Nervous System Flashcards
What are the 2 major cell types of the nervous system and what proportion are each of them of the total?
glia (90%) and neurones (10%)
What are the 2 types of glia?
macroglia and microglia
What shape are glia?
stellate (star shaped)
What are the macroglia within the CNS?
astrocytes, oligodendrocytes, ependyma
What makes up the largest count of macroglia in the CNS?
astrocytes
What are the functions of astrocytes?
assist transfer of nutrients and waste between neurones and blood, constitute blood brain barrier, phagocytic functions and physical support for neurones
What is the function of oligodendrocytes?
myelination in the CNS
How many axons can a oligodendrocyte myelinate at once?
up to 250
What is the function of ependyma?
line the ventricles and central canal of spinal cord for the circulation of cerebrospinal fluid
What are microglia used for?
immunity and inflammation
What are the macroglia of the PNS?
Schwann cells and sattelite cells
What is the function of schwann cells?
myelination of peripheral nerve axons
How many axons can a Schwann cell myelinate at once?
1 Schwann cell can myelinate 100microns of 1 axon
What is the role of satellite cells?
physical support of neurones
What are dendrites for?
increase the surface area of a cell body so that it can maintain contact with many cells
What are the features of cell bodies?
single, central nucleus, vary in shape, contain Nissl substance for protein synthesis and Golgi apparatus for packaging
What is grey matter?
Collections of cell bodies
Along a myelinated axon, where are the K+ and Na+ channels?
K+ channels = myelin sheath
Na+ channels = nodes of Ranvier
What is an axon hillock?
A kink in the axon, appears as an elevation of the membrane. there is a high density of Na+ channels for initiation of action potentials.
In which direction is the main transmission?
From the cell body towards the axon terminal
What does conduction velocity equal?
6 x fibre diameter
How many times can a Schwann cell wrap itself around the axon?
100 times
Name 3 diseases that can demyelinate axons
multiple sclerosis, guillain barre and diabetes
What is the relationship between diameter and conduction?
Larger diameter = faster conduction
What is the conduction along a myelinated neurone called?
Saltatory conduction
What makes up white matter?
Axons
What ensheaths a single axon?
Endoneurium
What ensheaths a nerve fascicle?
Perineurium
What ensheaths an entire nerve?
epineurium
What do we call the membrane envelopes of the brain?
Meninges
What are the layers of the meninges cells from outer to inner?
dura mater, arachnoid mater, pia mater
What happens when an axon is severed?
The proximal segment of axon seals to prevent leakage and a nerve stump formed. The distal segment is cut off from nutritional support of cell body, distal segment dies and undergoes Wallerian degeneration
What happens to reform an axon after severing?
The volume of cell body increases due to lots of protein expression.The nucleus gets pushed from centre. The axon usually regrows - Wallerian regeneration, but often ends up at the wrong target.
What is an afferent pathway?
conducting in-coming signals, periphery to CNS, sensory neurones
What is an efferent pathway?
conducting out-going signals, CNS to periphery, motoneurone or autonomic neurone
What is a ganglion?
A collection of neurone cell bodies in the PNS
How many pairs of cranial nerves do we have?
12 pairs
How many pairs of spinal nerves do we have?
31 pairs
How many autonomic ganglia pairs do we have?
25 pairs
How many sensory ganglia pairs do we have?
31 pairs
Where is the enteric nervous system?
Within the gut
What 2 systems is the autonomic nervous system split into?
parasympathetic and sympathetic
What are the features of the somatic nervous system?
voluntary, simplest layout possible, efferent neurone terminates directly on effector organ, affects skeletal muscle, inactive during REM sleep, under-developed at birth so that the environment can influence
Which of somatic or autonomic has the simplest layout?
Somatic
What are the features of the autonomic nervous system?
involuntary, fundamental for life functions, becomes active along with organogenesis, functions non-stop throughout life
Which NS is fight or flight?
Sympathetic
Which NS is rest and digest?
Parasympathetic
Which NS are sweat glands innervated with only?
sympathetic
What happens to the bladder under sympathetic control?
bladder fills, internal sphincter closes (relaxed) and detrusor muscle relaxes
What happens to the bladder under parasympathetic control?
bladder empties, internal sphincter opens (contract) and the detrusor muscle contracts
What can overactivity of the parasympathetic NS lead to?
dilated blood vessels and reduced substrate to brain causing fainting
What can overactivity of the sympathetic NS lead to?
constriction of blood vessels causing necrosis
Where does the sympathetic NS flow from and what is this called?
spinal cord only: T1-T12 and L1-L2 thoraco-lumbar division of the ANS
Which kind of matter is in the centre of the spinal cord?
Grey matter
Which horn connects with the outside of the spinal cord?
Dorsal horn
What are the 3 possible modes of termination from the spinal cord?
synapse in chain at same level as origin, synapse in chain at different level to origin or may not synapse in paravertebral chain
What are the 2 types of sympathetic effector organ receptors?
Alpha and beta (adrenergic)
How many types of alpha receptors are there?
2
How many types of beta receptors are there?
3
Name 4 cranial nerves
oculomotor, facial, glossopharyngeal and vagus
Where does the parasympathetic NS flow from?
brain and spinal cord, cranio-sacral division of ANS, cranial nerves III, XII, IX and X, and S2-S4
Which receptors are expressed on parasympathetic effector organs?
muscarinic receptors
What are muscarinic receptors blocked by?
Atropine
What are the 3 interdependent units of the nervous system?
brain, spinal cord and nerves
