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 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”

Three main types of neurons Sensory Neurons Interneurons Motor Neurons

Types of neurons Sensory Motor Inter (relay) Carries information from sensory organs to CNS (through somatic system) Carries information from CNS to muscles and glands (somatic & autonomic systems) Connect neurons to other neurons (lots of these in the CNS)

Sensory (Afferent) vs. Motor (Efferent) e.g., skin e.g., muscle 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

A neuron

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

Neurons Source: science photo library Neuronal cell bodies Synapses occur at the junctions Axons

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

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

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