Organization of Organization of The Nervous The Nervous

SystemSystem

By Prof. Saeed Abuel Makarem& Dr. Sanaa Sharawy

ObjectivesObjectives

At the end of the lecture, the students should be At the end of the lecture, the students should be able to:able to:

• List the parts of the nervous system.• Define the following terms: Grey matter, white matter, nucleus, ganglion, tract,

nerve.• List the parts of the brain.• List the structures protecting the central nervous

system.

How does the nervous system

work ?

The nervous system has three functions:

Collection of sensory input: Identifies changes occurring inside and outside the body by using sensory receptors. These changes are called stimuli.Integration: Processes, analyses and interprets these changes and makes decisions. Motor output: Response by activating muscles or glands (effectors).

CLASSIFICATIOCLASSIFICATIONN

STRUCTURAL• CNS.• PNS. FUNCTIONAL• Sensory division

(Afferent).• Motor division

(Efferent).– Autonomic.– Somatic.

The Nervous The Nervous SystemSystem

• It is the major controlling, regulatory, & communicating system in the body.

• It is the center of all mental activity including thought, learning, behaviour and memory.

• Together with the endocrine system, the nervous system is responsible for regulating and maintaining homeostasis.

Structural Structural OrganizationOrganization

Two subdivisions:Two subdivisions:• Central Nervous System Central Nervous System

(CNS):(CNS): Consists of Consists of Brain & Spinal Brain & Spinal

cordcord Occupies the dorsal body Occupies the dorsal body

cavitycavity Acts as the integrating and Acts as the integrating and

command centers.command centers.

• Peripheral Nervous Peripheral Nervous System (PNS):System (PNS): Consists of part of the Consists of part of the

nervous system outside nervous system outside the CNS: the CNS:

Nerves, ganglia, Nerves, ganglia, receptors. receptors.

Functional Functional OrganizationOrganization

• Two subdivisions:Two subdivisions: Sensory or afferent Sensory or afferent divisiondivision::

Consists of nerve fibers that convey impulses from Consists of nerve fibers that convey impulses from receptors located in various parts of the body, to receptors located in various parts of the body, to the CNS.the CNS.

Motor or efferent Motor or efferent divisiondivision: :

Consists of nerve fibers that convey impulses from Consists of nerve fibers that convey impulses from the CNS to the effector organs, muscles and glands.the CNS to the effector organs, muscles and glands.

• Both sensory and motor subdivisions are Both sensory and motor subdivisions are further divided into:further divided into: SomaticSomatic division: concerned with skin, skeletal division: concerned with skin, skeletal

muscles and joints.muscles and joints. AutonomicAutonomic division: concerned with the visceral division: concerned with the visceral

organs organs

Nervous Tissue

• Nervous system is Nervous system is composed of composed of nervous nervous tissuetissue, which contains , which contains two types of cells:two types of cells: Nerve cells or Nerve cells or

neuronsneurons Supporting cells or Supporting cells or

neuroglia (glia).neuroglia (glia).• Nervous system Nervous system

contains millions of contains millions of neurons that vary in neurons that vary in their shape, size, and their shape, size, and number of processes. number of processes.

The junction site of two neurons is called a ‘synapse

In the synapses the membranes of adjacent cells are in close apposition (contiguity not continuity).

Nervous tissue is organized as:

Grey matterGrey matter:Which contains :1-Cell bodies & 2-Processes of the neurons, 3-Neuroglia and 4-Blood vessels.

White matter:White matter:Which contains :1-Processes of the neurons (no cell bodies) 2-Neuroglia and,3-Blood vessels

Nucleus= Nucleus= A group of neurons

within the CNS

Ganglion= A group of neurons

outside the CNS

Tract Tract ==A

group of

nerve fibers

(axons) within

the CNS

Nerve =Nerve =A group of

nerve fibers (axons)

outside the CNS

Remember…

Prof. Saeed Makarem

It is the basic structural (anatomical) , functional and It is the basic structural (anatomical) , functional and embryological unit of the nervous system.embryological unit of the nervous system.

