Neuroscience 1c Organisation of Brainstem and Cranial Nerves



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Neuroscience 1c – Organisation of Brainstem and Cranial Nerves

Anil Chopra


  1. With the aid of diagrams show the approximate position of the following structures in the brainstem and state their function:

    1. inferior medullary olive

    2. substantia nigra

    3. superior and inferior colliculi

    4. reticular formation

    5. nucleus coeruleus

  2. Explain the origin and functions of cranial nerves III to XII

The brainstem is that part of the CNS that lies between the cerebrum and the spinal cord. It consists of the midbrain the pons and the medulla oblongata.





Functional component

Abbreviation

General function

Cranial nerves containing component

General somatic afferent

GSA

Perception of touch, pain, temperature

Trigeminal nerve [V]; facial nerve [VII]; vagus nerve [X]

General visceral afferent

GVA

Sensory input from viscera

Glossopharyngeal nerve [IX]; vagus nerve [X]

Special afferent*

SA

Smell, taste, vision, hearing and balance

Olfactory nerve [I]; optic nerve [II]; facial nerve [VII]; vestibulocochlear nerve [VIII]; glossopharyngeal nerve [IX]; vagus nerve [X]

General somatic efferent

GSE

Motor innervation to skeletal (voluntary) muscles

Oculomotor nerve [III]; trochlear nerve [IV]; abducent nerve [VI]; hypoglossal nerve [XII]

General visceral efferent

GVE

Motor innervation to smooth muscle, heart muscle, and glands

Oculomotor nerve [III]; facial nerve [VII]; glossopharyngeal nerve [IX]; vagus nerve [X]

Branchial efferent**

BE

Motor innervation to skeletal muscles derived from pharyngeal arch mesoderm

Trigeminal nerve [V]; facial nerve [VII]; glossopharyngeal nerve [IX]; vagus nerve [X]; accessory nerve [XI]



Nerves__Cranial_Nerves'>Classification of Nerves
Cranial Nerves

 

Components

 

 

Nerve

Afferent

Efferent

Exit from skull

Function

Olfactory nerve [I]

SA

 

Cribriform plate of ethmoid bone

Smell

Optic nerve [II]

SA

 

Optic canal

Vision

Oculomotor nerve [III]

 

GSE, GVE

Superior orbital fissure

GSE-innervates levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, and inferior oblique muscles
GVE-innervates sphincter pupillae for pupillary constriction; ciliary muscles for accommodation of the lens for near vision

Trochlear nerve [IV]

 

GSE

Superior orbital fissure

Innervates superior oblique muscle

Trigeminal nerve [V]

GSA

BE

Superior orbital fissure-ophthalmic division [V1]
Foramen rotundum- maxillary nerve [V2]
Foramen ovale- mandibular division [V3]

GSA-sensory from: ophthalmic division [V1]-eyes, conjunctiva, orbital contents, nasal cavity, frontal sinus, ethmoid sinus, upper eyelid, dorsum of nose, anterior part of scalp; maxillary nerve [V2]-dura in anterior and middle cranial fossae, nasopharynx, palate, nasal cavity, upper teeth, maxillary sinus, skin covering the side of the nose, lower eyelid, cheek, upper lip; mandibular division [V3]-skin of lower face, cheek, lower lip, ear, external acoustic meatus, temporal fossa, anterior two-thirds of tongue, lower teeth, mastoid air cells, mucous membranes of cheek, mandible, dura in middle cranial fossa BE-innervates temporalis, masseter, medial and lateral pterygoids, tensor tympani, tensor veli palatini, anterior belly of digastric, and mylohyoid muscles

Abducent nerve [VI]

 

GSE

Superior orbital fissure

Innervates lateral rectus muscle

Facial nerve [VII]

GSA, SA

GVE, BE

Internal acoustic meatus

GSA-sensory from external acoustic meatus, skin posterior to ear
SA-taste from anterior two-thirds of tongue
GVE-innervates lacrimal gland, submandibular and sublingual salivary glands, and mucous membranes of nasal cavity, hard and soft palates
BE-innervates muscles of face (muscles of facial expression) and scalp derived from the second pharyngeal arch, and stapedius, posterior belly of digastric, stylohyoid muscles

Vestibulocochlear nerve [VIII]

SA

 

Internal acoustic meatus

Vestibular division-balance
Cochlear division-hearing

Glossopharyngeal nerve [IX]*

GVA, SA

GVE, BE

Jugular foramen

GVA-sensory from carotid body and sinus, posterior one-third of tongue, palatine tonsils, upper pharynx, and mucosa of middle ear and pharyngotympanic tube
SA-taste from posterior one-third of tongue
GVE-innervates parotid salivary gland
BE-innervates stylopharyngeus muscle

