Neurons and Neurotransmitters Nervous System Central nervous system

Neurons and Neurotransmitters

Nervous System – Central nervous system (CNS): • Brain • Spinal cord – Peripheral nervous system (PNS): • Sensory neurons • Motor neurons (somatic and autonomic)

The Nervous System • A physical organ system like any other • 2 main kinds of cells – Neurons – Glia

Neurons § Basic units of the nervous system § Receive, integrate, and transmit information § Operate through electrical impulses § Communicate with other neurons through chemical signals § More about neurons and neuronal anatomy later

Glial cells • 100 billion neurons • 10 x more glial cells • Glial cells – Support neurons (literally, provide physical support, as well as nutrients) – Cover neurons with myelin – Clean up debris – “Housewives”

Three main types of neurons • Sensory Neurons • Interneurons • Motor Neurons

Sensory (Afferent) vs. Motor (Efferent) sensory (afferent) nerve Neurons that send signals from the senses, skin, muscles, and internal organs to the CNS e. g. , skin motor (efferent) nerve Neurons that transmit commands from the CNS to the muscles, glands, and organs Gray’s Anatomy 38 1999 e. g. , muscle

Neuron Anatomy and Neural Communication

Neurons Dendrite s Axon of another neuron Cell Body Myelin Sheath Axon Dendrites of another neuron

Neural Anatomy § Dendrite § the bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body § Axon § the extension of a neuron, ending in branching terminal fibers, through which messages are sent to other neurons or to muscles or glands

Neural Anatomy and communication § Synapse § junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron § tiny gap at this junction is called the synaptic gap or cleft

Specific Parts: The Neuron Structure

Action Potential When dendrites stimulated, the delicate balance is altered Membrane breaks down Causes release of chemicals from terminal buttons

Relay Race • Action Potential starts at dendrite – Through cell body – Down Axon – Axon Terminals • How does it get to the next cell’s dendrites? • Neurons don’t touch – Synapse = millionth inch gap – In synapse = vesicles w/ neurotransmitters » Chemical messengers that transmit info

Communication • Impulse releases neurotransmitter from vesicles • Neurotransmitter enters synaptic gap • Neurotransmitter binds to receptors on the receiving neuron

Myelin Sheath – Fatty material made by glial cells – Insulates the axon – Allows for rapid movement of electrical impulses along axon – Nodes of Ranvier: gaps in myelin sheath where action potentials are transmitted – Multiple sclerosis is a breakdown of myelin sheath – Speed of neural impulse Ranges from 2 – 200+ mph

Neurotransmitters § chemical messengers that traverse the synaptic gaps between neurons § when released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether it will generate a neural impulse

More neurotransmitters Receptor binding movie

More Definitions • Nucleus – Control Center of the Cell. • Synaptic Terminal – Contain neurotransmitters that makes contact with the dendrites of another neuron. • Cell Body – surrounds the nucleus, branches off into dendrites, and sends messages to the axon.