Physiology Chapters 7 And 8: Nerves

Front 1

Central nervous system (CNS) (2)

Back 1

-Brain
-Spinal cord

Front 2

Peripheral nervous system (PNS) (2)

Back 2

-Afferent information (input)
-Efferent information (output)

Front 3

Neurons

Back 3

Excitable cells

Front 4

Glial cells

Back 4

Support cells

Front 5

Soma (body)

Back 5

Contains nucleus and most organelles

Front 6

Dendrites

Back 6

Reception of incoming information

Front 7

Axon

Back 7

Transmits electrical impulses called action potentials

Front 8

Axon hillock

Back 8

Where axon originates and action potentials initiated

Front 9

Axon terminal

Back 9

Releases neurotransmitter

Front 10

Synapse

Back 10

Site of communication between two neurons or between a neuron and an effector organ

Front 11

Ion Channels: Neurons
Leak channels

Back 11

Always open

Front 12

Ion Channels: Neurons
Ligand-gated channels

Back 12

Open or close in response to ligand binding

Front 13

Ion Channels: Neurons
Voltage-gated channels

Back 13

Open or close in response to change in membrane potential

Front 14

Voltage-gated Channels (6)

Back 14

-Sodium and potassium channels
=Throughout, but more in axon (especially axon hillock)
=Action potentials
-Calcium Channels
=Axon terminal
=Release of neurotransmitter

Front 15

Glial Cells (5)

Back 15

-Astrocytes
-Ependymal cells
-Microglia
-Oligodendrocytes *
-Schwann cells *

Front 16

Myelin Forming Cells
Oligodendrocytes (4)

Back 16

-Central nervous system
-One oligodendrocyte
-Forms several myelin sheaths
-Myelinates sections of several axons

Front 17

Schwann cell (4)

Back 17

-Peripheral nervous system
-One Schwann cell
-Forms one myelin sheath
-Myelinates one section of an axon

Front 18

Resting Membrane Potential (4)

Back 18

-At rest, all cells have a negative internal charge & unequal distribution of ions:
-Approximately -70 mV
-Exists because more negative charges inside cell and more positive charges outside cell
-Na+/K+ pump & limited permeability keep Na+ high outside cell

Front 19

Potassium Equilibrium Potential (2)

Back 19

-K+ chemical driving force is out of cell
-K+ diffuses out of cell

Front 20

Forces Acting on Na+ (3)

Back 20

-Two forces acting on Na+
-Chemical to in (concentration gradient)
-Electrical to move out

Front 21

Sodium Equilibrium Potential

Back 21

-Chemical and electrical driving forces are
-Opposite in direction
-Equal in magnitude

Front 22

Resting Membrane Potential of Neurons (8) (typical neuron)

Back 22

-Typical neuron
-Permeable to potassium and sodium
=25 times more permeable to potassium
-Ion distribution
=Outside cell
+Sodium and chloride
=Inside cell
+Potassium and organic anions

Front 23

A Neuron at Rest (3) (leak test)

Back 23

-Small Na+ leak at rest (high force, low permeability)
-Small K+ leak at rest (low force, high permeability)
-Sodium pump returns Na+ and K+ to maintain gradients

Front 24

Electrical Signals: Neurons (5) (Membrane potential changes)

Back 24

-Membrane potential changes
-Due to gated channels
=Open or close in response to stimuli
=Affect movement of ions
=Ion movement—electrical signal

Front 25

Electrical Signals: Neurons
Types of gated channels (3)

Back 25

-Voltage-gated
-Ligand (chemically) gated
-Mechanically-gated

Front 26

Membrane Potential Changes (4)

Back 26

-Resting potential—reference point
-Depolariation
-Repolarization
-Hyperpolarization

Front 27

Types of Electrical Signals (3)

Back 27

-Graded potentials
=Small
-=Communicate over short distances
-Action potentials
=Large
=Communicate over long distances

Front 28

Action Potentials (5)

Back 28

-Excitable membranes have ability to generate action potentials
-Action potential
=Rapid large depolarization along axon
-In neurons
=Action potentials travel along axons from cell body to axon end (terminal)

Front 29

Phases of an Action Potential

Back 29

-Depolarization
-Repolarization
-After-hyperpolarization

Front 30

Depolarization to Threshold

Back 30

-Graded potentials bring membrane to threshold
-Threshold triggers
-Rapid opening of sodium channels
-Slow closing of sodium channels
-Slow opening of potassium channels

Front 31

Action Potential
Depolarization (4)

Back 31

-Depolarization:
-At threshold, Na+ channels open
-Na+ driven inward by its electrochemical gradient
-This adds to depolarization, opens more channels
-Causes a rapid change in MP from –70 to +30 mV

Front 32

Action Potential
Repolarization: (3)

Back 32

-Na+ channels close; K+ channels open
-Gradient drives K+ outward
-Repolarizes axon back to RMP

Front 33

All-or-None Principle

Back 33

-Threshold
-Minimum depolarization necessary to induce the regenerative mechanism for the opening of sodium channels
-Threshold depolarization --> action potential
-Subthreshold depolarization --> no action potential

