Chapter 3- Nerve Cells And Nerve Impulses Flashcards
Difference i between a mylienated and unmylienated fibre
Mylienated nerve fibres are covered with a myelin sheath of fatty material; unmylienated fibres do not have this covering
How is a myelinated fibre formed
In fibres outside the CNS, the myelin sheath is formed by Schwann cells that wrap around the axon and deposit layers of mylien between each coil
Three types of functional neurons
- Sensory: carry messages from the sense organs and skin to the CNS
- Motor: Carry messages from the CNS to muscles and glands
- Interneurons: Located in the CNS and link the sensory and motor neurons
What is the difference between the three functional types of neurons?
- Multipolar: one axon and many dendrite, include most of the interneurons in CNS and motor neurons that carries messages to the skeletal muscles
- Bipolar: have one axon and one dendrite, occur in eye, ear and nose, which transfer impulses from receptor cells to neurons
- unipolar: one extension, the axon, they are most sensory neurons that carry messages to the spinal cord
What is the difference between a nerve, neuron and nerve fibre?
- Neurons is a nerve cell
- Nerve fibre is a long extension of the nerve cell body (axon)
- Nerve is a bundle of nerve fibres held together by connective tissue
define ‘ electrical potential
- Positive and negative charges are attracted
- Electrical force pulls them together
- Group of pos and neg that are separated have a potential to come together and release energy
- This is the electrical potential or potential difference
What is the potential of the membrane of a cell when not conducting a nerve impulse
- Membrane of a potential unstimulated cell is approx. -70 mV
- It is 70mV less on the inside than the outside
How is the potential of a resting nerve cell membrane is maintained
- Membrane potential of neurons occur because of the distribution of K+ and Na+ on either side of the membrane
1. there is a sodium-potassium pump that transports Na+ out of the cell and K+ inside
2. Large negative ion inside the cell because they can not pass through the membrane, not enough K+ ions inside to balance the negative charge
This there fore has a negative charge in relation to the outside, this is the resting potential
Define ‘action potential’
- Rapid polarisation/depolarisation of the membrane of a nerve cell
- Nerve cell membrane is stimulated by the movement of Na+ into the cell so the membrane is depolarised
- rapidly restored to its original condition, it becomes repolarised
What is the all or nothing response
- strength of stimulus is not related to the size of the response
- If the stimulus of a nerve cell membrane is large enough to cause a change of 15mV the movement of Na+ is independent of the stimulus
What is the refractory period
During the refractory period of the action potential the nerve fibre can not be stimulated to respond again
Occurs during the action potential and a short time after
How does a nerve travel along a mylienated fibre
- Gaps in mylien sheath; nodes of Ranvier
- Insulates fibre from extracellular fluid; ions cant flow between membrane, action potential can not be formed
- Action potential jumps from one node of Ranvier to the next
This is a saltatory conduction, allowing the impulse to travel faster
How does a nerve impulse travel along an unmylienated fibre
In an unmylienated fibre a stimulus causes depolarisation of an area of a membrane
- Depolarisation occurs immediately adjacent to the site of original stimulus
- Repeats itself along the whole length of the membrane
WHat is a synapses
A small gap between one neuron and the next
How is a nerve message carried across a synapses
At the synapses the neurotransmitter molecules are released from the ends of the axons, they diffuse across the gap and attach to receptors of the next neuron
How come messages across a synapses only cross in one direction
- Transmission only occurs from axon to dendrite… from axon to cell body
- This is due to the receptors for neurotransmitter only occurring on membranes of dendrites on the cell body of neurons
What is the difference between a synapses and neuromuscular junction
- Synapse: small gap between end of axon and dendrites/cell body of another neuron
- Neuromuscular junction is a tiny gap between axon and skeletal muscle cell
How do nerve cells differe from most body cells
- Nerve cells contain organelles that most cells have
- Except, nerve cells have extensions of cytoplasm
- Nerve cells can be generated to have an action potential
