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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