Different Systems of the CNS & their functions

These systems are pathways formed of specific parts of the brain and the neurons connecting them. 

They include:
1.The pyramidal system 
2.The extrapyramidal system 
3.The limbic system 
4.The reticular formation 
5.The tuberohypophyseal system

The pyramidal system: 

It originates from the motor area of the cerebral cortex and passes through the spinal cord, therefore it is also known as the “corticospinaltract”. 
It is responsible for the regulation of the fine voluntary movements.

The extrapyramidal system: 

It also controls the motor functionbut involves areas other than the corticospinal tract. 
It is involved in the regulation of gross voluntary movements, thus it complements the function of the pyramidal system. 

The “basal ganglia” constitute an essential part of this system. 

Degenerative changes in the pathway running from the “substantianigra”to the “corpus striatum”(or nigrostriatal pathway) may cause tremors and muscle rigidity characteristic of “Parkinson’s disease”.

The limbic system: 

The major parts of this system are: the hypothalamus, the basal ganglia, the hippocampus(responsible for short term memory), and some cortical areas. 

The limbic system is involved in the control of “behavior”& “emotions”.

The reticular formation:

It is composed of interlacing fibers and nerve cells that run in all directions beginning from the upper part of the spinal cord and extending upwards. 
It is important in the control of “consciousness” and “wakefulness”.

The tuberohypophyseal system: 

It is a group of short neurons running from the hypothalamusto the hypophysis(pituitary gland) regulating its secretions.
 

Gastric acid neutralizers (antacids)

Antacids act primarily in the stomach and are used to prevent and treat peptic ulcer. They are also used in the treatment of Reflux esophagitis and Gastritis.

Mechanism of action: 

Antacids are alkaline substances (weak bases) that neutralize gastric acid (hydrochloric acid) they react with hydrochloric acid in the stomach to produce neutral or less acidic or poorly absorbed products and raise the pH of stomach secretion.

Antacids are divided into systemic and non-systemic.

• Systemic antacids (e.g. sodium bicarbonate) are highly absorbed into systemic circulation and enter body fluids. Therefore, they may alter acid–base balance. They can be used in the treatment of metabolic acidosis. 

Non-systemic: they do not alter acid–base balance significantly, because they are not well-absorbed into the systemic circulation. They are used as gastric antacids; and include:

• Magnesium compounds such as magnesium hydroxide and magnesium sulphate MgS2O3. They have relatively high neutralizing capacity, rapid onset of action, however, they may cause diarrhoea and hypermagnesemia.

• Aluminium compounds such as aluminium hydroxide. Generally, these have low neutralizing capacity, slow onset of action but long duration of action. They may cause constipation.

• Calcium compounds such as. These are highly effective and have a rapid onset of action but may cause hypersecretion of acid (acid - rebound) and milk-alkali syndrome (hence rarely used in peptic ulcer disease). 

Therefore, the most commonly used antacids are mixtures of aluminium hydroxide and magnesium hydroxide . 

Third Generation Cephalosporins 

Prototype drugs are CEFOTAXIME (IV) and CEFIXIME (oral). CEFTAZIDIME (for Pseudomonas aeruginosa.).

Further expansion of Gm negative spectrum to include hard to treat organisms such as Enterobacter, Serratia, and Pseudomonas. 
In addition to better Gm negative spectrum, this group has improved pharmacokinetic properties (longer half-lives) that allow once daily dosing with some agents. In general, activity toward Gm + bacteria is reduced. These are specialty antibiotics that should be reserved for specific uses. 

Enterobacteriaciae that are almost always sensitive (>95% sensitive)
E. coli
Proteus mirabilis (indole –)
Proteus vulgaris (indole +)
Klebsiella pneumoniae

Gram negative bacilli that are generally sensitive (>75% sensitive)
Morganella morganii
Providencia retgerri
Citrobacter freundii
Serratia marcescens
Pseudomonas aeruginosa (Ceftazidime only)

Gram negative bacilli that are sometimes sensitive (<75% sensitive)
Enterobacter
Stenotrophomonas (Xanthomonas) maltophilia (Cefoperazone & Ceftazidime only)
Acinetobacter

--> cefepime & cefpirome are promising for these bacteria

Bacteria that are resistant
Listeria monocytogenes
Pseudomonas cepacia
Enterococcus sp. 

Uses
1. Gram negative septicemia & other serious Gm – infections
2. Pseudomonas aeruginosa infections (Ceftazidime - 90% effective)
3. Gram negative meningitis - Cefotaxime, Ceftriaxone, Cefepime. For empiric therapy add vancomycin ± rifampin to cover resistant Strep. pneumoniae
4. Gonorrhea - Single shot of Ceftriaxone is drug of choice. Oral cefixime and ceftibuten are also OK.
5. Complicated urinary tract infections, pyelonephritis
6. Osteomyelitis - Ceftriaxone in home health care situations
7. Lyme disease - ceftriaxone in home health care situations

Amphotericin B

Main use is in systemic fungal infections (e.g. in immunocompromised patients), and in visceral leishmaniasis. Aspergillosis, cryptococcus infections (e.g. meningitis) and candidiasis are treated with amphotericin B. It is also used empirically in febrile immunocompromised patients who do not respond to broad-spectrum antibiotics.

MOA:

As with other polyene antifungals, amphotericin B associates with ergosterol, a membrane chemical of fungi, forming a pore that leads to K+ leakage and fungal cell death

Side effects: nephrotoxicity (kidney damage) , headache, vomiting, convulsions and fever

The side-effects are much milder when amphotericin B is delivered in liposomes

Selective serotonin reuptake inhibitors (SSRIs)

e.g. fluoxetine, paroxetine, citalopram, and sertraline
- Most commonly used antidepressant category
- Less likely to cause anticholinergic side effects
- Relatively safest antidepressant group in overdose
- Selectively inhibits reuptake of serotonin(5-HT)

Mode of Action;
- Well absorbed when given orally
- Plasma half-lives of 18-24 h allowing once daily dosagedaily dosage
- Metabolised through CYP450 system and most SSRIs inhibit some CYP isoforms
- Therapeutic effect is delayed for 2-4 weeks

ADVERSE DRUG REACTIONS

- Insomnia, increased anxiety, irritability
- Decreased libido
- Erectile dysfunction, anorgasmia, and ejaculatory delay
- Bleeding disorders
- Withdrawal syndrome

Stages of anesthesia

Stage I

Analgesia

Still conscious but drowsy

Stage II

Excitement stage

Loss of consciousness, however, irregular ventilation may be present which affects absorption of inhalation agents.

Reflexes may be exaggerated.

This is a very dangerous stage

Stage III

Surgical anesthesia

Loss of spontaneous movement

Regular, shallow respiration

Relaxation of muscles

Stage IV

Medullary paralysis

Death