Vagus nerve [X]*

GSA, GVA, SA

GVE, BE

Jugular foramen

GSA-sensory from skin posterior to ear and external acoustic meatus, and dura in posterior cranial fossa
GVA-sensory from aortic body chemoreceptors and aortic arch baroreceptors, mucous membranes of pharynx, larynx, esophagus, bronchi, lungs, heart, and abdominal viscera of the foregut and midgut
SA-taste from the epiglottis
GVE-innervates smooth muscle and glands in the pharynx, larynx, thoracic viscera, and abdominal viscera of the foregut and midgut
BE-innervates one tongue muscle (palatoglossus), muscles of soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), and larynx

Accessory nerve [XI]

 

BE

Jugular foramen

Innervates sternocleidomastoid and trapezius muscles

Hypoglossal nerve [XII]

 

GSE

Hypoglossal canal

Innervates hyoglossus, genioglossus, and styloglossus muscles and all intrinsic muscles of the tongue


B
Fig 6.2
rainstem Nuclei



Fig 6.6

Fig 6.5

Fig 6.4

Fig 6.3



Fig 6.8

Fig 6.7


Fig 6.7



Fig 6.8


  • Middle cerebellar peduncle  pons: cortex => cerebellum

  • Substantia nigra  midbrain: control of movement with basal ganglia

  • Cerebral peduncle  midbrain: carries corticospinal & corticobulbar tracts from cerebrum to pons

  • Inferior olivary nucleus  medulla: supplies proprioceptive input to the cerebellum


Functions of Brainstem

  • is located anterior to the cerebellum to which it is connected by three pairs of cerebellar peduncles

  • It contains the following:

    • The nuclei for 10 of the 12 cranial nerves (exceptions – olfactory and optic)

    • Apparatus for controlling eye movement including cranial nerves III, IV and VI

    • Monoaminergic nuclei that project widely through the CNS

    • Areas vital to the control of the CVS, respiration and the ANS

    • Areas important in the control of consciousness

    • Descending and ascending pathways lining the spinal cord to supraspinal structures such as cerebral cortex and cerebellum




  • Inferior Medullary Olive – Is in the medulla and receives inputs from a number of sources and provides the climbing fibre input to the cerebellum

  • Substantia Nigra – Is in the midbrain and contains both dopamine and γ-aminobutyric acid (GABA) neurones. It forms part of the basal ganglia and is involved in the control of movement. Loss of dopaminergic neurones in this part of the brain is the major pathological event in Parkinson’s disease

  • Superior and Inferior Colliculi – The inferior coliculus is in the midbrain and is part of the auditory system while the superior colliculus is involved with visual processing and eye movement control.

  • Reticular Formation – A loosely arranged network of cells in the brainstem that are left when all the identified tracts and nuclei in the brainstem are removed. Possibly a continuation of spinal cord interneurones. Cells use different neurotransmitters - noradrenaline, 5-HT (5-hydroxytryptamine), ACh and Dopamine transmitters depending on function of particular cells. There is a sensory portion in the lower medulla and lower pons, and a motor portion in the upper medulla and upper pons. The main function of the reticular formation is:

    • Sleeping and waking – parts of the formation are involved in producing sleep states and others in awakening mechanisms – the reticular activating system bases on the noradrenergic system

    • Modulation of sensory information across the thalamic relay nuclei – a role in gating sensations such as pain




    • Motor control via the modulation of spinal interneurons and transmitting information to the cerebellum – the lateral parts of the formation

    • Modulation of respiration

  • Nucleus Coeruleus – One of the medial reticular nuclei connected with the nucleus of the trigeminal nerve

  • Other structures of note:

    • The pyramid – which represents the descending corticospinal tract that decussates at the lower border of the brainstem

    • The cerebellar peduncles - which convey information to and from the cerebellum

    • The vestiblar nucleus - which has important connections from the ear and projects to the spinal cord and cerebellum

    • The periaqueductal grey matter – of the mesencephalon is an area rich in opioids and thus important in supraspinal modulation of nociception

    • The central aqueduct – running through the midbrain links the 3rd and 4th ventricles

Raised intracranial pressure causes the medulla and cerebellar tonsils to be pushed downward through the foramen magnum. This is characterised by headaches, neck stiffness and paralysis of some cranial nerves. Patients with this condition should never have a lumbar puncture as it may result in herniation of the brain through the foramen magnum even further.


Thrombosis of vertebral or posterior inferior communicating artery can occur. Symptoms include:

    • Vertigo

    • Ipsilateral cerebellar ataxia

    • Ipsilateral loss of pain/thermal sense (face)

    • Horner’s syndrome

    • Hoarseness, difficulty in swallowing

    • Contralateral loss of pain/thermal sense (trunk and limbs)

Relations to ventricles:

Lower Medulla: central canal

Upper Medulla: 4th Ventricle



Pons: 4th ventricle

M
idbrain: aqueduct


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