Neuroanatomy correlates





This chapter provides a foundational overview of basic structural and functional neuroanatomy relevant to brain injury. As such, the coverage is not exhaustive, and the reader is referred to authoritative texts for more comprehensive detail. Moreover, although descriptive, the summary of each neuroanatomical structure/connection is not prescriptive, in that similar structural lesions can result in strikingly diverse functional neurobehavioral presentations among individual patients. Finally, neuroanatomical structures and associated functions are presented as discrete units here for review, but the human brain is a highly complex, connected, and integrated organ such that lesions rarely produce a singular functional deficit.


Structural organization of the brain


The command center of the human CNS, the brain is enclosed in the skull and meninges and structurally divided into the brainstem, cerebellum, and cerebrum. Beneath the cerebral cortex lie several key subcortical structures and connective pathways. The brain is made up of gray matter (cell bodies), which comprises the cortex and some subcortical structures (e.g., basal ganglia), and myelinated white matter, which transmits information to and from connected gray matter for integration/processing. The cortex is folded to allow for greater surface area within the skull, which produces its characteristic grooves (sulci) and folds (gyri). Cardinal directions and key landmarks within the brain are summarized later ( Box 1.1 ; Figs. 1.1 and 1.2 ).



• BOX 1.1

Summary of Cardinal Directions and Key Landmarks in the Brain







































Anterior (rostral) Toward the front
Posterior (caudal) Toward the back
Dorsal Toward the top
Ventral Toward the bottom
Medial Toward the middle
Lateral Toward the side
Precentral (pre-Rolandic) In front of the central sulcus (Rolandic fissure)
Postcentral (post-Rolandic) Behind the central sulcus (Rolandic fissure)
Perisylvian Around the Sylvian fissure (lateral sulcus)
Forebrain Cerebral cortex, thalamus, and hypothalamus
Hindbrain Brainstem and cerebellum



Skull and meninges


The brain is encased within bone and surrounded by three membrane layers that provide protection and buoyancy and anchor it within the skull ( Box 1.2 ). Moving from inside the brain laterally to the skull, the mnemonic PADS ( p ia mater, a rachnoid mater, d ura mater, s kull) identifies the relative positions of the meninges ( Figs. 1.3–1.7 ). , ,



• BOX 1.2

Summary of the Coverings of the Brain (“PADS”)



























Meninge Location/Function Injury Characteristics
P ia mater

  • •

    Thin, innermost layer


  • •

    Attached to the brain


  • •

    Contours to the sulci and gyri of the brain


  • •

    Forms a perivascular space by surrounding initial entry point of blood vessels



  • •

    Bleeds below the pia mater, involves hemorrhage in the actual brain parenchyma (e.g., intraparenchymal bleeds, interventricular hemorrhage)

A rachnoid Mater

  • •

    Thin layer between the pia and dura


  • •

    Appears similar to a spider’s web


  • •

    Cerebrospinal fluid (CSF) is present and is reabsorbed in the arachnoid granulations



  • •

    Bleeds below the arachnoid are subarachnoid hemorrhages and can result from both traumatic and nontraumatic (e.g., aneurysm rupture) etiologies


  • •

    Hydrocephalus is common after subarachnoid hemorrhage caused by dense blood product resulting in poor CSF reabsorption

D ura Mater

  • •

    Thick and hard outermost layer between the arachnoid and inner skull surface


  • •

    Contains venous sinuses that drain cerebral blood


  • •

    Separates the right and left cerebral hemispheres (falx cerebri) and the cerebral hemispheres from the cerebellum (tentorium cerebri)



  • •

    Bleeds between the dura and skull are epidural hematomas and result in a rapidly expanding hemorrhage from tearing of meningeal arteries (e.g., middle meningeal artery)


  • •

    Bleeds between the dura and arachnoid are subdural hematomas and result from tearing of bridging veins; these can be acute or slow, in which symptoms do not become apparent until the bleed has enlarged

S kull

  • •

    Hard bone structure that encases the brain


  • •

    Skull base is internally divided by boney ridges that form the cavities in which the ventral aspect of different brain regions rest:



    • •

      Anterior cranial fossa: frontal lobe


    • •

      Middle cranial fossa: temporal lobe


    • •

      Posterior cranial fossa: cerebellum and brainstem




  • •

    Traumatic brain injury can occur from brain tissue striking the boney internal protuberances and cavities within the skull




Vasculature


This section presents a brief review of the primary circulations, arteries/branches, and neuroanatomical structures supplied by them ( Box 1.3 ). Broadly, the vascular supply in the brain can be segmented into anterior (fed by paired internal carotid arteries) and posterior circulations (fed by paired vertebral arteries). The three primary arteries are also listed, along with divisions, and underlying neuroanatomical regions/structures are supplied with Fig. 1.8 , providing coronal and axial visualization. ,



• BOX 1.3

Summary of Major Cerebral Arteries and Associated Distributions








































Artery Division Associated Neuroanatomical Region
Anterior cerebral artery (ACA) Main Anterior/medial frontal lobe and aspects of anterior parietal lobe (sensorimotor cortex)
Deep Head of the putamen/caudate
Inferior Lateral temporal lobe/parietal lobe
Middle cerebral artery (MCA) Superior (demarcated by Sylvian fissure) Lateral frontal lobe (dorsolateral region) and peri-Rolandic cortex
Deep Medial putamen/caudate
Lenticulostriate Smallest vessels of MCA Basal ganglia and internal capsule
Posterior cerebral artery (PCA) Main Inferior/medial temporal and occipital lobe
Deep Thalamus



Watershed areas (i.e., anterior cerebral artery [ACA] and middle cerebral artery [MCA] area and MCA and posterior cerebral artery[PCA] area) refer to cortical neuroanatomical regions fed by the most distal reaches of each artery that are most vulnerable to diminished blood flow.


