1 organisation and classification of nerves Flashcards
CNS = central components
brain + spinal cord
PNS = peripheral components
peripheral nerves = sensory + motor neurones
brain segments
forebrain, midbrain and hindbrain
spinal chord segments total
31
divisions of PNS = pas
Peripheral = autonomic + somatic
divisions of autonomic = SP + EC
- sympathetic
- parasympathetic
- enteric (gut) and cardiac plexuses
ENS = branch of ANS = both sympathetic and parasympathetic
enteric (or intrinsic) nervous system
PNS: both autonomic and somatic have
sensory and motor components
ANS…
- involuntary
- HR, respiration, digestion, pupil contraction
somatic nervous system…
- voluntary = conscious control
- sensory info relays to muscle commands
overlap between CNS and PNS…
part of ANS lies in CNS
The nervous system 2 main divisions
CNS + PNS
symp =
fight or flight response
paraSymp =
rest and digest
neurone =
a nerve cell
dendrites
receive information = signal inputs
axon terminals
transmit information
both axons and dendrites are…
NEURITES = projections from the neurone cell body
neurons main component of brains…
grey matter
all motor neurons transmit
acetylcholine
synapses are at
axon terminals
structural classes of neurones
- unipolar
- pseudo-unipolar
- bipolar
- multipolar
unipolar structure =
one structure extends off cell body
= has 1 axon
= has no dendrites
unipolar neuron function
found in sensory ganglia
no dendrites = no input, sends signal from cell body
unipolar vs pseudounipolar
unipolar = one unbranched axon
pseudounipolar = axon branches, goes in opposite directions, branch to different targets
bipolar structure =
cell body runs in the axon
one axon + one dendrite
cell body in between the 2 projections
bipolar neuron function
- found in sensory structures
- rare
- retinal neurones
multipolar neuron structure =
one long axon, multiple dendrites
multipolar neuron function
= motor and relay neurones
get signal from lots of dendrites, transmit long distance to effector
Weigert’s stain = goes dark
stains myelin
white matter = stains darker
mostly axons = myelin stains dark with Weigert’s = tracts
grey matter = stains pale
mostly cell bodies = nuclei
In CNS cell bodies =
nucleus/nuclei -> found in grey matter of CNS
In PNS cell bodies =
ganglion/ganglia
In CNS bundle of axon =
tracts -> found in white matter of CNS
In PNS bundle of axon =
nerves
4 main groups of nuclei (neuron cell bodies) in grey matter of CNS
- SS = somatosensory
- VS = viscerosensory
- VM = visceromotor
- SM = somatomotor
somatosensory area of grey matter CNS
superficial dorsal horn
= interneurones responding to inputs from sensory neurons from body’s external tissues (somato-)
viscerosensory nuclei
deep dorsal horn
= interneurones responding to inputs from sensory neurons from internal organs (viscero-)
visceromotor nuclei
intermediate/ lateral horn
= motor neuron cell bodies supplying body’s internal organs
somatomotor nuclei
ventral horn
= motor neuron cell body supplying body’s external tissues
somato-
external tissues = somatic nervous system
viscero-
internal organs = ANS
dorsal root ganglion
posterior/back
info into CNS
sensory neurons
ventral root ganglion
anterior/front
info away from CNS
motor neurons
ganglia definition (PNS)
nodular masses of neurone cell bodies (ganglion cell) & supporting neuroglia (satellite cell)
2 types of ganglia in PNS
- sensory ganglia = cell bodies of sensory neurons (dorsal root ganglia)
- autonomic ganglia = cell bodies of motor neurons only in the ANS (involuntary)
efferent
motor
afferent
sensory
structure of peripheral nerves = 3 layers of connective tissue
- Endoneurium = covers individual axons
- Perineurium = covers individual fascicles
- Epineurium = covers the whole nerve
bundle of axons is called
a fascicle
spinal nerves are mixed
contain both sensory (afferent) and motor (efferent) fibres
neuroglia = glia/glial cells which are
supporting cells for neurons
Glial cell dysfunction implicated in
neurological disorders e.g. autism, schizophrenia, neurodegeneration
types of glial cells in CNS -> eamo
- ependymal cells
- astrocytes
- microglia
- oligodendrocytes
types of glial cells in PNS -> ss
- satellite cells
- schwann cells
astrocytes = most common
CNS
- Structural
- Glucose metabolism - glucose -> lactate then can be taken up by neurons
- Growth - produce growth factors
- BBB regulation
- Potassium clearance -> pump K+ into capillaries
