A2 - Unit 1 - Communication and homeostasis Flashcards
Give 4 ways organisms can change their internal environment in order to survive
Blood glucose concentration
Internal temperature
Water potential
Cell pH
Give 4 ways organisms can change their external environment in order to survive
Humidity
External temperature
Light intensity
New or sudden sound
Why is coordination needed in an organism
Organisms have become specialised to perform specific functions, and different cells perform different functions
In order for the organism to work effectively these different functions need to be in coordination
What is homeostasis?
Coordination in order to maintain a relatively constant internal environment
What can cells do during cell signalling??
Transfer signals locally e.g. Between neurones at synapses (signal used is called a neurotransmitter)
Transfer signals across large distances, using hormones e.g. Cells of pituitary glad secrete ADH which acts on the kidneys
How do plants coordinate?
Plant stems grow towards a light source to maximise photosynthesis rate
Achieved through use of plant hormones
Describe the cell body in a neurone
Contains the nucleus surrounded by cytoplasm
Large amounts of ER and mitochondria involved in the production of neurotransmitters
These are chemicals used to pass signals from one neutrons to the next
Describe the dendrons in a neurone
Short extensions which comes from the cell body
Extensions divide into smaller and smaller branches known as dendrites
Responsible for transmitting electrical impulses towards the cell body
Describe the axons in a neuron
Singular elongated nerve fibres that transmit impulses away from the cell body
Fibres can be very long
Transmit impulses from the tips of the toes and fingers to the spinal cord
Cylindrical in shape
Very narrow region of cytoplasm surrounded by a plasma membrane
What are the three types of neurone?
Sensory
Relay
Motor
What is a sensory neurone?
Transmit impulses from a sensory receptor cell to a relay neurone, motor neurone, or the brain
They have one dendron
Carries the impulse to the cell body and one axon which carries the impulse away from the cell body
What is a relay neurone?
Transmit impulses between neurones e.g. Between sensory neurones and motor neurones
Have many short axons and dendrons
What are motor neurones?
Transmit impulses from a relay neurone or sensory neurone to an effector, such as a muscle or a glad
They have a long axon and many short dendrites
What route does the typical nervous response impulse travel?
Receptor- sensory neurone - relay neurone - motor neurone - effector cell
Describe the structure of myelinated neurones
Neurones are covered in a myelin sheath, made of many layers of plasma membrane
Schwann cells produce the thin layers of membrane, growing around the axon many times
Schwann cells stop growing when there’s 20 layers of membrane
Insulating layer
What is the node of Ranvier?
The gaps in the myelin sheath
Allows the electrical impulse to ‘jump’ from one node to the next
Allows the impulse to be transmitted much faster
How does an electrical impulse travelling through an non myelinated neurone differ to a myelinated neurone?
Myelinated, the impulse jumps across the neurone from one node of Ranvier to the other
Non myelinated impulse travels continuously along the nerve fibre much slower
What are the 4 different types of receptor??
Mechanoreceptor
Chemoreceptor
Thermoreceptor
Photoreceptor
Where are mechanoreceptors on the body?
Skin
Where are chemoreceptors on the body?
Nose
Where are thermoreceptor on the body?
Tongue
Where are photoreceptors in the body?
Eye
What is a transducer?
It converts a stimulus into a nerve impulse
What are pacinian corpuscles?
Specific sensory receptors that detect mechanical pressure
Located deep in the skin
Abundant in fingers and soles of the feet
What is a stimulus?
Any change in the environment that causes a response
What is a response?
A change in behaviour or physiology as a result of a change in the environment
What condition can affect how enzymes efficiently work?
Temperature
pH
An aqueous environment
Freedom from toxin and excess inhibitors
What are the two major systems of communication that work by cell signalling?
The neuronal system
The hormonal system
How does the neuronal system work?
Interconnected network of neurons that signal to each other across synapse junctions
The neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly
How does the hormonal system work?
Uses the blood to transport its signals
Cells in an endocrine organ release the signal directly into the blood
Carried all over the body but is only recognised by specific target cells
Hormonal system enables longer-term responses to be coordinated
What is negative feedback?
