Cells and communication in the nervous system Flashcards
What are the functions of the nervous system?
Sensation, integration and activation
What is sensation?
Receptors in skin and organs respond to changes in the internal or external environment and provide information to the central nervous system (CNS)§
What is integration?
Input from the internal and external environment is processed and integrated by the CNS. Decisions are made and appropriate responses formulated
What is activation?
Appropriate response forwarded to the appropriate muscles and glands (muscle contractions and secretions)
Give some mechanisms for nervous system dysfunction
- Damage by trauma or disease
- Neurons lose ability to produce transmitters
- Neurons over- or under-produce transmitters
- Neurons fail to recognise transmitters
- Effector organs fail to respond
How can dysfunction of the nervous system manifest as?
- Loss: of sensation or function
- Gain: appearance of new feature
- Change: alteration in behaviour/personality or perception
What are the 2 types of neurons?
Principal cells and interneurons
Name the 5 types of glial cells
Astrocytes, ependymal cells, microglia, oligodendroglia, Schwann cells. A E I O (and Schwann) Vowel frequency in each cell type to help remember.
What are astrocytes?
star-shaped cells which form a bridge between the neuron and blood vessels
What are ependymal cells?
simple, ciliated, cuboidal cells that form the lining of the ventricular system
What are microglia?
small glial cells, activated by trauma. Immune response.
What are oligodendroglia?
myelin producing cells, found in the CNS. Feet project and wrap many neurons
What are Schwann cells?
myelin producing cells, found in the PNS. One cell wraps one neuron.
What is the purpose of myelination?
Insulation, development (Not complete at birth), speeds communication, saltatory conduction
Name some disorders of myelination
Multiple Sclerosis (affects CNS); Guillain Barre (affects PNS)
Describe a chemical synapse
- Fast transmission (slower cell-cell, but can cope with higher. frequency of activity)
- Vesicles released from presynaptic terminal
- Act on receptors in postsynaptic terminal
- Major drug target
Describe an electrical synapse
- Slower transmission (faster cell-cell, but more effective at lower frequencies)
- Gap junctions
- Small molecules and current
- ‘low-pass filter’
- Synchrony
- Up and coming drug target
Describe communication at the neuromuscular junction
- Action potentials trigger the exocytosis of acetylcholine (ACh) from the synaptic terminal
- ACh crosses the cleft
- Acts on (nicotinic) cholinergic receptors in the motor end plate
- Initiates muscle contraction
- Impulse carried through muscle via T-tubules and sarcoplasmic reticulum
What is myasthenia gravis?
autoimmune disease affecting the NMJ. Circulating antibodies block Ach receptors, slowing muscle activity and reducing tone.
Describe the role of neurotransmitters
Used by neurons for rapid cell-cell communication
- Stored in vesicles in the presynaptic terminal
- Released when the terminal is depolarised during an AP
- Pass across the synaptic cleft
- Activate receptors on the postsynaptic terminal
- Binds to receptor
Describe neuromodulators
- Found in vesicles (or not), co-localised with NT
- Act on receptors or membranes to indirectly alter neuronal activity
- Changing sensitivity or kinetics of NT receptor
- Also act on glial cells
What are inotropic receptors?
Linked to ion channels
What are metabotropic receptors?
GPCRs
What are specialised receptors?
General sensation and sensory organs. Developed to respond to particular stimuli. Transduce physical to electrical activity.
What are the 4 main types of cutaneous specialised receptors?
- Mechanoceptors – detect tactile sensation (touch, pressure)
- Thermoceptors – detect temperature changes
- Nociceptors – detect painful/noxious stimuli
- Proprioceptors – detect changes in head and body position
What is the major excitatory transmitter? What is the major inhibitory neurotransmitter?
Excitatory - Glutamate
Inhibitory - GABA
What is direct inhibition?
Excitatory neurons have regular firing in absence of inhibition. Inhibitory input sculpts this firing producing patterns of activity (coding). Coding carries the information and can be read by the brain, like morse code. Some drugs that increase firing can lead to loss of coding, and psychological side effects
What is lateral inhibition?
Activation of excitatory cells also activates associated inhibitory cells.
Inhibition acts on neighbouring cells to reduce activity – allows brain to pinpoint where signal is coming from.
Strengthens response of cell directly stimulated.
Seen in sensory pathways:
Vision, touch, olfaction
What is disinhibition?
Two negative make a positive. Activation of inhibitory circuit leads to excitation. Important in basal ganglia.
What is synchrony?
Co-ordinates activity. cell-cell via gap junctions. Pacemaker cells, like heart. Investigated using electroencephalography (EEG).
Synchrony changes strength at network level!
What is plasticity?
Up- or down-regulation of synaptic strength. LTP and LTD. Synaptic morphology. Metabolic changes. Subunit changes.
Plasticity changes strength at neuronal level!
