The Brain
Poudre High School
By: Ben Kirk
The Brain
• General:
– Part of the Central Nervous System
– Large, mushroom shaped organ
• Approximately 3 lbs. In adults
– 4 major components
• Cerebrum, Cerebellum, Diencephalon, Brain Stem
The Brain
• Cerebrospinal Fluid (CSF):
Circulates
throughout the subarachnoid space surrounding the
spinal cord and brain, and within the ventricles of the
brain
– Ventricles: cavities within the brain that communicate with one
another
• 2 lateral ventricles
• 1, 3rd ventricle
• 1 4th ventricle
– 80-150 ml CSF
• Produce about 500 ml CSF per day (Total replacement of
CSF every 8 hours)
– Made of glucose, urea, proteins, and salt
– Functions as a shock absorber and circulatory medium
• Nutrients, waste, chemical messengers
The Brain
• Ventricles
http://www.cerebromente.org.br/n02/fundamentos/ventriculos_i.htm
The Brain
• Blood Supply:
– The brain is a highly active organ, thus
needing extensive vascularization (O2 and
nutrients)
– Arterial Blood: Delivered via internal carotids
and vertebral arteries
• Circle of Willis
– Venous Return: Delivered via internal jugular
veins
http://www.mscd.edu/~biology/2320course/2320images/Willis.gif
The Brain
• Blood Supply:
– Interruptions:
• Brief blockage or interruption = faint
– Karate chop to neck: Internal carotids
– Blow to jaw: Vertebral and brain stem
• 1-2 minute blockage = weakened cells
• >4 minutes of blockage = Permanent damage to
cells due to lysosomal enzyme attack
• Cerebrovascular accident (CVS)/Stroke: Neurons
die in localized areas
– Only specific functions impaired
– Neurons in CNS cannot regenerate
– Localized takeover by neighboring neurons
The Brain
• Blood-Brain Barrier (BBB):
– Regulates what can and cannot enter cerebral
circulation
– Made of tightly packed endothelial cells lining
the capillaries of the CNS
• Can enter: CO2, O2, ammonia, lipids (steroids,
alcohols)
• Cannot enter: antibiotics, H20, Ions
The Brain
• Parts of the Brain
– Brain Stem: Lower extension of the brain where it connects to
the spinal cord
• Medulla Oblongata: Continuation of the spinal cord that
contains ALL ascending and descending tracts
– White matter only (myelinated axons)
– All communication between brain and spinal cord passes
through the Medulla Oblongata
– Both pyramidal tracts cross over in the Medulla
• Decussation of pyramids: one side of brain controls the
other side of the body
– Severe blow to jaw twists this region of the brain stem resulting
in knockout
– Contains nuclei that control rate and force of heartbeat and
breathing rhythm.
The Brain
• Brain Stem:
– Pons: Structure just above the medulla
• Consists of nuclei and white matter
• Connects spinal cord to brain and brain parts together
• Helps regulate breathing, consciousness and sleep
– Midbrain: Between the Pons and the lower portion of
the diencephalon
• Contains motor fibers connecting the cerebral cortex to the
spinal cord
• Regulates most occulomotor responses (eye movement,
pupil dilation, responses to sight), hearing and body
movement
http://www.mhhe.com/socscience/intro/ibank/ibank/0012lll.jpg
The Brain
• Diencephalon:
– Integrates conscious and unconscious sensory information and
motor commands
– Thalamus (Gray Matter): Relay station for all ascending
sensory information.
