Task 1. Trigeminal nerve (V-th pair investigation)
a) Corneal reflex – the investigated person looks up and towards. The investigator touches with thin paper strip to the inferior-exterior eyeside without touching the eyelashes. The reflex arc - orbital nerve (Vth pair ramus), pons, facial nerve. Decreasing or lost of corneal reflex is found out at trigeminal nerve, facial nerve, pons injuries, at shock, in course of narcosis.
b) Conjunctival reflex – is caused by touching to conjunctive. Answer reaction- eyelid close. Reflectory arc – see like at corneal reflex.
c) Superciliar reflex - is caused by hummer shock at superciliar arc limb. Answer reaction - eyelid closure. Reflex arc – orbital nerve, pons, facial nerve.
d) Mandibular reflex - the investigated person slightly opens his mouth. Masticatory muscles contraction is caused by hammer shock down on chip from one than from another side. Answer reaction – mandible lifting. This reflex can be absent under normal conditions.
Task 2. Facial nerve (VII-th pair) investigation
For this gaim it’s necessary to perform face examination: difficulties at mastication, muscular volume diminishing, frontal and nasolabial plicas asymmetry, whether the face become distorted (mouth angle). They ask to perform masticatory movements putting their fingers to the facial muscles. The investigator asks the investigated person to wrinkle, to frown (knit) the eyebrows, to close eyes, to billow cheeks, to show teeth, to stretch lips.
а) Orbicular muscle force determining - the investigated person is asked to close his eyes strongly. The investigator tries to raise eyelid superior determining resistance force at this. To make the conclusion.
Task 3. Glossopharyngeal nerve (IX-th pair) investigation
The investigation must be begun from the determining of the investigated person voice timbre and sounding. At disorder of innervation of velum palatinum (if it doesn’t close nasopharynx cavity completely) the voice is nasal. At vocal chords injury one can aphony and wheezing. Then the investigator must examine soft palate. The investigated person is asked to tell “A” (at one-sided injury at given side soft palate doesn’t tighten).
Palatine and pharyngeal reflexes – with the paper rolling up into long strip to touch the soft palate and pharynx posterior wall mucosa. Answer reaction is swallowing and vomiting. Reflexes are realized by means of glossopharyngeal and vagus nerves. The decreasing or lost of these reflexes can be both at healthy people and at injury of IX-th and X-th pairs of cranial nerves or their nuclei in medulla oblongata (so-called bulbar syndrom).
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Task 4. Accessory nerve (XI-th pair) investigation
Accessory nerve is a motor one, it innerves sternocleidomastoid and trapezius muscles (head turn in an opposite side and shrugging one’s shoulders). The investigated person turns his head towards and up and restrains in such location. The investigator tries to oppose to this. For sternocleidomastoid muscle force you can tell according to resistance degree. Trapezius muscle is investigated by raising and fixating in such a situation. Shoulder girdle is lowered at paralysis.
Task 5. Hypoglossal nerve (XII-th pair) investigation
This nerve innerves the tongue. One should perform the tongue investigation. It’s necessary to put it forward behind the teeth line. At one-sided nerve injury – atrophy of the same tongue half, thinness, foldedness of mucosa, fibrillations. The tongue is sticked out in a sick side. At injury of two nerves – the tongue is almost immovable, the speech is disturbed as well as pushing of chilus in mouth.
The injury of V, IX, X, XIIth pairs leads to the disorders of swallowing (dysphagy), sounding voice loss (aphony), speech nasal shade (nasolaly), anomaly of correct order of articulate sounds prononciation (dysarthry).
5. Literature recommended:
1. Lecture course.
2. Mistchenko V.P., Tkachenko E.V. Methodical instructions for medical students (short lecture course).-Poltava, 2005.-P. 15-16.
3. Mistchenko V.P., Tkachenko E.V. Methodical instructions on Normal Physiology on practical classes for dental and medical students.-Poltava, 2005.-P. 47-48.
