Brain Organization

7/30/2019 Brain Organization

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Nervous

System

CNS PNS ANS

BRAIN

SPINAL

CORD

CRANIAL

NERVES

SPINAL

NERVES

SYMPATHETIC

PARA-

SYMPATHETIC


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Definition:

Unpaired, bilaterally symmetrical structuresextending along the longitudinal axis of the

midsagittal plane of the body.Structures arising directly from the neural tube.

Includes:

Brain

Spinal cord


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Definition:

Made up of transmission pathwayscarrying information between the CNS and

external/internal environments. Afferent (sensory) pathways:

Carry information to the CNS.

Efferent (motor) pathways:Carry information from the CNS.


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Includes:

Cranial nerves (12 pairs).

Spinal nerves (31 pairs).


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May be considered a subdivision of the PNS.

Entirely motor.

Innervates smooth muscle and glands (viscera).


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Sympathetic system (fight or flight):

Also called thoracolumbar.

Parasympathetic system (feed or breed):

Also called craniosacral.


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Cell body:

Trophic unit

Perikaryon

Dendrites:

Receptive unit

Axon:

Conductive unit


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Neuron Anatomy

Slide 7.9bCopyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cell body

Nucleus

Largenucleolus

Figure 7.4a


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Neuron Anatomy

Slide 7.10Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Extensionsoutside the cellbody

Dendritesconductimpulses towardthe cell body

Axons conductimpulses awayfrom the cellbody (only 1!)

Figure 7.4a


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That part of a neuron that encloses the nucleusand other organelles necessary to maintain andrepair the neuron.


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Branches off the cell body that carryinformation to the cell body.

Usually several to many.

Relatively short.

Often branched.

Have receptors for neurotransmitters.

Conduct local potentials.


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Carries information to another neuron ormuscle cell.

Often relatively long.

Single (one per neuron).

Conducts action potential


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Ends in short branched processes calledtelodendria.

May have collateral branches.

Cell membrane (= axolemma). Cytoplasm = (axoplasm).


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Covered by neurolemma:

Made up of Schwann cells.

Often myelinated:

Myelin is formed by Schwann cells.

Note: axon is the only part of a neuron that isever myelinated.


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Nucleus:

Aggregation of dendrites and nerve cellbodies in the CNS.

Ganglion:Aggregation of dendrites and nerve cellbodies in the PNS.


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White matter:

Areas of myelinated axons.

Gray matter:

Areas of unmyelinated axons, cell bodies,and dendrites.


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Definition:

Composite structure that allows two neurons or aneuron and a muscle cell to talk to each other.


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Presynaptic membrane:

With synaptic vesicles filled withneurotransmitters.

Synaptic cleft: Postsynaptic membrane:

With receptors for neurotransmitters.

Monosynaptic pathways.

Polysynaptic pathways.


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Afferent (sensory) pathways:

Somatic.

Visceral (splanchnic).

Efferent (motor) pathways:

Somatic.

Visceral (splanchnic).

Association neurons (interneurons).


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Schwann cells

Astrocytes

Microglial cells

Oligodendrocytes

Ependymal cells


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Derived from neural crest cells.

Myelinate axons in the PNS.


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Derived from embryonic mesenchyme.

May transform into phagocytes within CNS.


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Nerve Fiber Coverings


Schwann cellsproduce myelinsheaths in jelly-rolllike fashion

Nodes of Ranviergaps in myelinsheath along theaxon

Figure 7.5


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Structural Classification of Neurons

SlideCopyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Multipolar neurons many extensionsfrom the cell body

Figure 7.8a


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Bipolar neurons one axon and onedendrite

Figure 7.8b


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Unipolar neurons have a short singleprocess leaving the cell body

Figure 7.8c


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How Neurons Function

(Physiology)


Irritability ability to respond to stimuli

Conductivity ability to transmit an

impulse

The plasma membrane at rest ispolarized

Fewer positive ions are inside the cell thanoutside the cell


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Starting a Nerve Impulse


Depolarization astimulus depolarizes theneurons membrane

A deploarizedmembrane allowssodium (Na+) to flowinside the membrane

The exchange of ionsinitiates an actionpotential in the neuron

Figure 7.9ac


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The Action Potential


If the action potential (nerve impulse)starts, it is propagated over the entireaxon

Potassium ions rush out of the neuronafter sodium ions rush in, whichrepolarizes the membrane

The sodium-potassium pump restoresthe original configuration

This action requires ATP


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Nerve Impulse Propagation


The impulsecontinues to move

toward the cell body

Impulses travelfaster when fibers

have a myelinsheath

Figure 7.9ce


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Continuation of the Nerve Impulsebetween Neurons


Impulses are able to cross the synapseto another nerve

Neurotransmitter is released from a nervesaxon terminal

The dendrite of the next neuron has

receptors that are stimulated by theneurotransmitter

An action potential is started in the dendrite


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How Neurons Communicate atSynapses


Figure 7.10


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Fig. 48.20


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cerebrum corpuscallosum

thalamus

cerebellum

medullaoblongata

hypothalamus

pituitary

pons

spinal cord

Pineal gland


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Involved with higher brain functions. Processes sensory information.

