Download topic 6.5 Neurons

Neurons and
Neurotransmitters
Nervous System
– Central nervous system (CNS):
• Brain
• Spinal cord
– Peripheral nervous system (PNS):
• Sensory neurons
• Motor neurons (somatic and
autonomic)
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The Nervous System
The Nervous System
Central Nervous System (CNS)
Brain
Peripheral Nervous System (PNS)
Spinal Cord
•
Motor Neurons
Somatic Nervous System
voluntary movements via
skeletal muscles
Sympathetic
- “Fight-or-Flight” responses
•
Sensory Neurons
Autonomic Nervous System
organs, smooth muscles
Parasympathetic
- maintenance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Divisions of the autonomic nervous system
The Nervous System
• A physical organ system like any other
• 2 main kinds of cells
– Neurons
– Glia
Neurons
 Basic units of the nervous system
 Receive, integrate, and transmit
information
 Operate through electrical impulses
 Communicate with other neurons
through chemical signals
 More about neurons and neuronal
anatomy later
Glial cells
• 100 billion neurons
• 10x more glial cells
• Glial cells
– Support neurons (literally, provide physical
support, as well as nutrients)
– Cover neurons with myelin
– Clean up debris
– “Housewives”
Astrocytes
• Regulate
external
environment
(ions, etc.)
• Most abundant
glial cell
• May contribute
to blood-brain
barrier
and to synapses
Three main types of neurons
• Sensory Neurons
• Interneurons
• Motor Neurons
Sensory (Afferent) vs. Motor (Efferent)
sensory (afferent) nerve
e.g., skin
Neurons that send signals from the senses,
skin, muscles, and internal organs to the CNS
motor (efferent) nerve
Neurons that transmit commands from the
CNS to the muscles, glands, and organs
Gray’s Anatomy 38 1999
e.g., muscle
The Withdrawal Reflex
Neuron Anatomy and Neural
Communication
Neurons
Dendrites
Cell Body
Myelin
Sheath
Axon of another
neuron
Axon
Dendrites of
another neuron
Neural Anatomy
 Dendrite
 the bushy, branching extensions of a
neuron that receive messages and
conduct impulses toward the cell body
 Axon
 the extension of a neuron, ending in
branching terminal fibers, through which
messages are sent to other neurons or to
muscles or glands
Neural Anatomy and
communication
 Synapse
 junction between the axon tip of the sending
neuron and the dendrite or cell body of the
receiving neuron
 tiny gap at this junction is called the synaptic
gap or cleft
 Synapse movie
Specific Parts: The Neuron
Structure
Specific Parts: The Neuron
Function
1.
3.
2.
Neurons = 3 functions: Reception, Conduction, Transmission
Action Potential
When dendrites stimulated, the delicate
balance is altered
Membrane breaks down
Positively charged ions rush in
(depolarization)
Charge = less negative
Causes release of chemicals from
terminal buttons
Relay Race
• Action Potential starts at dendrite
– Through cell body
– Down Axon
– Axon Terminals
• How does it get to the next cell’s dendrites?
• Neurons don’t touch
– Synapse = millionth inch gap
– In synapse = vesicles w/ neurotransmitters
» Chemical messengers that transmit info
Communication
• Impulse releases
neurotransmitter from
vesicles
• Neurotransmitter
enters synaptic gap
• Neurotransmitter
binds to receptors on
the receiving neuron
Myelin Sheath
– Fatty material made by glial cells
– Insulates the axon
– Allows for rapid movement of
electrical impulses along axon
– Nodes of Ranvier: gaps in myelin sheath
where action potentials are transmitted
– Multiple sclerosis is a breakdown of
myelin sheath
– Speed of neural impulse Ranges from 2 –
200+ mph
Myelinization clip
Myelin conduction clip
Neurotransmitters
 chemical messengers that traverse the
synaptic gaps between neurons
 when released by the sending neuron,
neurotransmitters travel across the
synapse and bind to receptor sites on
the receiving neuron, thereby
influencing whether it will generate a
neural impulse
Neurotransmitters (>60)
• Acetylcholine (ACh)
– 1st substance identified as NT
– Links motor neurons and muscles (contract or relax)
• e.g. curare vs black widow spider
– Also involved in memory, learning, sleep, dreaming
(acetylcholine movie)
• Endorphins (the brain’s own morphine)
– 1973 injected rats with morphine
– Bound like NTs
– Brain had receptors for exogenous substance?
• Brain must produce its own morphine
• Released during pain and discomfort
More neurotransmitters
Receptor binding movie