Nervous excitable tissue L3 Flashcards
What is the nervous system split into?
The central nervous system (CNS) and the peripheral nervous system (PNS)
What is the CNS?
Brain and spinal cord
What is the PNS?
Cranial nerves, spinal nerves, somatic nervous system (SNS) and autonomic nervous system (ANS)
What colour is grey matter in living tissue and why?
It is pink due to blood in the many capillaries coursing through this tissue
What 2 major areas is the brain sectioned into?
Gray matter and white matter
What is gray matter made up of?
It is made up of neuron perikarya (cell bodies), glial cells, axons, dendrites, synapses
What is white matter made up of?
axons and myelin sheaths and glial cells. There are no neuron perikarya (cell bodies) and no synapses
What are the functional divisions of PNS? HINT SAME
Sensory (Afferent) and Motor (Efferent) divisions
What are the sensory (afferent) divisions?
They carry signals to the CNS - receptors to CNS. The somatic division such as touch and pressure and the visceral sensory division such as taste and hunger
What are the motor (efferent) divisions?
From the CNS to effectors. The somatic motor division with effectors such as skeletal muscles and visceral motor division (also called ANS) with effectors in the glands and cardiac/smooth muscles
What can the autonomic nervous system be split into to?
The sympathetic and parasympathetic divisions
What is the somatic nervous system?
Motor innervation of all skeletal muscles
What is the autonomic nervous system?
Motor innervation of smooth muscle, cardiac muscle and glands
Brain cell types?
Neurons, astrocytes, microglia, oligodendrocytes (CNS) and schwann cells (PNS)
What do astrocytes do?
They release growth factors, create scar tissue and control the blood-brain-barrier (BBB).
What do capillaries do in the brain?
They form the blood-brain-barrier (BBB)
What do the oligodendrocytes do?
They provide myelin sheaths that insulate axons
What are the microglia and what do they do?
They are the macrophages of the brain and they provide an immune system, against infections but they release molecules that kill neurons
What is the soma?
The cell body
What do dendrites do?
They receive information
What do axons do?
They conduct information away
What is the synapse?
It is where 2 neurons “meet”
What is the myelin sheath?
It is a protective neuronal “covering”
What is the trigger zone?
The axon hillock
What is the conducting zone?
The axon - may be from 1mm to more than 1m long
What is the output zone?
axon terminals
What is the input zone?
Dendrites and cell body
Neurons can be classified depending on the number of branches directly from cell body. What are these?
Unipolar which is 1 branch, biopolar which is 2 branches and multipolar which can be many branches
For studying neurons what does the H&E method do?
H&E stains the nucleus but no detail on the cytoplasm can be seen
For studying neurons what does the Nissl method do?
Stains RNA but note absence from axon
For studying neurons what does the heavy metal impregnation method do?
Shows detail of cytoplasm, negative image of nucleus.
For studying neurons what does the gold method do?
Shows detail of neuronal shape and presence of cytoskleton in dendrites and axons
What are sensory neurons?
They are nerves that make you feel. They deliver information from sensory receptors in PNS to CNS
What are motor neurons?
They are nerves that make you move.They deliver commands from CNS to PNS, muscle glands.
Explain the 6 steps of neurotransmission:
- Action potentials reach the presynaptic terminal
- This stimulates Ca2+ entry
- Neurotransmitters are then released from synaptic
vesicles - The neurotransmitter crosses the synaptic junction at synapse.
- On the postsynaptic terminal, the transmitter binds to the receptor
- The receptor is activated to transmit a signal in postsynaptic neuron
What is the diameter fo synaptic vesicles?
40-60nm
Where are synaptic vesicles concentrated?
In clusters at nerve terminals
What does neurotransmitter release involve for presynaptic transmitter release?
The targeting of synaptic vesicles (SVs) to release sites, the docking of SVs to plasma membrane and priming to fuse SVs during impulse and then fusion/exocytosis & transmitter release and finally the retrieval of SV by endocytosis.
What can this presynaptic transmitter release by known as?
The kiss and run process
What happens to synaptic vesicles after this?
They are recycled without collapsing into the membrane
List the 4 steps of postsynaptic receptor activation:
- Neurotransmitters bind receptors
- The receptors are then activated
- Activation of the receptors transmits signals into the cell
- These signals cause the cell to grow, die, move, etc…
How do many drugs work in regards to receptors?
Many drugs work by binding to receptors
What do agonist drugs do?
They activate receptors like neurotrasnmitters
What do antagonists drugs do?
They inhibit receptors and they block neurotransmitters binding to receptors
Does myelination aid signal conduction velocity down the axon?
YES
Where is myelin made?
Oligodendrocytes make myelin on CNS axons and Schwann cells make myelin on PNS axons
What is myelin?
It is an electrical insulator sheath wrapped around axons
What are the short gaps in myelin along axons called?
Nodes of Ranvier
What is the difference between oligodendrocyte and Schwann cell production of myelin?
Each oligodendroycte has several processes, each of which makes a myelin sheath on a different axon, whereas Schwann cells each form only a single myelin sheath
What is the function of myelin sheath?
Myelin sheath acts as insulation. It prevents the flux of ions across the membrane.
What is the function of the nodes of Ranvier?
Acts as interruptions in the myelin sheath approx 1mm apart
Where are ion channels concentrated and what happens here?
Ion channels are concentrated at the nodes of Ranvier and action potentials happen here
What properties does the nodes of Ranvier have in association with action potentials?
The nodes of Ranvier have cable properties which mean the action potentials jump from node to node which is called saltatory conduction.
What is saltatory conduction?
