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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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