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The Brain and Cranial Nerves

 


An Introduction to the Organization of the Brain

Major regions and landmarks

      Six regions in the adult brain

    Cerebrum

    Diencephalon

    Mesencephalon

    Pons

    Cerebellum

    Medulla oblongata

      Brain contains extensive areas of neural cortex

    Layer of gray matter on the surface of the cerebellum and cerebrum

 

Embryology of the brain

      Brain forms from three swellings at the tip of the developing neural tube

    Prosencephalon

   Forms the telencephalon and eventually the cerebrum and diencephalon

    Mesencephalon

    Rhombencephalon

   Forms the metencephalon (cerebellum and pons) and myelencephalon (medulla oblongata)

 

Ventricles of the brain

      Central passageway of the brain enlarges to form ventricles

    Contain cerebrospinal fluid (CSF)


Protection and Support of the Brain

The cranial meninges

      Continuous with the three layers of the spinal cord

      Folds of dura mater help stabilize the position of the brain

    Falx cerebri

    Tentorium cerebelli

    Falx cerebelli

 

Cerebrospinal fluid (CSF)

      CSF cushions delicate neural structures

      Supports the brain

      Transports nutrients, chemical messengers, and waste products

      Pathway of CSF

    Produced at the Choroid plexus,

    Travels through the lateral and medial apertures to the subarachnoid space,

    Diffuses across the arachnoid granulations into the superior sagittal sinus

 

Blood supply to the brain

      Blood brain barrier isolates neural tissue from general circulation

      Incomplete barrier in areas

    Parts of the hypothalamus

    Pituitary gland

    Pineal gland

    Choroid plexus

 


The Medulla Oblongata

Medulla oblongata

      Connects the brain with the spinal cord

      Contains relay stations and reflex centers

    Olivary nuclei

    Cardiovascular and respiratory rhythmicity centers

      Reticular formation begins in the medulla oblongata and extends into more superior portions of the brainstem


The Pons

The pons contains

      Sensory and motor nuclei for four cranial nerves

      Nuclei that help control respiration

      Nuclei and tracts linking the cerebellum with the brain stem, cerebrum and spinal cord

      Ascending, descending and transverse tracts


The Cerebellum

The cerebellum

      Adjusts postural muscles and tunes on-going movements

      Cerebellar hemispheres

    Anterior and posterior lobes

    Vermis

    Flocculonodular lobe

      Superior, middle and inferior cerebellar peduncles link cerebellum with brain stem, diencephalon, cerebrum, and spinal cord

    Interconnects the two cerebellar hemispheres


The Mesencephalon

The mesencephalon

      The tectum (roof) contains the corpora quadrigemina

    Superior and inferior colliculi

      The mesencephalon contains many nuclei

    Red nucleus

    Substantia nigra

    Cerebral peduncles

    RAS headquarters


The Diencephalon

The diencephalon is composed of

      Epithalamus

      Hypothalamus

      Thalamus

 

The thalamus

      Final relay point for ascending sensory information

      Coordinates the activities of the cerebral cortex and basal nuclei

 

The hypothalamus

      Controls somatic motor activities at the subconscious level

      Controls autonomic function

      Coordinates activities of the endocrine and nervous systems

      Secretes hormones

      Produces emotions and behavioral drives

      Coordinates voluntary and autonomic functions

      Regulates body temperature

      Coordinates circadian cycles of activity


The Limbic System

The limbic system or motivational system includes

      Amygdaloid body

      Cingulated gyrus

      Parahippocampal gyrus

      Hippocampus

      Fornix

      Functions of the limbic system involved emotions and behavioral drives


The Cerebrum

The cerebral cortex

      Surface contains gyri and sulci or fissures

    Longitudinal fissure separates two cerebral hemispheres

    Central sulcus separates frontal and parietal lobes

    Temporal and occipital lobes also bounded by sulci

 

White matter of the cerebrum

      Contains association fibers

      Commissural fibers

      Projection fibers

 

The basal nuclei

      Caudate nucleus

      Globus pallidus

      Putamen

    Control muscle tone and coordinate learned movement patterns

 

Motor and sensory areas of the cortex

      Primary motor cortex of the precentral gyrus directs voluntary movements

      Primary sensory cortex of the postcentral gyrus receives somatic sensory information

    Touch

    Pressure

    Pain

    Taste

    Temperature

 

Association areas

      Control our ability to understand sensory information and coordinate a response

    Somatic sensory association area

    Visual association area

    Somatic motor association area

 

general interpretive and speech areas

      General interpretive area

    Receives information from all sensory areas

    Present only in left hemisphere

      Speech center

    Regulates patterns of breathing and vocalization

 

cortex functions and hemispheric differences

      Prefrontal cortex

    Coordinates information from secondary and special association areas

    Performs abstract intellectual functions

      Hemispheric differences

    Left hemisphere typically contains general interpretive and speech centers and is responsible for language based skills

    Right hemisphere is typically responsible for spatial relationships and analyses

 

Electroencephalogram (EEG)

      Measures brain activity

    Alpha waves = healthy resting adult

    Beta waves = concentrating adult

    Theta waves = normal children

    Delta waves = normal during sleep

 

Focus: Cranial Nerves

      12 pairs of cranial nerves

    Each attaches to the ventrolateral surface of the brainstem near the associated sensory or motor nuclei

 

The Brain and Cranial Nerves

Olfactory nerves (I)

      Carry sensory information responsible for the sense of smell

      Synapse within the olfactory bulb

 

cranial nerves II, III, IV

      Optic nerves (II)

    Carry visual information from special sensory receptors in the eyes

      Occulomotor nerves (III)

    Primary source of innervation for 4 of the extraocular muscles

      Trochlear nerves (IV)

    Innervate the superior oblique muscles

 

cranial nerves V, VI, VII

      Trigeminal nerves (V)

    Missed nerves with ophthalmic, maxillary and mandibular branches

      Abducens nerve (VI)

    Innervates the lateral rectus muscles

      Facial nerves (VII)

    Mixed nerves that control muscles of the face and scalp

    Provide pressure sensations over the face

    Receive taste information from the tongue

 

cranial nerves VIII, IX

      Vestibulocochlear nerves (VIII)

    Vestibular branch monitors balance, position and movement

    Cochlear branch monitors hearing

      Glossopharyngeal nerves (IX)

    Mixed nerves that innervate the tongue and pharynx

    Control the action of swallowing

 

cranial nerves X

      Vagus nerves (X)

    Mixed nerves

    Vital to the autonomic control of visceral function

 

cranial nerves XI, XII

      Accessory nerves (XI)

    Internal branches

   Innervate voluntary swallowing muscles of the soft palate and pharynx

    External branches

   Control muscles associates with the pectoral girdle

      Hypoglossal nerves (XII)

    Provide voluntary motor control over tongue movement

 

Cranial Reflexes

Cranial reflexes

      Involve sensory and motor fibers of cranial nerves