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The nervous system is the master controlling and communicating system of the body. Every thought, action, and emotion reflects its activity. Its cells communicate by electrical and chemical signals, which are rapid and specific, and usually cause almost immediate responses.


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Functions of the Nervous System

  • Sensory input – gathering information

    • To monitor changes occurring inside and outside the body.

    • Changes = stimuli

  • Integration

    • To process and interpret sensory input and decide if action is needed.

  • Motor output

    • A response to integrated stimuli

    • The response activates muscles or glands


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For example, when you are driving and see a red light ahead (sensory input), your nervous system integrates this information (red light means “stop”), and your foot goes for the brake (motor output).


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Structural Classification of the Nervous System (sensory input), your nervous system integrates this information (red light means “stop”), and your foot goes for the brake (motor output).

  • Central nervous system (CNS)

    • Brain

    • Spinal cord

  • Peripheral nervous system (PNS)

    • Cranial nerves

    • Spinal nerves


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Functional Classification of the (sensory input), your nervous system integrates this information (red light means “stop”), and your foot goes for the brake (motor output).PNS

It is divided into TWO subdivisions:

1-Sensory(afferent) division

  • Nerve fibers that carry information to the central nervous system from:

  • sensory receptors in the skin, skeletal musclesand joints (somatic sensory fibers).

  • Sensory receptors in the visceral organs (visceral sensory fibers)

Figure 7.1


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2-Motor (efferent) division (sensory input), your nervous system integrates this information (red light means “stop”), and your foot goes for the brake (motor output).

  • Nerve fibers that carry impulsesaway from the central nervous system ( to Muscles &Glands).These impulses effect (bring about) a motor response.

    It has two subdivisions

    1-Somatic nervous system = voluntary, it controls skeletal muscles

    2-Autonomic nervous system= involuntary,

    it controls smooth &cardiac muscles &glands

    This also is divided into

    sympathetic &

    parasympathetic


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Organization of the Nervous System (sensory input), your nervous system integrates this information (red light means “stop”), and your foot goes for the brake (motor output).

Figure 7.2


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Despite the complexity of the nervous system, there are only two functional cell types

Neurons - excitable nerve cells that transmit electrical signals

Neuroglia (glial) cells - supporting cells

Histology of Nervous Tissue


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Neuroglia cells - 4 types in the Central NS

1-Astrocytes

star shaped with many processes

connect to neurons; help anchor them to nearby blood capillaries

control the chemical environment of the neurons

2-Microglia

- oval with thorny projections

- monitor the health of neurons

- if infection occurs, they change into macrophages (eating viruses, bacteria and damaged cells)


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3-Ependymal cells

range in shape from squamous to columnar; many are ciliated

line the dorsal body cavity housing the brain and spinal cord

form a barrier between the neurons and the rest of the body

4-Oligodendrocytes

- have few processes

- wrap themselves around axons

- form the myelin sheath – an insulating membrane


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Neuroglia cells - 2 types in the Peripheral NS

Satellite cells

- surround neuron cell bodies in the periphery

- Protective , cushioning cells

Schwann cells (neurolemmocytes)

- are vital to regeneration of damaged nerve fibers.

- adjacent Schwann cells along an axon do not touch one another, so there are gaps in the sheath. These gaps, called nodes of Ranvier occur at regular intervals (about 1 mm apart) along the myelinated axonand form the myelin sheath around larger nerve fibers in the periphery

- it acts as an insulators.


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Neuron (Nerve cell)

-The Cells are specialized

to transmit messages

-Differ structurally but

Have common features:

  • A Cell body with nucleus and the usual organelles, Except centrioles

  • One or more processes

Figure 7.4a


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Neuron Anatomy

  • Extensions outside the cell body

    • Dendrites – conduct impulses toward the cell body

    • Axons – conduct impulses away from the cell body

Figure 7.4a


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Axons and Nerve Impulses

  • Axons end in axonal terminals

  • Axonal terminals contain vesicles with neurotransmitters

  • Axonal terminals are separated from the next neuron (neuroneural ) junction or the muscle (neuromuscular) junction by a gap calledSynaptic cleft (Synapse).


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Nerve Fiber Coverings

- Most long nerve fibers are

covered with a whitish, fatty

material called Myelin with waxy

appearance. It insulates the fiber

&Increases transmission rate

- Axons outside CNS are wrapped

by Schwann Cells.

