Neurons & related cells Flashcards
Name the 3 types of neurons and their function
Sensory (transmit signals from receptors to CNS)
Relay (inter)(connects sensory to motor, found in brain)
Motor (transmits signal from CNS to effector muscle/gland)
Describe the function of the: dendrites, dendritic spines, axon & axon hillock
Dendrites- hey receive electrical signals from other neurons or sensory receptors and transmit these signals toward the soma.
Dendritic spines- These spines play a critical role in synaptic transmission, where signals are transferred from one neuron to another. They also play a role in synaptic plasticity, which is the ability of synapses to strengthen or weaken over time based on activity, contributing to learning and memory.
Axon- transmits electrical signals (action potentials) away from the soma to other neurons, muscles, or glands. The axon ensures that the electrical impulses are carried over long distances in the body, allowing communication between different parts of the nervous system.
Axon hillock- The axon hillock is the region where the axon connects to the soma. It acts as the trigger zone for the neuron. When the summed input from the dendrites reaches a certain threshold at the axon hillock, it triggers an action potential (an electrical impulse) that travels down the axon.
Describe the function of the: cell soma, intracellular components, terminal boutons and terminal branches
Soma- contains the nucleus and most of the cell’s organelles. It is responsible for maintaining the cell’s metabolic functions, including energy production, protein synthesis, and the integration of signals from the dendrites. The soma processes incoming signals and, if they are strong enough, sends an action potential down the axon.
Terminal branches- are secondary branches of the axon that allow the neuron to communicate with multiple other neurons or target tissues. These branches increase the reach of the axon and help transmit the signal to multiple destinations at once.
Terminal boutons- bulbous endings at the tips of the terminal branches. They contain synaptic vesicles filled with neurotransmitters. When an action potential reaches the terminal boutons, these vesicles release neurotransmitters into the synaptic cleft, allowing communication between neurons or between a neuron and a muscle or gland.
Intracellular components: e.g., RER, nucleus, golgi apparatus and mitochondria
Define resting membrane potential
RMP is where the cell is polarised is roughly -70mv, this is maintained via the Na/K+ pump, 3Na+ pumped out and 2K+ ions pumped in. AP triggers depolarisation of up to +20-30Mv
How is Membrane potential sensed via dendrites?
Are sensed through ligand-gated ion channel activation, ESPS lead to depolarisation and ISPS lead to hyperpolarisation
this is needed for neuronal processing
What is a graded potential?
This typically occurs in MP changes in dendrites, where the changes are proportional to the strength of the stimulus. Magnitude of change deoends on the number & type of neurotransmitter involved. These GP’s can pass through dendrites, but their magnitude decreases as they travel. strongest influence when close to synapse
Graded vs action potential
Graded potential and action potential are the two types of potential differences that can be generated during depolarization. The main difference between graded potential and action potential is that graded potentials are the variable-strength signals that can be transmitted over short distances whereas action potentials are large depolarizations that can be transmitted over long distances. Graded potential may lose the strength as they are transmitted through the neuron but, action potentials do not lose their strength during the transmission.
Mechanism of AP on RMP
- RMP: The base RMP is typically -70Mv, this is maintained by the Na/K+ pump
- Depolarisation: When a neuron recieves an AP, neurotransmitters are released from the synapse and bind to receptors on the post-synaptic membrane, this triggers the opening of Na+ gated channels to open and flow into cell, making RMP slightly more positive
- Threshold potential: If Depolarisation is strong enough, around -40Mv, it triggers further opening of Na+ channels, causing large influx of Na+
- Rapid depolarisation: large influx of Na+ triggers RMP to become less negative (+20-30Mv), this is the start of the AP
- APP: action potential propagation, where after peak, Na+ channels begin to close and K+ open to repolarize the membrane
- After AP: refactory period occurs where the neuron cannot be stimulated again during this time, no AP fired, RMP is restored, ion concentrations restored
Define hyperpolarisation
Where the RMP becomes more negative than -70Mv, due to influx of Cl-, this is needed so neuronal firing can be inhibited preventing generation of another AP. As well as regulation neuronal excitability, signaling & to ensure proper muscle function and neuronal activity
Define the refactory period
The time in which a neuron is unable to produce an AP
Explain action potential propagation
It refers to the movement of the AP along the axon, which enables transmission from the cell body to axon terminals.
AP travels in one direction by previous sections of the axon entering the refactory period, so the AP is unable to travel backwards.
Speed of propagation is dependent on diameter of axon and myelination of axon.
If axon is myelinated it is able to be sped up via saltatory conduction, where AP can jump between nodes of ranvier, speeding up transmission
Describe the importance & mechanism of the presynaptic terminal
Site where AP’s are converted to neurotransmitters, allowing communication between neurons and effector cells.
Mechanism:
1. AP arrives and depolarises presynaptic terminal
2. Ca2+ channels open causing large Ca2+ influx
3. SNARE proteins mediate vesicle fusion with presynaptic membrane
4. Neurotransmitters are released in to synapse and diffuse across
5. NT bind to receptors & trigger a response
6. Neurotransmitters are broken down or reabsorbed. Snare proteins are recycled
Describe SNARE complex and explain the stages involved in SNARE complex
Protein groups needed for vesicle fusion with presynaptic membrane.
2 types: T & V SNARES
T-type: found on the target membrane (presynaptic), main t-SNARE proteins in synaptic transmission are syntaxin and SNAP-25.
V-type: Located on vesicle membrane, The primary v-SNARE in synaptic vesicles is synaptobrevin (also known as VAMP).
