physiology ....final material .... CNS .... Nervous System for Bio Medical Engineering

8/3/2019 physiology ....final material .... CNS .... Nervous System for Bio Medical Engineering

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The nervous system

(NS)



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Organization of the nervoussystem

q Based on differences in the structure,location, and functions, nervous system is

subdivided into:

1. Central Nervous System (CNS)

2. Peripheral Nervous System (PNS)



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Organization of the nervous system



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Functional classes of neurons

1.

Afferent neurons:ü. Sensory receptor at peripheral ending

(generates AP)

ü. Convey input to the CNS

ü. Cell body outside CNS

2. Efferent neurons:

ü. Cell bodies in the CNS

ü. Convey output for the effector organs



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Structure and location of the three functional classesof neurons



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The CentralNervous System (CNS)



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CNS

q Consists of:

1. The brain2. Spinal cord



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The Brain

q Major brain functions:

ü

Regulates internal environmentü Experiences emotions

ü Voluntarily controls movements

ü Perceives own body and surroundings

ü Engages in other higher cognitive processes (e.G. Thought and memory)

q Brain functions as a whole (neurons

linked via synapsis).

S f h M j C f



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Structures of the Major Components of the Brain

• Based on anatomical distinction, functionalspecialization, and development, brain hasthe following regions:

1. Brain stem (Medulla, pons, midbrain)

2. Cerebellum

3. Forebrain

a. Diencephalon

§. Hypothalamus

§. Thalamus

b. Cerebrum§.



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unc on o or ompon n othe Brain



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Cerebral Cortex



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Cerebral Cortex



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Cortical lobes

Initial

processing of visualinput

Soundsensati

on



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The parietal lobes

q The somatosensory cortex:ü located in the front portion of each

parietal lobeü Immediately behind the central sulcus

q It is the site for initial corticalprocessing and perception of:

ü Somesthetic inputü Proprioceptive input

Th t



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The somatosensorycortex

q Each region within thesomatosensory cortex receivesinput from a specific area of thebody.

q Reception of opposite side inputs

q

Thalamus simple awareness of sensationq Somatosensory cortex full sensory

perception

q Capable of spatialdiscrimination

q Connections with higher brain

q Different parts of the body are not

equally represented



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The frontal lobes

q Primary motor cortex:ü Immediately in front of the central

sulcusü Next to the somatosensory cortex

q Confers voluntary control overmovement produced by skeletal

muscles.

q Involved in the planning, control,and execution of voluntary motorfunctions

q The motor cortex itself does notinitiate voluntar movement



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e pr mary mo orcortex

q Controls opposite side muscles of the body

q The extent of representation in themotor cortex is proportional to theprecision and complexity of motorskills required of the respective part

er ra n reg ons mpor an n mo or



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er ra n reg ons mpor an n mo orcontrol



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Brain plasticity

q When an area of the brain associated witha particular activity is destroyed, otherareas of the brain may gradually assume

some or all of the functions of thedamaged region

q

Mechanism:

??? formation of new neural pathways (not

new neurons, but new connections betweenexistin neurons



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Cortical control of language

q Areas of the brain responsible forlanguage ability are found in onlyone hemisphere - the left

hemisphere.

q Cortical language areas:

ü Broca’s area; speaking ability

(e xpression)



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Cortical language areas

Schematic linking of various regions of



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Schematic linking of various regions of the cortex



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Electroencephalogram(EEG)

q The recording of electrical activity alongthe scalp

q A tracing (measurement) of voltagefluctuations resulting from ionic currentflows within the neurons of the brain

versus time recorded from electrodesplaced over scalp in a specific array

q

Deep parts of the brain are not wellsam led



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EEG Elements

v Electrodes:

ü Activeelectrodes:Attached to thescalp

ü Referenceelectrode:Mastoid, nose, earlobe...

v Amplifier

The EEG records differences in voltage – difference in electrical potentialfrom one electrode to another



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EEG Rhythms

1. Alpha waves

o. Most common in adults.o.

Posteriorly (occipital) more than anteriorlyo. Especially prominent with closed eyes and with relaxation. o. Disappears normally with attention (eg, mental arithmetic, stress,

opening eyes).o. In most instances, it is regarded as a normal waveform.



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EEG Rhythms

2. Beta waveso. Small in amplitudeo. More evident anteriorlyo. Drugs, such as barbiturates and benzodiazepines, augment beta

waves



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EEG Rhythms

3. Theta waveso. Normally seen in sleepo.

In awake adults, these waves are abnormal if they occur in excess.



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EEG Rhythms

4. Delta waveso. Normally seen in deep sleep.o. Delta waves are abnormal in the awake adult.o. Often, they have the largest amplitude of all waves.

Theta and delta waves are known collectively as slow waves.



