Neurons Flashcards
What is a dendrite
short extension of the cytoplasm that carry nerve impulses/messages into the cell body
What is an Axon
long extensions of cytoplasm that carry messages/nerve impulses AWAY from cell body
What is a Myelin sheath
Fatty material that covers axon
Axons without Myelin sheath- unmyelinated
Axons with Myelin sheath- myelinated fibres
What is a nerve fibre
Long extension of a nerve cell
What is an axon terminal
The end of an exon divides into smaller branches. Each of these branches are named axon terminals
What are Nodes of Ranvier
Intervals along the axon where there are gaps in the myelin sheath
What are Schwann cells
Cells outside the brain and spinal chord that from the myelin sheath
Functions of the Myelin sheath
- Acts as insulator
- Protects axon from damage
- Speeds up movement of nerve impulses along the axon
What is neurilemma
Outermost coil of Schwann cell that helps in repair of injured fibres
What is a synapse
junction between an axon terminal of one nerve to the dendrite of another
What is a neurotransmitter
chemicals carried across the synapse that carry messages
What is a neuromuscular junction?
synapse where axon meets a skeletal muscle cell
What is a Sensory/Afferent neuron
carries messages from receptors on skin/sense organs to the CNS
What is a Motor/Efferent neuron
carries messages from CNS to the effectors
What are Interneurons
link between sensory and motor neurons
Describe transmitton across a synapse
1) When nerve impulses reach axon terminal, activated voltage gated calcium ion channels
2) As there is a high concentration of calcium ions in the extracellular fluid, they flow into the cell
3) Causes sympathetic vesicles to fuse with the membrane, releasing neurotransmitters (exocytosis)
4) Neurotransmitters diffuse across gap and attach to receptors on the membrane of the next neuron
5) Stimulates ligand-gated protein channels to open, allows for influx sodium ions and incites an action potential
6) Neurotransmitters are reabsorbed by the presynaptic membrane, and degraded by enzymes
What are the 4 different types of receptors
- Osmoreceptors
- chemoreceptors
- touch receptors
- thermo receptors
- pain receptors
What is depolarisation
started by a stimulus from another neuron to a receptor. This stimulus opens sodium channels
What is repolarisaton
The closing of sodium channels and opening of potassium channels. Flow of sodium ions into cell decreases + flow of potassium ions out of cell increases = making cell more negative than outside, reducing action potential
Action potential along nerves
Action potential in one area of membrane simulates action potential in adjacent area. Therefore, potential moves along the nerve fibres (nerve impulse)
What is action potential
Rapid depolarisation and repolarisation of cell membrane
What are reflexes
Rapid, automatic changes to a change in environment
