Transcript 7-Nerves - bloodhounds Incorporated

PHYSIOLOGY
Nervous System
Types of Neurons

Afferent
 Sensory

Efferent
 Motor

Interneurons also known as association
neurons
 Between
neuron
Classes of Sensory Receptors also known as Neurons
Mechano-receptors: mechanical forces- stretching alters membrane
permeability
(1) hair cells* (deflection = depolarization = AP's)
ie. lateral line of fish (mechanoreceptor=
neuromasts detect water movement, etc)
(2) stretch receptors of muscles
(3) equilibrium receptor of inner ear
(4) receptors of skin (touch, pain, cold, heat).
Chemo-receptors: chemicals sense solutes in solvents, taste, smell
Osmo-receptors: of hypothalamus which monitors blood osmotic
pressure
Photo-receptors: light - eye, eyespots, infrared receptors of snakes,
etc.
Thermo-receptors: radiant (heat) energy
Phono-receptors: sound waves
Electro-receptors: detect electric currents... electric eels, etc..
Nociceptors: pain receptors... naked dendrites of skin (epidermis)
Neuroglial Cells of the CNS
Astrocytes
In the CNS only
 Most abundant Neuroglial Cell
 Formation of Synapses
 Plays a role in making exchanges between
capillaries and neurons
 Helps to form the Blood Brain Barrier

 The
BBB protects the brain from intruders
Astrocytes
Microglial Cells

Macrophage
 Scavenges

apoptotic cells
May go bad causing Alzheimer’s Disease

Excessive secretion of Interleukin-1
 Helps
to maintain homeostasis in the brain
Ependymal Cells of the CNS
Ependymal Cells
Lines ventricles in the brain and the
central cavity of the spinal cord
 Cells have cilia

 Used
to circulate the cerebrospinal fluid
Oligodendrocyte Cells of the CNS
Oligodendrocyte

Oligodendrocytes
 Production
of myelin in
the CNS
 Can cover as many as
60 neurons with
myelin
Schwann/Satellite Cells

Schwann Cells
 Production
of myelin in the PNS
 Not able to cover one neuron, must use
multiple Schwann Cells
 Formation of the Nodes of Ranvier
 Produces Neuronal Growth Factor

Satellite Cells
 Function
unknown
Myelin Sheath

Myelin
 Insulates
the axon for rapid conduction of
action potentials

Nodes of Ranvier
 Gray
v. White matter in the brain
 Multiple Sclerosis is an autoimmune disease

http://www.youtube.com/watch?v=Naecv3
h868c
Neuron

Receptive Zone
 Where

the Graded Response occurs
Cell Body
Same information as a regular cell but no centrioles
 Amitotic
 Contains ligand regulated gates


Dendrites
Projections to help form synapses
 Contains ligand regulated gates

Neuron

Conducting Zone
 Axon
Hillock
Begins action potentials
 Accumulation of K+ ions
 Contains voltage regulated gates for Na+/K+

 Axon
Propagation of action potentials
 Contains voltage regulated gates for Na+/K+
 Anterograde vs. Retrograde and Polio

Secretory Zone
 Terminal
Boutons
Contains voltage regulated gates for Ca+2
 Contains vesicles filled with Neurotransmitter

Resting Membrane Potential


-70 mV
Membrane is said to be polarized
 Voltage
generated by ionic movement through the
membrane

Creates a current




Current = Voltage/ Resistance
Current generates a Kinetic Energy
More Na+ on the outside of the cell
More K+ on the inside of the cell
 Diffusion
down their electrochemical gradient
Resting Membrane Potential

Maintained by the Na+/K+ATPase pumps
 Will
not allow the neuron to reach equilibrium
across the membrane
 Actively transports 3Na+ out of the cell and
2K+ into the cell
Graded Response


Short lived
Localized changes in membrane potential
 Can depolarize or hyperpolarize
 Dependent on IPSP or EPSP

the membrane
The magnitude of the graded potential varies
directly with the stimulus strength
 The
stronger stimulus causes greater voltage change
and the current flows farther

The current dies out within a few millimeters of
its origin
 Graded
response only signals over a very short
distance
Graded Response

Ligand sensitive Na+ gates will open with
a stimulus
 Na+
diffuses into the cell down its
electrochemical gradient

