Transcript The Nervous System

The Nervous System
Chapter 11
Functions of the Nervous system I
Sensory (input):
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Light
Sound
Touch
Temperature
Taste
External Chemical
Smell
Internal Chemical
Pressure
Stretch
Functions of the Nervous system II
Integration:
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Integration means making sense of
sensory input. Analyzing stimuli based on
experience, learning, emotion & instinct
and reacting in a useful way (you hope).
Motor (output):
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The response to the sensory input and
subsequent integration. Sending signals to
the muscles and other organs of the body
instructing them how to respond to the
stimuli.
The Basic Scheme
Organization of the Nervous
system
The CNS
compared
with the
PNS
Support Cells of the Nervous system
the Central
Nervous System
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Astrocytes
Microglia
Oligodendrocytes
Ependymal Cells
the Peripheral
Nervous System
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Schwann Cells
(a.k.a.
Neurolemmocytes)
Satellite Cells
Astrocytes & microglia
Astrocytes & microglial cells protect the neurons of the CNS.
Astrocytes & microglia
Functions of astrocytes:
1. Connect neurons to capillaries. This makes up
the “blood-brain barrier”.
2. Maintain the the electrochemical environment
• Capture and recycle neurotransmitters
• Absorb and return K+ and other ions.
• Connected to one another and capable of
communicating via gap junctions.
Function of microglial cells:
1. Dendritic macrophages that phagocytize
microbes and necrotic (dead) tissue.
Ependymal Cells &
oligodendrocytes
Ependymal Cells &
oligodendrocytes
Functions:
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Ependymal Cells - Line the ventricles of
the brain an central canal of the spinal
cord. They aid in the circulation of
cerebrospinal fluid (CSF).
Oligodendrocytes - These cells have
processes that wrap around the axons of
neurons. This creates an insulation coating
called a myelin sheath.
Schwann Cells & satellite cells
•These are the support cells in the peripheral nervous
system.
•Schwann cells provide the myelin sheath for peripheral
axons.
•Satellite cells serve a slightly similar function to astrocytes,
supporting the cell bodies of peripheral neurons.
Neurons - the “action cells”
Characteristics of neurons
Long-lived
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Generally last a life time with 90% are formed
by the time you are 6 years old. The rest are
produced when as you go through puberty.
Amitotic
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Until recently it was thought that neurons
didn’t regenerate at all! Some may but
generally what you have at adulthood is all
you get.
High metabolic rate
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This means high oxygen demand and lots of
mitochondria. Neurons also require glucose.
Myelin
Myelin is a lipid-rich
component of the
cell membranes of
Schwann cells and
oligodendrocytes.
It acts kind of like
the insulation on an
electrical wire.
Chemically gated ion channels
Voltage gated ion channels
A Resting Membrane Potential
Because there is
a higher
concentration of
Na+ outside than
there is K+ inside.
This leads to an
electric charge or
electric potential.
Relative ion concentrations
Ions have differential permeability. The RMP is maintained by
the pumping action of a Na+/K+ pump, powered by ATP
Polarization (subthreshold) and hyperpolarization
A stimulus leads to a depolarization
A change in ion
concentrations
leads to a
reversal of the
charge
separation.
Ion flow in a neuron
The
depolarization
spreads along
the cell
membrane by
serial opening
and closing of
ion gates.
A graded potential
Graded
potentials are
not “all-ornone”, like
action potentials
The cycle of an Action Potential
Propagation of an Action Potential
Propagation of an Action Potential
Propagation of an Action Potential
Temporal summation
Anatomy of an Action Potential
Salutatory conduction
Different types of synapses
A Chemical Synapse
EPSPs &
IPSPs
Integration: summation of potentials
Synthesis of
Neurotransmitters
Mechanisms of Neurotransmitter activity
A Basic Neural Circuit
Type of neurons
Three structural classes of neurons
Multipolar
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Most numerous
Many dendrites
Motor and association neurons
Unipolar
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Second most numerous
Rounded body with one process
Somatic & general sensory neurons
Bipolar
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Least common, found in special sensory organs
Comparison of neuron types
Functional categories of neurons
This is it for 231
Lecture Final at 10 am next Tuesday.
Lab Practicals: Tuesday, 6/8 @ 2 pm
Thursday, 6/10 @ 10 am
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