Neurology Flashcards
How is the nervous system split?
Nervous System is split into Central, Peripheral and Enteric
Central = brain and spinal cord
Peripheral = nerves and the rest of the body
Enteric = involved in the gut
How is the Peripheral Nervous System split?
Split into Sensory and Motor:
Sensory = sensing the environment and feeding that back into the CNS
Motor = movements, split into Autonomic and Somatic
Somatic = can control the movement of skeletal muscles
Autonomic = no conscious control (automatic), split into sympathetic and parasympathetic
Sympathetic = fight or flight, prep for movement - outflows throughout the spinal cord
Parasympathetic = rest and digest - outflows at the cranial (head/neck) and sacrum (by pelvis)
Resting Membrane Potentials (Na+/K+ pump)
1) Na+/K+ pump uses ATP hydrolysis to pump 3 Na+ ions out and 2 K+ ions in to the cell constantly
2) Both Na+ and K+ channels are always open, but there are more K+ channels, so the axon membrane is more permeable to K+ ions
3) K+ ions diffuse down the gradient through K+ channels
4) Na+ ions diffuse into the cell through the Na+ channels down their concentration gradient
5) This maintains a difference in the concentration gradients
Action Potentials - Na+ ions
1) Voltage gated Na+ channels are closed at rest. High Na+ outside the cell and low inside the cell
2) When a neurone is stimulated, there is a wave of depolarisation through the neurone
3) Depolarisation causes the voltage gated Na+ channels to open and Na+ enters the cell down its concentration gradient
4) Once the threshold value (-55mV) is reached, an action potential is triggered
5) Eventually, the voltage gated Na+ channels become inactivated and then close
Action Potentials - K+ ions
1) K+ channels open so K+ ions can diffuse out of the cell down the concentration gradient
2) Membrane repolarises
3) The membrane may become too negative
Action Potentials - the Refractory Period
1) Hyperpolarisation in the membrane drops the membrane voltage below -70mV
2) Both the Na+ AND K+ voltage gated channels remain closed, so another action potential can’t pass down the cell - this is the refractory period
Synaptic Transmission
1) Action potential reaches the pre-synaptic knob
2) Depolarisation causes the voltage gated Ca2+ channels to open, and Ca2+ diffuses in down the concentration gradient
3) Ca2+ binds to vesicles and induces their movement down the pre-synaptic knob
4) Vesicles fuse with the pre-synaptic membrane, releasing the neurotransmitter into the synaptic cleft
5) Acetylcholine diffuses across the cleft and binds to ligand-gated Na+ channels
6) This induces the opening of the Na+ channels, so Na+ ions diffuse into the post-synaptic neurone
7) This depolarises the post-synaptic membrane and will eventually go on to trigger an action potential
Ionotropic Receptors
Ligand-gated ion channels
Neurotransmitter binds directly to the ion channel
This allows selective movement of ions into or out of the cell
This is very fast
Metabotropic Receptors
G-protein coupled receptors
Neurotransmitter binds to the G-protein receptor
This triggers an intercellular cascade that eventually activates transcription of DNA
This is very slow
Ganglions
Collection of neurones found in the PNS
Thought to act like synaptic relay stations
Myofibril
Cylindrical organelle running the length of the muscle fibre, containing actin and myosin filaments
Sarcomere
Functional unit of the myofibril
Divided into I, A and H bands
Actin
Thin, contractile protein filament
Myosin
Thick contractile protein filament with protrusions known as myosin heads
Tropomyosin
Actin-binding protein that regulates muscle contraction
