Repsonding To The Environment Flashcards
Some neurones are myelinated. What does this mean?
They have a myelin sheath, which is an electrical insulator. It is made of a Schwann cell. Between these cells, there are tiny patches of bare membrane called the nodes of Ranvier. Sodium channels are concentrated here. Depolarisation takes place here.
3 factors that affect the speed of conduction of action potentials
Myelination
Axon diameter
Temperature
How are impulses sent along a myelinated neurone
Myelin sheath made up of Schwann cell, between these cells are tiny patches of bare membrane called nodes of Ranvier. Sodium ion channels are concentrated here. Depolarisation only happens at nodes. The neurones cytoplasm conducts enough electrical charge to depolarise next node, so impulse jumps from node to node. Called saltatory conduction, very fast
How are impulses sent in a non-myelinated neurone
The impulse travels as a wave along the whole length of the axon membrane. It is slower than saltatory conduction
How does axon diameter affect the speed on conduction
Action potentials are conducted quicker along axons with bigger diameters as there is less resistance to the flow of ions than in the cytoplasm of a smaller axon. With less resistance, depolarisation reaches other parts of the neurone cell membrane quicker
How does temperature affect the speed on conduction
Speed of conduction increases as the temp increases as ions diffuse faster as they have more energy to move. The speed only increases up to around 40c, after this the proteins begin to denature and speed decreases
What is a synapse
A junction between a neurone and the next cell
The tiny gap between the cells at a synapse is called….
Synaptic cleft
Acetylcholine is a what? What does it do?
Neurotransmitter
It transmits the nerve impulse across a cholinergic synapse
What is a neuromuscular junction
A synapse between a motor neurone and a muscle cell
What do neuromuscular junctions use
Neurotransmitter acetylcholine which binds to cholinergic receptors called nicotinic cholinergic receptors. They work in the same way as the cholinergic synapse but…. The post synaptic membrane has lots of folds that form clefts. These clefts store the enzyme that breaks down acetylcholine. The membrane also has more receptors. When motor neurone fires an action potential, always triggers a response in muscle cell, this isn’t always the case for a synapse between 2 neurones
Neurotransmitters are either ……….. or ………….
Excitatory or inhibitory
Excitatory neurotransmitters info
Depolarise the post synaptic membrane making it fire an action potential of threshold reached. Eg acetylcholine binds to cholinergic receptors to cause an action potential in post synaptic membrane
Inhibitory neurotransmitters info
Hyperpolarise the post synaptic membrane (make the potential difference more negative), preventing it from firing an action potential. Eg GABA, when it binds to its receptors it causes potassium ion channels to open on the post synaptic membrane, hyperpolarising the neurone
What happens if the stimulus is weak
Only a small amount of neurotransmitter will be released from neurone into synaptic cleft. This might not be enough to excite the post synaptic membrane to the threshold potential and stimulate an action potential
What is summation
Where the effect of neurotransmitter released from many neurones (or one neurone that’s stimulated a lot in a short period of time) is added together
What are the 2 types of summation
Spatial and temporal
What is spatial summation
Many neurones connect to 1 neurone. The small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold potential in the post synaptic neurone and trigger an action potential. OR If some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential
What is temporal summation
Where 2 or more nerve impulses arrive in quick succession from the same pre synaptic neurone. Makes an action potential more likely because more neurotransmitter is released into the synaptic cleft
What is the function of summation at synapses
It means that synapses accurately process info
5 examples of how drugs can affect synaptic transmission
Some drugs are the same shape
Some block receptors
Some inhibit the enzyme that breaks down neurotransmitters
Some stimulate the release of neurotransmitter
Some inhibit the release of neurotransmitter
How do drugs that are the same shape affect synaptic transmission
Same shape as neurotransmitters so they mimic their action at receptors. Means more receptors are activated.
How do drugs that block receptors affect synaptic transmission
They block receptors so they can’t be activated by neurotransmitters. Means fewer receptors can be activated
How do drugs that inhibit the enzyme that breaks down neurotransmitters affect synaptic transmission
Inhibit the enzyme so there are more neurotransmitters in the synaptic cleft to bind to receptors and they’re there for longer
How do drugs that stimulate the release of neurotransmitter affect synaptic transmission
Stimulate the release of neurotransmitter from the presynaptic neurone so more receptors are activated
How do drugs that inhibit the release of neurotransmitter affect synaptic transmission
Inhibit the release of neurotransmitter from the presynaptic neurone so fewer receptors are activated
What is a stimulus
Any change in the internal or external environment of an organism
Receptors detect….
