Literature to prepare the topic7

General data of nervous system

The innervation of the cervical muscles

Cutaneous innervation of the neck

Autonomic (vegetative) nervous system

Autonomic innervation of the organs

 

General data of nervous system

According to anatomy and topography, the nervous system can be divided into central and peripheral. The central nervous system includes the brain and the spinal cord. The peripheral nervous system includes all the nervous structures outside the central nervous system.

Functionally, the nervous system consists of the somatic and vegetative. In general, the somatic nervous system innervates the soma: skin, muscles, skeleton. It accepts the various stimulations, analyzes them and provides the response to these stimulations. The vegetative nervous system is responsible for the innervation of viscera, glands, vessels, and in its turns, is divided into the sympathetic and parasympathetic.

The central nervous system is comprised of billions of neurons and glial cells. The glial cells support and protect the neurons, also playing the trophic role. The neurons are grouped into different centers (nuclei) of the spinal cord and brain.

The neuron is a structural and functional unit of the nervous system. A neuron has a body and certain number of processes.

They are different in form: they can be pyramidal, stellate, oval, round etc. According to they size, the neurons can be grouped into large (60-130 micrometers), middle (20-60 micrometers) and small (4-20 micrometers).

The neurons differ in the number of processes: can be unipolar (having one process), pseudounipolar (having one false process divided into two), bipolar (having two processes) and multipolar (having several or many processes) (fig.1).

Functionally, all the neurons are divided into sensory (afferent), having receptors, motor (efferent), having the effectors, and intermediate. The sensory neurons accept the stimulation from outside the body; the motor neurons transmit the stimulation to the organ; the intermediate neurons transmit the impulse from the sensory to motor neurons.

The sensory neurons are

pseudounipolar (for general sensitivity), or bipolar (for special sensitivity). The processes of the sensory neurons are called peripheral and central processes. The small multipolar neurons are intermediate, and the large multipolar are motor. The processes of the multipolar neurons are called axons and dendrites. One multipolar neuron has only one axon; other processes are dendrites.

The somatic sensory neurons and vegetative sensory neurons are placed in the spinal ganglia and in the cranial nerves sensory ganglia. The peripheral processes of the sensory neurons form the sensory spinal and cranial nerves, and the sensory portions of the spinal nerves. The central processes form the posterior root of the spinal cord, or the sensory roots of cranial nerves, therefore they run to the spinal cord and to the brainsteam to reach the intermediate neurons.

The somatic intermediate neurons are in the nuclei of the posterior horns of the spinal cord, in the sensory nuclei of cranial nerves, in different nuclei of the brainsteam, which form the various subcortical centers, and also in cortical centers. The vegetative intermediate neurons are in the nuclei of the lateral horns of the spinal cord, and in the vegetative nuclei of the cranial nerves.

The motor neurons are in the proper nuclei of the anterior horns of the spinal cord and in the motor nuclei of cranial nerves.

The peripheral process of a sensory neuron ends by a receptor in the periphery of the body (in the skin, muscle, joint, bone, viscera etc). Thus, all the receptors can be classified, according the location, into exteroceptors, proprioceptos, interoceptors and receptors of specialized sensory organs.

The exteroceptors are in the skin, mucous of the oral cavity, nasal cavity and in the conjunctiva. They accept tactile (touch), temperature and pain stimulations.

The proprioceptors are in the muscles, tendons, fasciae, periosteum, ligaments and joint capsules. They accept touch, weight, pressure, vibration, degree of muscle tension and relations between the parts of the body.

The interoceptors are in the viscera. They accept chemical composition of the substances, the degree of filling of the hollow organs and also pain.

The receptors of specialized sensory organs (organs of vision, hearing, balance, smell and taste) accept the respective stimulations: light and color, sound and noise, angular and vertical accelerations, smell and taste.


