Nervous system 1 13 Flashcards
What is the nervous system?
Network of fibres that span the body co-ordinating a diverse range of voluntary and involuntary actions
Which system does the nervous system work alongside?
Endocrine
What are the three areas of function of the nervous system?
Sensory (input)
Integration
Motor (response)
What is the sensory function of the nervous system?
Detect internal and external environment changes
Eg proprioception, sensation and touch
What impulse carries sensory information?
Sensory neurons
What is the integration function of the nervous system?
Processes sensory info
What carries integration info in the brain?
Interneurons
What are motor neurons?
Produce a response to sensory info to effect change
What 2 categories can the peripheral nervous system be divided into?
Somatic
Autonomic
2 categories of autonomic nervous system
Sympathetic
Parasympathetic
What controls the autonomic nervous system
Hypothalamus
How does the autonomic nervous system work and what’s it’s aim
Automatically and involuntarily to maintain homeostasis
What is the inversion of the sympathetic nervous system?
Thoraco-lumber
What is the inversion of the parasympathetic nervous system?
Cranio-sacral inversion
What happens to the body in a sympathetic state?
Pupils dilate
Bronchodilation
Heart rate and blood pressure increase
Git motility decreases
Liver converts glycogen to glucose
Adrenal glands release adrenaline
What happens to the body in a parasympathetic state?
Pupil constriction
Bronchoconstriction
Heart rate and blood pressure decease
GIT motility increases
Glycogen synthesis in liver
NO adrenaline
What is the enteric nervous system?
Brain of the gut containing 100 million neurons
What system regulates enteric nervous system?
Autonomic nervous system
Which nerve links the enteric nervous system to the CNS
Vagus nerve
What do sensory neurons monitor in the enteric nervous system?
Chemical changes
Stretch receptors
What do motor neurons do in the enteric nervous system?
Govern motility and secretions
What do interneurons do in the enteric nervous system?
Connect the two plexus
2 types of cell found in nervous tissue
Neurons
Neuroglia (glial cells)
What do neurons do?
Process and transmit info
Electrically excitable
Functional unit of the nervous system
What do neuroglia (glial cells)
Supporting cells that nourish, support and protect neurons
What percentage of the brain is made up of neuroglia?
90% brain volume
What is a nerve?
Bundle of one or more neurons
What is a neuron ability to create an electrical impulse called?
Action potential
What are collections of cell bodies known as? Note they have different names in the CNS and PNS
Nuclei - for functional and structural units of brain
Ganglia - in PNS
What are cell bodies known collectively as?
Grey matter
What do axons do?
Carry nerve impulses towards another neuron, away from the cell body
What are axon bundles called?
Tracts in CNS
Nerves in PNS
If injured how quickly can axons regenerate
1-2mm per day
What is the myelin sheath
Multi-layered lipid and protein covering around the axon
What is the benefit of the myelin sheath?
Increases the speed of nerve conduction
What are the gaps in the myelin sheath called?
Nodes if Ranvier
What vitamin (Co-factor) is needed for th production of myelin
Vitamin B12
3 facts about what grey matter is made from
Mostly cell bodies
Dendrites
Unmylinated axons
1 facts about what white matter is made from
Myelinated axons
Whiteish colour if myelin gives the region its name
What are neuroglia or glial cells?
Non-excitatory
Surround and bind neurons
Size and prevalence of neuroglia compared to neurons
Smaller than neurons
50 x more prevalent
They can multiply and divide (unlike neurons)
3 functions of neuroglia
1 surround neurons
2 supply nutrients
3 destroy pathogens
Name the 6 types of neuroglia
Astrocytes
Oligoendrocytes
Microglia
Ependymal cells
Schwann cells
Satellite cells
Facts about astroxytes
In CNS
Star-shaped
Most numerous and largest (in CNS)
Hold neurons to their blood supply
Contribute to BBB
Facts about oligodendrocytes
Glial cells that myelinate axons in the CNS
Facts about microglia
Derived from monocytes - migrate to CNS after birth
Immune cell in brain
Phagocytise
Mobil in brain
Facts about ependymal cells
Line the walls of the cerebrum & spinal cord central canal
Produce cerebrospinal fluid (csf)
Facts about Swann cells
Peripheral nervous system
Produce myelin
Myelin increases speed of nerve impulses
Unmylenated gaps called nodes of Ranvier
Facts about satellite cells
Surround cell bodies in the PND ganglia providing structural support & nutrients
PROTECTIVE & NUTRIENTS
What are the two types of electrical signal from a neuron?
Graded potential and action potential
Facts about graded potential
Short distance communication
Dendrites and cell body
Amplitude proportional to strength (no threshold)
Longer duration
Facts about action potential
Long-distance communication
Propagated down axon
All or nothing (as threshold) - think spider
Shorter duration
2 characteristics that facilitate graded and action potential
Specific ion channels that open and close
Electrical difference - resting potential
What do ion channels do?
Transport channels for ions created by transmembrane proteins within the neuron membrane
What happens when ion channels open?
They allow specific ions to move through the membrane across the concentration gradiant
What makes ion channels open?
