Learning Target: NeuronsLearning Target: NeuronsBasic Unit of the Nervous System

Learning Target: Neurons

I Can… List the three main types of neurons and their role in the nervous system and describe the general structure and function of a neuron

I Will…• Identify the three types of neurons and their

associated function• Label the main and accessory structures of a

typical neuron• Describe how neurons transmit impulses within

a neuron and between neurons

Learning Target: Neurons

Neuron – specialized cell that stores information and carries messages within the nervous system and between other body systems.• Communication Systems

Learning Target: Neurons

Three types:• 1) Sensory neuron (afferent)• Detects stimuli • Transmits signal to CNS

• 2) Interneuron (associative)• Receives signals from sensory neurons • Relays info within CNS and processes

information• 3) Motor neuron (efferent)• Transmits messages from CNS to targets

(organs, tissues, cells)

Learning Target: Neurons

Basic Neuron Structure:• All neurons have 3 basic structures• 1) Cell body• Contains nucleus and organelles

• 2) Dendrites• Branch-like extensions of cytoplasm and cell

membrane• Receive messages from neighboring cells

• 3) Axon• Long extension that carries electrical signal

away from cell body • Passes message to other cells

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Learning Target: Neurons

Main Structures:1) Cell Body2) Nucleus3) Dendrites4) AxonAccessory Structures:5) Myelin Sheath6) Schwaan’s cell7) Node of Ranvier8) Axon terminals

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Learning Target: Neurons

Before a Neuron is Stimulated …Resting potential – when a neuron is NOT transmitting an impulse.• Maintenance of ion concentrations across the

membrane.• Unequal inside & outside neuron.• More Na+ outside than inside cell.• More K+ inside than outside cell.

• Creates a “relative” negative charge inside the cell compared to the outside of the cell.

Learning Target: Neurons

Before a Neuron is Stimulated …Sodium-Potassium pump- Helps maintain resting potential by using energy to actively transport Na+ ions out of the cell and bring K+ ions into the cell.• Leak channels allow Na+ to diffuse into the cell.• Leak channels allow K+ ions to diffuse out.• More K+ than Na+ channels (positive charges

exit faster than enter – maintain relative negative charge)

Learning Target: Neurons

Before a Neuron is Stimulated …

Learning Target: Neurons

How neurons function…• Transmission of signal within a neuron• Based on “action potential” - change of distribution of

ion charges. Stimulation causes…• Opening of gated Na+ ion channels in cell membrane

allowing diffusion to take place (positive charges rush in).

• Stimulates adjacent channels to open.• Once ions rush in, channels snap shut. (traps Na+ ions)• K+ channels open and close more slowly.• Causes repolarization of part of the membrane.• Reversing electrical charges travel along membrane

Learning Target: Neurons

How neurons function…• All or None (like dominoes falling…

if the first goes, they all go)

Learning Target: Neurons

How neurons function…• Transmission of signal between neurons• Action potential must move from

axon terminal of one neuron to dendrite of next neuron• Tiny gap between cells – synapse• Axon terminals release neurotransmitters from

vesicles• Diffuses across synapse• Binds to receptors on dendrite cell membrane

surface• Initiates action potential in second neuron

Learning Target: Neurons

Learning Check√: Neurons

1. What are the three types of neurons and their function in the nervous system?a) _____________ Function: ___________b) _____________ Function: ___________c) _____________ Function: ___________

2. What are three main structures of all neurons and what is the function of each structure?a) _____________ Function: ___________b) _____________ Function: ___________c) _____________ Function: ___________