Neurophysiology Flashcards
Membrane Potential
The potential difference across a living cell membrane. Maintained by the ion gradient formed bw the 2 sides of the membrane, Na/K-ATPase pump (3 Na -> EC, 2 K -> IC). The equilibrium potential: K -> out, Na -> into it.
There are more open leak K channels than Na => RMP = result of a slow K outflow.
Electrogenic pump: maintain [] diff.
Presence of all ions => final value (calculated by Goldman-Hodkin-Katz equation).
A transient change of membrane potential:
- Change in []
- Change in permeabilities (nature- used for signaling)
Local response
Artificial change in MP:
- Depolarization: (+) charge to IC space => reduce MP
- Hyperpolarization: (-) charge to IC space => increase MP
If depolarization doesn’t reach a threshold potential -> Local response
If it does -> evokes “all-or-non” response -> AP
Hyperpolarization never evokes an AP.
Action Potential
Depends on voltage-dependent ion channels, which may be blocked by: TTX (from marine fish venom), TEA (specifically K channels)
Adaptation: when Na influx is inhibited even at higher potentials
Summation: sub-threshold stimuli is applied and AP may be trigerred by a potential weaker than threshold.
Absolute refractory period: additional stimuli during development of an AP => no further AP
Relative refractory period: strong stimuli, be RMP + threshold may elicit new AP
- Rheobase: min stimulus strength => response if applied for a long time
- Chronaxie: min time to elicit response if the stimulus strength is 2X the rheobase.
▪️ In myelinated fibers: in the nodes of Ranvier, fast propagation
▪️ In non-myelinated fibers: propagation step by step, slow velocity
Axonal transport
The AP in the synaptic nerve ending => NT stored in vesicles. Synthesis of peptides + vesicles is only possible in the neural soma => must be transported to the presynaptic nerve ending.
- From soma -> nerve ending = Anterograde (kinesin)
- From nerve ending -> soma = Retrograde (dynein)
Hyperpolarization: RMP increases
Depolarization: RMP decreases
GAP junction
Special synapse which allows free diffusion of charges bw cells. Hexamer connection => fastest communication. In case one of the directions is dominant, the phenomenon is called rectification.
Leads to either:
EPSP: excitatory postsynaptic potential; discharge frequency increase
IPSP: inhibitory ——–”——-; discharge frequency decrease
Involved in fast reflex arched in CNS, effects based on metabotropic transmitters.
Binding of ligand receptor -> IC 2nd messenger -> IC metabotropic effect -> long kasting de-/hyperpolarization
Receptors
Function of NS is based on sensing stimuli. The specific stimuli evokes a cation influx => receptor potential. Amplitude of the potential is proportional to the extent of the stimulus which is first coded by the amplitude + then by the frequency.
Classification:
- According to the receptor: primary (olfaction), secondary (sound), tertiary (eye)
- Location: exteroceptors (light, sound), interoceptors (heat, P)
- Form of energy: mechanical, thermal, photo, chemical
- Ability to adapt: fast, slow
Types:
- Free nerve ending: sense pain, T
- Panician corpuscles: sensitive to tough
- Golgi tendon organ: at the muscle-tendon border, sense from the int environment
Functional basis: specific stimulus is conducted through additional structures + finally reaching the free surface of the invaginated end of the fiber. Mechanical stimuli => electronic response
Ion channels
Increase/Decrease the flow of ions by increasing/decreasing the permeability.
Classification:
- Na,K,Cl: leak (maintain MP), voltage-dependent (generate AP), ligand dependent (n-Ach, glutamate: AMPA/NMDA/kainate, anion: causes hyperpolarization- GABA/glycine, G-protein), mechanoreceptive (uptake of mechanical stimuli, deformation of axon terminal), energy sensor (K channel sensitive to ATP => depolarization)
-Ca: ryanodine + DHP: mechanically activates Ca channels, IP3-receptor: mobilizes Ca from IC Ca stores, voltage-dependent: P-, T-, N-types
Spinal cord
Its most important somatic reflex arch give examples for mono- + polysynaptic reflex arches:
- Proprioceptive: receptor in same organ as effector
- Exteroceptive: in diff
At segmental/intersegmental level processes occur without the control of CNS, e.g.segments of HL -> inhibitory impulses to FL, scratch reflex
Tracts: Sensory, asc pathways- info is transmitted towards CNS
Motor, desc oathways- pyramidal + extrapyramidal system
Afferent, ascending pathways
Sensory, always form a path consisting of 3 neurons.
