INTRO TO HOMEOSTASIS UNIT 4

Question 1

WHAT IS ACTION POTENTIAL

Answer 1

• a nueron is polarized due to the charge difference across the membrane.
• depolarization occurs when the cell becomes less polarized and during it, the inside of the cell becomes less negative relativ to the outside.
• an action potential causes depolarization to occur.
• an action potential isthe movement of an electrical impulse along the plasma membrane of an axon.
• threshold potentials are usually close to -50mV.
• the strength fo an action potential does not change based on the strength of the stimulus.

Question 2

action potential steps

Answer 2

1. an action potential is triggered when the threshold potenetial is reached and causes a few sodium channels to open.
2. voltage gated sodium channels open and voltage gated potassium channels are closed. sodium ions move down their concentration gradient and rush into the axon, causing depolarization of the membrane. the potential diff is now +40mV
3. vg sodium channels close due to change in membrane potential and vg potassium are open. potassium ions move down their concentration gradient and exit the axon, causing the mebrane to be hyperpolarized to -90 mV.
4. vg potassium channels close. the the soidum potassium pump and natrually occuring leak diffusion channels restore the resting membrane potential of -70mV. the membrane is now repoalrized.
   the events that occur in an action potential continue down the length of the axon until it reaches the end where it initiates a response as the next cell.

Question 3

what is myelinated nerve impulse

Answer 3

a nerve impulse consists of a series of action potentials.
- conduction of a nerve impulse along a myelinated nueron is called saltatory conduction because action potentials jump from one node of ranvier to the next.
- saltatory conduction is faster at 120m/s than the conduction of nerve impulses in unmmyelinated nuerons which is 0.5 m/s.

Question 4

signal transmission across a synpase

Answer 4

a synapse is the junction between 2 nuerons or between a nueron and affector.
- nuerons are not directly connected, the small gap between is called the synaptic cleft.
- a nerve impusle cannot jump from one nueron to another.

Question 5

how does the nerve impulse proceed from the presynaptic nueron (sender of info) to the post synaptic nueron(recieves info)

Answer 5

chemical msgers called nuerotransmitters carry the nerve impulse across the synapse from one nueron to another or form a nueron to an effector.

Question 6

steps of transmission across a synapse.

Answer 6

1. the nerve impulse travels to the synaptic terminal.
2. synaptic vesicles containing nuerotransmitters move towards and fuse with the presynaptic membrane.
3. synaptic vesicles release nuerotransmitters into the synaptise cleft by exocytosis. nuerotransmitters diffuse across the synapse to reach the postynaptic nueron or the cell membrane of an effector.
4. nuerotransmitters bind to specific receptor proteins on the postsynaptic membrane. the receptor proteins trigger ion channels to oen and therefore depolarization of postsynaptic membrane occurs and an action potential is initiated if the threshold potential is reached.