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    FUCTIONAL

    Organization and basicfunctions

    of the Nervous Systemby

    Abeer El-Emam

    ass. Prof. Physiology

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    Men ought to know that from nothing else butthe brain come joys, delights, laughter and

    sports, and grief, despondency. And by this,in an especial manner, we acquire wisdom andknowledge, and see and hear and know whatare foul and what are fair, what are bad and

    what are good... And by the same organ webecome mad and delirious, and fears andterrors assail us All these things we endurefrom the brain when it is not healthy In

    these ways I am of the opinion that the brainexercises the greatest power in the man.Hippocrates, fourth century

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    Objectives:

    After studying this chapter you should able to

    Knowledge and understanding:

    - Name the component of the nervous system- Define reflex arc- Describe the component of a reflex arc and name its types- List the functional parts of the nervous system and their role in control

    of voluntary movement- Describe the function of each horn in the spinal cord sectioncomponent

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    The nervous system has three main functions:

    Sensory input

    Integration of dataMotor output.

    Sensory motor integration

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    Functions of the Nervous System

    Propagate sensory information (APs) from eyes, skin, blood

    vessels, ears, digestive tract, joints, muscles, lungs to theCNS

    Integration. Brain and spinal cord process sensory input andinitiate responses

    Motor output: Controls of muscles and glands

    conscious perception (awareness) of some sensoryinformation

    Mental activity. Consciousness, thinking, memory, emotion

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    Anatomical Organization of the Nervous System

    Central nervous system (CNS)

    the brain

    the spinal cord

    major information integration centers of the body

    large masses of neurons

    Peripheral nervous system (PNS)nerves that connect the CNS and other locations of the

    body

    neurons propagate APs towards and away from the

    CNSganglions(group of neuronal somas)

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    Types of neurons

    Sensory neurons (or afferent neurons) carry impulses from

    receptors to the central nervous system

    Motor neurons (or efferent neurons) carry impulses from the

    central nervous system to effectors (muscles and glands)

    Sensory and motor neurons make up the peripheral nervous

    system. Visceral motor neurons form the autonomic nervoussystem,

    Interneurons (association neurons) They connect the neurons,

    and are found entirely within the central nervous system..

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    Peripheral Nervous System

    The PNS consists of 12 pairs (left and right) of cranialnerves originate from the brain and 31 pairs (left and right)

    of nerves are attached to the spinal cord Sensory (afferent)

    all axons carry impulses from sensory receptors via thePNS to the CNS

    Motor (efferent)all axons carry impulses via the PNS from CNS

    Mixed

    a mixture of sensory and motor neurons that carryimpulses via the PNS to and from CNS

    most common type of nerve in the body

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    Sensory Division of the PNS

    Transmit nerve impulses over sensory neurons to theCNS from receptors

    Receptors are classified as:

    Somatic receptors - those found in skin, joints,skeletal muscles, and special sense organs

    Respond to touch, pressure, heat, stretch, pain,

    light

    Visceral receptors - located in walls of viscera

    Respond to stretch, pain, temperature, chemical

    stimuli (CO2)

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    Motor Division of PNS

    Transmits impulses away from the CNS to effectors

    Effector - any muscle or gland Somatic nervous system:

    Regulates contraction ofskeletal muscles.

    Under our voluntary control - I.e., under consciouscontrol

    Autonomic nervous system (ANS)

    Regulates contraction of smooth muscle, cardiac

    muscle and glands (visceral organs)

    Subconscious or involuntary control.

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    Divisions of the ANS

    Sympathetic. Prepares body for physical activity.

    Parasympathetic. Regulates resting or vegetative

    functions such as digesting food or emptying of

    the urinary bladder

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    Brain

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    The brain consists of many parts that function as an

    integrated whole. The major parts are the medulla, pons,and midbrain (collectively called the brainstem), the

    cerebellum, the hypothalamus, the thalamus, and the

    cerebrum.

