Neurons have a special shape that aids the signals to pass from one cell to another, there are three main parts to it cell body, multiple dendrites and one axon. In the cell body there is a nucleus and other organelles, the dendrites and axons connect to the cell body, the dendrites receive the impulses form other cells whereas the axon pass on the impulses to other cells. One neuron can have thousands of dendrites, so it is able to communicate with lots of other cells but one axon. Myelin sheath covers the axon and insulates the axon allowing the electrical signal to move much quicker. There are gaps in between the myelin sheath which exposes the axon, so it transmits signals faster, they are called node of Ranvier.

There are two types of neurons sensory and motor, the sensory neurons takes nerve impulses from sense organs and internal organs to the central nervous system and motor neurons carry impulses from the central system to organs, glands and muscles. Both of the neutrons work together, the sensory neutrons will take information about the environment found inside or outside of the body to the central system and the central system will take the information to send messages through the motor neutrons to tell the body how it should respond to the information given.

This is where the axon of one neuron meets the dendrite of another cell, it can be found between neurons and cells like the muscle cell. The dendrite and the axon do not touch there is a very small gap in between them which is called the synaptic cleft. The type of chemicals released are dopamine, serotonin and adrenaline. Scientists believe that the cause of low level of neurotransmitter of serotonin is caused by depression, so people with depression are given antidepressants which bring the serotonin level back up to normal. A lot of people use antidepressants to control the symptoms of their depression which helps them live happy lives.

Two branches of the autonomic nervous system controls the heart rate, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The SNS release the hormones catecholamines, epinephrine and norepinephrine to accelerate the heart as for the PNS it releases a hormone to do the opposite, the hormone is acetylcholine, it slow the heart rate. Factors like caffeine, stress and excitement can accelerate the heart rate temporarily but meditating and taking slow deep breaths can help slow the heart rate. When exercising the heart rate is elevated and will stay elevate for the duration of the exercise, when you start to exercise the body will remove the parasympathetic stimulation which will gradually increase the heart rate. As the exercise intensifies the sympathetic system will kick in and begin to accelerate the heart even more, routine participation in cardiovascular exercise over time will decrease the resting heart rate by increasing the heart size, the contractile strength and length of time the heart fills with blood. A reduced heart rate is a result from increase activity of the parasympathetic nervous system and will decrease the activity of the sympathetic nervous system.

Endocrine is as system of glans that produce and secrete hormones, these are the chemical substances produced int the body. They regulate the activity of cells and organs, they also regulate the body’s growth metabolism, sexual development and function, these hormones are released into the bloodstream where they can affect several organs throughout the body. Hormones are basically chemical messengers that is created by the body, they transfer information from a set of cells to another to direct the functions of different parts of our body.

This is found in the lower central part of the brain, this part is very important to regulate satiety, metabolism and body temperature, it also secretes hormones that stimulate or suppress the release of hormones in the pituitary gland. Most of the releasing hormones are secreted into the artery which will carry them directly to the pituitary gland. These hormones in the pituitary gland signal the secretion of stimulating hormones and the hypothalamus can also secrete a hormone called somatostatin which makes the pituitary gland the release of the growth hormone.

If the hypothalamus malfunctions it will impact the hormones related to the endocrine which may cause disruption in body temperature regulation, growth, weight, sodium and water balance, milk production, emotions and sleep cycles.

The pituitary gland is at the base of the brain under the hypothalamus and is as small as a pea, it is considered as the most important part of the endocrine system due to it being able to produce hormones that control multiple functions of other endocrine glands. 

The pituitary gland consists of two parts the anterior lobe and the posterior lobe, the anterior lobe produces hormones that are regulated by the hypothalamus:

·         The growth hormone, this stimulates growth of bones and tissues. A lack of the growth hormone results in growth failure, growth hormone deficiency in adults’ results in problems in maintaining the right amount of body fat and muscle bone mass and their emotional well-being.

·         Thyroid stimulating hormone also know as thyrotropin, this is stimulated by thyroid gland to produce thyroid hormones. Thyrotropin deficiency is because of a defect in the pituitary or thyroid, this is called hypothyroidism.

·         The adrenocorticotropin hormone, the adrenal gland is stimulated to produce several related steroid hormones.

·         Luteinizing hormone and the follicle-stimulating hormone, these are the hormones that control sexual function and production of sex steroid, estrogen and progesterone in females or testosterone in males.

·         Prolactin hormone, this is the hormone that stimulates milk production in females.

The posterior lobe hormones that are not regulated by hypothalamus:

·         Antidiuretic hormone, vasopressin and this controls water loss by the kidneys.

·         Oxytocin, this hormone contracts the uterus during childbirth and stimulates milk production.

These hormones secreted by the posterior pituitary are actually produced in the brain and carried to the pituitary gland through nerves and are also stored in the pituitary gland. When the pituitary gland is not producing one or more of its hormones or not enough it is called hypopituitarism an example is when the pituitary gland does not produce enough of the growth hormone in a child this can lead to permanently short stature. It doesn’t produce enough follicle-stimulating hormone and luteinizing hormone it can cause issues with sexual function, menstruation and fertility.

