Overview of the Nervous System Anatomy

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Overview of the Nervous System

Anatomy

Central Nervous System: Brain and Spinal

Cord.

Peripheral Nervous System: Cranial

Nerves and Spinal Nerves, Ganglia,

Sensory receptors.


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Regions of the Brain

Cerebralhemispheres

Diencephalon

Brain stem(Mid-Brain,Pons andMedulla)

Cerebellum


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Basic Pattern (Histology)

Central cavity surrounded by gray matter core.

External to this is the white matter (myelinatedfiber tracts)

Both cerebral hemispheres and the cerebellumhave an additional outer layer of gray mattercalled the cortex.

At the anterior parts of the brain stem the cortex

disappears but scattered gray matter nuclei areseen in white matter.


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Cerebral Hemispheres (Cerebrum)

Paired (leftand right)

superior partsof the brain

Include more

than half ofthe brainmass


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Cerebral Hemispheres (Cerebrum)

The surface

is made ofridges/elevations (gyri) and

grooves(sulci)


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Layers of the Cerebrum

SlideCopyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Gray matter

Outer layer

Composedmostly of neuron

cell bodies

Figure 7.13a


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Layers of the Cerebrum

White matter

Fiber tracts

inside the graymatter

Example:

corpus callosumconnectshemispheres

Figure 7.13a


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Lobes of the Cerebrum Deeper grooves are called fissures.

Longitudinal fissure separated the two cerebralhemispheres.

Transverse cerebral fissure separates the cerebralhemispheres from the cerebellum.

Central sulcus separates the frontal lobe from theparietal lobe (Pre-central gyrus anteriorly and post-central gyrus posteriorly).

The parieto-occipital sulcus separates the parietallobe from the occipital lobe.

Lateral sulcus separates the temporal lobe from thefrontal and parietal.

The fifth lobe insula lies at the floor of the lateralsulcus.


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Lobes of the Cerebrum


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Cerebral Cortex

Gray matter, hence made up of neuronal cell bodies,dendrites and unmyelinated axons.

Executive suite of the nervous system: enabling us tobe aware of ourselves, our sensations, rememberand understand and to initiate voluntary movements.

K Brodmann (1906) mapped the regions of the cortexaccording to the functions they were involved in,giving rise to an elaborate numbered mosaic of 52cortical areas. These are called the Brodmann areas.

Although specific sensory and motor functions arelocalized, higher mental functions like memory andlanguage have overlapping domains and extend overgreater areas of the cortex.


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Specialized Areas of the Cerebrum

Motor Areas Sensory Areas

Association Areas

Each hemisphere controls the sensory andmotor functions of the other side of the body.

There is specialization (Lateralization) of

function, with some functions localized at onlyone particular hemisphere.


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Sensory and Motor Areas of the

Cerebral Cortex


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Specialized Area of the Cerebrum


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Motor Areas

Primary (somatic) motor cortex.

Pre-motor cortex.

Brocas area. Frontal eye field.


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Sensory Areas

Primary somato-sensory cortex.

Somato-sensory association cortex.

Visual areas: Primary visual cortex and Visual

association area. Auditory areas: Primary auditory cortex and the

auditory association area.

Olfactory (smell) cortex.

Gustatory (taste) cortex.

Vestibular (equilibrium) cortex.


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Association Areas

Generally association areas are connected withprimary somato-sensory cortex or with otherspecial sense areas. Those that are not directlyassociated with sensory cortices are as follows.

Pre-frontal cortex (personality development).

Language areas: Wernicks, Brocas and Lateralpre-frontal cortex.

General common interpretation area. Visceral association area.


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Cerebral White Matter

Myelinated nerve fibers bundled into tracts.

There are three types of tracts.

Commissures: Connect corresponding gray areas ofthe two cerebral hemispheres. Ex. Corpus Callosum.

(Horizontal fibers) Association fibers: Connect different parts of the

same hemisphere (Horizontal fibers)

Projection fibers: Connect the cortex to lower brainand cord centers. (Vertical fibers). These form the

internal capsule between the thalamus and somebasal nuclei and later radiate anteriorly to formcorona radiata


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Basal Nuclei

Caudate nuclei, Putamen and Globus pallidus togetherconstitute the basal nuclei group of each hemisphere.

Putamen and Globus pallidus together constitute thelens shaped, lentiform nucleus flanking the internal

capsule laterally. Caudate nuclei and the lentiform nucleus together

constitute the corpus straitum.

Amygdala lies at the tail of the caudate nucleus,functionally belongs to the limbic system.

Basal nuclei regulate intensity of activities executed bythe cortex (refining movements).


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Diencephalon

Sits on top of the brain stem

Enclosed by the cerebral hemispheres

Made of three paired parts

Thalamus

Hypothalamus

Epithalamus


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Diencephalon


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Thalamus

Surrounds the third ventricle

The relay station for sensory impulses

Transfers impulses to the correct part ofthe cortex for localization and

interpretation


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Hypothalamus

Under the thalamus

Extends from the optic chiasma to the mammillarybodies.