• Interprets impulses such as pain, heat, pressure and light touch
– Hypothalamus: Contains homeostatic mechanisms primarily
• Autonomic Nervous System: (heart rate, gastrovascular movement,
bladder contractions
• Body Temperature
• Rage and Aggression
• Food intake/hunger
• Thirst center
• Consciousness and Sleep patterns
The Brain
• Reticular Activating System (RAS): Center of
arousal and activation
–
–
–
–
–
Cardiac Rhythm: 24 hour sleep and wake patterns
Consciousness results from RAS activation
Sleep results from RAS inactivation
Feedback causes increased activation and arousal
Altered by cocaine, alcohol. Anesthetics, meditation, and
amphetamines
– Faulty RAS
• ADHD: Increased RAS activation, leads to abnormal stimulation
• Coma: semi permanent sleep caused by faulty or injured RAS
Reticular Activating System
http://www.colorado.edu/epob/epob3730rlynch/image/figur
e5-29.jpg
The Brain
• Cerebrum: Bulk of the Brain
– Cerebral Cortex: Thin layer of gray matter making up
the outer covering of the cerebrum
• 6 layers of cell bodies
– Development: The brain increases in size, with gray
matter increasing in size faster than white matter
• Causes folds (fissures) to form
• Longitudinal Fissure: Separates right an left hemispheres
– Corpus Callosum: White matter that connects the
right and left hemispheres
• Larger in females
The Cerebrum
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/cerebru
m_1.gif
Corpus Callosum
http://www.disenchanted.com/dis/lookup.html?node=1852
The Brain
• Cerebrum:
– Lobes:
• Each hemisphere has 4 lobes divided by sulci
(shallow) or fissures (deep)
• Frontal, parietal, occipital, and temporal
• Functions:
– Frontal (primary Motor Cortex): Voluntary control of
skeletal muscles
– Parietal (primary Sensory Cortex): Conscious perception
of pain, temperature, taste, pressure, and vibration
– Occipital (Visual Cortex): Conscious perception of visual
stimuli
– Temporal (Auditory and Olfactory Cortex): Conscious
perception of auditory and olfactory (smell) stimuli
The Brain
• Cerebrum:
– Also has a function in memory
– Brain Lateralization:
• Left handed: parietal and occipital lobes of right
hemispheres are narrower and frontal lobe of left
hemisphere is narrower.
– Left hemisphere: right handed control, written and
spoken language, numerical and scientific skills, and
reasoning
– Right Hemisphere: Random, intuition, subjectivity,
synthesizing, and artistic
The Brain
• Cerebrum:
– White Matter: Myelinated Axons – 3 types
• Association Fibers: Transmit impulses between
gyri (bumps or elevated areas) of the same
hemisphere
• Commissural Fibers: Communicate one side of the
brain with the other (corpus callosum)
• Projection Fibers: Transmit impulses from
cerebrum to other parts of the brain
The Brain
• Cerebrum:
– Basal Ganglia: Paired masses of gray matter
within the white matter of each hemisphere
• Controls subconscious movement (ex. Swinging of
arms while walking)
• Does not initiate movement, but provides pattern
for repeated movements (walking, chewing, etc..)
• If damaged, uncontrolled shaking results
– Parkinson’s Disease
• Stroke in this area results in total paralysis of
opposite side of the body.
The Brain
• Limbic System
– Wishbone shaped group of structures
encircling the brain stem (between the
cerebrum and the diencephalon
– Controls emotions of pain, pressure, anger,
rage, fear, sorrow, sexual feelings and
affection
The Limbic System
http://www.mhhe.com/socscience/intro/ibank/ibank/0014lll.jpg
The Brain
• Cerebellum:
– 2nd largest part of the brain
• Behind the medulla and pons, and bellow the
occipital lobes
– Cortex (outer covering) consists of gray
matter
– White matter resembles tree branches
– Controls subconscious skeletal muscle
movements
• Balance, posture, coordination
– Ataxia: lack of coordination
The Cerebellum
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/cerebrum_1.
gif
The Brain
• Neurotransmitters:
– Acetylcholine: Usually excitatory, skeletal
neuromuscular junctions
– Dopamine: Emotional responses,
subconscious movements of skeletal muscles
• Parkinson’s Disease
– Norepinephrine: Neuromuscular and
neuroglandular junctions
• Related to arousal, dreaming, and mood
The Brain
• Neurotransmitters:
– Serotonin: Inhibitory, induces sleep, sensory
reception, temperature regulation and mood
– Gamma Aminobuteric Acid: Inhibitory, Target
of anti-anxiety drugs like Valium
– Substance P: Associated with pain
• Stimulates perception of pain
• Opposite of Endorphins
– Eukephalins: Suppresses substance P
The Brain
• Neurotransmitters:
– Endorphins: Inhibits substance P
• Also have a role in memory, learning, and sexual
activity
• Have been linked to depression and schizophrenia
The Brain
• Cranial Nerves
– 12 pairs of nerves
– 10 pair originating from the brain stem
– Designated by roman numerals.
– Part of the Somatic Nervous System
– Some are sensory only, while others are
mixed
Cranial Nerves
http://info.med.yale.edu/caim/cnerves/cn1/cn1_1.html