Neuroprosthetics

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Neuroprosthetics

• Presentation 2
• Implant Technologies

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Implantation Technologies

• Types of Augmentation technologies
• Restorative- restore lost functions and replace
  lost organs and limbs
• Normalising- restore some creature to
  indistinguishable normality
• Reconfiguring- creating post-human creatures
  equal to but different from humans
• Enhancing- the aim of most military / industrial
  research

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Restorative Application
Invasive vs. Non-invasive
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Nervous System
The basic unit of the nervous system is the
neuron, or nerve cell, which transmits signals
between the CNS and receptors (senses) and
effectors (muscles, glands, etc) in other parts
of the body
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Nerve Tissue

• Multipolar (motor function or within the CNS),
  Bipolar (sensory e.g. retina), Unipolar
  (sensory), Pyrimidal (within the brain only)
• The axon from a single nerve cell is sometimes
  referred to as a nerve fibre, and can be over a
  meter in length
• Many nerve fibres stream together to form a nerve
  or nerve fascicle - several fascicles may then
  coalesce to form a larger nerve trunk
• A nerve contains several tens of thousands of
  single nerve fibres of different diameters
  typically between 2 and 20 µm

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Nerve Tissue

• Nerves have three distinct connective tissue
  coats
• The epineurium is the outermost sheath of a nerve
  fascicle and consists of dense connective tissue.
  It also fills the spaces in-between the nerve
  fascicles and acts as a highway for capillaries
  and veins to enter the nerve
• A perineurium surrounds each nerve fascicle and
  consists of several concentric layers of
  flattened cells. These cells are joined together
  laterally by tight junctions which serve as a
  diffusion barrier to larger molecules
• The endoneurium is found within the nerve
  fascicle and consists of a thin matrix of fibres
  which surround the axon cylinders

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Neuroprosthesis
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Neuroprosthesis
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Neurons
Three functional classes of Neuron

• Afferent Neurons
• Transmit information into the CNS from receptors
  at their peripheral endings
• The cell body and axon is outside the CNS
• They have NO dendrites

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Neurons
Three functional classes of Neuron

• Interneurons
• Integrate groups of afferent and efferent
  neurons into reflex circuits
• Are entirely within the CNS
• Account for 99 of all neurons

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Neurons
Three functional classes of Neuron

• Efferent Neurons
• Transmit information out of the CNS to effector
  cells
• The cell body and dendrites are inside the CNS
• The axon is outside the CNS

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Efferent Neurons
Efferent neurons are subdivided Somatic Nervous
System Made up of all the nerve fibres going
from the CNS to skeletal-muscle cells Autonomic
Nervous System The efferent innervation of all
tissues other than the skeletal muscle
Because activity in the somatic neurons leads to
contraction of the innervated skeletal muscle
cells, these neurons are called Motor Neurons
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Nerve Communication
Action Potentials
When a neuron is not being stimulated, it is at
its Resting Potential If a sudden rise pushes
the membrane potential above the Threshold Value,
(usually 55mV), depolarisation spontaneously
occurs (Initiation) and an action potential is
generated Action potentials occur maximally or
not at all (All-or-None Response) Under normal
conditions the duration and magnitude is always
the same

Central to all nervous systems are the action
potentials, nerve signals that are generated in
response to stimuli or to control motor units
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(Peripheral) Neuroprosthesis

• Recording of neural activity
• From Afferent or Efferent Neurons
• Functional Electrical Stimulation (FES)
• Artificial stimulation of Efferent Neurons
• e.g. Stimulation of the sacral roots for bladder
  function
• Hand grasp for tetraplegic patients
• Ambulation for paraplegic individuals
• Sensory electrical stimulation
• Artificial stimulation of Afferent Neurons
• e.g. Cochlear implants
• Taste / Smell / Vision / Touch . . .
• Example Closed-loop ambulation control using
  natural sensors (i.e. glabrous skin
  mechanoreceptors)

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Electrodes (intraneural)
Interfacing methods MicroElectrode Array
(MEA) This technique provides highly selective
recording of individual responses of sensory and
motor neurons within the nerve fascicles Radius
of electrode tip is approximately 1-3 µm. The
active electrode region is approximately 50-80 µm
long Inserted into the nerve tissue during open
surgery
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Signal Processing
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Implementation
Fully implanted vs External?