Nervous System Flashcards
Development
- 3rd week of development ectoderm of dorsal midline thickens to form the neural plate
- Neural plate > Neural tube > CNS neurons
- Between neural plate / ectoderm > neural crest > peripheral neurons, PNS support cells (Schwann cells and satellite cells), adrenal medulla, meningeal coats (pia mater and arachnoid), melanocytes and facial cartilage
- *Neurons differentiate and stop dividing -> cannot repair themselves / regenerate = problem with neurodegenerative disease
- PNS - ganglia, nerves/endings, receptors on neurons, peripheral targets
- CNS - Nuclei or cortices, nerves, nerve endings, receptors on neurons (or glia, which support migrating neurons)
Neurons
- Cannot regenerate
- Vary in morphology and transmitter content
- Receive, integrate, conduct, transmit information
- 3 types:
- Multipolar motor neurons
- Pseudo-unipolar/bipolar sensory neurons
- Integrative neurons
- All made of dendrites, cell body, axon:
- Dendrites
- Increase surface area
- Dendritic spine “plasticity” to accommodate function (depends on stimulus)
- Receptors on dendrite and proteins hold synapse together
- Generally receive signal
- Sums excitatory/inhibitory signals
- Cell body
- Synthesizes proteins
- Nissl bodies (neurons with lots of RER and ribosomes, euchromatic nucleus, prominent nucleolus, big Golgi)
- Provides protein to axon (which lacks Nissl bodies)
- Axon
- Transmit info to target cell
- No Nissl, need cell body for protein synthesis
- Extensive cytoskeleton for support and axonal growth regulation (intermediate filament and microfilament)
- Microtubules for transport
- Fast transport active:
- Kinesin for anterograde transport (cell body->terminal)
- Dynein for retrograde transport (terminal->cell body) of vesicles, endosome, mitochondria)
- Slow-cytoskeleton elements, proteins
- Microfilament associated with Vesicle release
- Fast transport active:
- Dendrites
Chemical Synapse
- Pathway
- Action potential > calcium enters pre-synaptic membrane > synapsin I phosphorylated > vesicles released from actin microfilaments > dock vesicles to pre-synaptic membrane via VAMPs and t-snares > fusion and exocytosis > NT released via vesicles
- After exocytosis, NT can’t linger in cleft (or else will continuously interact with NT receptors at post-synaptic cleft)
- NT in cleft are:
- Degraded by enzymes (ie acetylcholine)
- Taken up by pre-synaptic terminal (norepinephrine, dopamine, glutamate)
- Taken up by glia (astrocytes)
- Diffuse away
- Exocytosis vesicles:
- Fused with early endosome > vesicular membrane recycled
- Retrograde transport > degraded by lysosome
Diseases Related to Synaptic Transmissions
o Botulinum and tetanus
o Lambert Easton Myasthenic Syndrome (LEMS)
o Congenital myasthenic syndromes
Peristalsis
- NT released by clusters of vesicles along the axons (aka varicosities)
- Pathway
- Action Potential > axon depolarized > vesicles release NT along the axon > lots of NT released
CNS support cells:
Ependymal
Astrocytes
Oligodendroctyes
Microglia
- Ependymal
- Ciliated > facilitate CSF movement
- Line central canal and ventricles
- Adhering junctions
- CSF can diffuse between brain/spinal cord and ventricles/central canal
- Tight junctions
- Choroid plexus
- Modified so blood can pass through choroid plexus but not to brain/spine
CNS support cells:
Ependymal
Astrocytes
Oligodendroctyes
Microglia
- Intermediate filaments (glial fibrillary acid protein)
- Between neurons and different cell type
- Found in electrically active areas > regulate ionic environment via gap junctions
- Nodes of Ranvier
- Initial segment
- Surround/regulate synapse
- Segregate synapse
- Regulate NT receptors
- Project to capillaries > control tightness of blood/brain barrier & blood flow
- Immune response
- Remove neuronal debris
CNS support cells:
Ependymal
Astrocytes
Oligodendroctyes
Microglia
- Unmyelinated > no ensheathment
- Myelinated
- Initial segment > axon terminal
- Nodes of Ranvier
- A lot of ion channels
- Internodal segments are myelin between nodes
- Paranodal region is the edge of the sheath
- Site of signal between axon and oligodendrocyte
- Loss of signal > MS / AD
- Sheath formation
- Dark lines, dense lines
- Inner membrane faces
- Light lines, intraperiod lines
- Outer membrane faces
- PLP (proteolipid protein)
