Second messenger system

The steps in the second messenger system:

• Start with a peptide hormone, like GH, binding to a membrane bound receptor.
  
• The binding causes a shape change and binding to a G-protein complex in the ICF.
  
• Inducing a shape change to the G-protein complex which releases GDP (guanosine diphosphate) from α subunit and binds to GTP. Causing α subunit with attached GTP (guanosine triphosphate) to break free.
  
• Α subunit then attaches to adenylate, cyclase inducing a shape change, which recruits ATP to attach to the AC.
  
• The AC brakes off two of the phosphate groups from the ATP to create cAMP (the second messenger).
  
• cAMP binds to PKA causing PKA (protein kinase A) to change shape
  
• When PKA changes shape it scoops up ATP and removes a phosphate group changing it to ADP.
  
• PKA then transfers the phosphate to key enzymes to induce mitosis.
  

This is the process peptide hormones go through to induce their effects on the body.

Endocrine system

The endocrine system releases hormones into the blood that control the bodies' activities. The endocrine system works more slowly than the nervous system. Most hormones enter the interstitial fluid and then the bloodstream. They exert their effects by binding to the target cells. There are two chemical classes of hormones, lipid-soluble and water-soluble. The receptors for lipid-soluble hormones are located inside the cell and water-soluble receptors are part of the plasma membrane. Lipid soluble hormones take longer to affect the body than water-soluble but the affects last longer.

The pituitary gland has two sections, the anterior pituitary made up of epithelial cells and the posterior pituitary made up of neuronal cells which are both controlled by the hypothalamus. The anterior pituitary hormones are stimulated by releasing hormones and suppressed by inhibiting hormones from the hypothalamus. These hormones reach the pituitary through the hypophyseal portal system. A portal system is when blood flows from one capillary network through a portal vein and then to another capillary network without passing through the heart. The hormones of the anterior pituitary are human growth hormone (Hgh), Thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), adrenocorticotropic hormone (ACTH), and melanocyte-stimulating hormone (MSH). The posterior pituitary does not synthesize hormones but it does store and release two hormones, oxytocin (OT) and antidiuretic hormone (ADH). The hypothalamus, neurosecretory cell produce these hormones. All these pituitary hormones are water-soluble.

The thyroid gland consists of the right and left lobes and the isthmus connecting the two lobes. The thyroid produces and secretes Triiodothyronine (T₃), Thyroxine (T₄), and calcitonin (CT). The production of T₃ and T₄ is controlled by TSH released by the anterior pituitary gland. Calcitonin is controlled by the levels of Ca²⁺ in the blood through a negative feedback system. When Ca²⁺ levels are high calcitonin inhibits the action of osteoclasts. The parathyroid glands are embedded in the posterior surface of the lateral lobe of the thyroid. The hormone they produce and secrete is the parathyroid hormone (PTH). Low Ca²⁺ levels in the blood stimulate the parathyroid gland to release PTH. This has the opposite effects of calcitonin on the Ca²⁺ levels in the blood.

The adrenal glands consist of the adrenal cortex and the adrenal medulla. The adrenal cortex is divided into three zones, the zona glomerulosa, zona fasciculate, and zona reticularis. The zona glomerulosa produces and secrets aldosterone to increase reabsorption of Na⁺ and H₂O and stimulate the excretion of K⁺. Zona fasciculate produces and secretes cortisol and cortisone. This increases protein breakdown, stimulates gluconeogenesis and lipolysis, and depresses immune system. The zona reticularis secreates androgens (mainly dehydroepiandrosterone or DHEA). We do not know what induces DHEA but it is turned into estrogen after menopause in females. The adrenal medulla hormones are epinephrine and Norepinephrine which are released by post-ganglionic neurons of the sympathetic division of the ANS.

Pancreas have alpha cells that secrete the hormone glucagon, beta cells that secrete insulin and delta cells that secrete somatostatins. Glucagon raise blood glucose levels, insulin lowers glucose levels and somatostatins regulate levels of glucagon and insulin.

The ovaries produce estrogen and progesterone and the testes produce testosterone. Estrogen and progesterone along with gonadotropic hormones regulate the female reproductive cycle, maintain pregnancy, prepare the mammary glands for lactation and promote development and maintenance of female secondary sex characteristics. Testosterone stimulates decent of testes before birth, regulates spermatogenesis, and promotes development and maintenance of male secondary sex characteristics.

Cranial Nerves I through VIII

This week we covered anatomy of the brain and spinal cord and the blood flow to and from the brain. We the first Discussed seven cranial nerves; The Olfactory I, Optic II, Oculomotor III, Trochlear IV, Trigeminal V, Abducens VI, Facial Nerves VII.

Cranial nerves III, IV and VI are all motor nerves that pass through the Superior Orbital Fissure and control movement of the muscles that move the eyeball and eyelids. The Oculomotor nerve III controls the Superior Rectus, Inferior Rectus, Inferior Oblique and the Medial Rectus muscles of the eye. The Trochlear nerve IV controls the Superior Oblique muscle of the eye. The Abducens nerve VI controls the Lateral Rectus muscle of the eye.

Cranial Nerves I, II, and VIII are all sensory nerves with afferent impulses. The Olfactory Nerve I function is the sense of smell and passes through the Olfactory Foramina of the cribriform plate of the Ethmoid bone. The Optic nerve II is for vision and passes through the Optic Foramen of the Sphenoid bone. The Vestibulocochlear nerve VIII conveys impulses related to equilibrium and hearing and passes through the Internal Acoustic Meatus of the Temporal bone.

