Nervous co-ordination and Muscles (complete) Flashcards
Summarise the differences between the nervous system and the hormonal system
Nervous system -
> Communication is by nerve impulses
> Transmission is by neurones and very rapid
> Nerve impulses travel to very specific parts of the body
> Response is localised and rapid but short-lived.
> Effect is temporary and reversible.
Hormonal system -
> Communication if by hormones.
> Transmission is by blood system and relatively slow
> Hormones travel to all parts of body, but only target cells respond.
> Response is widespread and long-lasting but slow.
> Effect is permanent and irreversible.
Name the three types of neurone that are involved in. reflex arc
- Sensory neurone
- Motor neurone
- Relay (intermediate) neurone
Describe sensory neurones
- transmit nerve impulses from a receptor to an intermediate or motor neurone.
- the have one dendron that is very long and it carries the impulse towards the cell body and one axon that carries it away from the cell body.
Describe motor neurones.
- transmit nerve impulses from an intermediate neurone to an effector.
- have a long axon and many short dendrites.
Describe an intermediate neurone
- transmit nerve impulses between neurones.
- they have numerous short dendrons.
How is a resting potential established?
- 3 Na+ ions are actively transported out of the axon by the sodium potassium pumps.
- 2 K+ ions are actively transported into the axon by the sodium potassium pimps.
- More +vely charged ions move out of the axon than into, therefore there is an overall positive charge outside.
- Some K+ ions may diffuse back out of the axon due to their downward concentration gradient and some potassium channels being open.
How is an action potential formed?
- A stimulus provides energy and causes some Na+ channels to open, allowing an influx of sodium ions into the axon along their electro-chemical gradient, triggering reversal in the potential difference across the membrane.
- As sodium ions diffuse into the axon, more sodium ion channels open, allowing for a larger influx by diffusion.
- once action potential is established (threshold exceeded) the sodium channels close and potassium channels begin to open.
- potassium ions then diffuse out of the axon, starting the repolarisation of the axon. Hyperpolarisation occurs when too many potassium ions move out of the axon, so the potassium channels close and resting potential is re-established.
Describe how the passage of an action potential changes along a myelinated axon.
- The myelin sheaths act as electrical insulators, so the action potential ‘jumps’ between the gaps between the myelin sheaths (Node of Ranviers).
- This allows the passage to be much quicker as not as much room for the action potential to need to pass along.
What are the factors that affect the speed of the nerve impulse and how?
- Myelin sheath; increases speed of conductance of action potential.
- Diameter of axon; greater axon diameter = faster speed of conductance due to less ions leakage from large axon.
- Temperature; higher temp = higher diffusion rate of ions = faster nerve impulse and increased efficiency of enzymes.
Describe the all-or-nothing principle
- The threshold (certain level of stimulus) must be reached to trigger the action potential.
- If not reached, no action potential reached.
How can the size of a stimulus be perceived?
- the number of impulses passing in a given time.
- different neurones with different threshold values.
What is the refractory period?
- The time after an action potential which leads back to the resting potential.
- Another action potential cannot be initiated in that part of the axon until the resting potential is restored.
What is the purpose of the refractory period?
- Ensuring action potentials are propagated in one direction.
- Ensures action potentials are separate.
- Limits number of action potentials.
What are the functions of synapses?
What do they enable?
- Act as junctions between one neurone and the next, allowing:
> A single impulse along one neurone to be transmitted to a number of different neurones at a synapse, enabling a single stimulus to create a number of simultaneous responses.
> A number of impulses to be combined at a synapse, allowing stimuli from different receptors to interact in order to produce a single response.
What are the different types of summation?
- Spatial summation
- Temporal summation
Describe spatial summation
- Multiple presynaptic neurones lead to one postsynaptic neurone, so multiple presynaptic neurones need to pass on the action potential for threshold to be reached.
- If only one presynaptic neurone passes on action potential, unlikely threshold will be reached so no action potential re-formed.
Describe temporal summation
- A single presynaptic neurone leads to a single postsynaptic neurone, so a higher frequency of action potentials (larger stimulus) are needed to reach threshold and pass on the action potential further.
- Not a large enough stimulus and action potential is not passed on as threshold not reached.
Describe how inhibition of synapses occurs.
- Presynaptic neurones releases neurotransmitter that binds to Cl- protein channels on the postsynaptic neurone, causing the channels to open, allowing diffusion of Cl- ions into postsynaptic neurone by facilitated diffusion.
- Binding of neurotransmitter also causes opening of nearby K+ protein channels, allowing K+ ions to move out of postsynaptic neurone.
- This combine effect results in more negatively charged inside of the postsynaptic neurone, making it harder for threshold to be reached as larger influx of Na+ ions needed, so less likely that new action potential passed on.
Name the different types of muscle found in the body.
- Cardiac - found only in the heart
- Smooth - found in the walls of blood vessels, the gut and the iris of the eye.
- Skeletal - makes up bulk of body muscles in vertebrates.
Describe the structure of skeletal muscle.
- Myosin molecules and actin molecules lined up together to form sarcomeres then myofibrils. Tropomyosin molecules wrapped around actin molecules.
Give the similarities between neuromuscular junctions vs synapses.
Both;
- have neurotransmitters that are transported by diffusion.
- have receptors that on binding with the neurotransmitter cause an influx of sodium ions.
- use a sodium-potassium pump to repolarise the axon.
- use enzymes to break down the neurotransmitter.
Give the differences between Neuromuscular junctions (NJ) and synapses (S).
- NJ: only excitatory - S: may be excitatory or inhibitory
- NJ: only links neurones to muscle - S: link neurones to neurones, or neurones to other effector organs.
- NJ: only motor neurones involved - S: motor, sensory and relay neurones may be involved.
- NJ: the action potential ends here - S: a new action potential may be produced along another neurone.
- NJ: acetylcholine binds to receptors on membrane of muscle fibre - S: acetylcholine binds to receptors on membrane of postsynaptic neurone.
Describe slow twitch muscles
- Adapted for endurance work, so contract more slowly, providing less powerful contractions over a longer period.
- Adaptations: large store of myoglobin (stores O2), rich supply of blood vessels to deliver oxygen and glucose for aerobic respiration, numerous mitochondria to produce ATP
Why are slow twitch muscles more adapted for aerobic respiration than anaerobic?
- avoids a build up of lactic acid which prevents long duration contractions and allows them to function most effectively.