The human nervous system is estimated to contain about 10The human nervous system is estimated to contain about 101010..

It is formed of cell body and many processes. It is formed of cell body and many processes.

Neurons

What is neurone?

Prof. Saeed Makarem

Most of the Most of the processes of the cell processes of the cell body are short with body are short with variable numbers variable numbers and are receptive in and are receptive in function.function.

They are known as They are known as DendritesDendrites..

Prof. Saeed Makarem

• OneOne of the processes leaving of the processes leaving the cell body is called the the cell body is called the axonaxon which carries which carries information away from information away from the cell the cell body. body.

• Axons are highly variable in Axons are highly variable in length and may divide into length and may divide into several branches or several branches or collateralscollaterals through which through which information can be distributed information can be distributed to a number of different to a number of different destinations.destinations.

• At the end of the axon, At the end of the axon, specializations called specializations called terminal buttonsterminal buttons occur. occur.

• Here information is Here information is transferred to the dendrites of transferred to the dendrites of other neurones. other neurones.

• Neuroglia, or glia cells constitute the other major cellular component of the nervous system.

• It is a specialized connective tissue for the nervous system.• Unlike neurones, neuroglia do not have a direct role in

information processing but they are essential for the normal functioning of nerve cells.

• Neuroglia, or glia cells constitute the other major cellular component of the nervous system.

• It is a specialized connective tissue for the nervous system.• Unlike neurones, neuroglia do not have a direct role in

information processing but they are essential for the normal functioning of nerve cells. Prof. Saeed

Makarem

Neuroglia or glia

Prof. Saeed Makarem

Three main types of neuroglial cell are recognized:1. Oligodendrocytes (oligodendroglia) they form the

myelin sheath that surrounds many neuronal axons, which increase the rate of conduction.

Prof. Saeed Makarem

2- Microglia have a phagocytic role in response to nervous system damage.

Prof. Saeed Makarem

3. Astrocytes are thought to form a selectively permeable barrier between the circulatory system and the neurons of the brain and spinal cord.

• This is known as the 'blood-brain 'blood-brain barrierbarrier'' and has a protective function.

Prof. Saeed Makarem

• Spinal nerves supplying Spinal nerves supplying the upper or lower limbs the upper or lower limbs formform plexuses plexuses e.g. e.g. brachialbrachial or or lumbar lumbar plexusplexus..

• Nerve cell bodies that Nerve cell bodies that are aggregated outside are aggregated outside the CNS are called the CNS are called GANGLIAGANGLIA

Prof. Saeed Makarem

• Neurones that Neurones that detect changes and detect changes and control the activity control the activity of, the viscera are of, the viscera are collectively collectively referred to as the referred to as the autonomic autonomic nervous system. nervous system.

• Its components are Its components are present in both the present in both the central and central and peripheral nervous peripheral nervous systemssystems. .

Autonomic Nervous System

SYMPATHETIC & PARASYMPATHETIC SYMPATHETIC & PARASYMPATHETIC SYSTEMSSYSTEMS

• The autonomic nervous The autonomic nervous system is divided into two system is divided into two anatomically and anatomically and functionally distinct partsfunctionally distinct parts::

• Sympathetic:Sympathetic: Or Or • Thoracolumbar outflowThoracolumbar outflow• ParasympatheticParasympathetic: Or: Or• Craniosacral outflowCraniosacral outflow..• SympatheticSympathetic and and

parasympatheticparasympathetic divisions are divisions are generally have generally have antagonisticantagonistic effects on the structures which effects on the structures which they innervate.they innervate.

• E.g. Sympathetic E.g. Sympathetic increasesincreases the the heat rate, while the heat rate, while the parasympathetic parasympathetic decreasesdecreases the the heart rate. heart rate.

Prof. Saeed Makarem

• The autonomic The autonomic nervous system nervous system innervates:innervates:

• Smooth muscle, Smooth muscle, • Cardiac muscle,Cardiac muscle,• Secretory glands. Secretory glands. • It is an important part It is an important part

of the homeostatic of the homeostatic mechanisms that mechanisms that control the internal control the internal environment of the environment of the body. body.

