Biomedical signals of the
nervous system and muscles
Martin Ulander, MD
Dept of Clinical Neurophysiology
University Hospital, Linköping
Methods in Clinical
Neurophysiology
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Electroencephalography
Stuff I will cover
Electroneurography
today.
Electromyography
Polysomnography
Quantitative sensory testing
Evoked potentials
Transcranial magnetic stimulation
Autonomic tests
Electrical Signals in Neurons
Dendrites and Cell Body:
Postsynaptic Potentials
Axon: Action potentials
The resting membrane potential, arising from the combination of an
electrostatic and a concentration gradient affecting the ions inside and outside
the neuron, affects the whole neuron.
Source of EEG signals
The EEG signal is the sum of postsynaptic potentials from the neocortex.
Classification of EEG signals
EEG signals are classified according to:
• Frequency
• Spatial distribution
• Morphology
• Reactivity and occurrence
Frequencies
EEG activity is divided into frequency bands
depending on their frequency.
Amp
Delta (0,5-4 Hz)
Theta (4-8 Hz)
Alfa (8-13 Hz)
Beta (13-30 Hz)
Gamma (>30 Hz)
Tid
EEG frequencies and their clinical
meanings
Normal
Delta
Theta
Alfa
Beta
Gamma
Neonates
Deep sleep
Hyperventilering
Infants
Light sleep
Relaxed
wakefulness
Mental activity
Mental activity
Pathological
Encephalitis
Postictality
Dementia
Coma
Bensodiazep.
Ep seizures
EEG and source localisation
Given certain brain activity,
what would the EEG look
like?
Given a certain EEG, what
does the underlying brain
activity look like?
The forward problem:
Has been solved.
The reverse problem:
Has been proved to be
unsolvable.
In order to solve the reverse problem, one has to impose restrictions to the
solutions. These can be based on biophysics or neurophysiology, and
depending on which restrictions are imposed, different solutions emerge.
Normal EEG
12 y.o. girl referred from school
physician. Not paying attention in
class.
Inga, 62 years old
• 62 year old female, known epilepsy since
childhood but well-regulated with medication and
no seizures.
• Sudden disease onset with vomiting, low-grade
fever and watery diarrheas.
• Contacted GP. Dx winter vomiting disease.
• Two days later her husband found her in the
kitchen, staring into the wall, and not reacting to
his presence.
• Brought to ER. Spoke with single words,
confused and disoriented.
EEG
Hannah, 16 y. o.
• Referred from school nurse to pediatric
psychiatry due to panic attacks.
• No effect from psychotherapy. No effect
from SSRI.
• During panic attacks she was absent and
despite reporting severe fear and panic,
you couldn’t tell from watching her.
• Temporal lobe epilepsy? Perfectly normal
EEG.
Sleep deprived EEG with
zygomatic electrodes
Johan, 17 y. o.
• Two days history of fever, headache and
photosensitivity.
• Brought to ER due to increasing
confusion.
EEG
Neurography
• Neurography measures the condictive
properties of peripheral nerves.
• It consists of a combination of electrical
stimulation and recording.
• Used mainly in the diagnosis of disorders
of the peripheral nervous system.
Peripheral nerve fibers
Ignacio Icke
CC-BY-SA
Disorders of peripheral nerves
• Mononeuropathies: disorders affecting one
nerve, due to trauma, ischemia,
compression etc. E.g., carpal tunnel
syndrome.
• Polyneuropathies: Disorders affecting
peripheral nerves in a more general,
systemic fashion.
Compound nerve action potentials
Preston&Shapiro:
Electromyography
and neuromuscular
disorders
Principles of neurography
diagnosis
Preston&Shapiro
Electromyography (EMG)
• EMG measures the electrical voltage that
is generated by a muscle.
• Myopathies (i.e., primary diseases of the
muscles) as well as neuropathies (i.e.,
diseases of the nerves) affects the EMG.
Motor units
EMG Activity: Spontaneous Activity
• Denervation activity
• End-plate activity
• Other, rare forms of complex discharges
EMG Activity: Motor Unit Analysis
• Amplitude
• Duration
• Phases/Baseline crossings
EMG Activity: Interference
• Recruitment
• Repetition frequency
Use of EMG
• Localising nerve lesions
• Assessing progress, reinnervation and
prognosis of nerve lesions
• Assessing myopathies