Flashcards in Nerves Deck (88):
What are the three gross level components of the nervous system?
How many pairs of cranial nerves are there?
How many pairs of segmental (spinal) nerves are there?
What are the two cells of the nervous system?
-Glia cells (90%)
What are the two groups of neurones and in which direction do the carry impulses?
-Sensory/afferent fibres carrying impulses towards the CNS
-Motor/efferent fibres carrying impulses away from CNS
What is the function of the neuroglia?
-They are the 'glue' of the nervous system
What two divisions of neuroglia are they?
What is the structure of neuroglia?
-Highly branched cells
What three groups can macroglia be divided into?
What are the functions of the astrocytes?
-Support cellular matrix of the nervous system
-Give shape to the brain and spinal cord
-Act as phagocytes
-Breakdown glucose->lactate for neuronal nourishment
-Comprise the blood brain barrier
What is the function of the oligodendrocytes?
-Myelinate CNS axons (upto 250 axons/cell)
What is the function of schwann cells?
-Myelinate PNS axons (one axon/schwann cell)
When are microglia present in the nervous system?
-When there is inflammatory insult to the CNS
What are the functions of microglia?
-Act as immune surveillance cells of CNS
-Act as phagocytes
What are ependyma?
-Cilia-like projections which line the ventricles and central canal of the spinal cord for circulation of CSF
What is the function of the satellite cells?
-Provide physical support of PNS neurones
What is a dendrite?
-Projections from the cell body which receive stimuli from environment or other neurones and carry impulse to cell body
Where is the nucleus located in the cell body?
What is nissl substance?
-aggregations of rER
What is the function of the rER and golgi in the cell body of a neurone?
-rER for protein synthesis
-Golgi for packaging of transmitters into vesicles
Are all axons myelinated?
When would an unmyelinated neurone be better?
-When the axon has a diameter<1um the impulse will travel faster
Where is the initial segment of an axon located?
-Directly next to the cell body
What is the conduction of electrical impulse correlated to?
-The level of axonal myelination-> CV=6FD
What makes up grey matter in the CNS?
-Collections of cell bodies
What are ganglia?
-Collections of cell bodies in the PNS
Do schwann cells just wrap themselves around an axon once?
-No it can be up 100x around
Where is the electrical impulse generated from?
-The initial segment
What makes up white matter?
-Collections of ascending and descending axons as well as glial cells
How are neurones arranged in the spinal cord?
-The grey matter takes a butterfly shape inside white matter and has dorsal and ventral horns which contain large cell bodies
What two roots serve the grey matter?
-Dorsal nerve root
-Ventral nerve root
What is the ventral median fissure?
-The central point at which white matter converges
What neurones do the ventral cell bodies belong to?
-Spinal motor neurones which innervate muscle
What does the dorsal nerve root do?
-Carries sensory fibre impulses to the grey matter
Why is white matter white?
-Due to its high myelin content
How are the peripheral nerves anatomically arranged?
-Axons are arranged into fascicles which make up the peripheral nerve
What is epineurium?
-Connective tissue which ensheaths the entire nerve
What is perineurium?
-Connective tissue which ensheaths fascicles and between fascicles carrying interfascicular blood vessels
What is endoneurium?
-Connective tissue which surrounds a single axon and carries capillaries
How does a nerve react to an axon being severed?
-Proximal segment seals up to prevent leakage of contents
-A nerve stump is formed
-Distal segment is cut off from nutritional support
-Distal segment dies and undergoes wallarian degeneration with infiltration of microglia
-Cell body puffs up with increased contents
-Nucleus is displaced from the central position to the periphery (known as chromatolysis)
What is multiple sclerosis characterised by?
-Selective and patchy loss of myelin sheath
-Axonal destruction and overgrowth of glial tissue
Name some diseases of degenerative changes in peripheral nerves
-Peripheral neuropathy (non-inflammatory disease of peripheral nerves)
-Neuritis (Inflammatory disease)
What are the results of degenerative changes in peripheral nerves?
Can nerves be regenerated?
