Mupedziswa Gideon Kudzai

BASIC NEUOROLOGY AND ENDOCRINOLOGY

Neurons and their functioning

  • Neurones are the building blocks of the nervoussystem
  • They are responsible for the production and transmit ion of electrochemical impulses and thus are the bases of the functioning of the nervous system
  • Neurons produce electrochemical impulses when they are stimulated and the stimulation exceeds the neurones threshold
  • When the neuron is not firing it is said to be in the resting potential and in the state of polarisation, the charge inside the neuron will be -70millivolts.
  • After stimulation the charge rises to 40millivolts and the neuron goes through what is termed the action potential, and the neurons is said to be in a state of de-polarization
  • When in rest sodium ions which are positively charged will be on the outside whilst negatively charged potassium ions will be in the inside, this state of affairs is maintained by sodium pumps found at the knodes of ranvier which actively keep out the sodium and the potassium inside
  • Upon stimulation the sodium pumps open up and the sodium enters the cell raising the charge of the neuron to 40millivolts, at this point the neuron fires and transmition occurs. An action potential only occurs when the charge reaches 40 millivolts only. This is called the all or none principle, meaning that transmition occurs only when a charge of 40millivolts is reached.
  • The depolarisation will self perpetuate along the axon of the cell until the action potential reaches the terminal buttons
  • Upon reaching the terminal buttons the neuron goes through anew process of communicating with other neurons
  • Neurons communicate through a system called synaptic transmission
  • A synapse is gap that exist between two terminals of adjustment neurons
  • The terminals of neurons have structures called terminal buttons, these terminal buttons also contain structuresin them called synaptic vesicles
  • These synaptic vesicles contain neurotransmitters; neurotransmitters are the chemicals that facilitate communication between two nerve cells.
  • When the action potential reaches the terminal buttons it causes the synaptic vesicles to fuse with terminal buttons membrane, this makes the membrane permeable
  • Neurotransmitters will be released through the semi permeable membrane into the synapse they will occupy the synapse and will be received by specific receptor cites on the adjacent neurone stimulating the adjacent neuron create its own electrochemical impulse

Neurotransmitters

These are chemicals that carry information in the nervous system, they can be inhibitory or excitatory. They are different types of neurotransmitters. Examples are:

a)Acetylcholine – found at various synapse in the body i.e. in the autonomic nervous system and at neuromuscular junctions. Its involved in muscular action as well as learning and memory. Its an excitatory neurotransmitter. Hyposecrition can lead to Alzheimer’s disease.

b)Norepinephrine/noradrenaline – found in the central nervous system. It by stimulating the intake of carbohydrates as well as stimulating wakefulness and awareness. Deficiencies can cause depression and sleeping disorders.

c)Dopamine – controls learning and memory. Mainly found in the central nervous system. Deficiency can lead to Parkinson’s disease and too much of it in schizophrenia.

d)Serotonin – found at various synapse in the body with greatest concentration in the central nervous system. Regulates mood, sleep aggression, and appetite. Abnormalities in serotonin secretion are associated with heightened aggression and eating disorders.

e)G.A.B.A (gamma amino butyric acid). Its found in the central nervous system. It’s the main inhibitory neurotransmitter, it helps in the regulation of anxiety. Abnormities in secretion can lead to anxiety disorders or bipolar disorder.

Psychoactive drugs

Psychoactive drugs are chemicals which when ingested into the body tamper with the functioning of neurotransmitters leading to alterations in the neurochemical structure and functionality .this ultimately leading to alterations in human behaviour. They can either be medicinal or recreational. However we will focus on recreational drugs. They are different type of psychoactive drugs and these will be discussed using examples.

