Development of Nervous System Flashcards
Cranial nerves
12 pairs
Spinal cord stops
Between L1 and L2. Vertebral column continues - inside canal below L2 has portions of spinal roots - not yet spinal nerves, as they have not yet exited vertebrae.
The vertebral canal
Does not separate central and peripheral systems. There are components of both systems in vertebral canal.
Nervous system
Branches to central and peripheral
Peripheral nervous system
PNS - branches to:
Autonomic nervous system
Somatic nervous system
Autonomic ns
Communicate with internal organs and glands Splits to: Sympathetic division (arousing) Parasympathetic division (calming)
Somatic ns
Sense organs and voluntary muscles.
Splits to:
Sensory (afferent - sensory input)
Motor (efferent - motor output)
Structural division - CNS
brain & spinal cord –develop from neural tube
Structural division - PNS
all other NS structures that connect the CNS with the rest of the body
–develop from neural crest and CNS outgrowths
Somatic - function
receives information from and responds to external world
–innervates structures that develop from somites
Visceral - function
Visceral
–innervates organ systems & its elements
–detects and responds to information within body
CNS - Neuron
Group of neuronal cell bodies=
–Nucleus
CNS Glia
Astrocyte, oligodendroglia, microglia
PNS - Neuron
Group of neuronal cell bodies - ganglion
PNS - Glia
Schwann cell (axon associating glia - myelination).
CNS organization
Covered by 3 meninges - dura, arachnoid, pia
Sub arachnoid space
have trabeculae connecting arachnoid and pia. Serves as a path for vasculature (vasculature found here). Deep to arachnoid layer. Also filled with cerebrospinal fluid.
PNS organization
3 connective tissues
-Epineurium, perineurium, endoneurium. Has fascicles surrounded by perineurium (bundles of axons). Individual axons have endoneurium. Epineurium covers the whole thing.
Dendrites
Stimulated by environmental changes or other cell activity.
Cell bodies
Have nucleus, mitochondria, ribosomes, other organelles and inclusions.
Axon
Conducts nerve impulse towards synaptic terminals.
Terminal Boutons
(synaptic button) affect another terminal or effector organ (muscle/gland).
Spinal nerves
Inner area = grey matter. Posterior and Ventral horns in this shape. This is where you find cell bodies in spinal cord (also other stuff as well). Lateral horns also present.
Dorsal root ganglion
Have PNS cell bodies, which go into the dorsal horn. These are principally information in - mainly sensory/afferent neurons.
Ventral root ganglion
PNS cell bodies. These are information out. Efferent motor neurons.
Spinal nerve
Where dorsal root and ventral root come together. This exits vertebral column at intervertebral foramen. This will branch to posterior and anterior ramus.
Contralateral
Left side of brain controls right side.
Ipsilateral
Right side of brain controls right side.
Bilateral
This means that both the left and right members of a pair of cranial nerves are innervated by the motor strip areas of both the left and right hemispheres.
Decussation
Crossing from one side to the other that involves axomal path. Axons from left side and axons of right cross without mixing so that cell bodies control muscles on opposite sides.
Commissure
Axons that connect one side to the corresponding structures on the other side (of brain). Primary sensory cortexes connect in brain through corpus callosum (right and left coordination helped).
Postganglionic cells
Sit in sympathetic chain or the prevertebral ganglia (via splanchnic nn)
Motor (efferent)
General - how we affect environment
Autonomic NS
Sympathetic, parasympathetic, enteric
Parasympathetic
2 neuron chain. Preganglionic. S2 to S4 (cord level is higher than vertebral - there is a separation during development). These will exit S2 to S4 - or cranial nerves (CNS nuclei). Cranial-sacral. Post-ganglionic - 4 cranial ganglia and ganglia in the walls of organs (everything below the head).
Sympathetic
2 neuron chain. Preganglionic - T1 to L2 (lateral horn). Thoracolumbar nerves (where cell bodies are). Connect to postganglionic cells. Postganglionic cells in ganglion near boutons of preganglionic cells. **Only cell body is in CNS.
2 neuron system
Modify - can now modify a signal at a given synapse. This system gives you control for this.
Somatic plexis
Cervical plexus (C1-C4 spinal nerves). Brachial plexus - C5 to T1. Lumbar = L1 to L5 Lumbosacral plexus = combo of S1 to S4.
Visceral plexis
All part of autonomics (control viscera). Cardiac, esophogeal, pulmonarytracheal, prevertebral (T5 to T12 + some lumbar - these have special names in thoracic region- greater and lesser splanchnic nerve, alise splanchnic nerve). Also some with S region.
All plexis are
peripheral nerves.
Development of NS
Occurs during weeks 3 and 4.
Cranial and caudal neuropores
Openings at either end of neural tube.
Embryonic Ectoderm
Epidermis
Neural tube (neuroectoderm)
Brain and spinal cord CNS. Caudal end is spinal cord, cranial is brain. Neural groove will lead to ventricular system.
Neural canal
Neural canal: ventricles of brain & central canal of spinal cord
Neural crest
Neural crest :
-Dorsal root/autonomic/CN ganglia
-Bones of face (viscerocranium)
-Melanocytes
-Schwann cells
-Leptomeninges (arachnoid & pia
mater)
-Adrenal medulla cellsLuminal side of neural canal
Neuroepithelial cells - pseudostratified columnar cells. As you go farther externally, you start to see mesenchyme.
