Cells of the Nervous System and the Neuromuscular Junction Flashcards
What is the CNS?
The Central Nervous System
Name the 4 main components of the CNS and their subcomponents?
- Cerebral hemispheres (brain):
4 functional regions - frontal, occipital, temporal and parietal
Gyri and valleys - meandering hills
- Brainstem:
Hindbrain separated into 3 main sections - in ascending order: midbrain, pons and medulla
Target of the cranial nerves - responsible for majority of the autonomic functions
- Cerebellum: At the back of the brain
Used for co-ordination - adjusting fine movement (people can survive without a cerebellum, just very unsteady)
- Spinal Cord:
Forms the PNS
Nerve cells protected by the vertebrae - important in reflex actions (don’t require thought processes)
What are the 2 broad types of cells in the CNS?
Neurons
Neuroglia
What are the main cells of the nervous system?
Neurons
What are neurons and what do they consist of?
Main excitable cells of the NS - can generate an action potential
Generally considered ‘non-dividing cells’ - an older view, as newer research suggests some neuronal cells are able to divide, and perhaps depression is caused by non-diving neuronal cells in the hippocampus
All have similar features: the cell body (soma / perikaryon) - main part containing the nucleus and neurofilaments (important for structure and cell support).
Always have one axon (regardless of the morphology), which projects out of the cell body. Normally covered in myelin
Cell body may have other projections too, e.g. dendrites - highly branched cell body
What are the 4 types of neurons in the nervous system and describe their features?
- Unipolar - Only one axonal projection, nothing else protruding out of the cell body, used for receiving visual stimuli (usually)
- Pseudo-unipolar - also only have one projection from the main cell body, but the one projection spreads out into many parts, used for sensory NS e.g. pain stimuli
- Bipolar - 2 projections, only one is an axon, and the other is e.g. a dentrite
- Multipolar - most common morphology, numerous projections form the cell body, but still only ever has one axon, others are usually dendrites; has multiple connections with multiple cells (vital for its function)
What are the 3 types of multipolar neurons?
Pyramidal cells - ‘pyramid’ shaped cell body
Purkinje cells - GABA neurons found in the cerebellum
Golgi cells - GABA neurons found in the cerebellum
How are dendrites different compared to axons?
Dendrites - involved in receiving signals
Axons - involved in the transmission of signals
What are the 2 types of neuroglia cells?
Astrocytes
Oligodendrocytes
What are astrocytes and what are their most important roles?
Most abundant in the NS (more than neurons)
Appearance similar to a multipolar nuronal cell
Have foot processes important for areas of the brain such as the blood brain barrier
Important for structure - forms blood brain barrier and holds the neurons in the correct places (structure of NS)
Important for growth, maintenance and repair of the cells of the CNS (neurons and other astrocytes) by synthesising neutrophic factors
Important to maintain homeostasis i.e. mop up neurotransmitters, other substances released etc. floating around the CNS
What are oligodendrocytes and what are their functions?
Produces myelin for CNS - coats the axons of the neuronal cells
Has a cell body and cell projects to myelinate the axons of neuronal cells
One oligodendrocyte tends to myelinate parts of many axons
What is a schwann cell and role?
Has the same function as the oligodendrocyte but for the neurons part of the PNS
In the diagram, the axon goes through the centre (circular fashion)
What are some other cells that are part of the CNS?
Microglial - immune cells of the CNS, specialised cells, macrophages
Ependymal - cover ventricles, essentially epithelial cells within the nervous system
What would the CNS anatomy together with all the cells look like?
First the neurons
Next the oligodendrocyte covering / providing myeline for these axons on the neurons
Astrocytes (much smaller than the neurons) closely associated with the neuron
Microglia - neuronal macrophages
Ependyma - cover the ventricles and blood vessels
Zoom out = grey and white matter of the brain
What are the 4 ions involved in maintaining RMP and causing an AP?
K+
Cl-
Na+
Ca2+
How do neuronal cells maintain their resting membrane potential (RMP)?
What do the MP values mean in terms of excitability?
What factors contribute to MP?
Uneven distribution of the ions inside and outside the cell
Regulated by channels and pumps inside cell (ions cannot freely pass through the membrane)
High extracellular concentration of Na+, Cl- and Ca2+, and high intracellular concentration of K+, high concentration gradients for all the ions (especially for Ca2+)
Difference / concentration gradients form membrane potential - concentrated towards the inside of the cell
The more negative the value of the MP, the less excitable, so the less likely it is to generate AP (usually around -70 mV) - and vice versa, closer to -40mV is more excitable and so more likely to generate AP
Other factors contribute to MP, not solely difference in charges inside and outside the cell e.g. production of proteins produces a negative charge
Which ion has the highest concentration gradient across the membrane of a neuron?
Calcium
An imbalance of these ions can cause which conditions?
Hypo or hyper natremia - fall / rise in sodium concentration in the blood
Hypo or hyper kalemia - fall / rise in potassium concentration in the blood
How does transmission work at the NMJ?
Basically A level again ACh - acetylcholine
binds to nicotinic ACh receptor
