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Neural Systems
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Circuits that do the same kinds of things are grouped into “systems”, for example sensory systems and motor systems.
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Many neurons function between these systems, called associational systems. These are very complex and the least well characterized systems.
2016-01-12 13:41:15
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Last time we learned some of the basic cellular anatomy of the nervous system. Today we will put the system in nervous system–– because nervous systems really are greater than the sum of its parts… in other words our brain is not just a blob of cells but it is the interconnections between cells, groups of cells, and brain regions that allow our fantastic feats of emergent biological computation. So lets discuss the overall the structure of the nervous system.
First of all it is a system of systems. In other words…
The Major Components of the Nervous System and Their Functional Relationships
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This illustrates the two top level systems of the nervous system, the CNS containing the brain and spinal cord and the PNS containing nerves and ganglia exiting the spinal cord.
The Major Components of the Nervous System and Their Functional Relationships
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This diagram outlines the functional hierarchy of different components or systems within the whole nervous system including relations between internal and external environment and sensory receptors in the PNS as well as skeletal muscle and smooth, cardiac muscles that the nervous system controls.
right vagus nerve primarily innervates the SA node, whereas the left vagus innervates the AV node
pns supplies smooth muscles, cardiac muscles, and glands. functions to maintain homeostasis, and is concerned with involunary functions.
Cell bodies that do similar things are grouped together
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PNS– Nerve cell bodies are located in ganglia (ganglia have neurons and glia in them). Dorsal root ganglia, cranial nerve ganglia
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CNS– Nuclei are compact accumulations of neurons having roughly similar connections.
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Cortices (cortex) sheets of cells of similar function.
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The term we use for cell bodies grouped together in the PNS is ganglia. In the CNS cell bodies are accumulated together as nuclei or if they are arranged in highly ordered sheets or lamina it is called cortex.
Cell groupings: cortex vs nuclei
Cerebral cortex
Thalamic Nuclei
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Anatomy terms
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Nerves– bundles of axons, enveloped by glial cells that myelinate them
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White matter– areas of axon tracts
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Grey matter– areas of cell bodies
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White and grey matter
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Basic parts of the CNS
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Spinal cord
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Brain stem
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medulla
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pons
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midbrain
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Cerebellum
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Forebrain
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diencephalon
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cerebral hemispheres
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These are the basic parts of the CNS
Words used to describe locations in the CNS
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Words used to describe the three axis of the brain
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Components of the Central Nervous System
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Think about how the nerves represent incoming and outgoing info from a specific location on the body.
Spinal cord
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Extends from the base of the skull to the first lumbar vertebra.
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Receives sensory info from skin, joints, and muscles of trunk and limbs and contains motor neurons responsible for both voluntary and reflexive movements.
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Nerve fibers bundled in 31 pairs of spinal nerves. There is a sensory division (dorsal root ganglia) and a motor division (ventral root).
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Is thicker in regions that innervate the limbs.
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Lets start with the spinal cord which in human contains about 1 billion of your 100 billion neurons in your nervous system.
It extends…
It receives sensory…
So it carries both afferent and efferent information.
Nerve fibers…
Is thicker…
Spinal cord
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This illustrates the overall structure of the spinal cord.
Internal anatomy of the spinal cord
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Contains both white and grey matter.
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Grey matter shaped like an “H”. Dorsal horns and ventral horns.
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Dorsal horns contain sensory relay neurons– receives input from periphery
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Ventral horns contains motor nuclei that innervate muscles– send output
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White matter contains longitudinal tracts of ascending and descending axons grouped together by function.
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Internal structure of the spinal cord
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- Gray matter expanded to incorporate more sensory input from limbs and more cell bodies for motor control of limbs
Cervical Enlargement
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General rules of spinal cord organization
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Neurons and axons that process and relay sensory information (afferents) are in dorsal spinal cord.
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Preganglionic visceral motor neurons (innervate glands) are found in the intermediate/lateral region.
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Interneurons are in intermediate zone.
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Motor neurons and axons are found in the ventral portion of the cord.
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Gray Matter: Organization
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Spinal cord tracts
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Dorsal column– sensory signals travels up it to the brain.
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Lateral columns– also called the cortico-spinal tracts. Take signals from brain and sends it to the muscles.
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Ventral columns (sometimes called anterolateral column)– carry pain signals up and motor signals down.
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Spinal cord tracts
Nissl stain (cell bodies)
Myelin stain
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Dorsal column-sensory info travels up to the brain.
