Coordination Flashcards
What are the two main forms of coordination in mammals?
The nervous system and the hormonal system.
Describe the coordination of the nervous system.
Uses nerve cells to pass electrical impulses along their length. They stimulate their target cells by secreting neurotransmitters directly onto them. -> rapid communication + responses produced are often short-lived and restricted to a localised region of the body
Describe the coordination of the hormonal system.
Produces hormones that are transported in the blood plasma to their target cells, which they then stimulate. Results are slower, less specific form of communication between parts of an organism. Responses are often long-lasting and widespread.
What are two examples of chemical mediators?
Histamine and prostaglandins
Histamine
Stored in certain white blood cells and released following injury or in response to an allergen. Causes dilation of small arteries and arterioles and increased permeability of capillaries, leading to localised swelling, redness and itching.
Prostaglandins
Found in cell membranes also cause dilation of small arteries and arterioles. Released following injury increases the permeability of capillaries. They also affect blood pressure and neurotransmitters -> pain sensation
Features of plant growth factors
- Exert their influence by affecting growth
- Made by cells located throughout the plant
- Some plant growth factors affect the tissues that release them rather than acting on a distant target organ
What is an example of a plant growth factor?
Indoleacetic acid (IAA)
Outline the control of tropisms by IAA in a plant shoot
- Cells in the tip of the shoot produce IAA, which is then transported down the shoot
- The IAA is initially transported to all sides as it begins to move down the shoot
- Light causes the movement of IAA from the light side to the shaded side of the shoot
- A greater conc. of IAA builds up on the shaded side of the shoot
- As IAA causes elongation of cells and there is a greater conc. on shaded sides, cells on this side elongate more
- The shaded side of the shoot grows faster, causing the shoot to bend towards the light
Neurones
Specialised cells adapted to rapidly carrying nerve impulses from one part of the body to another
What is a mammalian neurone made of?
A cell body, dendrons, an axon, Schwann cells, myelin sheath, nodes of Ranvier
Cell body of a neurone
contains a nucleus and a large amounts of RER prod. neurotransmitters + proteins
Dendrons
Small extensions of the cell body which subdivide into dendrites, carry nerve impulses towards cell body
Axon
Single long fibre that carries nerve impulses away from cell body
Schwann cells
Surround the axon, protecting it and providing insulation. Carry out phagocytosis + play a part in nerve regeneration. Wrap themselves around the axon many times, so that layers of their membranes build up around it.
Myelin Sheath
Forms a covering to the axon and is made up of the membranes of the Schwann cells. Membranes are rich in a the lipid, myelin.
Nodes of Ranvier
Gaps between adjacent Schwann cells were there is no myelin sheath.
Sensory neurone
One dendron that carries the impulse towards the cell body and one axon that carries it away from cell body
Motor neurone
Long axon and many short dendrites
Intermediate neurones
Numerous short processes
Outline the transition from a resting potential to an action potential
- Resting potential some K+ voltage-gated channels are open but Na voltage gated channels are closed
- Energy of stimulus causes some Na voltage-gated channels in axon membrane to open and => Na+ diffuses into the axon along electrochem. gradient. This triggers a reversal in p.d. across membrane
- As Na+ diffuses into the axon, more sodium channels open causing an even greater influx of Na+ by diffusion
- Once action potential of around +40mV is reached, voltage gates on Na+ channels close and voltage gates on K+ channels begin to open
- With some K+ voltage-gated channels open, the electrical gradient that was preventing further outward movement of K+ ions is now reversed, causing more K+ channels to open. , repolarising the axon
- The outward diffusion of K+ causes a temp. overshoot of the electrical gradient, with the inside of the axon being more negative than usual (hyperpolarisation). Gates on K+ channels now close and the activities of the Na-K pumps once again cause Na+ to be pumped out and K+ in. Axon is repolarised.
Passage of an action potential along a myelinated axon
In myelinated axons, the fatty sheath of myelin around the axon acts as an electrical insulator, preventing action potential from forming. Action potentials occur at nodes of Ranvier. -> localised circuits arise between adjacent nodes of Ranvier -> saltatory conduction.
Nerve impulse
transmission of the action potential along the axon of a neurone
How does the diameter of the axon affect the speed at which an a.p. travels?
The greater the diameter of an axon, the faster the speed of conductance. This is due to less leakage of ions from a large axon, leakage makes membrane potentials harder to maintain.
How does temperature affect the speed at which an a.p. travels?
rate of diffusion, respiration -> atp, atp-> enzymes in Na+ K+ pump and active transport
What is the refractory period?
When it is impossible for a further action potential to be generated due to shut Na voltage-gated channels
What 3 purposes does the refractory period serve?
- Ensures that an a.p. is propagated in one direction only
- It produces discrete impulses
- It limits the number of action potentials
What is the all or nothing principle?
Any stimulus, whatever strength, below the threshold value will fail to generate an a.p. and any above the threshold value will succeed in generating an a.p. no matter how much above the threshold value it will still only generate 1 a.p.
How can an organism perceive the size of a stimulus?
- the number of impulses passing in a given time
2. by having different neurones with different threshold values
What is the importance of reflex actions?
- Involuntary
- Protect from harmful stimulus
- Role in homeostasis
- Posture/balance
- Finding food
Why are there more hormones than neurotransmitters?
Hormones reach all cells, NT’s are direct to target cell. Different hormones are specific to different target cells.
Differences between a cholinergic synapse and neuromuscular junciton
- Neurone to neurone and neurone to muscle
- Action potential in neurone and no action potential in muscle/ sarcolemma
- No summation in muscle
- muscle response always excitatory (never inhibitory);
- some neuromuscular junctions have different neurotransmitters
Why is the rate of conduction of nerve impulse in myelinated neurones in mammals faster than in reptiles?
Higher body temperature so faster diffusion of ions