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    The forebrain Composed of the cerebrum and thediencephalon ( thalamus and hypothalamus )

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    Cerebral Cortex (Cerebrum) Largest portion of the brain 4 lobes (frontal, parietal, temporal and occipital)

    perception of all sensesmemory, emotion, learninginitiation of voluntary skeletal muscle contraction

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    Some Functional Areas of Cerebral Cortex

    Motor areas initiate action potential for skeletal musclecontraction (voluntary movement) (pre-central gyrus of thefrontal lobe)

    Somesthetic areas perceive sensory information from the

    skin, muscles and joints (post-central gyrus of parietal lobe) Broca and Wernicke areas function in learning language and

    speech

    - sulcus (i) & fissure (s) (lateral, central)

    - gyrus

    S A

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    Motor Areas

    Figure 13.10

    Sensory Areas

    L li i f h C b l C

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    Lateralization of the Cerebral Cortex

    The cortex is divided anatomically into right an left

    hemispheresconnected in the middle by the corpus callosum

    Right Side controls left & vice-versaLeft Hemisphere Functions

    e.g., language, analytical reasoning

    Right Hemisphere Functions

    e.g., spatial skills, processing music

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    Thalamus

    Major relaying center for both sensory (afferent) andmotor (efferent) information as it passes between thebrain and the PNS.

    Primitive center for crude sensations from oppositeside of the body such as pain, extreme of temperature.

    Parts of the thalamus are also involved in alertness

    and awareness and others contribute to memory.

    H th l

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    Hypothalamus

    Group of nuclei forms the floor and lower walls of the thirdventricle.

    Functions include the following:

    Control of the autonomic nervous system

    Control of emotional responses

    Regulation of body temperatureRegulation of hunger and thirst sensations

    Control of behavior

    Regulation of sleep-wake cyclesControl of the endocrine system

    Formation of memory

    i S

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    Brain Stem

    Comprised of midbrain, pons and the medulla oblongata.

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    The Brain StemThe Midbrain

    Cranial nerve III,IV emerge from mid brain sleep and wake cycles (RAS)

    concerned with righting reflexes, those thatkeep the head upright and maintain balance

    or equilibrium. contains the superior and inferior colliculi

    Superior colliculi nuclei that act in visualreflexes

    Inferior colliculi nuclei that act inreflexive response to sound

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    The Brain StemThe Pons

    Located between the midbrain and medulla

    oblongata

    Contains the nuclei of cranial nerves V, VI,and VII,VIII

    There are two respiratory center that

    work with those in the medulla toproduce a normalbreathing rhythm.

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    Clusters of neurons (brain centers) in regions of the ponsand medulla control the basic life functions:

    heart rate controlled by the cardioacceleratory and

    cardioinhibitory centers in the medulla

    blood pressure

    controlled by the cardioacceleratory,cardioinhibitory, and vasomotor centers in themedulla

    breathing rate

    controlled by the inspiratory and expiratory centersin the medulla and pons, respectively

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    The Cerebellum

    Figure 13.22a

    Th C b ll

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    The Cerebellum

    Located dorsal to the pons and medulla

    Composed of two cerebellar hemispheres Makes up 11% of the brains mass

    Modifies the motor information leaving the motor cortex

    provides precise timing and appropriate patterns ofskeletal muscle contraction to maintain balance andcoordination.

    Smoothes and coordinates body movements

    Helps maintain equilibrium

    - cognitive functions (with frontal lobe)

    Cerebellar activity occurs subconsciously

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    Basal Ganglia

    Subcortical masses of grey matter

    Striatum (Caudate & Putamen)- Globus Pallidus- SubstantiaNigra.They work with the cerebellum in planning and controlling thevoluntary movements.

    Control of muscle tone,and voluntary movementsSubconsciuos automaticmovements.

