2.2 - Cells of the Nervous System Flashcards
1
Q
What does the CNS consist of?
A
- brain and spinal cord
- two cerebral hemispheres, brainstem, cerebellum, spinal cord
2
Q
Cerebral hemispheres
A
- two cerebral hemispheres aka telencephalon - distinctive convoluted surface with ridges called gyri and valleys called sulci
Each hemisphere is split into: - frontal lobe - executive functions like personality
- parietal lobe - contains somatic sensory cortex responsible for processing tactile information
- temporal lobe - contains hippocampus (short term memory), amygdala (behaviour) and Wernicke’s area (auditory perception and speech)
- occipital lobe - processing of visual information
3
Q
What does the brainstem consist of?
A
- the midbrain, pons and medulla in descending order
- these structures have a multitude of important functions (e.g. control of respiration and heart rate)
- they are the target / source of all cranial nerves
4
Q
Where is the cerebellum and what is its role?
A
- located towards the dorsal region of the CNS and attached to the brainstem
- important role in motor coordination, balance and posture
5
Q
What is the spinal cord?
A
Extends down from medulla and acts as a conduit for neural transmission but can coordinate some reflex actions
6
Q
Neuron morphology
A
- unipolar - consists of a cell body with one axonal projection
- pseudo-unipolar - single cell body with single axonal projection that bifurcates (forks into) 2 different branches
- bipolar - single cell body with 2 projections - one is the axon, the other is the dendrite
- multipolar - numerous projections from cell body - 1 is axon, rest are dendrites: e.g.
- pyramidal cells - pyramid shaped cell body
- Purkinje cells - GABA neurons found in the cerebellum
- Golgi cells - GABA neurons found in the cerebellum
7
Q
How can neurons be described?
A
- excitable cells of the CNS - able to change their membrane potential to communicate with other cells
- have heterogenous morphology - look different to each other
- non-dividing cells (but there’s evidence of some dividing neurones in brain which can be important for growth)
8
Q
What do all neurones have in common?
A
Soma (cell body, perikaryon)
- contains nucleus and ribosomes
- has neurofilaments which are important for structure of neurone and transport of proteins e.g. to end of axons/dendrites
Axon - single projection of cell body that originates from soma at axon hillock
- can branch off into collaterals
- usually covered in myelin - allows signals to be transmitted at faster rate
- ‘voice’ of neuron - used to communicate
Dendrites - branches of cell body not covered in myelin
- receive signals from other neurons
- ‘ears’ - listens to communication from other neurons
9
Q
What are astrocytes?
A
- most abundant cell type in CNS
- structural cells - have an important role in cell repair (neurotrophic factors), synapse formation (NT removal and reuptake), neuronal maturation and plasticity
10
Q
What are oligodendrocytes and Schwann cells?
A
- oligodendrocytes - glial cells that are the myelin-producing cells of the CNS
- each cell body sends out numerous projections that form internodes of myelin covering the axon of neurons
- capable of myelinating a number of neurons
- Schwann cells are the myelin producing cells of the PNS - myelinates a single axonal segment
11
Q
What are microglial and ependymal cells?
A
- microglial - specialised cells similar to macrophages that perform immune functions in CNS
- ependymal - epithelial cells that line fluid filled ventricles regulating the production and movement of CSF
12
Q
What is the resting membrane potential?
A
- caused by uneven distribution of ions inside and outside cell
- 4 major physiological ions - K+, Na+, Cl-, Ca2+
- cell membranes are impermeable to these ions –> transportation regulated by channels and pumps
- this causes an uneven ion distribution: high extracellular Na+ and Cl-, low extracellular K+ = high concentration gradient for Ca2+
- difference in concentration –> creates a potential difference across the membrane
- neuronal cells - negative charge inside compared to outside
- RMP of -40 to -90 mV = RMP -70 mV
- positive and negative charges concentrated around membrane
13
Q
Action potentials
A
- at RMP, VGSCs and VGKCs are closed
- when the membrane is excited and there is a change in potential, membrane is depolarised which opens VGSCs and causes Na+ influx into cells which causes further depolarisation
- VGKCs open at a slower rate and cause efflux of K+ from cell - this causes membrane repolarisation
- there is a local imbalance of Na+ and K+ that needs to be restored
- Na+K+ATPase restores ion gradients
1) in pump’s resting configuration - Na+ enters vestibule and upon phosphorylation, the ions are transported through protein
2) in pump’s active configuration - Na+ removed from cell and K+ enters the vestibule
14
Q
What is saltatory conduction?
A
- AP spreads along the axon by ‘cable transmission’
- myelin prevents AP spreading because it has high resistance and low capacitance
- Nodes of Ranvier are small gaps of myelin intermittently along axon - contain high concentrations of VGSCs, VGKCs and Na+K+ATPase
- AP jumps between nodes in saltatory conduction
- AP is unable to jump across the synapse at the axon terminal which is where neurotransmitters come in
15
Q
What is the synapse?
A
- a junction consisting of a pre-synaptic nerve terminal (e.g. axon terminal) and a post-synaptic cell (e.g. dendrite of another neurone) by an extracellular space called the synaptic cleft
- electrical signal can’t jump over synaptic cleft so is converted into a chemical signal to cross the synapse then back into an electrical signal on the post-synaptic cell
