central nervous system

• Nervous system controls the functions of human body

• Nervous system is composed of nerve cells called neurons

• Each neuron has a body, a long process called axon and dendrites

• Nervous system co-ordinates and correlates sensory stimuli and the efferent impulses so that effector organs work harmoniously.

• What are the effector organs?

• Effector organs are muscles and glands

• Effector is a muscle which contracts in direct response to nerve impulses

• Effector is a gland which secretes in direct response to nerve impulses

• Nervous system has the ability to store sensory information received in past times and can integrate this information with other nervous impulses and channel into common efferent pathways

• Structurally nervous system has two main parts:

• Central nervous system

• Peripheral nervous system

• What are the component parts of PNS

• Central nervous system consists of brain and spinal cord

• Peripheral nervous system consists of cranial nerves, spinal nerves and ganglia.

• Functionally nervous system is also divided into two parts

• Somatic nervous system

• It is that part of nervous system which is concerned with the innervation of voluntary structures of the body

• For example skeletal muscles

• Autonomic nervous system

• It is the part of nervous system concerned with the innervation of involuntary structures of the body

• For example heart, smooth muscle, and glands

• Central nervous system has two main parts: • Brain

• Spinal cord

• The two parts are continuous with each others.

• Brain is placed in skull and spinal cord is present in vertebral column.

• Central nervous system has gray matter and white matter

• Gray matter consists of neurons embedded in neuroglia cells

• White matter consists of nerve fibers embedded in neuroglia cells

• Neuroglia cells are the supporting cells of nervous tissue

• Autonomic nervous system is distributed throughout the central and peripheral nervous systems

• Microscopic picture of cerebral cortex

• Silver stain

• Central nervous system is suspended in fluid called cerebrospinal fluid

• Both brain and spinal cord are surrounded by three meninges

• The meninges of brain and spinal cord are

• dura mater, arachnoid mater, pia mater,

• These meninges of brain and spinal cord are continuous with each other.

• Brain is divided into three main parts

• Forebrain or prosencephalon

• Midbrain or mesencephalon

• Hindbrain or rhombencephalon

• Prosencephalon is further subdivided into – Telencephalon or cerebrum

– Diencephalon (between brain)

• Mesencephalon is not further subdivided• Rhombencephalon is further subdivided into

– Metencephalon. It consists of pons, and cerebellum

– Myelencephalon. It is medulla oblongata

• Cerebrum is the largest part of brain• It consists of two cerebral hemispheres • The cerebral hemispheres are separated by a

deep cleft called longitudinal fissure, into which projects falx cerebri

• The two (right and left) cerebral hemispheres are connected through corpus callosum

• Cerebrum lies in the cranial cavity. From before backward it lies superior to anterior cranial fossa, middle cranial fossa and tentorium cerebelli

• Each cerebral hemisphere contains a cavity called lateral ventricle

• Lateral ventricles communicate with third ventricle through interventricular foramina.

• Diencephalon is the central part of forebrain.

• It is almost completely hidden.

• What are the component parts of diencephalon

• Name the cavity of diencephalon

• It consists of a dorsal thalamus and a ventral hypothalamus

• The cavity of diencephalons is third ventricle

• Thalamus is a large egg-shaped mass of gray matter that lies on either side of the third ventricle.

• The anterior end of thalamus forms the posterior boundary of interventricular foramen

• What is interventricular foramen

• Interventricular foramina are the openings between third ventricle and lateral ventricles

• How many interventricular foramina are in the brain

• two

• Hypothalamus forms the lower part of the lateral wall and floor of third ventricle

• Midbrain or mesencephalon is continuous superiorly to forebrain and inferiorly to hindbrain.

• What is the cavity of midbrain?

• Cerebral aqueduct

• It connects

• Third and fourth ventricles.

• Pons is connected superiorly to midbrain and inferiorly to medulla oblongata.

• It is connected anteriorly to cerebellum

• How. What connects these two?

• Middle cerebellar peduncles

• Medulla oblongata is conical in shape. It is continuous superiorly to pons and inferiorly to spinal cord

• It is connected posteriorly to the two cerebellar hemispheres through inferior cerebellar peduncles.

