Download Neurons

Neurons
• Vary in size and shape
• Share certain features
– Dendrites- receive signal
– Cell body- contains nucleus
– Axon- transmits signal to another neuron
Neuron structure
• Dendrites
– Receive incoming
signals
– Transfer to cell body
of neuron
• Cell body
– Typical cell structures
– cytoskeleton
Neuron structure
• Axon
– Transmits signal to
synapse
Neuron structure- synapse
• Region where axon meets target cell
• Space across which neurotransmitter diffuses
Myelination of axons
• Myelin- lipids and proteins that wrap around
an axon
• White matter
– Contains myelinated neurons
• Gray matter
– Contains unmyelinated neurons
Dendrite
Unmyelinated
region of axon
Myelinated region of axon
Node of Ranvier
Axon
Neuron
cell body
Neuron
nucleus
• http://www.youtube.com/watch?v=x4PPZCLn
VkA&list=PL3EED4C1D684D3ADF&index=26
Types of Neuroglial Cells
•Abundant (50 X more glial cells than neurons)
•Nourish neurons
•May send and receive messages
•Provide supportive framework
Types of Neuroglial Cells in the PNS
Schwann Cells
•produce myelin found on peripheral
myelinated neurons speed
neurotransmission
Satellite Cells
•support clusters of neuron cell bodies
(ganglia)
Types of Neuroglial Cells in the CNS
Astrocytes
• CNS, scar tissue
• mop up excess ions, etc
• induce synapse formation
• connect neurons to blood vessels
Microglia CNS phagocytic cell
Oligodendrocytes
• CNS
• myelinating cell
Ependyma
•CNS ciliated
• line central canal of spinal cord
• line ventricles of brain
Neurons
• Cell body
• Axon conducts impulses away from the cell
body
Nodes of Ranvier
Myelin sheath
• Dendrites transmit impulses into the cell body
Neuron Structure
10-7
Resting Membrane Potential
• inside is negative
relative to the outside
• polarized membrane
due to distribution of
ions by the Na+/K+
pump
10-14
•at rest membrane is
polarized
•threshold
stimulus reached
• sodium channels
•
open
and
membrane
depolarizes
• potassium leaves
cytoplasm and
membrane
repolarizes
Potential Changes
Action Potentials
10-18
Action potential
• All or none response
• Movement of Na+ and K+ ions
– Calcium ions are required to close sodium channels
– Low Ca+2 may cause tentany
• Changes in membrane permeability can change the
impulse conduction
– High K+ excitable convulsions
– Low K+ paralysis
– Some anesthetic medications can change membrane
permeability to sodium and prevent impulses (eg procaine)
20
Saltatory Conduction
10-20
10.3 Clinical Application
Factors Affecting Impulse Conduction
22
Videos
• http://www.youtube.com/watch?v=dSkxlpNs3tU
• http://www.youtube.com/watch?v=9euDb4TN3b0
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter
14/animation__transmission_across_a_synapse.ht
ml
The Synapse
Nerve impulses pass
from neuron to
neuron at synapses
10-21
Synapse Greek to clasp or join
• typical neuron has 1,000-10,000 terminals
• mechanism by which the action potential passes
from one neuron to another is NOT the same as
the way the action potential is conducted along the
neuron.
• transmission across the synapse is dependent on
chemical neurotransmitters
• the neurotransmitter diffuses across the synapse
and alters the membrane potential of the next
neuron
Synaptic Transmission
10-22
Synaptic Potentials
Excitatory postsynaptic potential (EPSP)
• Graded
• Depolarizes membrane of postsynaptic neuron
•Action potential of postsynaptic neuron becomes
more likely
Inhibitory postsynaptic potential (IPSP)
•
•Graded
• Hyperpolarizes membrane of postsynaptic neuron
• Action potential of postsynaptic neuron becomes
less likely
Summation of
EPSPs and IPSPs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• EPSPs and IPSPs are added
together in a process called
summation
• More EPSPs
•Increased probability of
an action potential
Neuron
cell body
Nucleus
Presynaptic
knob
Presynaptic
axon
• Summation usually occurs at
the trigger zone
29
30
Neurotransmitters
31
Neuropeptides
• Neurons in the brain or spinal cord synthesize
neuropeptides.
• Some act as neurotransmitters.
• Others act as neuromodulators (substances which alter
a neuron’s response to a neurotransmitter or block the
release of a neurotransmitter)
• Examples include:
• Enkephalins
• Beta endorphin
• Substance P
32
10.4 Clinical Application
Opiates in the Human Body
33
Regeneration of A Nerve Axon
10-13
Referred Pain