Nerves Flashcards
4 types of tissue in the human body
Nervous, epithelial, connective, muscle
Overall function of the nervous system
Communication, regulates internal events, memory, external behaviour, sensations, perceptions, emotions
Function of organs of the nervous system
receive and process internal/external information, and send signals to initiate a response. Organs include brain, spinal cord, receptors of sensory organs.
2 main divisions of the nervous system
CNS (brain and spinal cord) and PNS (all other nervous tissue outside the CNS and ENS)
2 functional systems within PNS
Somatic and autonomic / visceral NS
Function of CNS
Integrates, processes and coordinates sensory input and motor commands
Function of somatic nervous system
Regulates voluntary control over skeletal muscle
Function of autonomic NS (ANS)
Controls automatic activities like heart rate and breathing
Divisions of ANS
Parasympathetic and sympathetic divisions
Function of sympathetic NS (division of ANS)
Can act on smooth muscle, cardiac muscle, glands and adipose tissue when immediate action is required during the fight or flight response. Can increase the rate of functions.
Function of parasympathetic NS (division of ANS)
Rest and digest - regulates less urgent processes such as digestion, waste disposal, production of bodily fluids etc by control of smooth muscle, cardiac muscle and glands. Regulates the baseline rate of processes.
2 types of cells in the nervous system
neurones which are embedded in a mass of (neuro)glial cells
Function of neurones / nerve cells
They are the functional unit of NS which are specialised for intercellular communication
Function of glial / neuroglial cells
Support, protect, provide nutrients and immune function to neurones.
Which part of the PNS carries sensory information to the CNS
Afferent division
Which part of the PNS carries motor commands from the CNS to effectors?
Efferent division
Why do neurons have a high metabolic rate?
High energy demand required to generate and propagate AP
Basic structural features of neurons
dendrites, large cell body, single axon, terminal boutons
What are dendrites?
Highly branched processes that extend away from the cell body. They receive information from synapses / receptors and convey it to the cell body.
Features of the neuron large cell body
Large and prominent nucleolus (ribosome synthesis), nissl bodies, numerous mitochondria.
What are nissl bodies?
Clusters of RER surrounded by free ribosomes. Located in cell body of neurons.
Why do neuron cell bodies have a granular appearance and stain darkly?
High density of nissl cell bodies and other organelles
What is grey matter?
Area in CNS where cell bodies of neurons are located
What is white matter?
Area in CNS where the myelinated axons are
What gives grey matter its distinctive colour?
High density of nissl bodies present in neuronal cell bodies.
Structure and function of axons
Long processes extending from the cell body that are specialised to rapidly propagate APs toward axon terminals.
Which neurons have myelinated axons?
All neurons in the CNS, Some neurons in PNS.
Where are terminal boutons located?
Foot of branches in the axon terminal
Function of terminal boutons
they are communication junctions that form synapses with other neurons / effector organs. Location where electrical signal is converted into a chemical signal in the form of a neurotransmitter.
Functional property of all neurons
Excitability
Why are neurons excitable cells?
Due to small difference in charge between inside and outside of cell which enables the generation of an AP
What are neuroglia?
Highly branched cells occupying space between neurons.
4 neuroglial cells found in the CNS
Ependymal cells, astrocytes, microglia, oligodendrocytes
2 Neuroglial cells found in the PNS
Schwann cells and satellite cells
What cell type are ependymal cells?
Simple ciliated cuboidal epithelium
Where are ependymal cells located?
Lining fluid-filled cavities in the brain (ventricles) and spinal cord
What feature do ependymal cells display in place of a basement membrane?
They taper into long processes that merge with the underlying tissue (astrocytes)
Function of ependymal cells
Move cerebrospinal fluid (CSF) and regulate its composition (using cilia and microvilli)
Structure of astrocytes
Large, star-shaped cells with long processes that wrap around neurones and capillaries in the CNS
Which neuroglial cell is the largest and most numerous in the CNS?
Astrocytes (pack spaces between neurones and support cells)
Which neuroglia form the blood-brain barrier?
Astrocytes
Function of astrocytes
Provide mechanical support to neurons in the CNS. Regulate the chemical environment in the CNS by mediating the exchange of metabolites/nutrients between neurons and the vascular system (blood-brain barrier)
What are microglia?
Small, highly branched cells in the CNS that have a phagocytic capacity
Which neuroglia is derived from a monocyte / macrophage lineage?
Microglia
Function of microglia
Can respond to tissue damage by transforming into large, phagocytic cells which remove invading microbes and dead cells from the CNS.
Which is the predominant neuroglia of white matter in the CNS?
Oligodendrocytes.
Function of oligodendrocytes
Form myelin sheaths around all CNS axons which provides structural and metabolic support (increases speed of AP propagation).
Comparison of oligodendrocytes and Schwann cells
Both form myelin sheaths but oligodendrocytes are located in CNS while Schwann cells are located in the PNS. An oligodendrocyte can contribute to the myelination of over 50 axons whereas Schwann cells only contribute to the myelination of a single axon (one Schwann cell can have multiple non-myelinated neurons in its cytoplasm however).
Where are most cell bodies located in the CNS?
