6.5 Nerves, Hormones And Homeostasis Flashcards
State the two main parts of the Nervous System
Central Nervous System (CNS) and Peripheral Nervous System (PNS)
Outline the function of the Central Nervous System
- It is the processing centre of the nervous system
* Receives information from and sends information to the peripheral nervous system
Outline the function of the Peripheral Nervous System
- Sensory (afferent) neurons receive stimulus and send information to central nervous system
- Motor (efferent) neurons receive information from central nervous system and react to stimulus
State the three main types of neurons found in the Nervous System
- Sensory Neurons
- Relay Neurons
- Motor Neurons
Outline the function of Sensory Neurons
Conduct nerve impulses from receptors to the CNS (afferent pathway)
Outline the function of Relay Neurons
Conduct nerve impulses within the CNS (also called interneurons or connector neurons)
Outline the function of Motor Neurons
Conduct nerve impulses from the CNS to effectors (efferent pathway)
Outline the pathway of a reaction from stimulus to response.
Stimuli → Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector → Response
Define Resting Potential
The electrical potential across the membrane when the neuron is not firing, maintained by sodium-potassium pumps
Define Action Potential
The electrical potential across the membrane when the neuron is firing
Define Depolarisation
The change from a negative resting potential to a positive action potential, caused by opening of sodium channels
Define Repolarisation
The change from a positive action potential back to a negative resting potential (caused by opening of potassium channels)
Describe the state of a neuron at resting potential
• Na+ ions are concentrated outside the cell, K+ ions are concentrated inside the cell.
• The sodium-potassium pump (Na+/K+ pump) maintains the electrochemical gradient of the resting potential (-70 mV).
– Sodium ions are pumped out, potassium ions are pumped in.
– It expels 3 Na+ ions for every 2 K+ ions admitted.
Describe the state of a neuron in action potential
DO THIS
Define Synapse
A synapse (synaptic clef) is the physical gap between two neurons. It is between the axon terminal of the pre-synaptic neuron and the dendrite of the post-synaptic neuron.
Describe the process of chemical transfer across a synapse
- Action Potential reaches the axon terminal, triggering the opening of voltage-gated calcium channels
- Calcium ions diffuse into the cell, forming vesicles containing neurotransmitters
- Neurotransmitters released from the axon terminal by exocytosis and cross the synaptic clef
- Neurotransmitters binds to neuroreceptors (on the post synaptic neuron)
- Ligand gated sodium channels open
- Enzyme may be released into the synapse by post-synaptic neuron to breakdown the neurotransmitter
– Neurotransmitter may be recycled by reuptake pumps
Describe the function of neurotransmitters
When a neurotransmitter binds to a receptor on the post-synaptic neuron, the cell’s excitability is changed: it is either more or less likely to fire an action potential. If the number of excitatory post-synaptic events is large enough, the “message” will continue.
Outline an Endocrine Gland
A ductless gland in the endocrine (hormonal) system which secretes hormones directly into the bloodstream
Describe the function of hormones
A hormone is a chemical released by a cell, a gland, or organ in one part of the body which affects cells in other parts of the organism. They act as chemical messages. Hormones help control bodily activities and cause changes to metabolic processes. They typically tend to control slow, long term process such as growth and sexual development.
Outline how hormones are transported throughout the body
Hormones are secreted into the bloodstream by endocrine glands. They are then transported indiscriminately (through the entire blood stream) to their specific target organ/s.
Define Homeostasis
The process by which the internal conditions of an organism are maintained within narrow limits
List 5 factors maintained through homeostasis
Blood pH CO2 levels Blood glucose concentration Body temperature Water balance
Define Homeotherm
Homeotherms are organisms that are able to maintain a constant internal environment, even with dramatic changes to the external environment (e.g. mammals)
Outline the process of a negative feedback loop
- A detector detects the changes
- A control unit coordinates this information, and directs that actions which should be taken to rectify the problem
- An effector responds to the change with a response, equal in amount, and opposite in direction
Describe an example of a negative feedback loop
- Body temperature rises above normal
- Detectors send messages to the nerves in the hypothalamus
- Hypothalamus responds by informing blood vessels to dilate
- Heat is lost in the surrounding environment
- Temperature returns to acceptable level
- Hypothalamus detects return to equilibrium
- The message to dilate the vessels ceases
Define Negative Feedback
The process by which a process self-regulates. The consequences of a response ends the process carried out that response.
Outline the role of the hypothalamus in maintaining body temperature
The hypothalamus acts as the control centre for thermoregulation by detecting fluctuations in body temperature
List three responses to an increase in body temperature
Vasodilation
Sweating
Decreased Metabolism
Explain how Vasodilation aids in reducing body temperature
The skin arterioles dilate, bringing blood closer to the skin and allowing for greater transfer of heat (convective cooling)
Explain how Sweating aids in reducing body temperature
Sweat glands release sweat, which evaporates, taking with it heat, and thus cooling the skin (evaporative cooling)
Explain how a Decreased Metabolism aids in reducing body temperature
Leads to decreased heat production
List three responses to a decrease in body temperature
Vasoconstriction
Shivering
Increased Metabolism
Explain how Vasocontriction aids in increasing body temperature
The skin arterioles constrict, moving blood away from the skin, meaning less heat is lost over the surface
Explain how Shivering aids in increasing body temperature
Muscles begin to shake in small movements (spasm), creating heat through friction
Explain how an Increased Metabolism aids in increasing body temperature
Leads to increased heat production
Explain how Piloerection aids in maintaining body heat
Animals with furry coats make their hair stand on end, trapping pockets of warm air close to the body surface
Describe the function of Insulin
- Insulin is released from beta cells in the pancreas
- Causes a decrease in blood glucose concentration
- This may involve stimulating glycogen synthesis in the liver (glycogenesis), promoting glucose uptake into the liver or increasing the rate of glucose breakdown (increase cell respiration)
Describe the function of glucagon
- Glucagon is released from alpha cells in the pancreas
- Causes an increase in blood glucose concentration
- This may involve stimulating glycogen breakdown in the liver (glycogenolysis), promoting glucose release from the liver or decreasing the rate of glucose breakdown (decrease cell respiration)
State a response to high blood glucose concentration
Release of insulin
State a response to low blood glucose concentration
Release of glucagon
Compare insulin dependancy in Type I and Type II diabetes
Type I: Insulin-Dependant Diabetes Mellitus (IDDM)
Type II: Non Insulin-Dependant Diabetes Mellitus (NIDDM)
Compare onset of Type I and Type II diabetes
Type I: Usually during childhood (early onset)
Type II: Usually during adulthood (late onset)
Compare effects of Type I and Type II diabetes
Type I: Body does not produce sufficient insulin
Type II: Body does not respond to insulin
Compare the causes of Type I and Type II diabetes
Type I: Caused by destruction of beta cells (autoimmune)
Type II: Insulin receptors become insensitive to insulin due to overexposure
Compare treatments for Type I and Type II diabetes
Type I: Requires insulin injections to regulate glucose levels
Type II: Can be controlled with physical exersise and a carefully monitored diet
Define Diabetes
A condition in which a person’s blood glucose level is too high
