Neurons and Neurotransmitters

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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central Nervous System (CNS) Brain Spinal Cord Peripheral Nervous System (PNS) Sensory Neurons Motor Neurons Somatic Nervous System voluntary movements via skeletal muscles Somatic Nervous System voluntary movements via skeletal muscles Autonomic Nervous System organs, smooth muscles Autonomic Nervous System organs, smooth muscles Sympathetic - “Fight-or-Flight” responses Sympathetic - “Fight-or-Flight” responses Parasympathetic - maintenance Parasympathetic - maintenance The Nervous System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Divisions of the autonomic nervous system

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

 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 Neurons

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

Regulate external environment (ions, etc.) Most abundant glial cell May contribute to blood-brain barrier and to synapses Astrocytes

Three main types of neurons Sensory Neurons Interneurons Motor Neurons

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

The Withdrawal Reflex

Neuron Anatomy and Neural Communication

Neurons Axon of another neuron Cell Body Dendrites Axon Myelin Sheath 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  Synapse movie

Specific Parts: The Neuron Structure

Specific Parts: The Neuron Function Neurons = 3 functions: Reception, Conduction, Transmission

Action Potential When dendrites stimulated, the delicate balance is altered Membrane breaks down Positively charged ions rush in (depolarization) Charge = less negative Causes release of chemicals from terminal buttons

W. W. Norton

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

Myelinization clip Myelin conduction clip

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

Neurotransmitters (>60) Acetylcholine (ACh) –1 st substance identified as NT –Links motor neurons and muscles (contract or relax) e.g. curare vs black widow spider –Also involved in memory, learning, sleep, dreaming (acetylcholine movie) Endorphins (the brain’s own morphine) –1973 injected rats with morphine –Bound like NTs –Brain had receptors for exogenous substance? Brain must produce its own morphine Released during pain and discomfort

More neurotransmitters Receptor binding movie