-They do not undergo mitosis but damaged peripheral nerves with axons still attached to the cell body can undergo regeneration
Define afferent neurone
-Neurone which carries signals from periphery to CNS, ie a sensory neurone
Define efferent neurone
-Neurone which carries impulse from CNS to periphery/effector, ie a motor neurone
-Collection of neuronal cell bodies in the PNS
Define pre-ganglionic neurone
-Neurone immediately proximal to the ganglion
Define post-ganglionic neurone
-Neurone immediately distal to the ganglion
-Target organ through which the nervous system exerts its action
State the divisions of the nervous system
-CNS and PNS both have Afferent and Efferent
-Efferent split into Somatic and Autonomic
-Autonomic split into sympathetic, parasympathetic and enteric
Which of the efferent divisions is voluntary/involuntary?
What are the general actions of the autonomic nervous system?
-Constancy-> establishes and maintains homeostasis of the internal environment through regulating cardiovascular, digestive respiratory and thermoregulatory systems
-Control intermittent change in bias
What are the effector organs of the autonomic nervous system?
How are the synapses divided between the sympathetic and parasympathetic nervous systems?
-Equally in a series arrangement
What is the general layout of the autonomic nervous system?
-Always 2 neurones arranges in series
-One with cell body in CNS and another with cell body in PNS
What are the pre-gangloinic neurones also called?
What are the post ganglionic neurones also called?
Which axon (pre or post ganglionic) is myelinated?
-Pre-ganglionic in the CNS
How many meninges are there?
What is meant by organs receiving dual innervation?
-Receive innervation from both the parasympathetic and the sympathetic nervous systems
Which nervous system are most organs innervated by?
How do the effects of the sympathetic and parasympathetic relate to each other?
-The effects are often reciprocal
What is autonomic tone?
-The balance of inputs and outputs between sympathetic and parasympathetic and the dominance that arises
Which glands receive only sympathetic innervation?
What is another name for the sympathetic nervous system?
-'fight or flight' system
When is the sympathetic nervous system dominant?
-During stressful situations
-What are the overall results of the sympathetic NS?
-Expenditure of energy
-Diversion of blood to heart and muscles
-Increase in heart rate, inotropic and chronotropic
-Increase in bp
-Reduced blood flow to gut and skin
-Dilation of retina
What is inotrpic?
What is chronotropic?
Where do nerve fibres of the sympathetic NS exit the CNS?
-Spinal cord only
Where are the cell bodies of the sympathetic NS located?
-All 12 thoracic segments of the spinal cord (T1-12)
-The first 2 lumbar segments
Where are the pre-ganglionic neurones of the sympathetic NS located?
-In the spinal cord
Pre-ganglionic sympathetic nerve fibres are under what kind of innervation?
What type of receptors do the post ganglionic neurones of the sympathetic nervous system express?
-Express nicotinic receptors
What kind of innervation are post ganglionic neurones of the sympathetic NS under?
-Mostly noradrenergic and some adrenergic
Describe the lengths of the pre/post ganglionic neurones of the sympathetic NS?
-Short pre-ganglionic neurones and long post-ganglionic neurones (for the majority)
What receptors do target organs of the sympathetic NS possess?
-a and b
What are the three possible levels of neurone termination in the sympathetic NS?
1) May synapse in chain at a level corresponding to the level of origin (paravertebral)
2)May synapse at a different level to origin up or down the chain
3)May not synapse in paravertebral chain but at effector organs (splanchnic nerves)
-What two exceptions of sympathetic post-ganglionic fibres are not noradrenergic?
What are the general actions of the parasympathetic nervous system?
-Reduces heart rate and force of contraction
-Promotes bodily functions such as bladder emptying
Where do the nerve fibres of the parasympathetic NS leave the CNS
-Through 4 cranial nerves and the sacral segments S2-S4
Describe the lengths of the pre/post ganglionic neurones of the parasympathetic nervous system
-Long pre ganglionic neurones and short post ganglionic neurones
Under what type of innervation are pre-ganglionic neurones of the parasympathetic NS?
Where are most post-ganglionic neurones located?
-In the walls of the effector organ
What receptors do post-ganglionic neurones of the parasympathetic NS express?
Under what kind of innervation are the post-ganglionic neurones of the parasympathetic NS?