Depolarization of the membrane
 K+
is repelled down the membrane towards
the axon hillock

K+ can diffuse out of the cell because the plasma
membrane is very “leaky”
Action Potentials
Begins at the axon hillock
 Voltage regulated Na+ and K+ gates

 Along
with Na+/K+ATPase pumps along the
entire membrane

All or nothing response
Action Potentials

Depolarization
 -50mV
due to the accumulation of K+ at the axon
hillock triggers an action potential
 At -50mV Na+ voltage regulated gates open


Na+ diffuses into the cell down its electrochemical gradient
Na+ repels K+ down the membrane
 Positive Feedback “on”
 The more positive the voltage, due to Na+ diffusing into the
cell, the more Na+ gates open. This creates a more positive
voltage and more Na+ gates open
 Positive Feedback
 +30mV
“off”
Action Potential

Repolarization
 At
+30mV
All Na+ gates close quickly
 All K+ gates open



K+ diffuses out of the cell down its electrochemical
gradient
K+ gates close slowly at -70mV

K+ continues to diffuse out of the cell until it reaches
-90mV
 All K+ gates are closed
Action Potential

Hyperpolarization
 At

-90mV the Na+/K+ATPase pump turns on
Pumps 3Na+ out and 2K+ into the cell

Re-establishes resting membrane potential
Propagation of an Action Potential

As the influx of Na+ repels the K+ down
the membrane there is an accumulation of
K+
 The
K+ accumulation with change the
membrane voltage to -50mV
 The occurs when the previous action potential
reaches +30mV

Repolarization is chasing Depolarization
down the membrane
Refractory Period

Absolute refractory
 From
the opening of the Na+ channels until the Na+
channels begin to reset to their original resting state
 Cannot re-stimulate the neuron during this time

Relative refractory
 The


interval following the absolute refractory period
Na+ channels have returned to their resting state
K+ channels are still open and repolarizing the membrane
 Can
re-stimulate the neuron during this time with a
great stimulus
Synapse
Presynaptic neuron
 Postsynaptic neuron
 Synaptic Cleft

 About

10 angstroms between neurons
Synaptic Vesicles
 Filled
with neurotransmitter
Synapse
Voltage regulated Calcium channels
 Membrane reaches -50mV due the
accumulation of K+
 Calcium channels open

 Calcium
diffuses in down its electrochemical
gradient

2 Calcium ions bind to the vesicle
 The
vesicle fuses with the membrane for
exocytosis of the NT
Synapse

The Neurotransmitter crosses the synaptic
cleft
 NT
binds to the receptors on the postsynaptic
neuron

Neurotransmitter are removed from the
synaptic cleft by:
 Reuptake
 Phagocytosis
 Enzymatic
Degradation
Events at the Synapse
AP reaches axon terminal
Voltage-gated Ca2+ channels open
Ca2+ entry
Ca2+ = Signal for
Neurotransmitter
Release
Exocytosis of neurotransmitter containing
vesicles
1. Axon Diameter
Fig. 8-18
2. Signal Transduction in Myelinated Axon:
Animation
Demyelination
diseases (E.g. ?)
3 Classes of Neurotransmitters (of 7)
1.
Acetyl Choline (ACh)
–
–
–
–
Made from Acetyl CoA and choline
Synthesized in axon terminal
Quickly degraded by ACh-esterase
Cholinergic neurons and receptors – Nicotinic (agonistic)
and muscarinic (antagonist)
2.
Amines
–
Serotonin (tryptophane) and Histamine (histidine)

–
–
–
3.
Dopamine and Norepinephrine (tyrosine)
Widely used in brain, role in emotional behavior (NE used in ANS)
Adrenergic neurons and receptors -  and 
Gases
–
4.
SSRI = antidepressants
NO (nitric oxide) and CO
Others: AA, (e.g., GABA), lipids, peptides, purines
Neurotransmitters

Cholinergic Receptors
 Nicotinic
 Muscarinic

Catecholamine
 Alpha
 Beta
Nicotinic Receptors
Stimulated by ACh and nicotine, not
stimulated by muscarine.
 Found at all ganglionic synapses.
 Also found at neuromuscular junctions.
 A ligand sensitive gate