-

Figure 7.5


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Neuron Cell Body Location

  • Most are found in the central nervous system

  • Gray matter – cell bodies and unmyelinated fibers

    • Nuclei – clusters of cell bodies within the white matter of the central nervous system

    • Ganglia – collections of cell bodies outside the central nervous system

  • White matter- collection of myelinated fibers (Tracts) in the CNS.

  • Fibers outside the CNS are called nerves.


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Functional Classification of Neurons

1-Sensory (afferent) neurons

Carry impulses from the sensory receptors

  • Cutaneous sense organs

  • Proprioceptors – detect stretch or tension in muscles and tendons and joints

    2-Motor (efferent) neurons that carry impulses from the central nervous system to muscles and glands ,their cell bodies are always in CNS.

    3-Interneurons(association neurons)

  • Their cell bodies are always found in CNS.

  • Connect sensory and motor neurons in neural pathways.



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    Structural Classification of Neurons

    • Multipolar neurons – many extensions from the cell body.

    Figure 7.8a



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    Figure 7.8c


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    Functional Properties of Neurons cell body which is very short ,divides almost immediatly

    • Irritability – ability to respond to stimuli.

    • Conductivity – ability to transmit an impulse.

    • The plasma membrane at rest is polarized i.e.,Fewer positive ions are inside the cell than outside the cell


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    Starting a Nerve Impulse cell body which is very short ,divides almost immediatly

    • a- resting membrane electrical condition. The external face of the membrane is slightly positive, its internal face is slightly negative. The chief extracellular ion is sodium wheras the chief intracellular ion is potassium. The membranr is relatively impermeable to both ions.

    • b- Stimulus initiates local depolarization by changing permeability to sodium which rush inside the cell changing polarity of the membrane so the inside becomes more positive, the outside become more negative at that site.


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    • c- cell body which is very short ,divides almost immediatlyDepolarization and generation of an action potential. If the stimulus is strong enough , depolarization causes membrane polarity to be completely reversed and an action potential is initiated.

    • d- Propagation of action potential. Depolarization of the first membrane patch causes permeability changes in the adjacent membrane and the events described in(b) are repeated. Thus the action potential propagates rapidly along the entire length of the membrane.


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    • e- cell body which is very short ,divides almost immediatlyRepolarization.potassium ions diffuse out of the cell restoring the negative charge on the inside of the membrane and positive charge on the outside surface.repolarization occurs in the same direction as depolarization.

    • f- Initial ionic condition restored bythe sodium-potassium pump . Three sodium ions are ejected for every two potassium ions carried back into the cell


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    Nerve Impulse Propagation cell body which is very short ,divides almost immediatly

    • The nerve impulse is is an all-or-none response, like firing a gun. It is either propagated over the entire axon ,or it does not happen at all.

    • Impulses travel faster when fibers have a myelin sheath(saltatory conduction).

    • Until repolarization occur,a neuron can not conduct another impulse.

    Figure 7.9c–e


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    • HOMEOSTATIC IMBALANCE cell body which is very short ,divides almost immediatly

    • 1-A number of chemical and physical factors impair impulse propagation. Sedatives and anesthetics block nerve impulses by altering membrane permeability to sodium. As we have seen, no Na+ entry—no AP.    

    • 2-Cold and continuous pressure interrupt blood circulation (and hence the delivery of oxygen and nutrients) to neuron processes, impairing their ability to conduct impulses. For example, your fingers get numb when you hold an ice cube for more than a few seconds, and your foot “goes to sleep” when you sit on it. When you remove the cold object or pressure, impulses are transmitted again, leading to an unpleasant prickly feeling.


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    Continuation of the Nerve Impulse between Neurons cell body which is very short ,divides almost immediatly

    • Impulses are able to cross the synapse to another nerve by:

      • Neurotransmitter is released from a nerve’s axon terminal

      • The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter

      • The response is very brief because the neurotransmitter is quickly removed either by reuptake by the axonal trminal or by enzymatic breakdown. This limits the period to less than the blink of an eye.

      • An action potential is started in the dendrite of the next neuron propagating to cell body and its axon.

