StudySmarter: Study help & AI tools
4.5 • +22k Ratings
More than 22 Million Downloads
Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen LernstatistikenJetzt kostenlos anmelden
Nie wieder prokastinieren mit unseren Lernerinnerungen.Jetzt kostenlos anmelden
Nerve cells, otherwise known as neurones, use nerve impulses to communicate with one another and pass information.
Nerve impulses are waves of electrochemical changes across neurones that assist in the formation of an action potential in response to a stimulus.
A nerve impulse will cause a set of physiological changes that occur in a neurone due to a stimulus' mechanical, chemical, or electrical disturbance. This will be propagated across an axon. The nerve impulse is passed to neighbouring neurones over the synaptic cleft and to muscle fibres via neuromuscular junctions through the release of neurotransmitters.
A stimulus describes an internal or external change in the environment. Examples include heat, pressure, and sound.
A synaptic cleft (also known as a synapse) describes the junction between two or more neurones. Meanwhile, a neuromuscular junction describes the gap between a neurone and a muscle fibre.
There are several types of neurons in the body, including sensory, motor, and interneurones. Below are some key structural features:
Interneurones are also known as relay neurones. They are the same thing!
Let's summarise some of the differences between sensory and motor neurones.
|Carries sensory impulses from the sensory organ to the CNS
|Carries motor impulses from CNS to effectors
|Unipolar - contains a single extension from the cell body
|Multipolar - many dendrites
|Relatively short axon
|Relatively long axon
|Found in skin, nose, ears, tongue, and eyes
|Found in glands and muscles
Interneurones have a cell body in the middle of the axon, unlike motor and sensory neurones. They are found exclusively in the CNS and are the link point between sensory and motor neurones.
Let's cover the main factors affecting nerve impulse propagation speed.
An impulse will travel at a speed of up to 150 m/s in myelinated neurones, while only 0.5 to 10 m/s in unmyelinated neurones.
So why would you have neurones that are unmyelinated? Surely this would be inefficient? Some neurones will pass signals that do not travel very far, and myelination would not increase the speed by much. Exerting energy to myelinate cells is costly and "not worth" the energy required. As well as this, if a neuron's axon diameter is really small, the myelin sheath will add an unnecessary layer. Lastly, some signals do not need to be propagated at such high speeds, for example, long-lasting pain.
Warm-blooded animals maintain a constant body temperature by homeostasis (the maintenance of a constant internal environment), so temperature is not too important as a factor. However, in cold-blooded animals, when the environmental temperatures decrease, the propagation of nerve impulses will be comparatively slower.
Read our Size to Volume Ratio article to learn more about the phenomenon.
Neurones send and receive impulses to and from the CNS and are important in coordinating a response to a stimulus. Nerve impulses (the way neurones coordinate this response) are transmitted as action potentials along the neurone's axon. The steps of an action potential include:
The membrane potential is the difference in charge between both sides of the plasma membrane.
Nerve impulses can travel in two ways along the neurone's axon:
Saltatory conduction only occurs in myelinated neurones where the impulse jumps from one Node of Ranvier to the next. Conversely, continuous conduction occurs in unmyelinated axons, where the impulse travels along the whole length of the axon.
When you consider the steps of an action potential, saltatory conduction is more energy efficient. This is because repolarisation requires ATP, and due to the presence of the nodes, you essentially reduce the amount of repolarisation needed compared to continuous conduction.
As we mentioned earlier, a synapse describes the junction between a neurone and another neurone. This site contains three components:
For the information to be transferred, neurotransmitters are needed.
Neurotransmitters are produced in the neurone cell body. They are chemical messengers that transmit the nerve impulse across the synaptic cleft. They are released from the pre-synaptic membrane and diffuse across the synaptic cleft to reach the post-synaptic membrane, where they bind to specific receptors.
As a result of the neurotransmitters being released from the pre-synaptic membrane and receptors located on the post-synaptic membrane, nerve impulse transmission occurs in one direction only! This means the nerve impulse cannot travel back to the originating neurone.
Have a read of our articles on Types of Synapse and Transmission across a Synapse for a deeper dive!
Let's quickly recap how a nerve impulse travels to produce a response in effector cells and link that to the molecular aspect of nervous impulse that we just covered. A stimulus-response model can be used to describe this.
Effectors are cells that actively respond to a stimulus. This includes muscle cells and glands.
A nerve impulse is a wave of electrical chemical changes across a neurone that assists in the formation of an action potential in response to a stimulus
Nerve impulses are transmitted from one neurone to another via neurotransmitters.
Neurotransmitters released from the pre-synaptic membrane diffuse across the synaptic cleft and bind to receptors located on the post-synaptic membrane.
Neurotransmitters are released only from the pre-synaptic membrane and receptors are located only on the post-synaptic membrane. Due to this organisation, the transmission of nerve impulses occurs in one direction only!
Nerve cells, also known as neurones, are the primary units of communication in the neurological system.
Each neurone consists of a cell body, an axon and dendrites.
What is a nerve impulse?
A nerve impulse is a wave of electrical chemical changes across a neuron that assists in the formation of an action potential in response to a stimulus.
Why is continuous conduction slower?
Continuous conduction is a slower mechanism that requires more energy to transmit impulses. It takes longer to conduct signals because it employs a greater number of ion channels to change the neuron's resting state. Continuous conduction is slow as there are always voltage-gated Na + channels opening, and more and more Na + is rushing into the cell.
What is first needed to generated an action potential?
What are effectors?
Effectors are cells or tissues that generate the response to a stimulus. This includes skeletal muscle and glands
What does CNS stand for?
The Central Nervous System.
What are the two types of cells that are able to produce an action potential?
Nerve and muscle cells.
The first learning app that truly has everything you need to ace your exams in one place
Sign up to highlight and take notes. It’s 100% free.