PHYSIOLOGY OF THE BRAIN

• The Cerebrum (Telencephalon) Lobes of the cerebral cortex

   

  1. Frontal Lobe
     1. Precentral gyrus, Primary Motor Cortex, point to point motor neurons, pyramidal cells: control motor neurons of the brain and spinal cord. See Motor homunculus
     2. Secondary Motor Cortex repetitive patterns
     3. Broca's Motor Speech area
     4. Anterior - abstract thought, planning, decision making, Personality
  2. Parietal Lobe
     1. Post central gyrus, Sensory cortex, See Sensory homunculus, size proportional to sensory receptor density.
     2. Sensory Association area, memory of sensations
  3. Occipital Lobe
     1. Visual cortex, sight (conscious perception of vision)
     2. Visual Association area, correlates visual images with previous images, (memory of vision, )
  4. Temporal Lobe
     1. Auditory Cortex, sound
     2. Auditory Association area, memory of sounds
  5. Common Integratory Center - angular gyrus, Parietal, Temporal & Occipital lobes
     1. One side becomes dominent, integrats sensory (somesthetic, auditory, visual) information
  6. The Basal nuclei (ganglia)
     1. Grey matter (cell bodies) within the White matter of cerebrum, control voluntary movements
  7. Cauadate nucles - chorea (rapi, uncontrolled movements), Parkinsons: (dopamine neurons of substantia nigra to caudate nucles) jerky movements, spasticity, tremor, blank facial expression
  8. The limbic system - ring around the brain stem, emotions(w/hypothalamus), processing of olfactory information

• The Diencephalon

   

  1. The Thalamus - Sensory relay center to cortex (primitive brain!)
  2. The Hypothalamus
     1. core temperature control"thermostat", shivering and nonshivering thermogenesis
     2. hunger & satiety centers, wakefulness, sleep, sexual arousal,
     3. emotions (w/limbic-anger, fear, pain, pleasure), osmoregulation, (ADH secretion),
     4. Secretion of ADH, Oxytocin, Releasing Hormones for Anterior pitutary
     5. Linkage of nervous and endocrine systems

• The Mesencephalon or Midbrain -

   

  1. red nucleus, motor coordination (cerebellum/Motor cortex),
  2. substantia nigra
• The Metencephalon
  1. The Cerebellum -
     1. Performs automatic adjustments in complex motor activities
     2. Input from Proprioceptors (joint, tendon, muscles), position of body in Space
        1. Motor cortex, intended movements (changes in position of body in Space)
     3. Damping (breaking motor function), Balance, predicting, inhibitory function of Purkinji cells (GABA), speed, force, direction of movement
  2. The Pons - Respiratory control centers (apneustic, pneumotaxic)
     1. Nuclei of cranial nerves V, VI, VII, VIII

• Myelencephalon

   

  1. The Medulla
     1. Visceral motor centers (vasomotor, cardioinhibtory, respiratory)
     2. Reticular Formation RAS system, alert cortex to incoming signals, maintenance of consciousness, arousal from sleep
     3. All Afferent & Efferent fibers pass through, crossing over of motor tracts
  2. Corpus Callosum: Permits communication between cerebralhemispheres
• Generalized Brain Avtivity
  1. Brain Activity and the Electroencephalogram(EEG)
     1. alpha waves: resting adults whose eyes are closed
     2. beta waves: adults concentrating on a specific task;
     3. theta waves: adults under stress;
     4. delta waves: during deep sleep and in clinical disorders
  2. Brain Seizures
     1. Grand Mal: generalized seizures, involvs gross motor activity, affects the individual for a matter or hours
     2. Petit mal: brief incidents, affect consciousness but may have no obvious motor abnormalities
  3. Chemical Effects on the Brain
     1. Sedatives: reduce CNS activity
     2. Analgesics: relieve pain by affecting pain pathways or peripheral sensations
     3. Psychotropics: alter mood and emotional states
     4. Anticonvulsants: control seizures
     5. Stimulants: facilitate CNS activity
  4. Memory and learning
     1. Short-term, or primary, memories last a short time, immediately accessible (phone number)
     2. Secondary memories fade with time (your address at age 5)
     3. Tertiary memories last a lifetime (your name)
     4. Memories are stored within specific regions of the cerebral cortex.
     5. Learning, a more complex process involving the integration of memories and their use to direct or modify behaviors
     6. Neural basis for memory and learning has yet to be determined.
• Fibers in CNS
  1. Association fibers: link portions of the cerebrum;
  2. Commissural fibers: link the two hemispheres;
  3. Projection fibers: link the cerebrum to the brain stem

1) Storage - the stomach allows a meal to be consumed and the materials released incrementally into the duodenum for digestion. It may take up to four hours for food from a complete meal to clear the stomach. 
2) Chemical digestion - pepsin begins the process of protein digestion cleaving large polypeptides into shorter chains . 
3) Mechanical digestion - the churning action of the muscularis causes liquefaction and mixing of the contents to produce acid chyme. 
4) Some absorption - water, electrolytes, monosaccharides, and fat soluble molecules including alcohol are all absorbed in the stomach to some degree.