Stimuli
They can be cells or proteins on cell surface membranes
Organisms increase their chance of survival by responding to changes in their….
Internal and external Environment
What are effectors
Cells that bring about a response to a stimulus, to produce an effect. Effectors include muscle cells and cells found in glands like the pancreas
How do receptors communicate with effectors
Via the nervous system, the hormonal system or both
The nervous system sends info as…..
Electrical impulses
The nervous system is made up of a ……….
Complex network of cells called neurones
What are the 3 main types of neurone
Sensory neurone
Relay neurone
Motor neurone
What do sensory neurones do
Transmit electrical impulses from receptors to the central nervous system
What do motor neurones do
Transmit electrical impulses from the CNS to effectors
What do relay neurones do
Transmit electrical impulses between the sensory and motor neurones
A stimulus is detected by…
Receptor cells and an electrical impulse is sent along a sensory neurone. When an electrical impulse reaches the end of a neurone, neurotransmitters take the info to next neurone, which sends an electrical impulse. CNS processes the info and decides what to do about it and sends impulses along motor neurones to an effector
Define the central nervous system
Made up of the brain and the spinal cord
Define the peripheral nervous system
Made up of the neurones that connect the central nervous system to the rest of the body. It has 2 different systems, the somatic and the autonomic nervous systems
Define the somatic nervous system
Controls conscious activities like running
Define autonomic nervous system
Controls unconscious activities like digestion. It has 2 divisions that have opposite effects on the body, the sympathetic and parasympathetic nervous systems
Define the sympathetic nervous system
Gets the body ready for action, it’s the ‘flight or fight’ system
Define parasympathetic nervous system
Calms the body down. It’s the ‘rest and digest’ system
When an electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto cells, so the nervous system is…..
Localised
Neurotransmitters are quickly removed once they have done their job, so the response is …….
Short lived
Electrical impulses are really fast, so the response is…..
Rapid, allows animals to react quickly to stimuli
Receptors info
They are Specific, they only detect 1 particular stimulus eg light, pressure. There are many different types of receptor that each detect a different type of stimulus. Some receptors are cells, some are proteins on cell surface membranes
Pacinian corpuscles are….
Mechanoreceptors, they detect mechanical stimuli eg pressure and vibrations. Found in skin
Photoreceptors convert ………. into an ………….
Light
Electrical impulse
What happens during the refractory period
Ion channels recovering, can’t be opened. So period acts as a time delay between 1 action potential and the next. Makes sure action potentials don’t overlap but pass along as discrete (separate) impulses. Period also makes sure action potentials are unidirectional
Action potentials have an all-or-nothing nature. Explain
Once threshold potential is reached, action potential will always fire with same change in voltage no matter how big the stimulus. If threshold isn’t reached, action potential won’t fire, this is the all-or-nothing nature of action potentials. A bigger stimulus won’t cause a bigger action potential but will cause them to fire more frequently
What is a gland
A group of cells that are specialised to secrete a useful substance such as a hormone
What are hormones
Chemical messengers. Many hormones are proteins or peptides, some are steroids
What can glands be stimulated by
A change in conc of a specific substance or by electrical impulses
What are chemical mediators
Chemicals that are released from certain mammalian cells and have an effect on cells in their immediate vicinity. They are typically released by infected or injured cells and cause small arteries and arterioles to dilate. Leads to a rise in temp and swelling of the affected area (called inflammatory response)
What are 2 examples of chemical mediators
Histamine and prostaglandins
Histamine info
Chemical mediator, stored in certain white blood cells, released following injury or in response to an allergen eg pollen. Causes dilation of small arteries and arterioles and increased permeability of capillaries allowing more immune system cells to move out of blood to infected or injured area
Prostaglandins info
Chemical mediator, found in cell membranes, case dilation of small arteries and arterioles. Their release following injury increases permeability of capillaries. Also affect blood pressure and neurotransmitters. They affect pain sensation
Flowering plants increase their chance of survival by responding to changes in their …….
