The Nervous SystemThe Nervous System

ObjectivesObjectives

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

List the subdivisions of the nervous systemList the subdivisions of the nervous system

Define the terms: grey matter, white matter, nucleus, Define the terms: grey matter, white matter, nucleus, ganglion, tract and nerve.ganglion, tract and nerve.

List the parts of the brain.List the parts of the brain.

Identify the external and internal features of spinal cord.Identify the external and internal features of spinal cord.

Enumerate the cranial nervesEnumerate the cranial nerves

Describe the parts and distribution of the spinal nerve.Describe the parts and distribution of the spinal nerve.

Define the term ‘dermatome’Define the term ‘dermatome’

List the structures protecting the central nervous List the structures protecting the central nervous systemsystem

The nervous system has The nervous system has three functions:three functions: Collection of sensory

input: Identifies changes : Identifies changes occurring inside and occurring inside and outside the body by using outside the body by using sensory receptors. These sensory receptors. These changes are called stimulichanges are called stimuli

IntegrationIntegration: Processes, : Processes, analyses and interprets analyses and interprets these changes and makes these changes and makes decisionsdecisions

It then It then effects a effects a response response by activating by activating muscles or glands muscles or glands (effectors) via motor output(effectors) via motor output

Structural OrganizationStructural Organization

Central Nervous Central Nervous System (CNS): System (CNS): Brain & Spinal Brain & Spinal cordcord

Peripheral Peripheral Nervous System Nervous System (PNS): (PNS): Nerves & Nerves & gangliaganglia

Sensory/Motor divisionSensory/Motor division

Functional OrganizationFunctional OrganizationSomatic/AutonomicSomatic/Autonomic (Visceral)(Visceral) division

Nervous tissue consists of nerve cells (neurons) and Nervous tissue consists of nerve cells (neurons) and supporting (neuroglia) cellssupporting (neuroglia) cells

(Nerve fiber)

A typical multipolar neuron

Nervous tissue is organized as:Nervous tissue is organized as:

Grey matterGrey matter: which contains the cell bodies & the processes of the neurons, the neuroglia and the blood vessels.

White matter:White matter: which contains the processes of the neurons (no cell bodies), the neuroglia and the blood vessels

A group of neurons within the

CNS is called a nucleusnucleus

A group of neurons outside

the CNS is called a

ganglionganglion

Remember…

A group of nerve fibers (axons)

within the CNS is called a tracttract

A group of nerve fibers

(axons) outside the

CNS is called a nerve nerve

Remember…

The BrainThe Brain

Cerebrum Cerebrum (Cerebral

hemispheres)

CerebellumCerebellum

Brainstem: MidbrainPonsMedulla oblongata

Diencephalon: Diencephalon: Thalamus, Hypothalamus, Subthalamus & Epithalamus

The brain is a large mass of nervous tissue located in the cranial cavity. It has four major regions

p

mo

mb

Corpus callosum

Right hemisphere

Left hemisphere

Gyrus

The largest part of the brain, has two The largest part of the brain, has two hemispheres hemispheres

The cerebral hemispheres are The cerebral hemispheres are connected by a thick bundle of nerve connected by a thick bundle of nerve fibers called fibers called corpus callosumcorpus callosum

The surface shows ridges of tissue, The surface shows ridges of tissue, called called gyri, gyri, separated by grooves separated by grooves called called sulcisulci

Sulcus

Divided by deeper Divided by deeper grooves, into grooves, into 4 lobes:4 lobes: Frontal Frontal ParietalParietal TemporalTemporal Occipital Occipital

CEREBRUM CEREBRUM

Gyrus

Gyrus

TISSUE OF THE CEREBRAL HEMISPHERESTISSUE OF THE CEREBRAL HEMISPHERES

The outermost layer is called The outermost layer is called gray mattergray matter or cortex or cortex

Deeper is located the Deeper is located the white matterwhite matter, composed of , composed of fiber fiber tractstracts (bundles of nerve fibers), carrying impulses to and (bundles of nerve fibers), carrying impulses to and from the cortexfrom the cortex

Located deep within the white matter are masses of grey Located deep within the white matter are masses of grey matter called the matter called the basal nucleibasal nuclei . They help the motor . They help the motor cortex in the regulation of voluntary motor activities cortex in the regulation of voluntary motor activities

CEREBELLUMCEREBELLUM

The cerebellum has 2 hemispheres and a convoluted surface. It has an outer cortex made from gray matter and an inner region of white matter. It provides precise coordination for body movements and

helps maintain equilibrium.

The cerebellum has 2 hemispheres and a convoluted surface. It has an outer cortex made from gray matter and an inner region of white matter. It provides precise coordination for body movements and

helps maintain equilibrium.

