Transcript Efferent Neurons

Neuroprosthetics
Presentation 2
Implant Technologies
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
Restorative Application
Invasive vs. Non-invasive
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
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
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
Neuroprosthesis
Neuroprosthesis
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
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
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
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’
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
(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)
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
Signal Processing
Implementation
Fully implanted vs External?