Summarise nervous communication
- Fast
- Short lived
- Localised
What does the CNS consist of
Brain + Spinal Chord
What does the peripheral nervous system consist of
Somatic and Autonomic
What does the somatic consist of
Conscious control
What does the autonomic consist of
Unconscious activity such as homeostasis
Summarise a receptor
- Specialised cell designed to detect a stimulus
- Specific as will only detect one stimulus
- Cell or protein
- Transform stimulus into electrical nerve impulse
How is resting potential maintained?
- Sodium potassium pump using ATP to transport 3 Sodium OUT and 2 potassium IN
- Voltage gated sodium channel closed
- Potassium ion channel open so diffuses out by electrochemical gradient but no equilibrium due to diffusion and the positive outside charge
What is a generator potential
A weak stimulus where some NA+ channels open and NA+ diffuses in, reaching the threshold potential
Summarise an action potential
- Resting potential at first
- Generator potential
- Threshold reached
- Na+ in until 40mv, (depolarisation) and then potassium gates open
- Potassium diffuse out (hyper polarisation) when membrane potential more negative than resting potential due to slow closing of K+ channels
- Refractory period at the end and prevents new AP occurring, and that they are discrete (non-overlapping and separate) and unidirectional
Summarise the all or nothing law of action potentials
- If a generator potential reaches threshold, AP occurs
- Action potentials same size
- Strong stimulus generates more AP (frequency increased)
Why does myelination increase speed of an AP
- Schwann Cells that make myelin are an electrical insulator
- Impermeable to the movement of ions in and out
Summarise saltatory conduction
- Neurone myelinated
- Lots of Na+ and L+ in nodes of Ranvier
- Depolarisation can only occur in nodes
- AP jumps between nodes in a process called saltatory conduction
Define salutary conduction
When an action potential jumps between nodes of ranvier, so speeds up transmission of nerve impulse due to cytoplasm conducting enough charge to depolarise next node
How does temperature effect AP speed
More kinetic energy so faster speeds up to 40C
How does the diameter of an axon affect speed aP
Greater diameter = faster AP
due to greater SA for ion movement and so less resistance
Define synapse
Junction between neurones whereby chemical transmission occurs
Define cholinergic synapse
One the uses acetylcholine
Summarise synaptic transmission at a cholinergic synapse
- AP arrives at presynaptic knob
- Voltage gated Ca2+ ions open and diffuse in
- Cause vesicles to move towards membrane
- Fuse and release acetylcholine by exocytosis
- Diffuse across synaptic cleft and bind with receptors
- Binding causes Na+ channels to open causing further AP if threshold reached
- Acetylcholinesterase breaks down acetylcholine to stop response
How are synapses unidirectional?
- Receptor on post synapse and neurotransmitter released from pre synapse from high to low conc.
What is synaptic divergence?
- When neurones join many neurones
- AP spreads to other parts of body
What is synaptic convergance?
- When many neurones join a single neurone amplifying the signal
Summarise spatial summation
- When neurotransmitters from multiple neurones combine to trigger an AP
- Weak stimulus creates only a few AP
Summarise temporal summation
- Single AP does not always trigger an AP in next neurone
- Strong stimulus causes more frequent AP so more neurotransmitter increasing chance of next AP
Define neuromuscular junction
Synapse between motor neurone and muscle fibre
