Principal parts of the brain
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Principal Parts of the Brain PowerPoint PPT Presentation

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Principal Parts of the Brain. Cerebrum Diencephalon thalamus hypothalamus Cerebellum Brainstem midbrain pons medulla. Brain – midsagital section (photograph). Largest organ in the body at almost 3 lb. Brain functions in sensations, memory, emotions, decision making, behavior.

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Principal Parts of the Brain

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Principal Parts of the Brain

  • Cerebrum

  • Diencephalon

    • thalamus

    • hypothalamus

  • Cerebellum

  • Brainstem

    • midbrain

    • pons

    • medulla

Brain – midsagital section(photograph)

  • Largest organ in the body at almost 3 lb.

  • Brain functions in sensations, memory, emotions, decision making, behavior

Hydrocephalus and CSF Shunt

Ventricles of the Brain

Figure 14–2

Origins of Ventricles

  • Neural tube encloses neurocoel space, which expands to form chambers (ventricles) lined with ependymal cells

Embryology of the Brain

Table 14-1

CSF flow

  • lateral ventricles (R and L)

  • inter-ventricular foramen

  • 3rd ventricle

  • cerebral aqueduct

  • 4th ventricle

  • median and lateral apertures

  • subarachnoid space

    Arachnoid villi reabsorb CSF.


Why all this !$^%&*! trouble?

(8 layers of) Protection of the brainand three related disorders


Galea Aponeurotica



Dura Mater

Arachnoid mater

Pia mater

Reabsorption of CSF: Arachnoid Villi

  • Grapelike clusters (arachnoid granulations) penetrate inner (“endosteal”) layer of dura into venous blood of the venous sinus

  • 20 ml/hour

    Reabsorption rate = Production rate

The Cranial Meninges: Review

  • 3 layers:

    • dura mater

    • arachnoid mater

    • pia mater

  • Continuous with spinal meninges

  • Protects the brain from cranial trauma

Pia Mater

  • Deepest layer composed of delicate connective tissue that clings tightly to the brain.

  • Contains tiny blood vessels that enter the brain tissue.

  • Attached to brain surface by astrocytes

Arachnoid mater:

middle meningeal layer isseparated from dura mater bythe “subdural space”

Subarachnoid space:

between arachnoid mater and pia mater

CSF and large blood vessels

web-like extensions span the space and secure it to the underlying pia mater

CSF gets into the subarachnoid space from 3 foramina (openings) in the roof of the 4th ventricle

Arachnoid Mater

Dura Mater

Dura mater:

  • irregular connective tissue

  • inner fibrous layer (meningeal layer)

  • outer fibrous layer (endosteal layer) fused to periosteum

  • venous sinuses between 2 layers

The Dural Sinuses

  • Superior Sagital Sinus

  • Inferior Sagital Sinus

  • Straight Sinus

  • R and L Transverse Sinuses

  • R and L Sigmoid Sinuses

    …. R and L jugular veins and back to heart.

Dural Folds

  • falx cerebri

  • falx cerebelli

  • tentorium cerebelli

Figure 14–3b

Dural Folds

  • inner layer of dura mater (folded)

  • extend into cranial cavity

  • support brain

  • contain collecting veins (dural sinuses)

Don’t confuse the “arachnoid villi” of dural sinus with the “choroid plexus” of the ventricles!

Review: Principal Parts of the Brain

  • 750 to 2100 cc

  • about 98% of the body’s neural tissue

  • about 1.4 kg (3 lb)

Endocrine Preview: Pituitary Gland

  • Connects to hypothalamus by thin double stalk (infundibulum)

    • venous connection (anterior pituitary)

    • axonal connection (posterior pituitary)

Major Regions and Landmarks


3D Peel- Away of the Brain

Figure 14–1

Longitudinal fissure (green)

Frontal lobe

Central sulcus (yellow)

precentral & postcentral gyrus

Parietal lobe

Parieto-occipital sulcus

Occipital lobe

Lateral sulcus (blue)

Temporal lobe

Insula ?

Lobes and Fissures

Insula within Lateral Fissure

Gray vs.White Matter

  • Gray matter

    • cell bodies, dendrites, unmyelinated axons

    • cortex and deep nuclei

  • White matter

    • primarily myelinated axons

    • X-Y-Z connections

Gray vs. White Matter

Projection Fibers

  • Pass through diencephalon

  •  brain stem, cerebellum, and spinal cord

  • In lab: see the internal capsule

    • ascending and descending projection fibers

Review: Cerebral White Matter

  • Projection fibers form descending & ascending tracts

  • Commissural fibers from one hemisphere to other

  • Association fibers between gyri in same hemisphere

Association Fibers

  • within each hemisphere:

    • arcuate fibers:

      • are short fibers, connect 1 gyrus to another

    • longitudinal fasciculi:

      • longer bundles, connect frontal lobe to other lobes (in same hemisphere)

Commissural Fibers

  • Bands of fibers connecting 2 hemispheres:

    • corpus callosum

    • anterior commissure

Cortical Area Summary: Sensory (1 of 2)

Cortical Area Summary: Sensory (2 of 2)

Cortical Area Summary: Motor

Cortical Area Summary: Integration

Cortical Motor Areas

Premotor cortex

Primary motor cortex

Frontal Eye Field

Broca’s Area

Primary (Somatic) Motor Cortex

  • Located in precentral gyrus of the frontal lobe

  • “upper motor neurons” (pyramidal cells) may follow more than one pathway to “lower motor neuron” that controls contralateral skeletal muscles

    • corticospinal tracts

      • Old terminology – “pyramidal tract”


Primary (Somatic) Motor Cortex

  • Somatotopy

    • body map = “motor homunculus”

  • Strokes that are localized result in precise deficits.

