Unit 8: Grey Matter Flashcards
What are the three types of neurons?
Relay, Motor, Sensory
What is the role of the motor neuron?
Carry impulses from the CNS to the effector muscles/glands. Cell body, short dendrites, long axon. Cell body + dendrites in CNS and axon outside CNS.
What is the role of the sensory neuron?
Receptors to the brain and spinal cord. Cell body, medium dendrons, medium axon. Cell body (middle of the neurone) and dendrites outside CNS, axon inside CNS
What is the role of the relay neuron?
To connect the motor and sensory neurons. Cell body, short dendrons, short axon. Cell body etc. inside CNS.
What is the Schwann cell?
Cells that form the myelin sheath around the nerve cells/neurons in the peripheral system (nerves running to and from the CNS to all parts of the body).
What in the central nervous system made up of?
Brain and spinal cord
What would a transverse section of the myelin sheath look like?
1) Nucleus of the Schwann cell
2) Fold of Schwann cell around fibre
3) Nerve fibre
4) Lipoprotein membrane forming around the myelin sheath
What is MS (multiple sclerosis)?
Multiple sclerosis (MS) is a condition which can affect the brain and/or spinal cord. It involves the breakdown of the myelin sheaths within the central nervous system. Such de-myelinated nerve fibres are no longer able to transmit nerve impulses effectively.
What are the main symptoms of MS (multiple sclerosis)?
- fatigue
- difficulty walking
- vision problems, such as blurred vision
- problems controlling the bladder
- numbness or tingling in different parts of the body
- muscle stiffness and spasms
- problems with balance and coordination
- problems with thinking, learning and planning
Explain why it is important that neurones have insulating myelin sheaths.
Insulates the neurone, allows for rapid electrical impulses
What type of compound is myelin?
Lipid/fatty insulating sheath
Active transport is needed in the conduction of nerve
impulses. What is active transport? How is it different
from other forms of transport across cells?
Against a concentration gradient, uses ATP. Diffusion and osmosis are passive and down a concentration gradient.
Name one human reflex arc.
Blinking, sneezing
How is the neurone cell membrane polarised at rest?
Resting-state (not being stimulated), the outside membrane is positively charged compared to the inside. This is due to more positive ions outside the cell than inside. So the membrane is polarised - there is a difference in charge. The voltage across the membrane when it is at rest is called the resting potential- about -70mV.
What is the voltage in the membrane at resting potential?
70 mV
How is the resting potential created and maintained?
By sodium-potassium pumps and potassium ion channels in a neurone’s membrane
What are sodium-potassium pumps?
These pumps use active transport to move three sodium ions (Na+) out of the neurone for every two potassium ions (K+) moved in. ATP is needed to do this.
What is the potassium channel?
These channels allow facilitated diffusion of potassium ions (K+) out of the neurone, down their concentration gradient
What occurs due to the sodium ions being pumped out of the neurone by the sodium-potassium pumps?
The membrane isn’t permeable to sodium ions, so they can’t diffuse back in. This creates a sodium ion electrochemical gradient (a concentration gradient of ions) because there are more positive sodium ions outside the cell than inside.
How do the potassium ions move in the neuron?
Sodium-potassium pumps move potassium ions into the neurone, but the membrane is permeable to potassium ions so they diffuse back out through potassium ion channels.
What does the movement of potassium and sodium ions create in the neurone?
Makes the outside of the cell positively charged compared to the inside.
What is the stimulus and how does this affect the changes in an action potential?
excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neurone less negative.
What is depolarisation?
if the potential difference reaches the threshold (around -55 mV) more sodium ion channels open. More sodium ions diffuse into the neurone
What is repolarisation?
at a potential difference of around +30 mV the sodium ion channels close and potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient. This starts to get the membrane back to its resting potential.