• Cerebellum is situated posterior to brainstem. It lies within the posterior cranial fossa.

• It consists of two cerebellar hemispheres, connected by a median portion called vermis

• Cerebellum is situated posterior to brainstem.

• Where it lies in the skull

• It lies within the posterior cranial fossa.

• It consists of two cerebellar hemispheres,

• How these are connected with each other

• They are connected by vermis.

• Cerebellum is connected anteriorly to midbrain through superior cerebellar peduncles, to pons through middle cerebellar peduncles, and to medulla through inferior cerebellar peduncles

• What is the stem of the brain?

• Brainstem

• What are the parts of brainstem?

• Brainstem consists of midbrain, pons and medulla oblongata.

• Which part of brain is left after the cerebral and cerebellar hemispheres are removed.

• Brainstem is that part of brain which is left after the cerebral and cerebellar hemispheres are removed.

• Hindbrain consists of pons, medulla oblongata and cerebellum. The cavity of the hindbrain is fourth ventricle. Fourth ventricle is connected superiorly to third ventricle through cerebral aqueduct, and inferiorly it is continuous with central canal of spinal cord.

• Spinal cord lies in vertebral column. It begins at foramen magnum

• Where it terminates

• It terminates inferiorly at the level of the lower border of the first lumbar vertebra.

• It is continuous superiorly with medulla oblongata and tapers off inferiorly into the conus medullaris. Filum terminale descends from the apex of conus medullaris to the back of coccyx.

• What is filum terminale

• It is a prolongation of pia mater

• There are two fusiform enlargements in spinal cord.

• Name these enlargements

• Cervical enlargement. It is in cervical region. Here spinal cord gives origin to brachial plexus.

• Lumbar enlargement. It is in lower thoracic and lumber regions. Here spinal cord gives origin to lumbo-sacral plexus.

• Spinal cord (SC) has segments.

• One spinal nerve is attached to one segment of spinal cord.

• How many segments are there in spinal cord

• How many spinal nerves are attached to SC

• Along the entire length of the spinal cord are attached 31 pairs of spinal nerves.

• Each spinal nerve has two roots.

• Name those roots

• Anterior or motor root

• Posterior or sensory root

• Each root is attached to the spinal cord by a series of rootlets, which extend the whole length of the corresponding segment of the cord.

• Each posterior nerve root has a posterior root ganglion.

• Spinal cord is cylindrical in cross section. It has anterior median fissure on ventral surface and posterior median sulcus on dorsal surface

• In spinal cord gray mater is inside and white mater is outside.

• Gray mater is H-shaped and surrounds central canal.

• White mater surrounds gray mater and is divided into anterior, lateral, and posterior white columns.

• What are the components of Peripheral Nervous System

• Peripheral nervous system consists of

• Cranial nerves and their associated ganglia

• Spinal nerves and their associated ganglia

• Cranial and spinal nerves are grayish-white cords made up of bundles of nerve fibers supported by connective tissue.

• Nerve fibers transmit nerve impulses

• What is nerve impulse

• Nerve impulse is a massage either from central nervous system to the various structures of the body or from these structures to central nervous system

Efferent(Motor) Nerve Fibers

• The fibers carrying impulses from central nervous system to various organs and structures of the body are called efferent fibers. The efferent fibers that pass to the muscles to make them contract are given the name motor nerve fibers.

Afferent(Sensory) Nerve Fibers

• The fibers carrying impulses to central nervous system are afferent fibers. Because these fibers are concerned with conveying information about sensations of touch, pain, temperature, and vibration, they are called sensory fibers.

• In addition to the impulses which they carry, nerve fibers also transmit substances in both directions in the nerve cell process. Thus there is a flow of materials to and from the nerve cells which give rise to these processes.

• Cranial and spinal nerves are grayish-white cords made up of bundles of nerve fibers supported by connective tissue.

• The connective tissue forms three successive coverings.

• Endoneurium. It is a delicate sheath of connective tissue around each nerve fiber.

• Perineurium. It is a sheath of connective tissue around each bundle of nerve fiber.

• Epineurium. It is in a sheath of dense connective tissue around the nerve.