PARTS OF THE PARTS OF THE BRAINBRAIN

• Cerebral Cerebral hemisphereshemispheres

• DiencephaloDiencephalonn

• CerebellumCerebellum• Brain stemBrain stem

CEREBRAL CEREBRAL HEMISPHERESHEMISPHERES

• The largest part The largest part of the brain.of the brain.

• They have They have elevations, elevations, called called gyri.gyri.

• Gyri are Gyri are separated by separated by depressions depressions called called sulci.sulci.

• Each Each hemisphere is hemisphere is

divided into divided into 66 lobes.lobes.

• Lobes are Lobes are separated by separated by deeper grooves deeper grooves called called fissures fissures or sulci. or sulci.

FRONTAL

PARIETAL

TEMPORAL

OCCIPITAL

TISSUE OF THE CEREBRAL HEMISPHERES

• The outer layer is The outer layer is the the gray mattergray matter or or cortex.cortex.

• Deeper is located Deeper is located the the white matterwhite matter, , composed of composed of bundles of nerve bundles of nerve fibers, carrying fibers, carrying impulses to and impulses to and from the cortex.from the cortex.

• BBasal nucleiasal nuclei are are gray matter and are gray matter and are located deep within located deep within the white matter.the white matter.

• They help the motor They help the motor cortex in regulation cortex in regulation of voluntary motor of voluntary motor activities.activities.

Basal nuclei

DIENCEPHALONDIENCEPHALONThe diencephalon is located between the 2 hemispheres and is linked to them and to the brainstem.

The diencephalon is located between the 2 hemispheres and is linked to them and to the brainstem.

The major structures of the diencephalon are the Thalamus, Hypothalamus and Epithalamus.

The major structures of the diencephalon are the Thalamus, Hypothalamus and Epithalamus.

BRAIN STEMBRAIN STEM

The brainstem has three parts: Midbrain, Pons and Medulla oblongata.

The brainstem has three parts: Midbrain, Pons and Medulla oblongata.

CEREBELLUMCEREBELLUM

Cerebellum has 2 cerebellar hemispheres with convoluted surface. It has an outer cortex of gray matter and an inner region of white matter. It provides precise coordination for body movements and helps maintain equilibrium.

Cerebellum has 2 cerebellar hemispheres with convoluted surface. It has an outer cortex of gray matter and an inner region of white matter. It provides precise coordination for body movements and helps maintain equilibrium.

BRAIN VENTRICLESBRAIN VENTRICLES

• Brain is bathed by the Brain is bathed by the cerebrospinal fluid (CSF)cerebrospinal fluid (CSF)

• Inside the brain, there Inside the brain, there are are ventriclesventricles filled with filled with CSFCSF

• There are 4 ventriclesThere are 4 ventricles 22 lateral ventricles:lateral ventricles:

One in each One in each hemispheres hemispheres

33rdrd ventricle: ventricle:

in the diencephalon in the diencephalon 44thth ventricle: ventricle:

between the Pons, between the Pons, medulla oblongata & medulla oblongata & the cerebellumthe cerebellum

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N.B. CN.B. Cerebral erebral aqueduct: aqueduct: connects connects the 3the 3rdrd to the 4 to the 4thth ventricleventricle

CEREBROSPINAL FLUIDCEREBROSPINAL FLUIDCSF is constantly produced by the choroid plexuses inside each ventricle.

CSF is constantly produced by the choroid plexuses inside each ventricle.

Inside the brain, CSF flows from the lateral ventricles to the 3rd and 4th ventricles

Inside the brain, CSF flows from the lateral ventricles to the 3rd and 4th ventricles

From the 4th ventricle, part of the CSF flows down in the central canal of the spinal cord.

Most of the CSF drains from the 4th ventricle in the subarachnoid space around the brain and returns to the dural sinuses through the arachnoids villi.