13.1 Overview of the nervous system Nervous system – Allows for communication between cells through sensory input, integration of data and motor output 2 cell types: neurons and neuroglia

Expanding on neurons 3 types of neurons: Neuron structure: 13.1 Overview of the nervous system Expanding on neurons 3 types of neurons: Sensory – takes impulses from sensory receptor to CNS Interneurons – receive information in the CNS and send it to a motor neuron Motor – takes impulses from the CNS to an effector (i.e. gland or muscle fiber) Neuron structure: Cell body – main cell where organelles and nuclei reside Dendrite – many, short extensions that carry impulses to a cell body Axon (nerve fiber) – single, long extension that carries impulses away from the cell body

13.1 Overview of the nervous system Types of neurons

13.1 Overview of the nervous system The myelin sheath A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation and regeneration in the PNS Schwann cells – neuroglia that make up the myelin sheath in the PNS Nodes of Ranvier – gaps between myelination on the axons Saltatory conduction – conduction of the nerve impulse from node to node

13.1 Overview of the nervous system Neuron structure

The nerve impulse: resting potential (RP) 13.1 Overview of the nervous system The nerve impulse: resting potential (RP) Resting potential – when the axon is not conducting a nerve impulse More positive ions outside than inside the membrane There is a negative charge of -65mV inside the axon More Na+ outside than inside More K+ inside than outside

Threshold Stimulus Membrane must be made more permeable to sodium ions. Once a threshold permeability is reached, the entire impulse begins “All or None Principle”

The nerve impulse: action potential 13.1 Overview of the nervous system The nerve impulse: action potential Action potential – rapid change in the axon membrane that allows a nerve impulse to occur Sodium gates open letting Na+ in Depolarization occurs Interior of axon loses negative charge (+40mV) Potassium gates open letting K+ out Repolarization occurs Interior of axon regains negative charge (-65mV) Wave of depolarization/repolarization travels down the axon Resting potential is restored by moving potassium inside and sodium outside. Another action potential can be transmitted until the entire resting potential is restored. (Refractory Period)

The nerve impulse: action potential 13.1 Overview of the nervous system The nerve impulse: action potential

Plumbing Analogy A toilet flushing can be described in these steps: Tank above bowl is full of water Lever is pushed until flush initiates Water rushes into the bowl and flushes waste into sewer Tank above bowl fills with water Toilet can not flush again until tank is full.

Summary In your notes, Write a summary describing how the propagation of an action potential works like the flushing of a toilet. Include all 5 steps!

13.1 Overview of the nervous system The synapse A small gap between the sending neuron (presynaptic membrane) and the receiving neuron (postsynaptic membrane) Transmission is accomplished across this gap by a neurotransmitter (e.g. ACh, dopamine and serotonin) Neurotransmitters are stored in synaptic vesicles in the axon terminals

Close up look at your synapse (The Gray Matter) AXON What is this in the membrane? The synapse - where the action happens Transport protein The next cell’s plasma membrane

How does the Synapse carry the signal? 1. impulse travels down the axon (The White Matter) Vesicles with neurotransmitters move toward the membrane Neurotransmitters are released and diffuse toward the next cell’s plasma membrane 4. The chemicals open up the transport proteins and allow the signal to pass to the next cell

The synapse carries a signal from cell to cell 1 3 4 2

How many synapses are in one neuron? 1,000 to 10,000!!

Major Neurotransmitters in the Body Role in the Body Acetylcholine A neurotransmitter used by the spinal cord neurons to control muscles and by many neurons in the brain to regulate memory. In most instances, acetylcholine is excitatory. Dopamine The neurotransmitter that produces feelings of pleasure when released by the brain reward system. Dopamine has multiple functions depending on where in the brain it acts. It is usually inhibitory. GABA (gamma-aminobutyric acid) The major inhibitory neurotransmitter in the brain. Glutamate The most common excitatory neurotransmitter in the brain. Glycine A neurotransmitter used mainly by neurons in the spinal cord. It probably always acts as an inhibitory neurotransmitter. Norepinephrine Norepinephrine acts as a neurotransmitter and a hormone. In the peripheral nervous system, it is part of the flight-or-flight response. In the brain, it acts as a neurotransmitter regulating normal brain processes. Norepinephrine is usually excitatory, but is inhibitory in a few brain areas. Serotonin A neurotransmitter involved in many functions including mood, appetite, and sensory perception. In the spinal cord, serotonin is inhibitory in pain pathways. NIH Publication No. 00-4871

See it in action! https://www.youtube.com/watch?v=ZAmUjvgoO0A