Human anatamy

celiac ganglia

4. Communicative ramus

They are divided into white and grey ones to link the sympathetic ganglion with the corresponding spinal nerve.

1) White communicative rami

They are the preganglionic fibres send by the nerons of lateral horn in T₁~L₃ segments of the spinal cord.

Preganglionic fibresanterior rootspinal n. white communicative ramiparavertebral ganglion.

The preganglionic fibre of a white communicative ramus, after entering the sympathetic trunk, may terminate in three ways:

①Ending in corresponding paravertebral ganglia.

②Passing up and down in the trunk to terminate in paravertebral ganglia above and below.

③Passing through paravertebral ganglia.

2) Grey communicative rami

They are the postganglionic unmyelinated fibres, emitted by paravertebral neurons and situated between the sympathetic trunk and the 31 pairs of spinal nerve. They also course in three ways:

①Accompanying with corresponding spinal n. to peripheral blood vessels, sweat gland, and arrector pili m. (arrector m. of hair) .

②Surrounding artery as a layer of nerve plexus to innervate the branches of that arteries.

③Terminating in certain organs derectly.

5. The general distributions of sympathetic nerve

1) Cervical portion of sympathetic trunk

It is dorsal to the carotid sheath and ventral to the transverse processes of the cervical vertebrae.

superior cervical ganglion:

The distributions of postganglionic fibres are:

①Through 8 pairs cervical n. to vessels of upper limb, head and neck.

②Surround the arteries to form internal and external carotid plexus, subclavian plexus, vertebral plexus to smooth m. and gland of upper limb, head and neck.

③Pharyngeal branchpharyngeal plexuscardiac plexuscardiac m.

2) Thoracic portion of sympathetic trunk

It is in front of the heads of the ribs and 10~12 pairs in number.

①Through 12 pairs of intercostals n. to blood vessels, gland, arrector pili m. of abdominal and thoracic wall.

②The upper 5 ganglia to thoracic aorta, esophagus, trachea, bronchi and to take part in pulmonary and cardiac plexus.

③Greater splanchnic n.

It is formed by contributions from 5 (6) ~9 (10) thoracic ganglia (preganglionic neuron ), which terminate in the celiac ganglion.

④Lesser splanchnic n.

It is formed by branches (preganglionic fibres) of 10~12 thoracic ganglia, which end in the aorticorenal ganglion.

The postganglionic fibres of the celiac and aorticorenal ganglia supply the liver, spleen, kidney and digestive tract as far as the left colonic flexture.

3) Lumbar portion of sympathetic trunk

It is ventrolateral to the body of lumbar vertebra and along the medial margin of the psoas maior muscle.

①Distributing through 5 pairs lumbar n.

②Lumbar splanchnic n.

It is formed by the preganglionic fibres terminating in abdominal aortic plexus and mesenteric plexus. After exchanging neurons in these plexus, the postganglionic fibres supply the digestive tract below left colonic flexure, pelvic viscera, and lower limbs.

4) Pelvic portion of sympathetic trunk

It lies against the ventral surface of the sarum, and medial to anterior sacral foramen.

①Supplying through sacral and coccygeal n.

②Taking part in pelvic plexus.

Ⅱ）Parasympathetic System

1. Lower centre

It lies in the cranial parasympathetic nuclei in brain stem and S₂~₄segments of the spinal cord (sacral portion).

2. Peripheral part

apraorgan ganglia

parasympathetic ganglia

intraorgan ganglia

fibres sending off from these ganglia

parasympathetic plexus

ciliary ganglion

paraorgan submandibular ganglion

ganglia sphenopalatine ganglion

otic ganglion

3. Cranial portion of parasympathetic system

Their preganglionic fibres run in the cranial nerves Ⅲ, Ⅶ, Ⅸ, Ⅹ, the details about this will be presented here.

1) Parasympathetic nucleus of oculomotor nerve (Edinger-westphal nucleus)

Preganglionic fibres from E-W nucleusoculomotor n. (Ⅲ) ciliary ganglion (relay) postganglionic fibresciliary m. and pupillary sphincter m.

2) Superior salivatory nuclei

Preganglionic fibres from superior salivatory nucleifacial n. (Ⅶ) greater petrosal n. pterygopalatine ganglion (relay) 

maxillary n. zygomatic n. lacrimal n. lacrimal gland.

postganglionic fibres

gland in nasal, oral cavity and mucous membrane of palatine.

Facial n. chorda tympapnilingual n. submandibular ganglion (relay) postganglionic fibressubmandibular gland and sublingual gland.

3) Inferior salivatory nuclei

Preganglionic fibres from inferior salivatory nucleiglossopharyngeal n. (Ⅸ) tympanic n. tympanic plexuslesser petrosal n. otic ganglion (relay) postganglionic fibresauriculotemporal n. parotid gland.

