The BrainThe Brain

Poudre High SchoolPoudre High School

By: Ben KirkBy: Ben Kirk

The BrainThe 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 BrainThe 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 The Brain

• Ventricles

http://www.cerebromente.org.br/n02/fundamentos/ventriculos_i.htm

The BrainThe 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 BrainThe 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 BrainThe 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 BrainThe 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 BrainThe 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 BrainThe 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 BrainThe 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 SystemReticular Activating System

http://www.colorado.edu/epob/epob3730rlynch/image/figure5-29.jpg

The BrainThe 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 CerebrumThe Cerebrum

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/cerebrum_1.gif

Corpus CallosumCorpus Callosum

http://www.disenchanted.com/dis/lookup.html?node=1852

The BrainThe 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 BrainThe 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 BrainThe 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 BrainThe 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 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 SystemThe Limbic System

http://www.mhhe.com/socscience/intro/ibank/ibank/0014lll.jpg

The BrainThe 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 CerebellumThe Cerebellum

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/cerebrum_1.gif

The BrainThe 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 BrainThe 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 BrainThe Brain

• Neurotransmitters:– Endorphins: Inhibits substance P

• Also have a role in memory, learning, and sexual activity

• Have been linked to depression and schizophrenia

The BrainThe 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 NervesCranial Nerves

http://info.med.yale.edu/caim/cnerves/cn1/cn1_1.html