Lecture 4- Membrane potential and the Peripheral nervous system

Question 1

Do action potentials move in more than one direction? why?

Answer 1

no they move in one direction down neuron because behind them repolarisation is happening immediately as sodium channels are inactivated so they cannot move backwards

Question 2

How are action potentials triggered?

Answer 2

when the stimulus has reached the the threshold for an action potential

Question 3

If the stimulus is stronger what happens to the number of action potentials?

Answer 3

more action potentials are created- there is no change to the height of the peak

Question 4

What is an action potential?

Answer 4

the transient depolarisation of a cell

Question 5

What do you call cells that generate action potentials?

Answer 5

excitable cells

Question 6

How do action potentials transfer information?

Answer 6

information is coded by the frequency of action potentials passing along a nerve

Question 7

What kind of events do action potentials initiate?

Answer 7

cellular events such as muscular contraction

Question 8

What is the threshold of an action potential?

Answer 8

the critical potential necessary to depolarise the cell

Question 9

Can anything happen when the cell is repolarising?

Answer 9

no

Question 10

What is hyper-polarisation?

Answer 10

when the membrane potential how become more negative than the resting potential

Question 11

What is the all or nothing law?

Answer 11

once an action potential has been initiated varying the strength pf the stimulus does not alter the configuration of the action potential

Question 12

What did experiments by alan hodgkin and huxley show?

Answer 12

depolarisation was due to a transient increase in membrane Na+ permeability but eventually the membrane returns to its resting state

-membrane potential repolarises to the resting potential and the action potential terminates
- repolarisation is aided by an ever greater than normal increase of K+ permeability

Question 14

What does sodium influx and potassium efflux do?

Answer 14

sodium influx causes depolarisation
potassium efflux causes repolarisation

Question 15

Describe the process of an action potential

Answer 15

1. resting membrane potential exists
2. stimulus depolarises membrane potential to the threshold
3. voltage gated Na and K channels begin to open
4. rapid entry of Na+ depolarises the cell
5. Na channels close and slower K channels open
6. K+ moves from cell to extracellular fluid
   7.K+ ions remain open and additional K ions leave the cell causing hyperpolarization
   8.voltage gated K+ channels close and less K ions leak out of the cell
7. cell returns to resting ion permeability and resting membrane potential

Question 16

How is an action potential initiated?

Answer 16

the cell must be depolarized from the resting membrane potential to the threshold potential,
- at the threshold potential voltage activated ion channels open and allow cations to enter the cell- this generates the action potential

Question 17

what does a stimulus do?

Answer 17

• an action potential requires energy to be added to the sytem in the form of a stimulus
• if a cell needs a larger stimulus it is less excitable
• the magnitude of the required stimulus determined excitablility of the cell; if a small stimulus is required the cell is usually more excitable

Question 18

How can we get from a resting to a threshold potential? What are the different ways to make this happen?

Answer 18

• atrificial application of a current
• neurotransmitters bind to ligand-gated channels on a target cell
  -pacemaker cells can bring action potentials spontaniously
• sensory cells

Question 19

What is the trigger zone?

Answer 19

the region of a cell that generates an action potential- represented by the reversal of the membrane potential polarity

Question 20

what is the local circuit hypothesis?

Answer 20

that a local current precedes the action potential wavefront in the cytoplasm

Question 21

a local current precede the action potential wavefront in the cytoplasm, What happens if some of this current leaks across the membrane?

Answer 21

what happens is that voltage gated Na+ channels open and Na enters the axon
- this results in a positive charge flowing into the sections adjacent to the movement of the local current flow
;as the current leaks across the membrane it depolarises it

Question 22

What does local current flow from the active region do?

Answer 22

the local current flow from the active region causes new sections of the membrane to depolarize

Question 23

What does the refractory period do? How is the membrane repolarised?

Answer 23

the refractory period prevents backwards conduction; in the refractory period potassium is being lost from the cytoplasm in order to repolarise the membrane

Question 24

What factors affect how rapidly information can be sent from your brain to your body using action potentials?

Answer 24

-cell diameter
CV increases as the fibre diameter increases

-temperature
increasing temperature generally increases conduction velocity

-myelation
myelin increases CV sd the AP jumps from node to node; this is known as saltatory conduction

Question 25

What happens to the number of action potentials as the stimulus strength increases? What does this mean?

Answer 25

the number of action potentials generated increases
- this means action potential frequency codes stimulus intensity

Question 26

What are the consequences of low intracellular sodium?

Answer 26

you cannot have changes in membrane potential

Question 27

How can sodium be transported into the cell?

Answer 27

protein transporters like Glucose transporters which are very common in the kidneys
-simporter
-they are secondary active transporters

Question 28

What is used to pump sodium out of the cell?

Answer 28

Na pump which uses ATP

Question 29

What does the peripheral nervous system mean?

Answer 29

it is the somatic and autonomic nervous systems

Question 30

What is the difference between the somatic and autonomic nervous systems?

Answer 30

somatic interacts with the external enviroment
- it is the voluntary control
-skeletal muscle control
-relays sensory and motor information between the outside environment and the CNS

Autonomic nervous system
- interacts with the internal environment
- mediates involuntary movement controls vital functions such as heart rate, respiration and digestion
-regulates glands, blood vessels and internal organs

Question 30

Describe the layouts of the somatic and autonomic nervous systems

Answer 30

sensors->CNS->motor neurons->skeletal muscles

Question 30

How is afferent and efferent related to the somatic nervous system?

Answer 30

sensory nerves detect sensations such as heat or pain- message is sent down the afferent pathway to the CNS that interpret message and that then sends a message down the efferent pathway to motor neurons and skeletal muscles which act on the info by performing a function or reflex

Question 30

When is the ANS considered purely motor?

Answer 30

when it is sent down the efferent pathway

Question 30

Draw the layout of the muscle sense organs, skeletal muscles and smooth muscles

Answer 30

the Somatic nervous system
- transmits nervous impulse from CNS to end target organ and involves only one neuron

The autonomic nervous system
- transmits a nervous impulse from the CNS to an end target organ and there are 2 neurons involved that synapse at an intermediate ganglion

Question 31

What is the difference between parasympathetic and sympathetic branches

Answer 31

parasympathetic
- concerned with non-emergency tasks and replenishing stores, conserving energy
-the rest and digest response system

Sympathetic
- concerned with preparing body for emergencies
-the fight or flight response system

Question 31

What are the functions of the ANS?

Answer 31

the ANS involves the sympathetic and parasympathetic branches in order to maintain internal balance
- control of heart rate
- control of airway diameter
- control of secretions and motility in gastro-intestinal tract
-control of pupil diameter
-control of glandular secretions like sweating and saliva

Question 32

What does efferent and afferent mean?

Answer 32

Afferent pathways carry signals from sensory organs or receptors towards the central nervous system (CNS), such as the brain or spinal cord.

Efferent pathways carry signals away from the central nervous system (CNS) towards peripheral organs, muscles, or glands.

Question 33

Compare the divisions of the ANS- Sympathetic

Answer 33

sympathetic
- dilates pupils
reduces saliva production
-dilates airways
-increases heartrate
-stimulates adrenal function, glucose release
-controls sympathetic ganglions
-reduces stomach, intestine and pancrease activity
-limits micturition

Question 34

Compare the divisions of the ANS- paraSympathetic

Answer 34

-constricts pupils
-stimulates saliva production
-constricts airways
-slows heart rate
-stimulates stomach, intestinal and pancreas
-stimulates micturition
controls parasympathetic ganglions