Communication and Homeostasis Flashcards
What is the purpose of homeostasis?
- animals increase their chances of survival by responding to external stimuli like changes in their external environment
- they also respond to internal changes to maintain optimum conditons for thier metabolism
What is a stimulus?
- Any change in the internal or external environment is called a stimulus
What are receptors and how do they work?
- a receptor detects stimuli, they are extremely specific and tend to detect a particular stimulus.
- some receptors are cells while some are proteins on cell surface membranes
What are effectors?
Effectors are cells that bring about a response to a stimulus, to produce an effect. Effectors can be glands or muscles.
What happens for the body to produce a response?
To produce a response, receptors need to communicate with effectors which in turn may need to communicate with other cells. This happens via cell signalling.
How is cell signaling used in producing a response?
Cell signaling can occur between adjacent or distant cells.
- nervous system cells use chemicals calle neurotransmitters in the form of cell signalling between adjacent neurones
- hormone system uses secreted hormones which travel in the blood to distant cells
What is homeostasis?
Homeostasis involves control systems that keep your internal environment roughly constnat. This is important as it is vital for cells to function normally and to stop them from being damaged.
What is the optimum internal temperature in humans?
37 degrees
Why is thermoregulation particularly important?
It is important to maintain the right core body temperature. This is because temperature affects enzyme activity, and enzymes control the rate of metaboic reactions.
What is the process of negative feedback?
Receptors detect when a level is too high or too low and the information is communicated through the nervous or hormonal system to effectors which bring the level back to normal
When can negative feedback sometimes not work?
When the change is too extreme sometimes the negative feedback process cannot sucessfully bring it back to nromal levles. e.g a sudden drop in internal temperature to hypothermic levels cannot be easily brought back to normal
What is positive feedback and how does it work?
Positive feedback mechanisms are when the body amplifies the change to further increase the level from the normal level.
e.g increase platelets in blood when injured.
Positive feedback is useful to rapidly activate somethng
Why is positive feedback not used in homeostasis?
It doesn’t keep your internal environment constant.
What is the nervous system?
It is a complex network of cells called neurones that work in electrical communication throughout the body to transfer information
What do sensory neurons do?
Sensory neurones transmit nerve impulses from receptors to the central nervous system
What do motor neurones do?
Motor neurones transmit nerve impulses from the CNS to the effectors
What do relay neurones do?
Relay neurones transmit nerve impulses between sensory neurones and motor neurones
What is the passage a nerve impuse makes throughout the nervous system?
- stimulus
- receptors detect the stimulus
- the sensory neurone transmits an electrical impulse to the CNS
- the CNS with the relay neurone decides what to do with the information recieved
- the motor neurone transmits an electrical impulse to the effector
- the effector brings about a response
- response
Why do we need different receptors for different forms of stimuli?
Different stimuli have different forms of energy. However your nervous system only sends information in the form of nerve impulses.
What do sensory receptors do and why are they considered transducers?
Sensory receptors convert the energy of a stimulus into electrical energy. So, sensory receptors act as transducers.
What is a transducer?
Something that converts one form of energy into another
What is a nervous system receptor like in it resting state?
In its resting state it is not being stimulated, there is a difference in charge between the inside and outside of the cell. This difference creates a voltage which is called a potential difference.
What is resting potential-generator potential conversion process?
When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell which alters the potential difference. This change in potential difference is called the generator potential
What causes a bigger generator potential to be formed?
A bigger stimulus excited the membrane more, causing a bigger movement of ions and a bigger change in potential difference, so a bigger generator potential is formed?
How do generator potentials lead to an action potential?
If the generator potential is big enough it’ll trigger an action potential along a neurone. An action potential is only triggered if the generator potential reaches a certain level called the threshold level.
What happens when a stimulus is too weak?
If the stimulus is too weak the generator potential wont reach the threshold, so there’s no action potential.
What is the general structure of neurones?