Initiates motor functions.

Integrates information.


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The

cerebrum is

divided intofrontal,

temporal,

occipital,

and parietallobes.


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Frontal lobe. Contains the primary motor cortex.

Parietal lobe. Contains the primary somatosensory cortex.


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Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 48.25


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Integrative Function of the Association Areas.

Much of the cerebrum is given over to

association areas.Areas where sensory information is integrated

and assessed and motor responses areplanned.



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The brain exhibits plasticity of function.

For example, infants with intractable

epilepsy may have an entire cerebralhemisphere removed.

The remaining hemisphere can provide thefunction normally provided by both

hemispheres.



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Generatingwords

Max

Speakingwords

Hearingwords

Seeingwords

Min


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Language and Speech.

Brocas area.

Usually located in the left hemispheres frontal lobe Responsible for speech production.

Wernickes area. Usually located in the right hemispheres temporal lobe

Responsible for the comprehension of speech.

Other speech areas are involvedgenerating verbs to match nouns,grouping together related words, etc.



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Memory and Learning.

Short-term memory stored in the frontal

lobes.

The establishment oflong-term memory

involves the hippocampus.

The transfer of information from short-term tolong-term memory.

Is enhanced by repetition (remember that when you are

preparing for an exam).

Influenced by emotional states mediated by theamygdala.

Influenced by association with previously stored

information.



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Different types of long-term memories arestored in different regions of the brain.

Memorization-type memory can be rapid. Primarily involves changes in the strength of

existing nerve connections.

Learning of skills and procedures isslower.

Appears to involves cellular mechanismssimilar to those involved in brain growth and

development.



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Human Consciousness.

Brain imaging can show neural activity

associated with: Conscious perceptual choice

Unconscious processing

Memory retrieval

Working memory.

Consciousness appears to be a whole-brain phenomenon.



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Relay center for sensory tracts

from the spinal cord to thecerebrum.

Contains centers for sensationof pain, temperature, and touch.

Involved with emotions andalerting or arousal mechanisms.


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The Reticular System, Arousal, and Sleep.

The reticular activating system(RAS)of

the reticular formation. Regulates sleep

and arousal.

Acts as asensory filter.


Fig. 48.21


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Sleep and wakefulness produces patterns

of electrical activity in the brain that can

be recorded as anelectroencephalogram (EEG).

Most dreaming

occurs duringREM (rapid

eye movement)

sleep.


Fig. 48.22b-d


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autonomic control center- blood pressure,

rate and force of heart contraction, centerfor emotional response and behavior

body temperature water balance and thirst sleep/wake cycles

appetite sexual arousal control of endocrine functioning:Acts on the pituitary gland through the

release of neurosecretions.

Regulates:

H th l


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Hypothalamus

Midbrain


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Cerebellar peduncles

Tectum

Superior colliculi Inferior colliculi

Substantia nigra

Red nuclei

Midbrain

thalamus

Red nucleus

Substantia nigra

Posterior

Anterior


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Contains ascending and descendingtracts to the cerebrum andthalamus.

Reflex center for eye muscles. Also involved with processing visual

and auditory information (connects

head movements with visual andauditory stimuli).


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Connects the two

halves of the

cerebellum.

Regulates breathing.


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Composed of nerve tractsto and from the brain

(these tracts cross over

left to right and right to left) May be regarded as an

extension of the spinal

cord Almost all of the cranial

nerves arise from this

region


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Contains control centers formany subconscious

activities

Respiratory rate Heart rate

Arteriole constriction

Swallowing Hiccupping

Coughing

Sneezing


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On OldOlympus Towering Tops A Fat Voracious German Viewed A Hop

1. Olfactory- smell

2. Optic- vision

3. Oculomotor- 4 of the 6 extrinsic eye muscles4. Trochlear- extrinsic eye muscles

5. Trigeminal- sensory fibers to the face and motor fibers to

the chewing muscles

6. Abducens- controls eye muscles that turn the eye laterally7. Facial- facial expression

8. Vestibulocochlear- hearing and balance

9. Glosopharyngeal- tongue and pharynx

10.Vagus- parasympathetic control of heart, lungs &abdominal organs

11.Accessory- accessory part of vagus nerve, neck & throat

muscles

12.Hypoglossal- moves muscles under tongue


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Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

Vestibulocochlear

Glossopharyngeal

Vagus

Accessory Hypoglossal

Facial

P t ti f th C t l N


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Protection of the Central NervousSystem


Scalp and skin

Skull and vertebral column

Meninges

Figure 7.16a

M i


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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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C b i l Fl id


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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

Ventricles and Location of the


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Ventricles and Location of theCerebrospinal Fluid


Figure 7.17a

Ventricles and Location of the


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Ventricles and Location of theCerebrospinal Fluid


Figure 7.17b

Bl d B i B i


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Blood Brain Barrier

Includes the least permeable capillaries

of the body

Excludes many potentially harmfulsubstances

Useless against some substances

Fats and fat soluble molecules

Respiratory gases

Alcohol

Nicotine

Anesthesia

Documents

Brain Organization