- Ultimate layer of protection around brain and CNS
- Regulate neurotransmitters
ependymal cells
CNS
- Lining walls of ventricles (cavities in brain filled with CSF)
- Lining of CNS
- Produce CSF
- Have cilia on luminal side
microglia = less common
CNS
- Immune defence
- Become phagocytic
oligodendrocytes = myelinate axons
CNS
1 does about 50
most common in white matter
PNS glia = schwann cells
similar to oligodendrocytes =
- phagocytic activity
- myelinate axons in PNS
membranes wrap around axon - myelin lipid insulation
PNS glia = satellite cells
surround sensory, sympathetic, and parasympathetic ganglia
regulate external environment
similar to astrocytes
very sensitive to injury + inflammation
myelination occurs in both…
CNS (oligodendrocytes) and PNS (schwann cells)
process of myelination
wrap axon in spiral of concentric layers of fatty myelinated membrane
myelination ability for schwann cells vs oligodendrocytes
schwann cell (PNS) = only one part of one axon
oligodendrocytes (CNS) = around several full axons
unmyelinated axon
= not naked! still associate with schwann cell
- have supporting schwann cell
- axon lies in channel called mesaxon
- one schwann cell can support several axons
classifying demyelinating disease = damage to myelin sheath
- Demyelinating myelinoclastic
2. Demyelinating leukodystrophic
Demyelinating myelinoclastic =
secondary cause, damage due to toxins
Demyelinating leukodystrophic =
primary cause, damage due to abnormal myelin, degenerates
genetic causes, some idiopathic
MS = common demyelinating disease in CNS
aetiology = autoimmune
- Environmental/genetic factors lead to loss of tolerance to self-proteins
- Inflammation and injury to the myelin sheath and nerve fibres
- Multiple areas of scarring (sclerosis i.e. lesions/plaques)
- Physical, mental, psychiatric problems
parasympathetic preganglionic fibre length
long, myelinated
sympathetic postganglionic fibre
long, many branches
sympathetic preganglionic fibre
short, myelinated
parasympathetic postganglionic fibre
short, few branches
neurotransmitter preganglionic
symp = ACh parasymp = ACh
neurotransmitter postganglionic
symp = noradrenaline (=speed up response) parasymp = ACh
what is nerve classification based on
- fibre diameter
- conduction velocity
two nerve classification systems are
= applied to both somatic + autonomic
letters A, B, C = motor fibres + some non-muscle sensory fibres
roman numerals I, II, III, IV = sensory fibres from muscle
nerve classification I, II, III, IV
I = fastest
for sensory motor afferents
from dorsal root = sensory neurons
nerve classification A, B, C
A = fastest
for motor efferents
from ventral root = motorneurons
exception for nerve classification
non-myelinated sensory fibres are frequently referred to as C-fibres, not type IV
nerve conduction velocity (NVC)
-> greater the axon diameter and extent of myelination, the faster the conduction velocity
- A = ~120 m/sec; B = ~18 m/sec; C = 0.5-2.0 m/sec
* I = 75-120 m/sec; II = 35-75 m/sec; III = 5-35 m/sec; IV = 0.5-2.0 m/sec
NCV myelinated vs non-myelinated
Myelinated fibres thick (>4µm) - higher NCV than non-myelinated fibres thin (<2µm)
classifications of axons from skin
- A-alpha – group 1 – proprioceptors of skeletal muscle
- A-beta – group 2 – mechanoreceptors of skin
- A-delta – group 3 – pain or temperature
- C – group 4 – temperature, itch and pain
B = preganglionic sympathetic C = postganglionic sympathetic
sensory receptors classified by location
- Exteroceptors – external surface
- Interoceptors – internal organs
- Proprioceptors – internal, but concerned with position of muscles, tendons, joints
sensory receptors classified by stimulus detected
- Mechanoreceptors – touch, pressure, vibration, stretch
- Thermoreceptors – hot, cold, temperature change
- Photoreceptors - light
- Chemoreceptors – chemicals
- Nociceptors – pain (usually chemicals)
nociceptors detect…
pain
sensory receptor ending = muscle spindle
skeletal muscles – stretch – non-adapting
sensory receptor ending = free endings, unencapsulated
connective tissue, joints and skin – pain/touch/pressure and light – slow or fast adapting
sensory receptor ending = Meissner’s/ Krause’s bulbs
oral mucosa, lips, genitalia, fingertips – touch, vibration, light pressure – rapid adapting
sensory receptor ending = Ruffini organs
deep dermis, ligaments, joint, cartilage – stretch, deep pressure – very slow adapting
