Homeostasis Flashcards
State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that can carry rapid electrical impulses
The nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS), and contains cells called neurons that carry rapid electrical impulses.
Draw and label a diagram of the structure of a motor neuron
- dendrites
- cell body with nucleus
- axon
- myelin sheath
- nodes of Ranvier
- motor end plates
State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons
Sensory neurons - receptors to CNS
Relay neurons - within CNS
Motor neurons - CNS to effectors
Define the resting potential and action potential (depolarization and repolarization)
Resting potential
- electrical potential across plasma membrane of cell (eg. neuron) that is not conducting a pulse
- maintained by active transport and negative ions
- electrical potential of -70mV
• Na-K pumps use ATP to pump out 3Na+ for every 2K+ in
• establish electrochemical gradient (+ve outside, -ve inside)
• [-] organic molecules (eg. proteins, aa, phosphates) and Cl- are in cytoplasm
Action potential
- momentary reversals (depolarization) and restoration (repolarization) of electrical potential across plasma membrane
Explain how a nerve impulse passes along a non-myelinated neuron (axon)
A. Resting Potential - neuron’s initial state (-70mV)
B. Threshold Level - sufficient level of electrical stimulation causes depolarization of entire axon
- Na+ enter cell body by stimulation of dendrites
- frequent signals from another cell
- local currents in axon
C. Depolarization - cytoplasm net +ve while outside net -ve
- voltage-gated ion Na+ channels open
• Na+ diffuse into neuron down concentration gradient
• reversal of charges
- local currents occur when Na+ diffuses to next segment of axon
• Na+ gates along axon open as currents move
- +30mV electrical potential
D. Repolarization - restoration of net -ve inside and net +ve outside
- begins once inside is net +ve
- Na+ gates close so K+ gates open
• K+ diffuses out of neuron down concentration gradient
E. Refractory period/Undershoot - time required (1-2ms) before neuron can send another impulse
- resting potential restored by Na-K pumps
- inside cytoplasm is too negative until electrochemical gradient re-established
Explain the principles of synaptic transmission
- junctions between 2 neurons is a synapse
- plasma membranes separated by fluid-filled synaptic cleft
- neurotransmitters are chemicals that pass messages from pre- to post-synaptic neuron
- Nerve impulse reaches end of pre-synaptic neuron
- Depolarization of membrane opens Ca+ gates
- Vesicles of neurotransmitters fuse with membrane, releasing into synaptic cleft by exocytosis
- Neurotransmitter diffuses across cleft, binding to receptors on post-synaptic membrane
- Receptors (transmitter-gated ion channels) open; [+] ions diffuse into neuron, depolarizing membrane
- Depolarization passes down neuron as action potential
- Neurotransmitter in cleft broken down to prevent continuous transmission (ie. acetylcholine broken down by cholinesterase); Ca+ pumped out of pre-synaptic neuron
State that the endocrine system consists of glands that release hormones that are transported in the blood
The endocrine systems contains glands that release hormones (transported in blood)
State that homeostasis involves maintaining the internal environment at a constant level or between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance
Homeostasis involves maintaining the internal environment at a constant level or between limits
- blood pH (7.35)
- CO2 concentration
- blood glucose concentration (0.1%)
- body temperature (37 degrees C)
- water balance
Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms
- constant monitoring and feedback maintains a dynamic equilibrium (remain stable within fluctuating limits)
- negative feedback monitors levels of variables and activates mechanism to restore internal conditions to original state
• prevents large changes - changes always causes opposite effect
- Monitor (sensor/receptor)
- in organs
- receive signals
- send messages to integrator
eg. increased CO2 detected by chemoreceptors in brain stem - Coordinating Centre (integrator)
- receives informationfrom receptor and relays to regulator
eg. brain sends message to respiratory muscles - Regulator (effector)
- restores normal balance
eg. diaphragm and intercostal muscles contract more often to reduce CO2 levels
Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering
- thermoregulation is maintenance of body temperature within a range
- hypothalamus monitors blood temperature and compares it to a set point (37 degrees C)
- if higher/lower, sends signal to body parts making them respond (return temperature to normal)
- responses affect rate of heat production, transfer, and loss
- Response to chilling
- skin arterioles narrow to bring less blood to skin
- shunt vessel opens so less blood flows through capillaries
- temperature of skin drops so less heat is lost
- rapid contraction of skeletal muscles to generate heat (shivering)
- sweat glands do not secrete, skin is dry - Response to overheating
- skin arterioles widen so more blood flows through
- shunt vessel close so heat move from core to skin through capillaries
- temperature of skin rises so more heat is lost
- skeletal muscles are relaxed so no heat generated
- sweat glands secrete large amounts so skin is damp; water evaporates for cooling effect
Explain the control of blood glucose concentration, including the roles of glucagon, insulin and alpha and beta cells in the pancreatic islets
- increase/decrease in blood glucose results in decrease/increase in levels (ie. change causes opposite)
- pancreas monitors level and uses hormones to ensure concentration stays in normal limits
- Role of glucagon
- hormone produced by alpha islets in pancreas
- cause liver/muscle cells to metabolize glycogen into glucose
- release glucose into blood
- increase of blood glucose in response to low levels (eg. during heavy exercise) - Role of insulin
- hormone produced by beta islets in pancreas
- cause liver/muscle cells to absorb glucose from blood
- stores glucose as glycogen in cytoplasm
- decrease of blood glucose in response to high levels (eg. after eating)
- stimulates other cells to use glucose instead of fat for cellular respiration
Distinguish between type I and type II diabetes
- diabetes mellitus is when control of blood does not work and concentration rises/falls beyond normal limits
Type I
- onset during childhood
- beta cells produce insufficient insulin
- injections control glucose levels
- diet cannot control condition
Type II
- onset after childhood
- target cells insensitive to insulin
- injections unnecessary
- low carbohydrate diets control condition
State that hormones are chemical messengers secreted by endocrine glands into the blood and transported by the blood to specific target cells
Hormones are chemical messengers secreted by endocrine glands into blood and transported to specific target cells
State that hormones can be steroids, proteins and tyrosine derivatives, with one example of each
Steroids - estrogen, progesterone, testosterone
Proteins - PSH, LH, insulin
Tyrosine derivatives - thyroxin, epinephrine
Distinguish between the mode of action of steroid hormones and protein hormones
Steroids
- amphipathic, enter target cells through plasma membrane
- bind to receptors in cytoplasm to form hormone-receptor complex
• move to nucleus and attaches to DNA
• regulate gene transcription
Proteins
- water insoluble, cannot enter target cells
- bind to receptor in plasma membrane
• release of secondary messenger inside cell
• activation/inhibition of enzymes
