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
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.
Summary Why all this !$^%&*! trouble?
(8 layers of) Protection of the brainand three related disorders Skin Galea Aponeurotica Fascia Bone 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 PLAY 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
Gray vs.White Matter • Gray matter • cell bodies, dendrites, unmyelinated axons • cortex and deep nuclei • White matter • primarily myelinated axons • X-Y-Z connections
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 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”
Cerebrum Primary (Somatic) Motor Cortex • Somatotopy • body map = “motor homunculus” • Strokes that are localized result in precise deficits. • cortex lesion contralateral side paralyzed
Cerebrum 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)