      • Notice : impulse transmission is an electrochemical


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    How Neurons Communicate at Synapses cell body which is very short ,divides almost immediatly

    Figure 7.10


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    The Reflex Arc cell body which is very short ,divides almost immediatly

    • Reflexes are rapid, predictable, and involuntary responses to stimuli

    • Reflex arc follows a direct route from a sensory neuron, to an interneuron,then to an effector neuron.

    • Reflex arc have a minimum 5 elements


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    Simple Reflex Arc cell body which is very short ,divides almost immediatly

    Figure 7.11b, c


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    Types of Reflexes cell body which is very short ,divides almost immediatly

    • One classification:

    • - Autonomic reflexes eg.

      • Salivary gland secretion

      • Heart and blood pressure regulation

      • Changes in size of the pupil

      • Digestive system regulation

    • - Somatic reflexes

      • Activation of skeletal muscles

      • Other classification:

      • - Spinal reflexes ,involve spinal cord as the flexor reflex

      • -Cranial reflexes requires the brain as light reflex.


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    Exaggerated, Distorted or Absent indicate nervous system disorder.

    Reflex changes often occur before the pathological condition become obvious.

    Importance of REFEXES


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    Central Nervous System (CNS) disorder.

    • CNS develops from the embryonic neural tube.

      • By the fourth week the anterior end begins to expand and brain formation begins, The rest of the tube becomes the spinal cord.

      • The central canal becomes enlarged in 4 regions of the brain to form the ventricles which are:

        -Four chambers within the brain.

        -Filled with cerebrospinal fluid(CSF).


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    Regions of the Brain disorder.

    • Cerebral hemispheres

    • Diencephalon

    • Brain stem

    • Cerebellum

    Figure 7.12


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    • The cerebral hemispheres form the superior part of the brain. Together they account for about 83% of total brain mass.

    • Picture how a mushroom cap covers the top of its stalk, and you have a fairly good idea of how the paired cerebral hemispheres cover and obscure the diencephalon and the top of the brain stem .


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    Cerebral Hemispheres (Cerebrum) brain. Together they account for about 83% of total brain mass.

    Figure 7.13a


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    • Nearly the entire surface of the cerebral hemispheres is marked by elevated ridges of tissue called gyri (ji′ri; “twisters”), separated by shallow grooves called sulci (sul′ki; “furrows”). The singular forms of these terms are gyrus and sulcus. Deeper grooves, called fissures, separate large regions of the brain. The more prominent gyri and sulci are similar in all people and are important anatomical landmarks. The median longitudinal fissure separates the cerebral hemispheres .Another large fissure, the transverse cerebral fissure, separates the cerebral hemispheres from the cerebellum below


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    • Several sulci divide each hemisphere into marked by elevated ridges of tissue called four lobes— frontal, parietal, temporal,and occipital. The central sulcus, which lies in the frontal plane, separates the frontal lobe from the parietal lobe. Bordering the central sulcus are the precentral gyrus anteriorly and the postcentral gyrus posteriorly. More posteriorly, the occipital lobe is separated from the parietal lobe by the parieto-occipital sulcus (pah-ri″ĕ-to-ok-sip′ĭ-tal).


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    Layers of the Cerebrum marked by elevated ridges of tissue called

    • Gray matter

      • Outer layer

      • Composed mostly of cell bodies of the neurons

    Figure 7.13a


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    • White matter marked by elevated ridges of tissue called

      • Fiber tracts inside the gray matter

      • Example: corpus callosum connects between the two hemispheres.

    Figure 7.13a


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    Basal nuclei , or basal ganglia marked by elevated ridges of tissue called –islands of gray matter buried deep within the white matter of the cerebral hemispheres, They help regulate voluntary motor activities in relation to starting or stopping movements sent to skeletal muscles by the primary motor cortex.Disorders of the basal nuclei result in either too much or too little movement as exemplified by Huntington’s chorea and Parkinson’s disease, respectively.


