Unit IIINervous System and Electromyography

Content Introduction to Nervous System-Anatomy

The anatomy of the nervous system & The Autonomic nervous System

10-20 electrode placement system for EEG measurement

EEG machine

Evoked potentials and Types & significance of EEG signals

EEG Amplifiers& filters

Analysis of diseases using EEG Electromyography (EMG)

Muscle contraction mechanism,

Myoelectric voltages,

EMG Machine.

What is nervous system

The nervous system is a complex network of nerves and cells that carry

and transmit messages to and from the brain and spinal cord to

various parts of the body.

The Nervous system has three major functions:

Sensory – monitors internal & external environment through presence

of receptors (carry messages from body to brain (pain, pressure,

temperature))

Integration – interpretation of sensory information (information

processing); complex (higher order) functions

Motor – response to information processed through stimulation of

effectors(– carry messages from brain to body to respond )

Muscle contraction

Glandular secretion

Contd…..

Two types of neural cells in the nervous system:

Neurons - For processing, transfer, and storage of information

Neuroglia – For support, regulation & protection of neurons

NeurogliaCNS neuroglia:

Astrocytes

Oligodendrocytes

Microglia

Ependymal cells

PNS neuroglia: Schwann cells (neurolemmocytes)

satellite cells

Neuron

30,000 neurons can fit on a pinhead

Disorders are numerous and often difficult to diagnose and treat

sense organ

muscle

there are different types of neurone

sensory neuronemotor neurone relay neurone

direction of electrical

signal

sends signals to your muscles to tell them to move

sends signals from your sense organs

connects neurones to other neurones

dendritescell body

axon

myelin sheath

nerve endings

neurones communicate with each other using a mixture of electrical & chemical signals

Signal transmission at synapse

- Messages are sent across the synapses by special chemicals called- neurotransmitters- The use of neurotransmitters causes an electrical current- There is enough electrical current in the brain to power a flashlight- Neurons do NOT touch; there is a gap between them called a synapse

Functions of neurotransmitters– Cause muscles to contract or

relax

– Cause glands to secrete products

– Activate or inhibit neurons

cell body

axon

myelin sheath

dendrites

nucleus

signals cross between neurones at the synapse

neurotransmitter

vesicle

synaptic cleft

receptor

electrical impulse triggers vesicles to move to the synapse membrane

1

vesicles fuse with the membrane and release neurotransmitter into the synaptic cleft

2

neurotransmitter diffuses across the cleft and binds to receptors on the other side

3

Once enough receptors have neurotransmitters bound to them, the signal is transmitted…

4

The point where your muscles and nervous system meet is called the

neuromuscular junction (NMJ)

muscle

Signals sent from your central nervous system to the NMJ tell muscles to move

The synapses at the NMJ use a neurotransmitter called

acetylcholine

Important Terms

Synapse – junction between 2 neurons that communicates the

message from the presynaptic neuron to the postsynaptic neuron

Ganglion – a cluster of neuronal cell bodies in the PNS

Preganglionic neuron – cell body lies within the CNS

Postganglionic fiber (axon) of the ganglionic neuron extends to the

visceral organs

Dendrites - fibers that receive messages from other neurons

Axons - fibers that send messages to other neurons

Apply Your Knowledge

What is the function of neurotransmitters?

ANSWER: Neurotransmitters cause muscles to contract or relax, cause glands to secret products, activate neurons to send nerve impulses, or inhibit neurons from sending them.

Neural Tissue Organization

Gray matter Inner tissue with darker color Contains neuron cell bodies and their dendrites Divisions are called horns Central canal runs down the entire length of the spinal cord through

the center of the gray matter White matter

Outer tissue Contains myelinated axons Divisions are called columns (funiculi) Columns contain groups of axons called nerve tracts

Contd…….

