Transcript CNS: Brain C

Functional Brain Systems
• Networks of neurons that work together and
span wide areas of the brain
• Limbic system
• Reticular formation
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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
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Limbic System
Diencephalic structures
of the limbic system
Corpus callosum
Fiber tracts
connecting limbic
system structures
Cerebral structures of the
limbic system
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Figure 12.18
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
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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
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Reticular Formation
• Runs through brainstem (medulla, pons,
midbrain)
• Has far-flung axonal connections with
hypothalamus, thalamus, cerebral cortex,
cerebellum, and spinal cord
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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)
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Reticular activating system
Radiations
to cerebral
cortex
Visual
impulses
Auditory
impulses
Reticular formation
Ascending general
sensory tracts
(touch, pain, temperature)
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Descending
motor projections
to spinal cord
Figure 12.19
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
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Consciousness
• Clinically defined on a continuum that grades
behavior in response to stimuli
• Alertness
• Drowsiness (lethargy)
• Stupor
• Coma
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Protection of the Brain
• Bone (skull)
• Membranes (meninges)
• Watery cushion (cerebrospinal fluid)
• Blood-brain barrier
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Meninges
• Cover and protect the CNS
• Protect blood vessels and enclose venous
sinuses
• Contain cerebrospinal fluid (CSF)
• Form partitions in the skull
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Meninges
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater
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Superior
sagittal sinus
Subdural
space
Subarachnoid
space
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Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
Dura Mater
• Strongest meninx
• Two layers of fibrous connective tissue
(around the brain) separate to form dural
sinuses
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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
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Superior
sagittal sinus
Straight
sinus
Crista galli
of the
ethmoid
bone
Pituitary
gland
Falx cerebri
Tentorium
cerebelli
Falx
cerebelli
(a) Dural septa
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Figure 12.25a
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
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Superior
sagittal sinus
Subdural
space
Subarachnoid
space
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Skin of scalp
Periosteum
Bone of skull
Periosteal Dura
Meningeal mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Figure 12.24
Pia Mater
• Layer of delicate vascularized connective
tissue that clings tightly to the brain
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Cerebrospinal Fluid (CSF)
• Composition
• Watery solution
• Less protein and different ion concentrations
than plasma
• Constant volume
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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
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Superior
sagittal sinus
4
Choroid
plexus
Arachnoid villus
Interventricular
foramen
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
1
Right lateral ventricle
(deep to cut)
Choroid plexus
of fourth ventricle
3
Third ventricle
1 CSF is produced by the
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
(a) CSF circulation
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2
choroid plexus of each
ventricle.
2 CSF flows through the
ventricles and into the
subarachnoid space via the
median and lateral apertures.
Some CSF flows through the
central canal of the spinal cord.
3 CSF flows through the
subarachnoid space.
4 CSF is absorbed into the dural venous
sinuses via the arachnoid villi.
Figure 12.26a
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
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Ependymal
cells
Capillary
Section
of choroid
plexus
Connective
tissue of
pia mater
Wastes and
unnecessary
solutes absorbed
CSF forms as a filtrate
containing glucose, oxygen,
vitamins, and ions
(Na+, Cl–, Mg2+, etc.)
(b) CSF formation by choroid plexuses
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Cavity of
ventricle
Figure 12.26b
Blood-Brain Barrier
• Helps maintain a stable environment for the
brain
• Separates neurons from some bloodborne
substances
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Blood-Brain Barrier
Selective 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.)
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Blood brain barrier
Notice feet of astrocytes wrapping around capillaries
Capillary
Neuron
Astrocyte
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Figure 11.3a
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)
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