Communication and homeostasis Flashcards
What is a change to an internal or external environment called?
Stimulus
What detects a stimulus?
Receptors
What are effectors?
Cells that bring a response to a stimulus (muscle cells)
What are photoreceptors?
Receptor cells that that connect to the nervous system
How do receptors and effectors communicate?
Cell signalling
What is the biological word for nearby?
Adjacent
What is homeostasis?
The maintenance of a constant internal environment
What happens to enzymes if the body temp is too high?
Become deantured - molecules vibrate too much - breaks hydrogen bonds - active site shape changes
What happens to enzymes if body temp is too low?
Enzyme activity reduced - Slows metabolic reactions
What is a humans optimum temperature?
37°c
What does the homeostatic system involve?
Receptors
What does the communication system involve?
Effectors
What type of feedback is the controlling of body temperature? Why?
Negative feedback - too hot/cold means effectors respond to decrease/increase temp
What is positive feedback useful for in protecting the body?
To rapidly activate something - blood clot after an injury
What are sensory neurones?
Transmitting nerve impulses from receptors to CNS
What is the CNS?
Central nervous system - brain and spine
What are motor neurons?
Transmit nerve impulses from CNS to effectors
What a relay neurones?
Transmit nerve impulses between sensory and motor neurones
What is the pathway of impulses? (5 steps)
1) Stimulus
2) Receptors
3) CNS
4) Effectors
5) Response
What do sensory receptors do?
Convert the energy of a stimulus into electrical energy
What does sensory receptors act as? And what is that?
Transducers - convert one form of energy into another
What is voltage known as?
Potential difference
What is the potential difference called when a cell is at rest?
Resting potential
What is the change in potential difference due to a stimulus called?
The generator potential
What does a bigger stimulus do?
Excites the membrane more, causes a bigger movement of ions and a bigger change in the potential difference
What happens if the generator potential is big enough?
It will trigger an action potential along the neuron
How is a generator potential being big enough determined?
If the generator potential reaches above the threshold level
What are pacinian corpuscles?
Mechanoreceptors - they detect mechanical stimuli and they are found in your skin
What is the sensory nerve of a pacinian corpuscle wrapped by?
Connective tissue called lamellae
Where is the cell body on a sensory neurone?
In the middle between the dendron and the axon
Where is the cell body on a motor neuron?
On the left of the axon
Where is the cell body on a relay neuron?
In the middle surrounded by an axon and dendrites
What charge is the outside of the membrane when a neuron is at a resting state?
Positively charged
What is the voltage of the membrane at resting potential?
-70 mV
How is the resting potential created?
By sodium-potassium pumps and potassium ion channels
What ions does the sodium-potassium pump transport?
Three sodium ions out and two potassium ions in
What ions does the potassium ion channel transport? and how?
Potassium ions out of the neuron by facilitated diffusion
What does a stimulus trigger to open?
Sodium ion channels to open
What is the 5 step sequence of an action potential?
1) Stimulus
2) Depolarisation
3) Repolarisation
4) Hyperpolarisiation
5) Resting potential
What is step 1 of an action potential and what happens in it?
Stimulus - this excites the neurone cell membrane and causes sodium on channels to open. Sodium ions diffuse into the neurone. Inside of the neurone becomes less negative.
What is step 2 of an action potential and what happens in it?
Depolarisation - if the potential difference reaches the threshold value Then voltage – gated sodium ion channels open. More sodium ions diffuse into the neuron.
What is the threshold value?
-55 mV
What sort of process is depolarisation?
Positive feedback
What is step 3 of an action potential and what happens in it?
Repolarisation - when potential difference is +30, sodium are on channels close. Voltage – gated potassium ion channels open. Potassium ions diffuse out and membrane it begins to return to its resting potential.
What sort of process is repolarisation?
Negative feedback
What is step 4 of an action potential and what happens in it?
Hyperpolarisation - Potassium ion channels are slow to close, so too many potassium ions diffuse out of the neuron. Potential difference becomes more negative negative than the resting potential.
What is step 5 of an action potential and what happens in it?
Resting potential - ion channels are reset. The sodium-potassium pump returns the membrane to its resting potential.
What is the period between the beginning of repolarisation and the beginning of the resting potential called?
The refractory period
Why can’t there be another action potential straight after one?
The refractory period is occurring
How does an action potential move along the neuron?
A wave of depolarisation- sodium ions diffuse sideways, meaning that ion channels in the next region open and causes a wave to travel along the neurone.
Describe the impulses of small and big stimulus’.
A small stimulus will have less frequent action, potentials, and a big stimulus would have more frequent action potentials
What do myelinated neurons do to action potentials?
Speed up the action potential
What is a myelin sheath?
An electrical insulator made up of Schwann cells
What are nodes of Ranvier?
Tiny patches of membrane where the myelin sheath isn’t present - sodium ion channels are located here
What is saltatory conduction?
Where the cytoplasm of myelinated neurones conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node very fast
Why are non-myelinated neurons slower?