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    Specialized Area of the Cerebrum marked by elevated ridges of tissue called

    • Gustatory area (taste)

    • Visual area

    • Auditory area

    • Olfactory area

    • Speech/language region

    • Language comprehension region


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    Specialized Area of the Cerebrum marked by elevated ridges of tissue called

    Figure 7.13c


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    Diencephalon marked by elevated ridges of tissue called

    • Sits on top of the brain stem

    • Enclosed by the cerebral heispheres

    • Made of three parts

      • Thalamus

      • Hypothalamus

      • Epithalamus


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    Diencephalon marked by elevated ridges of tissue called

    Figure 7.15


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    Thalamus marked by elevated ridges of tissue called

    • Surrounds the third ventricle

    • The relay station for sensory impulses (except olfaction)

    • Transfers impulses to the correct part of the cortex for localization and interpretation


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    Hypothalamus marked by elevated ridges of tissue called

    • Under the thalamus

    • Important autonomic nervous system center

      • Helps regulate body temperature

      • Controls water balance

      • Regulates metabolism

    • An important part of the limbic system (emotions),as thirst , appetite , sex, pain and pleasure centers.

    • The pituitary gland hangs from the anterior floor of the hypothalamus by a slender stalk.


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    Epithalamus marked by elevated ridges of tissue called

    • Forms the roof of the third ventricle

    • Important parts are:

    • - pineal body (an endocrine gland). and

    • - the choroid plexus : knots of capillaries withen each ventricle, forms the cerebrospinal fluid (CSF).


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    Brain Stem marked by elevated ridges of tissue called

    • Attaches to the spinal cord

    • Parts of the brain stem are:

      • Midbrain

      • Pons

      • Medulla oblongata


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    Brain Stem marked by elevated ridges of tissue called

    Figure 7.15a


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    Midbrain marked by elevated ridges of tissue called

    • Mostly composed of tracts of nerve fibers

    • Anteriorly , it has two bulging fiber tracts – the cerebral peduncles which convey ascending and descending impulses.

    • Dorsally are four rounded protrusions – corpora quadrigemina which are reflex centers involved with vision and hearing.


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    Pons marked by elevated ridges of tissue called

    • The bulging center part of the brain stem.

    • Mostly composed of fiber tracts.

    • Includes nuclei involved in the control of breathing.


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    Medulla Oblongata marked by elevated ridges of tissue called

    • The lowest part of the brain stem

    • Merges into the spinal cord.

    • Includes important fiber tracts.

    • Contains important control centers

      • Heart rate control

      • Blood pressure regulation

      • Breathing

      • Swallowing

      • Vomiting

      • -The fourth ventricle lies posterior to the pons and medulla and anterior to the cerebellum.


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    Reticular Formation marked by elevated ridges of tissue called

    • Diffuse mass of gray matter along the brain stem.

    • Its neurons are involved in motor control of visceral organs.

    • A special group of its neurons are the reticular activating system(RAS) which plays a role in awake/sleep cycles and consciousness . Damage to this area can result in permanent unconsciousness.


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    Reticular Formation marked by elevated ridges of tissue called


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    Cerebellum marked by elevated ridges of tissue called

    • Two cauliflower-like hemispheres with convoluted surfaces projects dorsally from under the occipital lobe of the cerebrum.

    • Provides the precise timing for skeletal muscle activity

    • And controls our balance and equilibrium.

    • So movement is smooth and coordinated.


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    Cerebellum marked by elevated ridges of tissue called


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    Protection of the Central Nervous System marked by elevated ridges of tissue called

    • Scalp and skin

    • Skull and vertebral column

    • Meninges

    • Cerebrospial

    • fluid

    • Blood brain

    • barrier

    Figure 7.16a


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    Three connective tissue membranes lie external to the CNS – dura mater, arachnoid mater, and pia mater.

    Functions of the meninges

    Cover and protect the CNS

    Protect blood vessels and enclose venous sinuses

    Contain cerebrospinal fluid (CSF)

    Form partitions within the skull

    Meninges


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    Meninges

    Figure 12.24a


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    Leathery, strong meninx composed of – two fibrous connective tissue layers surrounding the brain:

    Periosteal layer – attached to the inner surface of the skull

    Meningeal layer – outer covering of the brain

    Folds inward in several areas to form a fold that attaches the brain to the cranial cavity.

    The two layers separate in certain areas and form dural sinuses

    Dura Mater


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    Three dural septa extend inward and limit excessive movement of the brain

    Falx cerebri – fold that dips into the longitudinal fissure

    Falx cerebelli – runs along the vermis of the cerebellum

    Tentorium cerebelli – horizontal dural fold extends into the transverse fissure

    Dura Mater


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    Dura Mater of the brain

    Figure 12.25


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    The middle meninx, which forms a loose brain covering. of the brain

    It is separated from the dura mater by the subdural space.

