The Brain (& CNS)
Lecture 12a
BIOL241
Final Exam (Exam 4)
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Chapters 11 – 15*
100 points
Multiple choice, T/F, matching, fill in
Short answer, essays (2)*
Labeling (brain [including functions],
cranial nerves, spinal cord)
Outline
• Overview of the human brain
• Tour through the brain – structures and
functions
• Cerebral hemispheres and higher mental
functions
• Meninges
• Ventricles and CSF
• Brain disorders
The Human Brain
• Composed of wrinkled, pinkish gray tissue
• Surface anatomy includes cerebral
hemispheres, cerebellum, and brain stem
• Ranges from 750 cc to 2100 cc
• Contains almost 98% of the body’s neural
tissue
• Average weight, adult: 1300 – 1400 gm (~3 lb)
• 1010 to 1011 neurons
• Trillions of connections
• men = larger
• Women = better connected
Major Regions and Landmarks
Figure 14–1
Embryology of the Brain
Table 14-1
Regions of the Adult Brain
• Telencephalon (cerebrum) – cortex, white
matter, and basal nuclei
• Diencephalon – thalamus, hypothalamus,
and epithalamus
• Mesencephalon –midbrain (brain stem)
• Metencephalon – pons (brain stem),
cerebellum
• Myelencephalon – medulla oblongata
(brain stem)
Basic Pattern of the Central Nervous System
• Spinal Cord
– Central cavity surrounded
by a gray matter core
– External to which is white
matter composed of
myelinated fiber tracts
• Brain
– Similar to spinal cord but
with additional areas of
gray matter
– Cerebellum has gray matter
in nuclei
– Cerebrum has nuclei and
additional gray matter in the
cortex
Figure 12.4
Some terms
• nucleus: collection of neuron cell
bodies in the CNS
• tract: collection of axons in the CNS
• ganglia: collection of neuron cell
bodies in the PNS
• nerve: collection of axons in the PNS
– Cranial nerves
– Spinal nerves
Tour of the brain
• From caudal/inferior to rostral/superior
The Brain Stem
• Processes information between spinal cord and
cerebrum or cerebellum
• Controls automatic behaviors necessary for
survival
• Associated with 10 of the 12 pairs of cranial
nerves (covered later)
• Includes:
–
–
–
–
mesencephalon (midbrain)
pons
medulla oblongata
Note: some consider the diencephalon part of the
brain stem as well
Brain Stem
Figure 12.15a
Anatomy:
Brain stem
Most cranial
nerves are
located in the
brain stem
Brain Stem
Figure 12.15b
Posterior view
Medulla Oblongata
• Most inferior part of brain, connects brain to
spinal cord
• Relays information
• Pyramids – two longitudinal ridges formed by
corticospinal tracts
• Regulates autonomic functions:
– regulates arousal, heart rate, blood pressure, pace
for respiration and digestion
• Cranial nerves IX, X, XI, XII come off or enter
Medulla Oblongata
Figure 12.16c
Medulla Oblongata
Medulla Nuclei
• Cardiovascular control center – adjusts
force and rate of heart contraction
• Respiratory centers – control rate and
depth of breathing
• Additional centers – regulate vomiting,
hiccupping, swallowing, coughing, and
sneezing
Pons
Pons
• Involved in somatic and visceral motor control
• Contain the nuclei for cranial nerves V, VI, VII,
VIII
• Contains nuclei of the reticular formation
• Control of respiration that modifies the info from
the medulla
• Nuclei and tracts passing through to the
cerebellum (motor and somatosensory info)
• Nuclei and tracts to other portions of the CNS
(just passing through)
Cerebellum
Cerebellum
• “little brain”
• Second largest part of brain (~10% mass)
• Provides precise timing and appropriate patterns of
skeletal muscle contraction to coordinate repetitive
body movements and help learning complex motor
behaviors
• Adjusts the postural muscles of the body, controls
balance and equilibrium
• Has 2 hemispheres, covered with cerebellar cortex
• Recognizes and predicts sequences of events
• Cerebellar activity occurs subconsciously (as does
all processing that occurs outside the cerebral
cortex)
Cerebellum – side view
Cerebellum
• Cerebellum receives impulses of the intent to
initiate voluntary muscle contraction
• Monitors all proprioceptive info and visual info
about body position
• Cerebellar cortex calculates the best way to
perform a movement
• Programs and fine tunes movements by
detecting mismatches in intended and actual
movements
-- when learning to ride a bike, throw a curve ball
or tie your shoe, cerebellum activity is high.