This is located in the lower front part of the neck, it produces the thyroid hormone called thyrotropin, this hormone regulates the body’s metabolism and can also take part in the role in bone growth and the development of the brain and nervous system in children. The release of the thyroid hormone is controlled by the pituitary gland, the thyroid hormone helps to maintain normal blood pressure, heart rate, digestion, muscle tone and reproductive functions. 

When there is a malfunction with the thyroid hormone like an abnormal production of thyroid hormones this can result to a condition called hyperthyroidism. This can accelerate the bodies metabolism which can cause unintentional weight loss and a fast and irregular heartbeat, there are many treatments for this disease.

Embedded in the surface of the thyroid gland are two pairs of small glands called the parathyroid glands one pair on each side. Parathyroid glands release the parathyroid hormone and this deals with regulating calcium levels in the blood and bone metabolism. If parathyroid hormone is over secreted then the person has hyperparathyroidism and their blood calcium will rise, the blood of someone with this disease will have very little calcium and too much phosphorous. This can be caused by injury to the gland, endocrine disorders and genetic conditions.

 

There are two triangular-shaped glands called adrenal glands and they are located on top of each kidney. On the outer layer it is called the adrenal cortex and the inner is called adrenal medulla, the outer part produces hormones called corticosteroids. This regulates the body’s metabolism, the balance of salt and water n the boy, the immune system and sexual function. The adrenal medulla creates the hormones called catecholamines and they help to cope with physical and emotional stress by increasing the heart rate and blood pressure. 

The adrenal gland create hormone that we can’t live without one of there is the cortisol and this helps to respond to stress and other important functions. Adrenal gland malfunctions are either it is producing too much or not enough hormones, if it is producing too much it is called Cushing’s syndrome which can lead to rapid weight gain, skin bruises easily, muscle weakness, diabetes and other health problems. When there is too little then it is Addison’s disease, there are people who are born unable to produce enough cortisol which causes weakness, fatigue and low blood pressure.

This is located in the middle of the brain and it secretes the hormone called melatonin and this hormone regulates the wake-sleep cycle of the body. If there is a reduction in the pineal gland hormone production, it can lead to a hormone imbalance which can affect some of the body systems for example sleep patterns can be disrupted if the pineal gland hormone is reduced. This is usually seen in the disorders jet lag and insomnia.

The pancreas is located toward the back of the abdomen behind the stomach, this has digestive and hormonal functions. The part of the pancreas which is called exocrine pancreas secretes digestive enzymes and the other part called the endocrine pancreas secretes hormones insulin and glucagon. These regulate the level of glucose in the blood.

Pancreatitis can occur when there is poor absorption of food causing diarrhoea and weight loss, this is due to the gland not releasing enough exocrine hormones to secrete digestive enzymes to break down food. Diabetes can also be developed if the endocrine hormone does not secrete enough insulin.

cK-12, 2019. Nerve impulse. [Online] 
 Available at: https://www.ck12.org/biology/nerve-impulse/lesson/Nerve-Cells-and-Nerve-Impulses-MS-LS/
 [Accessed 10 June 2019].

eMedicineHealth, 2019. Endocrine System. [Online] 
 Available at: https://www.emedicinehealth.com/anatomy_of_the_endocrine_system/article_em.htm#thyroid_gland
 [Accessed 10 June 2019].

Medline Plus, 2019. Adrenal Gland Disorders. [Online] 
 Available at: https://medlineplus.gov/adrenalglanddisorders.html
 [Accessed 11 June 2019].

UC Davis Health , 2019. Heart Rate. [Online] 
 Available at: https://health.ucdavis.edu/sportsmedicine/resources/heart_rate_description.html
 [Accessed 10 June 2019].

 

The concentration of ions isn’t static, Ions are flowing in and out of the neuron constantly as the ions try to equalize their concentrations. The cell however maintains a consistent negative concentration gradient this is between -40 to -90 millivolts. 

Action potentials the electrical impulses that send signals around your body, are nothing more than shifts from negative to positive in the neuron’s membrane potential caused by ions suddenly flowing in and out of the neuron. During the resting state this is before an action potential occurs, all of the gated sodium and potassium channels are closed. These gated channels are different from the leakage channels, and only open once an action potential has been triggered. These channels are “voltage-gated” because they are open and closed depends on the voltage difference across the cell membrane. Voltage-gated sodium channels have two gates m and h, while the potassium channel only has one gate n.

Voltage-gated potassium channels are either open or closed due to the cell membrane being very permeable to potassium so there is a constant leakage of potassium ions.
An event take place that depolarizes the cell body. This signal comes from other cells connecting to the neuron, and it makes positively charged ions to flow into the cell body. Positive ions still flow into the cell to depolarize it, but these ions pass through channels that open when a specific chemical, known as a neurotransmitter, binds to the channel and tells it to open. Neurotransmitters are released by cells near the dendrites, often as the end result of their own action potential! These incoming ions bring the membrane potential closer to depolarization. An object is polar if there is some difference between more negative and more positive areas. As positive ions flow into the negative cell, that difference, along with the cell’s polarity, decrease. If the cell body gets positive enough that it can trigger the voltage-gated sodium channels found in the axon, then the action potential will be sent.