Binding of transmitter molecule to receptor site

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