Nervous system

• Myelin sheath insultes the Axon and speeds up the action potential
• Unmyelinated axons are called gray matter because they do not contain much lipid material, so they look darker than myelinated fibers.
• The central nervous system (CNS) is composed of the brain and spinal cord.
• The peripheral nervous system (PNS) consists of all nerves outside the CNS.
• The speed of action potential largely depends on the thickness of the axon and whether it’s myelinated or not. The larger the diameter, the higher the speed of the action potential .The action potential is also faster if an axon is myelinated
• The nervous system controls and coordinates our movement.

  It allows us to interact with our surroundings by use of receptors
• The PERIPHERAL NERVOUS SYSTEM (PNS) consists of all the sensory neurones that connect receptors with the CNS as well as the motor neurones that connect to muscles/glands and bring about responses like movement or secretion of substa
• Neurons are cells that receive and facilitate nerve impulses, or action potentials

  • They consist of a large cell body called a soma with small projections called dendrites and an axon.

  • The end of the axon is called the axon terminal. It is separated from the dendrite of the following neuron by a small gap called an axon
• Sensory neurone - carries information from the body surface into the CNS
• A synapse is formed when two neurons meet at this junction. This is where neurotransmitters are released into the synaptic cleft which then bind to receptor sites on the next neurone's dendrite. If enough neurotransmitter molecules bind to these receptors, they will cause depolarisation of the membrane of the second neurone, causing an action potential to be generated. This process is known as transmission of information across the synapse.
• Soma(cell body) - contains the nucleus and cytoplasm.
• Axon-Extentions that send infomation in the form of nerve impulses
• Dendrites- Recieve information from other neurons and carry it to the cell body.
• Nodes of Ranvier- Gaps between myelinated axons that allow ions to pass through
• Shwann Cells- Form Myelin Sheath around the Axon
• Information travels along neurons in the form of electrical signals called nerve impulses. A nerve impulse is known as an action potential.
• Action potentials arise from a change in the ion balance in the nerve cell which spreads rapidly from one end of the neuron to the other.
• Myelin is made from specialised cells called Schwann cells that wrap

  themselves around the axon when they develop in an embryo.

  • The Schwann cells are thick and form a lipid insulating layer around the neuron called the myelin sheath. This insulates the axon and makes the action potential faster
• Polarisation: of a nerve or muscle cell refers to the different electrical charges on either side of the plasma membrane caused by active transport of ions.
• Depolarisation: the reversal of the charge difference (more negative)
• Repolarisation: the restoration of the original charge difference( postive)
• An action potential is only triggered if the generator potential reaches a certain level called the threshold level.
• Sodium-potassium pumps use ATP as energy source.
• What happens inside the axon during depolarization?

  Inside becomes more positive, up to +40mV due to an influx of sodium ions
• What happens inside the axon at rest (at resting potential)

  Inside is more negative than outside, down to around -70mV due to sodium ions being pumped out
• What is the role of the myelin sheath?

  To insulate an axon, speeding up axon potentials
• Name 3 things which effect the speed of an action potential

  Myelin or no myelin

  How many synapses

  Size of axon
• Exocytosis is the process by which a vesicle inside a cell moves to the cell surface membrane, fuses with the membrane and releases its contents out of the cell


  .
• What are neurotransmitters?

  Chemical transmitter molecules
• Where are they found in a neuron?

  Synaptic Bulb
• What is a neurotransmitters role?

  To diffuse across a synapse to continue

  action potentials along nerve cells
• What are neurotransmitters packaged in?

  Vesticles
• Give one example of a neurotransmitter

  Dopamine
• Parkinson’s disease is a genetic disease which affects the nervous system.

  • Sufferers are unable to produce the naturally occurring chemical

  dopamine, a neurotransmitter that helps smooth and normal movements.
• Neurotransmitters diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.

  This causes sodium ion channels in the postsynaptic neurone to open.

  The influx of sodium ions into the postsynaptic neurone causes depolarisation.

  An action potential on the post-synaptic neurone is generated if the threshold is reached
• At rest,  the outside of the axon membrane is positively charged compared to the inside. This is because there are more positive ions on the outside than there are on the inside.
• A sodium potassium pump moves 3 sodium ions out for 2 potassium ions in – which is getting rid of some positive charge,More positive potassium ions diffuse back to the outside of the membrane as well, and Sodium cannot get back in.This makes the outside positive compared to the inside!
• Hyperpolarisation- becomes too negative, so the NA/K pump has to restore it back to a normal level
• What are the functions of the nervous system?

  Gather information both inside and outside the body

  Processes information

  Make Decisions
• Justify the healthcare assistant’s suggestion of muscle weakness being a common symptom of mitochondrial myopathy.

  ATP is used to break the cross-bridge between the actin and myosin that enables the myosin heads to detach from the actin filaments (1). Without enough ATP, myosin heads cannot bind to the actin filament, preventing muscle contraction and leading to muscle weakness (1)

  ATP is needed for myosin to detach from actin after completing one power stroke (1). However, without enough ATP, myosin remains attached to actin, preventing muscle relaxation (1), which leads to muscle weakness