Chapter 13- Neurones Flashcards
(51 cards)
Key features of a mammalian neurone?
Cell Body
Dendrons
Axons
Function of sensory neurone?
Transmit impulses from sensory receptor cell to a relay neurone, motor neurone and the brain. Has one dendron and one axon.
Function of motor neurone?
Transmit impulses from a relay neurone or sensory neurone to an effector such as a muscle or a gland. One long axon and many short dendrites
What is the typical response pathway?
Receptor Sensory neurone Relay neurone Motor neurone Effector cell
What is the function of the myelin sheath?
The myelin sheath acts as an insulating layer and allows the myelinated neurone to conduct the electrical impulse at a much faster speed than unmyelinated neurones.
What is the node of ranvier?
Small gaps between each adjacent Schwann cell
What do the nodes of ranvier allow for?
Saltatory conduction.
What does MS do to neurones within the body?
Mistakenly attacks healthy tissue. Resulting in thinning or complete loss of myelin sheath and eventually leads to the breakdown of axons in the neurone
Symptoms of MS?
Problems with muscle movement
Problems with vision
Problems with balance.
What do sensory neurones do?
Convert a stimulus into a nerve impulse.
Features of sensory receptors?
Specific to a single type of stimulus
Act as a transducer - converts stimulus into nerve impulse.
How is a sensory neurone a transducer?
Receptor converts the stimulus into a nervous impulse called a generator potential.
What is a pacinian corpuscle?
Where are they found?
Sensory receptors that detect mechanical pressure. Located deep within skin and are most abundant in fingers abs on soles of the feet. Also found in joint and enable you to know which joints age changing direction.
Why are sodium ion channels important to pacinian corpuscle?
Responsible for transporting sodium ions across the membrane. The neurone ending in the corpuscle has special channels called stretch mediated sodium channels.
When the channels stretches, their permeability to sodium ions also changes.
How’s does a pacinian corpuscle convert mechanical pressure into a nerve impulse?
S-M channels too narrow to be permeable to sodium in beginning so Corpuscle has resting potential.
When pressure is applied, the corpuscle changes shape and the membrane surrounding the neurone stretches.
When the membrane stretches the sodium ion channels widen, becoming permeable to the diffusion of sodium ions into the channel.
Influx of positive sodium ions changes potential of membrane and it becomes depolarised.
In turn the generator potential creates an action potential that passes along sensory neurone to the CNS via other neurones.
At what potential difference is there a resting potential?
-70mv
What is the membrane at resting potential?
Polarised.
Outside more positively charged than inside of axon.
What allows a resting potential to occur?
The movement of sodium and potassium ions across the axon membrane.
How is resting potential created in cells?
Active transport of K+ ions IN to cell and Na+ ions OUT of the cell using sodium-potassium pump which requires ATP.
K+ and Na+ ions concentrate on opposite sides of membrane. More Na+ on outside and more K+ on inside.
Uneven distribution of ions causes facilitated diffusion of K+ ions OUT via leak channels.
Some Na+ diffuse in but channels are mainly closed so more K+ ions flow out that sodium in.
More positive ions on outside of axon than inside the cytoplasm.
Inside is more negatively charged and is now polarised and resting potential is at -70mv
At what value is an action potential?
+40mv
What is the membrane said to doing at action potential?
Depolarising
What is repolarisation?
A change in potential difference from positive back to negative.
When does an action potential occur?
When protein channels in the axon membrane can change shape as a result of the change in voltage across its membrane. Change in shape leads to channel opening or closing. Channels called voltage gated ion channels.
What sequence of events take place during an action potential?
Energy of stimulus causes Na+ voltage gated channels to open and permeability to Na+ increases.
Na+ ions diffuse in down EC gradient and cytoplasm becomes less negative.
Change in PD causes more Na+ voltage gated channels to open and more Na+ ions move in - positive feedback.
Continues until PD reaches +40mV = depolarisation
At 40mV Na+ channels close and K+ channels open.
K+ ions exit cell down EC gradient into tissue fluid, reducing the positive charge inside.
Large numbers of K+ ions diffuse out = hyperpolarisation.
Hyperpolarisation causes K+ channels to close
Resting potential (-70mV) re-established by pump and facilitated diffusion.