Cerebrospinal fluid system


Cerebrospinal fluid (CSF) is produced in the choroid plexus in the lateral ventricles, and its function is to cushion the brain and provide a mechanism for toxin/chemical transmission for cleaning. The relative volume of CSF remains generally stable (150 cc) in adults and is constantly being produced (20 cc/hour). Thus primary/secondary insults to the CNS that affect either production or absorption rates are relevant, as both can result in hydrocephalus ( Box 1.4 ).



• BOX 1.4

Overview of Hydrocephalus



















Cerebrospinal Fluid (CSF) Dysfunction Cause(s) Potential Etiologies
Communicating hydrocephalus

  • •

    CSF overproduction


  • •

    CSF underreabsorption



  • •

    Arachnoid granulation dysfunction


  • •

    Subarachnoid or interventricular hemorrhage


  • •

    Meningitis

Noncommunicating hydrocephalus

  • •

    Obstruction blocking flow at one or more points along the CSF pathway



  • •

    Space-occupying lesion or tumor


  • •

    Edema caused by injury/trauma


  • •

    Increased intracranial pressure


  • •

    Obstruction caused by worsening of a congenital defect






  • •

    CSF Flow Pathway (see Figs. 1.1–1.9 ): Lateral ventricles → foramen of Monro to the third ventricle → aqueduct of Sylvius to the fourth ventricle/foramina (medial and lateral) to subarachnoid space → reabsorbed at rate of 4 to 5 times per day in arachnoid granulations




    • Fig. 1.1


    Lateral and medial views of the adult brain; G = genu; R = rostrum; S = splenium.

    (From Gross anatomy and general organization of the CNS. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:58. Fig. 3.2.)



    • Fig. 1.2


    Explanation of directional terms for referring to the CNS.

    (From Gross anatomy and general organization of the CNS. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:57. Fig. 3.1.)



    • Fig. 1.3


    Electron micrograph of the meningeal layers of a dog.

    (From Meningeal coverings of the brain and spinal cord. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:85. Fig. 4.2.)



    • Fig. 1.4


    Prosections demonstrating the shape and spatial relationships of the dural folds.

    (From Meningeal coverings of the brain and spinal cord. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:86. Fig. 4.3.)



    • Fig. 1.5


    Coronal section through the superior sagittal sinus displaying the movement of cerebrospinal fluid (CSF); CNS = central nervous system.

    (From Meningeal coverings of the brain and spinal cord. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:86. Fig. 4.5.)



    • Fig. 1.6


    View of the base of the skull demonstrating the major sinuses; CN = cranial nerve. CN, Cranial nerve.

    (From Meningeal coverings of the brain and spinal cord. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:88. Fig. 4.6.)



    • Fig. 1.7


    View of the meningeal layers. CNS , Central nervous system.

    (From Meningeal coverings of the brain and spinal cord; CNS = central nervous system. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:96. Fig. 4.14.)



    • Fig. 1.8


    Coronal and axial views of the cerebral blood supply; a. = artery; aa. = arteries. a , Artery; aa , arteries.

    (From Blood supply of the brain. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:141. Fig. 6.22.)



    • Fig. 1.9


    View of the path of cerebrospinal fluid flow; a. = artery. a , Artery.

    (From Ventricles and cerebrospinal fluid. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:110. Fig. 5.10.)



Brainstem


In addition to connecting the spinal cord to the brain via sensory-motor tracts, the brainstem is responsible for consciousness and involuntary, life-sustaining functions ( Box 1.5 and Fig. 1.10 ). , , ,



• BOX 1.5

Structures of the Brainstem



















Brainstem Structure Function
Medulla

  • •

    Regulation of involuntary autonomic functions (e.g., heart rate, breathing, blood pressure) and reflexes (e.g., vomiting, swallowing)


  • •

    Junction between the spinal cord and brain


  • •

    Decussation of corticospinal fibers (pyramidal tracts)


  • •

    Neurotransmitter production (e.g., serotonin in the raphe nuclei)

Pons

  • •

    Modulation of arousal, consciousness, and sleep regulation via the reticular formation, which extends into the midbrain


  • •

    Breathing intensity


  • •

    “Bridge” connecting the brainstem to the cerebrum and cerebellum


  • •

    Sensory and motor relay


  • •

    Neurotransmitter production (e.g., norepinephrine in the locus coeruleus)

Midbrain

  • •

    Cerebrospinal fluid flow from third to fourth ventricle (cerebral aqueduct)


  • •

    Orienting eyes and directing visual attention toward relevant stimuli, notably moving stimuli; visual fixation (superior colliculus)


  • •

    Main auditory pathway hub; guiding auditory attention; auditory startle response (inferior colliculus)


  • •

    Motor control and coordination


  • •

    Connects the forebrain and basal ganglia to the hindbrain


  • •

    Neurotransmitter production (dopamine in the substantia nigra)





• Fig. 1.10


Views of the brainstem.