Spinal CordSpinal CordIt is a two-way conduction pathway It is a two-way conduction pathway to the brain & a major reflex centerto the brain & a major reflex center42-45 cm long, cylindrical in shape, 42-45 cm long, cylindrical in shape, lies within the vertebral canal. lies within the vertebral canal. Extends from Extends from foramen magnum foramen magnum to to L2 vertebraL2 vertebraContinuous above with Continuous above with medulla medulla oblongataoblongataCaudal tapering end is called Caudal tapering end is called conus conus medullarismedullarisHas 2 enlargements: Has 2 enlargements: cervicalcervical and and lumbosacrallumbosacralGives rise to 31 pairs of Gives rise to 31 pairs of spinal spinal nervesnervesGroup of spinal nerves at the end of Group of spinal nerves at the end of the spinal cord is called the spinal cord is called cauda cauda equinaequina

Cross Section of Spinal CordCross Section of Spinal CordThe spinal cord is The spinal cord is incompletely divided incompletely divided into two equal parts, into two equal parts, anteriorlyanteriorly by a short, by a short, shallow shallow median median fissure fissure and and posteriorlyposteriorly by a by a deep narrow deep narrow median septum.median septum.

• It is composed of It is composed of grey matter grey matter in the in the centre surrounded centre surrounded by by white matterwhite matter

• The arrangement of grey matter resembles the The arrangement of grey matter resembles the shape of the letter H, having shape of the letter H, having two two posteriorposterior,, two two anterioranterior and and two two laterallateral horns/columns.horns/columns.

Peripheral NervesPeripheral Nerves

CranialCranial: : • 12 pairs,12 pairs,• attached to brainattached to brain• named & numbered named & numbered

from 1-12 from 1-12

May be May be sensorysensory, , motormotor or or mixedmixed

Two types:Two types:

SpinalSpinal: : 31 pairs31 pairs

attached to spinal cord attached to spinal cord

named and numbered named and numbered according to the region of according to the region of the spinal cordthe spinal cord

CRANIAL NERVESCRANIAL NERVES

• 12 pairs• 4 pairs are mixed

• trigeminal n. (5th)• facial n. (7th)• glossopharyngeal n. (9th)• vagus n. (10th)

• 5 pairs are motor:• occulomotor n. (3rd)• trochlear n. (4th)• abducent n. (6th)• accessory n. (11th)• hypoglossal n. (12th)

• 3 pairs are sensory:• olfactory n. (1st)• optic n. (2nd) • vestibulocochlear n. (8th)

Spinal Nerves and Nerve PlexusesSpinal Nerves and Nerve Plexuses31 pairs31 pairs

Each spinal nerve is Each spinal nerve is attached by attached by two roots: two roots: dorsal (sensory) dorsal (sensory) & & ventral (motor)ventral (motor)

Dorsal root bears a Dorsal root bears a sensory ganglion (DRG)sensory ganglion (DRG)

Each spinal nerve exits Each spinal nerve exits from the intervertebral from the intervertebral foramen and divides into foramen and divides into a a dorsal and ventral dorsal and ventral ramusramus

The rami contain both The rami contain both sensory and motor fiberssensory and motor fibers

DRG

Ventral ramus

Dorsal ramus

The The dorsal ramidorsal rami are are distributed individually, distributed individually, supply the skin and supply the skin and muscles of the backmuscles of the back

the the ventral ramiventral rami form form plexuses (plexuses (except in except in thoracic region where thoracic region where they they formform the the intercostal intercostal nervesnerves), and ), and supplysupply the the anterior part of the bodyanterior part of the body

DermatomesDermatomes

The segment The segment of skin of skin supplied by supplied by one spinal one spinal nerve nerve is called is called a a ‘‘Dermatome’Dermatome’

PROTECTION OF THE CNSPROTECTION OF THE CNS

THE CNS IS PROTECTED BY:THE CNS IS PROTECTED BY:

BonesBones: Skull and the vertebral column: Skull and the vertebral column

MeningesMeninges (membranes): 3 layers (membranes): 3 layers

Cerebrospinal fluidCerebrospinal fluid in the in the subarachnoid spacesubarachnoid space

dura materdura mater (outermost) (outermost)

arachnoid materarachnoid mater (middle) (middle)

pia materpia mater (innermost) (innermost)

CEREBROSPINAL FLUIDCEREBROSPINAL FLUID

CSF is constantly producedproduced by the choroid plexuses inside the ventricles of brain.

CSF is constantly producedproduced by the choroid plexuses inside the ventricles of brain.

Most of the CSF drains from the ventricles into the subarachoid space subarachoid space around the brain and spinal cord. A little amount flows down in the central canal central canal of the spinal cord.

CSF is constantly draineddrained into the dural sinuses dural sinuses through the arachnoid villi.