    Beneath the arachnoid is a wide subarachnoid space filled with CSF and large blood vessels

    Specialized projections of the Arachnoid membrane, Arachnoid villi protrude through the dura mater and permit CSF to be absorbed into venous blood.

    Arachnoid Mater


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    Arachnoid Mater of the brain

    Figure 12.24a


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    Deep meninx composed of delicate connective tissue that clings tightly to the surface of the brain and spinal cord, following every fold .

    Pia Mater


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    HOMEOSTATIC IMBALANCE clings tightly to the surface of the brain and spinal cord, following every fold .

    • Meningitis, inflammation of the meninges, is a serious threat to the brain because a bacterial or viral meningitis may spread to the CNS. Meningitis is usually diagnosed by obtaining a sample of cerebrospinal fluid via a lumbar tap and examining it for microbes.

    • This condition of brain inflammation is called encephalitis (en′sef-ah-li′tis).


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    Cerebrospinal Fluid clings tightly to the surface of the brain and spinal cord, following every fold .

    • Similar to blood plasma composition.

    • Formed by the choroid plexuses that hang from the roof of each ventricle .These plexuses are clusters of broad, thin-walled capillaries lining the ventricles. These capillaries are fairly permeable, and tissue fluid filters continuously from the bloodstream. However, The choroid plexuses also help cleanse the CSF by removing waste products and unnecessary solutes.

    • In adults, the total CSF volume of about 150 ml (about half a cup) is replaced every 8 hours or so; hence about 500 ml of CSF is formed daily.

    • Forms a watery cushion to protect the brain.

    • Circulated in arachnoid space. Ventricles , and central canal of the spinal cord.


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    Ventricles and Location of the Cerebrospinal Fluid clings tightly to the surface of the brain and spinal cord, following every fold .

    Figure 7.17a


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    HOMEOSTATIC IMBALANCE clings tightly to the surface of the brain and spinal cord, following every fold .

    Ordinarily, CSF is produced and drained at a constant rate. However, if something (such as a tumor) obstructs its circulation or drainage, it accumulates and exerts pressure on the brain. This condition is called hydrocephalus (“water on the brain”). Hydrocephalus in a newborn baby causes its head to enlarge; this is possible because the skull bones have not yet fused. In adults, however, hydrocephalus is likely to result in brain damage because the skull is rigid and hard, and accumulating fluid compresses blood vessels serving the brain and crushes the soft nervous tissue. Hydrocephalus is treated by inserting a shunt into the ventricles to drain the excess fluid into a vein in the neck or into the abdomen.


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    Blood Brain Barrier clings tightly to the surface of the brain and spinal cord, following every fold .

    • Excludes many potentially harmful substances

    • Useless against some substances

      • Fats and fat soluble molecules

      • Respiratory gases

      • Alcohol

      • Nicotine

      • Anesthesia


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    Blood-Brain Barrier clings tightly to the surface of the brain and spinal cord, following every fold .Is a protective mechanism that helps maintain a stable environment for the brain. Includes the least permeable capillaries of the body.

    • It is selective, rather than absolute:

      - Nutrients such as glucose, essential amino acids, and some electrolytes move passively by facilitated diffusion through the endothelial cell membranes.

      - Bloodborne metabolic wastes, proteins, certain toxins, and most drugs are denied entry to brain tissue.


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    - Small nonessential amino acids and potassium ions not only are prevented from entering the brain, but also are actively pumped from the brain across the capillary endothelium.- The barrier is ineffective against fats, fatty acids, oxygen, carbon dioxide, and other fat-soluble molecules that diffuse easily through all plasma membranes. This explains why bloodborne alcohol, nicotine, and anesthetics can affect the brain.


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    Traumatic Brain Injuries only are prevented from entering the brain, but also are actively pumped from the brain across the capillary endothelium.

    • Concussion

      • Slight brain injury,may be dizzy or loose consciousness briefly.

