Unit 9- Nerve Transmissions Flashcards
Wha 2 control systems do humans have?
Nervous system Endocrine system (hormonal system)
What 3 basic steps make up the nervous system?
- detecting a stimuli
- coordinating a response
- effecting a response
What is a stimuli? Give an example involving the eye
Changes in the internal or external environment
Light waves which stimulate the pupils to dilate or contract
What is the role of the coordinator?
The network of interneurones connecting the sensory and motor systems, in humans this is the CNS
- receive impulses from sensory neurones and transmit impulses to motor neurones
What is the effector? And what 2 kinds are there?
The cells that effect a response
- muscles
- hormone secreting glands
What are exocrine and endocrine glands? And examples of them in action
Endocrine- secrete hormones into the blood stream eg insulin
Exocrine- secrete hormones the the outside of the body eg sweat, milk
What is a nerve?
A bundle of several thousand neurone axons and dendrons
Structure of a neurone:
- cell body
- dendrites(fingers) and dendrons (arm) carry impulses towards the cell body
- axon carries nerve impulse away from the cell body
- axon and dendrons are also coated in a myelin sheath formed from Schwann cells
Purpose of dendrites?
- to provide a large surface area for connecting with other neurones
- carry impulses towards the cell body
How is the myelin sheath formed and what is its purpose?
- Schwann cells are wrapped around the axon many times forming a thick lipid layer (myelin sheath)
- provides physical protection and electrical insulation
What are gaps in the myelin sheath surrounding the axon called?
Nodes of ranvier
What types of neurones do we have?
- sensory
- effector
- interneurones
What are the differences between the 3 kinds of neurones
Sensory- long dendrons(sensory receptors -> CNS)
Effector- long axon (CNS->muscle/gland)
Interneurone- smaller, many inter connections, make up the CNS 99.9% of neurones
What does the Na+K+ATPase protein pump do?
- simultaneously pumps 3 sodium ions out of the cell
- while pumping 2 potassium ions into the cell
What do the ion channels do? Refer to leaking
- sodium channels let the Na+ ions diffuse into the cell
- potassium channels let the K+ ions diffuse out of the cell
- they are normally closed but still leak so ions continue to diffuse
Are there more sodium or potassium channels in the membrane?
- more potassium ion channels, so potassium diffuses out the cell much faster to increase the rate of depolarisation
What is the membrane potential?
A stable imbalance of Na+ ions and K+ ions across the cell membrane
What charge is the membrane potential held at?
Normally -70mV but can range in different cells, however its always negative
What is an action potential:
A change in the potential difference at a point on the membrane of a nerve cell
What 2 phases make up the action potential?
- depolarisation
- repolarisation
What occurs in depolarisation?
-The sodium channels open, sodium ions diffuse quickly into the cell down the conc. gradient
-Inside of the cell gets more positive
- Na+ gates then close
(Charge in cell is reversed, negative -> positive)
What happens in repolarisation?
- potassium channels open, potassium ions diffuse quickly out the cell down the conc. gradient
- charge inside cells gets more negative
- K+ gates close again
(Repolarisation is return to -70mV)
What happens in the recovery period?
- K+ ions are attracted back into the cell by negative charge when membrane is hyperpolarised
- resting potential is restored
How is an action potential started?
- special receptor cells containing sodium gate receptor proteins that open to a specific stimulus
- stimulus causes the sodium gate to open
- sodium ions diffuse into the cell causing depolarisation
- this affects voltage gated sodium channels nearby starting the action potential
Give an example of a specialised sodium gate receptor protein:
Chemical gated sodium channels in the tongue
Mechanically gated sodium channels in the hair cells of ears that are opened by vibrations
How is a nerve impulse propagated?
- sodium ions entering during an action potential flow along the inside of the nerve fibre
- the addition of sodium ions makes the charge less negative reducing the potential difference to the threshold
- this opens nearby voltage-dependant sodium gates
What features do ion channels have that help the nerve impulse work effectively?
- Na+ ions will flow both ways along the membrane but the refractory period prevents the impulse from returning upstream as the channels cannot open again
- the ion channels are either open or closed, so action potential always reaches 40mV along the axon and this never reduces
How do nerve impulses convey strength?
- strength of an stimulus is indicated by frequency of the nerve impulse
A strong stimulus will cause a high frequency impulse along a sensory neurone
What 3 factors affect speed of conduction in nerves?
1- Temperature
2- Axon diameter
3- myelin sheath
Why do squids have such thick axons?
- live in freezing cold conditions
- thicker axons result in faster nerve conduction
Why do warm blooded animals tend to have faster responses to a stimulus?
- warmer blood, so higher body temperature and faster nerve conduction
How dos the myelin sheath speed up nerve conduction?
- voltage gated ion channels are only found at nodes of ranvier
- myelin sheath electrically insulates the axon
- action potential can jump from node to node (saltatory conduction)
