review of neurophysiology (sensory system) 2016

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الرحیم ٰم�ن الرح اللہ بسم

Prof. DR.Rashid Mahmood

Review of Neurophysiology(Sensory System)

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Introductory LectureCourtesy: Prof. Dr. Abid Hussain,

Vice Principal, Northwest School of Medicine ,

PeshawarProf..Rashid Mahmood

NeurophysiologyNeurophysiology

What is Neurophysiology?What is Neurophysiology?Neurophysiology is the study of

nervous system function

Control of body functionsControl of body functions

Nervous systemNervous system

Hormones Hormones

Skeletal muscles

Visceral functions

Somatic NSAutonomic NS

Organization of Nervous System

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A system that controls all of the activities of the body.

The nervous system is made of:The brain The spinal

cord

The nerves The sensesProf..Rashid Mahmood

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The Central Nervous System is made of the brain and the spinal

cord.

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CNSCNS Spinal CordSpinal Cord Brain StemBrain Stem

Medulla, pons, and midbrainMedulla, pons, and midbrain CerebellumCerebellum DiencephalonDiencephalon

Thalamus and hypothalamusThalamus and hypothalamus Cerebral HemispheresCerebral Hemispheres

Cerebral cortex, basal ganglia, Cerebral cortex, basal ganglia, hippocampus, and amygdalahippocampus, and amygdala

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An organ that controls your emotions, your thoughts, and every movement you make.

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* The brain controls everything in the body.* The brain is made of more than 10 billion nerves!

* The brain is divided into three parts and is protected by the skull.

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Brain Stem

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Major Levels of Central Nervous System Function

(1) the spinal cord level, (2) the lower brain or subcortical level:

medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, and

basal ganglia (3) the higher brain or cortical level

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* The Cerebrum is the largest part of the brain. It controls:1. thinking.

2. memory.

3. speaking.

4. movements 5. Receives/ identifies /processes sensory

information and integrates motor functionsProf..Rashid Mahmood

Cerebral Hemispheres

• 3 deep nuclei within hemispheres:• Basal Ganglia

– Receives input from cerebral cortex and project to frontal cortex

– Regulates movement• Hippocampus

– Involved in memory• Amygdala

– Involved with emotions

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Functions of Different Areas of brain

CerebellumCerebellum

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* The cerebellum is below and to the back of the cerebrum.

1. controls balance.

2. controls posture.

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* The spinal cord sends messages to the brain.* The spinal cord is the part of the nervous system that connects the brain to the rest of the nervous system.

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Spinal Segments

Spinal Nerves(Contain both sensory

and motor nerves)

Spinal Cord

• Ascending pathways– Carry sensory info from periphery to higher levels of

CNS• Descending pathways

– Carry motor info from higher levels to motor nerves that innervate periphery

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* The outer nervous system is made of the nerves and the sense

organs.

Ear EyeSkin

Nerves

Tongue

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It carries messages between the central nervous system and the rest of the body

Nose

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Peripheral Nervous System• Two subdivisions

– Sensory or afferent– Motor or efferent

• Divisions• Somatic nervous system• Autonomic nervous

system (ANS)» Sympathetic » Parasympathetic» Enteric

Sensory Pathway

Motor Pathway

Interneuron(Integration)

CNSPNS

Receptors

EffectorTissue

1. Sensory Neuron

3. Motor Neuron

2. In

tern

euro

n

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Functional classification

of Neurons– Sensory or afferent: Action potentials

toward CNS

– Motor or efferent: Action potentials away from CNS

– Interneuron : Within CNS from one neuron to another

Other Classifications of Neurons

• Based on Myelin Sheath1. Myelinated2. Unmyelinated

• Based on Structure Self-Study 1. Unipolar2. Multipolar, 3. Bipolar,4. Pseudo-unipolar

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* An automatic reaction that happens without thinking about

it.* A reflex happens quickly in

less than a second.

