the role of the nervous system in locomotion
TRANSCRIPT
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Control
The Role of the Nervous System in Locomotion
Dr Dan Dudek
North Cross School [email protected]
http://sites.google.com/a/northcross.org/dr-dan-dudek/
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Outline
• Nerves• Structure of the Nervous System• Role of Higher Centers• Controlling Locomotion
» Reflexes» Central Pattern Generation (CPG’s)
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Neural Control
Sensory Receptors
Central Nervous System
Muscles
Peripheral Nervous System
Afferent
Efferent Motor Output
Sensory Input Higher Centers (Brain)
Nerve Cord
Central Pattern
Generator (CPG)
Neural Clock
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Neurobiology
What is the Functional Unit of
the Nervous System?
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Structure of Neuron
Axon
SPIKE INITIATION
TRANSMITTER SECRETION
Dendrite
Neuron is the
Functional Unit of the Nervous System
SIGNAL CONDUCTION
INTEGRATION Receive
signals from many
neurons
Send signals to other neurons
Soma
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Real Neuron
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Diversity Enables Discovery
“For a large number of problems there will be some animal of choice, on which it can be most conveniently studied.” ___ August Krogh
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Swimming Squid?
Foundations of Modern
Neurobiology Discovered using Squid
Axon
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Tentacle Strike Video
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Swimming Squid = Nobel Prize!
The Nobel Prize in Physiology or Medicine – 1963 John C Eccles, Alan L Hodgkin, Andrew F Huxley
"for their discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane".
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Excitable Cells
Axon
SPIKE INITIATION
TRANSMITTER SECRETION
Dendrite Sum all continuous signals
Send discrete signals or spikes
Action Potentials
Soma
Monitor
Amplifier
0 mV _
_ +
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Signal transmission
Graded Passive Potential
Analog
All or none Action Potenital
Digital
All or none Action Potenital
Digital
Graded Passive Potential
Analog
Graded Passive Potential
Analog
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Neuromorphic Chip Computer Chips are typically digital in operation. 0 or 1
Dendrites of neurons are analog
(continuous)
New neuromorphic chips are part analog
(continuous)
Greater information transfer with less power!
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Functional Characterization
1. Afferent (to carry) - Sensory (skin, sense organs) to brain/spinal cord
2. Efferent (to carry away) - Motor (brain/spinal cord) to muscles, glands
3. Interneuron - conduction among neurons (in C.N.S.), integrate and store information from other neurons
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Types of Sensory Receptors • Electromagnetic and thermal energy
» light» infrared radiation» thermal - heat and cold» electro-magnetic
• Mechanical energy» sound and sonar» touch and vibration» pressure» gravity» inertia
• Chemical energy» taste» smell» humidity
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Energy Transduction
Withers, 1992
Deformation Temperature Taste Olfaction Light Voltage
Olfacto- receptor
Gustato- receptor
Thermo- receptor
Mechano- receptor
Photo- receptor
Electro- receptor
Stimulus
Stretch-mediated Na channel
Temperature Dependent Na/K channel enzymes
Phosphorylation-mediated Na/K channel
cAMP- mediated Na/K channel
GMP- mediated Na channel
Voltage dependent Na channel
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Receptor Potentials
Stimulus
Receptor Membrane
Chemical Synapse
Receptor Potential
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Frequency vs Intensity St
retc
h (D
ispl
acem
ent)
A
ctio
n Po
tent
ials
Increasing Stimulation
Frequency
Intensity
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Saturation vs Sensitivity
Stimulus IntensityResp
onse
Fre
quen
cy(A
ctio
n Po
tent
ials
/ sec
) Saturation
Slope = Sensitivity
High Sensitivity
Low Sensitivity
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Response vs Intensity
Stimulus Intensity
Resp
onse
Fre
quen
cy
Log Stimulus Intensity
Weber-Fechner Relationship
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Tonic Receptors
Log DisplacementResp
onse
Fre
quen
cy
Displacement Detector
Displacement
Action Potentials
TONIC
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Tonic vs Phasic Receptors
Log VelocityResp
onse
Fre
quen
cy
Velocity Detector
Log DisplacementResp
onse
Fre
quen
cy
Displacement
Action Potentials
Displacement Detector
TONIC PHASIC
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Range Fractionation
Stimulus IntensityResp
onse
Fre
quen
cy(A
ctio
n Po
tent
ials
/ sec
)Individual receptor cells sensitive over narrow range.
Group of receptors sensitive over broad range
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Outline
• Nerves• Structure of the Nervous System• Role of Higher Centers• Controlling Locomotion
» Reflexes» Central Pattern Generation (CPG’s)
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The Brain
Eckert
Motor Cortex Stimulate & Move
Sensory Cortex Stimulate & Feel
Brain sends commands for initiation and
navigation
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Structure of Nervous System
Nerve Net
Diffuse
Ganglia - cluster of nerve cell bodies
Directional Repeated in all segments
Condensation Specialization
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Nerve Cords
Invertebrate Ventral
Vertebrate Dorsal
Segmentation Condensation Specialization
Remarkable Similarities
X-section
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Outline
• Nerves• Structure of the Nervous System• Role of Higher Centers• Controlling Locomotion
» Reflexes» Central Pattern Generation (CPG’s)
30
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Neural Control
Sensory Receptors
Central Nervous System
Muscles
Peripheral Nervous System
Afferent
Efferent Motor Output
Sensory Input Higher Centers (Brain)
Nerve Cord
Central Pattern
Generator (CPG)
Neural Clock
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Motion Restoration
Many strategies are available depending on what is functional and
where in the path malfunction is present.
