sectn 1 nervous syst orgnzn

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PRINCIPLES OF MOTOR CONTROL IN

THE NEUROLOGICALLY IMPAIREDPATIENT


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From: miss-thrifty.co.uk

'The Highwayman'It was a dark, moonless night.

The country road wound likea pale ribbon over the moor.

The highwayman rode out in frontof the rumbling carriage, gun

gleaming, and the horses reared infright.

He demanded all the earl's gold.

When the nobleman refused, hepointed his gun at him and shot himin a fit of rage!

His aim was true, even though the

trigger felt unexpectedly stiff.


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SECTION 1ORGANIZATIONAL PRINCIPLES OF THE

NERVOUS SYSTEM

From: abstract.desktopnexus.com


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Introduction

Several Rx approaches used in treatment ofneuro patients.

All are based in some basic principles and

tenets of the normal and abnormal nervoussystem.

Solid understanding of above facilitatesunderstanding of patient problem anddetermination of appropriate, patient-specifictreatment approach.


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1. Definition of the Nervous System

In early 1900s... 'black box'...information wentin, modified information came out.

Now....'information processing system'.

RECEIVESinputfrom environment; PROCESSESit through sensory,motor and

limbic systems, and

PRODUCES an output.....Motor/limbic systemsproduce action orbehavior.

Major function is to link incoming sensory inputto appropriate outgoing motor output.


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Basic Division of the Nervous SystemFrom: colorado.edu


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2. Hierarchical organization of CentralNervous System

Six main regions:

REGION 1: SPINAL CORD

Receives all input from periphery (skin, joints, muscles

in trunk and limbs) Directs it to next level

Orderly arrangement of motor and sensory nucleicontrolling limbs and trunk, as well as ascending

(afferent) and descending (efferent) pathways or tracts Organizes automatic and stereotyped responses

(reflexes)


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Parts of the Central Nervous System


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Region 1: Spinal Cord (contd..)

Also receives sensory information from

internal organs Controls many autonomic functions.

Motor neurons are final common pathway,i.e., they are responsible for all NS output

or commands for movement toperiphery.


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Hierarchical Organization (contd...)

Spinal Cord continues rostrally as brain stem,

which comprises next 3 regions of CNS: Medulla,pons and midbrain.

Basic Function of Brainstem:

Integrates motor commands from higher centers withascending input from spinal cord.

Cranial nerve nuclei process select categories of afferent(incoming) input.

Contains motor and sensory nuclei related to head andneck structures, senses, circulatory system and viscera

Contains the reticular formation... the 'awake center'.


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Hierarchical Organization (contd.)

REGION 2 : MEDULLA

Most direct rostral extension of spinal cord, resembles it inits organization.

REGION 3 : PONS

Lies rostral to medulla Contains massive set of neurons that relay info from

cerebral hemispheres to cerebellum.

REGION 4 : MIDBRAIN

Lies rostral to pons

Important in control of eye movement. Also containsimportant auditory pathway, and structures critical toskeletal muscle motor control.


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REGION 5 :DIENCEPHALON (THALAMUS &HYPOTHALAMUS)

Thalamus is important relay stationto and fromanywhere in the nervous system ('railway junction').

Integrates and correlates ascending (sensory) inputfrom periphery and descending (motor) output fromcerebral cortex).

Hypothalamuslies below the thalamus.

Autonomic NS integration

Regulation of hormonal secretion by pituitary gland


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REGION 6 :CEREBRUM

Consist of cerebral cortex and basal ganglia

Concerned with perceptual, cognitive and higher motor

functions Many folds and fissures called gyriand sulci.

Further divided into 4 lobes or cortices:

Frontal (motor and premotor)

Parietal (sensory)

Temporal (speech, language and auditory)

Occipital (visual)


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Areas of Cerebral Cortex


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Posterior parietal cortex: transitional between

sensory and motor functions Integrates sensory and motor function

Association areas: Lie outside primary, secondary andtertiary areas

Function is mainly to integrate diverse information to makemovement more purposeful

Parietal-temporal-occipital association cortex : Concerned

with higher perceptual functions related to primary

sensory inputs for somatic sensation, hearing andvision.

Prefrontal association cortex : Planning of voluntary movt

Limbic association cortex: In portions of parietal, frontal andtemporal lobes. Concerned with motivation, emotion andmemory


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3. CNS surrounds interconnected system of 4cavities called ventricles

System consists of:

Twolateral ventricles:One in each hemisphere

Third ventricle : in diencephalon

Fourth ventricle : In medulla

Connected to third ventricle by narrow aqueduct ofSylvius

Cerebrospinal fluid (CSF) circulates within this system.