The neurons are connected by synapses which can be axo-somatic (between the axon and the body of neuron), axo-dendritic (between the axon and dendrite), axo-axonal (between the two axons), or dendro-dendritic (between two dendrites), dendro-somatic (between the dendrite and body of neuron) and somato-somatic (between bodies of two neurons). Also synapses between the neuron and tissue exist; they can be neuro-muscular and neuro-secretory, and they are termed the effectors.
The process of a neuron forms the nerve fiber which serves for conduction of the nervous impulse. Each nerve fiber consists of the process of a neuron, termed the axial cylinder, surrounding by glial cells (fig. 2). The nerve fibers can be myelinated or unmyelinated. In myelinated fiber, the layer of myelin surrounds the process of neuron; that is why the myelinated fibers are thicker. The speed of the nervous impulse conduction is much greater in the myelinated than in the unmyelinated fibers. The myelinated fibers are typical for the somatic nervous system; the unmyelinated fibers chiefly form the vegetative nervous system.

 The synapse consists of presynaptic part, synaptic slit and postsynaptic part. Presynaptic part is usually formed by the terminal part of the axon and contains the vesicles filled with neurotransmitter. The following substances can be the neurotransmitters: acetylcholine, noradrenalin, histamine, glycine, dophamin etc. The neurotransmitter passes through the synaptic slit to react with chemoreceptors of the postsynaptic membrane. After the reaction the neurotransmitter is inactivated, and the inactivated molecules are absorbed through the presynaptic membrane.

The nervous system works, using the reflex. The latter is a response of the body to the outer and inner stimulation. All the reflexes are divided into congenital and conditioned. The congenital reflexes are performed with the spinal cord or brainsteam; they are simple. The conditioned reflexes are performed with obligatory participation of the cerebral cortex; they are complex. The morphological base of the reflex is the reflex arch. The latter is a chain of the neurons connected by their processes. The simple reflex arch, as usual, consists of three neurons: sensory, intermediate and motor, which form three parts: sensory, intermediate and motor. The complex reflex arch also has the same parts, but it includes many neurons. The parts of the complex reflex arch are formed by the ascending and descending conducting tracts, passing through the spinal cord and brainsteam and making their white matter. Ascending tracts form the sensory parts of the complex reflex arches; descending parts form their motor parts. The intermediate part of the complex reflex arch is included into the ascending and descending tracts.

The sensory neuron of the simple somatic reflex arch, as mentioned above, is in the spinal ganglion or in the sensory ganglion of some cranial nerve. The intermediate neuron is in some nucleus of the posterior horn of the spinal cord or in the sensory nucleus of some cranial nerve. The motor neuron is in the proper nucleus of the anterior horn of the spinal cord or in the motor nucleus of some cranial nerve.

The sensory neuron of the complex somatic reflex arch is in the spinal ganglion or in the sensory ganglion of some cranial nerve. The intermediate neuron is in some nucleus of the posterior horn of the spinal cord or in the sensory nucleus of some cranial nerve, or in some nucleus of the brainsteam (it means in some subcortical center), or in some cortical center. The motor neuron is in the proper nucleus of the anterior horn of the spinal cord or in the motor nucleus of some cranial nerve.

 

The innervation of the cervical muscles

  1. Superficial cervical muscles.

Platysma — facial (VII cranial) nerve;

Sternocleidomastoid — accessory (XI cranial) nerve

2. Middle cervical muscles.

Suprahyoid muscles (common action is depression of the mandible and elevation of the hyoid bone):

Genyohyoid — hypoglossal (XII cranial) nerve;

Mylohyoid — trigeminal (V cranial) nerve;

Anterior belly of digastric  — trigeminal (V cranial) nerve;

Posterior belly of digastric — facial (VII cranial) nerve;

Stylohyoid — facial (VII cranial) nerve

Infrahyoid muscles (common action is to depress the hyoid bone):

Sternohyoid, sternothyroid, thyrohyoid, omohyoid — muscular branches of the cervical plexus (ansa cervicalis profunda)

3. Deep cervical muscles (common action is flexion of the neck, and also rotation and lateral flexion of the head and neck): 

Longus capitis, longus colli, recti capitis anterior and lateralis, scaleni muscles — muscular branches of the cervical plexus

4. Muscles in the posterior cervical region (common action is extension of the neck; and also rotation and lateral flexion of the head and neck):