- Holds intraperiod line together
- Dark lines, dense lines
- *1 oligodendrocyte: many internodes
CNS support cells:
Ependymal
Astrocytes
Oligodendroctyes
Microglia
- Small phagocytes that remove neuronal debris
- Immune response > recruit WBC across blood/brain barrier
PNS support cells
Satellite cells
Schwann Cells
Cell bodies
PNS support cells
Satellite cells
Schwann Cells
- Associated with peripheral nerve axons
- Surround all peripheral neurons (both myelinated and unmyelinated)
- 1 Schwann cell: 1 internode (associated with 1 axon)
- 1 axon surrounded by several Schwann cells, many internodes
- Sheath formation
- Dark lines, dense lines
- Inner membrane faces
- Light lines, intraperiod lines
- Outer membrane faces
- Po (transmembrane glycoprotein)
- Holds intraperiod line together
- Dark lines, dense lines
- Connective tissue coats
- Endoneurium
- Perineurium
- Epineurium
- Basal lamina
Nerve Injury
- Mature neurons can’t divide > injury = serious
- Regeneration depends on arrangement of glial cells and connective tissue coats
- In PNS, if cell body, basal lamina, endoneurium, perineurium, epineurium are intact > functional reconnections may form > axons may regrow along tubes of connective tissue
- Lesion:
- Close to axon terminal > can regenerate
- No tube of connective tissue > cannot regenerate
- Lesion:
- In CNS, nerve and myelin degenerate on either side of the lesion > cell death
- Unable to regenerate because no connective tissue coat?
Sympathetic Distribution to the Trunk
Enter paravertebral ganglion via white ramus communicans
Synapse in corresponding paravertebral ganglion
Exit to corresponding spinal nerve
- Pre-ganglionic multi-polar motor neuron at lateral horn of T2
- T2 ventral root
- T2 spinal nerve
- T2 ventral ramus
- T2 white ramus communicants
- Paravertebral ganglion > SYNAPSE
- Post-ganglionic multi-polar motor neuron at T2 paravertebral ganglion
- T2 gray ramus communicans
- T2 ventral ramus
- Blood vessels / sweat glands
Sympathetic Distribution to the Upper Limb
Enter paravertebral ganglion via white ramus communicans
Ascend sympathetic chain to corresponding ganglion and synapse
Exit to corresponding spinal nerve
- Pre-ganglionic multi-polar motor neuron at lateral horn of T2
- T2 ventral root
- T2 spinal nerve
- T2 ventral ramus
- T2 white ramus communicants
- T2 paravertebral ganglion
- Ascend to C5 paravertebral ganglion
- C5 Paravertebral ganglion > SYNAPSE
- Post-ganglionic multi-polar motor neuron at C5 paravertebral ganglion
- C5 gray ramus communicans
- C5 ventral ramus
- Blood vessels / sweat glands
Sympathetic Distribution to the Lower Limbs
Enter paravertebral ganglion via white ramus communicans
Synapse in corresponding paravertebral ganglion
Exit to corresponding spinal nerve
- Pre-ganglionic multi-polar motor neuron at lateral horn of L1
- L1 ventral root
- L1 spinal nerve
- L1 ventral ramus
- L1 white ramus communicants
- L1 paravertebral ganglion
- Descend to L5 paravertbral ganglion > SYNAPSE
- Post-ganglionic multi-polar motor neuron at L5 paravertebral ganglion
- L5 gray ramus communicans
- L5 ventral ramus
- Blood vessels and glands
Somatic Nervous System
Mapped very specifically
Can sense exactly where pain is coming form
Visceral Afferent
Sympathetic motor innervation of the heart
Spinal nerves do NOT innervate organs (three branches out of ganglion)
Follow course taken by efferents
Ascend and synapse at higher paravertebral ganglion > post-ganglion does not go to spinal nerve, but rather goes internally to the organs
Post-ganglionic sympathetic route > unmyelinated but doesn’t go to spinal nerve > not gray ramus… visceral nerve to the heart > heart beats faster (sympathetic response)
Ischemia
Visceral afferent pathway
Exact opposite pathway
Heart ischemia > visceral nerve > sympathetic ganglion > descend down > white ramus communicans > ventral ramus > spinal nerve > dorsal root ganglion > T2 dorsal horn >> neurons in T2 fire > brain perceives pain as coming from arm or chest side (when true pain is coming from the heart) = referred pain
Autonomic NS
- Carries signals to/from viscera
- Sensory Neurons
- 1 neuron pathway
- Same as motor until spina nerve > follows dorsal root to dorsal horn
- Do NOT use spinal nerves
- Motor Neurons
- 2 neurual pathway
- Pre ganglionic
- Post ganglionic
- 2 neurual pathway
