Neurons, or nerve cells that carry nerve impulses, are made up of the cell body, the axon, and several dendrites. Signals move across the synapse, the place where the axon of one neuron meets the dendrite of another, using chemicals called neurotransmitters.
How a nerve impulse is generated?
cell neuron ions membrane. When a stimulus is strong enough, a nerve impulse is generated in an "all or none" response which means that a stimulus strong enough to generate a nerve impulse has been given. The stimulus triggers chemical and electrical changes in the neuron.
How nerve impulses are initiated and transmitted?
The transmission of a nerve impulse along a neuron from one end to the other occurs as a result of electrical changes across the membrane of the neuron. The membrane of an unstimulated neuron is polarized—that is, there is a difference in electrical charge between the outside and inside of the membrane.
A nerve impulse is the way nerve cells (neurons) communicate with one another. Nerve impulses are mostly electrical signals along the dendrites to produce a nerve impulse or action potential. The action potential is the result of ions moving in and out of the cell.
"Some kinds of signals, like the ones for muscle position travel on extra-fast nerve impulses at speeds of up to 390 feet per second (119 meter/second). Close your eyes and wave your arms around: you can tell where they are at every moment because the muscle-position nerves are very fast ….
At the end of the axon from which the impulse is coming, the membrane depolarizes, gated ion channels open, and calcium ions (Ca2+) are allowed to enter the cell. When the calcium ions rush in, a chemical called a neurotransmitter is released into the synapse. The neurotransmitter binds with receptors on the neuron.
When a nerve impulse reaches the end of an axon, the axon releases chemicals called neurotransmitters. Neurotransmitters travel across the synapse between the axon and the dendrite of the next neuron. Neurotransmitters bind to the membrane of the dendrite.
Two types of phenomena are involved in processing the nerve impulse: electrical and chemical. Electrical events propagate a signal within a neuron, and chemical processes transmit the signal from one neuron to another or to a muscle cell.
The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside. At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.
How are Nerve Impulses Propagated? [back to top] Once an action potential has started it is moved (propagated) along an axon automatically. The local reversal of the membrane potential is detected by the surrounding voltage-gated ion channels, which open when the potential changes enough.
When we feel pain, such as when we touch a hot stove, sensory receptors in our skin send a message via nerve fibres (A-delta fibres and C fibres) to the spinal cord and brainstem and then onto the brain where the sensation of pain is registered, the information is processed and the pain is perceived.
A motor neuron carries the message from the central nervous system to the effector. In a knee-jerk reflex arc the sensory neuron directly connects to the motor neuron in the spinal cord. This is called a simple reflex arc. from the spindle (receptor) to where it connects with the motor neuron in the spinal cord.
The central nervous system (CNS) controls most functions of the body and mind. It consists of two parts: the brain and the spinal cord. The brain is the center of our thoughts, the interpreter of our external environment, and the origin of control over body movement.
The nervous system consists of two main parts: the central nervous system and the peripheral nervous system: The central nervous system is made up of the brain and spinal cord.
For the spinal cord though, we can say that there are three types of neurons: sensory, motor, and interneurons.
- Sensory neurons.
- Motor neurons.
- Neurons in the brain.
The neuron is labeled in this image: The dendrites "attach" (they don't really attach they form "bridges" called synapses) to the axon terminals of another neuron where the neuron can transfer the impulse through neurotransmitters.
The Propagation of a Nerve Impulse. Like the other cells of the body neurons contain charged ions including potassium, sodium and chlorine. A mechanism in its cell membrane has to "pump" the sodium ions back out again, restoring the negative charge and the "action potential" to the cell.
It is specialised to react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus. Nervous tissue is composed of neurons, which transmit impulses, and the neuroglia, which assist propagation of the nerve impulse as well as provide nutrients to the neuron.
Increased Conduction Velocity as a Result of Myelination. By acting as an electrical insulator, myelin greatly speeds up action potential conduction (Figure 3.14). For example, whereas unmyelinated axon conduction velocities range from about 0.5 to 10 m/s, myelinated axons can conduct at velocities up to 150 m/s.
The main purpose of a myelin sheath is to increase the speed at which impulses propagate along the myelinated fiber. Along unmyelinated fibers, impulses continuously move as waves, but, in myelinated fibers, they "hop" or propagate by saltatory conduction.
When the neuronal membrane is at rest, the resting potential is negative due to the accumulation of more sodium ions outside the cell than potassium ions inside the cell.
A Nerve electrical impulse only travels in one direction. There are several reasons nerve impulses only travel in one direction. The most important is synaptic transport. In order for a "nerve impulse" to pass from cell to cell, it must cross synaptic junctions.
Most nerve fibres are surrounded by an insulating, fatty sheath called myelin, which acts to speed up impulses. The myelin sheath contains periodic breaks called nodes of Ranvier. By jumping from node to node, the impulse can travel much more quickly than if it had to travel along the entire length of the nerve fibre.