Copyright © 2010 Pearson Education, Inc. Functional Brain Systems Networks of neurons that work...

Copyright © 2010 Pearson Education, Inc.

Functional Brain Systems

• Networks of neurons that work together and span wide areas of the brain

• Limbic system

• Reticular formation


Limbic System

• Structures on the medial aspects of cerebral hemispheres and diencephalon

• Includes parts of the diencephalon and some cerebral structures that encircle the brain stem

Copyright © 2010 Pearson Education, Inc. Figure 12.18

Corpus callosumDiencephalic structuresof the limbic system Fiber tracts

connecting limbic system structures

Cerebral struc-tures of the limbic system

Limbic System


Limbic System

• Emotional or affective brain

• Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response

• Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict

• Puts emotional responses to odors

• Example: skunks smell bad


Limbic System: Emotion and Cognition

• The limbic system interacts with the prefrontal lobes, therefore:

• We can react emotionally to things we consciously understand to be happening

• We are consciously aware of emotional richness in our lives

• Hippocampus and amygdala—play a role in memory


Reticular Formation

• Runs through brainstem (medulla, pons, midbrain)

• Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord


Reticular Formation: RAS and Motor Function

• Reticular Activating System (RAS)

• Sends impulses to the cerebral cortex to keep it conscious and alert

• Filters out repetitive and weak stimuli (~99% of all stimuli!)

• Severe injury results in permanent unconsciousness (coma)


Visualimpulses

Reticular formation

Ascending generalsensory tracts(touch, pain, temperature)

Descendingmotor projectionsto spinal cord

Auditoryimpulses

Radiationsto cerebralcortex

Reticular activating system


Consciousness

• Conscious perception of sensation

• Voluntary initiation and control of movement

• Capabilities associated with higher mental processing (memory, logic, judgment, etc.)

• Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired


Consciousness

• Clinically defined on a continuum that grades behavior in response to stimuli

• Alertness

• Drowsiness (lethargy)

• Stupor

• Coma


Protection of the Brain

• Bone (skull)

• Membranes (meninges)

• Watery cushion (cerebrospinal fluid)

• Blood-brain barrier


Meninges

• Cover and protect the CNS

• Protect blood vessels and enclose venous sinuses

• Contain cerebrospinal fluid (CSF)

• Form partitions in the skull


Meninges

• Three layers

• Dura mater

• Arachnoid mater

• Pia mater


Skin of scalpPeriosteum

Falx cerebri(in longitudinalfissure only)

Blood vesselArachnoid villusPia materArachnoid mater

Duramater Meningeal

Periosteal

Bone of skull

Superiorsagittal sinus

Subduralspace

Subarachnoidspace


Dura Mater

• Strongest meninx

• Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses


Dura Mater

• Dural septa limit excessive movement of the brain

• Falx cerebri—in the longitudinal fissure; attached to crista galli

• Falx cerebelli—along the vermis of the cerebellum

• Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure

Copyright © 2010 Pearson Education, Inc. Figure 12.25a

Falx cerebri


Straightsinus

Crista galliof theethmoid bone

Pituitarygland

Falxcerebelli

(a) Dural septa

Tentoriumcerebelli


Arachnoid Mater

• Middle layer with weblike extensions

• Separated from the dura mater by the subdural space

• Subarachnoid space contains CSF and blood vessels

• Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption


Skin of scalpPeriosteum

Falx cerebri(in longitudinalfissure only)

Blood vesselArachnoid villusPia materArachnoid mater

Duramater Meningeal

Periosteal

Bone of skull


Subduralspace

Subarachnoidspace


Pia Mater

• Layer of delicate vascularized connective tissue that clings tightly to the brain


Cerebrospinal Fluid (CSF)

• Composition

• Watery solution

• Less protein and different ion concentrations than plasma

• Constant volume


Cerebrospinal Fluid (CSF)

• Functions

• Gives buoyancy to the CNS organs

• Protects the CNS from blows and other trauma

• Nourishes the brain and carries chemical signals



Arachnoid villus

Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater

Right lateral ventricle(deep to cut)Choroid plexusof fourth ventricle

Central canalof spinal cord

Choroidplexus

Interventricularforamen

Third ventricle

Cerebral aqueductLateral apertureFourth ventricleMedian aperture

(a) CSF circulation

CSF is produced by thechoroid plexus of eachventricle.

1

CSF flows through theventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord.

2

CSF flows through thesubarachnoid space. 3

CSF is absorbed into the dural venoussinuses via the arachnoid villi. 4

1

2

3

4


Choroid Plexuses

• Produce CSF at a constant rate

• Hang from the roof of each ventricle

• Clusters of capillaries enclosed by pia mater and a layer of ependymal cells

• Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes

Copyright © 2010 Pearson Education, Inc. Figure 12.26b

Ependymalcells

Capillary

Connectivetissue ofpia mater

Wastes andunnecessarysolutes absorbed

Sectionof choroidplexus

(b) CSF formation by choroid plexuses

Cavity ofventricle

CSF forms as a filtratecontaining glucose, oxygen, vitamins, and ions(Na+, Cl–, Mg2+, etc.)


Blood-Brain Barrier

• Helps maintain a stable environment for the brain

• Separates neurons from some bloodborne substances


Blood-Brain BarrierSelective barrier

• Allows nutrients to move by facilitated diffusion

• Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics

Formed by

• Continuous endothelium of capillary walls

• Basal lamina

• Feet of astrocytes

Absent in brain areas that “need to know” about blood composition (vomiting center, etc.)


Capillary

Neuron

Astrocyte

Blood brain barrierNotice feet of astrocytes wrapping around capillaries


Traumatic brain injuries

• Concussion—temporary alteration in function

• Contusion—permanent damage

• Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death

• Cerebral edema—swelling of the brain associated with traumatic head injury

• Contrecoup injury (to opposite side)

Copyright © 2010 Pearson Education, Inc. Functional Brain Systems Networks of neurons that work...

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