Transcript Nervous System PPT - Old Saybrook Public Schools

Neurons, Synapses and
Signaling
A peek inside the nervous system
Peripheral vs Central Nervous System
Neural Networks
Neurons
Nerve - bundle of axons
Supporting Cells
Glial Cells
Functions of
Supporting Cells
Schwann Cells - surround axons of PNS, form myelin sheaths
Oligodendrocytes - form myelin sheaths around axons in CNS, white matter of CNS
Microglia - phagocytose pathogens and cellular debris in CNS
Astrocytes - cover capillaries, create blood-brain barrier
Ependymal cells - epithelial lining of ventricles (brain cavities) and
central canal of the spinal cord
Neurons are excitable
neurons and muscle cells are excitable
transmit signals 20-100 meters/second
cell membrane generates impulses or action
potentials
Resting Potential
voltage - measures the electrical charge difference between 2 points
(potential energy), produce currents
ions carry electric current (Na+, K+, Ca2+, Cl-)
membrane potential - different ion concentrations across a membrane ->voltage
inactive neuron -60 to -70 mV
due to many negatively charged proteins the inside of the cell is more negatively
charged compared to the outside
maintained by K+ leak channels
+
+
Na -K Pump
(ATPase)
plasma membrane impermeable to ions
channels and ion transporters, glycoproteins, all animal cells
uses ATP to pump 3 Na+ outside and pumps 2 K+ inside against the
gradient
creates concentration gradients
generates resting potential
[Na+] higher outside the cell while [K+ ] is higher inside the cell
+
K Leak
Channels
always open, K+ diffuses out due to concentration gradient
leaves behind an overall negative charge
negative charges want to pull K+ back in
the tug-and-pull created is the resting potential
maintains the resting potential
Gated Channels
voltage-gated - open or close due to changes
in membrane potential
stretch-gated - open or closed to due to tension
applied to the cell membrane
ligand-gated - ligand binding sites, open and
closed based on the binding of the matching
ligand (neurotransmitter)
Action Potential
Brief, rapid changes in membrane potential
Originates in the axon hillock, after
-50mV or greater membrane potential
reached
Voltage gated Na+ channels open, depolarizing
the membrane
Na rushes into the axon, briefly creating a positive
charge within the axon, from -65mV to +40 mV
Each region stimulates the next region of the axon
K+ channels open restoring the membrane potential
Depolarization - charge on inside of membrane
becomes less negative relative to the outside
Hyperpolarization - charge on inside becomes
more negative
Positive feedback
Synapses
signal transmission via cell-to-cell contact
points
synaptic cleft is 20-30 nm (human hair 20,000 nm)
chemical synapse - neurotransmitters
electrical synapse - gap junctions that spread
the action potential
Chemical Synapse
Neuromuscular Junction
Neurotransmitters
Acetylcholine -muscle stimulation, memory, learning; nicotine binds to
receptor, sarin (nerve gas) blocks enzymatic breakdown of, botulinum
toxin inhibits release of
Glutamine - long term memory
GABA - amino acid in brain, inhibitory synapse; Valium reduces anxiety
by binding to a GABA receptor
Biogenic amines - dopamine, serotonin: LSD binds to receptors leads
to hallucinations; Parkinson’s due to lack of dopamine; Prozac inhibits
reuptake of serotonin
Neuropeptides - endorphins- relieve pain, produce euphoria; opiates
bind to same receptors
Multiple Sclerosis
Loss of myelin in the CNS - demyelinating
immune mediated response
damage to nerve fibers
most common autoimmune disorder
Lou Gehrig’s
Amyotrophic lateral sclerosis
5-10% inherited, autosomal dominant
Death of neurons that control voluntary
muscles
Neurotransmitter Glutamate may be involved
potentially many causes
Parkinson’s