It describes the way an electrical impulse skips from node to node down the full length of an axon
Is conduction faster in myelinated or unmyelinated axons?
Myelinated axons is faster
What does myelination do?
It aids signal propogation down the axon
What is a consequence of demyelination?
MS - Multiple Sclerosis
What is MS?
It is an auto-immune disease which is when the body starts to destroy itself. It is a life-long disease with no cure
What happens with MS and what does it affect?
In MS, the body attacks and destroys the fatty tissue called myelin that insulates an axon/nerve and this is called demyelination. If the damage is severe it will destroy the axon/nerve itself. MS affects the CNS and inflames the white matter in the brain that makes plaques.
How does the PNS communicate with the CNS?
3 classes of neurons - sensory, afferent and interneurons (1) Sensory (afferent) neurons in the PNS conduct signals from receptors to the CNS
(2) Interneuorns with are also called associated neurons are then confined to the CNS.
(3) Motor (efferent) neurons conduct signals from CNS to effectors such as muscles and glands.
An example of this is detecting your own pulse at your wrist.
What are the 3 neurons that the sensory system is composed of?
Primary neuron at the synapse from body (PNS) which goes to, secondary neurons that runs up the thalamus at the synapse and then tertiary neurons that runs up the cortex and then interepretation happens in the cortex
What is sensory afferent from? HINT B-B
Body to brain: To feel
What is motor efferents from? Hint B-B
Brain to body: to move
What are the 3 neurons that the motor system is made up of?
The upper motor neurons (UMN) in the cortex of the brain goes to the middle motor neurons (MMN) in spinal cord which goes to Lower motor neurons (LMN) where it leaves the spinal cord and innervates muscles
What is a general synaptic junction connecting?
Nerve - nerve
What is a neuromuscular synaptic junction covering?
Nerve-muscle
What are some key features of the generalised synapse? hint around 6
The Nerve-nerve synapse is smaller than a NeuroMuscular Junction and has a narrower synaptic cleft. It has a smooth postsynaptic membrane which gives a small surface area. May be excitatory or inhibitory and has numerous transmitter substances.
What are the key features of the neuromuscular junction? HINT: 6
NMJ is larger than a nerve-nerve synapse and has a wider synaptic cleft. The folds of postsynaptic membrane gives a larger surface area. The NMJ is always
excitatory and has only one transmitter – Acetylcholine.
What is a large motor unit?
for example 1000s fibres in biceps
What is a small motor unit?
For example 10 muscle fibres in eye
A motor unit is…
One motor neuron and all fibres it innervates, where one fiber is only innervated by one motor neuron and all fibres of a motor unit will contract together providing a stronger force.
What effect does the drug Curare have on neurotransmission and on muscle?
Curare blocks nicotinic acetylcholine receptor which causes muscle weakness
What effect does the drug Atropine have on neurotransmission and on muscle?
Atropine blocks muscarinic acetylcholine receptor which causes pupils to dilate and increases heart rate
What effect does the drug Botulinum Toxin have on neurotransmission and on muscle?
Botulinum toxin blocks acetylcholine release which causes muscle weakness
What effect does the drug Black Widow Venom have on neurotransmission and on muscle?
Black Widow venom promotes acetylcholine release and causes continuous contraction in the muscle
What effect does the drug Organophosphates (pesticides and nerve gas) have on neurotransmission and on muscle?
Organophosphates (pesticides and nerve gas) blocks acetylcholine-esterase and causes continuous contraction of the muscle
What is myasthenia gravis?
It is an autoimmune disorder
What does myasthenia gravis do to the body?
The body makes antibodies that attack nicotinic ACh receptors and with myasthenia gravis at NMJ, there are smaller End Plate Potential which may be sub-threshold and so fewer Action potentials happen in muscle so muscle contractile force is reduced and muscular weakness develops
How many cases per million is there of Myasthenia gravis?
200-400 cases per million
What are the symptoms of Myasthenia gravis?
Eye muscle weakness, weakness of other limbs, respiratory muscles – may need intubation to maintain airway
What treatments is there for myasthenia gravis?
Treatments include cholinesterase inhibitors eg
neostigmine and Immunosuppressants
Is summation needed for nerve synapse?
Yes summation is needed
What is the potential like for nerve synapse?
Potential is lower and there is always subthreshold
Is summation needed for the neuromuscular junction?
No summation is needed
What is the potential like for neuromuscular junction?
The potential is higher - it is always suprathreshold
What are neuroglia?
Neuroglia are supporting cells to neurons, they outnumber neurons in the nervous system
What is the function of neuroglia?
They protect the neurons and help them function, there are no axons or dendrites. For example in the fetus, neuroglia guide young migrating neurons to their destinations
What are the 4 types of neuroglial cells in CNS?
Astrocytes which are star shapes, oligodendrocytes, ependymal cells and microglia
What are astrocytes?
They are the most abundant glial cells that form the framework of CNS. They link neurons to blood vessels and contribute to the blood-brain barrier.
What are oligodedrocytes?
They form myelin sheaths in the CNS and must distinguish these from Schwann cells
What are ependymal cells?
They are epithelial cells which line ventricles of the brain and central canal of spinal cord and the produce CSF - cerebrospinal fluid
What are microglia?
Microglia are formed by monocytes which are engulf invading microbes. Microglia are in areas of infection, trauma or stroke
What are the 2 types of Neuroglial cells in the PNS?
Schwann cells and Satellite cells
What do Schwann cells do?
They myelinate fibers of the PNS and they assist in the regeneration of damaged fibers.
What do satellite cells do?
They surround cell bodies in the ganglia and regulate the chemical environment of the neurons