Brain

A memory is not a snapshot stored in the brain – it must be put together from information stored in various parts of the brain

Brain : A mass of 100 billion neurons located inside the skull

- Learning occurs as more and stronger connections are made between neurons

Nervous System

Central NervousSystem

Brain Spinal Cord

Forebrain Midbrain Hindbrain

Thalamus Hypothalamus

Cortex Limbic SystemCorpus

Callosum

Peripheral NervousSystem

SomaticSystem

AutonomicSystem

ParasympatheticDivision

SympatheticDivision

Organization of nervous system

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your nervous system

is divided into the central nervous system (CNS)

and the

peripheral nervous system (PNS)

which is the brain and

spinal cord

which connects everything to the brain and spinal cord

The ANS and Visceral Sensory Neurons

19

Contd…. The central nervous system can be broken down structurally as follows:

– Spinal Cord – Hindbrain

• Medulla (myelencephalon) • Pons (metencephalon) • Cerebellum

– Midbrain (mesencephalon) – Forebrain

• Telencephalon – Cerebral Cortex

Frontal Lobe Temporal Lobe Parietal Lobe Occipital Lobe

– Subcortical Structures

Basal Ganglia Hippocampus and Amygdala (parts of the Limbic System)

– Corpus Collosum• Diencephalon

– Thalamus – Hypothalamus

Central Nervous System

Impulses may travel as fast at 268

miles/hr throughout the body from

brain to all body parts via spinal cord

The brainstem refers to the midbrain and portions of the hindbrain.

Specifically, the brainstem comprises:

Midbrain (mesencephalon) - Controls both visual and auditory

reflexes

Medulla (myelencephalon)

Pons (metencephalon)

Contd….

Spinal cord The spinal cord is one of the two major components of the central

nervous system:

Like the brain, it is completely encased in bone. It resides within the

vertebral column

Connects directly to the medulla section of the brain

It is approximately 45 cm long in an adult

Ascending tracts Receives sensory messages and sends them to the

brain

Descending tracts carry motor information down from the brain to

muscles and glands

Also acts independently from the brain called reflexes

Reflexes – a predictable, automatic response to stimuli

Receptor Sensory Neurons

Effectors Motor Neurons

Interneurons

Contd……

31 spinal segments:

– 8 pairs of cervical nerves (C1 through C8)

– 12 pairs of thoracic nerves (T1 through T12)

– 5 pairs of lumbar nerves (L1 through L5)

– 5 pairs of sacral nerves (S1 through S5)

– 1 pair of coccygeal nerves (C0)

Hindbrain

Oldest part of the brain

Located between the spinal cord and the brain hemispheres

Consists of the medulla, pons and cerebellum

Contains many nuclei, including those that produce the

neurotransmitters for the whole brain

Controls many involuntary, life-sustaining processes including

Respiration

Circulation

Digestion

Contd….

Medulla (myelencephalon)

Full name: Medulla Oblongata ("oblong marrow") Connects the spinal cord to pons Inferior portion of brain stem Controls many vital activities, such as heart rate, blood pressure, and

breathing

Contd….

Pons (metencephalon)

Full name: Pons Varolii. Originally means 'bridge‘ Bridges the cerebrum and the cerebellum through cerebellar peduncles Responsible to Regulates respiration

Cerebellum Location

– Inferior to the occipital lobes of the cerebrum– Posterior to the pons and medulla oblongata

Coordinates – Complex skeletal muscle contractions that are needed for

body movements– Fine movements, provide balance to the body

Contd….

Midbrain

Controls posture and walking

Handles reflexes of eye movements

Forebrain

TelencephalonCerebral Cortex

The cerebral cortex is composed of two hemispheres comprising four lobes: the frontal,

temporal, parietal, and occipital lobes.

Frontal Lobe

Motor areas for voluntary body movements

Largest of the four lobes

Language production

Memory and higher cognitive function

Temporal Lobe Auditory processing - interpretation Memory Understanding language

Contd….

Parietal Lobe Spatial processing Attention Somatosensory – interprets sensations

Contd….

Occipital Lobe Visual processing

Contd….

Contd….

Contd….

Contd….

lobes

Apply Your Knowledge

Match the following:

___ Meninges A. Carry motor information from brain

___ Ascending tracts B. Stores memories and creates emotions

___ Descending tracts C. Grooves on the surface of the cerebrum

___ Cerebral cortex D. Carry sensory information to the brain

___ Hypothalamus E. Predictable, automatic response to stimuli

___ Sulci F. Maintains homeostasis

___ Cerebellum G. Coordinates skeletal muscle contractions

___ Reflexes H. Protects the brain and spinal cord

B

F

C

G

E

D

A

H

Peripheral Nervous System

Nerves that branch off the CNS Peripheral nerves

– Two types:• Cranial nerves • Spinal nerves

Cranial NervesI. Olfactory nerves

– Carry smell information to the brain for interpretation

II. Optic nerves – Carry visual information to the brain for interpretation

III. Oculomotor nerves – Found within the muscles that move the eyeball, eyelid, and

iris

IV. Trochlear nerves – Act in the muscles that move the eyeball.

V. Trigeminal nerves – Carry sensory information from the surface of the eye, the

scalp, facial skin, the lining of the gums, and the palate to the brain for interpretation