4) Dorsal motor nucleus of vagus

Preganglionic fibres dorsal motor nucleus of vagusvagal n. (Ⅹ) abdominal and thoracic viscera (synapse) postganglionic fibrescorresponding abdominal and thoracic organs (except descending colon, sigmoid colon and pelvic viscera).

4. Sacral portion of parasympathetic system

Their preganglionic fibres arising from parasympthetic nuclei in S₂~₄ segments of spinal cord form pelvic splanchnic nerve, which takes part in pelvic plexus. After exchanging the neurons, the postganglionic fibres innervate the alimentary canal distal to left colonic flexure, pelvic viscera and external genital organs.

Ⅲ）Differences between Sympathetic and Parasympathtetic Nerve

1. Different central centre

sympathetic----thoracolumbar part: C₈ (T₁) ~ L₂ (L₃)

cranial part: brain stem

parasympathetic----

sacral part: S₂~₄

2. Different locations of peripheral ganglia

prevertebral

sympathetic paravertebral

preganglionic fibre is shorter

paraorgan

parasympathetic intraorgan

preganglionic fibre is longer

4. Different distributions

sympathetic----much wider

parasympathetic----much narrowly, without nerve supply in blood vessels, sweat gland, arrector pili m., medullary part of suprarenal gland.

5. Different actions to a visceral organ

The viscera receives a dual autononic supply. In most cases, the two sets of nerves function antagonistically to one another. Such as:

increasing heart-beating

elevating blood pressure

sympathetic dilating bronchi

wider opening of pupil

inhibiting digestive activity

parasympathetic: on the contrary

Ⅳ）The Visceral Plexuses

The sumpathetic nerve and parasympathetic nerve are usually combined with the visceral sensory nerve into extensive plexuses called visceral plesuses in the way to viscera.

1. Caridiac plexus

It is formed by superior, middle, infeior cervical ganglia, cardiac branches sending off from T₁~₅ ganglia and supplies the cardiac muscles.

superficial cardiac plexus----below aortic arch.

deep cardiac plexus----between aortic arch and bifurcation of trachea.

2. Pulmonary plexus

It lies in front of and behind the root of lung called anterior and posterior pulmonary plexus respectively, which supply the lung.

3. Celiac plexus

It is located in front of abdominal aorta, and surrounds the roots of the celiac and superior mesenteric arteries.

Secondary plexus----hepatic, splenic, pancreatic, superior mesenteric, gastric, renal plexuses.

4. Abdominal aortic plexus

It is caudalward continuation of celiac plexus.

5. Hypogastric plexus

superior hypogastric plexus

Ⅱ. The Visceral Sensory Nerves

They conduct the impulse from enterioceptor of the viscera to the central nervous system.

The visceral sensory fibres have their own features in function and morphology which are different from those of the somatosensory ones.

1. The mumber of the visceral sensory fibres is less.

2. A high pain threshold.

3. Poorly localized visceral sensation (general feeling).

4. Insensitive to cutting, crushing, burning.

5. Sensitive to excessive tension, contraction of smooth m., and certain pathological condition.

Chapter 3 The Central Nervous System

Section 1 The Spinal Cord

Ⅰ. External Features

Ⅰ）The Spinal Cord: a culindrical structure and slightly flattened anteroposteriorly, is locatedin the vertebral canal and invested by meninges.

upper end: continuing with medulla oblongata at the level of foramen magnum.

Inferior border of L₁ vertebra in adult.

lower end:

L₃ vertebra in baby.

The spinal cord tapers gradually and becomes conical termination known as midullary cone. A slender nerveless structure descending from medullary cone is termed filum terminale. Cauda equine, a divergent sheaf of caudal spinal roots, is gathered around the filum terminale.

Ⅱ）Segments of Spinal Cord

The spinal cord is consisted of 31 segments in corresponding to the rootlets of a pair of spinalnerves, viz. C₈, T₁₂, L₅, S₅, C₀₁.

Ⅲ）Two Enlargements

cervical enlargement

Ⅳ）Fissure and Sulcus

anterior median fissure

Ⅴ）Corresponding Relation between Spinal Segment and Vertebrae

Ⅱ. Internal Structure

central canal:

on transverse section grey matter: meurons and nerve fibres

grey matter posterior horn: posterolaterally

(butterfly-shaped core) lateral horn: laterally

grey commissure: around central canal

anterior funiculus: between andterior median fissure and anterolateral sulcus.

white matter posterior funiculus: between poslerior median sulcus and posterolateral sulcus.

Ⅰ）Grey Matter

The grey matter of the spinal cord contains an enormous mumber of neurons of varying in size and shape. Cell collection with common cytological characteristics, whose axons can be followed to a common termination and subserve the same function, are referred to as nucleus.

