1. Neurons, Synapses, and Signaling
Nervous System
Neurons, Synapses, and Signaling

2. Sensory input
Integration
Sensor
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)

3. NEURONS Presynaptic cell Postsynaptic cell Dendrites Stimulus Nucleus
body
Axon
Synapse
Synaptic terminals
Postsynaptic cell
Neurotransmitter

4. Transmit information from a sense receptor to the brain
Dendrites
Axon
Cell
body
Portion
of axon
80 µm
Cell bodies of
overlapping neurons
Sensory neuron
Interneurons
Motor neuron
Type of Neuron
Function
Sensory Neuron
Transmit information from a sense receptor to the brain
Interneuron
Forms connections between neurons (i.e. relay neurons)
Motor Neuron
Transmits information from the brain to a muscle/gland

5. Glial Cells: neuron helper cells, nourish, insulate, regulate factors in neurons

6. Membrane Potentials - Inside of neuron is negative -Outside is positive -Involves sodium potassium pumps & ion channels
OUTSIDE
CELL
[Na+]
150 mM
[Cl–]
120 mM
[K+]
5 mM
INSIDE
CELL
[K+]
140 mM
[A–]
100 mM
[Na+]
15 mM
[Cl–]
10 mM
Each cell has a voltage (a difference in charge) across their membrane.
Resting potential = -60 to -80 mV (millivolts)

7. Key
Na+
Sodium-
potassium
pump
Potassium
channel
Sodium
channel K+
OUTSIDE
CELL
INSIDE
CELL

8. Membrane potential (mV)
Key
Na+
Sodium
channel
Sodium
channel K+
Potassium
channel 3
Rising phase of the action potential 4
Falling phase of the action potential
+50
Action
potential
Sodium
channel 3
Membrane potential
(mV) 2 4
Threshold
–50 1 1 5
Resting potential 2
Depolarization
–100
Time
Extracellular fluid
Potassium
channel
Sodium
channel
Potassium
channel
Plasma
membrane
Cytosol
Inactivation loop 5
Undershoot 1
Resting state

9. +50
+50
+50
Action
potential
Stimuli
Stimuli
Strong depolarizing stimulus
Membrane potential (mV)
Membrane potential (mV)
Membrane potential (mV)
–50
Threshold
–50
Threshold
–50
Threshold
Resting
potential
Resting
potential
Resting
potential
Hyperpolarizations
Depolarizations
–100
–100
–100 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 6
Time (msec)
Time (msec)
Time (msec)
(a) Graded hyperpolarizations
(b) Graded depolarizations
(c) Action potential
Hyperpolarization (neuron is opening K+ channels which increases the negative charge) Depolarization ( neuron is opening Na+ channels thus decreasing the negative charge) Threshold (a set point of membrane potential measurement) Action Potential (wave of depolarization)

10. Action potentials are the nerve impulses (or signals) that carry information along an axon.
Once initiated, the action potential has a magnitude that is independent of strength of the triggering stimulus.
Because action potentials occur fully or not at all, they represent an all-or-none response to stimuli.
This positive feedback loop of depolarization and channel opening triggers an action potential whenever the membrane potential reaches the threshold.
Action Potentials

11. Conduction of A.P.
At the site where an A.P. is initiated, Na+ inflow depolarizes the neighboring region of the axon membrane (past threshold)
The neighboring area on the axon starts to depolarize as the original area is repolarizing by K+ outflow.
Only moves in one direction due to this pattern of depolarizing and repolarizing
BUT A.P. are not transmitted from neurons to other cells…
Axon
Plasma
membrane
Action
potential
Na+
Cytosol
Action
potential K+
Na+ K+
Action
potential K+
Na+ K+

12. 5
Na+ K+
Synaptic vesicles
containing
neurotransmitter
Presynaptic
membrane
Voltage-gated
Ca2+ channel
Postsynaptic
membrane 1
Ca2+ 4 2 6
Synaptic
cleft 3
Ligand-gated
ion channels
Majority of synapses are chemical synapses (release of neurotransmitters)
At end of the A.P. increased Ca2+ concentration causes N.T vesicles to fuse and enter the synaptic cleft.
The neurotransmitter bind to the receptor proteins to depolarize the next cell (create a response.)

13. Neurotransmitters Common Neurotransmitters: Norepinephrine Epinephrine
Dopamine
Serotonin
Nitric Oxide
Neurotransmitters

14. Several factors affect the speed at which action potentials are conducted:
Axon Diameter: Wider the axon, the fast the signal (wider=less resistance for ion flow)
Myelin Sheath: insulation of the signal, signal jumps from node to node.
Conduction Speed of A.P.

15. Helpful Links: 1. ) https://www. youtube. com/watch. v=ZscXOvDgCmQ 2

16. SUMMARY / REVIEW Large Concepts: Pathway of neural response
Vocab:
Sensory neuron
Interneuron
Motor neuron
Synapse
Action potential
Sodium potassium pump
Ion channels
Resting potential
Depolarization
Hyperpolarization
Threshold
Refractory period
Neurotransmitter
Plasma membrane
Large Concepts:
Pathway of neural response
Structure of a Neuron
Types of Neurons
A.P. Stages (Depolarize, Threshold, Repolarize…)
Ions involved in A.P.
Chemical & Electrical communication via neurons
Speed,/strength of AP
SUMMARY / REVIEW