Week 1 - nerve and muscle Flashcards
What are nerves and muscle cells known as and what does this mean?
- They are known as excitable cells meaning they can undergo transient, rapid fluctuations in their membrane potentials which serve as electrical signals
- These signals are used to recieve, process, initiate and transmit messages

What does the nervous system consist of at the highest level?
- The central nervous system (CNS) and the peripheral nervous system (PNS)
At the second, level what does the nervous system consist of?
- CNS:
- Brain
- Spinal chord
- PNS:
- Numerous nerves in the body
- Special sense organs required for:
- Sight
- Hearing
- Taste
- Smell
- Touch
What are the subdivisions of the PNS and what do they do?
- The autonomic nervous system encompasses the structures involved in regulating involuntary functions, e.g. heart rate & contractions of the stomach and intestine
- The somatic nervous system is under voluntary control

Describe the structure of nerve cells
Neurones, or nerve cells, are specialised cells and consist of three main parts:
- Soma (cell body) - contains the nucleus and other cellular organelles
- Dendrites - extend from the cell body and receive signals from other neurones
- Axon - long extensions that transmit signals away from the cell body

What is myelin and what does it do?
- Myelin is a lipid produced by Schwann cells which forms a layer around the axon called the myelin sheath
- The myelin sheath insulates the axon to allow electrical impulses to travel rapidly along it
- Myelinate neurons conduct impulses more quickly than unmyelinated neurons
- At regular intervals in the myelin sheath there are Nodes of Ranvier which are areas enriched with voltage-gated sodium channels and they potentiate the impulse along the axon
- The axon branches at the end to form axon terminals - sites wherer signal is passed onto other neurons or effector cells
How are neurons classified and what are the types of neurons?
- Neurons are classified according to the direction they transmit electrical impulses
- Sensory (afferent) neurons - transmit impulses from all areas of the body to the CNS
- Moter (effent) neurons - transmit impulses away from the CNS to muscle and glandular epithelial tissues
- Interneurons - transmit impulses from sensory to motor neurons (sometimes called connecting neurons)
What are glial cells?
- They are dervived from the Greek word glia meaning “glue”
- One of the functions of glial cells is to hold neurons together and protect them
- Generally they function to support the nervous system and assist in repair and maintainance
- Different types of glial cells differ in shape and size
Name three types of glial cells
- Astrocytes
- Microglia
- Oligodendrocytes
Outline astrocytes
- Astrocytes are a type of glial cell
- They are larger cells with threadlike extensions that attach neurons to blood vessels
- These branches form a two layer structure called the blood-brain barrier (BBB)

Outline microglia
- They are a type of glial cell
- Extremely small cells of the CNS, their primary function is to remove cellular waste and protect against microorganisms
- They are usually stationary but when the CNS is inflammed or degenerating, they enlarge, move around and draw microorganisms into their cytoplasm by phagocytosis and digst them
Outline oligodendrocytes
- They are a type of glial cell
- Produce the lipid myelin that surrounds the axons of neurons in the CNS
- They differ from the Schwann cells which only produce myelin around the neurons of the PNS
- Oligodendrocytes form part of the myelin sheath around several nerve fibres at once wheareas Schwann cells wrap themselves entirely around one fibre

Outline multiple sclerosis and how it relates to oligodendrocytes
- The most common primary disease of the CNS
- It is an autoimmune condition where the body mistakenly attacks healthy myelin covering the axons
- Loss and destruction of myelin is accompanied by oligodendrocyte cell injury or death
- Loss of myelin in CNS impairs nerve conduction & can lead to impaired vision and speach and muscle weakness and incoordination
- Occurs in both men and women but more common in women ages 20-40
- Women with MS are more likely to have gene which produces high levels of protein interferon gamma which promotes inflammation and tissue damage - aggrefvates MS
- No cure & treatments are aimed at relieving symptoms
Describe the complete / greater structure of neurons
- Nerve is a group of nerve fibres (axons) bundled together
- Myelin is which and neurons in the PNS are usually myelinated - these nerve fibre bundles often look white
- In CNS there are both myelinated and unmyelinated nerve fibres, myelinated nerves for white matter of brain and spinal chord, unmyelinated forms grey matter
- Each individual axon is surrounded by endoneurium - thin layer of fibrous connective tissue
- Groups of these axons form fascicles
- Each fascicle is surrounded by another thin layer of fibrous tissue called the perineurium
- The entire nerve is covered by a tough fibrous sheath called the epineurium

