Organization & Development of the Nervous System Lecture 2

The Central Nervous System n CNS l Brain l Spinal cord ~

Peripheral Nervous System n Somatic Nervous System - SNS l Sensory & Motor n Autonomic Nervous System - ANS l Sympathetic Division l Parasympathetic Division n Cranial Nerves - 12 Pair n Spinal Nerves - 31 Pair ~

Divisions of the Brain n Different schemes l Forebrain, midbrain, hindbrain l 5 major subdivisions n Forebrain 1. Telencephalon 2. Diencephalon ~

n Midbrain - 3. Mesencephalon n Hindbrain 4. Metencephalon 5. Myelencephalon ~ Divisions of the Brain

n Dorsal - toward the back n Ventral - toward the stomach n Anterior & Posterior n Rostral & Caudal ~ Terminology

Dorsal Ventral In reference to the BRAIN Anterior Posterior RostralCaudal Inferior Superior

Brainstem & spinal cord VentralDorsal Rostral Caudal AnteriorPosterior Superior Inferior

Neural Axis

Neural Axis

Terminology n Medial - toward the midline n Lateral - away from the midline n Ipsilateral - same side n Contralateral - opposite side n Decussate - crossover ~

Terminology n Afferent - toward l Sensory n Efferent - away from l Motor ~

n Coronal or frontal l cross-section - salami n Sagittal - side view l hot-dog bun n Horizontal l top view ~ Planes

Coronal Section

Horizontal Section

Mid-sagittal Section

Development of the Nervous System

Embryological Origin n Embryo has 3 layers l endoderm internal organs l mesoderm muscles & skeleton l ectoderm nervous system & skin ~

Embryological Origin n About 3 weeks l Neural plate forms l sheet of cells ~

Embryological Origin n Neural groove l folds rostral to caudal will form tube ~

Development of N.S. n Neural tube l CNS develops from walls spina bifida - caudal tube fails to close l as tube develops dorsal portion pinches off & forms...~

Development of N.S. n Neural crest l develops into all neurons of PNS n Mesoderm l somites ---> vertebrae & muscles ~

Neural Tube Defects: Rostral n Neural tube fails to close n anencephaly l skull & brain partially or totally absent l perinatal mortality n Encephalocele l parts of brain protrude outside skull l mental disability depends on extent ~

Neural Tube Defects: Caudal n Spina Bifida l Cleft spine l neural tube fails to close n Incidence l Spina bifida occulta 40% of Americans l Spina Bifida Manifesta 1 in a 1000 births ~

Spina Bifida Manifesta n Meningocele (4%) l fluid-filled meningeal cyst l protrudes through unfused vertebral arches l SC/nerves not in sac l repaired surgically l less severe disability than myelomeningocele ~

Spina Bifida Manifesta n Myelomeningocele (96%) l protruding cyst as with meningocele l spinal cord / nerves in protruding sac n Effects l paralysis, incontinence, learning disabilities l 70-90% also hydrocephalus can cause severe brain damage l Repaired surgically ~

Neural Tube Defects: Prevention n Possible genetic component l reoccurrence in families l ethnic/racial relationship n Folic Acid (Folate) Deficiency l 50-70% of cases preventable l CDC guidelines not planning pregnancy: 400  g/day planned pregnancy: 4000  g/day under direction of health care provider ~

Stages of Cellular Activity n 6 distinct stages 1. Neurogenesis 2. Cell migration 3. Differentiation 4. Synaptogenesis 5. Neuronal cell death 6. Synaptic rearrangement ~

Stages of Cellular Activity n 6 distinct stages 1. Neurogenesis l mitosis l nonneural cells neurons do not divide l develop into neurons or glia glia produced throughout life ~

Stages of Cellular Activity 2. Cell migration l to specific “brain” locations l along radial glia l later: along other neurons ~

Stages of Cellular Activity 3. Differentiation l into specific neuron types l by induction influenced by surrounding cells l or cell-autonomous~

Stages of Cellular Activity 4. Synaptogenesis l formation of synapses l growth of axons & dendrites growth cones l neurotrophic factors~

Stages of Cellular Activity 5. Neuronal cell death l apoptosis: programmed cell death l 20-80% of neurons in a region l genetically programmed l lack of neurotrophic factors ~

Stages of Cellular Activity 6. synaptic rearrangement l elimination of synapse l formation of new synapses l dependent on neural activity ~

Differentiation n Specialization of structures n 3 primary vesicles l rostral end of tube l develops into brain n Prosencephalon ---> forebrain n Mesencephalon ---> midbrain n Rhombencephalon ---> hindbrain ~

Prosencephalon n Secondary vesicles form & separate l optic ---> retinas retina & optic nerve CNS not PNS l telencephalic ---> telencephalon l remainder ---> diencephalon ~

Other Primary Vesicles n Mesencephalic ---> mesencephalon l dorsal - tectum l ventral - tegmentum l tube - cerebral aqueduct n Rhombencephalic l rostral - metencephalon l caudal - myelencephalon l tube - 4th ventricle ~

Telencephalon n Cortical areas n Fiber systems n Landmarks l Fissures /Sulci l Lobes l Gyri ~

Superior surface Longitudinal Fissure (sulcus)

Central Lateral

Frontal Parietal Occipital Temporal

M1 Superior temporal gyrus S1 A1 Postcentral gyrus Precentral gyrus Gyri

The Meninges n Tough connective tissue n Dura mater - tough outer layer n Arachnoid membrane - soft middle layer n Pia mater - soft inner layer, next to brain ~

Subarachnoid space n Gap between arachnoid membrane and pia mater n Filled with CSF n Brain floats in CSF ~

Dura mater Arachnoid membrane Subarachnoid space CSF Pia mater Brain The Meninges

Ventricular System n 4 interconnected ventricles l chambers n Cerebral Spinal Fluid (CSF) l manufactured in choroid plexus l 125 ml, t 1/2 = 3 hrs n Hydrocephalus l blockage of CSF flow ~

Ventricular System L V 3 rd Lateral Ventricles Third Ventricle Fourth Ventricle Cerebral Aqueduct Central Canal 4 th