidermis basal)
Pacinian corpuscle (deep in dermis)
Free nerve endings (dermis into epidermis)
What are meisnners corpuscles sensitive to?
Light touch.
What are Pacinian corpuscles sensitive to?
Vibration and deep pressure
What are Ruffini’s corpuscles sensitive to?
Stretch/twisting and kinesthetic sense
What are Merkel corpuscles sensitive to?
Light touch and texture
What are free endings sensitive to?
Nociception and thermal
Describe arrangement of free nerve endings?
Network of them surround hair follicles and attach to their external root sheath -sensitive to hair movements (mechanoreceptors)
Describe structure of Pacinian corpusle?
Inner core of corpuscle formed by schwann cell lamellae, respond to pressure via displacement of capsule lamellae - depolarisation of axon
Which sensory endings are present in the dermis, what are deepest?
Meissner, Ruffini, Pacinian (deepest), free (epidermis too)
Which sensory endings are in the epidermis?
Merkel, free (dermis too)
Describe the structure of a Meissner corpuscle
Meissner corpuscles appear as coiled, spring-like structures composed of stacked, disk-like lamellar cells.
Describe the difference between the PNS and CNS regeneration
Peripheral nerve axons are able to regenerate throughout life but CNS regenerative capacity decreases form birth.
How does the PNS regenerate?
Schwann cells divide and form hollow tubes enclosed by the endoneurium.
Proximal end of nerve sends out sprouts of axons towards the tubes.
Growth factors produces by Schwann cells signals sprouts of axons to grow, 3-4mm per day regrowth.
What is Wallarian degeneration?
Distal part of the nerve axon atrophies
What are small dots on a nerve TEM?
Often collagen fibres
What type of bone has osteon structure?
Osteons constitute compact bone tissue.
Describe spongy bone structure…
Trabeculae, which are lamellae that are arranged as rods or plates.