(From Organization of the brainstem. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:278. Fig. 11.6.)


Cranial nerves


The brainstem also contains 10 of the 12 cranial nerve pairs. The cranial nerves are part of the peripheral nervous system and control sensory and motor functions of the head and neck ( Box 1.6 ). In general, cranial nerves innervate ipsilaterally, though one notable exception is the trochlear nerve (IV), which innervates the superior oblique muscles of the contralateral eye ( Figs. 1.11 and 1.12 ). , ,



• BOX 1.6

Overview of the Cranial Nerves













































































Nerve Location Sensory/Motor Primary Function(s)
Olfactory (I) Olfactory bulb Sensory Smell
Optic (II) Retina Sensory Vision
Oculomotor (III) Midbrain Motor All eye movements except for downward and lateral gaze
Pupillary constriction
Trochlear (IV) Midbrain Motor Eye movements (downward gaze)
Trigeminal (V) Pons Both Facial sensation
Muscles of mastication
Abducens (VI) Pons Motor Eye movements (lateral gaze)
Facial (VII) Pons Both Taste (anterior 2/3 of tongue)
Lacrimation
Salivation
Muscles of facial expression
Vestibulocochlear (VIII) Pons Sensory Hearing
Equilibrium
Glossopharyngeal (IX) Medulla Both Taste (posterior 1/3 of tongue)
Visceral sensory and motor functions
Gag reflex
Pharyngeal muscles (swallowing)
Vagus (X) Medulla Both Parasympathetic innervation to organs
Abdominal visceral sensation
Laryngeal muscles (voice)
Palate elevation
Pharyngeal muscles (swallowing)
Accessory (XI) Medulla Motor Sternomastoid and trapezius muscles
(head turning; shoulder elevation)
Hypoglossal (XII) Medulla Motor Tongue movement




• Fig. 1.11


Inferior view of the brain displaying cranial nerves (CNs) II through XII.

(From Gross anatomy and general organization of the CNS. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:68. Fig. 3.17.)



• Fig. 1.12


Close-up of the inferior view of the brain with cranial nerves.

(From Gross anatomy and general organization of the CNS. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:68. Fig. 3.18.)


Cerebellum


The cerebellum is a large structure in the posterior fossa and is connected to dorsal aspects of the brainstem by the cerebellar peduncles. Its primary function is to smoothly coordinate motor movements and assist with motor planning. Lesions typically result in ipsilateral ataxia. Recent research has also identified contributions of the cerebellum to cognition, including implicit learning, although this is still developing. Neuroanatomically, the cerebellum is made up of the vermis and two hemispheres that are divided into intermediate and lateral regions. These have been divided into three distinct areas with specific functions: (1) vestibulocerebellum, (2) spinocerebellum, and (3) cerebrocerebellum ( Box 1.7 and Fig. 1.13 ). ,



• BOX 1.7

Overview of the Cerebellum and Functions by Region























Region Neuroanatomical Composition Key Functions
Vestibulocerebellum

  • •

    Flocculonodular lobe


  • •

    Inferior vermis



  • •

    Regulates balance and eye movements through connections with the vestibular system




  • Spinocerebellum



  • •

    Vermis


  • •

    Intermediate portions of the cerebellar hemispheres



  • •

    Controls the medial motor systems (proximal trunk muscles)


  • •

    Maintaining posture, gait, and eye movements




  • Cerebrocerebellum



  • •

    Lateral cerebellar regions



  • •

    Controls lateral motor systems (distal appendicular muscles)


  • •

    Planning and executing movements





• Fig. 1.13


Schematic of the cerebellum.

(From Cerebellum. In: Vanderah TW, Gould DJ. Nolte’s the Human Brain: An Introduction to Its Functional Anatomy. 7th ed. Philadelphia, PA: Elsevier; 2016:498. Fig. 20.4.)


Cerebrum


The cerebrum comprises four paired lobes (discussed later; Fig. 1.14 ). In normal/typical functional neuroanatomical organization, the dominant left cerebral hemisphere is responsible for language functions, whereas the nondominant right hemisphere is specialized for visuospatial processing, although intraindividual variability certainly exists. In right-handed individuals, a majority (92%–96%) have left hemisphere language dominance. Among left-handed individuals, the majority (∼77%) also have left hemisphere language dominance, but there is a larger percentage with right hemisphere or bilateral language dominance. Box 1.8 provides a summary of common functional neurobehavioral specializations by hemisphere.


Tags:
Jan 1, 2021 | Posted by in NEUROLOGY | Comments Off on Neuroanatomy correlates

Full access? Get Clinical Tree
Get Clinical Tree app for offline access