In grey matter
Where are most cell bodies located in the PNS?
Ganglions
What are ganglions?
Aggregations of neuronal cell bodies located near the spinal column
Where are satellite cells located?
In PNS in ganglions on the surface of neuronal cell bodies
What are satellite cells?
Flattened cells that cover the surface of neuronal cell bodies
What is the presumed function of satellite cells?
Structural and functional protection of PNS cell bodies
Function of Schwann cells
Form myelin sheath around PNS axons, and can envelope multiple non-myelinated, small diameter PNS axons in its cytoplasm.
Which neuroglia are Schwann cells similar to?
Oligodendrocytes
Function of Schwann cells
Protection, structural and metabolic support
How is a myelin sheath created around PNS large diameter axons?
The axons are gradually wrapped in the Schwann cell membrane
What is the axon hillock?
Triangular part of neuronal cell body that connects it to the axon
Type of neuron found in cerebellum
Purkinje cell - lots of dendrites and one axon demonstrates ability to collect information from different sources and coordinate it into one response
Type of neuron found in retina
Bipolar cell - central cell body, almost symmetrical appearance. One input, one output.
Type of neuron located in the dorsal root
Sensory neuron - cell body extends out from the middle of the cell. The cell bodies create the gray matter, while the myelinated axons are in the white matter.
Which nerves are part of the peripheral nervous system?
Spinal nerves and cranial nerves
Which part of the peripheral NS is known as the autonomic NS?
Visceral efferent
Which part of the peripheral NS contain sensory neurons?
afferent
Which part of the peripheral NS contains motor neurons?
Efferent
How many pairs of spinal nerves are there?
31 pairs - 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.
What is a dermatome?
An area of skin supplied by a single spinal nerve.
What is a myotome?
A group of muscles innervated by a single spinal nerve.
What does each spinal nerve contain?
They are mixed - contain sensory/afferent nerves and motor/efferent nerves.
How are groups of nerves classified?
Into plexuses that supply particular regions of the body
3 plexuses of the spinal nerves
Cervical plexus, brachial plexus, lumbosacral plexus
What does the cervical plexus innervate?
The diaphragm, shoulders and neck
What does the brachial plexus innervate?
Upper limbs
What does the lumbosacral plexus innervate?
Lower extremities
What are the 12 pairs of cranial nerves?
I - Olfactory
II - Optic
III - Oculomotor
IV - Trochlear
V - Trigeminal
VI - Abducens
VII - Facial
VIII - Vestibulocochlear
IX - Glossopharyngeal
X - Vagus
XI - Accessory
XII - Hypoglossal
Function of cranial nerves
Provide sensory and motor nerve supply to head and neck
Which is the only cranial nerve to leave the head and neck?
CN X - Vagus nerve travels into the thoracic and abdominal cavities to provide parasympathetic supply for viscera.
Which cranial nerves contain autonomic nerve (parasympathetic) fibres?
CN III (Oculomotor), VII (facial), IX (Glossopharyngeal), X (vagus)
Function of afferent/sensory nerves?
carry information from the periphery to the CNS
Which nerve division of the peripheral NS is associated with sensations/perceptions?
Somatic afferent nerves (visceral afferent nerves do not usually give rise to sensation as they are from internal organs)
Function of efferent/motor nerves?
Carry information from the CNS to the periphery which causes actions (muscle contraction, gland secretion)
Which division of the peripheral NS controls voluntary muscle?
Somatic efferent
Which part of the peripheral NS controls smooth and cardiac muscle and some glands?
Visceral efferent / ANS
What is the endoneurium?
Delicate connective tissue layer surrounding Schwann cell-axons in peripheral nerves.
What is the perineurium?
(condensed collagenous) Connective tissue layer surrounding each fascicle in peripheral nerves.
What is the epineurium?
Loose collagenous connective tissue that binds fascicles together to form the outermost layer of peripheral nerves.
What is a fascicle?
A bundle of nerve fibres. A collection of fascicles forms a nerve.
What is a C nerve fibre?
An unmyelinated, small diameter nerve fibre. Usually sensory neurons and some autonomic nerves.
What is a AB (A beta) nerve fibre?
Myelinated, large diameter sensory neuron.
What is an Ad (delta) nerve fibre?
A myelinated, small diameter sensory neuron.
What does axon calibre refer to?
The diameter and myelination of an axon
Name of the neuron cell body
Perikaryon
How does the lipid-solubility of a local anaesthetic affect its potency?
More lipid soluble LAs require a lower dose because they diffuse more readily into the myelin sheaths of myelinated neurons. E.g. lidocaine is less lipid soluble so requires a higher dose.
How does the diameter of a neuron affect the dose of LA required to block it?
A larger diameter neuron requires a higher dose compared to a small diameter neuron which is blocked at a lower concentration.
How does myelination affect the dose of LA required?
Myelinated neurons are more easily blocked and require a lower dose because the LA (which is lipid soluble) pools within the myelin sheath.
What is differential block?
The differing speed at which axons are blocked by local anaesthetics. Autonomic fibres are blocked first followed by sensory, then motor. Smaller diameter axons and myelinated axons are most susceptible to LAs.