Because the impulse travels along the whole length of the axon membrane
What is a synapse?
The junction between a neuron and another neuron
What is the gap between the cells at the synapse?
The synaptic cleft
What part of the neuron contains vesicles?
The end of the pre-synaptic neuron - the synaptic knob
When are neurotransmitters released into the synaptic cleft?
When an action potential reaches the end of a neuron
What are the three outcomes of a neurotransmitter binding to a receptor?
1) trigger an action potential
2) cause muscle contraction
3) cause a hormone to be secreted
Why doesn’t the response keep happening after the neurotransmitters have been secreted into the cleft?
Neurotransmitters are removed from the cleft by the pre-synaptic neuron and broken down
What are the two examples of neurotransmitters?
Acetylcholine and noradrenaline
What are signups is that use Acetylcholine called?
Cholinergic synapses
What is the enzyme that breaks down acetylcholine called?
Acetylcholinesterase (AChE)
What are three steps of neurotransmitters transmitting nerve impulses between neurons?
1) an action potential triggers a calcium influx
2) A calcium influx causes a neurotransmitter release
3) the neurotransmitter triggers an action potential in the post synaptic neuron
How do calcium ions? Enter enter enter the pre and post synaptic neurons?
Voltage gated sodium ion channels
What is an excitatory synapse?
Neurotransmitters depolarise the post synaptic membrane - this fires an action potential if the threshold is reached
What is an inhibitory synapse?
Neurotransmitters bind to receptors on the post-synaptic membrane and hyper polarise it, preventing an action potential from being fired
How do synapses allow information to be dispersed? What is this called?
One neuron connects to many neurons and disperses the message to different parts of the body - Synaptic divergence
How do synapses allow information to be amplified? What is this called?
Many neurons connect to one neuron - synaptic convergence
What is summation?
The effect of neurotransmitters can be combined
What is spatial summation?
Neurons converge meaning the small amount of neurotransmitter released from each neuron can be enough altogether to reach the threshold
What is temporal summation?
Two or more nerve impulses arrive in quick succession from the same neuron - action potential is more likely
How do you signup is ensure impulses are only transmitted one way?
Receptors are only located on the post-synaptic membranes
What are endocrine glands?
A group of cells that are specialised to secrete hormones
What are hormones?
Chemical messengers, that are usually proteins, peptides or steroids
When are hormones secreted?
When an endocrine gland is stimulated by either an electrical impulse or a change in the concentration of a specific substance
Where do hormones go?
Directly into the blood and taken around the body by the circulatory system
Where do hormones end up?
They bind to specific receptors found on the membranes of target cells
What is the five step hormonal system?
1) stimulus
2) receptors
3) hormone
4) effectors
5) response
What is the first messenger in the hormonal system? Why?
The hormone - it carries the message from the endocrine gland to the receptor on the target cell
What happens when a hormone binds to its receptor?
It activates an enzyme in the cell membrane
What does the enzyme released after a hormone bind to its receptor do?
Catalyses the production of a signalling molecule inside the cell
What does a signalling molecule do?
Activates a cascade of events - carries the chemical message from the receptor to the other parts of the cell
Describe the steps of the hormone adrenaline working.
1) adrenaline binds to specific receptors
2) this activates adenylyl cyclase
3) adenylyl cyclase catalyses the production of cAMP
4) cAMP activates a cascade of events to make more glucose available (glycogen to glucose)
Where are adrenal glands located?
Above your kidneys
What is the structure of an adrenal gland?
An inner part called the medulla and an outer part called the cortex
What does the cortex of an adrenal gland do? Give an example
Secretes steroid hormones when you’re stressed - cortisol
What does the medulla of an adrenal gland do? Give an example.
Secrets catecholamine hormones when you’re stressed - adrenaline and noradrenaline
What type of responses do the steroid hormones from the cortex produce?
Short and long-term responses
What type of responses do the hormones in the medulla produce?
Short term responses
What type of gland is the pancreas?
And endocrine gland
Describe how the pancreas functions.
Islets of langerhans Secrete hormones directly into the blood to help control blood glucose concentration
What are the two cells that make up the islets of langerhans and what do they secrete?
Alpha cells that secrete glucagon hormone and beta cells that secrete insulin hormone
How can you differentiate between alpha and beta cells?
If a special stain has been used to make them different colours
Once the special stain is used, how can you tell apart alpha and beta cells?
Alpha cells are pink stained and beta cells are purple stained
What are ectotherms?
Reptiles and fish that can’t control their body temperature internally
What are endotherms?
Mammals and birds that can control their body temperature internally by homeostasis
How do ectotherms control their temperature? Give an example.
By altering their behaviours - reptiles gain heat by basking in the sun
How can endotherms control their body temperature? Give two examples.
Internally by homeostasis, but also by altering behaviour such as finding shade to cool down
What is the metabolic rate of an ectotherm?
Variable and they generate little heat themselves
What is the metabolic rate of an endotherm?
