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Functional Types of Nerve Endings

Q: How are receptor nerve endings classified according to their morphological structure?

Morphologically, receptor nerve endings can be: Free nerve endings — terminal branches of axis cylinders lacking glial wrappings.Non-encapsulated (non-free) endings — branches of sensory neuron dendrites accompanied by glial cells (lemmocytes); in the papillary layer, they perceive temperature and pain.Encapsulated endings — receptors possessing a connective tissue capsule; these include Meissner corpuscles, Vater-Pacini corpuscles, and Ruffini corpuscles. Meissner corpuscles feature three components: terminal dendritic branches, modified lemmocytes, and a thin connective tissue capsule.

*Terminationes nervorum*

For medical students2 min readUpdated 2026-10-10

Nerve endings (Terminationes nervorum) are specialized terminal apparatuses of nerve fibers that ensure the proper functioning of the nervous system. They are responsible for perceiving external and internal stimuli, transmitting signals between cells, and directly regulating the activity of effector organs and the vascular bed.

Classification4 main functional types are distinguished

ReceptorsTransmit data from sense organs to the CNS

EffectorsTransmit impulses to muscles and glands

SecretionForm axovasal synapses with capillaries

Classification of Nerve Endings

For the nervous system to function as a single entity, specialized structures are required at the ends of neuronal processes. Depending on their role and exact localization, histology traditionally distinguishes four functional types of nerve endings:

Receptor (sensory or afferent).
Interneuronal synapses (contacts between nerve cells themselves).
Effector (motor or secretory).
Neurosecretory (releasing active substances into the blood stream).

Each of these types possesses a unique morphology and strict affinity for specific parts of the neuron (axons or dendrites).

Type I: Receptor (Afferent) Endings

Receptor endings represent the initial link of the reflex arc.

Localization: These structures are always located at the ends of dendrites of sensory (afferent) neurons.
Function: The main task of receptors is the adequate perception of information. They record stimuli coming both from the external environment (via sense organs) and from the body's internal receptors.
Purpose: After perceiving a stimulus, the signal is transformed and transmitted for further complex analysis to the structures of the central nervous system (CNS).

Type II: Interneuronal Synapses

This type of ending is necessary for the formation of neural networks.

Function: Direct transmission of a nerve signal from one neuron to another. Interneuronal synapses ensure reliable communication among all existing types of nerve cells (afferent, association, and efferent neurons).
Structural components: A synapse consists of two key parts. The transmitting part is typically the axon. The receiving part can be the dendrite or the cell body (soma) of the next neuron.

Depending on which parts of the cells come into contact, the following morphological types of synapses are distinguished:

Axodendritic — contact between the axon of the first neuron and the dendrite of the second.
Axosomatic — signal transmission from the axon directly to the cell body (soma).
Axoaxonic — a specific contact between two axons.
Somatodendritic — a rare type of connection where the neuron body contacts a dendrite.

Type III: Effector Endings

Effector endings serve as the final link, transmitting commands from the nervous system to the working organ.

Localization: Located exclusively at the ends of axons of efferent neurons. They logically complete the efferent (descending) nerve pathways.
Structure: Together with the plasma membrane of the executive cell (muscle fiber or glandulocyte), they form specialized neuroeffector synapses.
Function: Implementation of nerve impulse transmission to effector organs. Target organs are typically muscles (skeletal or smooth) and various glands.

Type IV: Neurosecretory Endings

This type of ending connects the nervous system with the endocrine system.

Localization: Located at the ends of axons of specialized neurosecretory neurons.
Structure: A feature of these endings is that they directly contact blood vessels (capillaries). This contact forms so-called axovasal synapses.
Function: Targeted release of synthesized hormones (neurosecretion) directly into the bloodstream to regulate systemic body functions.

Mnemonic

To remember the four types, use the acronym R-I-E-N (or think R-M-E-S): Receptor (perceive), Interneuronal (transmit within the network), Effector (make organs work), Neurosecretory (secrete into blood).

Frequently asked questions

How are receptor nerve endings classified according to their morphological structure?

Morphologically, receptor nerve endings can be:

Free nerve endings — terminal branches of axis cylinders lacking glial wrappings.
Non-encapsulated (non-free) endings — branches of sensory neuron dendrites accompanied by glial cells (lemmocytes); in the papillary layer, they perceive temperature and pain.
Encapsulated endings — receptors possessing a connective tissue capsule; these include Meissner corpuscles, Vater-Pacini corpuscles, and Ruffini corpuscles. Meissner corpuscles feature three components: terminal dendritic branches, modified lemmocytes, and a thin connective tissue capsule.

Which neurotransmitters mediate signal transmission in interneuronal synapses?

Signal transmission in chemical interneuronal synapses is carried out by neurotransmitters that diffuse across the synaptic cleft from the presynaptic ending to the postsynaptic membrane.

Based on the neurotransmitter type, cholinergic, adrenergic, GABAergic, serotoninergic, dopaminergic, and glutamatergic synapses are distinguished.

Sources explicitly mention the following neurotransmitters:

Acetylcholine — the mediator of cholinergic synapses.
GABA — the mediator of GABAergic synapses, inhibitory type.
Glycine — the mediator of glycinergic synapses, also inhibitory type.

Many interneuronal synapses in the brain may have multiple co-transmitters: usually, one is non-peptidergic, while the others are neuropeptides.

Where are the bodies of neurosecretory neurons located whose axons form axovasal synapses?

The bodies of neurosecretory neurons whose axons form axovasal synapses are localized in the magnocellular nuclei of the hypothalamus. These include:

Supraoptic nuclei — located above the optic chiasm (chiasma opticum).
Paraventricular nuclei — located in the lateral walls of the third brain ventricle.

Axons descend from these cell bodies into the posterior pituitary gland (neurohypophysis), where they form synapses on blood capillaries to release hormones.

On which processes are receptor nerve endings located?

Receptor endings are localized on the dendrites of sensory (afferent) neurons.

What is an axovasal synapse?

It is a contact between the axon terminal of a neurosecretory neuron and a blood capillary, serving to release hormones into the blood.

Which morphological types of interneuronal synapses are the rarest?

According to morphological classification, somatodendritic synapses (contact between the cell body and a dendrite) are the rarest.

Go deeper

Mechanisms of synaptic delay in interneuronal synapses
Action potential generation process
Structural features of neuroeffector synapses in muscle tissue
Specifics of axonal transport in neurosecretory cells