Transcript Synapses
Synapses 1. Electrical Synapses 2. Chemical Synapses a. ionotropic (chemically gated) b. metabotropic (G-protein mediated) Synapse: junction between the axon terminus of one neuron and another neuron or effector (muscle or gland). Electrical Synapse (rare) In an electrical synapse, current passes directly from one cell to the next. Very rapid (a few milliseconds) Examples include neurons that control the “snap” of a crayfish tail and the flip of a caudal fin of a fish. Chemical Synapse: ionotropic Requires neurotransmitter for transmission Requires chemically gated channels on post-synaptic membrane May involve degradative enzymes May involve reuptake transporters on pre-synaptic membrane Chemical Synapse: ionotropic Examples of Neurotransmitters • Acetyl choline: found at all nerve-muscle synapses (neuromuscular junctions) • Norepinephrine: important neurotransmitter found throughout the central nervous system and peripheral nervous system. • Serotonin: found primarily in the brain – effects mood. • Dopamaine: found primarily in the brain – controls motor pathways and effects mood. • What is the function of degradative enzymes at the synapse? • What is the function of reuptake transporters at the presynaptic membrane? • Therapeutic and Recreational Drug Effects A. monoamine oxidase inhibitors (MAOI) B. Prozac (selective serotonin reuptake inhibitors) C. Cocaine ( dopamine reuptake inhibitor) Post-Synaptic Effects of Ionotropic Synapses • Excitatory Post-Synaptic Potentials • Inhibitory Post-Synaptic Potentials Summation at the Hillock Excitatory: opens Na+ channels and causes graded depolarization. Excitatory Inhibitory: opens K+ channels and causes graded hyperpolarization. + Inhibitory - Summation of excitatory and inhibitory post-synaptic potentials - may lead to threshold and initiate an action potential. Chemical Synapse: metabotropic Requires neurotransmitter for transmission Requires G-protein coupled receptor on post-synaptic membrane G-protein activates an enzyme on the cytoplasmic side of the membrane May involve degradative enzymes May involve reuptake transporters on pre-synaptic membrane Examples: transmission of smell, control of cardiac muscle Cells of The Nervous System Two neurons releasing neurotransmitters that act on a third neuron. The first two neurons could be in the Central Nervous System, and the third might be a motor neuron leading out to a muscle or gland. Schwann Cells form a myelin sheath Around the axon of motor neurons Neurons Neuroglia (supporting cells) - Detect physical and chemical changes in their environment - Provide physical support to neurons -Transmit electric impulses (action potentials) from one end to the other (one cell may be more than 3 feet long) - May be involved in processes such as memory. - Communicates with other neurons, muscles and glands using chemicals called neurotransmitters. - Provide electrical insulation to neurons Motor neurons have their cell bodies in the spinal cord, but their axons extend outward into the body to stimulate muscles or glands. Spinal cord smear Dendrites Microglia Pyramidal cells (neurons) of the cerebral cortex (Golgi stain) Cells of the Central Nervous System Microglia - immune-like cells Oligodendrocyte produce myelin sheath Ependymal cells - line ventricles and help produce cerebrospinal fluid Astrocyte - blood brain barrier Cerebrum Cerebellum Brain Stem Central Sulcus Gyrus Transverse Fissure Sulcus Lateral Fissure Parietal Lobe Lobes of the Cerebrum Frontal Lobe Occipital Lobe Temporal Lobe Cerebrum Corpus Callosum Thalamus Hypothalamus Pons Midbrain Medulla Cerebrum Corpus Callosum Thalamus Basal Ganglia Limbic System = amygdala, hippocampus, hypothalamus and cingulate gyrus The four F’s