4. Ganong W.F. Review of Medical Physiology.-21st ed.-2003.-Section II.
5. Guyton A.C. Textbook of Medical Physiology.-NY, 1992.-P. 625-626.
6. Materials for self- control:
А. Control questions:
1. Medulla oblongata centers.
2. Medulla oblongata reflectory activity.
3. Posterior brain vegetative reflexes.
4. Posterior brain conductory function.
5. Reflexes the mostly often determined in dentistry (for dentists).
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LESSON 14
Midbrain physiology. Midbrain role investigation in motor and sensor functions regulation
The topic studied actuality.
Masticatory and mimic muscles function can be changed at this brain part injury. Particularly, black substance is responsible for co-ordination of movements connected with food taking.
Dentists can get in touch with patients suffering from oral cavity motor and sensor functions disorders due to midbrain pathology.
Study aims:
To know: midbrain morphological-functional peculiarities; midbrain reflectory activity; brain stem sensory function; stem reticular formation structure, connections and role; midbrain cranial-cerebral nerves role; midbrain vegetative reflexes.
To be able to: explain mechanisms explaining muscular tone disorders in “mesencephalic” animals.
2. Pre-auditory self-work materials.
3.1.Basic knowledge, skills, experiences, necessary for study the topic:
| Histology | Midbrain histological structure | Recognize midbrain preparation |
| Anatomy | Midbrain anatomical structure and conductive ways, cranial-cerebral nerves (IV, VI pairs) location | Draw midbrain ascending and descending conductive ways, cranial-cerebral nerves nuclei location |
| Biochemistry | Dophamine oigin and role in human organism | |
| Neurology | Midbrain external and internal structure, conductive ways, cranial-cerebral nerves (IV, VI) morphology and functions (norm and pathology) | Draw midbrain conductive ways, cranial-cerebral nerves nuclei location. |
| Dentistry | Mentioned cranial-cerebral nerves anatomy, physiology, midbrain role in mastication, swallowing and their alternation with respiration during food taking | Analize posterior brain and cranial-cerebral nerves pathology signs. |
Topic content.
Midbrain lies between pons and diencephalon. It consists of two parts:
A. Tectum - comprising superior and inferior colliculi
B. Cerebral peduncles - consisting of basis pedunculi, substantia nigra and tegmentum, which includes red nucleus.
Superior Colliculus
It is a small structure and is an important center for reflexes. Through the tectospinal tract, the superior colliculus controls the movements of eyes, head, trunk and limbs in response to visual impulses. The efferent fibers from superior colliculus going to the nucleus of III cranial (oculomotor) nerve cause constriction of pupil during light reflex. Thus, it forms the center for light reflex. Superior colliculus also receives afferents from optic tract, which helps in the integration of optical and postural reflexes.
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Inferior Colliculus
It consists of single layer of neurons to which the lateral lemniscus (auditory fibers) synapses. The inferior colliculus is the center for auditory reflexes. Stimulation of this also produces reflex vocalization.
Cerebral peduncles
Basis Pedunculus
It consists of pyramidal tract fibers in the middle, temporopontine fibers laterally and frontopontine fibers medially.
Substantia Nigra
It is situated below the red nucleus. Substantia nigra is considered as one of the components of basal ganglia. Its pathology is known as parkinsonism. The distinguishing features are like at Parkinson’s disease. Reason is one: dophamine deficiency.
Tegmentum
This lies dorsal to substantia nigra and is actually the upward continuation of the reticular formation in pons.
Three decussations take place in tegmentum. It also contains red nucleus.
1. Superior cerebellar peduncle: This is formed by fibers between cerebellum and other parts of central nervous system. The fibers are predominantly efferent fibers from dentate nucleus ofcerebellum; and few fibers are from other cerebellar nuclei—nucleus globosus and nucleus emboliformis.
2. Forel's decussation: This is due to the crossing of rubrospinal tracts from either side.
3. Mynert's decussation: It is due to the crossing of medial longitudinal bundle formed by the efferents of 3rd, 4th and 6th cranial nerves.
Red Nucleus
Red nucleus is a large oval or round mass of gray matter extending between the superior colliculus and hypothalamus.
Red nucleus has two parts:
1) Nucleus magnocellularis, which is formed by large cells. Fibers from this form the rubrospinal and rubrobulbar tracts.