Front 34

Refractory Period

Back 34

-Period of time following an action potential
-Marked by decreased excitability

Front 35

Propagation of Action Potentials

Back 35

Mechanisms depend on presence or absence of myelin

Front 36

Factors Affecting Propagation (3)

Back 36

-Refractory period
=Unidirectional
-Axon diameter
=Larger
+Less resistance, faster
=Smaller
+More resistance, slower
-Myelination
=Saltatory conduction
=Faster propagation

Front 37

Maintaining Neural Stability (3)

Back 37

-Graded potentials and action potentials will disperse Na+ and K+ ions
-But only small percent of ions actually move
+
-Na+ and K+ pump continues

Front 38

Synapse (2)

Back 38

-Functional association of a neuron with
=Another neuron
=Effector organs (muscle or gland)
-Types
=Electrical
+Two neurons linked together by gap junctions
=-Chemical

Front 39

Components of a Synapse

Back 39

-Presynaptic neuron (membrane)
-Postsynaptic neuron (membrane)
-Synaptic cleft

Front 40

Anatomy of a Synapse (7)

Back 40

-Axon terminal
-Synaptic vesicles with neurotransmitter
-Voltage-gated calcium ion channel
-Synaptic cleft
-Receptor
-Enzyme
-Reuptake molecule

Front 41

Communication Across a Synapse (8)

Back 41

1 . Action potential
2 . Voltage-gated Ca channels open
3 . Calcium triggers exocytosis
4 . NT diffuses and binds to receptor
5 . Response in cell
-Response terminated by removing neurotransmitter from synaptic cleft
6 . Degradation
7 . Reuptake
8. Diffusion

Front 42

Postsynaptic Potential (4)

Back 42

-PSP
-Change in membrane potential in response to receptor-neurotransmitter binding
-Some are excitatory (EPSP)
-Some are inhibitory (IPSP)

Front 43

Neurotransmitters

Back 43

Chemical messengers of neurons

Front 44

Acetylcholine (2)

Back 44

-Found in PNS and CNS
-Most abundant neurotransmitter in PNS

Front 45

Breakdown of Acetylcholine (2)

Back 45

Acetylcholine --> acetate + choline
-Degradation occurs in synaptic cleft
-Enzyme of degradation = acetylcholinesterase (AChE)

Front 46

Cholinergic Synapse (2)

Back 46

-Synapse utilizing acetylcholine
-CAT = choline acetyl transferase

Front 47

Other Neurotransmitters
-Derived from amino acids (6)

Back 47

-Derived from amino acids
-Catecholamines—derived from tyrosine
-Dopamine
-Norepinephrine
-Epinephrine
-Serotonin—derived from tryptophan
-Histamine—derived from histidine

Front 48

Serotonin (3)

Back 48

-CNS neurotransmitter
-Main location
-Brainstem
-Functions
-Regulating sleep
-Emotions

Front 49

Amino Acid Neurotransmitters (2)

Back 49

-Amino acid neurotransmitters at excitatory synapses
-Aspartate
-Glutamate
-Amino acid neurotransmitters at inhibitory synapses
-Glycine
-GABA

Front 50

Neuropeptides

Back 50

-Examples
-Vasopressin (ADH)
-Oxytocin

Front 51

Drug Action on Nerves
Less Depolarizaton: (3)

Back 51

Less Depolarizaton:
-Novocain – harder to reach threshold
-Alcohol - harder to reach threshold
-Barbiturates-Ach release slowed

Front 52

Drug Action on Nerves
More Depolarizaton: (2)

Back 52

-Caffeine –easier/threshold
-Nicotine - binds to Ach receptors (nicotinic)

Front 53

Drug Action on Nerves
Insecticides
Succinylcholine
Curare
Tetrodotoxin

Back 53

-Insecticides - inhibits acetylcholinesterase
-slows clearing out of synapse nerve cannot be used again until cleared
-Succinylcholine - binds to receptor, decomposes slowly - relaxed muscles

-Curare - blocks Ach binding sites

-Tetrodotoxin –blocks channels

Front 54

Stimulus

Back 54

- if strong enough may cause depolarization and graded potential

Front 55

Graded Potential (2)

Back 55

- localized change in membrane potential
if strong enough -action potential
-Threshold reached

Front 56

Action potential

Back 56

- rapid change in membrane potential - along axon

Front 57

Refractory Period

Back 57

- Period after impulse when nerve is not able to respond to another stimulus

Front 58

Neurotransmission

Back 58

- Conduction of impulse through nervous system

Front 59

Resting membrane potential

Back 59

- Polarized (more positive outside, negative inside)

Front 60

Chemical Transmission (3)

Back 60

- between two neurons
- neurotransmitter (chemical substance)
- Occurs across synapse

Front 61

Depolarization

Back 61

- change in resting membrane potential from Neg. inside to positive.

Front 62

Repolarization

Back 62

- back to resting state