6B Nervous coordination Flashcards
When a neurone is resting is the outside or inside more positive?
Outside because there is more positive ions so the membrane is polarised
What does polarised mean?
There is a difference in charge (potential difference)
What do sodium potassium pumps do and how many?
Active transport to move 3 sodiums (na) out for 2 pottasiums (k) in
What is the function of potassium ion channels
Allow facilitated diffusion of potassium ions out of the neurone down their concentration gradient
What is the movement of sodium and potassium ions across a resting cell membrane?
- Sodium potassium pump moves sodium out but since the membrane is impermeable they wont diffuse back in
- This creates an electrochemical gradient because more positive outside the cell than inside
- The sodium potassium pump also pumps potassium ions in
- At rest more potassium ion channels are open so potassium can diffuse back out
Why are the sodium ion channels voltage gated?
They only open when the potential difference reaches a certain voltage
What are the 5 steps during an action potential
- Stimulus
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Resting potential
What happens in the first stage during an action potential?
Stimulus
- Excites cell membrane so sodium ion channels open
- Membrane more permeable to sodium so they diffuse in creating an electrochemical gradient as inside becomes less negative
What happens in the second stage during an action potential?
Depolarisation
- If potential reaches threshold of -55mv more sodium channels open diffuse in
What happens in the third stage during an action potential?
Repolarisation
- At +30mv the sodium channels shut and potassium open
- Potassium ions diffuse out of neurone down gradient
- Membrane returns to resting potential
What happens in the fourth stage during an action potential?
Hyperpolarisation
- Too many potassium ions diffuse out
- Becomes more negative than resting potential of -70mv
What happens in the fifth stage during an action potential?
Resting Potential
- Ion channels at rest
- Sodium potassium pump return to resting potential by pumping sodium out and potassium in until stimulated again
What is the refractory period?
A time delay between one action potential and the next so they do not overlap, travel in one direction and allow the ion channels to recover
What is the all or nothing principle?
An action potential will always fire with the sane change in voltage no matter how big the stimulus but if a threshold isnt reached it will not fire
A bigger stimulus will not cause a bigger action potential but cause them to fire more frequently
What 3 factors affect the speed of conduction
- Myelination
- Axon diameter
- Temperature
How does myelination affect the speed of conduction
- it is an electrical insulator made up of schwann cells with nodes of ranvier between them where sodium ion channels are concentrated
- myelinated neurones allow depolarisation to happen as the electrical charge can jump from node to node instead of as a wave along the whole length - SALTATORY CONDUCTION
How does axon diameter affect speed of conduction
Bigger diameter = quicker conduction as there is less resistance to the flow of ions in the cytoplasm so depolarisation reaches other parts of cell membrane faster
How does temperature affect speed of conduction
Speed increases as temperature increases as ions diffuse faster
After 40c the pumps and channels (proteins) start to denature
What is a synapse?
The junction between a neurone and a neurone, or neurone and effector
What is the synaptic cleft
The tiny gap between cells at a synapse
What is the presynaptic neurone
The one before the synapse that has a swelling called a synaptic knob
What is inside a synaptic vesicle
chemicals which are Neurotransmitters
What happens when an action potential reaches the end of a neurone?
- Neurotransmitter to be released into synaptic cleft
- Diffuse across postsynaptic membrane and bind to specific receptors
- Triggering an action potential causing an effect eg muscle contraction or hormone secretion from gland cell
- Neurotransmitters removed from cleft do response doesnt keep occuring and taken back to presynaptic or broken down by enzymes
What does acetylcholine bind to
Cholinergic receptors at Cholinergic synapses
How is a nerve impulse transmitted across a cholinergic synapse?
- Action potential arrives at synaptic knob of presynaptic neurone
- Stimulates voltage gated calcium ions in presynaptic to open
- Calcium ions diffuse into synaptic knob
- Influx causes synaptic vesicles to fuse with presynaptic membrane releasing acetylcholine into synaptic cleft by exocytosis
- ACh binds to cholinergic receptors on post synaptic membrane so sodium ion channels open
- This causes depolarisation allowing an action potential to be generated if the threshold is reached
- ACH removed and broken down by acetylcholinesterase and reabsorbed by presynaptic neurone to make more ach
What is the difference between excitatory and inhibitory neurotransmitters and some examples
Excitatory - depolarise postsynaptic membrane making it fire an action potential if it is reaches
eg acetylcholine which binds to receptors to cause an action potential
Inhibitory - hyperpolarise the postsynaptic membrane so it is prevented from firing an action potential
eg acetylcholine as it also causes potassium ions to open on post membrane hyperpolarising it
What is Summation?