Stimulants

These excite neural activity and arouse bodily function

a)Amphetamines – act on dopamine, serotonin and noradrenaline pathways. Effects include raising of blood pressure, respiration rate and reduced appetite. A commonly used amphetamine is (ecstasy) M.D.M.A methylene –dioxy-methamphetamine. It acts directly on serotonin pathways in the brain blocking the recycling of serotonin at the synaptic cleft. The drug reduces autonomic arousal and when combined with physical activity produces overheating, dehydration and even death through heat stroke. It can lead psychoses.

Depressants

They slow down neural activity

a)Alcohol – in small doses it acts as a stimulant enliving the drinker. In larger doses it stimulates G.A.B.A pathways reducing activities in the nervous system.This leads to the slowing down of an individual’s reaction time and perception ability. Too much use can lead to Korssakoffs syndrome.

Opiates

These are groups of drugs derived from the opium poppy

a)Morphine – this drug depresses neural activity slowing down the breathing rate and lead to euphoria, overdose can lead to death. They function by stimulating endorphin areas of the brain since they are similar in structure to them.

Hallucinogens

These cause sensations of seeing, hearing, or feeling things with no physical stimuli.

a)L.S.D (lysergic acid diethylamide) – acts by stimulating serotonin pathways in the brain. Effects incudes euphoria, detachment, panic and seeing of things. It can lead to psychoses.

Psychedelics

These are referred to as mind expanding drugs since they lead to a rush of ideas.

a)Cannabis/ marijuana – the plant has many chemicals but the most psychoactive is delta-9-tetrahydrocannabinnis. When smoked the chemical reaches the brain in 7 seconds. Effects include euphoria, mild hallucinations, and amplification of sensation, impaired -motor co-odination, perceptual skills and reaction time. Continual abuse can lead to psychoses.

Endocrine system

This is a system of communication in the body that is made up of hormone secreting glands . Hormones are chemicals that help to regulate bodily functions, the glands produce hormones and release them into the bloodstream which will in turn take the respective hormones to the organ tissue that they are supposed to act on. The endocrine system works alongside the nervous system. The difference between the two being that the endocrine system is slow acting, distributes hormones through the bloodstream and it produces widespread and long lasting effects whilst on the other hand the nervous system is fast acting and has narrow targets that have short lasting effects and neurotransmitters are found mainly at synapses.

They are different types of glands that produce various hormones and we are going to look at the main ones below.

a)Pituitary gland – this is a pea sized organ found just below the hypothalamus. It’s often referred to as the master gland since it produces hormones that control the functioning of other glands. It has two parts the Posterior pituitary and the anterior pituitary. These produce different hormones

Posterior pituitary

  • Oxytocin – triggers uterine contractions during birth and is also stimulates milk production
  • Antidiuretic hormone (ADH) – controls the water levels in the body through reducing of the flow of blood to the sweat glands and encouraging re uptake of water in the kidneys

Anterior pituitary

  • Thyroid stimulating hormone (TSH) – controls the function of the thyroid gland
  • Adrenocorticotropic hormone (ACTH) control the adrenal cortex of the adrenal gland
  • Prolactin hormone (PRL) – stimulates mammary glands to produce milk
  • Follicle stimulating hormone – stimulates the follicle cells of the gonads to produce sperm and ova
  • Human growth hormone(HGH) – controls growth and repair of cells in the bodytoo much production of the growth hormone can lead to acromegaly
  • Luteinizing hormone (LH) – stimulates the gonads to produce sex hormones , estrogens in females and testosterone in males

b)Adrenal glands – this are rectangular shaped glands found atop each kidney. They a comprised of two distinct layers the adrenal cortex and the adrenal medulla. These produce different hormones.

Adrenal cortex

  • Gluco-corticoids –these regulate metabolism of carbohydrates, protein and fat thus controlling blood sugar levels
  • mineral corticoids – regulate the water salt balance ultimately controling the blood volume and pressure
  • cortisol - metabolism of muscle protein ,amino acids and fatty acids

adrenal medula

produces catecholamines ie adrenaline(epinephrine) and noradrenaline( norepinephrine) ,these increase blood pressure and herat rate when the body is under stress .they wrk in hand with the autonomic nervours system.to

Abnormalitiesin the functioning of these hormones leads to supression of the bloods defence system and in Addison’s disease.