Basic Properties of Gases

A.    Dalton's Law of Partial Pressures

1.    partial pressure - the "part" of the total air pressure caused by one component of a gas 

     Gas            Percent            Partial Pressure (P)
    ALL AIR        100.0%                760 mm Hg
    Nitrogen       78.6%                   597 mm Hg    (0.79 X 760)
    Oxygen          20.9%                l59 mm Hg    (0.21 X 760)
    CO₂              0.04%                  0.3 mm Hg    (0.0004 X 760) 

2.    altitude - air pressure @ 10,000 ft = 563 mm Hg
3.    scuba diving - air pressure @ 100 ft = 3000 mm Hg

B.    Henry's Law of Gas Diffusion into Liquid

1.    Henry's Law - a certain gas will diffuse INTO or OUT OF a liquid down its concentration gradient in proportion to its partial pressure

2.    solubility - the ease with which a certain gas will "dissolve" into a liquid (like blood plasma)

HIGHest solubility in plasma            Carbon Dioxide
                                                      Oxygen
                                        
LOWest solubility in plasma             Nitrogen

C.    Hyperbaric (Above normal pressure) Conditions

1.    Creates HIGH gradient for gas entry into the body

2.    therapeutic - oxygen forced into blood during: carbon monoxide poisoning, circulatory shock, asphyxiation, gangrene, tetanus, etc.

3.    harmful - SCUBA divers may suffer the "bends" when they rise too quickly and Nitrogen gas "comes out of solution" and forms bubbles in the blood

CNS PROTECTION

- Bones of the Skull       Frontal, Temporal, Parietal, Sphenoid, Occipital

- Cranial Meninges         Dura mater, Arachnoid Space, Pia mater

- Cerebrospinal Fluid

Secreted by Chroid Plexi in Ventricles

Circulation through ventricles and central canal

Lateral and Median apertures from the 4th ventricle into the subarachnoid space

Arachnoid villi of the superior sagittal sinus return CSF to the venous circulation

Hydrocephalic Condition, blockage of the mesencephalic aqueduct, backup of CSF, Insertion of a shunt to drain the excess CSF

The large intestine (colon)

The large intestine receives the liquid residue after digestion and absorption are complete. This residue consists mostly of water as well as materials (e.g. cellulose) that were not digested. It nourishes a large population of bacteria (the contents of the small intestine are normally sterile). Most of these bacteria (of which one common species is E. coli) are harmless. And some are actually helpful, for example, by synthesizing vitamin K. Bacteria flourish to such an extent that as much as 50% of the dry weight of the feces may consist of bacterial cells. Reabsorption of water is the chief function of the large intestine. The large amounts of water secreted into the stomach and small intestine by the various digestive glands must be reclaimed to avoid dehydration.

Vital Capacity: The vital capacity (VC) is the maximum volume which can be ventilated in a single breath. VC= IRV+TV+ERV. VC varies with gender, age, and body build. Measuring VC gives a device for diagnosis of respiratory disorder, and a benchmark for judging the effectiveness of treatment. (4600 ml)

Vital Capacity is reduced in restrictive disorders, but not in disorders which are purely obstructive.

The FEV₁ is the % of the vital capacity which is expelled in the first second. It should be at least 75%. The FEV₁ is reduced in obstructive disorders.

Both VC and the FEV₁ are reduced in disorders which are both restrictive and obstructive

Oxygen is present at nearly 21% of ambient air. Multiplying .21 times 760 mmHg (standard pressure at sea level) yields a pO₂ of about 160. Carbon dioxide is .04% of air and its partial pressure, pCO₂, is .3.

With alveolar air having a pO₂ of 104 and a pCO₂ of 40. So oxygen diffuses into the alveoli from inspired air and carbon dioxide diffuses from the alveoli into air which will be expired. This causes the levels of oxygen and carbon dioxide to be intermediate in expired air when compared to inspired air and alveolar air. Some oxygen has been lost to the alveolus, lowering its level to 120, carbon dioxide has been gained from the alveolus raising its level to 27.

Likewise a concentration gradient causes oxygen to diffuse into the blood from the alveoli and carbon dioxide to leave the blood. This produces the levels seen in oxygenated blood in the body. When this blood reaches the systemic tissues the reverse process occurs restoring levels seen in deoxygenated blood.