1. Structures and Processes of the Nervous System
Chapter 8.2
McGraw-Hill Ryerson
Biology 12 (2011)

2. Overview of Nervous System
Looks overwhelming, doesn’t it?

3. Here’s a chart that’s a little simpler

4. Central Nervous System: brain & spinal cord integrates and processes information sent by nerves from peripheral nervous system

5. Peripheral Nervous System: network of nerves that carry messages to CNS and send commands from CNS to the muscles and glands

6. Nerve Cells (Neurons) Neurons are different by
Neurons are similar to other cells in the body
Surrounded by cell membrane
Have a nucleus that contains genes
Contain cytoplasm, mitochondria and other organelles
Carry out basic cellular processes such as protein synthesis and ATP production
Neurons are different by
- Specialized extensions called dendrites and axons
- Communicate with each other by electrochemical process
- Contain some specialized structures (synapses) and chemicals (neurotransmitters)

7. Neurons Dendrites carry impulses towards cell body
Most neurons consist of a cell body and extensions called dendrites and axons.
Dendrites carry impulses towards cell body
Axons carry impulses away from the cell body
Cell Body contains the nucleus

8. Neurons Axons enclosed in fatty, insulating layer called myelin sheath
Myelin sheath protects neurons and speeds up rate of nerve impulse transmission
Schwann cells form myelin by wrapping themselves around the axon
Nodes of Ranvier are gaps in myelin sheath
Capable of electrical activity

9. Types of Neurons Sensory neurons Motor neurons Interneurons
Carry nerve impulses from a receptor to the CNS
Have long dendrites and short axons
Motor neurons
Carry nerve impulses from the CNS to an effector
(ex. muscle or gland)
Have short dendrites and long axons
Interneurons
Found completely within the CNS
Provide a link within the CNS between sensory neurons and motor neurons
Have short dendrites and long or short axons

11. Reflex Arc Simplest nerve pathway Occurs without brain coordination
Five components
Receptor
Sensory neuron
Interneuron in spinal cord
Motor neuron
Effector

12. Animation
Very cool animation

14. Electrical Nature of Nerves
Neurons use electrical signals to communicate with other neurons, muscles, and glands
Signals = nerve impulses
Caused by changes in the amount of electric charge across a cell’s plasma membrane

15. Resting Membrane Potential
Uneven concentrations of Na+ (outside) and K+ (inside) on either side of neuron membrane
results in the inside of the neuron being -70 mV
Electrical charge inside of the cell is negative relative to outside of the cell

16. Resting Membrane Potential
3 factors contribute to maintaining resting membrane potential
1) Large, negatively charged protein molecules present inside the cell
2) Ion-specific protein channels on cell membrane allow passive movement of Na+ and K+
K+ channels open at resting allowing K+ to leave cell, making inside cell negative relative to exterior
3) Sodium-Potassium pump actively transports Na+ and K+ in ratios that leave the inside of the cell negatively charged

17. Resting Membrane Potential
Sodium-potassium pump
Most important contributor to separation of charge
Every 3 Na+ transported out of cell, 2 K+ brought in
Excess positive charge accumulates outside cell

18. Resting Membrane Potential
Polarization: The process of generating a resting membrane potential of -70mV

19. Action Potential
A nerve cell is polarized because of the difference in charge across the membrane
More negative inside the cell than outside
Depolarization occurs when the cell becomes less polarized (membrane potential is reduced to less than resting potential of -70mV)
Action Potential causes depolarization to occur

20. Action Potential Nerve signals are transmitted by action potentials
Abrupt, pulse-like changes in membrane potential (few ten thousandths of a second)
Can be divided into three phases
Resting/polarized state
Depolarization
Repolarization
The amplitude is nearly constant and is not related to the size of the stimulus. Therefore action potentials are all-or-nothing events.
Threshold potential: a certain level in membrane potential. Once it’s crossed action potential occurs (point of no return)

21. Action Potential timeline

22. Saltatory Conduction

23. Saltatory conductions
Nodes of Ranvier contain many voltage-gated Na channels
Na moves into cell, charge moves quickly through cytoplasm to next node
Causes next node’s membrane to dpolarize to threshold
Previous node’s membrane in refractory state (prevents action potential going backward)
Depolarization initiated to conduct action potential
This continues until pulse reaches end of neuron

24. Terminology
Synapse
Region at which neurons come nearly together to communicate. (neuron or effector organ)
Synaptic Cleft
Gap between neurons (at a synapse)
Impulses can not propagate across a cleft
Synaptic Vesicle
Packets of neurotransmitter in presynaptic neuron
Presynaptic Neuron
Neuron sending a signal (before the synapse)
Postsynaptic Neuron
Neuron receiving a signal (after the synapse)

25. Neurotransmitters
Classical transmitters are small molecules (often amino acid based)
Non-classical transmitters can be peptides or even gasses
5 general criteria:
1) synthesized and released by neurons
2) released at the nerve terminal in a 'chemically identifiable' form
3) the chemical should reproduce the activity of the presynaptic neuron
4) can be blocked by competitive antagonist based on concentration
5) active mechanisms to stop the function of the neurotransmitter

27. Types of Neurotransmitters
Acetylcholine
+ muscles, learning, memory
Serotonin (a derivative of tryptophan)
+ sleep, relaxation, self esteem, too little = depression, perception
Norepinephrine (aka noradrenaline)
+ stress and fight/flight response, sympathetic NS:+BP & heart rate
Dopamine
+ prolactin (milk production), involved in pleasure, movement
Endorphins
(-) pain, involved in pleasure
GABA (gamma aminobutyric acid)
(-) anxiety, too little in parts of brain can lead to epilepsy
Glutamate
Most common NT, memory, toxic

28. Homework
Pg 362 #1, 2, 3, 6, 7, 9, 10