Flashcards in Lecture 11 Neurons and Neural signals Deck (40)
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1
Functions of the Nervous system
sensation
communication
integration
control
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Neurons
functional cells of the nervous system
excitable cells- generate electrical signals (changes in membrane potentials)
communicate information in the form of electrical and chemical signals
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Cell body of a neuron
contains the nucleus and most organelles
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dendrites
branch from the cell body
receive signals from other cells through synapse
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axon
extends from the cell body, conducts action potentials
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axon hillock
region where axon joins the cell body
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Trigger zone
initial segment adjacent to the axon hillock is the trigger zone for AP
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axon terminals
contain vesicles with neurotransmitter, form synapses with other cells
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Central Nervous system
brain and spinal cord
where most neurons are located
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Peripheral Nervous System
Nerves, ganglia and sensory receptors
Afferent Division
Efferent Division
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Afferent Division
Sensory neurons, input to CNS from sensory receptors
somatic sensory- from skin, muscles, bones & joints
Visceral sensory- from internal organs
Special senses- vision, hearing, equilibrium, olfaction, taste
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Efferent Division
Motor neurons, output from CNS to effectors
Somatic Motor- to skeletal muscles (voluntary)
Autonomic (ANS) - to heart, smooth muscle, gland, adipose tissue (involuntary)
a.sympathetic
b. parasympathetic
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Enteric Nervous System
Nerve network of the GI tract
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Functional Types of Neurons
Sensory neurons
Motor neurons
Interneurons
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Sensory Neurons
afferent
Input to CNS from sensory receptors; dendrites located at receptors, axon in nerves, cell bodies in ganglia outside the CNS
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Motor Neurons
efferent
Output from CNS to effectors
cells bodies and dendrites located in the CNS, axons in nerves
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Interneurons
communicate and integrate information within the CNS
located entirely within the CNS
Most common
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Astrocytes
CNS
structural and chemical support, blood-brain barrier
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Oligodendrocytes
CNS
Myelin in CNS
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Microglia
CNS
Phagocytes
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Ependymal cells
CNS
produce CSF
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Schwann cell
myelin in PNS
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satellite cells
in PNS ganglia
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Graded Potentials
small, localized changes in membrane potential
formed at the cell body and dendrites
can be depolarization or hyperpolarization
spread passively and weaken with distance
size depends on stimulus strength
seen at cell bodies and sensory receptors
Stimulates action potentials
caused by opening of chemically gated channels
must exceed threshold to start AP
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Action Potentials (nerve impulses)
large change in membrane potential
formed along the axon
rapid depolarization followed by repolarization
actively conducted along the axon
all or none- size is not dependent on stimulus strength
Doesn't weaken with distance
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Phase 1 of action potentials
Rising (Depolarization) phase
-initial depolarization stimulus must be above threshold to form an AP
-voltage gated Na+ channels open
-activation gate opens in response to initial depolarization
-> rapid Na+ inflow -> rapid depolarization
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Phase 2 of action potentials
Falling (repolarization) Phase
-Voltage gated Na+ channels close
inactivation gate - closes when depolarization reaches peak
-voltage gated K+ channels open
->rapid K+ outflow-> repolarization
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Phase 3 of action potentials
Undershoot
voltage gated K+ channels remain open, high K+ permeability results in hyperpolarization
resting states of channels and resting potential restored at end of undershoot phase
-both voltage gates closed only the leak channels open when RP is restored
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Name the properties of action potentials
threshold
all or more
regenerative
refractory period
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