Important autonomic nervous system center.

Center for emotional response Helps regulate body temperature.

Controls water balance and thirst.

Regulates metabolism.

Regulation of food intake.

Regulation of sleep wake cycles.

Control of endocrine functions.


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Hypothalamus

An important part of the limbic system

(emotions)

The pituitary gland is attached to thehypothalamus


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Epithalamus

Forms the roof of the third ventricle

Houses the pineal body (an endocrinegland)

Includes the choroid plexus forms

cerebrospinal fluid


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Brain Stem

Attaches to the spinal cord

Parts of the brain stem

Midbrain

Pons

Medulla oblongata


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Brain Stem


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Midbrain Mostly composed of tracts of nerve fibers.

Reflex centers for vision and hearing

Cerebral aqueduct connects 3rd-4th ventricles

Pair of Cerebral peduncles ventrally. Contain cortico-

spinal motor tracts descending down from the cortex Cerebellar peduncles present dorsally connect the

midbrain to the cerebellum.

Dorsal roof of midbrain is called the tectum

Peri-aqueductal gray matter involved in fearsuppression.

Nuclei scattered in the white matter include, corporaquadrigemina (Superior colliculi and inferior colliculi),the substantia nigra (Parkinsons) and the red nuclei.


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Pons

The bulging center part of the brain stem

Mostly composed of fiber tracts, middle cerebellarpeduncle present ventrally and oriented transversely anddorsally, connecting motor cortex and cerebellum.

Includes nuclei involved in the control of breathing(Pneumotaxic center)


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Medulla Oblongata The lowest part of the brain stem

Merges into the spinal cord

Includes important fiber tracts: Pyramids on the ventralsurface, these are tracts connecting motor cortex tospinal cord after crossing over to the opposite side at thedecussation of the pyramids.

Lateral side are olives: inferior olivary nuclei.

Cranial nerves arise from the groove between thepyramids and the olives

Contains important control centers

Heart rate control

Blood pressure regulation

Breathing

Swallowing


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Cerebellum

Two hemispheres with convoluted surfaces connect medially by thevermis.

Pleat like convolutions or the gyri are called the folia.

Fissures divide each hemisphere into anterior, posterior and theflocculonodular lobes.

The white matter of the cerebellum is called the arbor vitae (tree oflife)

Cerebellar peduncles (CP): Superior CP connects cerebellum tomidbrain, Middle CP connects cerebellum to pons and Inferior CPconnects cerebellum to medulla.

Provides subconscious coordination of body movements. Processesinputs received from the cerebral cortex , the brain stem nuclei andthe sensory receptors. Provides precise patterns of skeletal musclecontraction, for smooth, coordinated movements and agility.


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Cerebellum

Figure 7.15a


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Functional Brain Systems

These are networks of neurons that work

together but span relatively large distances in

the brain. Hence, they cannot be localized to

specific brain regions.

Example: The limbic system and the Reticular

formation.


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Protection of the Central NervousSystem

Scalp and skin

Skull and vertebral column

Meninges

Figure 7.16a


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Protection of the Central NervousSystem

Cerebrospinal fluid

Blood brain barrier

Figure 7.16a


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Meninges

Dura mater

Double-layered external covering

Periosteum attached to surface of theskull

Meningeal layer outer covering of the

brain

Folds inward in several areas


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Meninges

Arachnoid layer

Middle layer

Web-like

Pia mater

Internal layerClings to the surface of the brain


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Cerebrospinal Fluid

Similar to blood plasma composition

Formed by the choroid plexus

Forms a watery cushion to protect thebrain

Circulated in arachnoid space,ventricles, and central canal of thespinal cord


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Ventricles and Location of theCerebrospinal Fluid

Figure 7.17a


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Spinal Cord

Extends from the medullaoblongata to the region of T12at conus medullaris.

Divided into the cervical,thoracic, lumber and sacralregions.

Below T12 is the cauda equina(a collection of spinal nerves)

Filum terminale anchors thespinal cord t the posteriorsurface of the coccyx.

Enlargements occur in thecervical and lumbar regions Figure 7.18


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Posterior median sulcus and Anterior median

fissure divide the spinal cord partly into right

and left halves.


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Spinal Cord Anatomy

Exterior white mater conduction tracts Dorsal root: Afferent fibers from peripheral sensory receptors.

Ventral root: Efferent motor fibers

Roots are short and fuse laterally to form the spinal nerves.

Figure 7.19


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Spinal Cord Anatomy

Internal gray matter - mostly cell bodies

Dorsal (posterior) horns (interneurons)

Ventral (anterior) horns (interneurons and somatic motorneurons). Largest at the cervical and the lumber regions.

Lateral horns (autonomic motor neurons).

Figure 7.19

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Overview of the Nervous System Anatomy