plus... 100 x 10*9 neurons in our body
neurons in CNS do not have centrioles so they cannot mitotically divide
material can move from soma to/from axon (axonal transport) along tubules by little motors called kinesin (to) and dynein (from) via fast (300mm/day) or slow (5mm/day) stream mechanism.
Neuron Structure
1. Sensory neurons/afferent neurons receive external stimuli like light, sound, smell, contact, heat from the environment and convey this information to the brain/spinal cord. Sensory neurons are often unipolar with an axon that branches into two extensions; one dendritic that receives the stimulus and and one axon that transmits the sensory info to the spinal cord.
Their cell bodies are found in sensory ganglia.
Sensory neurons may be:
1. somatic: receive info about outside environment
2. visceral: receive info about internal environment
Sensory neurons exhibit:
interoceptors: monitor organ systems re stretch, pressure,
exteroceptors: monitor external environment re
touch, temp, pressure, taste, sight, hearing, etc
proprioceptors: monitor skeletal system re
position/movement
2. Motor/efferent neurons have cell bodies in the CNS. Their axons extend outside of the CNS to control muscles via a neuromuscular junction. Motor neurons is multipolar with
a single axon and multiple dendrites. May be:
1. somatic: innervate skeletal muscles
cell body in CNS...axon runs to NMJ
2. visceral: innervate all else...smooth/cardiac muscle and glands
axons of CNS motor neurons
synapse with second motor neuron
at autonomic ganglia
(preganglionic -> postganglionic fibers)
3. Interneurons are found in the CNS and serve to relay info between sensory and motor neurons. Their structure is also multipolar.
demyelination: destruction of myelin results in the loss of motor control and sensation.
functional classification of neurons
types of neuroglial (glial) cells
CNS:
1. Astrocytes:
maintain the blood brain barrier
stabilizes damaged tissue
cytoskeleton provides
CNS framework
direct fetal neuron development
regulate interstitial fluid
(ions/nutrients/Co2)
2. Oligodendrocytes:
provide myelination (membranous
wrapping) for CNS axons
via cytoplasmic "pad"
wrapping around axolemma =
myelin internodes
provide structural framework
by binding adjacent neurons
3. Ependymal cells:
line the ventricles/central canal
of brain/spinal cord and
produce CSF.
4. Microglia: roving phagocytes that
remove wastes and pathogens
PNS:
1. Schwann cells: myelinate
axons of PNS neurons
2. Satellite cells: regulate
levels of nutrients
and neurotransmitters
next up...what is an action potential and how is it initiated/propagated...
schwann cells and myelination
the myelin sheath allows electrical impulses to travel along the length of the axon quickly.
Neural Tissue
Types of
Neural Tissue
Neurons
notice pre/post ganglionic neurons of visceral motor/efferent pathway ANS
anaxonic neurons: many dendrites but no visible axons
nobody is sure what they do...
bipolar neurons: rare, tiny (<30micrometers) cells that are found in sense organs like the eye
unipolar neurons: sensory neurons of PNS with axons that may run >1 meter long! axon starts where the dendritic branches converge
multipolar neurons: two + dendrites and one axon
most common type
these are the motor neurons that convey directions to effectors
in summary...
Welcome to Dr. Kate Brilakis' Learning Portal
structural classification of neurons
blood brain barrier (bbb)
peripheral nerve regeneration =
Wallerian degeneration
in addition to above structures:
perikaryon-cytoplasm (around nucleus)
neurofibrils-neurofilament bundles
nissl bodies-RER/ribosome clusters
axoplasm-axon cytoplasm
axolemma-membrane of axon
collaterals-side branches off axon
telodendria- tiny extensions at end of axon
axon terminal-end of telodendria
(synapse interface)
c
notice single neuron of somatic efferent/motor pathway with soma in CNS and axon running to effector