Trapezius — accessory (XI cranial) nerve 

Splenius capitis and cervicis — dorsal rami of C1-C8 nerves

Levator scapulae — dorsal scapular nerve (from the brachial plexus, C5)

Semispinalis capitis, longissimus capitis, longissimus cervicis, iliocosatlis cervicis, multifidi, interspinales cervicis, intertransversale cervicis, recti capitis posterior major and minor, oblique capitis superior and inferior — dorsal rami of C1-C8 nerves

 

Cutaneous innervation of the neck

 

Face region is innervated by the trigeminal nerve divisions (ophthalmic, maxillary, mandibular)

Anterolateral cervical region is innervated by cutaneous branches of the cervical plexus (supraclavicular, transverse cervical, lesser occipital, great auricular nerves)

Posterior cervical region is innervated by the dorsal branches of the cervical nerves (C2-C8)

Autonomic (vegetative) nervous system

 

There are two kinds of nervous systems in the body: somatic and autonomic (vegetative). The first one innervates the “soma”: skeletal muscles, sense organs; the second one innervates smooth muscles and glands of the viscera, vessels and the glandular tissues of the body.
The autonomic nervous system (ANS) as well as the somatic NS has central and peripheral parts: the central part is localized in the brain and the spinal cord; the peripheral part includes the following structures:
1. Vegetative ganglia;
2. Vegetative fibers and nerves;
3. Vegetative plexuses;
4. Vegetative nerve endings
The ANS consists of two parts: sympathetic nervous system (SNS) and parasympathetic nervous system (PNS).
The central part of the ANS controlling both systems is placed in the brain. It comprises the hypothalamic nuclei; reticular formation; cerebellum; limbic system; cerebral cortex (picture 1). They are called the suprasegmental vegetative centres.

Each part of ANS (SNS and PNS) has own controlling centres; they are called the segmental centres.
The segmental centres for SNS are placed only in the spinal cord; they are so called intermediolateral nuclei located in the lateral spinal horns. These nuclei exist only in the spinal segments from 8th cervical to 3d lumbar (picture 2, 3).

The segmental centres for PNS are placed both in the spinal cord and in the brain stem. In the spinal cord they are the parasympathetic sacral nuclei located in the lateral horns of the spinal segments from 2d to 4th sacral (picture 3).
In the brain stem they the parasympathetic nuclei of the following cranial nerves: III (oculomotor); VII (facial); IX (glossopharyngeal); and X (vagus) (picture 4).

The action of the ANS is realized through the reflexes. As well as in the somatic NS, the autonomic reflexes can be simple and complex. The simple reflexes occur at the level of the segmental vegetative centres (i.e. the spinal lateral horns and the brain-stem vegetative cranial nerve nuclei); the complex reflexes involve the suprasegmental centres.
The autonomic reflex arch has the same parts as the somatic: afferent part, association part and efferent part.
Let`s remember the structure of the simple somatic reflex arch: the first-order (sensory) neuron is in the spinal ganglion (located near each spinal segment within the vertebral column); the second-order (association, relay) neuron is in some nucleus located in the posterior spinal horn; the third-order (efferent) neuron is in the nuclei proprii located in the anterior spinal horns (picture 5).
Now is about the structure of the simple autonomic reflex arch. The neurons of the SYMPATHETIC reflex arch: the first-order (sensory) neuron is in the spinal ganglion (located near each spinal segment within the vertebral column); the second-order (association) neuron is in intermediolateral nucleus located in the lateral spinal horn (C8-L3 segments); the third-order (efferent) neuron is outside the spinal cord, in the sympathetic ganglia (later we will talk about them) (picture 6).

The neurons of the PARASYMPATHETIC reflex arches can occur at the level of the brain stem or spinal cord because its segmental centres are the vegetative cranial nerve nuclei (III, VII, IX and X) located in the brain stem and the parasympathetic sacral nuclei located in the spinal lateral horns (S2-S4).