When they become automatic, cerebellum is no
longer involved
Mesencephalon
Mesencephalon
• Also called midbrain
• Processes sight, sound, and associated
reflexes
• Maintains consciousness
• Cranial nerve nuclei III and IV
• 2 basic divisions
– tectum (roof)
– tegmentum
Mesencephalon
• Process of visual and auditory sensations
– corpora quadrigemina (in tectum) = superior colliculi (visual
reflex) and inferior colliculi (auditory reflex)
• Substantia nigra (in tegmentum)
– Neurons inhibit activity of cerebral nuclei by releasing
dopamine
– If damaged, results in less dopamine released and muscle
tone increases: muscle rigidity, difficulty initiating movement
= Parkinson’s Disease
• Reticular formation: maintain consciousness
Midbrain Nuclei
Figure 12.16a
Mesencephalon
Diencephalon
Figure 12.12
Diencephalon
• Located under
cerebrum and
cerebellum
• Links cerebrum
with brain stem
• Integrates sensory
information and
motor commands
• Cranial nerve II
Diencephalon
• Pineal Gland
– Secretes hormone melatonin
• Thalamus:
– relays and processes sensory information
• Hypothalamus:
– hormone production
– emotion
– autonomic function
Diencephalon: Thalamus
• Paired, egg-shaped
masses connected
at the midline by the
intermediate mass
• Nuclei project to
and receive fibers
from the cerebral
cortex
Figure 14–9
Thalamus
• Sensory Relay station
• All sensory that is projected to the cerebral
cortex stops here first except smell
• Filters ascending sensory information for
primary sensory cortex
• Relays information between basal nuclei
and cerebral cortex
• Mediates sensation, some motor activities,
cortical arousal (thus learning, and
memory)
Diencephalon: Hypothalamus
• Lies below
thalamus
Figure 14–10a
Hypothalamus
• Captain of the Autonomic nervous system,
master overseer of homeostasis
– Emotions and behavior: mediates perception of
pleasure, fear, and rage
– Regulation of body temperature, blood pressure,
digestive tract motility, rate and depth of breathing,
and many other visceral activities
– Food intake (drives)
– Water balance/thirst
– Day/night rhythms
– Endocrine functions- ADH and oxytocin
Structures of the Hypothalamus
• Mamillary bodies:
– Relay station for olfactory information
– control reflex eating movements
Pituitary Gland
• Major endocrine gland, controls all
others
• Connected to hypothalamus via
infundibulum (stalk)
• Interfaces nervous and endocrine
systems because it is controlled by
the hypothalamus
Telencephalon
• Basal nuclei
• Cerebrum
The Basal Nuclei (Ganglia)
Figure 14–14b, c
Basal Nuclei
• Also called basal ganglia
• Masses of gray matter found deep within the
cortical white matter
• The corpus striatum is composed of three
parts
– Caudate nucleus
– Lentiform nucleus = putamen and the globus
pallidus
– Fibers of internal capsule running between and
through caudate and lentiform nuclei
• Direct subconscious activities
Functions of Basal Nuclei
• Are involved with:
– Subconscious control of skeletal muscle tone
– Regulate attention and cognition
– Regulate intensity of slow or stereotyped
movements (walking, lifting)
– Inhibit antagonistic and unnecessary
movement
– Subconscious habit learning
– May store simple movement patterns
Basal Nuclei
Figure 12.11b
Cerebrum
• Largest part of brain (make up 83% of its
mass)
• Controls higher mental functions including
all conscious thoughts and experience
including all intellectual functions (more
about this later)
• Processes somatic sensory and motor
information
• Divided into left and right cerebral
hemispheres
• Surface layer of gray matter (cerebral cortex)
(Cerebral) Cortex
• Gray matter covering cerebral
hemispheres
• Accounts for 40% of the mass of the
brain
• Folded surface increases surface area
• Elevated ridges = gyri (gyrus)
• Shallow depressions = sulci (sulcus)
• Deep grooves = fissures
Cerebral Gray and White Matter
• Gray matter:
– Cell bodies
– Found in cerebral cortex and basal nuclei
• White matter:
– Fiber tracts (axons)
– Deep to cerebral cortex
– Surrounding basal nuclei
White Matter of the Cerebrum
• Myelinated fibers (axons)
– Association fibers:
• arcuate: local
• longitudinal: within one
hemisphere
– Commissural: between
hemispheres
– Projection: link
cerebral cortex with
rest of CNS
Figure 14–13
Examples
• Projection Fibers: Internal capsule
– all ascending and descending projection
fibers to and from cerebral cortex, passes
though basal nuclei
• Commissural fibers: corpus callosum
– Connect the two cerebral hemispheres
Fiber Tracts in White Matter
Figure 12.10b
Limbic System
Figure 12.18
The Limbic System
• One of two networks of neurons working
together and spanning wide areas of the brain –
the other is the consciousness regulating
reticular formation (where?)