Produced by choroid plexus in each ventricle. Chemical

composition is similar to extracellular fluid surrounding braincells.

Bathes brain cells, providing important means of chemicalcommunication between brain regions and all of CNS

Cushions brain, flows through sub-arachnoid space to cushionall of the CNS.


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Ventricles of Brain


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4. All Behavior Recruits Activity of Three MajorFunctional Systems

Sensory, Motor and Motivational (limbic).

Localized in separate neural pathways.

Work together to produce appropriate motor

responses to sensory stimuli.

Motor and sensory systems act through tractsof the central nervous system (CNS).

Motivational system acts through both theautonomic (ANS) and somatic nervoussystems.


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5. Motivational Systems act through two indepmotor systems: autonomic and somatic

ANS provides innervation for endocrine and exocrineglands, viscera and smooth muscles in all areas ofbody. Controls onlymotor output.

Two parts, segregated anatomically

Both important in mediating emotional and motivationalstates and monitoring basic body physiology.

Sympathetic:from thoracic and lumbar regions of spinal

cord. Mediates stress response.Parasympathetic: from brainstem nuclei associated with

cranial nerves, and sacral regions of spinal cord. Acts toconserve body resources and restore homeostasis

(opposite of sympathetic)


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Autonomic Nervous System


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PRINCIPLES OF INFORMATIONPROCESSING IN THE NERVOUS SYSTEM


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1. Functional Systems of CNS are governed byFour Principles

(A) Each major system is comprised of several distinctpathways in parallel

Ascending pathways = sensory

Descending pathways = motor(B) Each pathway contains synaptic relays

(C) Each pathway is topographically organized

(D) Most pathways are crossed. Sensory and motorevents one one side of body are controlled byopposite cerebral hemisphere.


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2. Ascending and Descending Pathways

In general, Ascending pathways or tracts = sensory

Descending = motor

Sensory: Also called 'Afferent' From lower system to higher system, e.g.

Periphery to CNS

'FEEL' 'REALIZE' 'SENSE' Motor: Also called 'Efferent'

From higher system to lower system

'DO' 'EXECUTE'


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3. Parallel Processing

The amazing capabilities of the brain tocompensate fully or partially for loss of functionis due to this important trait in its organization.

'Redundancy' is built into the system.... manysensory, motor and other cognitive pathwaysare governed by more than one neuralpathway. Brain believes that 'it is better to be

safe than sorry'. Each major system is composed of several

distinct pathways in parallel.


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4. Method of transfer of information in


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4. Method of transfer of information inNS

All neurons have an input TO them, and an output

FROM them. Projections of neuron(dendrites) receive input

(innervation);

Axon projecting from cell body takes output of cell

away from it.

Inputs can be positive (excitatory): shown as abifurcation or unfilled triangle in circuit diagrams

ornegative (inhibitory):shown as dark filled triangle incircuit diagrams

All neurons have an output, which is regulated bythe sum of the various inputs received by it. Outputcan be positive or negative (excitatory or inhibitory).


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5. Synaptic Relays

Each pathway or tract contains synaptic relays.

Synaptic Relay:complex convergence ofneurons breaking continuity of pathway.

Present in all pathways except corticospinaltract,which is monosynaptic.

Target neurons in synapse have multiple input

potentials converging on them, both positive(excitatory) and negative (inhibitory).

Constant delicate balancing act betweenpotentials.


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Diagram of a Synapse

In Vitro photo of synapse


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In Vitro photo of synapse


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A Synaptic Relay


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6. Temporal and Spatial Summation

Two waysto reach firing threshold of nerve cell andcause it to fire an action potential:

(a) Excitatory Post-Synaptic Potential (EPSP)'saresuccessively fired, adding up to threshold potential

over time Temporal Summation

(b) EPSP's from several inputs converge ontosynapse neurons and coincide in time with each other,summate to reach threshold potential Spatial

Summation.

( c ) Inhibitory Post-Synaptic Potentials (IPSP's),ifsuccessively fired in space or time, progressivelyinhibit the target neuron.

EPSP d IPSP d th i ff t


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EPSP and IPSP and their effect on a synapseFrom:bioap.wikispaces.com

Illustration of Temporal and Spatial


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ust at o o e po a a d Spat aSummation

From:classes.midlandstech.com

Methods of Synaptic Transmission


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Methods of Synaptic Transmission


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6. Temporal and Spatial Summation (contd..)