So, for the reflex arches which occur at the level of the brain stem the first-order (sensory) neuron is usually located in the sensory cranial nerve ganglion (of the V, VII, IX, X cranial nerves); the second-order (association) neuron is in the vegetative cranial nerve nuclei (III, VII, IX and X); the third-order (efferent) neuron is in the parasympathetic ganglia (later we will talk about them). It should be noted that the parasympathetic fibres of the cranial nerves mainly innervate the organs of the head (when we describe the innervation of these organs, we will describe each reflex arch in details); only the vagus nerve passes outside the head organs and innervate all the viscera until the sigmoid colon.

For the reflex arches which occur at the level of the spinal cord the first-order (sensory) neuron is located in the spinal ganglion; the second-order (association) neuron is in the parasympathetic sacral nuclei (S2-S4 segments); the third-order (efferent) neuron is in the parasympathetic ganglia.

So, PAY ATTENTION: the autonomic segmental centres contain the secon-order (association, or intermediate, neurons) of the reflex arches.

Now is about the autonomic ganglia. The autonomic ganglion is a cluster of nerve cell bodies. They are efferent in function (third-order in the autonomic reflex arch).
The sympathetic ganglia are located lateral to the vertebral column (paravertebral ganglia) or anterior to it (prevertebral). The paravertebral ganglia form the sympathetic trunks. There are two sympathetic trunks situated alongside the vertebral column; each is a chain of the paravertebral ganglia (about 22-26) interconnected by the interganglionic fibres (picture 7).
The prevertebral ganglia are situated in the abdominal cavity near the large abdominal vessels (picture 8). So, the sympathetic ganglia are close to the vertebral column and far from the viscera.
The parasympathetic ganglia are intraorganic (intramural) or paraorganic: the first kind is in the wall of the hollow organs; the second kind is near the parenchymatous organs. So, the parasympathetic ganglia are close the viscera.
The paraorganic ganglia situated in the head region have been already known for you; they are the ciliary, pterygopalatine, otic and submandibular ganglia (picture 9, 10, 11). The ciliary ganglion is associated with the III cranial nerve; the pterygopalatine – with VII cranial nerve; the otic – with the IX cranial nerve and the submandibular – with the VII cranial nerve.

 

 

To understand the autonomic innervation, we need to repeat the location of the neurons in the autonomic reflex arch. So, for the sympathetic reflex arch the sensory (afferent) neuron is in the spinal ganglion; the association (intermediate) neuron is in the segmental centres (intermediolateral nucleus situated in the lateral horns of C8-L3 segments); the motor (efferent) neuron is in the paravertebral ganglia (which form the sympathetic trunk) or in the prevertebral ganglia.
For the parasympathetic reflex arch the sensory (afferent) neuron is in the cranial or spinal ganglion; the association (intermediate) neuron is in the segmental centres (cranial nerve parasympathetic nuclei situated in the brain steam (of the III, VII, IX and X cranial nerves) or in the parasympathetic sacral nuclei situated in the lateral horns of S2-S4 segments); the motor (efferent) neuron is in the paraorganic or intraorganic ganglia.

Now, let`s talk about the organs of different body parts, which need the vegetative innervation.
In the head they are: the vessels; sweat glands and sebaceous glands of the skin; minor and major salivary glands; nasal glands; lacrimal glands; smooth muscles of the eye (ciliary, sphincter and dilator of pupil). They are innervated by the sympathetic plexuses arising from the cervical ganglia of the sympathetic trunk. They receive the parasympathetic innervation through the III, VII, IX and X cranial nerves.
In the neck they are: the vessels; sweat glands and sebaceous glands of the skin; the oesophageal and tracheal muscles; the mucosal glands of the larynx, trachea, pharynx and oesophagus. They are innervated by the sympathetic plexuses arising from the cervical ganglia of the sympathetic trunk. They receive the parasympathetic innervation through the X cranial nerve.

