12/3 Psych Review Neurons, synapses, and behavior Each communicates with many other neurons via networks Communication involves changes in RPs: PSPs and APs Many different types Many circuits (spine, thalamus) Many neurotransmitters Dendritesomaaxon hillockaxons/myelin sheathpresynaptic terminals Communication occurs at the synapses through EPSPs and IPSPs Synapses between neurons in the spinal cord Synapses at the neuromuscular junction EPSPs and IPSPs Presynaptic cell: releases transmitter that cross the cleft and act on receptors of the postsynaptic cell Reuptake: presynaptic terminal grabs transmitter and brings it back into cleft degradation: destroyed so they don?t act on postsynaptic cell Many drugs act on these processes Antidepressants Antipsychotics Recreational drugs The effects of the transmitters: changes ion flow or production of 2nd messengers Change in ion flowregulates the rate of action potentials Action potentials: Rapid major depolarization and re polarization as channels open and close Travels down axon to transmit a signal Triggered by threshold level of depolarization at axon hillock All or none Doesn?t degrade Examples: Sensory neurons in the DRG Sleepincreased synchrony of APs (slow wave sleep) What causes postsynaptic potentials to occur at the dendrites and cell body and action potentials to occur along the axon? Different channels within the membrane Open: ions cross Close: they don?t Channels can be opened by transmitters (chemicals) or by a change in the balance between positive and negative ions across the membrane (voltage) Dendrites and cell body are chemically gated (post synaptic) Channels open when transmitter binds Axon is voltage gated (pre synaptic) Open by change in voltage What does that have to do with behavior? Some of the circuits: Dopamine VTA(ventral tegmental area) and NAc (Nucleus accumbens) Sex and drugs Reward and addiction Cortex and beyond schizophrenia and DA antagonists of DA 2 receptor Basal ganglia Parkinson?s disease: problems with coordination Examples from motor systems: APs leading to release of transmitter sent along pathways that are hierarchical, parallel and functionally segregated Controls laughter and speech Motor neurons form circuits Some more examples Signals converge on motor neurons Final common pathway leading to behavior Action potentials traveling down the axon of the motor neuron Synapses between motor neurons and the muscle What sets of the action potential of the motor neuron? Input from DRG cells: reflexes Circuits within the spinal cord representing complex motor programs and pattern generators Direct pathways from the brain Motor cortex Primary cortex: a cortical map Mirror neurons Action potentials when producing behavior and when watching others produce the same behavior Neural basis of empathy? Readiness potential May represent behavioral decisions made at an unconscious level Change in brain occurs before person made a conscious decision Representing one of Gazzaniga?s ?modules? of the mind? Synapses and behavior: DA and Parkinson?s Symptoms Rigidity; trouble initiating movement Tremors Late stages: language, cognition, emotion Cells in midbrain substantia nigra projecting to BG Multiple factors: genes, toxins, concussions Treatment Current L-dopadopamine Deep brain stimulation Future: transplants and stem cells How does the brain develop? Cell plates fold to form a tube More cells form at one end of tube than the other The front end develops into the brain The back end becomes the spinal cord Most neurons born early in life Myelin is still forming until age 20 Causes brain to grow for a long time Myelin increases rate of signals in brain Basic developmental processes Neurogensesis Cell migration Cell differentiation Synaptogenesis Cell death Synapse refinement Developmental processes altered in schizophrenia Neurogenesis: reduced in hippocampus Cell migration; stuck in the frontal cortex Cell differentiation Synaptogenesis Cell death: accelerated and amplified in many areas Synapse refinement Development of schizophrenia? Multiple factors and GXE interaction Adoption/ twin studies Concordance rates and genetic relatedness The genes: some correlates, no single gene The environment prenatal: Shared vs. separate placenta Birth weights of discordant MZ twins some of the environmental correlates Nutrition maternal antibodies premature birth traumatic delivery How do these factors alter development? Hormones Chemical agents Secreted by lands Travel through the blood stream Act on target cells such as neurons with specialized receptors Melatonin is secreted by the pineal gland Hormone development 2 part primordial gonad in the beginning SRY genemale Testosterone MIF hormone External genitalia and behavior Initially undifferentiated In males Tested secrete T T causes fusion of folds Enlargement of genital tubercle In females Absence of T permits the development of the clitoris and labia Behavior: organizational effects of T
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