To Restore Function: 1. Express cognitive control
over relevant motor functions in residual anatomy
2. Device to pick up and decipher the cognition
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Pre-Motor Commands Plan motor events in the premotor cortex
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Direct Connections
A direct electronic interface is proving
useful in brain-computer interfaces
and opens the possibility of neural
prosthetics
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By-passing Spine and Limbs
Human Brain Machine
Interface is allowing “thought” control of prosthetic
limbs
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Brain-Machine Interface
Implant microwires into owl monkey
Measure signals as monkey performs reaching tasks
Analyze data to interpret signals
Wessberg et al., 2000 Nature
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Real-time Decoding of Brain Signals
Signals are decoded using simple linear models and artificial
neural networks (ANN), predictions made and signals
sent to a robot arm locally and over the
internet
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Thought Control of Cursor
Monkey moves arm to track target. Brain
signals recorded and correlated with hand position. Brain signals alone used to track cursor - no
arm movement needed.
Serruya et al. 2002 Nature
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Thought Control of Arm
Velliste et al. 2008 Nature
Use motor cortical activity to control a mechanized arm in 3-D movement with proportion grasp
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Outline
• Nerves• Structure of the Nervous System• Role of Higher Centers• Controlling Locomotion
» Reflexes» Central Pattern Generation (CPG’s)
40
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Neurobiology
Two ways to control Biomotion:
1. Chain of reflexes 2. Motor programs (CPGs)
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Chain of Reflexes
Sensory Receptors
Central NS
Muscles
Afferent
Efferent Motor Output
Sensory Input
Chain of Reflexes
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Neural Reflexes
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Golgi Tendon Organ
Ib Afferent Nerve
Muscle Spindle Organ
Ia Afferent Nerve
Extrafusal Muscle Fiber
Intrafusal Muscle Fiber
Efferent α-Motor Nerve
Length and Force Sensors
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Muscle Spindle Fibers
Stretch activated sensors to detect
length AND velocity of muscle
Have there ownγ-motor neurons to
adjust length
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Spindle Fibers
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γ-motor neurons maintain sensitivity as length changes
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Neural Reflex Pathway
Length Sensors
Sense stretch and feedback signal to contract muscle to
shorten. Locomotion can provide rhythmic
signal.
Spinal Cord Cross-section
Interneuron
Length Sensor (muscle spindle)
Afferent Sensory Neuron
Efferent Motor Neuron
Withers
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Pathways
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Interneurons relay sensory information to other levels (and
limbs) within the spinal cord, as well
as to opposing muscles within the
same limb
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Pathways
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Spindle afferents synapse directly back onto motor
neurons of the same muscle, forming a
monosynaptic pathway which
facilitates a rapid motor response to
stretch of the muscle
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Pathways
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Interneurons mediate reciprocal
inhibition (or activation) of
opposing sets of muscles within and
between limbs.
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Examples - Pain Flexion and Crossed-
Extension Reflex
Noxious stimulus causes activation of flexor and
inhibition of extensor on “injured” limb
Opposite limb activates extensors and inhibits
flexors to maintain stance
Ouch! 50
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Examples - Stretch
Tendon Stretch Reflex
Unexpected stretch causes activation of flexor and inhibition of extensor
Maintains original joint angle
Tap! 51
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Golgi Tendon Organs
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http://www.ualberta.ca/~aprochaz/research_spindle_intro.html
Stretch activated sensors to detect force of muscle
Tends to inhibit muscle contraction,
protects from developing too high
force
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GTO Firing Rate and Force
Linear increase in firing rate is unusual
for neurons
Good for negative feedback control of
fine forces
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Force (N)
Ib A
ffere
nt F
iring
Rat
e (H
z)
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GTO’s Are Team Players
The Ib inhibitory interneurons receive
convergent input from GTO’s, muscle
spindles (not shown), joint and cutaneous
receptors, and descending pathways
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GTO’s Don’t Just Inhibit At rest, stimulation of Ib afferent fibers from
the ankle extensor muscle inhibits ankle
extensor motor neurons
During locomotion the same stimulus excites the motor neurons (via
polysynaptic excitatory pathways)
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The Motor Servo
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Descending Commands α a. p. Motor
Unit force Load Kinematics
-position -length
-velocity
-
GTO
Spindles
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Adjusting Stiffness
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Descending Commands α a. p. Motor
Unit force Load Kinematics
-position -length
-velocity
- GTO
Spindles
Hypothesis Motor Servo acts to
adjust muscle stiffness
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Reciprocal Inhibition
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Descending Commands α a. p. Motor
Unit force Load Kinematics
-position -length
-velocity
- GTO
Spindles
Motor Servo reciprocally
inhibits opposing
muscles and limbs
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Neurobiology
Two ways to control Biomotion:
1. Chain of reflexes 2. Motor programs (CPGs)