Neurology - physiology Flashcards
Types of synapses
Chemical: uses a neurotransmitter that will act on receptor proteins in the membrane of the postsynaptic neuron. Main type in CNS.
Electrical: cytoplasm of adjacent cells are directly connected by ion channels (AKA gap junctions), allowing free movement of ions - less common in CNS but still present.
Types of neurotransmitters
- Small molecules, rapid acting NT
- Neuropeptides - slower, prolonged action
Small neurotransmitters - classification
Class I - acetylcholine (excitatory except on Vagus N.)
Class II - the amines: Norepinephrine (excitatory), epinephrine (excitatory), dopamine (inhibitory), serotonin (inhibitory), histamine
Class III - amino acids: gamma aminobutyric acid (GABA - inhibitory), glycine (inhibitory), glutamate (excitatory), aspartate (excitatory)
Class IV: nitric oxide
Neuropeptides - what is an examples
Larger molecules with prolonged action compared to small neurotransmitters. Synthesized in ribosomes, modified in Golgi apparatus (split and placed into vesicles), released into the cytoplasm then transferred to the synaptic terminal via the axon.
Examples: ACTH, prolactin, GH, thyrotropin, LH, ADH, oxytocin, substance P, gastrin, CCK, insulin, glucagon, angiotensin II, calcitonin…
Resting membrane potential of nerves
- 65mV for SOMA of spinal motor neurons
- 90 mV for PERIPHERAL nerve fibers
Nerst potential + equation
A potential that exactly opposes movement of an ion (potential inside the membrane)
EMF (mV) = +/- 61 / Z x Log (Ci / Co)
Where:
EMF: electromotvie force
Z: electrical charge of the ion (for example, K: +1, Ca: +2, Cl: -1)
Ci: concentration inside the cell
Co: concentration outside the cell
Goldman potential + equation
(AKA Goldman - Hodgkin - Katz equation)
Used to calculate the diffusion potential when the membrane is permeable to several different ions. Depends on:
1) Charge of the ion (positive or negative)
2) Concentration inside and outside the cell
3) Permeability of the membrane to that ion - main ones are Na, K and Cl
EMF (mV) = -61 x [log (CNai + PNai) + (CKi + PK) + (CClo + PCl) / (CNao + PNa) + (CKo + PK) + (CCli + PCl)
Where:
EMF: electromotive force
C: concentration
P: permeability
I: inside
O: outside
Types of sensory receptors
Mechanoreceptors - compressing / stretching
Nociceptors - pain
Thermoreceptors - temperature changes
Photo / electromagnetic receptors - light in retina
Chemoreceptors - O2, CO2, taste, smell, osmolality
Types of cells in the NS
- Neurons
- Glial cells
- Astrocytes - for metabolic support for neurons, synthetize the neurotransmitters
- Oligodendrocytes - synthesize myelin in CNS
- Schwann cells - synthesize myelin in PNS
- Microglial cells - proliferate after neuronal injury - scavengers for cellular debris.
What is presynaptic inhibition
Release of an inhibitory substance onto the outside of the presynaptic nerve. In most instances is GABA.
Erlanger & Gasser nerve fiber classification
CN
On - I - Olfactory Some - sensory
Occasions - II - Optic Say - sensory
Our - III - Occulomotor Money - motor
Trusty - IV - Trochlear Matters - motor
Truck - V - Trigeminal But - both
Acts - VI - Abducens My - motor
Funny - VII - Facial Brother - both
Very - VIII - Vestibulocochlear Says - sensory
Good - IX - Glosopharyngeal Big - both
Vehicle - X - Vagus Brains - both
Any - XI - Accessory Matter - motor
How - XII - Hypoglossal More - motor
Organization of the NS
CNS
Autonomic centers (brainstem and hypothalamus)
Medulla:
- Vasomotor center
- Respiratory center (dorsal respiratory group - DRG and ventral respiratory group - VRG)
- Swallowing, coughing and vomiting center
Pons:
- Pontine respiratory group - pneumotaxic center and apneustic center
Midbrain:
- Micturition center
Hypothalamus:
- Thirst and food intake centers
Major determinants for resting membrane potential?
- Na/K ATPase pump
- Diffusion potentials (chemical and electrical - where an ion will move towards a dynamic equilibrium as long as it can flow across the membrane.
- Membrane permeability to the different ions.