W1 Neuromodulation Flashcards
What is Neuromodulation?
“the alteration of nerve activity through the delivery of electrical stimulation or chemical agents to targeted sites of the body”
“the process of inhibition, stimulation, modification, regulation or therapeutic alteration of activity, electrically or chemically, in the central, peripheral or autonomic nervous systems”
How does ‘neuromodulation’ in medicine differ from that in biology?
Medical neuromodulation is the unnatural and controlled electrical/chemical stimulation of targeted sites of the nervous system.
Biologically, neuromodulation is a natural physiological process in the nervous system where chemicals regulate diverse populations of neurons
What are example application treatments of neuromodulation and the conditions targeted?
- Spinal Cord Stimulation for Chronic Pain, Cardiovascular disorders and Gastrointestinal disorders
- Deep Brain Stimulation (DBS) for Chronic Pain, Movement disorders and Epilepsy
- Sensory prostheses for Functional restoration
Where does neuromodulation fit in the market?
Within the industry of Neurotechnology and the Neurotherapeutics sector of Neurodevice.
~$3b in the Neuromodulation market (mostly spinal cord stimulation, some DBS), and ~$1.5b in the Neuroprosthetic market (mostly cochlear implants)
Who are the main manufacturers of the industry?
In order of $ spent:
- Medtronic (Cardiac and Restorative Therapies [DBS, Spinal Cord])
- St Jude Medical (Abbott: Cardiac and Pain Control)
- Boston Scientific (Cardiac and Restorative Therapies)
- Cochlear Ltd (Auditory Prosthesis)
- Other Emerging: Cyberonics (VNS), Synapse Biomedical, Neurosigma
What are the Main Modalities of Neuromodulation?
- Spinal Cord stimulation (chronic pain, failed back surgery, ischemia)
- DBS (PD, tremor, depression, others)
- Cochlear prostheses (sensorineural deafness)
- Sacral nerve stimulation (urine incontinence, fecal incontinence)
- Vagus nerve stimulation (epilepsy, others)
- Gastric electrical stimulation (gastro paresis, obesity)
What element of the nervous system are the most likely to be stimulated by electrical stimulation?
Axons, along which info flows as a result of ‘action potentials’ (waves of ionic transfer across the cell wall which occur at the Nodes of Ranvier). This info is insulated from other axons and protected by an insulating sheath of myelin.
What two molecular structures make the nerve membrane particularly important for its specific electrical properties that allow neurons to receive, process and pass on info?
- – Ion Pump: continuously pumps 3 sodium ions out and 2 potassium ions in (to cell)
- – Ion Channels (voltage-dependent): allow only one specific ion type (different gates for Na & K) to pass across the mbr. The rate of leakage varies w voltage across the mbr.
Describe the Action Potential.
When the cell is at rest, the Na and K gates are mostly closed. When the intracellular potential is raised above a critical threshold voltage (~-55mV), Na channels begin to open, increasing the voltage further causing a runaway opening of all Na channels.
This triggers a similar opening of the K channels which then reverses the potential.
What is Lateral Inhibition?
A form of spatial high-pass filtering, this pre-processing of sensory information is used to extract edges from spatial patterns (e.g. cartoons from images).
What is Adaptation?
“A change over time in the responsiveness of the sensory system to constant stimulation”.
A form of temporal high-pass filtering of nerve signals, this pre-processing of sensory information is used to emphasise temporal (time domain) changes in sensory signals.
Adaptation occurs in most sensory systems, peripheral and central. What methods does the eye employ for adaptation?
The eye (can sense light intensities over 9 orders of magnitude).
- pupil diameter ranges for 10-2 mm depending on the light intensity in response to bright lights
- rods are more sensitive than cones. The fovea contains only cones and is used for daylight viewing only.
- Changes in intracellular Ca ion levels and other biochemical effects modify lateral inhibition and rod/cone sensitivity
Adaptation occurs in most sensory systems, peripheral and central. What methods does the ear employ for adaptation?
The ear (can sense sound pressure levels over 6 orders of magnitude).
- – Stapedius reflex disarticulates the stapes to reduce transmission efficiency in response to loud sounds
- – Outer hair cells “tune” basilar membrane motion over 3 orders of magnitude
- – Spontaneous nerve firing enables modulation of very quiet sounds
Different functions of nerves
- CNS - integrative & control centres.
- PNS - cranial & spinal nerves; communication lines bw CNS & rest of body.
- Sensory (afferent) division - conducts impulses from receptors to CNS.
- Motor (efferent) division - conducts CNS impulses to effectors (muscles, glands)
- ANS; sympathetic - mobilizes body for activity, ‘fight or flight’
- ANS; parasympathetic - conserves energy, housekeeping functions, ‘rest & digest’