      • No permanent brain damage

    • Contusion

      • Nervous tissue destruction occurs

      • Nervous tissue does not regenerate

    • Cerebral edema

      • Swelling from the inflammatory response

      • May compress vital brain tissue


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    Cerebrovascular Accident (CVA) only are prevented from entering the brain, but also are actively pumped from the brain across the capillary endothelium.

    • Commonly called a stroke

    • The result of blocking of blood vessel supplying a region by a clot or ruptured blood vessel to the brain.

    • Brain tissue supplied with oxygen from that blood source dies

    • Loss of some functions or death may result


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    • Not all strokes are “completed.” Temporary episodes of reversible cerebral ischemia, called transient ischemic attacks (TIAs), are common. TIAs last from 5 to 50 minutes and are characterized by temporary numbness, paralysis, or impaired speech. While these deficits are not permanent, TIAs do constitute “red flags” that warn of impending, more serious CVAs.


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    Spinal Cord reversible cerebral ischemia, called transient ischemic attacks (TIAs), are common. TIAs last from 5 to 50 minutes and are characterized by temporary numbness, paralysis, or impaired speech. While these deficits are not permanent, TIAs do constitute “red flags” that warn of impending, more serious CVAs.

    • Extends from the medulla oblongata to the region of T12

    • Below T12 is the cauda equina (a collection of spinal nerves)

    • Enlargements occur in the cervical and lumbar regions

    Figure 7.18


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    Spinal Cord Anatomy reversible cerebral ischemia, called transient ischemic attacks (TIAs), are common. TIAs last from 5 to 50 minutes and are characterized by temporary numbness, paralysis, or impaired speech. While these deficits are not permanent, TIAs do constitute “red flags” that warn of impending, more serious CVAs.

    • External white mater – conduction tracts

    Figure 7.19


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    Spinal Cord Anatomy reversible cerebral ischemia, called transient ischemic attacks (TIAs), are common. TIAs last from 5 to 50 minutes and are characterized by temporary numbness, paralysis, or impaired speech. While these deficits are not permanent, TIAs do constitute “red flags” that warn of impending, more serious CVAs.

    • Internal gray matter - mostly cell bodies

      • Dorsal (posterior) horns

      • Anterior (ventral) horns

    Figure 7.19


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    Spinal Cord Anatomy reversible cerebral ischemia, called transient ischemic attacks (TIAs), are common. TIAs last from 5 to 50 minutes and are characterized by temporary numbness, paralysis, or impaired speech. While these deficits are not permanent, TIAs do constitute “red flags” that warn of impending, more serious CVAs.

    • Central canal filled with cerebrospinal fluid

    Figure 7.19


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    • Spinal Cord Trauma reversible cerebral ischemia, called transient ischemic attacks (TIAs), are common. TIAs last from 5 to 50 minutes and are characterized by temporary numbness, paralysis, or impaired speech. While these deficits are not permanent, TIAs do constitute “red flags” that warn of impending, more serious CVAs.Any localized damage to the spinal cord or its roots leads to some functional loss, either paralysis (loss of motor function) or sensory loss. Severe damage to ventral root or ventral horn cells results in a flaccid paralysis (flak′sid) of the skeletal muscles served. Nerve impulses do not reach these muscles, which consequently cannot move either voluntarily or involuntarily. Without stimulation, the muscles atrophy. When only the upper motor neurons of the primary motor cortex are damaged, spastic paralysis occurs. In this case, the spinal motor neurons remain intact and the muscles continue to be stimulated irregularly by spinal reflex activity. Thus, the muscles remain healthy longer, but their movements are no longer subject to voluntary control. In many such cases, the muscles become permanently shortened.


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    •  Transection (cross sectioning) of the spinal cord at any level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T1 and L1, both lower limbs are affected, resulting in paraplegia (par″ah-ple′je-ah; para = beside, plegia = a blow). If the injury occurs in the cervical region, all four limbs are affected and the result is quadriplegia. Hemiplegia, paralysis of one side of the body, usually reflects brain injury rather than spinal cord injury.