In the thoracic and abdominal cavities the organs which need the vegetative innervation are the vessels; smooth musculature and glandular tissue of all the viscera. They are innervated by the sympathetic plexuses arising from the thoracic and lumbar ganglia of the sympathetic trunk; and the sympathetic plexuses arising from the prevertebral ganglia. They receive the parasympathetic innervation through the X cranial nerve.
As for the pelvic organs, they receive the sympathetic innervation through the sympathetic plexuses arising from the sacral ganglia of the sympathetic trunk; and the parasympathetic innervation from the parasympathetic sacral nuclei.
In the extremities the organs which need the vegetative innervation are the vessels; sweat glands, sebaceous glands and pilomotor muscles of the skin.
NB: the organs which do not have parasympathetic innervation are blood vessels (except for the coronary vessels); sweat glands; pilomotor muscles; suprarenal medulla.
So, there are no parasympathetic fibres in the limbs.

Autonomic innervation of the organs

Here we will talk about the autonomic innervation of the organs. We will describe this like a reflex arch. And we start from the parasympathetic innervation of the pupillary sphincter. This muscle is inside the iris; it contracts as a response to the light rays entering the eye.
So, the afferent part of this reflex starts from the cones and rods (they are the receptors of the light); then the light impulse passes to the bipolar retinal cells and then to the ganglion retinal cells (they are the sensory neurons). Then through the optic nerve the information about light comes to the subcortical visual centre (the nuclei of the midbrain superior colliculi). From here it passes to the accessory nucleus of the oculomotor nerve (Edinger-Westphal`s nucleus) situated in the midbrain; it is one of the parasympathetic segmental centres. So the nuclei of the superior colliculi and accessory nucleus of the oculomotor nerve contain the association neurons of this reflex arch. The parasympathetic fibres arising from the Edinger-Westphal`s nucleus run via the oculomotor nerve through the superior orbital fissure into the orbit to reach the ciliary ganglion (so called preganglionic fibres). The latter is a paraorganic parasympathetic ganglion situated behind the eyeball. It contains the efferent neurons of this reflex arch. The fibres arising from these neurons reach the sphincter of pupil via the short ciliary nerve (so called postganglionic fibres) and cause the contraction of the pupillary muscle.
So, you see that the afferent part of this reflex arch passes through the somatic nervous system (retinal cells and optic nerve).
The attached presentation shows the way of the nerve impulse through the pupillary reflex arch.
Now is about the innervation of the thoracic organs on the example of the heart. The parasympathetic innervation of the heart as well as all other viscera until the sigmoid colon occurs via the vagus nerve. This nerve is mixed, comprises all kinds of nerve fibres: sensory, motor and vegetative (parasympathetic). Its nuclei lie in the brain stem. It has the sensory ganglia located at the jugular foramen. So, the sensory neurons of the reflex arch through the heart are in the inferior sensory ganglion of the vagus nerve. These neurons are pseudounipolar; their peripheral processes end in receptors in the cardiac tissues. Their central processes are included in the vagus nerve root. The afferent impulse from the heart travels via the processes of the pseudounipolar neurons to reach the dorsal vagal nucleus containing association neurons. After that it runs through the parasympathetic vagus nerve fibres (the preganglionic fibres) to reach the organic ganglion. The postganglionic fibres run to the heart, inhibiting its activity and constricting the coronary arteries.

Pupillary reflex

If the pupillary sphincter is innervated by the parasympathetic fibres, the pupillary dilator is innervated by the sympathetic fibres. The afferent pathway is the same as for the pupillary reflex because the dilation of the pupil occurs as a response to amount of light rays.
So, the afferent pathway starts from the cones and rods (they are the receptors of the light); then the light impulse passes to the bipolar retinal cells and then to the ganglion retinal cells (they are the sensory neurons). Then through the optic nerve the information about amount of light rays comes to the subcortical visual centre (the nuclei of the midbrain superior colliculi).
From here the nerve impulse descends via the efferent vegetative pathway called the posterior longitudinal fasciculus to reach the sympathetic segmental centres (the intermediolateral nuclei situated in the lateral horns of C8, Th1 and Th2; here they are called centrum ciliospinale).
Thus, the nuclei of the superior colliculi and intermediolateral nuclei contain the association neurons of this reflex arch.
From the neurons of the intermediolateral nuclei the preganglionic fibres arise; they leave the spinal cord through the anterolateral sulcus and synapse with the efferent neurons situated in the superior ganglion of the sympathetic trunk. From here the nerves creating the ophthalmic plexus arise; they reach the pupillary dilator causing the dilation of pupil.

