organization of the cns i

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Organization of the CNS I


Phrenology


Review of the Nervous System

MAJOR FUNCTION:

COMMUNICATION


Neuronal Morphology


The Neuronal Synapse


Glia – the Particular Role of Astrocytes


Astrocyte


Astrocytes Help Form the Blood Brain Barrier• Basal lamina of the astrocytes

+ the astrocytic endfeet produce help maintain the BBB.

• Notice how astrocytes send processes to the external surface of the CNS where the endfeet form the glia limitans externa, which separate the pia mater from the nervous tissue.

• Gap junctions and desmosomes join the endfeet to form a space between neurons and vascular endothelial cells (Fig. 2.2).


Schwann cells surrounding a (myelinated) axon:


General Orientation Terms• Rostral • Caudal• Posterior• Anterior• Dorsal• Ventral• Sagital• Horizontal• Coronal


Terms of Orientation:


Planes of Section:

Horizontal Transverse (Coronal) Saggital


• 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

Major regions and landmarks


The Adult Brain


7 Major Divisions of the CNS


A. Spinal Cord

• Conduit for flow of information from PNS to CNS.

• Participates directly in body movement control.

• Processes sensory information from limbs, trunk, and internal organs.

• Has segmental organization (most like primitive or early developmental NS).

• Each segment has a pair of nerve roots.


B. Brainstem and Cerebellum1. Brainstem = medulla + pons + midbrain.

a. ‘spinal cord’ for the head (sensory, motor control).-use of cranial nerves in place of spinal nerves.

b. Transmission of information between brain and SC.

c. Regulation of arousal (via reticular formation at the core of brainstem).

d. Regulation of important visceral functions (e.g., bp and respiration).


Brain Stem:Ventral Surface


Brain Stem:Dorsal Surface


B. Brainstem and Cerebellum

2. Cerebellum – regulation of movement, maintenance of posture and balance. -Works closely in concert with pons (derived from same embryonic brain division).


• 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 Cerebellum


The Cerebellum


Cerebellum:


C. Diencelphalon

• Diencephalon – 2nd only to cerebrum as the most highly developed division.

1.Thalamus – key for transmitting information to cerebral hemispheres.

2.Hypothalamus – integrates functions of the ANS – controls endocrine hormone release from pit.


• Final relay point for ascending sensory information

• Coordinates the activities of the cerebral cortex and basal nuclei

The Thalamus


Thalamus• Part of diencephalon – relay nuclei through which sensory and motor information pass to and from the cortex.

• E.g., in the 2 1° systems we have discussed:

- from sc 1° sensory cortex- from 1° motor cortex sc.

• This is also the case for neural signals controlling other functions, such as learning and memory and emotions – and projecting to other parts of the cortex.

A. Relay Nuclei have distinct roles, transmitting info from particular subcortical inputs to a specific portion of the cerebral cortex.


The Thalamus


Thalamus:


The Diencephalon and Brain Stem


D. Cerebral Hemispheres

• These structures mediate the most complex and sophisticated human behaviors.

1.Cerebral cortex – highly convoluted to accommodate large surface area: gyri, sulci, fissures – deeper grooves – often separate major divisions.4 lobes:


Frontal

• Motor behavior• The 1° cortex at precentral gyrus.

-nearby premotor areas-prefrontal asociation cortex-cingulate gyrus- important for reasoning and emotional control.


Parietal

• Sensory areas.• The 1° cortex at postcentral gyrus.

-Superior parietal lobule-spatial perception, self-image

-Inferior parietal lobule-integrating sensory information

for speech and perception


Occipital

• The 1° cortex within calcarine fissure on medial surface.

• Surrounding association cortex elaborates the sensory message so that we can see and integrate forms and colours.

• Situated at the division of parietal and occipital lobes is an area important for recognizing faces.


Temporal

• Sensory functions, plus memory and emotions.

• The 1° auditory cortex: on superior temporal gyrus – speech centre.

• Much integration with nearby areas:-inferior temporal gyrus – perception of visual forms and colours.- works with nearby occipital.-temporal pole + medial temporal areas – mediate emotions along with nearby frontal cortical areas.


• Central passageway of the brain enlarges to form ventricles• Contain cerebrospinal fluid (CSF)

Ventricles of the Brain


Ventricles of the Brain


• 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

The Cranial Meninges


Meninges of the CNS• 3 layers:1.Dura - thickest2.Arachnoid – “spider-like”3.Pia – delicate, adheres to surface.• Protective• Circulating function (contain blood

vessels) – many veins and arteries in subarachnoid space.Dural sinuses are major venous areas carrying blood away from the brain.


Meninges:


The Medulla Oblongata and Pons


• 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 Mesencephalon


The Mesencephalon


• Epithalamus• Hypothalamus• Thalamus

The Diencephalon is Composed of


Internal Capsule

• White matter underling the cortex (seen as a band over the thalamus in sagital section).

• Path of transmission of info immediate to and from the cortex.


Internal Capsule


Internal Capsule

• In the following horizontal section, it lies between the thalamus and the caudate and other basal ganglia (putamen and globus pallidus).


• 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 Hypothalamus


The Hypothalamus in Sagital Section


Hypothalamus:


• Caudate nucleus• Globus pallidus• Putamen

• Control muscle tone and coordinate learned movement patterns

The Basal Nuclei


The Limbic System


The Brain in Section


• 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

The Cerebral Cortex


Laminar Organization of the Cerebral Cortex• All cortical regions are organized in

layers.A.Most cortical regions in humans are

the most advanced form (neocortex, isocortex).

B.Allocortex – phylogeneticaly older, has fewer layers: 2 types:i. Paleocortex – sense of smell, emotions (olf bulb).ii. Archicortex – memories (hipp, 3 layers)


Laminar Organization of the Cerebral Cortex

C. Brodmann’s Areas – Thickness of each of the 6 layers varies between these areas, which are also distinct functionally.

Areas that subserve sensation have a thick layer IV (thalamic n. project here)

1° motor areas have a thick layer V.


The White Matter of the Cerebrum


The Cerebral Hemispheres

PLAY


• Control our ability to understand sensory information and coordinate a response• Somatic sensory association area• Visual association area• Somatic motor association area

Association areas


• General interpretive area• Receives information from all

sensory areas• Present only in left hemisphere

• Speech center• Regulates patterns of breathing

and vocalization

General Interpretive and Speech Areas


• 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

Cortex Functions and Hemispheric Differences


Hemispheric Lateralization

PLAY


• 12 pairs of cranial nerves• Each attaches to the ventrolateral

surface of the brainstem near the associated sensory or motor nuclei

Focus: Cranial Nerves


Origins of the Cranial Nerves

PLAY


• Amygdaloid body• Cingulated gyrus• Parahippocampal gyrus• Hippocampus• Fornix• Functions of the limbic system involved

emotions and behavioral drives

The Limbic System or Motivational System includes


• 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

The Cerebral Cortex


• Contains association fibers• Commissural fibers• Projection fibers

White Matter of the Cerebrum


• Control our ability to understand sensory information and coordinate a response• Somatic sensory association area• Visual association area• Somatic motor association area

Association Areas


• General interpretive area• Receives information from all

sensory areas• Present only in left hemisphere

• Speech center• Regulates patterns of breathing

and vocalization

General Interpretive and Speech Areas


• 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

Cortex Functions and Hemispheric Differences

organization of the cns i

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