1. NOTES- Nervous System part 2
Neuron Repair, Synapse, & Neurotransmitters

2. Repair of Nerve Fibers
Mature neurons cannot undergo mitosis so damage to nervous tissue can be permanent
Neurons have a limited capacity to repair themselves and can be repaired if the damage is not extensive
Neurons can repair themselves if the cell body and neurilemma (cell membrane) remain intact and scarring has not occurred

3. Stages of the Healing Process in the PNS
An injury occurs resulting in a cut axon
Immediately after, the distal portion of the axon degenerates
Macrophages (immune system cells) move into the area and remove the debris
A tunnel is formed by the neurilemma to the effector
New Schwann cells grow in this tunnel and leave a path for the axon
The axon bud begins to regrow in the path
It will grow 3-5 mm a day

6. During this time, the muscle stimulated by the damaged nerve atrophies
If the neuron fails to repair itself, an adjacent neuron may form a connection with the muscle
Neuron repair does not take place in the CNS, so most damage is permanent!
Photo caption: An adult rat nerve cell called a neuron normally grows or regenerates only poorly (red-colored nerve cell at top of photo taken through a microscope). But when a neuroscientist manipulated an integrin gene, the adult neuron (green) displayed extensive regenerative growth by extending nerve fibers called axons (green fibers). Photo credit: Maureen L. Condic, University of Utah.

8. SYNAPSE: junction between a neuron and another cell; found between:
-2 neurons
-sensory receptor
& sensory neuron
-motor neuron & muscle cell
-neuron & gland cell

9. Motor Neuron and Muscle Cell
Real vesicles!!

10. elec. signal  chem.signal  elec.signal
most synapses are CHEMICAL SYNAPSES
these cells are separated by a synaptic cleft & a series of events converts:
elec. signal  chem.signal  elec.signal
NEUROTRANSMITTERS: intercellular chemical messengers

13. Synaptic Transmission Review…
An action potential (the electrical signal) reaches the end of the axon/synaptic end bulb
The action potential cannot cross the synaptic cleft
Causes neurotransmitters to be released from vesicles in the synaptic end bulb
The neurotransmitter reaches receptors in the cell of the postsynaptic membrane and causes a new impulse to be initiated

15. There are Different Neurotransmitters!
Some will cause an action potential
in the next cell (excitatory)
Some will inhibit an action potential
in the next cell (inhibitory)
About 50 different neurotransmitters have been identified

16. Example of EPSP (EXCITATORY)

18. Examples of neurotransmitters:
Functions in:
Acetylcholine (ACh)
Neuromuscular junction; stimulates muscle contraction
epinephrine/ norepinephrine
attention & mental focus, cognition
*epin. & norep. also function as hormones in “fight or flight” response
dopamine/ serotonin
dop. & ser. both affect sleep, mood, attention, learning; *LSD & mescaline bind to serotonin receptors*
endorphins
Decrease perception of pain by CNS (inhibitory); *heroin & morphine mimic endorphins*
histamine
Release in hypothalamus promotes alertness