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• Nerve cell


  Also called the neuron, has the ability to change a stimulus into an impulse or an electric signal that travels in it
• Neuron


  • Cell body contains the nucleus and other cell organelles
  • Dendrites are the receiving parts of the neuron
  • Axon transmits impulses to another neuron
• Types of neurons


  • Sensory neuron (afferent neurons)
  • Motor neuron (efferent neurons)
  • Relay neuron (interneurons)
• Sensory neuron


  Receive stimuli and transmit them towards the central nervous system
• Motor neuron


  Carry the impulse away from the central nervous system to the effectors such as the muscles and the glands
• Relay neuron


  Also called association neurons, responsible for processing the sensory information carried by the sensory neurons and giving a response through the motor neurons
• Neuroglia


  Also called glia or glial cells, majority found in the central nervous system, their main function is to connect the nervous tissues together
• Neuroglia are smaller than neurons, but they are 5-25 times more in number</b>
• Neuroglia cannot transmit nerve impulses, they can replace neurons in cases of injuries or diseases, and they can cause glioma, a highly malignant brain tumor that grows rapidly
• The nervous system plays a significant role in the normal functioning of many body parts and processes
• Disorders of the nervous system

  • Alzheimer's disease
  • Epilepsy
  • Poliomyelitis
• Alzheimer's disease


  Decrease in brain size that leads to loss of neurons in the brain, resulting in intellectual deficiency, memory loss and disoriented thoughts
• Epilepsy


  Huge neuronal discharge in the brain, resulting in involuntary muscle contraction
• Poliomyelitis


  Viral infection in the central nervous system, resulting in muscle paralysis and degeneration
• The endocrine system, through the different glands, secrete hormones that control the growth and development of the body
• Glands in the endocrine system

  • Pituitary gland
  • Thyroid gland
  • Parathyroid glands
  • Pancreas
  • Adrenal glands
• Pituitary gland


  Often called the master gland because it controls the functions of other endocrine glands, secretes several hormones that affect specific parts of the body
• Hormones secreted by the pituitary gland

  • Human growth hormone (HGH)
  • Thyroid-stimulating hormone (TSH)
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
  • Prolactin
  • Adrenocorticotropic hormone (ACTH)
  • Oxytocin
  • Antidiuretic hormone (ADH)
• Human growth hormone (HGH)


  Promotes the release of insulin-like growth factors (IGFs), maintains muscle and bone mass for growth, helps in healing injuries and repair of tissues
• Thyroid-stimulating hormone (TSH)


  Helps in producing and secreting the thyroid hormones by the thyroid gland
• Follicle-stimulating hormone (FSH)


  Targets the ovaries by initiating the development of the follicles in the ovary, which happens monthly
• Luteinizing hormone (LH)


  Initiates ovulation, also controls the secretion of progesterone (female sex hormone)
• Prolactin


  Affects the mammary glands by initiating and maintaining the production of milk especially during pregnancy
• Adrenocorticotropic hormone (ACTH)


  Responsible for the production and secretion of glucocorticoids, the hormones released by the adrenal gland
• Oxytocin


  Activated during and after giving birth, targets the uterus to cause it to contract during giving birth, also controls milk secretion in the breasts after giving birth
• Antidiuretic hormone (ADH)


  Causes the kidneys to decrease urine production, which helps in conserving more body water, also known as vasopressin
• Hypothalamus


  Gland located in the brain, controls the function of the pituitary gland, secretes hormones that affect the release of some hormones by the pituitary gland
• Hormones secreted by the hypothalamus


  • Thyrotropin-releasing hormone (TRH)
  • Gonadotropin releasing hormone (GnRH)
  • Corticotropin-releasing hormone (CRH)
• Thyroid gland

  Located below the larynx, secretes the hormones thyroxine (T4) and triiodothyronine (T3), also called thyroid hormones, responsible for protein synthesis, regulation of oxygen use, metabolism, and growth and development of the body, also secretes calcitonin which is responsible for maintaining the calcium level in the body
• Parathyroid glands


  Located on the posterior surface of the thyroid gland, secrete the parathyroid hormone which is the major regulator of the calcium, magnesium, and phosphate levels in the blood
• Pancreas


  Located in the duodenum of the small intestine, secretes the hormones insulin and glucagon, which are responsible for regulating the blood sugar level
• Insulin


  Helps in lowering the amount of glucose in the blood when it is too high
• Glucagon


  Helps in increasing the level of glucose in the blood when it is too low
• Adrenal glands


  Located on top of each kidney, adrenal cortex secretes mineralocorticoids, glucocorticoids, and androgens, adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)
• Mineralocorticoids


  Maintain the balance of minerals in the body such as sodium and potassium
• Glucocorticoids


  Break down proteins and triglycerides needed by the body, help in the formation of glucose, have anti-inflammatory effects, cause suppression of immune responses
• Androgens


  Secreted by both males and females, but it is an important hormone especially for females because these are converted into estrogen
• Epinephrine (adrenaline) and norepinephrine (noradrenaline)


  Released during strenuous activities, such as exercise, control the heart rate, blood pressure, blood level, and breathing rate
• Figure 6.4
• After transcription, translation happens. The nucleotide sequence carried by the mRNA will be used in this process.