The effect of neurotransmitters released from many neurones or one neurone is added together
What are the two types of summation
Spatial
Temporal
What is the difference between the two types of summation
Spatial is where 2 or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone to trigger an action potential
Temporal is where 2 or more nerve impulses arrive in quick succession from the same presynaptic neurone into the synaptic cleft
What is a neuromuscular junction
A specialised cholinergic synapse between a motor neurone and a muscle cell
What is the name of the receptor that ACh binds to at a neuromuscular junction
Cholinergic receptors called Nicotinic cholinergic receptors
What is the differences between neuromuscular junctions and cholinergic synapses
At NeuroMuscular Junctions :
- the postsynaptic membrane has lots of folds that forms clefts that store Ache
- Postsynapticmembrane has more receptors
- ACh is always excitatory
What are drug agonists and antagonists and example ?
Agonists - mimic neurotransmitters action at receptors as they are the same shape
eg NICOTINE mimics ACh binding to nicotinic cholinergic receptors
Antagonists - block receptors so less activated
eg CURARE blocks ach by blocking cholinergic receptors at junctions so muscle cells not stimulated and become paralysed
What are the types of muscle in the body and what do they do
- Smooth muscle - contracts without conscious control eg stomach, intestine, blood vessel
- Cardiac Muscle - contracts without conscious control only in the heart
- Skeletel Muscle - used to move eg biceps and triceps
What are skeletel muscles attached to?
Bones by tendons
What attaches bones to eachother
Bones to other bones
What are muscles that work together to move a bone called
Antagonistic pairs
Which one out of contracting muscle and relaxing muscle is the agonist
Contracting is agonist and relaxing antagonist
What is the structure of skeletal muscle
- Made up of long cells called muscle fibres
- Cell membrane of muscle fibres is called Sarcolemma which fold into fibre and stick int sarcoplasm
- Folds are known as transverse tubules which help to spread electrical impulses throughout sarcoplasm
- Internal membranes known as Sarcoplasmic Reticulum releasing calcium ions needed for muscle contraction
- Mitochondria for ATP
- Many myofibrils
What do myofibrils contain?
Bundles of thick and thin myofilaments that move past eachother to make muscle contracrs
What are thick myofilaments made up of?
Myosin
What are thin myofibrils made up of
Actin
What are the A bands?
Dark bands that contain thick myosin filaments and some overlapping actin
What are the I bands?
Thin actin filaments
What is a sarcomere?
Short units in a myofibril
What is the Z line?
The ends of a sarcomere
What is the m line?
The middle of myosin filaments
What is the H zone?
Only myosin filaments
What is the sliding filament theory?
- Myosin and Actin filaments slide over one another to make the sarcomeres contract
- The simultaneous contraction of lots of sarcomeres means myofibrils and muscle fibres contract
In the sliding filament theory what gets shorter and what stays the same?
A bands stay the same
I bands get shorter
H zones get shorter
What is the structure of myosin filaments
- Hinged globular heads that move back and forth
- Actin binding site
- ATP binding site
What is the structure of Actin filaments
- Binding sites for myosin heads (actin-myosin binding site)
- Tropomyosin protein found between actin filaments helping myofibrils move past each other
What occurs at the binding sites in resting muscles?
Actin Myosin Binding site blocked by Tropomyosin so myofilaments cant slide past eachother
What is the process of muscle contraction?
- Action potential from motor neurone stimulates a muscle cell so sarcolemma depolarises
- Depolarisation spreads down t tubules to sarcoplasmic reticulum so stored calcium ions released into sarcoplasm
- Triggering a muscle contraction
- Calcium bind to tropomyosin pulling trop. out of actin myosin binding site so myosin head can bind
- This forms an actin myosin cross bridge
- Calcium activates atp hydrolase to provide energy causing the myosin head to bind pulling the actin filament along
- Another ATP provides the energy to break actin myosin cross bridge so myosin head returns to starting position
- When muscles stops being stimulated calcium ions leave binding sites and moved by active transport back into sarcoplasmic reticulum
- Sarcomere relengthens and tropo. moves back
What are the 3 ways energy for muscle contraction is generated
- Aerobic resp
- oxidative phosphorylation - Anaerobic resp
- end of glycolysis pyruvate produced converted into lactate which can build up - ATP- phosphocreatine system
- ATP made from phosphorylating ADP
adp + pcr –> atp + cr
- cr broken down into creatinin which is removed via kidneys
What is the difference between slow twitch and fast twitch muscle fibres?
-
Slow twitch contract slowly
Work for a long time
Endurance activities
Energy released through aerobic resp
Many mitochondria and blood vessels
Rich in myoglobin
- [Fast twitch]
contract quickly
Tired quickly
Short bursts
Found mainly in arms,legs, eyes
Anaerobic using glycogen
Stores of pcr to generate energy quickly
Few mitochondria and blood vessels**
GABA is a neurotransmitter released in some inhibitory synapses in the
brain.
GABA causes negatively charged chloride ions to enter postsynaptic
neurones.
Explain how this inhibits postsynaptic neurones
- (Inside of postsynaptic) neurone becomes more
negative/hyperpolarisation/inhibitory postsynaptic potential; - More sodium ions required (to reach threshold)
- For depolarisation/action potential