Constantly high and they generate a lot of heat from metabolic reactions
What are the three mechanisms to reduce a mammal body temperature?
1) sweating
2) hairs lying flat
3) vasodilation
How does sweating reduce body temperature?
The water in sweat evaporating takes heat from the body
How does hair lying flat reduce body temperature?
Less air is trapped meaning that the skin is less insulated
How does vasodilation reduce body temperature in mammals?
Arterioles near surface of the skin dilate - causes more blood to flow through capillaries in the surface layer of the dermis - resulting in heat loss from the skin by radiation
What are the five mechanisms to increase the body temperature of mammals?
1) shivering
2) much less sweat
3) hairs stand up
4) vasoconstriction
5) hormones
How does shivering increase body temperature?
More heat is produced from the increased respiration as a result of muscle spasms
How does much less sweat increase body temperature?
Less sweat secreted means heat loss is reduced
How does hair standing up increase body temperature?
Has standing up traps more air and prevents heat loss
How does vasoconstriction increase body temperature?
Arterioles near the surface constrict so less blood flows through the capillaries and reduces heat loss
How do hormones increase body temperature?
Adrenaline and thyroxine increase metabolism so more heat produced
How do hairs stand up and lie flat?
Erector pilli muscles contact and relax
What part of the brain is responsible for controlling body temperature in mammals?
The hypothalamus
What is the name of the temperature receptors responsible for giving information to the hypothalamus?
Thermoreceptors
What do firmer receptors in the hypothalamus detect?
Internal temperature - the blood
What do Thermo receptors in the skin detect?
External temperature - temperature on the skin
What are the thermoreceptors on the skin called?
Peripheral temperature receptors
What happens to blood glucose concentration after eating food containing carbohydrates?
Blood glucose concentration rises
What happens to blood glucose concentration after exercise?
Blood glucose concentration falls - glucose used in respiration
What does insulin do?
Lowest the blood glucose concentration when it’s too high
How does insulin lower blood glucose concentration?
1) defines two specific receptors on liver and muscle cells
2) increases permeability of cell so cell takes up more glucose
3) Cells store glycogen in the cytoplasm via glycogenesis
How is glycogen formed?
By insulin activating glycogenesis to convert glucose to glycogen
What does glucagon do?
Raises blood glucose concentration when it’s too low
How does glucagon raise blood glucose concentration?
1) glucagon binds to specific receptors on the liver cells
2) glucagon, activates enzymes that breaks down glycogen to glucose
3) glycogenolysis occurs
4) Glucagon also promotes formation of glucose from glycerol and amino acids
What is glycogenolysis?
The breaking down of glycogen to glucose
What is the process of forming glucose from non-carbohydrates called?
Gluconeogenesis
What occurs in gluconeogenesis?
Glycerol and amino acids are converted to glucose
What type of feedback does insulin and glucagon trigger?
Negative feedback
How do beta cells secrete insulin?
1) when blood glucose concentration is high, more glucose enters the beta cells
2) high glucose causes rate of respiration to increase - more ATP
3) Potassium ions can’t get through membrane, so they build up inside cell
4) inside of the cell becomes less negative (potassium positive) so membrane is depolarised
5) calcium ion channels open
6) vehicles containing insulin fuse with membrane and release by exocytosis
What is diabetes?
A condition where blood glucose concentration can’t be controlled properly
What is the main difference between type one diabetes and type two diabetes?
Type one is where the body attacks and destroys beta cells and type two is where beta cells can’t produce enough insulin or when the body doesn’t respond properly to insulin
What age group does type one diabetes usually develop in?
Children or young adults
What are the three treatment types for type one diabetes?
1) insulin therapy - injections
2) islet cell transplantation
3) monitoring their diet (balanced diet and regular exercise)
What age group does type two diabetes usually develop in?
Later in life than type one
Why don’t the body cells respond properly to insulin in type two diabetes?
Insulin receptors on their membranes don’t work properly so the cells don’t take up enough glucose
What are the three treatment options for type two diabetes?
1) lifestyle changes
2) medication
3) insulin therapy - injections
What sort of lifestyle changes would be required in type two diabetes?
Healthy eating and regular exercise
What is the main example of a medicine that can be prescribed for type two diabetes? How does it work?
Metaformin - it acts on liver cells to reduce the amount of glucose they release into the blood and also increases the sensitivity of cells to insulin so more glucose can be taken up
How did insulin used to be extracted?
From pancreases of pigs or cattle to treat type one diabetes
How is insulin produced nowadays?
Genetically modified bacteria
Why is using genetically modified bacteria to produce insulin better than extracting from animal pancreases?
• It is cheaper
• Larger quantities can be produced
• It is more ethical
• GM bacteria produces human insulin, which is more effective than pig or cattle insulin
How could stem cells be used to cure diabetes?
Because stem cells are unspecialised and can develop into any type of cell, they could be grown into beta cells and then implanted into the pancreas of a person with type one diabetes