Lateral columns-also called the cortico-spinal tracts. Take info from brain and sends it to the muscles.
Ventral columns (sometimes called anterolateral column)- carry pain info up and motor info down.
Brain stem
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Target or source for all cranial nerves that deal with sensory and motor function in the head and neck.
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Nuclei within brainstem are the targets and sources of these nerves.
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Also is a throughway which all info going up and down must pass.
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Because of its small area and restricted blood supply-it is very susceptible to damage.
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Now let’s talk about the brain stem, which is located more rostrally to the spinal cords locations we just discussed.
The brain stem is a target or source…
And all information from higher order or more rostral brain structures that goes to or from the spinal cord must pass through the brain stem.
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Brain stem
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Close up of the brain stem
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Brain stem
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Medulla– regulates blood pressure and respiration.
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Ventral pons– pontine nuclei, relay signals from cortex to the cerebellum
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Dorsal pons– respiration taste and sleep
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Midbrain– auditory and visual systems, substantia nigra pars compacta (dopaminergic neurons). Deteriorates in Parkinson’s disease.
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Brain stem
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From the brain stem there emerges 12 left-right pairs of cranial nerves that carry afferent or efferent information mostly concerned with sensory and motor functions of the head. The exception is the the vagus nerve arising from the medulla which carries critical autonomic signals for your visceral organs and heart without which you cannot live.
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Cranial nerves
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This lists these 12 cranial nerves and their relevant sensory and/or motor function they carry. Notice that many of the nerves carry mixtures of sensory and motor information, which you could see with the color coding on the previous slide. Also notice that 4 of the 12 nerves concern sensory and motor information from the eyes. In fact the cranial nerve containing the most fibers is the optic nerve which contains 1.2 million axons that carries all the information necessary to perceive the visual world around you (compare with 130 million photoreceptors and 0.7 to 1.5 million RGCs)
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Cranial nerve nuclei of the brainstem
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Cranial nerve nuclei of the brainstem
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Midbrain
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The tectum of the midbrain, which is latin for ‘roof’ contains the superior and inferior colliculi and is important for processing visual and auditory information as well as shaping motor commands for orienting the head and body.
Ventral to the cerebral aqueduct through which cerebral spinal fluid circulates, you will find the tegmentum of the midbrain which contains the —>
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Parkinson’s- loss of dopamine making neurons in the midbrain
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substantia nigra pars compacta, a nucleus containing neurons making the neurotransmitter dopamine that are important for regulating motor movements via their connections with the basal ganglia and which are devastated in parkinson’s disease.
Now you’ve all heard the phrase ‘running around like a chicken with its head cut off’ —>
dark appearance due to high levels of neuromelanin in dopaminergic neurons
Neuromelanin is directly biosynthesized from L-DOPA, precursor to dopamine, by tyrosine hydroxylase (TH)
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The brainstem is all you need to live
http://www.youtube.com/watch?v=ATz3AdbjyRI
Mike, as everyone knows, was the arguably lucky fowl who survived a beheading
by a Colorado farmer in 1945, thriving for 18 months with only a brain stem. Fed
on corn dropped directly into his gullet, Mike choked to death during a sideshow
tour in 1947, when the farmer — after forging a new and profitable relationship
with Mike — was unable to clear his esophagus, having forgotten to bring along
the eyedropper he used for that purpose.
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Well here is a grotesque way of convincing you that all you need to live is your brainstem…
Cerebellum
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The cerebellum is located dorsal to the brainstem.
Cerebellum
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Two hemispheres, several lobes divided by fissures
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Neurons in sheets, called cortex.
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Receives sensory input from spinal cord, motor info from cerebral cortex, balance info from inner ear and vestibular organs
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Primarily used motor control, particularly in making postural adjustments and in fine-tuning movements.
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Essential for the coordination, planning of movements, learning motor tasks and storing this information.
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It has two…
Neurons are form cortical sheets.
Receives…
Cerebellum
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Cerebellum is latin for ‘little brain’, and it does have a striking organization with lobes and fissures similar to the folding of the cerebral cortex to increase surface area and packing density of neuronal interconnections. You can see here its main cell body layer, obvious in this purple nissl stain for cell bodies here. It’s in this layer where you will find the beautiful purkinje neurons that we saw images of in lecture 01.
Forebrain
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Now let’s use our forebrains to learn about the forebrain.
