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Cellular communication and recognition:
-Glycoproteins from the plasma membrane act as unique identifiers for cells. These glycoproteins can be called antigens.
-Cells communicate by binding to the glycoproteins using specific shaped receptors.
-Cells can also secrete cytokines (chemical signals) which again bind to specific shaped receptor molecules to elicit certain cellular behaviour.
Homeostasis:
Simply put, homeostasis is the constant maintenance of an internal environment. This includes water, pH, temperature etc, and is often controlled by negative feedback loops.
How homeostasis is achieved:
Sensory receptors: Specific shaped proteins/glycoproteins/glycolipids which detect changes in the internal conditions. Examples include osmoreceptors (water), baroreceptors (pressure) and chemoreceptors (pH).
Effectors: Glands or muscles which when active can help carry out the negative feedback loop and bring equilibrium about and provide a response. Examples can be the pituitary gland or hair erector muscles.
Neuronal/hormonal system: The system to which the sensory receptor passes the message to, in order to carry it to the effector in question.
Nervous vs Hormonal:
Nervous: Faster action due to electrical impulses, shorter acting.
Hormonal: Slower action due to chemical messenger in blood, longer acting.
Cell A
Cell B
= Antigen (glycoprotein)
= Receptor
Temperature is regulated by negative feedback
Negative feedback is opposing the change made to equilibrium and bringing about the original state
Thermoregulation in endoderm's using the hypothalamus:
As mentioned, homeostasis, this case in the regulation of temperature, requires receptors in the form of thermoreceptors, and a neuronal system (the hypothalamus) to coordinate the signal to the effector(s). The neuronal signals are transmitted to the effectors which include hair erector muscles, sweat glands, arterioles and skeletal muscles.
Temperature too high: Hair erector muscles relax so hairs lie flat, sweat glands produce sweat which absorbs heat from blood by radiation, arterioles dilate.
Temperature too low: Hair erector muscles contract raising hairs. This traps a layer of still warm air that reduces heat loss by radiation, shivering by contraction of skeletal muscles raises the mean kinetic energy of cells and generates heat, vasoconstriction reduces diameter of arterioles. Sweat glands inactive.
Control of heart rate through the medulla oblongata:
Heart rate must be increased and decreased for many different reasons. High CO2 concentration (from exercise) or low pH from the CO2 dissolving in the blood as carbonic acid, or low blood pressure are three examples of why heart rate might be increased. Adrenaline can also cause this.
Increase in heart rate: Impulses are sent from the sinoatrial node to the medulla oblongata via a neurone. Once the signal is processed by the MO, impulses are sent along the accelerator nerve (sympathetic nervous system) back to the sinoatrial node to increase rate of contraction.
Decrease in heart rate: Impulses are sent from the SA node to the MO, and then down the vagus nerve to the SA node to decrease heart rate.
Receptors involved:
-pH of blood detected by chemoreceptors.
-Pressure of blood measured by baroreceptors.
-Movement of muscles detected by stretch receptors.
-Adrenaline detected by adrenergic receptors
The fight-or-flight response: Adrenaline mechanism of action
When a potentially dangerous stimulus is detected, a hormone called adrenaline is released in the endocrine system (carried in the blood). Outcomes of adrenaline secretion involve widening of the pupils, the inhibition of the digestive system and increased blood flow/stroke rate volume.
It binds to and interacts with adrenergic receptors present on the walls of cells. Binding of adrenaline activates the membrane-bound enzyme adenylate cyclase, which converts ATP to cAMP. cAMP acts as a secondary messenger and triggers a cascade of intracellular events, such as the activation of kinase enzymes (PKA) which phosphorylate specific targets. Since cAMP is the secondary messenger, adrenaline is the primary messenger.
The Brain: Structure and Function:
Cerebrum: Main area of the brain, made out of two hemispheres (left and right, separated by the corpus callosum). Within these hemispheres, there are different lobes which control different things. The occipital lobe controls visual signals, the temporal lobe processes auditory signals. The parietal lobe processes orientation movement and some forms of memory.
Cerebellum: Small area of the brain which controls muscle movement and balance.
Hypothalamus: Controls temperature regulation and is also used in making hormones for the pituitary gland.
Medulla oblongata: Found at the base of the brain, the MO controls speeding up or slowing down of the heart rate.
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