A neuron is a nerve cell. These cells are vital for communication and coordination in the body. They utilize electrical and chemical signals to transmit information within the brain, between the rest of the central nervous system, and with the muscles and glands of the body.
Neurons communicate with each other at synapses. These are contact points where the axons of one neuron meet up with the dendrites of the next. Thus, the dendrites of one neuron form many synapses with other neurons, and the axons branch off to connect to many neurons in the other direction as well. This is how the nervous system forms such an intricate communication system.
When organized by structure, there are four different types of neurons. They are differentiated by the number and location of structures extending from the cell body that they have.
- Unipolar neurons have only one extension from the soma. They are not found in vertebrates, only insects.
- Bipolar neurons have two arms that come out from the cell body, one axon, and one dendrite.
- Pseudounipolar neurons have one extension from the soma, but it quickly divides into two distinct structures. Many sensory neurons are shaped like this.
- Multipolar neurons are most common. They have one axon and many dendrites branching off of the cell body.
Afferent neurons, also known as sensory neurons, are a type of nerve cell in the peripheral nervous system (PNS) that play a role in the transmission of sensory information from the body’s sensory organs to the central nervous system (CNS), which includes the brain and spinal cord. These neurons are responsible for detecting various sensory stimuli from the external environment and the body’s internal conditions, and they transmit this information to the CNS for processing and interpretation.
What you need to know about afferent neurons
- Sensory Reception: Afferent neurons have specialized sensory receptors at their peripheral endings. These receptors can detect various stimuli, such as touch, temperature, pain, pressure, light, sound, taste, and smell, depending on their location in the body.
- Transmission: When a sensory receptor is activated by a specific stimulus, it generates electrical signals (action potentials) that travel along the afferent neuron’s axon toward the CNS.
- Conduction: Afferent neurons are equipped with long axons that can transmit these electrical signals over relatively long distances without significant signal loss or degradation.
- Signal Processing: The information carried by afferent neurons is transmitted to specific regions of the CNS, where it is processed and integrated. This processing allows the brain to perceive and interpret sensory experiences, leading to conscious awareness and appropriate responses.
- Types of Afferent Neurons: Afferent neurons come in various types, depending on the type of sensory information they transmit. For example, photoreceptors in the retina of the eye are a type of afferent neuron responsible for detecting light and transmitting visual information, while nociceptors detect pain, and mechanoreceptors sense mechanical pressure or touch.
- Receptor Specificity: Afferent neurons are highly specialized, with different types of receptors designed to respond to specific types of stimuli. For instance, the receptors in your skin are different from those in your eyes or ears, ensuring that sensory information is accurately relayed to the brain.
Efferent neurons, also known as motor neurons, are a type of nerve cell in the peripheral nervous system (PNS) and central nervous system (CNS) that play a role in transmitting signals from the CNS to the muscles, glands, and other effector organs. These neurons are responsible for initiating and controlling motor responses, allowing the body to carry out various actions and functions.
What you need to know about efferent neurons
- Motor Control: Efferent neurons are involved in controlling voluntary and involuntary movements of the body. They transmit signals from the CNS to muscles, causing them to contract or relax in response to specific commands or stimuli.
- Target Organs: Efferent neurons synapse with muscles, glands, and other effector organs, depending on the type of response needed. For example, motor neurons innervate skeletal muscles to control voluntary movements, while autonomic motor neurons regulate involuntary processes like heart rate, digestion, and glandular secretion.
- Effector Specificity: Efferent neurons are highly specialized, with different types of motor neurons responsible for different types of effector organs. For instance, somatic motor neurons control skeletal muscle movement, while autonomic motor neurons control smooth muscles, cardiac muscles, and glands.
- Neurotransmitter Release: When an efferent neuron reaches its target organ, it releases neurotransmitters at the neuromuscular junction or synapse. These neurotransmitters bind to receptors on the target cells, leading to muscle contraction, glandular secretion, or other appropriate responses.
- Divisions of Efferent Neurons: Efferent neurons can be further divided into two main categories:
- Somatic Efferent Neurons: These neurons are responsible for controlling voluntary muscle movements and are part of the somatic nervous system. They transmit signals from the CNS to skeletal muscles, allowing for conscious movements like walking, talking, and reaching.
- Autonomic Efferent Neurons: These neurons are involved in regulating involuntary bodily functions, such as heart rate, digestion, and respiratory rate. The autonomic nervous system is further divided into sympathetic and parasympathetic branches, each with its specific functions.
Afferent vs Efferent Neurons: Key Differences
|Elements of Comparison
|Afferent neurons are the neurons that carry sensory impulses towards the CNS.
|Efferent neurons are the neurons that carry motor impulses away from the CNS.
|Afferent neurons are also known as sensory neurons.
|Efferent neurons are also known as motor neurons.
|Afferent neurons carry signal from sensory organs to the CNS.
|Efferent neurons carry signal from the CNS to effector organs and tissues.
|Afferent neurons consist of a short axon.
|Efferent neurons consist of a long axon.
|Afferent neurons consist of a receptor.
|Efferent neurons lack a receptor.
|Cell body of the afferent neuron is situated in the dorsal root ganglion of the spinal cord and no dendrites are found in it.
|Cell body of the efferent neuron is situated in the ventral root ganglion of the spinal cord and consists of dendrites.
|Afferent neuron consists of one long dendron.
|Efferent neuron consists of many short dendrons.
|Afferent neurons carry signals from the outer part of the body into the central nervous system.
|Efferent neurons carry signals from the central nervous system to the outer parts of the body.
|Afferent neurons are unipolar.
|Efferent neurons are multipolar.
|Afferent neurons are found in skin, eyes, ears, tongue, and nose.
|Efferent neurons are mainly found in muscles and glands.