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    Peripheral Nervous System level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    • Nerve = bundle of

    • neuron fibers outside

    • the central nervous

    • system

    • Neuron fibers are

    • bundled by connective

    • tissue


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    Classification of Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    • Mixed nerves – both sensory and motor fibers

    • Afferent (sensory) nerves – carry impulses toward the CNS

    • Efferent (motor) nerves – carry impulses away from the CNS


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    Cranial Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    • 12 pairs of nerves that mostly serve the head and neck

    • Numbered in order, front to back

    • Most are mixed nerves, but three are sensory only


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    Distribution of Cranial Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    Figure 7.21


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    Cranial Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    • I Olfactory nerve – sensory for smell

    • II Optic nerve – sensory for vision

    • III Oculomotor nerve – motor fibers to eye muscles

    • IV Trochlear – motor fiber to eye muscles


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    Cranial Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    • V Trigeminal nerve – sensory for the face; motor fibers to chewing muscles

    • VI Abducens nerve – motor fibers to eye muscles

    • VII Facial nerve – sensory for taste; motor fibers to the face

    • VIII Vestibulocochlear nerve – sensory for balance and hearing


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    Cranial Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    • IX Glossopharyngeal nerve – sensory for taste; motor fibers to the pharynx

    • X Vagus nerves – sensory and motor fibers for pharynx, larynx, and abdominal viscera

    • XI Accessory nerve – motor fibers to neck and upper back

    • XII Hypoglossal nerve – motor fibers to tongue


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    Spinal Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    • There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs

    • Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord

    • Spinal nerves are named for the region from which they arise


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    Spinal Nerves level results in total motor and sensory loss in body regions inferior to the site of damage. If the transection occurs between T

    Figure 7.22a



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    Autonomic Nervous System limbs

    • The involuntary part of the peripheral nervous system

    • Consists of motor nerves only

    • Divided into two divisions

      • Sympathetic division

      • Parasympathetic division


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    Differences Between Somatic and Autonomic Nervous Systems limbs

    • Nerves

      • Somatic – one motor neuron

      • Autonomic – two, preganglionic and postganglionic nerves

    • Effector organs

      • Somatic – skeletal muscle

      • Autonomic – smooth muscle, cardiac muscle , and glands

    • Nerurotransmitters

      • Somatic – always use acetylcholine

      • Autominic – use acetylcholine, epinephrine, or norepinephrine



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    Anatomy of the Sympathetic Division( limbsthoracolumber)

    Slide 7.70

    • Originates from T1 through L2

    • Ganglia are at the sympathetic trunk (near the spinal cord)

    • Short pre-ganglionic neuron and long postganglionic neuron transmit impulse from CNS to the effector

    • Acetylcholine is the transmitter at the ganglion.

    • Norepinephrine and epinephrine are neurotransmitters to the effector and are classified as adrenergic fibers.


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    Sympathetic Pathways limbs

    Slide 7.71

    Figure 7.26


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    Anatomy of the Parasympathetic Division(craniosacral) limbs

    • Originates from the brain stem and S1 through S4

    • Terminal ganglia are at the effector organs

    • Always uses acetylcholine as a neurotransmitter so calledcholinergic fibers (ko″lin-er′jik) fibers.



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    Autonomic Functioning limbs

    • Sympathetic – “fight-or-flight”

      • Response to unusual stimuli

      • Takes over to increase activities

    • Parasympathetic – housekeeping activities

      • Conserves energy

      • Maintains daily necessary body functions


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    • An easy way to remember the most important roles of the two ANS divisions is to think of:

      - the parasympathetic division as the D division [digestion, defecation, and diuresis (urination)], and

      - the sympathetic division as the E division (exercise, excitement, emergency, embarrassment).

    • Remember, however, that their is a dynamic antagonism exists between the two divisions, and fine adjustments are made continuously by both.


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    Development Aspects of the Nervous System ANS divisions is to think of:

    • The nervous system is formed during the first month of embryonic development.

    • Any maternal infection can have extremely harmful effects as rubella .

    • The hypothalamus is one of the last areas of the brain to develop.

    • No more neurons are formed after birth, but growth and maturation continues for several years.

    • The brain reaches maximum weight in Young adults.


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    • Many elderly people complain fainting episodes due to ANS divisions is to think of:orthostatic hypotension (ortho = straight; stat = standing), a form of low blood pressure that occurs because :

      1-the aging pressure receptors respond less to changes in blood pressure following changes in position.

      2- of slowed responses of sympathetic vasoconstrictor centers.

      These problems can be managed by changing position slowly to gives the sympathetic nervous system time to adjust the blood pressure.