Development of nervous system: Gastrulation Formation of 3 germ layers 1. Ectoderm (epidermis / neural tissue) 2. Mesoderm (muscle / CT) 3. Endoderm (epithelium of GI & resp. tracts) Neural plate formation Beginning of 3rd week notochord induces overlying ectoderm to form neural plate End of 3rd week lateral edges of neural plate form neural folds (depressed mid-region = neural groove) What is neurulation? Neural tube formation by fusion of neural folds (rostro-caudal direction) Rostral neuropore (cranial opening) & caudal neuropore are open to amniotic fluid When does closure of neuropores occur? Coincides with establishment of blood supply to the neural tube Where is the spinal cord derived from? neural tube (caudal to 4^th pair of somites) What does the alar plate become? Dorsal horn of spinal cord Sensory (afferent) What does the basal plate become? Ventral horn of spinal cord Motor (efferent) 3 zones of spinal cord development Ventricular zone: cell proliferation into neurons / macroglia Intermediate zone: neurons differentiate / form axons and dendrites (a.k.a mantle layer) Marginal zone: edge of cord where longitudinal axon fasicles grow Where is the brain derived from? neural tube (rostral to 4th pair of somites) Outline brain development from primary vesicles Forebrain - Prosencephalon - Telencephalon - Diencephalon Midbrain - Mesencephalon - Mesencephalon Hindbrain - Rhombencephalon - Metencephalon - Myelencephalon Differential growth in brain development Causes folding / bending of developing brain 3 main flexures (folds): - midbrain flexure - pontine flexure - cervical flexure CNS Gray Matter Neuron cell bodies in nuclei Astrocytes Microglia Some oligodendroglia CNS White Matter Myelinated axons (myelin formed by oligodendroglia) Where is the PNS derived from? Neural crest Peripheral nerve components Myelinated axons (covered by endoneurium) Fascicles (covered by perineurium) Nerves (covered by epineurium) Where are peripheral ganglia of the ANS derived from? Neural crest Purpose of ANS Visceral innervation Components of ANS 3 Components - sympathetic - parasympathetic - enteric Neuron systems in ANS Preganglionic neuron - gray matter of CNS Postganglionic neuron - sympathetic = autonomic ganglia - parasympathetic = visceral wall / ganglia close to organ Origins of parasympathetic fibers CN III, VII, IX, X Spinal nerves C1 - S2/S4 Origins of sympathetic fibers Spinal nerves T1 - L2 Sympathetic Preganglionic Neurons Neurons in the spinal cord lateral horn from T1-L2 or 3 Some synapse in paravertebral ganglia Others travel via splanchnic nerves to prevertebral ganglia cholinergic Sympathetic Postganglionic Neurons Neurons in paravertebral (sympathetic chain) or some prevertebral (collateral) ganglia adrenergic (except to eccrine sweat glands = cholinergic) Parasympathetic Preganglionic Neurons Neurons in brainstem nuclei or sacral spinal cord Cholinergic Parasympathetic Postganglionic Neurons Neurons in wall of viscera Cholinergic