Diencephalon
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Contains the thalamus and hypothalamus
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Thalamus– “relay station to the cerebral cortex”- an essential link in the transfer of most sensory information from periphery to cerebral cortex. Also plays a role in filtering information from the periphery.
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Hypothalamus– lies ventral to thalamus. Controls a variety of functions, growth, eating, drinking, maternal behavior by regulating hormonal secretions of the pituitary gland. Connects to virtually every part of brain. Important in initiating and maintaining behaviors that the organism finds rewarding
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The diencephalon contains the…
The thalamus can be generally thought of as the relay station to the cortex.
The hypothalamus lies ventral to the thalamus and controls an array of important physiological functions such as feeding, fluid balance, and hormonal secretions of the endocrine system.
Thalamus
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Pair of ovoid structures.
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Incoming sensory information relays in the thalamus before entering the cerebral cortex. Many sensory, motor, and cognitive functions
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Highly organized connections with cortex
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Connections are mostly reciprocal
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Thalamus is essentially the relay nuclei that routes sensory information into the cortex. This routing of information is highly organized with different subdivisions sending information in parallel pathways to different visual, auditory, and somatosensory regions of the cerebral cortex. But the connections are highly reciprocal with cortical areas, such that the thalamus is integral to many sensory, motor, and cognitive functions as well as the generation of different electrical rhythms that underly different sleep states.
Thalamus– gateway to the cerebral cortex
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The thalamus is located in the middle of the brain…
Thalamus subdivisions
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…and is the gateway for routing information into the cerebral cortex. It contains a number of different nuclei and subdivision that take information from other brain regions including the brain stem and sends to appropriate primary sensory or higher order regions of the cerebral cortex.
Thalamus subdivisions
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Hypothalamus
hypothalamus
thalamus
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Controls a variety of functions, growth, eating, drinking, maternal behavior by regulating hormonal secretions of the pituitary gland. Connects to virtually every part of brain. Important in initiating and maintaining behaviors that the organism finds rewarding
Cerebral Hemispheres
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Largest portion of the human brain
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Cerebral cortex– cognitive functioning
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Hippocampus– memory
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Basal ganglia– control of fine movement
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Amygdala– social behavior and expression of emotion
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Now let’s finally talk about highest order parts of teh central nervous system the cerebral hemispheres.
The two cerebral hemispheres sit atop and surround the diencephalon and much of the brain stem.
Seat of cognition, but it doesn't work alone!
limbic system includes both the amygdala is the integrative center for emotions, emotional behavior, and motivation
Cerebral Cortex
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Highly convoluted shape-grooves (sulci) and elevated regions (gyri). If sulci are especially deep called fissures.
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About 2 to 4 mm thick, 100K neurons/mm2
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Segregated into left and right hemispheres connected to each other at the corpus callosum
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Anatomically divided into four lobes
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Functionally distinct regions
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Organized into layers
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Greatly expanded in humans
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Cerebral Cortex
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Sulci (fissures) and Gyri
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Lobar Anatomy
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frontal
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parietal
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temporal
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occipital
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Cortico-cortical pathways come in two flavors
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within hemisphere
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short vs. long (fasciculi)
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between hemisphere
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mostly homologous connections
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commissures
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corpus callosum
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Primary versus Non-Primary Cortex
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Primary cortex
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cortical areas that are the primary projection fields targeted by the sensory input pathways
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cortical areas that are the principal fields which have neurons that project down into the spinal cord to control
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Primary visual (calcarine sulcus)
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Primary auditory
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Primary somatosensory (post-central gyrus)
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Primary motor (pre-central gyrus)
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Non-primary cortex
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everything in between
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referred to collectively as association cortex
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4 lobes of the cerebral cortex
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frontal– planning responses to stimuli, contains: motor cortex (precentral gyrus)
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parietal– somatic sensory cortex (postcentral gyrus)
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temporal– audition and insular cortex (taste)
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occipital– vision
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Lobes of the cerebral hemispheres
Primary motor cortex
Primary somatosensory cortex
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Ventral View of the Human Brain
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Internal Structures of the Brain Seen in a coronal section
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Internal Structures of the Brain Seen in a coronal section
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Internal structures of the brain seen in a coronal section
http://www.youtube.com/watch?v=snO68aJTOpM
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Cerebral cortex anatomy
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The cerebral cortex is a layered structure
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Layers can be seen when the brain is stained with dyes that highlight cell bodies (e.g. Nissl stain)
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Cortical neurons are organized into layers
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Laminar organization of neocortex
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Cortex itself has a thickness of only about 3-4mm.