All neurons have:
- cell body
- dendrites/dendrons towards the cell body
- axons away from the cell body
What is the structure and function of a sensory neurone?
Sensory neurons have short dendrites and one long dendron to carry nerve impulses from receptor cells to the cell body, and one short axon that carries impulses from the cell body to the CNS
What is the structure and function of a relay neurone?
Motor neurones have many short dendrites that carry nerve impulses from the central nervous system to the cell body, and one long axon that carries nerve impulses from the cell body to effector cells.
What is the structure and function of a motor neurone?
Relay neurones have many short dendrites that carry nerve impulses from sensory neurones to the cell body, and one axon that carries nerve impulses from the cell body to motor neurones
Which neurones are myelinated?
Only relay neurones are not myelinated as they are so short it wouldn’t make much difference in the speed of the electrical impulse.
What is a neurones resting state?
This is the state of a neurone when it isn’t being stimulated. The outside of the membrane is positively charged compared to the inside. This is because there are more positive ions outside of the cell than inside. (polarised membrane)
What is the value for a neurones resting state?
around -70 mv
How is a neurones’ resting potential and state maintained?
It is regulated by sodium-potassium pumps and potassium ion channels in a neurones membrane.
How do do sodium-potassium pumps maintain resting potential?
The pumps move 3 sodium ions out of the cell for each 2 potassium ions entering. As the sodium ions cannot diffuse back in this creates an electrochemical gradient as the inside of the cell membrane is more negative than the outside. The membrane also becomes even more negative as potassium ions diffuse out of the membrane via potassium ion channels as the membrane is permeable to these ions.
What are the steps in a neurone to develop an action potential in response to a stimulus?
- The stimulus causes the sodium ion channels to open so the membrane is more permeable to sodium ions and there is an influx into the cell. This makes the inside membrane less negative
- If it reaches the threshold level, the voltage gated ion channels open and even more sodium ions move in as a form of positive feedback. (Depolarisation)
- When a potential difference of around 30 mv is reached the sodium ion channels close and the potassium channels open so potassium ions diffuse out of the neurone as an attempt to get the membrane back to its negative resting state. (Repolarisation)
- As the potassium ion channels are slow to close there is a slight overshoot so too many potassium ions have left and the membrane is too negative. (hyperpolarisation)
- The sodium-potassium pump helps return the membrane back to its original resting potential until it’s excited by another stimulus.
Why can the neurone not be excited again directly after an action potential?
The ion channels are recovering and they can’t be made to open. This period of recovery is called the refractory period.
What is the same across all action potentials?
An action potential will always fire with the same change in voltage, no matter how big the stimulus is.
What actually is an action potential?
When an action potential happens some of the sodium ions diffuse sideways which causes sodium channels in the next region to open and sodium ions to diffuse into that area. This causes a wave of depolarisation to travel along the neurone. The wave more away from the aprts of the membrane in the refractory period because these parts can’t fire an action potential.
What happens to an action potential if the threshold is not reached?
If the threshold isn’t reached, an action potential won’t fire. This is the all-or-nothing nature of action potentials.
How will a bigger stimulus affect the neurone?
A bigger stimulus won’t cause a bigger action potential, but it will cause them to fire more frequently- and the brain identifies this and will response accordingly.
What is the purpose of the myelin sheath in neurones?
The schwann cells are made of lipids which act as an electrical insulator. Between the cells are small patches of bare membrane called nodes of ranvier where there is a high concentration of sodium ion channels.
How do myelinated neurones work with saltatory conduction?
The neurones cytoplasm conducts enough electrical charge to depolarise the next node so the impulse jumps from node to node which makes transmission really fast.
What is a synapse?
A synapse is the junction between a neurone and another neurone or between a neurone and an effector cell.
What is the synaptic cleft?
The tiny gap between the cells at a synapse is called the synaptic cleft
What is the presynaptic neurone?
This is the neurone before the synapse and it has a swelling called a synaptic knob. This contains synaptic vesicles filled with chemicals called neurotransmitters.
