Learning Target: Neurons Basic 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 1 2 3

Learning Target: Neurons Main Structures: 1)Cell Body 2)Nucleus 3)Dendrites 4)Axon Accessory Structures: 5)Myelin Sheath 6)Schwaan’s cell 7)Node of Ranvier 8)Axon terminals 3

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: ___________