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6 layers (neocortex)
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Layer IV is the primary input layer
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Layers II and III are cortico-cortical output layers
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Layers V and VI descending output layers to connect with subcortical regions (basal ganglia, thalamus, brain stem, spinal cord)
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Defects in cortical development
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lissencephaly: smooth brain
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do not have characteristic gyri patterns
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leads to death, severe epilepsies and mental retardation
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cause is defects in neural migration during development
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Question
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a. Do specific regions of the brain control specific functions?
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or -
b. Does each part of the brain do all functions?
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c. Does a specific function come from many parts of the brain?
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Now lets expand on how functions are organized in the brain. Do you think that…
Question
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a. Do specific regions of the brain control specific functions?
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or -
b. Does each part of the brain do all functions?
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or -
c. Does a specific function come from many parts of the brain?
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it’s a bit of a trick question because both of these answers are partially right depending on how you define a part of the brain or what kind of function you’re talking about, but it is not the case that
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Early 1800’s Franz Joseph Gall
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all behavior emanates from the brain
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particular regions of the cerebral cortex controlled specific functions, i.e. the brain does not act as a single organ.
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each function grew with use such as a muscle with exercise
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this growing causes the skull to budge creating a pattern of bumps “phrenology”
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Franz Joseph Gall– phrenology
Standing at his lectern, the priest stared steadily upon one man in the congregation: Franz Joseph Gall. With his angry voice echoing off the church's hallowed walls, he pronounced,"There are those amongst us, who have lost their way from our Lord's divine path. With pomposity, they state the mind is situated in an organ as mushy and insubstantial as the brain. What ludicrousness is this, when all intelligent men know that God has imbued our thinking into our very soul, whereupon no one can put his finger precisely on the spot!"
http://thevictoriantimes.blogspot.com/2011/10/galls-phrenology.html
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Phrenology
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Pierre Flourens (French)
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Tested Gall’s ideas by removing different parts of the brain (dogs and rabbits) and asked if specific functions were compromised.
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Showed medulla important for respiration, cerebellum important for movements.
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Lesions in cortex affected either zero or many behaviors. Concluded that the cortex was one organ and not regionalized.
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Korbinian Brodmann (early 1900s)
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Used subtle anatomical differences in the brain to divide it into discrete areas or regions
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Based on distinctive nerve structures and characteristic arrangements of layers
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52 discrete areas– many still used today.
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So first lets discuss how we came to define different parts of the brain, specifically cerebral cortical areas
Cortical regions have slightly different laminar organization
cell body stain
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Brodmann areas
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Brodmann areas
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Paul Broca
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Believed that functions could be localized but were in the brain, phrenology of convolutions not of bumps.
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Studied patients with aphasia-language disorders found in patients who have had a stroke.
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1861-had a patient that could understand language but could not speak, problems with the organizational aspects of language-found lesion in posterior frontal lobe-
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This kind of aphasia is called motor or expressive aphasia
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Eight patients with similar problems all had similar lesions, always on the left side.
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“Nous parlons avec l’hemisphere gauche!”
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We also define regions of the brain based on studies of brain lesions in patients. Recall the guy with the railroad spike from last lecture. Well the French physician Paul Broca in the 19th c.
Broca and a patient’s brain
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Carl Wernicke
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Had a patient that could speak but not understand language. Called receptive aphasia.
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Damage was to a different area-left side, posterior part of the left temporal lobe. Argued that only simple perceptual and motor activities were localized to a specific area and that most functions result from interconnections between areas. Idea of “distributive processing”.
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The Major Brain Areas Involved in the Comprehension and Production of Language
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Characteristics of Broca's and Wernicke's Aphasias
https://www.youtube.com/watch?v=67HMx-TdAZI
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syntax: the arrangement of words and phrases to create well-formed sentences in a language.
grammar: in linguistics it is set of structural rules governing the composition of clauses, phrases, and words in any given natural language. The term refers also to the study of such rules, and this field includes morphology, syntax, and phonology, often complemented by phonetics, semantics, and pragmatics.
Conduction aphasia
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Inability to produce appropriate responses to heard communication, even though the communication is understood.
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Can speak fluently but bad at making the connection from what has been heard to how to reply.
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Often associated with damage in the Arcuate fasiculus –an axon tract that connects wernike and broca areas.