A stimulus which changes the permeability of the membrane
Stimuli include changes in voltage, hormones and mechanical pressure
How is resting potential created?
By a build up of negative ions on the inside of the cell membrane relative to the extracellular fluid which contains more positive ions
How many mV is the resting potential
-70mV
What is the term for a cell exhibiting a membrane potential
Polarised or charged
What is the extracellular fluid rich in and is it positive or negatively charged?
Sodium NA - positively charged
What is the intracellular fluid rich in and which charge does it carry?
Potassium K negatively charged
What controls the separation of charges?
The sodium potassium pump
What ratio of molecules does the sodium potassium pump allow through?
It pumps 3 NA (sodium) for every 2k (potassium) back in using ATP
What is an action potential
The formulation of a nerve impulse
A series of events that reverses the membrane potential and then restores it to its resting state.
What are the two phases of action potential
Depolarisation
Repolarisation
What happens in depolarisation
The negative membrane potential -70mV becomes positive +3-mV
It must reach a threshold of -5∞mv to generate an action potential
Sodium channel opens to allow potassium to flood in up to +3-mv
What happens in repolorisation
The membrane is restored ot -70mv
Potassium channel opens more slowly
Allows potassium to flood out of the the cell and restores the membrane potential
What is the action potential refractory period?
After repolarisation where the nerve cannot generate another action potential because sodium and potassium are on the wrong sides of the membrane.
What is the absolute refractory period?
Even a strong impulse cannot generate an action potential
What is the relative refractory period?
A larger than normal stimulus is needed to generate an action potential
What is conduction
Movement of a nerve impulse along the axon of a neuron
Facts about unmyelinated axons
No myelin sheath around the nerve
membrane depolarised in a continuous conduction away from cell body
Step-by-step repolarisation and repolarisation in one direction only
Facts about myelinated axons
Myelin is an insulator
At nodes of Ranvier there is a high concentration of Sodum gates
Action potentions leap accross myelinated axon
Saltatory conduction is more energy efficient
What is saltatory conduction
‘leaping’ of currents from node to node
Continuous conduction key facts
Unmyelinated
Step-by-step depolarisation
Slower
Less energy efficient
Saltatory conduction
Myelinated
‘leaps’ of depolarisation
Faster
More energy efficient
How do local anaesthetics work?
Block sodium gates - stopping action potential
What are synapses?
Gaps between neurons
What is a synaptic end bulb?
End of an axon terminal
What is a synaptic cleft
Space between synaptic end bulbs filled with interstitial fluid
What is the chemical messenger which carries the nerve impulse along the synaptic cleft?
Neurotransmitters
4 stages for a synapse transmitting a signal
- action potential at synaptic end bulb
Depolarisation - calcium channels open - Increase in calcium concentration - exocytosis (movement out) of synaptic vesicles - neurotransmitters released
- Neautrotransmitters diffuse and bind to receptors
- Ion channels open generating action potential
What is a neurotransmitter
Chemical messenger
Released from a pre-synaptic terminal causing and effect on a post-synaptic cell
100’s have been indentified
4 categories of neurotransmitters
Amino acids
Monoamines
Peptides
Unique molecules
2 examples of amino acid neurotransmitters
glutamate and GABA
2 examples of monoamine neurotransmitters
dopamine and serotonin
1 example of a peptide neurotransmitter
Endorphin
1 example of a unique molecule neurotransmitter
Acetylcholine
2 ways to classify neurotransmitters
Excitatory or inhibitory
Compare excitatory and inhibitory neurotransmitters
Excitatory - causes depolarisation
Opens sodum channels
Inner membrane becomes more positive
Inhibitory - causes - hyperpolarisation
Opens postassium channels
Inner membrane becomes more negative
How can neurotransmitters be inactivated or removed
Diffusion
Enzyme breakdown
re-absorption
What is glutamate and what does it do?
Excitatory NT in CNS. Plays a role in memory and learning
What is GABA and what is it produced by?
Major inhibitory NT in the brain - produced by glutamate
What vitamin is the conversion of glutamate of GABA dependant on ?
B6
What is glutamate produce from?
Glutamine
What is Serotonin produced from?
The animo acid tryptophan
Where is most serotonin produced?
95% in enteric nervous system - digestive tract
What is serotonin’s role in the GIT
Peristalsis and secretion
What does serotonin play are role in
peristalsis, sleep, attention and pain regulation
Where is dopamine located?
Several areas of the brain including the substantia nigra
What is dopamine produce from?
The animo acid tyrosine
What does dopamine play a role in?
Movement, reward mechanisms, muscle tone, cognition and emotion
What disease is dopamine depletion associated with?
Parkinson’s disease
Key facts about adrenaline and noradrenaline
Monoamine
Produced from tyrosine
Excitatory - open sodium channels
What are neuropeptides?
Small proteins acting as neurotransmitters and hormones
What are common neuropeptides?
Endorphins
Dynorphins
substance P
What does substance P enhance?
The feeling of pain
What are enkephalins, endorphins and dynorphins?
Opioids - body-s natural analgesics
