Human Bio Ch 3 Flashcards
What are the main parts of a neuron?
- cell body = contains the nucleus and controls the functioning of the cell
- dendrites = short extensions off the cell body and carry messages into the cell body
- axon = single long extension of the cytoplasm, carries nerve impulses away from the cell body at the end it branches out into axon terminals which send the message to the next neuron
What is Myelin Sheath and what does it do?
Myelin sheath is made by the schwann cells and is a white fatty sheath that covers most axons. There are gaps in the myelin sheath called nodes of ranvier. 3 important functions:
1. it acts as an insulator
2. protects the axon from damage
3. speeds up movement of nerve impulses along the axon.
What is a synapse?
A synapse is the gap between where the axon terminal of one neuron meets with the dendrites or cell body of the next neuron. They do not actually touch so the gap that is formed is known as the synapse.
How are messages carried across the synapse? (5 steps)
- when the nerve impulse reaches the axon terminal it activates voltage gated calcium ion channels
- these calcium ions flow into the cell at the pre-synaptic axon terminal
- this causes the synaptic vesicles to fuse to the membrane, which causes the release of neurotransmitters by exocytosis.
- the neurotransmitters diffuse across the gap (synapse) and attach to receptor on membrane of the next neuron
- this then stimulates the release of sodium ions which allows for the next action potential to begin.
What are the 3 types of neurons?
- sensory (Afferent) = carry messages from receptors in the sense organs to the brain and spinal cord.
- motor (Efferent) = carry messages from the brain and spinal cord to the effectors (muscles and glands)
- interneurons = are located in the CNS and are a link between the sensory and motor neurons.
What are the 4 different structural types of neurons and give an example for each?
- Multipolar = motor neuron and interneuron (standard neuron)
- Bipolar = neurons in the eye, ear and nose (cell body in the middle)
- Unipolar = not found in humans (cell body at the top with no dendrites)
- Pseudounipolar = sensory neuron (cell body branches off)
What is a membrane potential?
The electrical voltage across the membrane of a cell. This is caused by the potential difference in charges ( - / +) of the inside and outside of the cell membrane. The extracellular fluid is more positively charged than the intracellular fluid which is due to the higher number of sodium ions outside.
What is the sodium (Na+) potassium (K+) pump and how does it work?
Is a mechanism in the membrane of a nerve cell that transports sodium ions out of the cell and potassium ions into the cell by active transport. STEPS:
1. sodium-potassium pump binds 3 sodium ions and a molecule of ATP
2. the splitting of ATP provides energy to change the shape of the channel which causes the sodium ions to be driven through the channel.
3. sodium ions are moved released to the outside and the new shape allows for 2 potassium ions to bind.
4. release of the phosphate allows the channel to revert back to original shape, releasing the potassium ions back into the cell.
When the inside of the cell is more negative than the outside the membrane is said to be polarised.
What happens in the DEPOLARISATION stage of an action potential?
- started by a stimulus from another neuron
- stimulus has to reach -15mv for action potential to happen
- stimulus opens some sodium ion gated channels which causes sodium to rush into the cell making the inside of the cell more positively charged
- happens during the -55mv and 30mv
What happens in the REPOLARISATION stage of an action potential?
- happens when the sodium channels close and the potassium ion gated channels open.
- increase flow of potassium out of the cell making the outside of the cell more positively charged.
- goes from 30mv to -55mv
What happens in the HYPERPOLARISATION stage of an action potential?
- potassium channels have been open for too long
- creates a lower membrane potential than normal
- sodium/potassium pump restores the charges (for every 3 sodium ions out of the cell 2 potassium ions enter the cell) this bring the membrane potential back to -70mv.
What is the refractory period?
a short period following the a stimulus during which a nerve cell of muscle fibre cannot be stimulated again. This is because the sodium ion gated channels have been opened and have become unresponsive to a new stimulus. Refractory period lasts from when the stimulus reaches the -55mv threshold to when the membrane potential is back to -70mv.
How does the transmission of a nerve fibre differ between myelinated and unmyelinated axons?
Myelinated:
- myelin acts as an insulator therefore the action potential cannot travel through it
- action potentials therefore only occur at the nodes of ranvier
- action potential ‘jumps’ from one node of ranvier to the next = Saltatory Conduction
- this makes the impulse much faster (140 m/s)
Unmyelinated
- each action potential has another action potential right in front of it as it travels the whole length of the axon.
- the the nerve impulse is prevented from going backwards due the refractory period
- each part of the axon only has one action potential
- called continuous conduction
- much slower (2m/s)
What are Thermoreceptors?
Thermoreceptors = peripheral thermoreceptors in the skin are nerve endings and respond to hot and cold stimulus. Core body temperature is monitored by thermoreceptors in the hypothalamus
What are Osmoreceptors?
Located in the hypothalamus and detect changed in the osmotic pressure. Osmotic pressure is determined by the concentration of substances dissolved in the water, the higher the concentration the greater the osmotic pressure,
