Nerves Flashcards
How many pairs of cranial nerves are there?
-12
What are the three gross level components of the nervous system?
- Brain
- Spinal cord
- Nerves
How many pairs of segmental (spinal) nerves are there?
-31
What are the two cells of the nervous system?
- Glia cells (90%)
- Neurones (10%)
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?
- Macroglia
- Microglia
What is the structure of neuroglia?
-Highly branched cells
What three groups can macroglia be divided into?
- Astrocytes
- Oligodendrocytes
- Schwann cells
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?
-Centre
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?
-No
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?
- Sensory loss
- Motor weakness
- Both
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
Define ganglion
-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
Define effector
-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?
- Somatic-> voluntary
- Autonomic-> 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?
- Visceral organs
- Smooth muscle
- Secretory glands
- Cardiac muscle
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?
-White rami
What are the post ganglionic neurones also called?
-Grey rami
Which axon (pre or post ganglionic) is myelinated?
-Pre-ganglionic in the CNS
How many meninges are there?
-3
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?
-Autonomic
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?
-Sweat glands
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
- Increased sweating
- Dilation of retina
What is inotrpic?
-Increased strength
What is chronotropic?
-Increased rate
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?
-Cholinergic
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?
- Perspiration
- Ejaculation
What are the general actions of the parasympathetic nervous system?
- Reduces heart rate and force of contraction
- Promotes digestion
- Promotes bodily functions such as bladder emptying
- Promotes sleep
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?
-Cholinergic
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?
-Nicotinic
Under what kind of innervation are the post-ganglionic neurones of the parasympathetic NS?
-Cholinergic
What effects do the sympathetic and parasympathetic have on the following structures, respectively:
- Eye
- Saliva
- Heartbeat
- Bronchi
- Peristalsis
- Liver
- Bladder
- Adrenal gland
- Dilates;Constricts
- Stop production;Increases production via medulla oblongata
- Inotropic + chronotropic increase; decreases via vagus nerve
- Dilates;Constricts via vagus nerve
- Inhibits via solar plexus;Stimulates via vagus nerve
- Stimulates glycogenolysis vua solar plexus;Stimulates glycogenesis and bile secretion
- Inhibits contraction;Contracts
- Stimulates adrenaline release via solar plexus