– Also found within the muscles needed for chewing

VI. Abducens nerves – Act in the muscles that move the eyeball

VII. Facial nerves – Found in the muscles of facial expression as well as in the salivary

and tear glands– Also carry sensory information from the tongue

VIII. Vestibulocochlear nerves – Carry hearing and equilibrium information from the inner ear to

the brain for interpretation

IX. Glossopharyngeal nerves – Carry sensory information from the throat and tongue to the brain

for interpretation– Also act in the muscles of the throat

X. Vagus nerves – Carry sensory information from the thoracic and abdominal organs to

the brain for interpretation– Also found within the muscles in the throat, stomach, intestines, and

heart

Contd…….

XI. Accessory nerves – Found within the muscles of the throat, neck, back, and

voice box

XII. Hypoglossal nerves – Found within the muscles of the tongue

Spinal Nerves Dermatome

Ventral root

Dorsal root

Contd…….

Introduction to ANS Regulates activity of smooth muscle, cardiac muscle and glands

Operates without conscious control

Named autonomic because was thought to be AUTONOMUS (working without CNS)

Comparing the ANS and Somatic NS

Structurally then SNS includes:

Somatic sensory neurons

Integrating centers in the CNS (Cortex)

Somatic motor neuron to skeletal muscles only

Somatic- the effect of a motor neuron is always excitation

Autonomic- the effect of a motor neuron is either excitatory or

inhibitory

Contd……….

45

Autonomic Nervous System

Makes all routine adjustments in physiological systems.

The ANS pathway from the CNS to the effector always involves 2

neurons synapsing in an autonomic ganglion.

Preganglionic – cell body is in the CNS, axon extends to the

ganglion outside the CNS

Postganglionic – cell body is in the ganglion, axon extends to the

visceral effector

Autonomic regulation & stress

A stressful situation activates three major communication systems in the

brain that regulate bodily functions.

The first of these systems is the voluntary nervous system, which sends

messages to muscles so that we may respond to sensory information.

The second communication system is the autonomic nervous system. It

combines the sympathetic or emergency branch, which gets us going in

emergencies, and the parasympathetic or calming branch, which keeps

the body’s maintenance systems, such as digestion, in order and calms

the body’s responses to the emergency branch.

The brain’s third major communication process is the neuroendocrine

system, which also maintains the body’s internal functioning.

Apply Your Knowledge

Match the following:

___ Somatic nervous system A. Motor nerves

___ Autonomic nervous system B. Governs skeletal or voluntary muscles

___ Afferent nerves C. Governs respiratory and GI systems

___ Efferent nerves D. Go-betweens or interpreters

___ Interneurons E. Sensory nerves

C

A

E

D

B

ANSWER:

Subdivisions of the ANS

Sympathetic Division Fight-or-flight

Parasympathetic Division Rest-and-digest

These divisions are anatomically distinct Sympathetic Stimulates

heart beat tissue metabolism, increases alertness, prepares the body to deal with emergencies (“fight or flight” division)

Contd…..

Synapses of neurons are in a chain of ganglia that run alongside the

spinal cord

Extends on both sides of the vertebral column

Carries preganglionic fibers and cell bodies of postganglionic neurons

Rami communicantes from the spinal nerves connect to the chain

Effects of Sympathetic StimulationWidespread

• The sympathetic chain allows one preganglionic fiber to synapse with many postganglionic neurons

Enhanced & prolonged by the adrenal medulla

Neurotransmitters of Sympathetic Division

Preganglionic fibers release acetylcholine (Ach) Therefore they are

called:

Cholinergic

Postganglionic fibers (most) release norepinephrine (NE) (=

noradrenaline)

Adrenergic

Adrenal medulla releases norepinephrine and epinephrine

(adrenalin)

Functions of the Sympathetic Division

Heart: increases rate

Lung bronchioles: dilates bronchioles

Salivary glands: produce viscous fluid

Stomach: decreases motility

Pupil: dilates

Sweat glands: produce secretions

Sympathetic Division of the ANS

Parasympathetic Parasympathetic division (craniosacral)

– Cell bodies reside in the brain stem (cranial nerves) or in the sacral

portion of the spinal cord

– Slows the heart rate,

– Inhibits senses,

– Prepares the body for rest and relaxation; (“rest and digest” division).