• Nerves are classified into two categories– Cranial nerves – Spinal nerves

• There are 12 pairs of cranial nerves. They are attached to brain. They leave brain and emerge from the skull or cranium through foramina in the skull.

• There are 31pairs of spinal nerves. They are attached to spinal cord. They leave spinal cord and pass through intervertebral foramina in vertebral column.

• Spinal nerves are named according to the regions of vertebral column with which they are associated.

• Name the cranial nerves

• Olfactory nerve or first cranial nerve

• Optic nerve or second cranial nerve

• Occulomotor nerve or third cranial nerve

• Trochlear nerve or fourth cranial nerve

• Trigeminal nerve or fifth cranial nerve (V)

• Abducent nerve or sixth cranial nerve

• Facial nerve or seventh cranial nerve (VII)

• Vestibulocochlear nerve or eighth cranial nerve (VIII)

• Glossopharyngeal nerve or ninth cranial nerve (IX)

• Vagus nerve or tenth cranial nerve (X)

• Accessory nerve or eleventh cranial nerve

• Hypoglossal nerve or twelfth cranial nerve

• Cranial ganglia are found along the course of following cranial nerves – Trigeminal nerve– Facial nerve– Vestibulocochlear nerve– Glossopharyngeal nerve– Vagus nerve

• Cranial ganglia found along the course of Trigeminal nerve, Facial nerve, Vestibulocochlear nerve, Glossopharyngeal nerve, Vagus nerve are called

• Sensory ganglia of these nerves.

• There are 31pairs of spinal nerves.

• 8 cervical nerves

• 12 thoracic nerves

• 5 lumber nerves

• 5 sacral nerves

• 1 coccygeal nerve

• Please note two very important points

• There are 7 cervical vertebrae in vertebral column and there are 8 cervical nerves arising from spinal cord.

• There are 4 coccygeal vertebrae and there is only 1 coccygeal nerve.

• All the spinal nerves emerge caudal to the corresponding vertebrae except cervical nerves.

• The first seven cervical nerves emerge cranial to the corresponding vertebrae while the eighth emerges between the seventh cervical and first thoracic vertebrae.

• Each spinal nerve is attached to spinal cord by two roots. They are

• Anterior or ventral or motor root

• Posterior or dorsal or sensory root

• A typical spinal nerve is formed by the union of anterior and posterior roots attached to the sides of the spinal cord within the vertebral canal.

• Anterior or ventral root consists of bundles of efferent nerve fibers. It is formed by axons of spinal neurons occupying anterior and lateral gray columns. Their cells of origin lie in the anterior gray horn of the spinal cord. In thoracic region lateral horn also share.

• Each root arises as a series of 2-3 regular rows of rootlets attached to anterolateral surface of the spinal cord. These nerves carry motor (efferent) fibers passing on to skeletal muscles.

• Posterior or dorsal root consists of bundles of sensory or afferent nerve fibers. The cell bodies of the nerve fibers in dorsal root are situated in posterior root ganglion. Each of these ganglion cells sends one process into the spinal nerve (peripheral process) and another into the spinal cord through the dorsal root (central process).

• Posterior or dorsal nerve root is also attached to the posterolateral surface of the spinal cord by a series of rootlets.

• The rootlets of adjacent dorsal are often connected by oblique filaments.

• A spinal ganglion is present along the course of each posterior root. They are called posterior root ganglia. They are fusiform structures. These spinal ganglia are also called sensory ganglia of spinal nerves.

• Each ganglion is composed of large groups of sensory neurons. It is oval and reddish, and the size corresponds to that of the root of spinal nerve.

• Immediately lateral to the dorsal root ganglion, the ventral and dorsal roots unite to form a mixed spinal nerve which emerges through the intervertebral foramen.

• Anterior and posterior roots unite to form the trunk of a spinal nerve at the level of their respective intervertebral foramina. The trunk is short. Here the motor and sensory fibers become mixed together, so that a spinal nerve is made up of a mixture of motor and sensory fibers.

• The nerve passes out via intervertebral foramina. After emerging from the intervertebral foramen, each spinal nerve gives of a recumbent meningeal branch and divides into an anterior or ventral ramus and a posterior or dorsal ramus. Each ramus contains both efferent and afferent fibers.