Both types of summation form basis of motor learningat neurocellularlevel

Important to use variety of therapeutic interventions,give patient many methods of feedback.communicate

in several ways, to facilitate spatial summation,eitherexcitatory or inhibitory in nature(e.g...inhibiting abnormal tone in trunk and extremitiesby emphasizing normal posture and dynamic trunk

position). In addition, repetition of movement components

facilitates motor learning by temporal summation.


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7. Control and Release of NS Function

The nervous system exerts control throughINHIBITION, not facilitation.

Tunes down, not turns up.

Thus, when higher control is lost, lower systemsexpress themselves uninhibitedly and

uncontrollably... ('When the cat's away, themice will play!')

8 Upper and Lower Motor Neurons


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8. Upper and Lower Motor Neurons

UPPER MOTOR NEURON

From motor neuron in cortex to motor neuron in spinalcord (alpha and gamma motor neurons).

Carries inhibition from higher centers which inhibitexcessive expression of lower level responses.

Upper motor neuron lesions:

disengagement from higher center control

Input short-circuited through lower motor centers withoutbeing processed in higher centers.

Subsequent unchecked activity of lower areas of nervoussystem (brainstem, spinal centers) causes emergence ofprimitive and abnormal movement patterns.

Lesions characterized byspasticityand lack of muscleatrophy.


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8 Upper and Lower Motor Neurons


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8. Upper and Lower Motor Neurons(contd...)

LOWER MOTOR NEURON From spinal motor neurons to peripheral receptors via

peripheral nerves (these are lower motor neuron..LMN)

It is controlled by higher centers through Upper Motor

Neuron (UMN).

Lesions of LMN:

Direct interruptionof signals from receptors; pathwayfrom periphery to Spinal Cord is cut.

Sensory input thus not present at all.

Lesions characterized by flaccidityand muscleatrophy.

9 M l M t


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9. Muscles vs. Movement

Initial 1950s research said that muscles wererepresented in the brain.

Later, it was asserted that brain 'thinks' in

terms ofmovements. Now, research shows that bothmuscles and

movements are represented in the brain, incontinually varying proportions according to

motor response required.

9 M l M t ( td )


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9. Muscles vs. Movement (contd...)

Motor responses consist ofgroups of muscles movingin a pattern or sequence.

Wide variety of patterns in normal movement. In UMN lesions... patient becomes 'locked' into a few

finite stereotyped patterns.

In LMN lesions.... no movement orlimited movement.

10 R l f P t


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10. Role of Posture

All movements performed against background ofposture.

Posturegenerally determined by position of head inspace. Tone is modified through vestibular system.

UMN lesions... abnormal posture results fromabnormal tonal patterns.

LMN lesions... low or no postural tone results ininability to superimpose skilled movement.

11 T hi l O i ti


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11. Topographical Organization

Nervous system and brain pathways aretopographically organized throughout.

Motor and sensory cortices have body maps(homunculi)on their surfaces.

Maps 'distorted' according to importance givenby brain to body parts, i.e., functionalimportance.

Homunculi in sensory and motor cortices


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From: harmonicresolution.com

12 Decussation (Crossing) of Pathways


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12. Decussation (Crossing) of Pathways

Decussation: Latin = to cross in shape of an 'X'

(a) Many bilat symmetrical pathways crossmidline.

Due to above, sensory and motor events onone side of body are controlled by oppositecerebral hemisphere.

Pathways cross at different anatomical levels indifferent systems:



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( g) y(contd..)

Sensory systems : Cross afterfirst synapticrelay, i.e., the medulla.

Motor systems : Higher up in brain. Visual systems : More complicated, only half

the visual fieldis represented on the otherside.


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( g) y(contd..)

Other types of crossing found in braincommisurae (Latin = joining together)

e.g. Corpus callosum (Latin = hard body).... bigbundle of fibers which connects the twohemispheres.

13 Function of Gray and White Matter


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13. Function of Gray and White Matter

Gray matter= nerve cell bodies

In cortex and brainstem = deep and superficialnuclei of brain

In spinal cord = butterfly-shaped, divided intodorsal horn, intermediate zone and ventral horn.All collectively divided into 6 nuclei.

In 1952, Rexed classified spinal cord graymatter into 10 laminae or layers, eachsubserving a different function.

13 Function of Gray and White Matter (contd )


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13. Function of Gray and White Matter (contd..)

White matter= axons of the nerve cells

In brain = fibers: Commisural: between 2hemispheres

Intracortical: within local cortical region Association: different cortical regions on same

side

Projection: from cortical neurons to subcorticalstructures

sectn 1 nervous syst orgnzn

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