Muscarinic Receptors





Stimulated by ACh and muscarine, not stimulated by nicotine.
Found at target organs when ACh is released by post-ganglionic
neurons (all of parasympathetic, and some sympathetic).
Stimulated selectively by Muscarine, Bethanechol.
Blocked by Atropine.
Stimulation causes:








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Increased sweating.
Decreased heart rate.
Decreased blood pressure due to decreased cardiac output.
Bronchoconstriction and increased bronchosecretion.
Contraction of the pupils, and contraction of ciliary body for near vision.
Tearing and salivation.
Increased motility and secretions of the GI system.
Urination and defecation.
Engorgement of genitalia.
Catecholamine Receptors


NE and epinephrine, each act on α- and β-adrenergic
receptors
Two subclasses of α-adrenergic receptors




Activation of α1-receptors usually results in a slow depolarization
linked to the inhibition of K+ channels
activation of α2-receptors produces a slow hyperpolarization due
to the activation of a different type of K+ channel.
There are three subtypes of β-adrenergic receptor
Agonists and antagonists of adrenergic receptors

β-blocker propanolol (Inderol®).

However, most of their actions are on smooth muscle receptors,
particularly the cardiovascular and respiratory systems
α1 adrenergic receptors
Mainly involved with contraction of smooth
muscle
 G protein, cAMP action

α2 adrenergic receptors

Three types of receptors
 α2A,

α2Β, and α2C
These receptors have a critical role in
regulating neurotransmitter release from
sympathetic nerves and from adrenergic
neurons in the central nervous system
β1 adrenergic receptors

Specific actions of the β1 receptor include:
 Increases

cardiac output
by raising heart rate and increasing the volume
expelled with each beat (increased ejection
fraction).
 Renin
release from juxtaglomerular cells.
 Lipolysis in adipose tissue.
β2 adrenergic receptors

Specific actions of the β2 receptor include:
 Smooth
muscle relaxation, e.g. in bronchi.
 Relax non-pregnant uterus.
 Relax detrusor urinae muscle of bladder wall
 Dilate arteries to skeletal muscle
 Glycogenolysis and gluconeogenesis
 Contract sphincters of GI tract
 Thickened secretions from salivary glands.
 Inhibit histamine-release from mast cells
 Increase renin secretion from kidney
β3 adrenergic receptors

Specific actions of the β3 receptor include:
 Enhancement
 CNS
effects
of lipolysis in adipose tissue.
Neurological Communication
There’s no one-to-one communication
between neurons
 May be as many as 500 neurons
communicating with a single neuron

 Convergence
 Divergence
Postsynaptic Responses
Can lead to either EPSP or IPSP
Any one synapse can only be either excitatory or inhibitory
Fast synaptic potentials
Opening of chemically gated ion channel
Rapid & of short duration
Slow synaptic potentials
Involve G-proteins and 2nd messengers
Can open or close channels or change protein composition of
neuron
Integration of Neural Information
Transfer
Multiple graded potentials
are integrated at axon
hillock to evaluate
necessity of AP
1. Spatial Summation:
stimuli from different
locations are added up
2. Temporal Summation:
sequential stimuli added
up
1. Spatial Summation
2. Temporal Summation
General Adaptation Syndrome
General Adaptation Syndrome

Hans Selye
Alarm Phase
A
stressor disturbs
homeostasis
 Cerebral Cortex alerts
Hypothalamus which
alerts the Sympathetic
Nervous System
General Adaptation Syndrome

Resistance Phase
 Body
reacts to
stressor
 Attempts to return to
homeostasis
 Down and Up
Regulation
General Adaptation Syndrome

Exhaustion Phase
 Physical
and Psychological
energy is sapped

Atypical depression




Mood disorder
Dysphoria -generally
characterized as an unpleasant
or uncomfortable mood, such as
sadness (depressed mood),
anxiety, irritability, or
restlessness
Serious illness(es) may occur
Hits person at weakest genetic
point


Autoimmune Disease(s)
Endorphins Increase and inhibit
the immune system response
General Adaptation Syndrome

Final Phase is Death
Dermatomes
Dermatomes
Bipolar Neuron

Two processes
 An
axon and a
dendrite

They extend in opposite
directions
 Used
for sensory
organs


Olfactory neurons
Retina
Unipolar Neurons


Presence of only a
single axon,
branching at the
terminal end.
True unipolar neurons
not found in adult
human; common in
human embryos and
invertebrates