Mesenchymal area of neural tube.
Lead to development of part of meninges (Dura mater - arachnoid and pia come from neural crest).
Leptomeninges
Arachnoid and pia (from same source - neural crest).
Spinal cord zone reference
Luminal surface - right next to it you have ventricular (actively dividing) zone - neuroepithelial layer. Neuroepithelial cells divide and move deeper into intermediate zone. More pseuodstratified, and you see them differentiate into neuroblasts and neurons. This will become part of the grey matter. Outer most layer is the marginal zone. Some glial cells forming, mainly formation of white matter. Spinal meninges are superficial to all of this.
Mantle layer
Cells organize into layer on dorsal aspect in a circular fashion. These areas are called Alar plates.
Alar plates
2 of them:
Afferent (sensory functions). Will form dorsal sensory horns.
Basal plates
Anterior - form more efferent (motor function). Will form ventral motor horns.
Spinal Nerve Development
Motor nerve fibers collect into ventral nerve roots
Dorsal nerve roots (sensory) originate outside spinal cord (in DRG) derived from neural crest cells.
These processes grow into dorsal horns of spinal cord
Eventually the dorsal nerve roots meet the ventral motor roots.
Spinal nerve
Distal processes of dorsal roots join ventral nerve roots to form a spinal nerve
Dorsal root fibers = sensory
Ventral root fibers = motor
Spinal nerve contains both sensory & motor fibers
Spinal cord extension
At 3 months extends entire length of vertebral column. At the end of 5 months, the spinal cord is at 1rst sacral nerve. A newport’s spine is around L3, will end at L1.
conus medullaris
spinal cord ends between L1 + L2 vertebrae
Ventricles of the Brain
lateral, interventricular foramen, third ventricle, aqueduct of midbrain, fourth ventricle. No first and second, those are lateral. Big point is where they come from.**look into this.
Brain dev.
Same basic organization of spinal cord. Distinct alar and basal plates. Higher centers = accentuation of alar plates and regression of basal plates.
Brain dev overview.
Cells grow and divide to form swellings. Initially you have 3 primary vesicles (swellings) - forebrain (prosencephalon) , midbrain (mesencephalon), hindbrain (rhombencephalon) Then this goes to 5 secondary vesicles.
Prosencephalon
2 swellings - telencephalon leads to 2 cerebral hemispheres. Lateral ventricles
Caudal to this is diencephalon - forms thalamus (hypo, epi). Third ventricle
Mesencephalon
Nothing really happens to this. This will become the midbrain with aquaduct. First part of brain stem.
Rhombencephalon
Metencephalon - forms pons and cerebellum - upper part of 4th ventricle.
Myencephalon - medulla -lower part of 4th ventricle.
Lumen of telencephalon
Leads to formation of lateral ventricles.
Lumen of diencephalon
Leads to formation of 3rd ventricle
Mesencephalon lumen
Aquaduct
Lumen of myencephalon and metencephalon
Fourth ventricles.
Myelencephalon - alar and basal
Leads to medulla of brain. Shift of medulla walls changes position of plates so that basal plates (motor) will be medial to alar plates (sensory). Alar shift to form 3 bilateral cell columns - form afferent sensory nuclei. Same organization occurs in basal plates - efferent motor nuclei.
Metencephalon - pons
Cell bodies in basal plate medial - shifting still occurs.
Organize into 3 bilateral cell columns again.
Mesencephalon
MIdbrain - superior part of brainstem. Gets more complicated. Basal plates contain two groups of motor nuclei - marginal layer of basal plate enlarges to form crus cerebri.
Alar plates are organized posteriorly (dorsally) into two longitudinal elevations. Divides into superior & inferior colliculi
Crus cerebri
Marginal layer of basal plate (the ventral swellings).
Diencephalon
Three pairs of swellings in lateral wall of 3rd ventricle.
Caudal part of roofplate - epithalamus
Thalamus from second swelling
Hypothalamus from ventral swelling.
Alar plates form:
Thalamus
Hypothalamus - huge autonomic feature.
Basal plates form epithalamus.**
Telencephalon
Forms two cerebral hemispheres. Neural canals form the two lateral ventricles.
Cells in neural tube grow the quickest. Grows so much that it covers the diencephalon structures.
Surface grows rapidly to form the lobes as well as gyri (elevations) separated by fissures (deep grooves) and sulci (shallow grooves). cerebrum is originally a smooth structure.
Sympathetic ANS origin
All ganglia as well as the sympathetic trunk originate from neural crest cells.
Parasympathetic ANS origin
Postganglionic neurons derived from neural crest cells.
Parasympathetic ANS origin
Postganglionic neurons derived from neural crest cells.
Myelinated
Series of Schwann cells lined up along axon
Each having a wrapped coating of myelin insulating axon
Unmyelinated
Encased by Schwann cell cytoplasm
No wrapped coating of myelin surrounding axon
PNS myelination
Schwann Cells (derived from neural crest cells). Nuclei of cells pushed outward as it wraps. in CNS, you have oligodendrocytes.
One schwann cell per one internodal segment of one axon
CNS myelination
Oligodendrocytes (derived from neuroepithelial cells of spinal cord). Sends out arm extensions so it can wrap around multiple axons.
One oligodendrocyte can myelinate up to 50 axons
