11.10 Neural Integration

11.10 Neural Integration • Neural integration: neurons functioning together in groups • Groups contribute to broader neural functions • There are billions of neurons in CNS – Must have integration so that the individual parts fuse to make a smoothly operating whole Organization of Neurons: Neuronal Pools • Neuronal pool: functional groups of neurons – Integrate incoming information received from receptors or other neuronal pools – Forward processed information to other destinations Organization of Neurons: Neuronal Pools (cont.) • Simple neuronal pool – Single presynaptic fiber branches and synapses with several neurons in pool – Discharge zone: neurons closer to incoming fiber are more likely to generate impulse – Facilitated zone: neurons on periphery of pool are farther away from incoming fiber; usually not excited to threshold unless stimulated by another source Simple Neuronal Pool Figure 11.18 Simple neuronal pool. Patterns of Neural Processing (1 of 3) • Serial processing – Input travels along one pathway to a specific destination  One neuron stimulates next one, which stimulates next one, etc. – System works in all-or-none manner to produce specific, anticipated response – Best example of serial processing is a spinal reflex Patterns of Neural Processing (2 of 3) • Serial processing (cont.) – Reflexes  Rapid, automatic responses to stimuli  Particular stimulus always causes same response  Occur over pathways called reflex arcs that have five components: – Receptor – Sensory neuron – CNS integration center – Motor neuron – Effector A Simple Reflex Arc Figure 11.19 A simple reflex arc. Patterns of Neural Processing (3 of 3) • Parallel processing – Input travels along several pathways – Different parts of circuitry deal simultaneously with the information  One stimulus promotes numerous responses – Important for higher-level mental functioning – Example: A sensed smell may remind one of an odor and any associated experiences Types of Circuits • Circuits: patterns of synaptic connections in neuronal pools • Four types of circuits – Diverging – Converging – Reverberating – Parallel after-discharge Types of Circuits in Neuronal Pools (1 of 4) Figure 11.20a Types of circuits in neuronal pools. Types of Circuits in Neuronal Pools (2 of 4) Figure 11.20b Types of circuits in neuronal pools. Types of Circuits in Neuronal Pools (3 of 4) Figure 11.20c Types of circuits in neuronal pools. Types of Circuits in Neuronal Pools (4 of 4) Figure 11.20d Types of circuits in neuronal pools. Developmental Aspects of Neurons (1 of 4) • Nervous system originates from neural tube and neural crest formed from ectoderm • The neural tube becomes CNS – Neuroepithelial cells of neural tube proliferate into number of cells needed for development – Neuroblasts become amitotic and migrate – Neuroblasts sprout axons to connect with targets and become neurons Developmental Aspects of Neurons (2 of 4) • Growth cone: prickly structure at tip of axon that allows it to interact with its environment via: – Cell surface adhesion proteins (laminin, integrin, and nerve cell adhesion molecules, or N-CAMs), which provide anchor points – Neurotropins that attract or repel the growth cone – Nerve growth factor (NGF), which keeps neuroblast alive – Filopodia are growth cone processes that follow signals toward target Developmental Aspects of Neurons (3 of 4) • Once axon finds its target, it then must find right place to form synapse – Astrocytes provide physical support and the cholesterol needed for construction of synapses • About two-thirds of neurons die before birth – If axons do not form a synapse with their target, they are triggered to undergo apoptosis (programmed cell death) – Many other cells also undergo apoptosis during development Developmental Aspects of Neurons (4 of 4) • During childhood and adolescence learning reinforces certain synapses and prunes away others – Recent evidence suggests genes that promote excessive synaptic pruning may predispose an individual to schizophrenia • Neurons are amitotic after birth; however, there are a few special neuronal populations that continue to divide – Olfactory neurons and hippocampus A neuronal growth cone Figure 11.21 A neuronal growth cone.