Describe the stages in the SNARE complex
- Docking: where the vesicle containing neurotransmitters approaches PSM, V-snare on vesicle interacts with t-snare on membrane
- SNARE complex formation: V & T SNARE bind to each other forming a bundle that helps pull PSM & vesicle together
- Membrane fusion: Lipid bilayers of TM & vesicle fuse, SNARE complex forms & fusion occurs
- SNARE complex is broken down and parts are recycled, NSF & alpha snap facilitates this which uses ATP hydrolysis to detach and reuse proteins.
Describe the effects of tetanus & botulinum on the SNARE complex
Tetanus affects V-snares, they prevent release of inhibitory neurotransmitters e.g., GABA, this causes spastic paralysis, muscle spasms etc, due to uncontrolled excitatory signalling
Botulinum affects T-snares & V-snares as it prevents released of ACH at the NMJ leading to muscle paralysis
Describe the similarities & differences between effects of tetanus and botulinum
Botulinum and tetanus both effect V-snare proteins, they both act on SNARE complex
Botulinum acts on V & T SNARES, causes muscle paralysis & weakness, prevents muscle contraction, whereas tetanus causes uncontrolled spasms and excessive muscle contraction
How are neurotransmitters removed from the synapse?
- Diffusion: they diffuse away after entering synaptic cleft
- enzymes: they are broken down via enzymes
- Uptake: they are retake up by neuron & transported to neighboring cell
Describe & explain the function of nicotinic & muscarinic receptors
NR: found at NMJ, ACH binds to these receptors allowing entry of Na+ & Ca2+, leads to depolarisation creating an AP, Nicotinic receptors mediate fast excitatory responses, primarily in muscle contraction and autonomic nervous system function.
MR: are g-coupled receptors, ACH binds signalling pathways that can inhibit or excite cellular activity, In the heart (M2 receptors): They slow the heart rate by inhibiting adenylyl cyclase and decreasing cAMP levels.
In smooth muscles and glands (M3 receptors): They stimulate contraction and secretion (e.g., in the digestive system).
Summary: Muscarinic receptors mediate slower, more complex responses that can either increase or decrease activity in target cells, particularly in the heart, smooth muscles, and glands.
Define neuronal intergration
Refers to which neurons intergrate or combine incoming signals from multiple sources, to conclude whether or not to generate an AP.
It is needed to:
- process information & patterns of input to respond correctly, whether to fire an AP or stay at RMP
- Complex behaviours: involved in memory, processing and learning
- allows the NS to adapt by integration of different signals and respond to stimuli
Describe the function of glial cells & Name them
Glial cells are needed to provide the brain with nutrients, CSF, remove toxins from the brain, immune defense, formation and production of mylein sheath. They support neurons, help provide insulation, provide nutrients, maintain chemical environment and destroy pathogens & toxins
Function of glial cells involved in CNS
Microglial cells: act as immune cells, removes dead cells, and surveys the brain for threat, also involved in pruning of the brain, mediate an immune response
Oligodendrocytes: produce myelin for cell axons, provide insulation and improves electrical transmission
Astrocytes: regulate ion concentrations, reinforce the blood brain barrier and maintain a balance of neurotransmitters
Ependymal cells: needed to produce CSF and maintain stability of the brain
Function of glial cells involved in PNS
Schwann cells: form mylein sheath on cell axons, enable fast transmission of signals
Satellite cells: protect the brain from toxic substances, involved in growth, maintenance & repair of muscles
What are the key causes of nerve ageing?
Loss of myleination: The myelin sheath, which insulates nerve fibers and speeds up electrical signal transmission, tends to deteriorate with age. Reduced myelin production leads to slower nerve conduction and decreased efficiency of nerve signaling.
Decreased nerve regeneration: As we age, the capacity of nerves to regenerate after injury or damage decreases. This is due to a decline in the activity of certain proteins and factors that promote nerve growth and repair.
Neuronal atrophy refers to the shrinkage or degeneration of neurons (nerve cells) and their associated structures, leading to a loss of function. Neurodegenerative Diseases: Conditions like Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease cause progressive neuronal atrophy due to the accumulation of toxic proteins or other pathological changes in the brain.
Desecribe the nervi nervorum & vasi nervorum
The nervi nervorum are small nerve fibers that provide sensory innervation to the connective tissues of nerves, such as the epineurium, perineurium, and endoneurium. Their primary function is to detect sensations like pain, tension, and mechanical changes within the nerve itself. Essentially, they help monitor the health and condition of the nerve by sending feedback about potential damage or stress to the nerve tissue.
Vasi Nervorum: The vasa nervorum are small blood vessels that supply oxygen and nutrients to the nerves, particularly the nerve fibers and their surrounding connective tissue layers (such as the epineurium and perineurium). Their primary function is to maintain the health and metabolic needs of the nerve tissue, as nerves require a constant blood supply to function properly and repair themselves.
Describe the nerve anatomy layers of Perineurium, epineurium & endoneurium
Perineurium: protective layer that surrounds each nerve fasicle, provides a barrier to prevent spread of toxins/pathogens
Endoneurium: thin connective tissue layer that surround each axon within the nerve, provides nutrients & support to nerve
Epineurium: Outermost connective tissue layer, surrounds whole nerve giving protection, structure and elasticity
Describe the function of the: nerve fasicle, Nerve fiber & BV’s
Fasicle: refers to a bundle, which nerves are grouped into, surrounded via perineurium
Nerve fiber: also known as the axon that conducts electrical signals away from the cell body, some are myleinated, some contain nodes of ranvier which speeds up neuronal propagation
BV: Nerves have blood vessels that supply oxygen and nutrients to the nerve tissues. These vessels are located within the epineurium and bring vital substances to the nerve fibers.
Describe the function & importance of schwann cells
They are a type of glial cell involved with the myelination of axons in the PNS. Schwann cells wrap around the axon & provide insulation & speed up electrical conductivity, improve electrical transmissions
