The Nervous System Flashcards
(41 cards)
Stimulate axon A before 1st EPSP dies down, so 2nd synaptic potential adds to the 1st
Temporal summation
Stimulate axon A & B resulting in input from 2 different neurons
Spatial summation
PNS at neuromuscular junction and in the brain
Acetylcholine
- Synthesized from amino acids
- Catecholamines
* Dopamine, Epinephrine
* From tyrosine
* Catechol ring & amine group
* Brainstem & hypothalamus - Serotonin
* Every structure in CNS
* From tryptophan
* Slow onset
* Inhibitory on sensations
* Excitatory on muscles
Biogenic Amines
- Prevalent in CNS
- Glutamate - excitatory
- GABA - inhibitory in brain
- Glycine - inhibitory in spinal cord and brainstem
Amino acids
- 2+ amino acids
- Can affect neurons at a distance
Neuropeptides
- Nitric oxide
- Carbon monoxide
- Do not bind
Gases
- Neuromodulators
- ATP
- Adenosines
Purines
- Modify postsynaptic cell’s response to specific neurotransmitters
- Associated with slower events - learning, development, motivational states
Neuromodulators
Mechanism of Synaptic Release
1 - AP reaches terminal
2 - Ca2+ channels open
3 - Calcium enters axon terminal
4 - Neurotransmitter is released and diffuses into cleft
5 - Neurotransmitter binds to postsynaptic receptors
6 - Neurotransmitter removed from synaptic cleft
- Generate EPSP
- Bring membrane closer to threshold
- Open channels permeable to Na+ and K+
- Na+ drove into cell
- Small number of K+ removed, large number of Na+ brought in
- Net movement of positive ions result in depolarisation
Excitatory chemical synapse
- Generate IPSP
- Make cell membrane potential more negative
- Activated receptors open Cl- or K+ channels
- Cl- equilibrium is more negative than resting membrane potential = hyperpolarisation
- Increased K+ permeability decreases resting membrane potential
Inhibitory chemical synapse
Absolute refractory period
- Stimulus will not produce 2nd AP
- When Na+ channels are open or in inactivated states
- Repolarisation must occur
Relative refractory period
- A 2nd AP can be produced
- 1 to 15 msec
- Period after hyperpolarisation
- Some Na+ channels are in resting state and some K+ channels open
- Stimulus is large in magnitude
Role of refractory periods
- Limit the number of APs
- Contribute to separation of APs
- Help determine direction
Saltory Conduction
- On myelinated axons, APs occur only at nodes of Ranvier
- Faster because less charge leaks out
- Metabolically more efficient, the membrane needs to pump fewer ions
- Responds as a single unit
- Fight or flight
- Thoracic and lumbar regions
- Ganglia close to spinal cord
Sympathetic nervous system
- Activates specific organs
- Rest or digest
- Brainstem and sacral region
- Ganglia within or around organs
Parasympathetic nervous system
Tail bone
Coccygeal
- Genitals
- Lower digestive tract
Sacral
- Lower abdomen
- Hips
- Legs
Lumbar
- Chest
- Upper abdomen
Thoracic
- Control muscles and glands
- Shoulders
- Neck
- Arms
- Hands
Cervical
Resting membrane potential depends on:
- Differences in specific ion concentrations
- Differences in membrane permeability