Neurotransmitter of Parasympathetic Division

Preganglionic fibers: Acetylcholine

Postganglionic fibers: Acetylcholine

Effects on various organs:

Heart: decreases rate

Lung bronchioles: constricts bronchioles

Salivary glands: produces watery fluid fluid

Stomach: increases motility

Sweat glands: reduces secretions

Parasympathetic Division of ANS

56

Combined ANS

Relationship Between the Sympathetic and Parasympathetic Divisions

Most organs receive dual innervation It is a tug of war between the two

ANS either increases excitation or inhibits the activity

– Ex1. Sympathetic fibers increase heart rate, parasympathetic

fibers decrease heart rate.

– Homeostasis comes from the balance of the two.

Ex.#2 Sympathetic fibers decreases stomach motility.

Parasympathetic fibers increase stomach motility.

All division together

Apply Your Knowledge

What is the difference between the sympathetic and parasympathetic nervous systems?ANSWER: The sympathetic nervous system prepares the body for stress. It releases norepinephrine, causing an increase in heart and respiratory rate, slows down the GI system, and dilates pupils. The sympathetic system also controls constriction of blood vessels.

The parasympathetic system prepares the body for resting and digesting. It releases acetylcholine, which slows heart and respiratory rate, constricts pupils and stimulates the GI system. It has no effect on most blood vessels.

What is an EEG? EEG stands for electroencephalogram

EEG signals are created by measuring the difference in electrical currents

across neuron membranes

EEG is a mixture of waves at different frequencies and amplitudes.

Electrodes attached to the body pick up these signals

There can be a only a few electrodes or many attached to the head

Many naturally occurring signals in the human body effect EEG signals

Frequency Analysis helps to separate the different signals

62

Contd….

EEG

Types of EEG signals

EEG signals have been classified into 4 categories:

– Delta 0.3 to 4 Hz

• Dreamless sleep

– Theta 4 to 8 Hz

• Associated with thoughts which produce dreams

– Alpha 8 to 13 Hz

• Result of unfocused thoughts

– Beta above 13 Hz

• Result of interactions with environment

65

Types of EEG

Electrode placement

Electrode placement can effect signals received

67

If two electrodes are “active”, it is called “bipolar” recording.If one electrode is “silent”, it is called “monopolar” recording. The

reference sites: ear lobe, mastoid, nose.

10-20 Electrode System

F = FrontalP = ParietalT = TemporalO = OccipitalC = Central

A = Auxiliary

Although any number of electrodes can placed for EEG measurement, but 21

or 25 electrodes can be used for adequate analysis

The grounding electrode and referencing electrode are placed at forehead

and right ear lobe respectively.

Placement of Electrodes

10-10 Electrodes Arrangement

10-20 Electrodes Arrangement

Cont….

SCHEMATIC DIAGRAM OF AN EEG MACHINE

Physiology and Input Design of EEG

Electrode Input 1

Low-PassFilter

High-PassFilter

Preamplifier Amplifier

Summer/Averager

A/DConverter

Processor

Electrode Input 2

Preamplifier AmplifierLow-Pass

Filter

High-PassFilter

16

Cont…….

8 – 64 identical channels

recording simultaneously

from as many different

pairs of electrodes

Electrodes & electrode

board

Amplifiers

Filters

Pen & chartdrive (screen)

EEG Transducer(Recording set up)

• Electro encephalography - study of electrical activities of the brain.

• Electrodes attached to different parts of the skull of a patient.

• 8 channel EEG recorder:-

Patient cable consists of 21 electrodes

Electrodes connected to selector in groups of 8- Montage of

electrodes

Right ear electrode reference electrode right brain

electrodes

Left ear electrode reference electrode left brain electrodes

EEG Transducer(Recording set up)

Interference problem is reduced by differential

amplifier(preamplifiers)

Filter bank:- consists of appropriate filters to select different types of

brain waves.

Output can be given to 8-channel pen recorder, display unit, computer

storage memory for further processing.

Evoked Potential:- Measure of the “disturbance” in the EEG pattern

that results from external stimuli.

Time delay between stimulus and response can be measured in signal

processing unit.

EEG Amplifiers & Filters

Cont…….

