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
• 1) Cell body
• Contains nucleus and organelles
2
• 2) Dendrites
• Branch-like extensions of cytoplasm and cell
membrane
• Receive messages from neighboring cells 3
• 3) Axon
• Long extension that carries electrical signal
away from cell body
• Passes message to other cells
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: ___________