The attached presentation shows the noted pathway.

Sympathetic innervation of eye

Now is about the parasympathetic innervation of the salivary glands (on the example of the parotid gland). The afferent nerve impulse originates in the receptors of the oral cavity, the receptors of general sense or gustatory receptors. The afferent impulses from the receptors of general sense pass through the trigeminal nerve fibres; those from the gustatory receptors pass via the glossopharyngeal or intermediate nerve sensory fibres.
Thus, the sensory neurons of these reflex arches are placed in the trigeminal ganglion, glossopahryngeal nerve sensory ganglion or in the genicular ganglion.
The impulses from these ganglia pass through the root of the corresponding nerve into the brain stem to reach the association neurons.
The association neurons are in the trigeminal nerve sensory nuclei (probably in its pontine nucleus), glossopharyngeal and intermediate nerve sensory nucleus (nucleus of solitary tract).
The impulses from these neurons switch on other association neurons situated in the inferior salivatory nucleus of the glossopharyngeal nerve.
Via the glossopharyngeal nerve the impulses run to the efferent neurons situated in the otic ganglion (preganglionic fibres). The postganglionic fibres arising from the otic ganglion reach the parotid gland to increase its secretion.
The attached presentation shows the described reflex arch through the trigeminal nerve.

.
Parasympatetic innervation of parotid gland

Let`s continue about the sympathetic innervation of the salivary glands (on the example of the parotid gland). The afferent nerve impulse originates in the receptors of the oral cavity, the receptors of general sense or gustatory receptors. The afferent impulses from the receptors of general sense pass through the trigeminal nerve fibres; those from the gustatory receptors pass via the glossopharyngeal or intermediate nerve sensory fibres.
Thus, the sensory neurons of these reflex arches are placed in the trigeminal ganglion, glossopahryngeal nerve sensory ganglion or in the genicular ganglion.
The impulses from these ganglia pass through the root of the corresponding nerve into the brain stem to reach the association neurons.
The association neurons are in the trigeminal nerve sensory nuclei (probably in its pontine nucleus), glossopharyngeal and intermediate nerve sensory nucleus (nucleus of solitary tract).
The impulses from these neurons run to the spinal cord via the posterior longitudinal fasciculus to reach the segmental sympathetic centres, the intermediolateral nuclei.
From the neurons of the intermediolateral nuclei the preganglionic fibres arise; they leave the spinal cord through the anterolateral sulcus via the anterior spinal roots and synapse with the efferent neurons situated in the superior cervical ganglion of the sympathetic trunk. From here the nerves creating the external carotid plexus arise; they reach the parotid gland decreasing its secretion.

The attached presentation shows the noted reflex arch through the trigeminal nerve.

Sympathetic innervation of parotid gland

Now is about the innervation of the thoracic organs on the example of the heart. The parasympathetic innervation of the heart as well as all other viscera until the sigmoid colon occurs via the vagus nerve. This nerve is mixed, comprises all kinds of nerve fibres: sensory, motor and vegetative (parasympathetic). Its nuclei lie in the brain stem. It has the sensory ganglia located at the jugular foramen. So, the sensory neurons of the reflex arch through the heart are in the inferior sensory ganglion of the vagus nerve. These neurons are pseudounipolar; their peripheral processes end in receptors in the cardiac tissues. Their central processes are included in the vagus nerve root. The afferent impulse from the heart travels via the processes of the pseudounipolar neurons to reach the dorsal vagal nucleus containing association neurons. After that it runs through the parasympathetic vagus nerve fibres (the preganglionic fibres) to reach the organic ganglion. The postganglionic fibres run to the heart, inhibiting its activity and constricting the coronary arteries.