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The Synapse• Junctional point

between two neurons that

transmits impulse from first to the second Neuron.(Junction between muscle+

neuron=Synapse?)

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Classification of Synapses

• Anatomical Classification • (on the Basis of Communication )

– 1. Axo-Dendritic– 2. Axo-Somatic– 3. Axo-Axonic– 4. Dendro-dendritic (amacrine cells in Eye)

PHYSIOLOGICAL Classification: (According to Nature)

1. Electrical2. Chemical

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1.Axo-Dendritic

2. Axo-Somatic

3. Axo-Axonic4. Dendro-

dendritic

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Electrical Synapse

Gap Junctions inCardiac & Smooth Muscle

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Chemical Synapses

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Properties of Synapses 1. One Way Conduction2. Synaptic Delay3. Excitation (EPSP)4. Inhibition

1. Presynaptic Inhibition2. Postsynaptic Inhibition3. Reciprocal Inhibition

5. Synaptic fatigue6. Summation

1. Spatial summation 2. Temporal summation

7. Facilitation

8. Occlusion& Subliminal Fringe9. Convergence10. Divergence11. Recruitment12. Afterdischarge13. Posttetanic Potentiation14. Habituation15. Effect of Acidosis & Alkalosis16. Effect of Hypoxia on Synaptic

Transmission17. Effect of Drugs on Synaptic

Transmission

Classification of Senses

Conscious– Somatic senses

• Touch / pressure• Temperature• Pain• Proprioception

– Special senses• Vision• Hearing• Taste• Smell• Equilibrium

Subconscious– Somatic stimuli– Muscle length and

tension– Visceral stimuli– Blood pressure– pH / oxygen content in

blood– pH of cerebrospinal fluid– Lung inflation / Deflation– Osmolarity of body fluids– Blood glucose level

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Receptors• Receptors are transducers which detect the

Change in the environment (stimulus)& converts it into Propagated action Potential ( impulse).

• The complexity of sensory receptors ranges from

free nerve endings to specialized nerve endings and receptor organ.

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Classification of Receptors5 types of classification

1. On the basis of Modality of sensations Carried by Receptors ( Five Major Groups )

I. .Mechanoreceptors – ( Mechanical Change ) i. skin tactile – Free Nerve Endings, Hair end organs etc

ii. Deep tissues - ( Pacinian Corpuscles )iii. Muscles / Tendons (Muscle spindles & Golgi tendons Organsiv. Hearing - ( Organ of Corti )v. Equilibrium – ( Vestibular apparatus)vi. B.P. ( Baroreceptors )

II. Thermoreceptors - Cold & Warm Receptors

III. Nociceptors (pain) - Free Nerve Endings

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Classification of Receptors- contd

• IV. Electromagnetic Receptors (Vision)- Rods & Cones.

• V. CHEMORECPTORS; - Taste- Taste Buds

- Smell – Olfactory Epithelium. - Arterial PO2- Aortic & Carotid Bodies

- PCO2 - Central Chemoreceptors

- Osmolality - Neurons in Supraoptic Nucleus of Hypothalamus, and

- Blood Glucose, A.A & F.A- Receptors in Hypothalamus

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Classification of Receptors…contd 2. On the Basis of Distribution in the Body i.e

Somatic (Somesthetic) & Special Senses

3. On the basis of Origin of Stimuli: Interoceptors

Proprioceptors Exteroceptors

4. Structural Classification Non Encapsulated

Encapsulated

5. On the Basis of Adaptation: Phasic ( Rapidly Adapting)- Pacinian Corpuscles

Tonic ( Slowly Adapting)- Pain (free Nerve endings)

Classification of Somatic Senses

Somatic Senses • Mechanoreceptive

Somatic Sensations– Tactile – Position

• Thermoreceptive Senses– Heat– Cold

• Pain Senses

Special senses• Vision• Hearing• Smell• Taste• Equilibrium

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Based on Modality of sensation

