Binding of transmitter molecule to receptor site produces chemical reaction that can have 2 different effects: Reaction will depolarize (excite) postsynaptic cell membrane
o Excitatory transmitters: neurotransmitters that create depolarization Reaction will hyperpolarize postsynaptic membrane makes membrane potential even more –ve o Makes it more difficult for excitatory transmitters to depolarize neuron to its action potential threshold ( inhibitory ) ° Balance between excitatory and inhibitory must be maintained for nervous system to function properly ° When neurotransmitter molecule binds to its receptor, continues to activate/inhibit until shut off (d eactivated ) Deactivation 1: Other chemicals in synaptic space break down transmitter molecules Deactivation 2: reuptake: transmitter molecules are reabsorbed into presynaptic axon terminal Transmitter molecules can assume many different shapes o Various systems in brain recognize only certain chemical messengers ° 2 widespread neurotransmitters are simple amino acids glutamate (or glutamic acid) and gamma-aminobutyric (GABA) found throughout central nervous system have some role in mediating all behaviors Glutamate (excitatory) involved in learning and memory GABA (inhibitory) motor control, anxiety control ° Acetylcholine (ACh): neurotransmitter involved in memory and muscle Underproduction of ACh important factor in Alzheimer’s disease drugs that black action of ACh can prevent muscle action and lead to paralysis ° Dopamine: neurotransmitter that mediates wide range of functions including motivation, reward, feelings of pleasure, voluntary motor control, control of thought processes Parkinson’s Disease: group of dopamine-producing neurons degenerate and die loss of voluntary motor control ° Serotonin: neurotransmitter that influences mood, eating, sleep and sexual behavior
Abnormal sensitivity to serotonin leads to depression ° Endorphins: neurotransmitter that reduces pain and increases feeling of well-being ° Neuromodulators: have more widespread and generalized influence on synaptic transmission Play important role in functions such as eating, sleep and stress The Nervous System Sensory neurons: carry input messages from sense organs to spinal cord and brain Motor neurons: transmit output impulses from brain and spinal cord to body’s muscles and organs Interneurons: perform connective or associative functions within nervous system o Far outnumber sensory or motor neurons o Ex: allows to recognize song by linking sensory output from song we’re hearing to memory of song stored in brain ° 2 major divisions of nervous system Central Nervous System : consisting of neurons in brain and spinal cord Peripheral Nervous System : composed of all neurons that connect central nervous system with muscles, glands and sensory receptors Peripheral Nervous System Contains all neural structures that lie outside of brain and spinal cord 2 major divisions: somatic nervous system and autonomic nervous system Somatic Nervous System: consists of sensory neurons
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- Spring '09