PINEAL GLAND

  • Referredto as the third eye. It is located deep within the brain.
  • Controls the circadian rhythmi.e. the sleep wake cycle synchronised into a 24 hour system
  • Controls through the production of melatonin, production is low in daylight and high at night.
  • Melatonin induces sleep
  • It also blocks the production of gonadotropins (luteinizing hormone and follicle stimulating hormone)
  • Low melatonin production implicated in sleep disorders.

Pancreas

  • Its flat shaped organ found deep within the abdomen between the stomach and the spine and is connected to the duodenum
  • Produces the following hormones:
  1. Gastric; aids digestion by stimulating the production of stomach acids
  2. Glucagon; controls blood glucose levels. It works antagonistically to insulin. it stimulates cells to release glucose and it raises blood glucoselevels
  3. Insulin; controls blood sugar level by stimulating cells to absorb and use glucose which i n turn drops blood glucose levels
  4. Somatostatin; released in reaction to high levels of insulin or glucagon to maintain a blood glucose balance
  5. Vasoactive intestinal peptide; helps control water secretion and absorption from the intestines by stimulating the intestinal cells to release water & salts into the intestines.
  • Malfunctioning leads to the diabetes, hyperglycemias’ and hypoglycaemia

THYROID GLAND

  • Found in the neck below the thyroid cartilage
  • Controls the body’s metabolism ( use of energy & protein synthesis)
  • Produces triodothyronine, thyroxine,(stimulates oxygen and energy consumption, stimulates RNA polymerase promoting protein syntheses)
  • Calcitonin,( stimulates osteoblasts leading to borne construction,inhibits release of calcium from bones reducing blood calcium levels)
  • Hyperthyroidism leads to fatigue and muscle weakness, hand tremors, anxiety,irregular heartbeat,skin dryness, trouble sleeping, weight loss, increased bowel movement, or goitre may develop.
  • Hypothyroidism leads tofatigue, weakness, weightgain, hair loss, cold intolerance, muscle cramps, constipation, depression, memory loss, decreased libido.

PARATHYROID

  • Found close to the thyroid hormone, they are 4 structeres about the size of a grain of rice
  • Regulates calcium levels in the body that ultimately controlling the functioning of the nervous system and muscular system.
  • Calcium facilitates conduction of electrochemical impulses by nerve cells and is responsible for controlling contraction of muscles
  • Produces the parathyroid hormone which stimulates the release of calcium from bones into the bloodstream, controls how much of calcium is excreted from the kidneys, and how much is store in the bones, increases the syntheses of vitamin D which in turn increases intestinal calcium and phosphorus absorption
  • Hyposecrition leads low calcium levels (hypoglycaemia) and increase in body phosphorous which is toxic to the body
  • Hypersecrition leads to release of calcium from bones continuously leading to weak brittle bones

GONADS

  • Include the testes and the ovaries
  • Testes ; control the male reproductive system and normal male development and produce male sex cells (sperms)
  • Produce the testosterone; it regulates development during puberty and throughout the lifetime maintains libido, sperm production as well as maintaining muscle mass
  • Low production leads to decreased sex drive, diminished mass, low sperm count. Too much can lead to baldness or high levels of aggression
  • Ovaries ; control the female reproductive system , normal female development, production of ovum,
  • Produces progesterone and oestrogen
  • Progesterone; prepares the body for pregnancy by causing the uterine lining to thicken. It is produced by the corpus luteum a temporary part of the ovaries which appears during ovulation and disappears if the individual does not fall pregnant.
  • Estrogens ; controls the development and maintenance of secondary female characteristics
  • Abnormities in production can lead to osteoporosis , low libido, infertility