The Nervous System Flashcards
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
Action potential mechanism
1 - Resting membrane potential close to K+ equilibrium
2 - Stimulus binds to specific ion channel, allowing Na+ to enter
3 - Na+ channels stimulated to open by depolarisation
4 - Na+ channels become inactivated & K+ channels open with a delayed effect halting depolarisation
5 - K+ fluxes out of cell rapidly, repolarising membrane
6 - Resting membrane potential closes Na+ channels, but K+ results in hyperpolarisation
7 - K+ channels close, resting membrane potential returns
- Interneurons
- Cell bodies and dendrites of efferent neurons
- Entering axons of afferent neurons
- Glial cells
Grey matter of spinal cord
Afferent neurons enter spinal cord via …
Dorsal roots
Efferent neurons enter spinal cord via …
Ventral roots
- Surround soma, axon and dendrites
- Physical and metabolic support
Glial cells
Regulate extracellular fluid by removing K+ and nuerotransmitters
Astrocyte
Specialised macrophage-like cells
Microgial
Ependymal
Regulate flow of cerebrospinal fluid
Convey information within CNS
Interneurons
Convey information away from the CNS to effector cells
Efferent neurons
Convey information from tissues/organs towards the CNS
Afferent neurons
Nerve
Group of axons in PNS
Tract
Group of axons in CNS
Links right and left in CNS
Commissure
Cell bodies of neurons with similar functions in the PNS
Ganglia
Cell bodies of neurons with similar functions in the CNS
Nuclei
Oligodendrocytes
Myelin in the CNS