Parasympathetic innervation of heart

As for the sympathetic innervation of the heart, its afferent path passes through the cervical and cardiac thoracic nerves arising from the three cervical and upper five thoracic ganglia of the sympathetic trunk. But actually these afferent fibres are the peripheral processes of the corresponding spinal ganglia which connect to the cardiac nerves through the white communicating rami. So the sensory neuron of this reflex arch is in the spinal ganglion. The association neuron is in the sympathetic segmental centres (the intermediolateral nucleus). Their axons as preganglionic fibres reach the efferent neurons situated in the corresponding sympathetic trunk ganglia. The postganglionic fibres arising from these ganglia reach the heart increasing the heart rate.
The attached presentation shows the noted reflex arch.

Sympathetic innervation of heart

Now is about the innervation of the abdominal organs on the example of the stomach. The parasympathetic innervation of the stomach as well as all other viscera until the sigmoid colon occurs via the vagus nerve. This nerve is mixed, comprises all kinds of nerve fibres: sensory, motor and vegetative (parasympathetic). Its nuclei lie in the brain stem. It has the sensory ganglia located at the jugular foramen. So, the sensory neurons of the reflex arch through the stomach are in the inferior sensory ganglion of the vagus nerve. These neurons are pseudounipolar; their peripheral processes end in receptors in the gastric tissues. Their central processes are included in the vagus nerve root. The afferent impulse from the stomach travels via the processes of the pseudounipolar neurons to reach the dorsal vagal nucleus containing association neurons. After that it runs through the parasympathetic vagus nerve fibres (the preganglionic fibres) to reach the organic ganglion. The postganglionic fibres run to the stomach, increasing its peristalsis.

The attached presentation shows the noted reflex arch.

Parasympathetic innervation of stomach

 

As for the sympathetic innervation of the stomach, its afferent path passes through the branches of the celiac plexus arising from the lower thoracic ganglia of the sympathetic trunk or from the coeliac (prevertebral) ganglia. But actually these afferent fibres are the peripheral processes of the corresponding spinal ganglia which connect to the thoracic nerves through the white communicating rami. So the sensory neuron of this reflex arch is in the spinal ganglion (5-10 thoracic). The association neuron is in the sympathetic segmental centres (the intermediolateral nucleus). Their axons as preganglionic fibres reach the efferent neurons situated in the corresponding sympathetic trunk ganglia or coeliac ganglia. The postganglionic fibres arising from these ganglia reach the stomach decreasing the peristalsis and contracting the pyloric sphincter.
The attached presentation shows the noted reflex arch through the sympathetic trunk ganglion.

Sympathetic innervation of stomach

And finally is about the innervation of the pelvic organs on the example of the urinary bladder. The parasympathetic innervation of the pelvic organs occurs through the pelvic splanchnic nerves that are included in the pelvic plexus (the latter comprises both parasympathetic and sympathetic fibres). The sensory neuron of the bladder`s reflex arch lies in the spinal ganglion of the sacral spinal segments (S2-S4). The peripheral processes of the sensory neurons end by receptors in the bladder`s wall. The central processes enter the spinal cord and synapse with the neurons of the parasympathetic sacral neurons situated in the lateral horns of S2-S4 segments. The axons of these neurons leave the spinal cord as the preganglionic fibres; they pass via the pelvic splanchnic nerves to reach the parasympathetic (intramural) ganglia containing efferent neurons of this reflex arch. The axons of the efferent neurons reach the bladder`s muscles, relaxing the internal sphincter and contracting the detrusor muscle.

The attached presentation shows the described reflex arch.

Parasympathetic innervation of urinary bladder

As for the sympathetic innervation of the urinary bladder, its afferent path passes through the branches of the inferior hypogastric plexus arising from the lumbar ganglia of the sympathetic trunk. But actually these afferent fibres are the peripheral processes of the corresponding spinal ganglia which connect to the lumbar nerves through the white communicating rami. So the sensory neuron of this reflex arch is in the lumbar spinal ganglia. The association neuron is in the sympathetic segmental centres (the intermediolateral nucleus). Their axons as preganglionic fibres reach the efferent neurons situated in the corresponding sympathetic trunk ganglia. The postganglionic fibres arising from these ganglia reach the bladder`s muscles, contracting the internal sphincter and relaxing the detrusor muscle.

The attached presentation shows the noted reflex arch.

Sympathetic innervation of urinary bladder

 

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