Classification of Somatic Senses

• Exteroceptive Sensations• Interoceptive sensations

– Proprioceptive sensations• Position• Muscle, tendon

– Visceral sensations• Viscera

– Deep sensations • Bone, fasciae

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Based on Origin of sensation

Functions of Thalamus

1. Relay center for somatic sensory information to cerebral cortex

2. Perception of group tactile sensations3. Perception of Pain sensation 4. Perception of temperature sensation 5. Center for integration & modification of sensory signals6. Capacity to determine whether a sensation is pleasant or

unpleasant and agreeable or disagreeable7. Center for sexual sensation8. Arousal and alertness reaction (connection with reticular

nuclei)9. Center for reflex activities10. Center for integration of motor function (cerebellum + Basal

ganglia)

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SensoryPathways

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Transmission of Somatic Sensations• All sensory information enter the spinal cord through

dorsal route (Bell Magendie Law) from where they are carried through any of the following

Ascending Pathways:1. Dorsal column-medial Laminiscal System.

1. Fasciculus Gracilus (Medial)2. Fasciculus Cuneatus (Lateral)

2. Antero-lateral system (Spino-thalamic). 1. Anterior Spinothalamic Tract

2. Lateral Spinothalamic tract

3. Spinocerebellar tracts1. Dorsal2. ventral

4. Spinotectal, Spino olivary, Spino Vestibular

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Dorsal Column-Medial Laminiscal system

• Ist Order N. From Receptor Enter the spinal cord & divide into Lateral & Medial Branches.

- The medial Branch goes to the Medulla (Gracile or Cuneate Nucleus).

- The lateral branch divide & relay in the

Ventral horn to serve as:1. Local spinal Reflex action2. for formation of Spino-Cerebellar Tract3. May accompany dorsal column Tract

• 2nd. Order N. From Gracile or Cuneate N in the Medulla to the VPL nucleus of the Thalamus (Ventrobasal Complex)

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Antero-Lateral Path

2nd Order N. From Laminae I,IV,V & VI Cross to opposite side obliquely, Ascend up & relay in Anterior & Lat.

White columns of the spinal cord 1. Reticular formation of Brain stem. 2. VPL N & Intralaminar Nuclei of the

Thalamus

3rd Order N. From Thalamus – Passthrough Internal capsule to the Primary Sensory Cortex

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Dorsal Column & Anterolateral

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Somatosensory Cortex I & II

I II

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Representation of different areas of the Body in the Somatosensory Cortex-I

Humunculous

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Recommended BooksRecommended BooksTextbooksTextbooks::1.1. Textbook of Medical Textbook of Medical

Physiology, Physiology, GuytonGuyton & Hall, 13& Hall, 13thth Edition Edition

2.2. Ganong’sGanong’s Review of Review of Medical Physiology, Medical Physiology, 2424thth Edition Edition

3.3. Neurophysiology by Neurophysiology by Prof. Dr. Masood Prof. Dr. Masood (3(3rdrd International International Edition)Edition)

4.4. Lecture Notes of Lecture Notes of Neurophysiology Neurophysiology by by Prof. Dr. M. Tariq Prof. Dr. M. Tariq (2(2ndnd Edition) Edition)

Reference booksReference books SherwoodSherwood Human Physiology Human Physiology

from cells to systems 8th edition from cells to systems 8th edition SherwoodSherwood Principals of Principals of

Human Physiology 9th editionHuman Physiology 9th edition K. K. SembulingamSembulingam

Essentials of Medical PhysiologyEssentials of Medical Physiology6th Edition 6th Edition

StuartStuart IraIra FoxFox Human Human Physiology Physiology 13th Edition13th Edition

Vander,sVander,s Human Physiology Human Physiology (The Mechanism of Body (The Mechanism of Body function) 11th Editionfunction) 11th Edition

Guyton & Hall Physiology Guyton & Hall Physiology Review Review (2nd Edition)(2nd Edition)

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The EndThank You