Explain
Environment
They sense the direction of light and grow towards it to maximise light absorption for photosynthesis. They sense gravity so their roots and shoots grow in the right direction. Climbing plants have a sense of touch, so they can find things to climb and reach the sunlight
What is tropism
The response of a plant to a directional stimulus (a stimulus coming from a particular direction)
What is a positive tropism
Growth towards the stimulus
What is a negative tropism
Growth away from the stimulus
What is phototropism
Growth of a plant in response to light
What is geotropism
Growth of a plant in response to gravity
Plants respond to stimuli using….
Growth factors
What are growth factors
Chemicals that speed up or slow down plant growth
Where are growth factors produced
In the growing regions of the plant (eg shoot tips, leaves) and they move to where they’re needed in the other parts of the plant
Give 2 examples of a growth factor and what they do
Gibberellin- Stimulates flowering and seed germination
Auxin- stimulates the growth of shoots by cell elongation (where the cell walls become loose and stretchy so the cells get longer. The shoots grow towards the light for photosynthesis. However, High conc of auxins inhibit growth in roots
Example of type of auxin and what it does
IAA, produced in tips of shoots in flowering plants. It is moved around the plant, via diffusion and active transport over short distances and via the phloem over long distances, to control tropisms. Results in different parts of the plants having different amounts of IAA. The uneven distribution means uneven growth of plant. Plant grows towards light for photosynthesis
Control of heart rate involves which 2 things
Brain
Autonomic nervous system
What is a reflex
Where the body responds to a stimulus without making a conscious decision to respond
What is the importance of a reflex
It helps organisms to avoid damage to the body as the response is so rapid
What is a reflex arc
The pathway of neurones linking receptors to effectors in a reflex
The pathway of neurones linking receptors to effectors is called…
A reflex arc
A simple reflex arc involves 3 neurones. These are…
Sensory, relay, motor neurones
Example of a simple reflex arc in hand withdrawal response to heat
Thermo receptors in skin detect heat stimulus
Sensory neurone carries impulses to relay neurone
Relay neurone connects to motor neurone
Motor neurone sends impulses to effector (biceps muscle)
Muscle contracts to stop hand being damaged
What do simple responses do to simple/mobile organisms. Examples of responses
Simple responses keep simple/mobile organisms in a favourable environment
Eg taxes and kineses
Taxes info
Organisms move towards or away from a directional stimulus
Eg woodlice show tactic response to light (photo taxis), they move away from light source. Helps them survive as keeps them concealed under stones during day and in damp conditions
Kineses info
Organisms movement is affected by a non directional stimulus
Eg woodlice show a kinetic response to humidity. In high humidity they move slowly and turn more often so that they stay where they are. As air gets drier they move faster and turn less often so they move into a new area. Response helps woodlice move from drier air to more humid air and then stay there. This improves their survival chances as it reduces water loss and helps keep them concealed
Skeletal muscle is made up of….
Long muscle fibres
Muscles are stimulated to contract by…
Neurones
Skeletal muscle info
Also called striated muscle, type of muscle used to move. Made up of large bundles of long cells called muscle fibres. The cell membrane of muscle fibre cells is called the sarcolemma. Bits of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm (a muscle cells cytoplasm). Folds are called transverse tubules and help to spread electrical impulses throughout the sarcoplasm so they reach all parts of muscle fibre. Network of internal membranes called sarcoplasmic reticulum runs through sarcoplasm. Sarcoplasmic reticulum stores and releases calcium ions that are needed for muscle contraction. Muscle fibres have a lot of mitochondria to provide the ATP needed for muscle contraction. They are multinucleate. Muscle fibres have lots of long cylindrical organelles called myofibrils, these are made of protein
Thick myofilaments are made from which protein
Myosin
Thin myofilaments are made of which protein
Actin
Muscle contraction is triggered by what
An influx of calcium ions
What are the 3 main ways that ATP is generated during muscle contraction
Aerobic respiration
Anaerobic respiration
ATP-phosphocreatine system
Which 2 things provide energy for muscle contraction
ATP and phosphocreatine
In a myelinated neurone, why does depolarisation only happen at the nodes of Ranvier
This is where the sodium ions can get through the membrane
You can use an optical microscope and a slide of stained muscle tissue to find the diameter of one of the muscle fibres. Explain how
Measure field diameter using ruler
Estimate number of fibres to cover diameter
How do chemical mediators reach the cells they affect
Diffuse directly to where they are needed
How are synapses uni-directional
Acetylcholine is released from the presynaptic membrane
Diffusion from high to low conc
Receptors only on post synaptic membrane
Name the process by which IAA moves from growing regions to other tissues
Diffusion