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EEG Rhythms



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Neural basis of the EEG

q For the electrical activity of the brain to be recorded from scalp:ü It must be of sufficient strengthü It must be of sufficient duration

i. Action potentials are difficult to measure;

ü. They are rapid, transient, all-or-none nerve impulses of 100mv aprox.ü. Very short duration of ~1ms that flow from the body to the axon terminal of

a neuron.

q Two options:i. Record action potentials of brain

neuronsii. Record of postsynaptic potentials



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1) The postsynaptic neuron getsdepolarized (Na+ inward currents –excitatory - EPSP) or hyperpolarized(Cl- inward currents – inhibitory-IPSP).

1) EPSP and IPSP summate temporally

and spatially.

1) If the postsynaptic neuron reachesa given depolarization threshold, anaction potential is generated.

APthreshold

Actionpotential

ii. Post-synaptic potentials are easier tomeasure



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When an EPSP is generated in thedendrites of a neuron anextracellular electrode detects anegative voltage difference,resulting from Na+ currents flowinginside the neuron’s cytoplasm.

The current completes a loopfurther away the excitatory input(Na+ flows outside the cell), beingrecorded as a positive voltage

difference by an extracellularelectrode.

This process can last hundreds of milliseconds.

Thus, a small dipole isenerated!!



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Pyramidal neuronsare spatially alignedand perpendicular tothe cortical surface.

Thus, EEG representsmainly thepostsynapticpotentials of pyramidal neuronsclose to the recording

electrode.

The electrical activityfrom deepergenerators gets

dispersed andattenuated by volume



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The International 10 20



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The International 10-20System

The International 10-20 System of Electrode Placement is the most widely used method todescribe the location of scalp electrodes. The 10-20 system is based on the relationship betweenthe location of an electrode and the underlying area of cerebral cortex. Each site has a letter (toidentify the lobe) and a number or another letter to identify the hemisphere location.

The letters used are: "F" - Frontal lobe, "T" - Temporal lobe ,"C" - Central lobe , "P" - Parietal lobe, "O" - Occipital lobe.(Note: There is no central lobe in the cerebral cortex. "C" is just used for identification purposes only.) Even numbers (2, 4, 6, 8) refer to the right hemisphere

odd numbers (1, 3, 5, 7) refer to the left hemisphere."Z" refers to an electrode placed on the midline.The smaller the number, the closer the position to the midline.

"Fp" stands for Front polar.



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EEG uses

1. To distinguish various stages of sleep

2. A clinical tool in the diagnosis of cerebraldysfunction (e.G. Epilepsy)

3. Legal determination of brain death



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The basal nuclei

q Masses of gray matter (neuron cell bodies) locateddeep within the cerebral white matter

q Functions:ü Inhibiting muscle tone throughout the body

ü Selecting and maintaining purposeful motor activitywhile suppressing useless or unwanted patterns of

movementü Helping monitor and coordinate slow, sustained

contractions, especially those related to posture andsupport



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The basal nuclei

q Improper function: parkinson’s disease

q Deficiency of dopamine, an important

neurotransmitter in the basal nuclei

q Signs and symptoms:

ü Increased muscle tone, or rigidity

ü Involuntary, useless, or unwanted movements, such asresting tremors (e.g., hands rhythmically shaking)

ü Slowness in initiating and carrying out different motor



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The thalamus

q “Relay station” and synaptic integratingcenter for preliminary processing of allsensory input on its way to the cortex

q It screens out insignificant signals androutes the important sensory impulses toappropriate areas of the somatosensorycortex (e.G., Attention to stimuli of interest)



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The hypothalamus

• Important link between the autonomicnervous system and the endocrine systemvia the pituitary gland

• Controls body temperature, hunger, thirst,fatigue, sleep, and circadian cycles



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The limbic system

q Not a separatestructure

q Associated with emotions, basic

survival and socio-sexual behavioralpatterns, motivation, and learning



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Cerebellum

q Attached to the back of the upper portionof the brain stem

q Lies underneath the occipital lobe of thecortex

q Does not initiate movement, butcontributes to coordination, precision,and accurate timing.

q It receives input from sensory systems

and from other parts of the brain & spinalcord, and integrates these inputs to finetune motor activity

q Damage to the cerebellum does notcause paralysis, but instead produces

disorders in fine movement, equilibrium



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Cerebellum



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Brain stem

q The brain stem is a vital link between the spinal cord andhigher brain regions

q Main functions:

ü The majority of the 12 pairs of cranial nerves arise from thebrain stem

ü “Centers,” that control heartand blood vessel function,respiration, and many digestiveactivities

ü Regulating muscle reflexesinvolved in equilibrium andposture.

