Nervous System Flashcards
What are nissl bodies?
Large Rough ER, a lot of protein synthesis
Why are nerve cells incapable of regeneration?
They have no centrioles
What are ependymal cells?
Simple cuboidal ciliated epithelial cells. Line fluid filled ventricles and spinal cord, determines composition and helps move fluid along
What are astrocytes?
Star shaped cells surrounding blood vessels in brain and spinal cord. Any molecules passing from blood to brain must pass through this first, blood brain barrier
What are microglial cells?
From phagocytic lineage, clear up debris in CNS, either micro-organisms or dead nerve cells
What are oligodendrocytes?
They myelinate axons in the CNS, one of these can myelinate up to 50 axons
What are schwann cells?
Myelinate axons in the PNS, they wrap their membrane around the axons - if unmyelinated, only cytoplasm wrapped around for protection
What are satellite cells?
Flattened cells covering cell bodies to provide protection
How is the membrane potential maintained?
In two ways. Passive diffusion of K ions out of cell, these channels are always open so constant leakage of K from the cell. Also, the Na/K active transport, 3Na out of the cell, 2K into the cell, net loss of one +ve ion. So ICF is negative to ECF.
Describe 2 ways in which the membrane potential can be altered.
By excitatory post-synaptic potentials - depolarises the membrane, bringing it closer to threshold
By inhibitory post-synaptic potentials - hyperpolarises the membrane, moving it further from threshiold
What is the threshold of membrane potential for an AP?
-55mV
What occurs at -55mV?
voltage-gated Na channels open, causing the membrane to depolarise as there is an influx of Na ions
What occurs at +35mV?
voltage-gated Na channels are closed and voltage-gated K channels are opened - K leaves the cell, causing hyperpolarisation
How does local anaesthetic work?
Blocks Na channels, AP cannot be generated
How can an AP be propagated?
Along the membrane, from a positive part of the membrane to the adjacent negative part, can only travel in one direction due to refractory period
What is the refractory period?
When voltage-gated Na channels are inactivated so an AP cannot be generated
What increases the speed of an action potential?
The diameter of the axon and myelination
How does myelination increase the speed of an AP?
It insulates the membrane so the ICF is not in contact with the ECF and there is no membrane potential. However, it leaves areas unmyelinated, so are exposed to ECF, thus can achieve an AP - node of ranvier. So the AP jumps from node to node
What stimulates the synaptic vesicles to move to the membrane?
As AP arrives at the axon terminal, it stimulates the release of calcium, this then activates the vesicles
How can a neurotransmitter be inactivated?
Enzymes breaking it down - e.g. acetylcholinerase or by re-uptake into pre-synaptic cleft
How can the same neurotransmitter exert a different effect on the same cell?
By binding to different receptors, it stimulates different 2nd messenger systems, thus different response
What is summation?
When several post-synaptic potentials act on the one cell at the same time, come together to generate a response - e.g. many required to reach threshold
What neurotransmitter is released at the neuromuscular junction?
Acetylcholine
Where does acetylcholine bind to on the muscle cell?
Sacrolemma - t-tubules
