The Central Nervous System Components Brain Spinal Cord 1 - - PowerPoint PPT Presentation

The Central Nervous System

• Brain
• Spinal Cord

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Components

Protection of the Brain

• The brain is protected from injury by

– The skull – enough said! You already know this.

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What else

protects your Brain?

Protection of the Brain – The Meninges

• Cover and protect the CNS
• Enclose and protect the vessels that

supply the CNS

• Contain the cerebrospinal fluid
• Consists of three layers

– Dura Mater – Arachnoid Layer – Pia Mater

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The Meninges

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Protection of the Brain – Cerebrospinal Fluid (CSF)

• Provides a liquid

cushion for the brain and spinal cord

• The brain “floats”

in CSF

• Formed in choroid

plexuses in the brain ventricles

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Protection of the Brain – CSF

• Circulation of CSF

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Protection of the Brain ‐ CSF

• Reabsorption of CSF

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Protection of the Brain – Blood‐Brain Barrier

• Prevents most blood‐borne toxins

from entering the brain

– Impermeable capillaries, surrounded by astrocyte projections creating a double layer, throw in some tight junctions and it works pretty effectively!

• Not an absolute barrier

– Nutrients such as oxygen pass through – Allows alcohol, nicotine, and anesthetics through

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Brain Ventricles

• Ventricles – General Information

– Expansions of the brain’s central cavity – Filled with cerebrospinal fluid – Lined with ependymal cells – Continuous (interconnected) with each

• ther
• Though flow of CSF is unidirectional

– Continuous with the central canal of the spinal cord

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Brain Ventricles

• The brain’s ventricles and associated structures:

– Lateral ventricles – located in cerebral hemispheres

• Horseshoe‐shaped from bending of the cerebral

hemispheres

– Third ventricle – lies in diencephalon

• Connected with lateral ventricles by interventricular foramen

– Cerebral aqueduct – connects 3rd and 4th ventricles – Fourth ventricle – lies in hindbrain

• Connects to the central canal of the spinal cord
• Contains median and lateral aperatures

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Brain Ventricles

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Brain Components & Organization

• Brain is divided into four general regions:

– Cerebral hemispheres – Diencephalon – Brain stem – Cerebellum – All of which contains gray & white matter

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Brain Components & Organization

• Organization of neural matter (gray vs.

white)

– Deeply (internally) located gray matter – Intermediately located white matter – Additional layer of gray matter superficial to white matter

• Due to groups of neurons migrating externally
• Forms the Cortices – outer layers of gray matter

– Formed from neuronal cell bodies – Located in cerebrum and cerebellum (the cerebral cortex & cerebellar cortex respectively)

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The Cerebral Hemispheres

• General Information & Terminology

– Account for 83% of brain mass

• Superficial thin (1‐2 mm) cortex & a deep cortex
• Deep white matter with localized centers of gray matter

(basal ganglia)

– Fissures – deep grooves – separate major regions of the brain, generally have dura mater in the fissure

• Transverse fissure – separates cerebrum and cerebellum
• Longitudinal fissure – separates cerebral hemispheres

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The Cerebral Hemispheres

– Sulci – shallow grooves on the surface of the cerebral hemispheres, does not contain dura mater in the sulci

• Several deep sulci define the lobes (which are named

according to the overlying skeletal structures)

– Central sulcus

» Separates the frontal and parietal lobes

– Parieto‐occipital sulcus

» Separates the occipital from the parietal lobe

– Lateral sulcus

» Separates temporal lobe from parietal and frontal lobes

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The Cerebral Hemispheres

– Gyri – twisted ridges between sulci

• Important gyri
• Prominent gyri and sulci are

similar in all people

– Insula – deep region within the lateral sulcus

• Has it’s own cortex

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The Cerebral Hemispheres

• Frontal section through

forebrain showing organization

• f gray and white matter

– Cerebral cortex – Cerebral white matter – Deep gray matter

• f the cerebrum

(basal nuceli/ ganglia)