ü Reticular formation: controls



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CranialNerves

R ti l ti ti



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Reticular activatingsystem



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Sleep

q States of consciousness:

ü Maximum alertness

ü Wakefulness

ü Sleep (several different types)

ü Coma

q Sleep is an active process, the brain’soverall level of activity is not reducedduring sleep



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Types of sleep

1. Slow-wave sleep

1. Paradoxical, or REM (rapid eye

movement), sleep



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Comparison of Slow-Wave andParadoxical Sleep



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EEG patterns during differenttypes of sleep



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SPINAL CORD



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Spinal cord

q Descends through the vertebral canal of thevertebral column

q Paired spinal nerves emerge from the spinal cordat:

ü 8 pairs of cervical (neck) nerves (C1–C8)

ü 12 thoracic (chest) nerves (T1-T12)

ü 5 lumbar (abdominal) nerves (L1-L5)

ü 5 sacral (pelvic) nerves (S1-S5)

ü 1 coccygeal (tailbone) nerve



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Spinal cord

q The spinal cord itself extends only to the level of the first or second lumbar vertebra

qNerve roots of the remainingnerves are greatly elongated(cauda equina), to exit thevertebral column at theirappropriate space.

p na cor n cross



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p na cor n crosssection

q Gray matter consists primarily of neuronal cell bodies and their dendrites,short interneurons, and glial cells

q The white matter is organized into tracts, which are bundles of nerve fibers(axons of long interneurons) with a similar function

q Bundles are grouped into columns that extend the length of the cord:

ü Ascending tracts

ü Descending tracts

q The dorsal and ventral roots

at each level join to form



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Reflex arc

q Reflex:

ü Any response that occursautomatically without consciouseffort

ü Motor response to a specificsensory stimulus

q Reflex arc:



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Types of Reflexes

A. Based on complexity:

1. Simple, or basic reflexes,ü. Built-in, unlearned responsesü. e.g., pulling the hand away from a burning

hot objectü. Usually integrated in spinal cord or brain

stem

2. Acquired, or conditioned reflexes,ü. Result of practice and learningü. Usually integrated at higher brain levels



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Types of Reflexes

B. Based on neural processing level:

1. Cranial reflexese.g., Pupillary reflex

2. Spinal reflexes* Reflex activity between afferent input and efferent output without involving

the brain* The controlling center of the spinal reflex is located in one or more spinal

cord segmentse.g., Skeletal muscle stretch reflex

C. Based on synapse number

1. Monosynaptic reflexesA. Two neurons (one synapse)

2. Polysynaptic reflexesA. Many neurons (many synapses)



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Types of Reflexes

D. Based on effector

1. Autonomic [visceral] reflexesSmooth muscle, cardiac muscle, glands

2. Somatic [muscle] reflexesSkeletal muscles

E. Based on side of effect

1. Ipsilateral reflexesThe response is on the same side of the

body as the stimulus

2. Contralateral [crossed extensor]reflexes

The response is on the opposite side of



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Spinal Reflexes

q Integrating center for the reflex activity betweenafferent input and efferent output is located in oneor more spinal cord segments

q The brain can facilitate or inhibit them

q Examples:

1. Withdrawal reflex (flexor reflex)

2. Stretch reflex



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Withdrawal reflex

reciprocalinnervation



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Withdrawal reflex

q The brain can modify the withdrawal reflex

q Impulses from the brain (voluntary) can

override the input from the receptors(reflex)

q Example: pricking finger for bloodsampling



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Stretch reflex

q Two muscle receptors are important forproprioceptive inputs:

1. Muscle spindles (monitor changes in muscle length)

1. Golgi tendon organs ( monitor changes in muscletension)

Both are activated by muscle stretch, but convey different

messages

Muscle spindles



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Muscle spindles

q Distributed throughout skeletal musclefibers

q Each spindle consists of 3-10 intrafusalspecialized muscle fibers enclosed in aconnective tissue capsule

q Each intrafusal fiber has

ü Noncontractile central portion

ü Contractile ends

Musclespindle

skeletal muscle

fibers



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Muscle spindles

qEach spindle has:

üAfferent nerve supplysensory nerve endings

detect change in muscle length and speed

üEfferent nerve supplymotor, gamma neurons

Skeletal muscle fibers are supplied via motorα

neurons



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Stretch reflex

stretch reflex)



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stretch reflex)

Sensory fromspindles

To skeletal musclefibers

Tapping stretchesthe musclespindlesin the quadricepsfemoris muscle

1

2

3



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Golgi tendon organs

q In the tendons of the muscle

q Respond to changes in the muscle’s tension

q Increased firing with increased muscle tension

q Its firing leads to inhibition of motorneuron andα

thus relaxation of skeletal muscle



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Contractionincreasesmuscle tension

1Increasedtensionincreases GTOfiring

2

Inhibitorymotorneuron

34

Musclerelaxes

5



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Golgi tendon reflex

q Opposite of those elicited by muscle spindlereflexes

q Golgi tendon organs help ensure smooth onset andtermination of muscle contraction

q Particularly important in activities involving rapidswitching between flexion and extension such as inrunning



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• The electroencephalogram (EEG) isthe depiction of the electrical activityoccurring at the surface of the brain.

This activity appears on the screen of the EEG machine as waveforms of varying frequency and amplitudemeasured in voltage (specificallymicrovoltages).

• EEG waveforms are generallyclassified according to their



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