Cranial nerve V, the Trigeminal nerve, is a mixed nerve and has three branches, the Ophthalmic, Maxillary, and the Mandibular branch. The Ophthalmic (V1) branch passes through the Superior Orbital Fissure and is a sensory nerve. It has axons in the skin of the forehead, nasal cavity, upper eyelid, and eyebrow. The Maxillary (V2) branch is also sensory and passes through the Foramen Rotundum of the sphenoid bone. It has axons in the Superior lip, superior gums superior teeth, and palate. And the Mandibular (V3) branch is both motor and sensory and passes through the Foramen Oval of the sphenoid bone. The sensory axons are found in the inferior lip, inferior gums, and inferior teeth. The motor axons are found in the Masseter, Temporalis, and the Pterygoids muscles.

If you're still awake I applaud you. Because that is about the most boring read there is so I'm not going to put in the pathway the blood flows to the brain. And I can't think of anything in my life that I can relate to the cranial nerves

Autonomic Nervous System

The ANS consists of the parasympathetic Nervous System and the Sympathetic Nervous System. The impulses are all efferent to the effector tissue. The Parasympathetic Nervous System stimulates the rest and digests response. The cranial nerves associated with it are the Oculomotor nerve III, Facial Nerve VII, Glossopharyngeal Nerve IX, and the Vagus nerve X. There are two neurons in ANS pathways, Preganglionic neurons and postganglionic neurons, to the effector tissues. Preganglionic neurons of the ANS always release the neurotransmitter Ach. In the Parasympathetic division they have long axons, and the postganglionic neurons also release Ach and have short axons. Preganglionic neurons of the Sympathetic division are short, and postganglionic neurons are long and release Norepinephrine or epinephrine. The Adrenal medulla is part of the Sympathetic division but the postganglionic neurons release Epinephrine, Norepinephrine, and dopamine directly into the blood stream. These neurotransmitters bind to Muscarinic receptors on the effector tissue. These are secondary messenger systems and are found in the membrane of Cardiac Muscle cells, Smooth Muscle cells, and glands.

I was diagnosed with IBS last year due to a prolonged period of cronic diarrhea. I did have all the symptoms of IBS but I noticed when I was on vacation the symptoms went away and the medicine they gave me did nothing. So I believe this was due to prolonged high levels of stress. When we talked about cortisol levels being high with long term stress it made wonder if cortisol could cause that.

week 2

We went into more detail about the action potential of a neuron in this class. There are chemically regulated and voltage regulated ion channels. chemically regulated channels open with the binding of a chemical NT. This allows a controlled number of ions to influx. Whereas voltage regulated channels are activated at a certain depolarizing voltage and allows a massive influx of ions. this massive influx creates a positive feedback system opening more VR channels.
When the positive charge reaches the synaptic bulb calcium channels open and push the synaptic vesicles to the membrane where they are released into the synaptic cleft. the amount of NT released into the SC depends on the amount of calcium in the ECF, which is regulated by astrocytes. There are many factors that determine if a neuron reaches action potential. The total excitatory effects must be greater than the inhibitory effects to a degree that the neuron is able to reach its threshold (Spacial summation). The neuron could also be stimulated by rapid and frequent release of NT (temporal summation).

Schwan cells are also important to the speed of the conduction. They wrap around the axons of the neurons in the PNS. One schwan cell around one axon and and there are multiple schwan cells that wrap around the neuron. Schwan cells insulate the axon creating a fast signal conduction. When an axon becomes damaged in the PNS the schwan cells go through mitosis extending the axon so it can repair its connection. The neuron cells of the CNS are wrapped by oligodendrocytes. one oligodendrocyte wraps many CNS neurons. because of this the neurons of the CNS are not able to repair axons when they are damaged.

I can see how carpal tunnel syndrome occurs. the nerves to the hand become damaged or inflamed from the repetitive movements and you start to lose feeling, movement or strength. that's why the brace helps. it gives your nerves time to heal without further damage. but I' not sure how the stretches would help.

week 1 neurons

This week we discussed the anatomy of a neuron, types of neurons, and how they send and receive electrochemical signals. The three different structural types of neuron are unipolar (sometimes called pseudounipolar), bipolar and multipolar. A neuron has three categories of potential; resting potential, graded/local/receptor potential, or action potential. For a neuron to go from resting to graded potential a neurotrasmitter must bind to a dendrite. This allows Na+ ions to trickle into the neuron. if the signal is strong enough and the ICF reaches -55mv the neuron will reach action potential. This causes the axon hillock to open up and allow a massive rush of Na+ ions in, that flow down the axon. The positive charge causes the permeability of the synaptic bulb to change allowing an influx of calcium ions. the calcium causes the synaptic vessels to move to the membrane and burst, releasing neurotransmitters into the synaptic cleft. These NT then bind to another neuron. This process is responsible for all your bodies perceptions, behaviors, memories, and movements.
For the last year or so I have noticed pain, tingling, and loss of strength in my hands when I am on the computer or doing a lot of writing. I was aware that it was the beginning of carpal tunnel syndrome but didn't know what was the actual cause of the pain and loss of strength. after reading the text I now know its due to the myelin sheath being damaged or the nerves being squeezed and irritated. I try to remember to stretch my hands every now and then while i am working but I usually forget until they start to hurt. The stretching does help and if I do it regularly my hands will return to normal.