• A of the medial functional grouping of the medial
cerebral hemispheres and diencephalon that:
– establishes emotional states and drives
– links conscious functions of cerebral cortex with
autonomic functions of brain stem
– Allows us to react emotionally to conscious
understanding and to be aware of emotions
– facilitates memory storage and retrieval
The Limbic System
Figure 14–11a
Components of the Limbic System
• Amygdala
– deals with anger, danger, and fear responses,
along with emotional smell memories
• Limbic lobe of cerebral hemisphere:
– Cingulate gyrus: plays a role in expressing
emotions via gestures, and resolves mental
conflict (emotion)
– Hippocampus: convert new information into
long-term memories (patient H.M.?)
Components of the
Limbic System Continued
• Fornix:
– tract of white matter that connects
hippocampus with hypothalamus
• Diencepalic structures:
– Portions of thalamus, hypothalamus
Reticular Formation
Sends
impulses to
the cerebral
cortex to
keep it
conscious
and alert
Figure 12.19
Higher Level Functions of
Cerebral Hemispheres
The Cerebral Cortex
4 Lobes:
Frontal
Parietal
Temporal
Occipital
Figure 14–12b
Cerebral cortex
• It enables sensation, communication,
memory, understanding, and voluntary
movements
• Temporal lobe: memory, hearing
• Frontal lobe: executive function, language
• Parietal lobe: sense of self
• Occipital lobe: vision
Cerebral Cortex landmarks
•
•
•
•
•
•
Lateral sulcus
Longitudinal fissure
Central sulcus
Precentral gyrus (primary motor)
Postcentral gyrus (primary sensory)
Association areas are for integrating
information
Motor and Sensory Areas
of the Cortex
• Central sulcus separates motor and
sensory areas
Figure 14–15a
Functional Areas of the Cerebral
Cortex
• The three types of functional areas are:
– Motor areas – control voluntary movement
– Sensory areas – conscious awareness of
sensation
– Association areas – integrate diverse
information
Functional Areas of the Cerebral Cortex
Figure 12.8a
Functional Areas of the Cerebral Cortex
Figure 12.8b
Motor Areas
• Precentral gyrus of frontal lobe:
– directs voluntary movements
• Primary motor cortex:
– is the surface of precentral gyrus
Sensory Areas
• Postcentral gyrus of parietal lobe:
– receives somatic sensory information
(touch, pressure, pain, vibration, taste, and
temperature)
• Primary sensory cortex:
– surface of postcentral gyrus
Association Areas
• Any brain region that receives input from
more than one sensory modality
• aka “integrative areas” or higher level
association areas
• Relative abundance determines intellectual
capacity
• Include:
–
–
–
–
Prefrontal cortex
Language areas
General (common) interpretation area
Visceral association area
Functional Principles
of the Cerebral hemispheres
1. Each cerebral hemisphere receives sensory
information from, and sends motor
commands to, the opposite side of body
2. The 2 hemispheres have somewhat
different functions although their
structures are alike
3. Correspondence between a specific
function and a specific region of cerebral
cortex is not precise
4. No functional area acts alone; conscious
behavior involves the entire cortex
Higher level: Prefrontal Cortex
• Most complicated region, coordinates
info from all other association areas
• Important in intellect, planning,
reasoning, mood, abstract ideas,
judgement, conscience, and accuratley
predicting consequences
• Phineas Gage?
