Nervous Coordination Flashcards
Nervous co-ordination
- Short lived
- Fast
- Localised
Peripheral nervous system
All neurones not in the brain or spinal chord
Central nervous system
- Brain
- Spinal chord
Somatic nervous system
Division of peripheral
- Conscience control
- Skeletal muscles
Autonomic nervous system
Division of peripheral
- Unconscience control
- Heart/lungs
Parasympathetic nervous system
Division of autonomic
- Slows things down
- Acetylcholine (neurotransmitter)
- e.g. decreasing heart rate
Sympathetic nervous system
Division of autonomic
- Speeds things up
- Noradrenaline (neurotransmitter)
- e.g. increasing heart rate
Reflex arc
Stimulus - Receptor - Sensory neurone - Relay neurone - Motor neurone - Effector - Response
Receptor
- Specific so will only detect one type of stimulus
- Cell or protein
- Transform stimulus into an electrical nerve impulse
Sensory Neurone
- Single long dendron
- Single short axon
Relay neurone
- Within CNS
- Many short dendrites
- Many short axons
Motor neurone
- Many short dendrites
- Single long axon
- Ends with a neuromuscular junction
Effector
- Muscle or gland
Resting potential: sodium - potassium pump
- Active transport using ATP
- 3 sodium out the cell
- 2 potassium into cell
Resting potential: voltage gated sodium ion channels
- Closed
- Membrane not permeable to sodium
Resting potential: sodium - potassium ion channels
- Open
- Some potassium diffuse out down the electrochemical gradient
- Doesn’t reach equilibrium because of the positive charge outside
Action potential order
1- Resting potential 2- Generator potential 3- Threshold 4- Depolarisation 5- Repolarisation 6- Hyperpolarisation 7- Refractory period
Resting potential
- sodium potassium pump
- active transport
- sodium out
- potassium in
- some potassium diffuses out via potassium channel
Generator potential
- weak stimulus
- some sodium channels open
- some sodium diffuses in
- does not reach threshold
- sodium potassium pump restores resting potential
Threshold
- Generator potential reaches threshold
- many voltage gated sodium channels open
- sodium diffuses into axon
- positive feedback
Depolarisation
- sodium channels all open
- sodium diffuses in
Repolarisation
- voltage gated potassium channels open
- potassium diffuses out
- voltage gated sodium close
Hyperpolarisation
- membrane potential more negative than resting potential
- potassium channels start to close
Refractory period
- another action potential cannot be generated
- makes action potentials discrete so they don’t overlap
- uni-directional
All or nothing
- If a generator potential reaches threshold it triggers an action potential
- all action potentials same size
- strong stimulus generates ore frequent action potentials
- sodium ions diffuse along the neurone
- ahead of action potential the neurone is in resting potential
- sodium triggers threshold
- action potential moves as a wave of depolarisation
- behind depolarisation phase is refractory period
- action potential cannot go backwards
Myelin sheath
- Schwann cells make myelin
- electrical insulator
- prevents depolarisation
- prevents movement of ions in and out of the neurone
Nodes of ranvier
- gaps in myelin sheath
- lots of sodium and potassium channels
- depolarisation only happens at nodes
- action potentials jump between nodes in a process called saltatory conduction
Temperature
- higher temp = faster speeds up to 40 degrees
- molecules diffuse faster at higher temps (more kinetic energy)
Saltatory conduction
- action potential jumps between nodes
- speeds up transmission of nerve impulse
- cytoplasm conducts enough charge to depolarise the next node
Diameter of axon
- greater diameter means faster action potential speed
- less resistance
- more surface area for ion movement
What is a synapse
- junction between neurones
- chemical transmission by neurotransmitters
- e.g. acetylcholine
What happens at synapses
1 - Action potential arrives at pre-synaptic knob
2 - Voltage gated calcium ion channels open and calcium ions diffuse in
3 - vesicles full of neurotransmitters fuse with pre-synaptic membrane
4 - acetyl choline diffuses across synoptic cleft
5 - acetyl choline binds with receptor on post synaptic membrane
6 - some sodium channels open and sodium diffuses in
IF THRESHOLD IS REACHED
7 - voltage gated sodium channels open
8 - action potential is triggered in the post synaptic membrane
9 - acetylcholinesterase breaks down acetyl choline and stops the response
10 - products reabsorbed in presynaptic knob and recycled
Synapses are unidirectional
- Only receptors on post-synaptic
- Neurotransmitters released from pre-synaptic
- Diffuse from high - low concentration across synaptic cleft
Synaptic divergence
- one neurone joins many neurones
- spreads action potential to other parts of the body
Temporal summation
- a single action potential doesn’t always trigger an action potential in the post-synaptic embrane
- a strong stimulus will cause more frequent action potentials and release more neurotransmitters which add up to trigger an action potential in post synaptic membrane
Synaptic convergence
- many neurones join a single neurone
- amplifies the signal
Spacial summation
- weak stimulus may only create a few action potentials which doesn’t always trigger an action potential in the post synaptic neurone
- when neurotransmitters from multiple neurones combine to trigger an action potential in a post synaptic neurone
Neuromuscular junction
synapse between a motor neurone and a muscle fibre
Sarco
muscle
Neuromuscular differences with colmergic synapses
- more receptors on post synaptic membrane
- action potential always generated in post - synaptic
- enzymes found in pits in post synaptic