    • cortex lesion contralateral side paralyzed


Premotor Cortex

  • anterior to the primary motor cortex

  • planning of movements

  • “skills”

    • Learned motor patterns

  • Neurons project through corticospinal tract.

Medical Example

  • Stroke affecting the premotor cortex will cause loss of motor skills

  • Muscle strength and ability to perform individual movements are not hindered

  • If you damage the area controlling typing, you would not be able to type at the regular speed, but you could make the same movements. You would need to relearn the rhythmic movements.

Broca’s Area

  • Speech production and articulation

  • anterior to the premotor area of frontal lobe

  • unilateral (usually the left hemisphere)

  • motor speech area

    • “planning” speech mechanics including direction of the tongue

Medical Example:Broca’s Aphasia

  • A stroke to Broca’s area of the brain makes patients unable to speak.

    • They are still able to understand speech

    • …..frustrating!!!

    • Give them a pad and pencil; they can still write the words!

Frontal Eye Field

  • Controls voluntary eye movements.

synapse in thalamus & visual cortex

Preview: Brain Pathways of Vision

Visual fields

  • Left occipital lobe receives visual images from right side of an object through impulses from nasal 1/2 of the right eye and temporal 1/2 of the left eye

  • Left occipital lobe sees right 1/2 of the world

  • Fibers from nasal 1/2 of each retina cross in optic chiasm

Sensory Association Areas

  • Visual association area:

    • occipital lobe

    • interprets activity in primary visual cortex

  • Auditory association area:

    • temporal lobe

    • monitors auditory cortex

  • Somatic sensory association area:

    • interprets input to primary sensory cortex (e.g., recognizes and responds to touch)

Somatosensory Cortex

  • anterior part of parietal lobe

  • somatotopy

    • spatial discrimination

Somatic Sensory Association Cortex

  • posterior to the primary sensory cortex

  • Synthesizes multiple sensory inputs to create a complete comprehension of the object being felt.

    Example: Touch a coin in your pocket; this area would help you identify a small coin as a dime

Gustatory and Vestibular Cortex

  • Gustatory cortex

    • taste

    • parietal lobe

  • Vestibular cortex

    • Cranial Nerve VIII (8)

    • balance and equilibrium (position of head)

    • posterior part of the insula (deep to the temporal lobe)


Olfactory Cortex

  • Cranial Nerve I (1)

    • Receptors in the olfactory epithelium extend through the cribriform plate and send their info to the olfactory cortex.

    • frontal lobe above the orbits, medial temporal lobe

  • linked to “limbic system” for memory and emotion

Limbic System

  • Emotional brain--intense pleasure & intense pain

    • Strong emotions increase efficiency of memory

    • arahippocampal & cingulate gyri & hippocampus

More Cerebral Functions later

  • Start at the spinal cord and work our way back up to the cerebrum…

    The Medulla Oblongata

  • Continuous with spinal cord


  • Controls visceral functions

    • Coordinates complex autonomicreflexes

  • Hard blow to the back of the head  fatal

Nuclei in the Medulla

  • Autonomic nuclei:visceral activities

  • Sensory and motor nuclei:cranial nerves

  • Relay stations:sensory and motor pathways

Figure 14–6b

Medulla Nuclei

  • Cardiovascular control center:

    • force and rate of heart contraction (can override the autorhythmic pacemaker cells of the heart)

  • Vasomotor center:

    • tone of vascular smooth muscle

  • Respiratory rhythmicity centers:

    • rate and depth of breathing

  • Additional Centers:

    • Emesis, coughing, choking, hiccupping, and sneezing

Sensory and Motor Nuclei

  • Associated with 5 of 12 cranial nerves (VIII, IX, X, XI, XII)

  • Can you match their names to their basic functions?

Relay Stations

  • Nucleus gracilis and nucleus cuneatus:

    • pass somaticsensory information to thalamus (lower and upper extremities, respectively)

  • Solitary nucleus:

    • receives visceralsensory information

  • Olivary nuclei (olives):

    • relay information about somatic motor commands (descending pathway)

    • Some somatic motor command do NOT cross here.

Medulla: Decussation of the Pyramids

  • Lateral corticospinal tract (i.e., not all motor fibers) cross to the opposite side in the medulla.

Summary: The Medulla Oblongata

Table 14-2

The Pons

  • Link cerebellum to mesencephalon (midbrain), diencephalon, cerebrum, and spinal cord

  • somatic and visceral motor control

Figure 14–6c

The Pons: 4 Groups

  • Sensory and motor nuclei of cranial nerves V, VI, VII, VIII

  • Nuclei involved with respiration:

    • apneustic center and pneumotaxic center

    • modify respiratory rhythmicity center activity

The Pons: 4 Groups

  • Nuclei and tracts:

    • process and relay information to and from cerebellum

  • Ascending, descending, and transverse tracts:

    • transverse fibers (axons)

      • link nuclei of pons with opposite cerebellar hemisphere

continues with part 2

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