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2) Nucleus parvocellularis, which is formed by smaller cells. The fibers from this form mainly the rubroreticular tract.
Connections of Red Nucleus
1) Afferent connections: Red nucleus receives fibers from:
a). Motor cortex (area 6) to nucleus parvocellularis—corticorubral fibers
b) The globus pallidus and subthalamic nuclei to nucleus magnocellularis—pallidorubral fibers.
c) Dentate nucleus (of opposite side) to nucleus magnocellularis - cerebellorubral or dentatorubral tract.
2) Efferent connections: Red nucleus sends efferent fibers to various parts of brain and spinal cord.
a) Rubrospinal tract to spinal cord
b) Rubrobulbar tract to medulla
c) Rubroreticular fibers to reticular formation
d) Rubrothalamic tract to lateral ventral nucleus of thalamus
e) Rubroolivary tract to inferior olivary nucleus
f) Fibers to nuclei of 3rd, 4th and 6th cranial nerves.
Functions of Red Nucleus
1) Control of muscle tone: Because of its connections with cerebellum, vestibular apparatus and skeletal muscle, the red nucleus plays an important role in maintaining the muscle tone.
2) Control of complex muscular movements: Red nucleus controls the complex muscular movements.
3) It plays an important role in the integration of various impulses received from many important areas of brain.
4). Control of skilled movements: Red nucleus plays an important role in controlling skilled muscular movements by its connections with spinal cord and cerebral cortex.
Decerebrative rigidity. Cutting at the level of Varolii pons anterior limb (rubro-spinal tract) causes in muscles extensors tone increasing in animals. Such animals do not save equilibrium and fall down. This phenomenon is known as decerebrative rigidity. It is considered that such a state is delt with cerebellum and red nuclei descendant influencings liquidating to bulbar centers.
Animals with brain cutting at anterior colliculi level are known as mesencephalic animals. Mesencephalic anaimals differ from spinal ones with muscular tone regulation and body position in a space. Decerebrative rigidity is absent in them. Red nuclei in midbrain causes inhibitory influencing on vestibular nucleus of Deuters to which afferentation from auricular labirinthiums and muscular proprioreceptors comes through vestibular-spinal tract. Red nuclei decomposition causes expressed decerebrative rigidity in animals. Red nuclei irritation leads to significant muscular tone decreasing – the animals become “like a sac”. Decerebrative rigidity is determined also by afferentation coming to Deuters’ nuclei from muscles proprioreceptors and vestibular apparatus. Spine posterior radici and vestibular nerves cutting also cancels decerebraive rigidity.
If red nuclei do not give inhibitory influencings at posterior brain level, than central excitements are increased and get diffused. Thus, extensors activity is increased selectively.
MIDBRAIN AND BASAL NUCLEI STRUCTURES PARTICIPATION IN MASTICATION AND SWALLOWING REGULATION:
They are black substance in midbrain (dophamine source regulating respiration, mastication and swallowing alternation) and caudate nucleus, shell (putamen) among basal ganglii because they inhibit substantia nigra (black substance) activity with inhibitory mediator gama-amino-oleic acid secretion through third basal ganglium - globulus pallidus.
| Reflex | Center | Animal preparation to demonstrate | |
| General static reflexes (Righting reflexes) | 1.Labyrinthine righting reflexes acting upon the neck muscles | Midbrain | Thalamic or normal blind folded animal |
| 2.Neck righting reflexes acting upon the body | |||
| 3.Body righting reflexes acting upon the head | |||
| 4.Body righting reflexes acting upon body | |||
| 5. Optical righting reflexes | Occipital lobe | Labyrinthectomized animal | |
| Local static reflexes | 1. Positive supporting reflexes | Spinal cord | Decorticate animal |
| 2. Negative supporting reflexes | |||
| Segmental static reflexes | Crossed extensor reflex | Spinal cord | Spinal animals |
| Statotonic or attitudinal reflexes | 1. Tonic labyrinthine and neck reflexes acting on the limbs | Medulla oblongata | Decerebrate animal |
| 2. Labyrinthine and neck reflexes acting upon the eyes | |||
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