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The Cerebral Cortex

• Composed of gray matter

– Neuronal cell bodies, dendrites, and short axons, axon terminals, synapses

• Folds in cortex – triples its size

– Unfolded gives a surface about that of a pillowcase

• Approximately 40% of brain’s mass
• Brodmann areas – 52 structurally distinct

areas

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Functional and Structural Areas of the Cerebral Cortex

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Figure 13.11a

Functional and Structural Areas of the Cerebral Cortex

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Figure 13.11b

The Cerebral Cortex Motor Areas – Primary Motor Cortex

• Controls motor functions
• Located in precentral gyrus (Brodmann area 4)
• Pyramidal cells – large neurons of primary

motor cortex

• Corticospinal tracts descend through

brainstem and spinal cord

– Axons signal motor neurons to control skilled movements – Contralateral – pyramidal axons cross over to

• pposite side of the brain

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The Cerebral Cortex Motor Areas – Primary Motor Cortex

• Motor homunculus –

body map of the motor cortex

– Specific pyramidal cells control specific areas of the body – Face and hand muscles – controlled by many pyramidal cells

• Somatotopy – body is

represented spatially in many parts of the CNS

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The Cerebral Cortex Sensory Areas Primary Somatosensory Cortex

• Located at/on/in the postcentral gyrus

– Corresponds to Brodmann areas 1‐3

• Involved with conscious awareness of general

somatic senses

• Spatial discrimination – precisely locates a

stimulus

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Cerebral Cortex Sensory Areas – Primary Somatosensory Cortex

• Projection is

contralateral

– In that the cerebral hemispheres receive sensory input from the opposite side of the body

• Sensory homunculus

– a body map of the sensory cortex

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Cerebral White Matter

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Figure 13.13a

Deep Gray Matter of the Cerebrum

• Consists of:

– Basal forebrain nuclei (Meynert’s nucleus) – Basal nuclei (ganglia)

• Caudate nucleus
• Lentiform nucleus

– Putamen – Globus pallidus

• Claustrum

– Amygdala

• located in cerebrum

but is considered part of the of the limbic system

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The Diencephalon

• Forms the center core of the

forebrain

• Surrounded by the cerebral

hemispheres

• Composed of three paired

structures:

– Thalamus, hypothalamus, and epithalamus

• Border the third ventricle
• Primarily composed of gray matter

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The Diencephalon

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The Diencephalon – The Thalamus

• Makes up 80% of the diencephalon
• Contains approximately a dozen major nuclei
• Send axons to regions of the cerebral cortex
• Nuclei act as relay stations for incoming sensory

messages

• Afferent impulses converge on the thalamus

– Synapse in at least one of its nuclei

• Is the “gateway” to the cerebral cortex
• Nuclei organize and amplify or tone down signals

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The Thalamus

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The Diencephalon – The Hypothalamus

• Lies between the optic

chiasm and the mammillary bodies

• Pituitary gland projects

inferiorly

• Contains approximately a

dozen nuclei

• Main visceral (autonomic)

control center of the body

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The Diencephalon – The Epithalamus

• Forms part of the “roof” of the third ventricle
• Includes the pineal gland (pineal body)

– Secretes the hormone melatonin – Under influence of the hypothalamus

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Epithalamus highlighted in red

The Brain Stem and Diencephalon

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Figure 13.20a, b

The Brain Stem

• Includes the

– Midbrain – Pons – medulla oblongata

• Several general functions

– Produces automatic behaviors necessary for survival – Passageway for all fiber tracts running between the cerebrum and spinal cord – Heavily involved with the innervation of the face and head

• 10 of the 12 pairs of cranial nerves attach to it

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The Brain Stem – The Midbrain

• Lies between the diencephalon and

the pons

• Central cavity – the cerebral aqueduct

with gray matter surrounding (periaqueductal gray matter)

• Cerebral peduncles located on the

ventral surface of the brain

– Contain pyramidal (corticospinal) tracts

• Superior cerebellar peduncles

– Connect midbrain to the cerebellum

• Corpora quadrigema –large nuclei

– Superior & Inferior colliculi

• visual and auditory reflex centers

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The Brain Stem – The Pons

• Located between the

midbrain and medulla

• blongata
• Contains the nuclei of

cranial nerves V, VI, and VII

• Contains the

pneumotaxic and apneustic centers of respiration

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The Brain Stem – The Medulla Oblongata