Body of the 1st is in the spinal ggl (pseudounipolar neuron), entering the spinal cord => collaterals
2nd + 3rd reach cerebral structures
1. Light tactile sensation: Goll + Burdach
2. Motor afferents: Goll + Burdach
3. Cerebellar muscle afferents: dors (Flechsig)/ ventr (Gowers) spinocerebellar tract
4. Thermal + nociceptive sensor afferents: L + ventr spinothalamic
Efferent, descending pathways
- Pyramidal tracts: O from the sensorimotor areas of cerebral cortex. Motor fibers -> control of voluntary mvms:
L corticospinal tract: reaches contralateral alphaMN + gammaMN
Ventr corticospinal tract: ipsilateral alphaMN + gammaMN - Extrapyramidal tracts: concerned with coordination of stereotype reflex mvms
Rubrospinal tract
Vestibulospinal tract
Tecto- + olivospinal tract
Reticulospinal tract
Vegetative desc pathway
Desc analgetic pathway
Proprioceptive reflex
Receptors in the same organ.
Diff from exteroceptive: no latency, does not fatigue, reflex arch = monosynaptic, immediate response
Common with exteroceptive: intensity of response is proportional to intensity of stimulus, reciprocal innervation, response has local character
3 main types:
- Myotatic reflex: Annulospinal receptors (as Ia fibers), alpha MN (large motor cell of ventral horn, muscle stretching: increase excitatory), gamma MN (cerebral motorcenters activate/inhibit the fusimotor system). Recurrent inhibition: Renshaw cells
- Inverse myotatic reflex: at further stretching => sudden relaxation
- Flexor stretch reflex: light stretching causes extension in both flexor + extensor mm
- Extensor thrust: extension of interosseus mm => muotatic stretch reflex.
Exteroceptive reflex
Receptor- outside the effector organ.
Basis of preventing, nociceptive, pain-avoiding behaviour. Actiovation of flexors + contralateral extensors
Nociceptive + thermoreceptors: group III + IV
Afferent activation: relaxes ipsilateral extensors + activates ipsilateral flexors -> limb is moved away from stimulus.
Effect also on contralateral mm: alpha MN lf extensors are excited + flexors inhibited.
- Useful in case of injuries: injury can be localized, they occur segmentally => spinal injury can be specifies, under upper CNS control => injuries of higher structures will cause changes in reflex patterns.
Autonomic nervous system
Peripheral Sympathetic:
Thoracolumbar segments -> mobilization of stored energy + increase in reactions.
Redistribution of blood: dilation- smooth m, constrict- vessels.
Preggl fibers: B type, myelinated
Postggl fibers: C tyoe, non-muelinated
Chromaffin cells respond to preggl stimulation: endocrine -> adrenaline/epinephrine, NT -> noreadrenaline/dopamine
Sympathetic ggl: cran cerv, stellate, coeliac, mesenteric
Peripheral PS:
Increasing energy storage + conservation, vasodilation
Cran nn: oculomotor, facial, glossopharyngeal, vagus
Sacral: in grey matter, long preggl + short postggl axon
PS postggl transmission: Ach release, muscarinic type receptors
Sensory in the CNS
Primary -> postcentral gyris (mechanical sensation)
Secondary -> sylvian fissure (pain sensation)
- Mechanical sensation: vibration (pacinian corpuscles), P (Ruffini corpuscles), touch location (Meissner’s corpuscles), hair follicle (hair follicle receptors).
- Thermal sensation: warm receptors = A delta + C fibers => AP (30 - 45 degrees), cold receptors (bw 15-42 degrees)
- Pain sensation: A delta -> fast, C fibers -> slow-lasting
Noxious stimuli -> tissue damage, degranulation of basophils, antidromic
Posture control in CNS
- Upper Motor System -> supraspinal level: normal posture + complex voluntary mvm.
Cerebellar + Basal ggl: mvm initiation, mvm planning, mvm plan reconsideration, mvm execution - Low Motor System -> spinal level: basis of spinal organization
LMS + UMS => antigravitational support, stabilization
Nucleus rubber, reticular formation, dieter’s
▪️Postural reflexes: tonic reflex, supporting reflex, statokinetic reflex, Planking-Hopping reflex.