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    The Limbic System

    LocationMedial aspect of cerebral hemispheres

    Also within the diencephalon

    Composed of:

    Septal nuclei, cingulate gyrus, and hippocampal

    formation

    Part of the amygdala

    concerned with; control of emotion, regulation of

    autonomic function, motivation, memory, feeding, sexual

    behavior.

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    The Reticular Formation

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    Large masses of neurons scattered within the brain stem.

    Concerned with adjustment of stretch reflex, contains many

    areas for regulation of heart rate, blood pressure.

    Modify pain through raphe nucleus which secrets serotonin.

    Regulation of sleep

    RAS:

    Upward extension of facilitatory reticular formation

    responsible for wakefulness

    Spinal Cord

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    Spinal Cord

    The spinal cord is attached to the brain and extends to the

    lumbar region of the vertebral column

    Functions include:

    integration of basic stimuli presented to the body below

    the neck through simple reflex arcs

    withdrawal reflex in response to pain

    Walking movements.

    Reflexes that stiffen the legs to support the body

    against gravity. Reflexes that control local blood vessels,

    gastrointestinal movements.

    sending sensory and motor information to and from the

    brain

    Spinal Cord Anatomy

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    Spinal Cord Anatomy

    Dorsal (posterior) horns (left and right)

    sensory neurons enter the cord on the dorsal aspect wherethey synapse with interneurons or motor neurons

    extend into dorsal roots and ganglia

    Ventral (anterior) horns (left and right)motor neurons exits the cord on the ventral aspect where

    they control effectors (muscle or glands)

    extend into motor roots

    Dorsal and ventral roots merge together to form spinal

    nerves

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    VentriclesThe ventricles are four cavities within the brain: two lateral

    ventricles, the third ventricle, and the fourth ventricle . Eachventricle contains a capillary network called a choroidplexus, which forms cerebrospinalfluid (CSF) from bloodplasma.

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    Cerebrospinal fluid

    Volume, 140ml in adult man

    Pressure, 10 mmHgColorless, salty solution

    Continuously secreted from specialized cells (ependymal

    cells) in the choroid plexus in ventricles

    Ependyma actively transport Na+ and solutes into

    ventricles

    Functions: Physical and chemical protection

    Contains little protein and lower K+, Ca++, HCO3-, andglucose

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    The Blood-Brain Barrier (BBB)

    Function - protection

    Brain capillaries much less permeable than others

    Protects the brain from blood composition fluctuations

    This barrier is permeable to respiratory gases, glucose,

    volatile anestheticsExceptions(circumventricular organs) posterior

    pituitary and vomiting center

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    The reflex actionAll activities of the nervous system are in the form of reflex

    action. A reflex action is an unavoidable beneficial inbornresponse brought about by a stimulus (a sudden change of the

    external or internal environment)

    Types of reflex action:

    - Somatic reflex action: if the responding tissue is skeletal

    muscle.e.g., withdrawal of the limb away from painful stimuli.

    - Visceral (autonomic) reflex action: concerned with reflexes

    of internal organs or viscera such as gastrointestinal tract,

    urinary bladder .

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    The reflex action is carried out through a pathway called a

    reflex arc

    Somatic reflex action visceral reflex action

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    Nomenclature

    Telencephalon

    Diencephalon

    Mesencephalon

    Metencephalon

    Myelencephalon

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    Collection of neurons

    Gray matter, collection of neuronal cell bodies in the CNS

    Cortex, any collection of neurons that form a thin sheet,usually at the brain surface.

    Nucleus, distinguishable mass of neurons deep within the

    brain

    Substantia, a group of related neurons deep within the brainbut with less distinct border than those of nucleus

    Locus, a small well defined group of cells

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    Collection of axons

    White matter, collection of CNS axons

    Tract, a collection of CNS axons having a common site oforigin and a common destination

    Bundle, a collection of axons that run together but do not

    necessarily have the same origin and destinationCapsule, a collection of axons that connect the cerebrumwith the brain stem

    Lemniscus, atract that meander through the brain like a

    ribbon

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