Organization Organization of Theof The

Nervous Nervous SystemSystem

DR. SANAA ALSHAARAWY &PROF. SAEED ABUEL MAKAREM

ObjectivesObjectivesAt the end of the lecture, the students At the end of the lecture, the students

should be able to:should be able to:• List the parts of the nervous system.• List the function of the nervous system.• Describe the Structural & Functional

Organizations. • Define the terms: Nervous tissue, 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 or outside the body by using sensory receptors. These changes are called stimuli.Integration: Processes, analyzes , and interprets these changes and makes decisions. Motor output, or response by activating muscles or glands (effectors).

CLASSIFICATIOCLASSIFICATIONN

I- Anatomical or Structural classification:

1- Central NS• 2- Peripheral NS II- Physiological or

Functional classification:• 1-Sensory division

(Afferent)• 2-Motor division

(Efferent)– Autonomic– Somatic

Structural Structural OrganizationOrganization

Two subdivisions:Two subdivisions:• Central Nervous System (CNS)Central Nervous System (CNS)

Consists of Consists of Brain & Spinal Brain & Spinal cordcord

Occupies the Occupies the dorsal body dorsal body cavitycavity

Acts as the integrating and Acts as the integrating and command centers.command centers.

• Peripheral Nervous System Peripheral Nervous System (PNS)(PNS) Consists of Consists of nerves, ganglia, nerves, ganglia,

receptors.receptors. It is the It is the part of the nervous part of the nervous

system system outside the CNS.outside the CNS.

Functional Functional OrganizationOrganization

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

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

Motor or efferent Motor or efferent divisiondivision: :

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

• Both Both sensorysensory and and motormotor subdivisions are subdivisions are further divided into:further divided into: SomaticSomatic division: concerned with division: concerned with skinskin, , skeletal skeletal

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

organs. organs.

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,• Behavior and • Memory.• Together with the

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

Nervous Tissue

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

1- Nerve cells or 1- Nerve cells or neuronsneurons

2- Supporting cells or 2- Supporting cells or neuroglia (glia).neuroglia (glia).

• Nervous system Nervous system contains millions of contains millions of neuronsneurons that vary in 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 or relay”.In the synapses the membranes of adjacent cells are in close apposition (contiguity=contact, not continuity).

Prof. Saeed Makarem

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

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

Neurons

What is neurone?

Nucleus= Nucleus= A group

of neurons

within the CNS

Ganglion= 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…

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 2- Neuroglia and3- Blood vesselsNO cell bodies in the white matter.

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

• It is a specialized connective tissue supporting framework 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 the neurons, they act as supporting and nutrition for neurons.

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

• It is a specialized connective tissue supporting framework 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 the neurons, they act as supporting and nutrition for neurons.

Neuroglia or glia or glial cells

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

They They are known as are known as DendritesDendrites. .

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

• AxonsAxons are highly variable in are highly variable in length and may length and may divide into 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 At the end of the axon, of the axon, specializations called specializations called terminal buttonsterminal buttons occur.occur.

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

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

Peripheral NS

• NeuronesNeurones that that detect changes and detect changes and control the control the activity of the activity of the viscera viscera are 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 present in both both the the centralcentral and and peripheral peripheral nervous systemsnervous systems. .

Autonomic Nervous System

SYMPATHETIC & PARASYMPATHETIC SYMPATHETIC & PARASYMPATHETIC SYSTEMSSYSTEMS

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

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

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

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

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

• Smooth muscles, Smooth muscles, • Cardiac muscle,Cardiac muscle,• Secretory Secretory

glands. glands. • It is an important It is an important

part of part of the the homeostatic homeostatic mechanisms mechanisms that that control the control the internal internal environment of environment of the body the body with the with the endocrine endocrine system.system.

PARTS OF THE PARTS OF THE BRAINBRAIN

• The brain The brain composed of composed of 4 parts:4 parts:

• Cerebral Cerebral hemisphereshemispheres

• DiencephaloDiencephalonn

• CerebellumCerebellum• Brain stemBrain stem

CEREBRAL CEREBRAL HEMISPHERESHEMISPHERES

• The largest The largest part of the part of the brain.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 intodivided into 4 4 lobes lobes named named according to according to the bone above. the bone above.

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

FRONTAL

PARIETAL

TEMPORAL

OCCIPITAL

TISSUE OF THE CEREBRAL HEMISPHERES

• The outer layer The outer layer is is the the gray mattergray matter or or cortexcortex

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

• Basal nuclei Basal nuclei are are gray matter gray matter that that are located deep are located deep withinwithin the the white white mattermatter

• They help the They help the motor cortex in motor cortex in regulation of regulation of

voluntary voluntary motor motor activitiesactivities..

Basal nuclei

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

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

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

The major structures of the diencephalon are the Thalamus, Hypothalamus, Subthalamus 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.

It is connected to theIt is connected to the cerebellum cerebellum with with 3 paired 3 paired peduncles peduncles Superior, middle and inferiorSuperior, middle and inferior

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.

MENINGESMENINGES• There areThere are three three

connective tissue connective tissue membranes membranes invest invest the the brain brain and the and the spinal cord.spinal cord.

• These are from These are from outward to inward outward to inward are:are:

• 1- 1- Dura mater.Dura mater.• 2- 2- Arachnoid Arachnoid

matermater..• 3- 3- Pia mater.Pia mater.

BRAIN VENTRICLESBRAIN VENTRICLES

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

• Inside the brain, there Inside the brain, there are are 4 4 ventriclesventricles filled filled with CSF.with CSF.

• The 4 ventricles are:The 4 ventricles are: 22 lateral ventricles:lateral ventricles:

One in each One in each hemispheres. hemispheres.

33rdrd ventricle: ventricle:

in the in the Diencephalon. Diencephalon.

44thth ventricle: ventricle:

between Pons, between Pons, Medulla oblongata & Medulla oblongata & Cerebellum.Cerebellum.

N.B. Cerebral N.B. Cerebral aqueduct: aqueduct: connects connects the 3the 3rdrd to the 4 to the 4thth ventricle.ventricle.

CEREBROSPINAL FLUID

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

CSF is constantly produced by the choroid plexuses inside the 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 to distribute in the subarachnoid space around the brain and returns to the dural venous sinuses through the arachnoids villi.

•Arachnoid villi are small protrusions of the arachnoid.•Villi absorb cerebrospinal fluid and return it finally to the dural venous circulation.

GOOD LUCK

•Which one of the following is related to the tract?•Neurons outside the CNS.•Neurons inside the CNS.•Nerve fibers within the CNS.•Nerve fibers outside the CNS. •Which structure is concerning with formation of CSF ? •The arachnoid villi.•The choroid plexus. •The subdural space.•The dural venous sinus. •The peripheral nervous system involves :•The spinal ganglia.•The spinal cord.•The brain.•The tracts.•The lateral ventricle lies in :•The cerebrum.•The diencephalon.•The midbrain.•The cerebellum.

Examine Yourself