How Nerves Work 1-5 Flashcards
Describe the anatomical organisation of the nervous system.
The nervous system has two main parts: The central nervous system is made up of the brain and spinal cord. The peripheral nervous system is made up of nerves that branch off from the spinal cord and extend to all parts of the body.
Describe the general structure of a neurone.
A neuron has three main parts: dendrites, an axon, and a cell body or soma (see image below), which can be represented as the branches, roots and trunk of a tree, respectively. A dendrite (tree branch) is where a neuron receives input from other cells.
Define the different types of glia.
Oligodendrocytes form the myelin sheath around axons. Astrocytes provide nutrients to neurons, maintain their extracellular environment, and provide structural support. Microglia scavenge pathogens and dead cells. Ependymal cells produce cerebrospinal fluid that cushions the neurons.
Microglia. The microglia are phagocytic cells. …
Macroglia. The macroglia are the larger neuroglia present in the nervous system. …
Ependymal Cells. The ependymal cells are of three variants. …
Schwann Cells. The Schwann Cells are like a counterpart to the oligodendrocytes. …
Satellite Cells. small multipotent cells with very little cytoplasm found in mature muscle. Satellite cells are precu.sors to skeletal muscle cells,
Describe the ionic basis of the resting membrane potential.
What generates the resting membrane potential is the K+ that leaks from the inside of the cell to the outside via leak K+ channels and generates a negative charge in the inside of the membrane vs the outside. At rest, the membrane is impermeable to Na+, as all of the Na+ channels are closed.
Explain the properties and functions of graded potentials.
Graded potentials are variable strength signals occurring when ion channels open or close in response to stimuli, typically on. In contrast, action potentials are brief, identical depolarization events that propagate along axons, initiated only when the membrane reaches a threshold of approximately -55 mV.
Describe the classification of nerve fibre types.
Group A Nerve Fibres: Group A nerve fibres are heavily myelinated nerve fibres that are further subdivided into four types: alpha Aα; beta Aβ; gamma Aγ; and delta Aδ. The fibres with larger diameters and more myelination tend to transmit the impulses at a faster rate.
Group B Nerve Fibres: Group B nerve fibres are less myelinated than group A, but more myelinated than group C nerve fibres. They include visceral nerves such as the vagus nerve.
Group C Nerve Fibres: Group C nerve fibres are unmyelinated fibres that usually have a smaller diameter and low conduction velocity.
Describe the ionic basis of the action potential.
An action potential is a rapid sequence of changes in the voltage across a membrane. The membrane voltage, or potential, is determined at any time by the relative ratio of ions, extracellular to intracellular, and the permeability of each ion. Depolarization during an action potential results from a transient rise in membrane Na+ permeability.
Define conduction velocities and their relationships to fibre types.
A types are fastest with decreasing velocity from alpha (70-120m/s) followed by beta then gamma and finally delta (12-30m/s)
B types are between 3-15m/s
C types are Dorsal horns at 0.5-2 and sympathetic at 0.7-2.3m/s
Conduction velocity refers to the speed at which action potentials propagate along a muscle fiber, which can be estimated by measuring the time delay between two recorded signals from electrode locations a certain distance apart.
Describe the consequences of demyelinating diseases.
When the myelin sheath is damaged, nerve impulses slow or even stop. This can cause neurological symptoms such as trouble walking or seeing, or changes in bowl and bladder function. Common symptoms of a central nervous system demyelinating disease may include: Vision changes, including blurry vision, impaired color vision, pain with eye movement or double vision. Tingling or numbness in various parts of your body. MS hug or a squeezing sensation around your chest or abdomen.
Describe the structure of the neuromuscular junction.
For convenience and understanding, the structure of NMJ can be divided into three main parts: a presynaptic part (nerve terminal), the postsynaptic part (motor endplate), and an area between the nerve terminal and motor endplate (synaptic cleft).
Describe the process of neuromuscular transmission.
- Action Potential: An electrical signal travels down a motor neuron to the neuromuscular junction.
- Calcium Influx: The action potential opens calcium channels, allowing calcium ions to enter the neuron.
- Release of Acetylcholine: Calcium triggers the release of acetylcholine (ACh) into the synaptic cleft.
- ACh Binding: ACh binds to receptors on the muscle fiber, opening sodium channels and depolarizing the muscle membrane.
- Action Potential in Muscle: The depolarization generates an action potential that travels along the muscle membrane and into the T-tubules.
- Calcium Release: The action potential causes the sarcoplasmic reticulum to release calcium ions, which initiate muscle contraction.
- Contraction: Calcium binds to proteins in the muscle, allowing actin and myosin to interact, resulting in contraction.
- Termination: Acetylcholine is broken down, stopping the signal, and calcium is pumped back into the sarcoplasmic reticulum, leading to muscle relaxation.
Describe the ultrastructure and functions of synapses between neurons.
A synapse is made up of a presynaptic and postsynaptic terminal. The presynaptic terminal is at the end of an axon and is the place where the electrical signal (the action potential) is converted into a chemical signal (neurotransmitter release).
Describe the processes of synaptic transmission in the CNS.
Synaptic transmission is the process at synapses by which a chemical signal (a transmitter) is released from one neuron and diffuses to other neurons or target cells where it generates a signal which excites, inhibits or modulates cellular activity.
Explain the role of synapses in integration of neuronal function.
Synapses can be thought of as converting an electrical signal (the action potential) into a chemical signal in the form of neurotransmitter release, and then, upon binding of the transmitter to the postsynaptic receptor, switching the signal back again into an electrical form, as charged ions flow into or out of the postsynaptic neuron.
Describe common excitatory and inhibitory neurotransmitters.
Examples of excitatory neurotransmitters include glutamate, epinephrine and norepinephrine. Inhibitory. Inhibitory neurotransmitters block or prevent the chemical message from being passed along any farther. Gamma-aminobutyric acid (GABA), glycine and serotonin are examples of inhibitory neurotransmitters.