1. Nuclei in anterior horn

α-motor neuron----large multipolar neuron, innervating skeletal m. (extrafuasl fibres), producing contraction of muscle.

γ-motor meuron----smaller neuron, innervating intrafusal fibres, regulating muscular tonus.

medial group----presented in most segments of spinal cord, innervating skeletal m. of head and neck.

lateral group----presented in cervical and lumbosacral enlargements, innervating skeletal m. of four extremities.

2. Nuclei in posterior horn

intermediolateral column nuclei: preganglionic neurons of sympathetic n. presented in T₁~L₃ spinal segments.

sacral parasympathetic nuclei: preganglionic neurons of parasympathetic n. presented in S₂~₄ spinal segments.

3. Nuclei in posterior horn

genlatiniform substance:

4. Cutoarchitectural lamination

Laminal Ⅰ: correspond to posteromarginal nucleus.

Laminal Ⅱ: gelatiniform substance.

Laminal Ⅲ, Ⅳ: proper nucleus.

Laminal Ⅴ, Ⅵ: base of posterior horn.

Laminal Ⅶ: thoracic nucleus, intermediolateral column in intermedial zone.

Laminal Ⅷ: base of anterior horn.

Laminal Ⅸ: several distinct groups of somatic motor neurons----α, γ cell of anterior horn.

Laminal Ⅹ: area surrounding central canal.

Ⅱ）White Matter

In general, tract of fasciculus indicates the functional fibre bundles having the same origin, course and termination.

asending tracts

1. Ascending tracts

1) Gracile fasciculus and cuneate fasciculus

Gracile fasciculus Cuneate fasciculus

origin spinal ganlia below spinal ganglia above T4 spinal segment T4 spinal segment termination gracile nucleus cuneate nucleus inmedulla oblongata inmedulla oblongata location medial part of lateral part of posterior funiculus posterior funiculus function conscious proprioceptive sensation, and fine of discriminating tactile in muscles, tendon, joint and skin.

2) Posterior and anterior spinocerebellar tracts

3) Spinothalamic tract

2. Descending tracts

1）Corticospinal tracts

Lateral Anterior corticospinal tract corticospinal tract

location media to posterior bothe sides of anterior spinocerebellar tract median fissure in lateral funiculus in anterior funiculus origin precentral gyrus and other cerebral cortex course crossed fibres uncrossed fibres termination motor cells of anterior horn of spinal cord function voluntary movements

2) The other descending tracts

Ⅲ. Function fo the Spinal Cord

1. Conduction of excitation.

2. Reflexing activity.

3. Connecting trunk and extremities through 31 pairs spinal nerves.

Section 2 The Brain

It is deivided into four principal areas: the brain stem, cerebellum, diencephalons and telecephalon.

Ⅰ. External Features of Brain Stem

The brain stem consists of three parts, from below upwards, the medulla oblongata, pons and midbrain. Its upper border is optic tract, lower border is foramen magum.

Ⅰ）External Features of Medulla Oblongata.

1. Ventral surface

pontomedullary groove: upper border of medulla oblongata.

anterior median fissure: continuing with that of spinal cord.

pyramid: formed by corticospinal tract.

decussation of pyramids: formed by crossing fibres.

olive: posterolateral to pyramid (inferior olivary nucleus).

anterolateral sulcus: CN Ⅻ emerging from it.

posterior olivary sulcus: dorsal to olive, from above downwards, CN Ⅸ, Ⅹ, Ⅺ emerging from it.

2. Dorsal surface

The superior part of the dorsal surface forms the lower half of the floor of the fourth ventricle.

gracile tubercle: an elongated swelling produced by gracile nucleus.

cuneate tubercle: cuneate nucleus.

inferior cerebellar peduncle: superolateral to cuneate tubercle formed by fibres entering cerebellum.
Ⅱ）External Features of Pons

1. Ventral surface

pontomedullay sulcus:

2. Dorsal surface

The dorsal surface of the pons forms the upper half of the floor of the fourth ventricle.

superior cerebellar peduncle: foming lateral wall of the fourth ventricle.

anterior medullary velum: a delicate lamina of white matter connecting two superior cerebellar peduncle, CN Ⅳ emerging from it .

Ⅲ）Rhomboid Fossa

The floor of the fourth ventricle is rhomboidal in shape, named rhomboid fossa. It si formed by the dorsal surface of both superior part of the medulla oblongata and the pons.

lower border: gracile tubercle, cuneate tubercle, and inferior ferebellar peduncle.

upper boder: superior cerbellar peduncle.

lateral angle: lateral recess curving ventrally.
medullary striae: from lateral angle to median sulcus, dividing medulla oblongata.