Download CNS: Brain C

Functional Brain Systems
• Networks of neurons that work together and
span wide areas of the brain
• Limbic system
• Reticular formation
Copyright © 2010 Pearson Education, Inc.
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.
Limbic System
Diencephalic structures
of the limbic system
Corpus callosum
Fiber tracts
connecting limbic
system structures
Cerebral structures of the
limbic system
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Reticular Formation
• Runs through brainstem (medulla, pons,
midbrain)
• Has far-flung axonal connections with
hypothalamus, thalamus, cerebral cortex,
cerebellum, and spinal cord
Copyright © 2010 Pearson Education, Inc.
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)
Copyright © 2010 Pearson Education, Inc.
Reticular activating system
Radiations
to cerebral
cortex
Visual
impulses
Auditory
impulses
Reticular formation
Ascending general
sensory tracts
(touch, pain, temperature)
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Consciousness
• Clinically defined on a continuum that grades
behavior in response to stimuli
• Alertness
• Drowsiness (lethargy)
• Stupor
• Coma
Copyright © 2010 Pearson Education, Inc.
Protection of the Brain
• Bone (skull)
• Membranes (meninges)
• Watery cushion (cerebrospinal fluid)
• Blood-brain barrier
Copyright © 2010 Pearson Education, Inc.
Meninges
• Cover and protect the CNS
• Protect blood vessels and enclose venous
sinuses
• Contain cerebrospinal fluid (CSF)
• Form partitions in the skull
Copyright © 2010 Pearson Education, Inc.
Meninges
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater
Copyright © 2010 Pearson Education, Inc.
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
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.
Superior
sagittal sinus
Straight
sinus
Crista galli
of the
ethmoid
bone
Pituitary
gland
Falx cerebri
Tentorium
cerebelli
Falx
cerebelli
(a) Dural septa
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Cerebrospinal Fluid (CSF)
• Composition
• Watery solution
• Less protein and different ion concentrations
than plasma
• Constant volume
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Cavity of
ventricle
Figure 12.26b
Blood-Brain Barrier
• Helps maintain a stable environment for the
brain
• Separates neurons from some bloodborne
substances
Copyright © 2010 Pearson Education, Inc.
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.)
Copyright © 2010 Pearson Education, Inc.
Blood brain barrier
Notice feet of astrocytes wrapping around capillaries
Capillary
Neuron
Astrocyte
Copyright © 2010 Pearson Education, Inc.
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)
Copyright © 2010 Pearson Education, Inc.