• Most caudal level of the brain stem

– Continuous with the spinal cord – Choroid plexus lies in the roof of the fourth ventricle – Pyramids of the medulla – lie on its ventral surface

• Decussation of the pyramids – crossing over of motor

tracts

– Cranial nerves VIII–XII attach to the medulla

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The Brain Stem – The Medulla Oblongata

• The core of the medulla contains:

– Additional nuclei of the reticular formation

• Nuclei influence autonomic functions

– Cardiac center – Vasomotor center – The medullary respiratory center – Centers for hiccupping, sneezing, swallowing, and coughing

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The Cerebellum

• Located dorsal to the pons and

medulla

• Consists of two cerebellar

hemispheres

• Surface folded into ridges called

folia

– Separated by fissures

• Hemispheres each subdivided

into:

– Anterior lobe – Posterior lobe – Flocculonodular lobe

• Functionally

– Smoothes and coordinates body movements – Helps maintain equilibrium & body posture

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The Cerebellum – Cerebellar Peduncles

• Thick tracts connecting the cerebellum to the

brain stem

– Superior cerebellar peduncles – Middle cerebellar peduncles – Inferior cerebellar peduncles

• Fibers to and from the cerebellum are

ipsilateral

– Run to and from the same side of the body

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The Spinal Cord

• Runs through the vertebral canal
• Extends from the foramen magnum

to the level of the vertebra L1 or L2

• Protected by bone, meninges, and

CSF

• Dura mater of the spinal cord
• The spinal dural sheath – only one

layer

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The Spinal Cord

• Conus medullaris – the inferior end
• f the spinal cord
• Filum terminale – long filament of

connective tissue

– Attaches to the coccyx inferiorly

• Cervical and lumbar enlargements

– Where nerves for upper and lower limbs arise

• Cauda equina – collection of nerve

roots

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The Spinal Cord

• Denticulate ligaments – anchor spinal cord to

vertebrae

• Two deep grooves run the length of the cord

– Posterior median sulcus – Anterior median fissure

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Anatomy of the Spinal Cord

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Figure 13.30a

Anatomy of the Spinal Cord

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Figure 13.30b

Gray Matter of the Spinal Cord and Spinal Roots

• Shaped like the letter H, or a butterfly
• Gray commissure

– contains the central canal

• Anterior horns

– contain cell bodies of motor neurons

• Posterior & lateral horns

– consist of interneurons

• Gray matter

– divided according to somatic and visceral regions

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Gray Matter of the Spinal Cord and Spinal Roots

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Figure 13.32

White Matter of the Spinal Cord

• Composed of myelinated and unmyelinated

axons

• Three types of fibers

– Ascending, Descending & Commissural

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Sensory and Motor Pathways

• Most motor pathways:

– Decussate at some point along their course – Consist of a chain of two or three neurons – Exhibit somatotopy

• Tracts arranged according to the body region they

supply

• All pathways are paired

– One of each on each side of the body

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Ascending (Sensory) Pathways

• Conduct general somatic sensory impulses
• Chains of neurons composed of:

– First‐, second‐, and third‐order neurons

• Four main ascending pathways

– Dorsal column pathway – Spinothalamic pathway – Spinocerebellar Pathway

• Composed of anterior & posterior spinocerebellar

pathways

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A s c e n d i n g P a t h w a y s

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Descending (Motor) Pathways

• Deliver motor instructions from the brain to

the spinal cord

• Divided into two groups

– Pyramidal, or corticospinal, tracts – Other motor pathways

• Tectospinal tracts

– responsible for coordinating head and eye movements

• Vestibulospinal tract

– responsible for equilibrium and balance movements

• Rubrospinal tract

– responsible for large movements of the appendages (mostly in other primates – nearly absent in humans)

• Reticulospinal tract

– regulate muscle tone in the anti‐gravity muscles (postural)

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D e s c e n d i n g P a t h w a y s

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Neat Brain Atlas (real!)

• http://www.brainmaps.org

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