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

Biological Functions are Extremely Sensitive to pH

• H+ and OH- ions get special attention because they are very reactive
• Substance which donates H+ ions to solution = acid
• Substance which donates OH- ions to solution = base
• Because we deal with H ions over a very wide range of concentration, physiologists have devised a logarithmic unit, pH, to deal with it
  • pH = - log [H⁺]
  • [H⁺] is the H ion concentration in moles/liter
  • Because of the way it is defined a high pH indicates low H ion and a low pH indicates high H ion- it takes a while to get used to the strange definition
  • Also because of the way it is defined, a change of 1 pH unit means a 10X change in the concentration of H ions
    • If pH changes by 2 units the H+ concentration changes by 10 X 10 = 100 times

• Human blood pH is 7.4
  • Blood pH above 7.4 = alkalosis
  • Blood pH below 7.4 = acidosis
• Body must get rid of ~15 moles of potential acid/day (mostly CO₂)
  • CO₂ reacts with water to form carbonic acid (H₂CO₃)
  • Done mostly by lungs & kidney
• In neutralization H⁺ and OH^- react to form water
• If the pH changes charges on molecules also change, especially charges on proteins
  • This changes the reactivity of proteins such as enzymes
• Large pH changes occur as food passes through the intestines.

Oxygen Transport

In adult humans the hemoglobin (Hb) molecule

• consists of four polypeptides:
  • two alpha (α) chains of 141 amino acids and
  • two beta (β) chains of 146 amino acids
• Each of these is attached the prosthetic group heme.
• There is one atom of iron at the center of each heme.
• One molecule of oxygen can bind to each heme.

The reaction is reversible.

• Under the conditions of lower temperature, higher pH, and increased oxygen pressure in the capillaries of the lungs, the reaction proceeds to the right. The purple-red deoxygenated hemoglobin of the venous blood becomes the bright-red oxyhemoglobin of the arterial blood.
• Under the conditions of higher temperature, lower pH, and lower oxygen pressure in the tissues, the reverse reaction is promoted and oxyhemoglobin gives up its oxygen.

GENERAL SOMATIC AFFERENT (GSA) PATHWAYS FROM THE BODY

Pain and Temperature

Pain and temperature information from general somatic receptors is conducted over small-diameter (type A delta and type C) GSA fibers of the spinal nerves into the posterior horn of the spinal cord gray matter .

Fast and Slow Pain

Fast pain, often called sharp or pricking pain, is usually conducted to the CNS over type A delta fibers.

Slow pain, often called burning pain, is conducted to the CNS over smaller-diameter type C fibers.

Touch and Pressure

Touch can be subjectively described as discriminating or crude.

Discriminating (epicritic) touch implies an awareness of an object's shape, texture, three-dimensional qualities, and other fine points. Ability to recognize familiar objects simply by tactile manipulation.

The conscious awareness of body position and movement is called the kinesthetic sens

Crude (protopathic) touch,  lacks the fine discrimination described above and doesn't generally give enough information to the brain to enable it to recognize a familiar object by touch alone.

Subconscious Proprioception

Most of the subconscious proprioceptive input is shunted to the cerebellum.

Posterior Funiculus Injury

Certain clinical signs are associated with injury to the dorsal columns.

 As might be expected, these are generally caused by impairment to the kinesthetic sense and discriminating touch and pressure pathways.

 They include

 (1) the inability to recognize limb position,

 (2) as­tereognosis,

 (3) loss of two-point discrimination,

 (4) loss of vibratory sense, and

 (5) a positive Romberg sign.

Astereognosis is the inability to recognize familiar objects by touch alone. When asked to stand erect with feet together and eyes closed, a person with dorsal column damage may sway and fall. This is a posi­tive Romberg sign.

Proteinuria—Protein content in urine, often due to leaky or damaged glomeruli.

Oliguria—An abnormally small amount of urine, often due to shock or kidney damage.

Polyuria—An abnormally large amount of urine, often caused by diabetes.

Dysuria—Painful or uncomfortable urination, often from urinary tract infections.

Hematuria—Red blood cells in urine, from infection or injury.

Glycosuria—Glucose in urine, due to excess plasma glucose in diabetes, beyond the amount able to be reabsorbed in the proximal convoluted tubule.

Regulation of glomerular filtration :

1. Extrinsic regulation : 

- Neural regulation : sympathetic and parasympathetic nervous system which causes vasoconstriction or vasodilation respectively .
- Humoral regulation : Vasoactive substances may affect the GFR , vasoconstrictive substances like endothelin ,Angiotensin II , Norepinephrine , prostaglandine F2 may constrict the afferent arteriole and thus decrease GFR , while the vasodilative agents like dopamine , NO , ANP , Prostaglandines E2 may dilate the afferent arteriole and thus increase the filtration rate .

2. Intrinsic regulation : 

- Myogenic theory ( as in the intrinsic regulation of cardiac output) .
- Tubuloglomerular feedback: occurs by cells of the juxtaglomerular apparatus that is composed of specific cells of the distal tubules when it passes between afferent and efferent arterioles ( macula densa cells ) , these cells sense changes in flow inside the tubules and inform specific cells in the afferent arteriole (granular cells ) , the later secrete vasoactive substances that affect the diameter of the afferent arteriole.