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Conduction aphasia
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Difficulty repeating words
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Fluent, but with many incorrect word substitutions
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Good comprehension
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Arcuate Fasciculus: Major association fiber tract in CNS connects Broca’s and Wernicke’s areas
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Other evidence of brain regionalization
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1870 Fritsch and Hitzig– discrete limb movements in dogs can be produced by electrical stimulation of the contra-lateral motor cortex. Thus the right hand is controlled by the left hemisphere. Same as language. Dominant hemisphere.
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1950 Wilder Penfield– neurosurgeon, localized motor functions by stimulating specific areas of the brain.
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Split brain studies by Roger Sperry 1960’s
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And there is lots of other evidence for localization of brain function, especially for sensory and motor information for limbs and body. In fact Fritsch…
And the Canadian physician Wilder Penfield performed classical mapping of motor function in the cerebral cortex by localized electrical stimulation.
And then there is the fascinating split brain studies of Sperry and Gazzaniga in the 1960s
Penfield stimulation studies
http://www.youtube.com/watch?v=l1SAC1HcAzc
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Start about minute 3.
Split Brain studies: Nobel prize 1981
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The corpus callosum and anterior commissure are the two axon tracts that connect the two sides of the brain. They are sometimes cut to prevent the spread of severe epilepsies.
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Each side of the brain works independently from the other
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Roger Sperry showed that the left hemisphere dominates speech, writing, right hand stereognosis, analysis of right visual field
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Right hemisphere dominates, emotional coloring of language, spatial abilities, left hand stereognosis, analysis of left visual field
“for his discoveries concerning the functional specialization of the cerebral hemispheres"
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The classic split brain studies which Roger Sperry got the Nobel for in 1981 showed the lateralized localization of language that Broca and Wernicke anticipated as well as several other higher functions. They took advance of the fact that in patients with severe epilepsies, sometimes the commisures connecting the two hemispheres are cut to prevent the spread of seizures.
And since each side of the brain to some degree can work indpedently of the other
humans are 90% right handed as a population and the degree of lateralization among individuals is strong, regardless of left or right-handedness
96% of right handers having left hemisphere speech, compared with 70% of left handers
Twin studies have demonstrated some genetic influence on handedness, but 75% of the variance is nongenetic and individually specific, with only 25% explained by genes [#Bishop:2013]. Even the segregation of of handedness and language laterality suggests a complex polygenic set of factors, with 96% of right handers having left hemisphere speech, compared with 70% of left handers [#Bishop:2013].
Confirmation of hemispheric specialization for language
“a cube”
“a non-round thing”
“a cube”
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Here is an illustration of the experiment performed by by Sperry and his colleagues for these split brain studies. After the corpus callosum connecting the two hemisphere was cut to alleviate epileptic seizures, the patients were asked to fixate on a point and name objects presented in each visual field. Now you haven’t about the visual system yet, but as sensory information from your left hand goes to your right hemisphere, visual information from the lateral part of your left visual field goes to your right visual cortex. Split brain patients could not correctly name objects presented in their left visual field, presumably because that info could not reach the left hemispheres because the callosal connections were severed. But split brain patients could correctly name an object when presented in their right visual field, because that information was received by the left visual cortex and could be passed onto the language centers.
In all Sperry and his colleagues showed that language, mathematical, and logical reasoning is dominant in the left hemisphere and that shape recognition, spatial attention, emotional processing, and creativity in more dominant in the right hemisphere.
Brain imaging techniques
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Computerized tomography (CT) scan– uses X-rays in 3-dimensions to generate a brain image.
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Can be digitally sectioned to show internal areas of the brain.
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Can distinguish between grey matter and white matter, see the ventricles, has resolution of several millimeters.
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Magnetic resonance imaging (MRI)
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Uses rotating magnets to generate image
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Non-invasive
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Can view images from any angle
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Resolution under 1 mm
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Can be adapted to do functional MRI imaging.
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Tumor detection
MRI
CT-SCAN
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Magnetic resonance imaging (MRI)
http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation01-01MagneticResonanceImaging.mov
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functional magnetic resonance imaging (fMRI)
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Oxy-hemoglobin and deoxy-hemoglobin have different magnetic resonance signals
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Brain areas activated by a specific task utilize O2, then a pulse of O2 comes back and creates an influx of oxy-hemoglobin.
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Can repeat task many times over.
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Spatial resolution– millimeters
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Temporal resolution– seconds
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fMRI
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Mapping brain activity with fMRI
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Lie detection with fMRI
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build a new age lie detector