A process that brings about a reversal of any change in conditions
It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change
Give 6 conditions that the body needs to keep constant
Body temperature Blood glucose concentration Blood salt concentration Water potential of the blood Blood pressure Carbon dioxide concentration
What three processes must occur in order to maintain a constant internal environment?
Any change to the internal environment must be detected
The change must be signalled to other cells
There must be a response that reverses the change
What pathway has to happen for negative feedback to work effectively?
Stimulus —> receptor —> communication pathway (cell signalling —> effector —> response
What structures are needed for the negative feedback pathway to work?
Sensory receptors e.g. temperature receptors, glucose concentration receptors
Communication system e.g. nervous system, hormonal system
Effector cells e.g. liver cells or muscle cells
What is positive feedback?
A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis
How does the Pacinian corpuscule convert mechanical pressure into a nervous impulse
In normal state, sodium ion channels in the sensory neurones membrane are too narrow to allow sodium ions to pass through
Neurone of the Pacinian corpuscule has a resting potential
When pressure is applied to the Pc it changes shape. Causes the membrane surrounding its neurone to stretch
When membrane stretches, sodium ion channels widen. Sodium can now diffuse into the neurone
Influx of sodium ions changes the potential of the membrane
Becomes depolarised
Results in a generator potential
In turn, generator potential creates an action potential (a nerve impulse) that passes along the sensory neurone
Give 4 features of the synaptic knob
Many mitochondria
Large amount of smooth endoplasmic reticulum
Vesicles of a chemical called acetylcholine
Voltage-gated calcium ion channels in the membrane
What happens in the transmission of an action potential across a synapse
Action potential arrives
Voltage-gated calcium ion channels open
Calcium ions diffuse into synaptic knob
Calcium ions cause synaptic vesicles to move to and fuse with the presynaptic membrane
Acetylcholine is released by exocytosis
AcH molecules diffuse across the cleft
AcH binds to receptor sites on the sodium ions channels in the postsynaptic membrane
Sodium ion channels open
Sodium ions diffuse across the postsynaptic membrane into the postsynaptic neurone
Generator potential or excitatory postsynaptic potential (EPSP) is created
If sufficient generator potentials combine then the potential across the postsynaptic membrane reaches the threshold potential
New action potential is created in the postsynaptic neurone
What is acetlycholinesterase
An enzyme in the synaptic cleft
It breaks down the transmitter substance acetlycholine into ethanoic acid and choline
Stops the transmission of signals so that the synapse does not continue to produce action potentials
What happens to ethanol and choline after they have been broken down by acetlycholinesterase?
They are recycled
Re-enter the synaptic knob by diffusion and are recombined to acetylcholine using ATP from respiration
What is summation?
A term that refers to the way that several small potential changes can combine to produce one larger change in the potential difference across the membrane
Why might several presynaptic neurones cover one postsynaptic neurone?
Allows signals from different parts of the nervous system to create the same response
Useful where several different stimuli are warning us of danger
Why might one presynaptic neurone diverge into several postsynaptic neurones?
Allows one signal to be transmitted to several parts of the nervous system
Useful in a reflex arc
One postsynaptic neurone elicits the response while another informs the brain
How do neurones ensure that signals are transmitted in one direction?
Only the presynaptic knob contains vesicles of acetylcholine
What is acclimatisation?
After repeated stimulation a synapse may run out of vesicles containing the transmitter substance
Synapse is said to be fatigued
Means nervous system no longer responds to the stimulus
Helps to avoid overstimulation
What are hormones??
Molecules that are released by endocrine glands directly in the blood
Act as messengers carrying a signal from the endocrine glad to a specific target organ or tissue
What is an endocrine gland? Yeah
A gland that secretes hormones directly into the blood
What is an exocrine gland?
A gland that secretes molecules into a duct that carries the molecules to where they are used
What are target cells?
Those that possess a specific receptor on their plasma membrane
The shape of the receptor is complimentary to the shape of the hormone molecule
Many similar cells together form a tissue
That is adenyl cyclase?
An enzyme associated with the receptor for many hormones including adrenaline
Found on the inside of the cell surface membrane
What is an ectotherm?
An organism that relies on external sources of heat to regulate its body temperature
Why is it important to maintain and regulate body temperature?
Temperature can have a dramatic effect on the structure of your proteins including enzymes
Without the proper function of these enzymes in your body, it wouldn’t be able to work at all!