Nervous system Flashcards
(33 cards)
What is a ganglion
Collection of cell bodies outside of the CNS
Different types of neural processing
Divergent, convergent, parallel, serial processing and reverberation (homeostasis)
Types of neurons
Bipolar, unipolar, anaxonic, multipolar (single axon, multiple dendrites)
Glial cells in the CNS
Oligodendrocytes (myelination), astrocytes (form blood brain barrier, structural support and regulate ion + neurotransmitter), Microglia (immune cells of CNS), Ependymal cells (line ventricle’s)
Glial cells in PNS
Schawnn cells (myelination and repair after injury), Satellite cells (surround neuron and cell bodies, regulate O2/Co2, nutrients and transmitter levels)
What is myelination
Fatty layer surrounding neurons that increases transduction speed.
What is RMP and how is this achieved
-70 mV.
This is achieved by the imbalance of ions. The ICF is much more negatively charged than the ECF. Resting membrane is very permeable to K ions meaning RMP is closet to the Nerest value for K (90). K higher inside and Na higher outside.
Ion flow underlying action potentials
Depolarisation opens voltage gated Na channels causing influx due to concentration gradient. This causes further depolarisation causing more Na to open
Action potential propagation in unmyelinated axons
The influx of sodium causes a depolarisation in the adjacent part of the axon, causing opening of Na channels. This can only move in one direction due to the inactivated state of the Na channels (refractory period). Remember that even if artificially stimulated a nerve can only give a response at one end due to the release of neurotransmitter.
Saltatory conduction (AP propagation in myelinated axons)
Action potentials can jump from one node of Ranvier to another. This is driven by the adjacent spread of depolarisation. Refractory periods are still present.
What are the refractory periods
Absolute – No action potential can be generated due to the Na channels being in the inactivated state
Relative – Action potential can be generated if the stimulus is large enough as some Na channels are in the closed state
Factors effecting rate of conduction
Temperature, axon diameter and degree of myelination
Contrast action potentials and graded potentials
Action – causes by depolarisation, all or nothing response (change frequency for increasing stimulus), always movement of K and Na, constant duration (1-2 ms), refractory period, no summation, propagates throughout membrane without diminishing.
Graded – multiple causes (stimulus, neurotransmitter with receptor, changes in channel permeability), movement of ions across membrane (Na, K, Cl, Ca), magnitude and duration varies with magnitude and duration of triggering event, magnitude decreases with distance, temporal and spatial summation.
Synaptic transmission termination
This occurs via the removal of the neurotransmitter which can occur in one of three ways. Breakdown by enzymes, diffusion away from synaptic cleft where it is broken down or the reuptake back into the presynaptic terminal (or astrocytes)
Process of synaptic transmission
Action potential propagates down action causing voltage gated calcium channels to open. Influx of calcium causes the release of the neurotransmitter from presynaptic neuron into synaptic cleft. Neurotransmitter then binds to specific chemically gated ion channels that will then let specific ions into the post synaptic neuron, this can cause either a inhibitory or excitatory response.
Summation of synaptic inputs
Temporal summation – two EPSPs from the same pre synaptic neuron occur close in time and depolarise
Spatial summation – two EPSPs form different pre synaptic neurons occurs close in time
EPSPs and IPSPs cancel each other out
What effects synaptic transmission
The type of cell it terminates on (Skeletal, neuron, cardiac), type of chemical release (excitatory or inhibitory) and the type of neurotransmitter receptor on the postsynaptic neuron (ligand gated will cause direct changes to membrane potential while G protein coupled receptor will have an indirect off on this and other cellular functions.
What is a ligand gated ion channel
Ion channel in membrane that are open through the binding of a ligand (neuro transmitter, chemical messenger). Causes ions to flow in or out and therefore has a direct impact on membrane potential creating a local response that can either be EPSP or IPSP. Has a fast response (10-100 ms)
Organisation of muscles
Sarcomere →myofibril → muscle fibre → skeletal muscle
Components within sarcomere
Z line - holds the thin filaments (between 2 of these is referred to as a sarcomere)
M line - proteins that hold the thick filaments
A band - Thick and thin overlap
I band - Thing filaments that dont overlap with thick
H zone - middle of A band where thin dont reach
Thick Filament
Myosin chains
This is a protein with a long tail and a head which contains the actin binding site
Thin Filament
Chain of many actin protein molecules
Actin has multiple myosin binding sites which are often blocked by tropomyosin.
Another protein known as troponin binds to tropomyosin and via calcium can move the troponin-tropomyosin complex to expose myosin binding sites.
Calcium cross bridges pre req
During muscle relaxation, tropomyosin is blocking the myosin binding sites.
However, during excitation calcium is released into the muscle which binds troponin causing it to move the troponin-tropomyosin complex and expose the myosin binding sites. This then causes the cross bridge cycle to occur
Calcium cross bridge cycle
- Myosin head binds to actin
- Myosin performs power stroke pulling the thin filament relevant to the thick
- Myosin head detaches and “unflexes”
- Myosin head is now able to bind to another actin binding site
Multiple of these cross bridges and the flexion of multiple myosin heads allow the thin filament to be moved towards the thick (muscle contraction)
Energy (ATP) required to detach myosin head after power stroke