What is an action potential?
- Impulses and action potentials are terms that are use interchangeably
- An action potential is a self-propagating wave of membrane depolarisation, i.e a change in membrane potential to more +ve (less -ve)
- Cells that generate and transmit action potentials are known as excitable cells
- In excitable cells the rapid and transient change in membrane potential serves as the basis of information transfer
How is the membrane potential of a nerve cell determined?
- By the relative permeability of the membrane to specific ions such as Na+, K+ and Cl-
- The concentration gradient of those ions across the membrane
Define the four terms associated with a voltage time graph of an action potential
-
Resting potential is the term given to describe the membrane potential of a nerve cell when unstimulated
- For nerve cells this is typically -70 mV because there is usually an excess of Na+ ions outside the cell
- Depolarisation is when the inside of the cell becomes less negative with respect to the outside of the cell, i.e. becomes closer to 0 mV
- Repolarisation is when the inside of the cell becomes more negative, i.e. further away from 0 mV
- Hyperpolarisation is when the membrane repolarises but beyond the initial state

Describe what is happening at each stage of the voltage / time graph of an action potential
- Impulses are not continuously transmitted by neurons, they must be initiated by a stimulus e.g. temperature
- Stimulus initiates change in membrane potential by causing sodium channels to open allowing Na+ to flow across that area of the membrane into the cell - causing membrane depolarisation
- If the magnitude of depolarisation is sufficient and reaches the threshold potential an action potential is initiated - this is an all-or-nothing event
- When the membrane potential reaches the threshold potential, votlage-gated (v. g.) Na channels are opened causing a large influx of Na+ and a rapid and substantial depolarisation of the membrane
- Depolarisation rapidly recovers as the v. g. Na channels shut and the v. g. K channels open (allowing K+ out of the cell) causing repolarisation
- Depolarisation has already stimulated Na channels in the neighbouring section of membrane to open and action potential travels along the membrane
- After depolarisation the membrane repolarised beyond the initial resting state - hyperpolarisation
- This is due to the v. g. K+ channels not closing as quickly as the v. g. Na+ channels & threshold potential is increased momentarily
- This period is the refractory period in which a second action potential cannot be initiated in this time

How does the nervous system detect changes in both the internal and external environment?
- It is able to detect stimuli by means of receptors that are sensitive to chemical and physical stimuli
With regards the nervous system, what does the term “integration” mean?
- The process by which information from internal and external sensory receptors is coordinated to initiate appropriate responses is called integration
Why are synapses necessary?
- In order for stimuli to be translated into an appropriate response, information needs to be passed along the neuron pathway, for this to happen the neurons need to communicate and this is done via synapses
What is a synapse?
- It is the site where nerve impulses are transmitted from one neuron, called the presynaptic neuron, to another, called the postsynaptic neuron
What does a synapse consist of ?
- The synaptic knob - a bulge at the end of an axon terminal branch of the presynaptic neuron
- The plasma membrane of the postsynaptic neuron
- A synaptic cleft - the gap between the presynaptic knob and the postsynaptic plasma membrane

What is the purpose of the synaptic vesicles in the presynaptic knob?
- The vesicles contain neurotransmitters which, when a action potential reaches the presynaptic terminal, are stimulated to release the neurotransmitter into the synaptic cleft
























