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, 3 rd ventricle • 1 4 th 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

•

Ventricles The Brain

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

The Brain

•

Blood Supply:

– The brain is a highly active organ, thus needing an extensive blood supply (O nutrients) 2 and – 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 • 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: CO 2 , O 2 , ammonia, lipids (steroids, alcohols) • Cannot enter: antibiotics, H 2 0, Ions

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

•

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

•

Diencephalon:

– Integrates conscious and unconscious sensory information and motor commands –

Thalamus (Gray Matter):

sensory information.

Relay station for all ascending • 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

• 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

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 Cerebrum

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/cerebru m_1.gif

The Brain

•

Cerebrum:

– Also has a function in memory – Brain Lateralization: – 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:

– 2 nd • 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