EEG is characterized by:

1) Voltage

2) frequency (is used for BF)

3) spatial location (is used for BF)

4) inter-hemispheric symmetries

5) reactivity (reaction to state change) 6) Character of waveform occurrence (random, serial, continuous)

Cont…….

Design goal Stage 1 Gain should be in the range of 50-80 Common Mode Rejection Ratio Provides noise reduction and signal

centering

Stage 2 Gain of 390 Capacitors stabilize power supply

Design Aspects

Low signal levels require very low noise devices

Battery powering could introduce too much signal noise unless

properly shielded.

Two channels sufficient to measure frequency content

– Differential voltage measurements

– Fifth electrode along scalp midline to create unbiased ground

Risks Too much noise in system

– Will distort signal and render it useless– Can use commercial electrodes, conductive paste– Filters should assist in removing noise, also use shielding

techniques for battery and twisted pairs for wires

Evoked PotentialsEvoked potentials or event-related potentials (ERPs) are significantvoltage fluctuations resulting from evoked neural activity. Evoked potential is initiated by an external or internal stimulus • Visual

Auditory evoked Potentials

Motor Evoked Potentials

30

Event-Related Potentials (ERP)

• Many trials over the same time averaged together

EEG Electrodes

Disposable (gel-less, and

pre-gelled types)

Reusable disc electrodes

(gold, silver, stainless steel or

tin)

Cap (different numbers of

electrodes)

saline-based electrodes

Needle electrodes

EEG artifact

Block diagram for emg recording set up

Block diagram for emg recording set up

Electro myography :- study and interpreting of muscle action

potential.

Potentials measured by placing surface electrodes on the skin.

Individual cell potential measured by means of needle electrode

EMG appears like random noise waveform.

Contraction of muscle fibers produce action potentials

Block diagram for emg recording set up

Amplitude of EMG signals depends

• Type & placement

• Degree of muscular exertions

Normal frequency of EMG signals is 60 Hz

EMG signal amplitude ranges from 0.1 to 0.5 mV.

Amplifier with high CMRR and input impedance

Output can be given to oscilloscope, tape recorder or AF amplifier.

Electromyogram-emg

Problems of the Nervous System

ConcussionA temporary disturbance of the brain’s ability to function due to a

hard blow to the head

ParalysisA loss of sensation and

movement of part of the body due to an injury of the spinal cord or brain

Contd…….

Parkinson’s DiseaseThe brain does not produce enough of the neurotransmitter that transmits messages from the brain to the musclesSymptoms: tremors, rigid muscles, shuffling walk, and loss of facial

expression

Red areas show where chemical is stored

Contd…….

Alzheimer’s DiseaseA gradual shrinking of the neurons in the cerebrumSymptoms: memory loss, emotional disturbances, inability to

function on own, death

Contd…….

EpilepsyAbnormal transmission of messages between the neurons in the brain Symptoms: seizures

Contd……. OtherDisease/Disorder Description

Amyotrophic lateral sclerosis (ALS)

Lou Gehrig’s diseaseDegeneration of neurons in the spinal cord and brain

Bell’s palsy Weak or paralyzed facial muscles

Brain tumors and cancers

Abnormal growths Can be primary or secondary tumorsMost common – gliomas

Guillain-Barré Syndrome

Body’s immune system attacks the PNS

HeadachesTension MigrainesCluster

Episodic or chronicWith aura/without auraForm of migraines; occurs in groups

Disease/Disorder Description

Multiple sclerosis (MS)

Chronic disease of CNSMyelin is destroyed

Neuralgias Disorders causing nerve pain

Sciatica Damage to sciatic nerve

Stroke Brain cells die because of an inadequate blood flow; “brain attack”

Contd…….

Neurologic Testing: Diagnostic Procedures

Lumbar puncture

Magnetic resonance imaging

(MRI)

Positron emission tomography

(PET) scan

Cerebral angiography

Computerized tomography (CT)

scan

Electroencephalogram (EEG)

X-ray

Different types of bio signals

Electroencephalogram (EEG)

Electrocardiogram (ECG or EKG)

Phonocardiogram(PCG)

Electromyogram (EMG)

Electroretinogram(ERG)

Electrogastrogram (EGG)

Electrooculogram (EOG)

Galvanic skin response (GSR)

Magnetoencephalogram (MEG)

Mechanomyogram (MMG)

University Model Questions: Q1.