• Posterior or dorsal ramus passes posteriorly around vertebral column into the muscles on the back of vertebral column. Here it divides into lateral and medial branches that supply the muscles, and one of them sends a branch to the overlying skin.

• Name the spinal nerves where the dorsal rami do not divide into lateral and medial branches

• First cervical and coccygeal dorsal rami do not divide into medial and lateral branches.

• In cervical region which branch supply skin

• In cervical dorsal rami medial branches give branches to skin.

• Name the dorsal cervical rami which do not supply skin

• Lower three dorsal cervical rami

• Posterior or dorsal ramus passes posteriorly around vertebral column into the muscles on the back of vertebral column. Here it divides into lateral and medial branches that supply the muscles, and one of them sends a branch to the overlying skin.

• Which branch supply skin in thoracic region

• The medial branches of upper six thoracic dorsal rami supply skin while lateral branches of lower six thoracic dorsal rami supply skin.

• Regarding lumbar dorsal rami

• upper three give of cutaneous nerves through their lateral branches.

• Sacral dorsal rami

• They supply skin through lateral branches.

• Anterior or ventral ramus is larger. It runs laterally and anteriorly to supply the

• muscles and skin over the antero-lateral body wall, and

• all the muscles and skin of the limbs.

• Anterior rami in thoracic region run along the lower border of corresponding ribs.

• They form eleven intercostal nerves and

• one subcostal nerve (twelfth nerve).

• Each of these ventral rami supplies the strip of muscle in which it lies.

• Each intercostal nerve gives off a collateral branch, which follows the inferior border of the same intermuscular space.

• The collateral branch rejoins the main trunk before it is distributed as anterior cutaneous nerve.

• Each intercostal nerve also gives off a lateral cutaneous branch, which accompanies the main trunk for a short distance. Lateral cutaneous branch pierces the intercostal muscles obliquely and divides into anterior and posterior branches. The anterior branch runs forward while posterior branch runs posteriorly. Both supply the overlying skin.

• The cutaneous branches of ventral and dorsal rami supply a strip of skin from anterior median line to posterior median line.

• This strip of skin supplied by a single spinal nerve is called a dermatome.

• It is interesting to note that no area of skin is supplied solely by a single spinal nerve because adjacent dermatomes overlap.

• The total mass of muscle supplied by a single spinal nerve is called a myotome.

• Muscles receive afferent as well as efferent nerve fibers.

• Central Nervous system (CNS) contains two types of cells

1. nerve cells proper called neurons

2. neuroglia cells forming the connective tissue of CNS

• Name the different types of neuroglia cells

• Neuroglia consists of three types of cells

1. Astrocytes

2. Oligodendroglia

3. Microglia

• It is believed that astrocytes play an important part in nerve cell metabolism and transfer of substances from the blood to the nerve cells. Their own biochemistry also alters with that of the nerve cells adjacent to them.

• What is the reason?

• Astrocytes are star-shaped cells with processes radiating from them. They form the surface layer of CNS as well as pervade CNS and ensheathe the capillaries of CNS.

• Astrocytes have numerous processes. At least one of the processes passes to form an end-foot on an adjacent capillary.

• There are two main types of astrocytes

• Name them

• Where they are located

• How will you differentiate them structurally

• Protoplasmic Astrocytes

They are found in grey matter, where nerve cells predominate.

• Fibrillary Astrocytes

They are found in white matter, where bundles of nerve fibers predominate.

• Protoplasmic Astrocytes

Their processes branch and rebranch to form a dense bush.

• Fibrillary Astrocytes

Their processes are long and thin and they branch infrequently.

• Neuroglia cells develop from which germ layer

• Astrocytes from ectoderm

• Oligodendroglia from ectoderm

• Microglia from mesoderm

• What is ependyma?

• It is a single layer ciliated columnar or cuboidal epithelium. It lines the cavities of brain and covers the vascular pia mater that invaginates the ventricles of brain to form the choroid plexuses.

• What are tracts and fasciculi in CNS

• The axons are usually grouped together and form bundles called tracts and fasciculi.

• What are nuclei in brain?

• The cell bodies and dendrites are grouped to form clusters called nuclei.