Phineas Gage
Phineas Gage
• In 1848 in Vermont, had a 3.5-foot-long,
13 lb. metal rod blown into his skull,
through his brain, and out of the top of his
head. Gage survived. In fact, he never
even lost consciousness.
• Friends reported a complete change in his
personality after the incident. He lost all
impulse control.
“Right Brain – Left Brain”
Hemispheric Lateralization
• Functional differences between left and
right hemispheres
• In most people, left hemisphere
(dominant hemisphere) controls:
– reading, writing, and math, decisionmaking, logic, speech and language
(usually)
• Right cerebral hemisphere relates to:
– recognition (faces, voice inflections), affect,
visual/spatial reasoning, emotion, artistic
skills
Brain Waves
• Alpha waves – regular and rhythmic, lowamplitude, slow, synchronous waves
indicating an “idling” brain (drifting off)
• Beta waves – rhythmic, more irregular
waves occurring during the awake and
mentally alert state
• Theta waves – more irregular than alpha
waves; common in children but abnormal
in adults
• Delta waves – high-amplitude waves seen
in deep sleep and when reticular activating
system is damped
Types of Brain Waves
Figure 12.20b
Ventricles of the brain
Ventricles
• Lined by ependymal cells which help to
form the choroid plexus
• There are two lateral ventricles in the
cerebral hemispheres
• Third ventricle is located in the
diencephalon
• Fourth ventricle is located between the
pons and the cerebellum
Cranial
meninges
Cranial meninges
• Dura mater consists of an outer
(endosteal layer) and an inner (meningeal
layer)
– In between the layers find the dural sinus
• Arachnoid membrane covers the surface
of the brain, have a subarachnoid space
• Pia mater is anchored to the brain by
astrocytes, wraps brain tightly like saran
wrap
Inter-Layer Spaces –
just like in the brain
• Subdural space:
– between arachnoid mater and dura mater
• Subarachnoid space:
– between arachnoid mater and pia mater
– contains collagen/elastin fiber network that’s
“spiderweb-like” (arachnoid trabeculae)
– filled with cerebrospinal fluid (CSF)
Subdural, subarachanoid spaces are
frequent sites of intracranial bleeding
Cerebrospinal Fluid (CSF)
•
•
•
•
Surrounds all exposed surfaces of CNS
Cushions, supports, and transports
Interchanges with interstitial fluid of brain
Like plasma or interstitial fluid elsewhere
except much more pure
• Arachnoid villi protrude superiorly into
dural sinus and permit CSF to be
absorbed into venous blood
Choroid Plexuses
• Clusters of capillaries
lined by ependymal
cells that form tissue
fluid filters, which
hang from the roof of
each ventricle
• Have ion pumps that
allow them to alter ion
concentrations of the
CSF
• Help cleanse CSF by
removing wastes
CSF flow: through
ventricles, to
arachnoid space, to
dural sinuses (back
to circulation)
Blood Supply to the Brain
• Supplies nutrients and oxygen to brain
• Delivered by internal carotid arteries
and vertebral arteries
• Removed from dural sinuses by
internal jugular veins
Blood–Brain Barrier
• Isolates CNS neural tissue from general
circulation
• Formed by network of tight junctions
between endothelial cells of CNS capillaries
and by feet of astrocyte processes
• Astrocytes control blood–brain barrier by
releasing chemicals that control permeability
of endothelium
Blood–Brain Barrier
• Lipid–soluble compounds (O2, CO2),
steroids, and prostaglandins diffuse
into interstitial fluid of brain and spinal
cord
• Other things have to be transported in
Cerebrovascular Disease
• Disorders interfere with blood circulation to
brain
• Stroke or cerebrovascular accident (CVA):
– shuts off blood to portion of brain
– neurons die
• Tissue plasminogen activator (TPA) is the
only approved treatment for stroke (except
aspirin)
• Transient Ischemic Attach (TIA)
Degenerative Brain Disorders
• Alzheimer’s disease – a progressive
degenerative disease of the brain that results
in dementia (usually frontotemporal)
• Parkinson’s disease – degeneration of the
dopamine-releasing neurons of the substantia
nigra
• Huntington’s disease – a fatal hereditary
disorder caused by accumulation of the
protein huntingtin that leads to degeneration
of the basal nuclei