Organisms Respond to changes in the In/Ex Environments Flashcards
What is a stimulus?
A change in the internal / external environment
What is the function of the co-ordinator?
Formulates a suitable response to a stimulus
What is the function of a receptor?
It detects a stimulus
What is the function of an effector?
Produces a response to a stimulus
What is taxis?
A directional response to a stimulus. The organisms will move directly towards or away from the stimulus
What is kinesis?
A non-directional response to a stimulus. The rate of movement is affected by the intensity of the stimulus i.e move faster / slower or turn more / less frequently.
What is Tropism?
Growth Response to a stimulus that occurs in flowering plants
What are the 2 types of Tropism?
- Phototropism - Response to light
* Gravitropism – Response to Gravity
State 2 features of a reflex action
- Rapid
- Automatic responses
What is the normal 7 stage Reflex arc pathway?
1) Stimulus
2) Receptor
3) Sensory neurone
4) Connector neurone
5) Motor neurone
6) Effector
7) Response
Where does the sensory neurone come from and go to?
From receptor to spinal cord
Where is the Connector neurone located?
Within Spinal Cord
Where does the Motor Neurone come from and go to?
From Spinal Cord to Effector
What is the CNS (Central Nervous system) made up of?
Brain + Spinal Cord
What is the function of Dendrites?
Synapse to / with connector neurones
What is the function of axon?
Very long and it conveys nerve impulses from spinal cord to effector
Structure & Function of Myelin Sheath?
Made from Schwann cells wrapped around the axon. Forms a fatty layer around the axon + increases speed of transmission of the nerve impulses.
What are the Nodes of Ranvier?
Gaps between Schwann cells where ions can move between the cell and tissue fluid
How is a resting potential of -70mV maintained?
- Active transport (needing ATP + Protein carriers), 3Na+ are pumped out for every 2K+ pumped in.
- Facilitated diffusion – K+ diffuse rapidly out of the cell as the membrane is more permeable to K+. Na+ can only diffuse back slowly as membrane is less permeable to Na+.
- Results in tissue fluid outside having more positive ions than inside (negative electrical charge inside than outside) so the membrane is polarised and an electrochemical gradient has been established
Explain the process of depolarisation (graph line sharply increases?
- Membrane becomes more permeable to Na+ ions
- This is due to the Sodium Volted Gated Channels open
- Sodium ions diffuse into the axon
What is the Threshold Value usually?
-40mV
Explain the process of Repolarisation?
- Membrane becomes more permeable to K+ ions
- This is due to the potassium ion Volted Gated Channels open
- Potassium ions diffuse into the axon
Explain the process of Hyperpolarisation?
- Potential difference may overshoot the resting potential
- So Potassium Volted Gated Channels close
- Sodium/Potassium pump restores the resting potential
What is a Nerve Impulse?
The depolarisation of one part of the neurone which sets off the depolarisation of the next section along the entire neurone
What is a Refractory Period?
The time while the membrane is unable to respond to another depolarisation
State 3 factors affecting the speed of conduction
- Myelin Sheath
- Axon Diameter
- Temperature
What is the gap between 2 neurones where synaptic transmission occurs?
Synaptic cleft
How is information conveyed during synaptic transmission?
This is via diffusion of a neurotransmitter
In cholinergic neurones, what is the neurotransmitter?
Acetylcholine
In Adrenergic neurones, what is the neurotransmitter?
Noradrenaline
Explain the 6 events at a synapse?
1) Action Potential arrives at synaptic knob, increasing the permeability of the presynaptic membrane to Calcium ions (Ca2+ channels open) allowing calcium ions to diffuse in
2) Ca2+ make synaptic vesicles move towards and fuse with the presynaptic membrane. Acetylcholine released into synaptic cleft via exocytosis
3) Acetylcholine diffuses across cleft and binds to complementary shaped receptor on the postsynaptic membrane. This causes sodium ion channels to open and sodium ions diffuse in
4) Depolarisation of the postsynaptic membrane takes place; Action Potential started
5) Enzyme, actylcholinesterase, hydrolyses acetylcholine into acetate + chlorine which shuts Na+ channels
6) Products diffuse back across cleft, reabsorbed, resynthesised using ATP into acetylcholine and repackaged into vesicles
This is an excitatory synapse
What is an excitatory synapse?
An action potential is initiated at the postsynaptic membrane
What is meant by an inhibitory synapse?
This is when an action potential is NOT initiated at the postsynaptic membrane. Instead K+ channels open and the membrane becomes hyperpolarised.
What is the function of the synapse?
- Transmit info between neurones
* Pass impulses in one direction (unidirectionality)
Why can impulses only go in one direction?
This is because neurotransmitters can only be released from the presynaptic membrane and receptors are only found on the postsynaptic membrane
What is Temporal Summation?
Several Action Potentials arrive in rapid succession at 1 synaptic knob, a high frequency of impulses = Intense Stimulus. The effect is additive and leads to above threshold = depolarisation at the postsynaptic membrane
What is Spatial Summation?
2 or more Action Potentials arrive at one synapse from different presynaptic neurones at the same time. The effect is additive leading to an above threshold depolarisation at the postsynaptic membrane.
What is the structure of a Neuromuscular Junction?
- Synapse between Motor Neurone & Muscle Fibre (Muscle cell)
- Postsynaptic membrane is the Sarcolemma (muscle fibre membrane)
- Muscle Fibre contains Sarcoplasm (cytoplasm) and bundles of Myofibrils
What is the structure & Function of Myofibrils?
They consist of protein filaments which are involved in Muscle Contraction (More later)
What is the structure of the Sarcolemma?
Folded deeply into muscle fibre forming extensive network of T-tubules
What does the Sarcoplasmic Reticulum contain?
Calcium ions
What is the neurotransmitter at the neuromuscular junction?
Acetylcholine
Where is the action potential initiated at the neuromuscular junction?
Sarcolemma so the muscle contracts
