Nerve Impulse Flashcards
Define a Nerve Impulse
A nerve impulse is a wave of electrochemical changes that travel along the length of a neuron.
It is a response signal to a stimulus that is transmitted from receptors to CNS and from the CNS to the effectors.
How many types does membrane potential have?
Membrane potential has 2 types:
- Resting Membrane Potential
- Active Membrane Potential
Describe RMP in detail
Resting membrane potential is the difference of voltage between the inside and outside of a cell. It is characterized by presence of more positive charges on the outer surface of the neuron membrane. It is a polarized state. There is unequal distribution of positive ions and thus it generates a potential. The average RMP is -70 mV. It occurs when a neuron is at rest and not conducting impulses.
3 Na ions are pumped out of the cell whereas simultaneously 2 K ions are moved inside the cell. These ions are continuously moved against their concentration gradient via Na-K pumps. This requires expenditure of energy which is acquired from ATP. The inside becomes more negative due to the lack of +ve ions.
Till when is AMP regulated?
It is maintained until the membrane is disturbed or stimulated by a sufficiently strong stimulus, called a threshold stimulus. If it is stimulated, an action potential will be produced. A stimulus that fails to arise any response is called a sub threshold stimulus.
Describe AMP in detail.
Active membrane potential is the presence of more positive ions inside the cell than the outside.
This is a depolarized state. On receiving a particular stimulus the positive ions move inside the cell. This change happens for a short period of time after which AMP is generated again.
What factors is AMP characterized by?
-Threshold Stimulus
- Influx of Na+ ions
- Repolarization of neuron fibre
- Hyper-polarization
- Refractory period
Describe the repolarization of neuron fiber briefly.
After the Na+ gates open, depolarization of axon membrane causes the K+ gates to open. Potassium therefore diffuses out of the cell. Since potassium is positively charged, this makes the inside of the cell more negative than the outside and thus repolarization starts.
What is hyperpolarization
At the peak of action potential, the Na gates close. Thus the permeability of Na declines. The Na-K pump continues to work to restore the potential. Na gates close before the K gates so the potassium ions continue to move outside the cell. This increases the concentration of K+ ions on the outside. This slight period is known as hyperpolarization.
What is the refractory period?
After an action potential, nerve fiber undergoes a period of recovery in which it regains its original ionic distribution and polarity and prepares itself for the next stimulus. This period is known as the Refractory period.
It lasts for about 4 milliseconds. Due to this, a neuron can conduct 250 impulses per second.
What is a reflex arc
The path of a nerve impulse during a reflex action is called a reflex arc.
Describe a reflex action with an example
A reflex action is an involuntary and simultaneous response to a stimulus.
A typical reflex involves effector, receptor, sensory neurons, interneurons and motor neurons.
Hypothetical Scenario: Bringing a finger near a candle
The receptors in the finger sense the heat coming from the candle. This generates a stimulus that sends an impulse to the sensory neuron. The impulse then travels from the sensory neuron to the spinal cord and enters the spinal cord at the dorsal nerve root. From there, it enters the interneurons and from its denderites it enters the motor neurons via a synapse. The motor neuron are attached to skeletal muscles on one branched end and the impulse causes the muscles to contract. Thus a reflex action is produced.
How many types of neurons are there
There are three types of neurons
- Sensory
- Motor
- Interneurons
Describe sensory neurons.
Sensory neurons carry impulses towards the central nervous system.
The cell body is attached to a small stalk on one side of the main conducting fiber.
One branched end is attached to receptors.
What are motor neurons?
Motor neurons carry impulses away from the central nervous system.
The denderites of motor neurons make contact with other neurons.
The terminal branches are connected to an effector.
