THE NERVOUS THE NERVOUS SYSTEM SYSTEM

FUNCTIONSFUNCTIONS• collection of collection of

sensory inputsensory input• integrationintegration• motor outputmotor output

The function of the nervous system is to detect changes in the: External or Internal External or Internal environmentsenvironmentsSo, it bring about So, it bring about appropriate responses appropriate responses in in Muscles,Muscles,Organs and Organs and Glands. Glands.

ORGANIZATIONORGANIZATION

STRUCTURAL• CNS• PNS FUNCTIONAL• Sensory division

(Afferent)• Motor division

(Efferent)– autonomic– somatic

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 The human nervous system is estimated to contain about 10101010. .

Neurons

What is neurone?

Prof. Saeed Makarem

• The functions of the neuron is The functions of the neuron is to receive and integrate to receive and integrate incoming informationincoming information from sensory receptors or from other from sensory receptors or from other neurons and to transmit information to other neurons or neurons and to transmit information to other neurons or effector organs. effector organs.

Prof. Saeed Makarem

Information is passed Information is passed between neurons at between neurons at specialized regions specialized regions called called synapsessynapses

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

Prof. Saeed Makarem

• There is wide diversity in There is wide diversity in the shape and size of the shape and size of neurons in different parts neurons in different parts of the nervous system.of the nervous system.

• But all share certain But all share certain common characteristics. common characteristics.

• There is a single There is a single cell cell bodybody from which a from which a variable number of variable number of branching processes branching processes emerge. emerge.

Prof. Saeed Makarem

Most of these Most of these processes are processes are receptive in function.receptive in function.

They are known as They are known as DendritesDendrites..

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The dendrites possess: The dendrites possess: A variable number of A variable number of shot processes.shot processes.They form the receptive They form the receptive element of the neurone.element of the neurone.

Prof. Saeed Makarem

• One of the processes leaving One 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 information can be distributed to a number of distributed to a number of different destinations different destinations simultaneously. simultaneously.

• 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 transferred to the dendrites of other neurones. of other neurones.

Prof. Saeed Makarem

• Transmission of information Transmission of information between neurons almost between neurons almost always occurs byalways occurs by chemicalchemical rather than electrical means. rather than electrical means.

• Action potential causes Action potential causes release of specific chemical release of specific chemical that are stored in that are stored in synaptic synaptic vesiclesvesicles in the presynaptic in the presynaptic ending. ending.

• These chemicals are known These chemicals are known as as neurotransmittersneurotransmitters and and diffuse across the narrow diffuse across the narrow gap between pre- and gap between pre- and postsynaptic membranes to postsynaptic membranes to bind to bind to receptorsreceptors on the on the postsynaptic cell.postsynaptic cell.

• 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

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.

Central & Central & peripheral peripheral

nervous systems nervous systems

Prof. Saeed Makarem

The nervous system is The nervous system is divided into: divided into:

• 1- Central nervous 1- Central nervous system (CNS).system (CNS).

• 2- Peripheral nervous 2- Peripheral nervous system (PNS). system (PNS).

Prof. Saeed Makarem

• The The central nervous central nervous systemsystem consists of consists of the the brain and the spinal brain and the spinal cord,cord, lying within the lying within the protection of the cranium protection of the cranium and vertebral column, and vertebral column, respectively. respectively.

• This is the most complex This is the most complex part of the nervous system. part of the nervous system.

• It contains the majority of It contains the majority of nerve cell bodies and nerve cell bodies and synaptic connections. synaptic connections.

Prof. Saeed Makarem

• The The peripheral nervous peripheral nervous systemsystem constitutes the constitutes the link between the CNS & link between the CNS & structures in the periphery structures in the periphery of the body. of the body.

• It receives sensory It receives sensory information from the body.information from the body.

• It sends controlling It sends controlling impulses in response to impulses in response to these information. these information.

• The peripheral nervous The peripheral nervous system consists:system consists:

• 1- Cranial nerves1- Cranial nerves• 2- Spinal nerves.2- Spinal nerves.

Prof. Saeed Makarem

• Spinal nerves Spinal nerves supplying the upper or supplying the upper or lower limbs form the lower limbs form the brachialbrachial or or lumbar lumbar plexusplexus..

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

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• 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 referred collectively referred to as the 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 system is divided into two anatomically and two anatomically and functionally distinct functionally distinct partsparts::

• Sympathetic: Or Sympathetic: Or • Thoracolumbar outflowThoracolumbar outflow• Parasympathetic: OrParasympathetic: Or• Craniosacral outflow.Craniosacral outflow.

Prof. Saeed Makarem

• SympatheticSympathetic and and parasympatheticparasympathetic divisions are divisions are generally have generally have antagonistic effects antagonistic effects on the structures that on the structures that they innervate. they innervate.

Prof. Saeed Makarem

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

Afferent, Efferent & Afferent, Efferent &

InterneuronInterneuron • Nerve cells that carry Nerve cells that carry

information from information from peripheral receptors to peripheral receptors to the the CNSCNS are referred to are referred to as as afferentafferent neurones neurones

• Efferent neuronesneurones carry impulses away carry impulses away from the from the CNSCNS

• If they innervate If they innervate skeletal muscle to skeletal muscle to cause movement they cause movement they are also referred to as are also referred to as motormotor neurons neurons..

• The vast majority of The vast majority of neurones, however, lies neurones, however, lies entirely within the CNS entirely within the CNS and are usually called and are usually called interneuroninterneuron

PARTS OF THE PARTS OF THE BRAINBRAIN

• Cerebral Cerebral hemisphereshemispheres

• DiencephaloDiencephalonn

• CerebellumCerebellum• Brain stemBrain stem

CEREBRAL CEREBRAL HEMISPHERESHEMISPHERES • The largest The largest

part of the part of the brainbrain

• They have They have elevations, elevations, called called gyrigyri

• Gyri are Gyri are separated by separated by depressions depressions called called sulcisulci

• Each Each hemisphere is hemisphere is

divided into divided into 44 lobeslobes

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

• 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 cortexfrom the cortex

• BBasal nucleiasal nuclei are are made from gray made from gray matter and are matter and are located deep within located deep within the white matterthe white matter

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

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 and a 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 and a 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 cerebrospinal fluid (CSF)(CSF)

• Inside the brain, there Inside the brain, there are spaces are spaces (ventricles)(ventricles) filled with CSFfilled with CSF

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

are in the are in the hemispheres hemispheres

33rdrd ventricle: ventricle:

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

between the Pons & between the Pons & the cerebellumthe cerebellum

CCerebral aqueduct: erebral aqueduct: connects the 3connects the 3rdrd to to the 4the 4thth ventricle ventricle

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.