Lecture CNS 1

The Brain

The Spinal Cord

Evolutionary development of the rostral (anterior) portion of the CNS

Each evolutionary level has an increased number of neurons in the head

Highest level is reached in human brain

• 1. Cerebrum
• 2. Diencephalon
• 3. Brain stem (midbrain, pons, medulla)
• 4. Cerebellum

central cavity is surrounded by gray matter core


external white matter composed of myelinated fiber tracts

They care connected to one another and to the central canal of the spinal cord

Lines by ependymal cells

• Contain Cerebrospinalfluid (CSF)
• -two lateral C shaped ventricles in the cerebal hemispheres
• -thies ventrucle in diencephalon
• -fourth ventricle in hindbrain, dorsal to the pons, develops from lumen of the neural tube
• -contains choroid plexus which creates CSF

Cerebral Hemispheres make up 83% of the brain

• Gyri-ridges
• Sulci-shallow grooves
• Fissures- deep grooves

Central sulcus: seperates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe

Longitudinal Fissue: seperates the two hemispheres

Transverse Cerebral Fissue: separates the cerebrum and the cerebellum

• 1 .Frontal
• 2. Parietal
• 3. Temporal
• 4. Occipital
• 5. Insula: deep to lateral sulcus, covered by portions of the temporal, parietal, and frontal lobes
• 

-Thin (2-4 mm) superficial layer of gray matter

-40% of the brain mass

-Site of concious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding

-Each hemisphere connexts to the ctralateral side of body (left brain to right side of body)

-There is a lateralization (specialization) of cortical function in the hemispheres

• The three types of functional areas are:
• 1. Motor areas: control voluntary movment
• 2. Sensory areas: conscious awareness of sensation
• 3. Association areas: integrate diverse information

• *conscious behavior involves the entire cortex
• 

1. Primary (somatic) motor cortex

2. Premotor cortex

3. Broca's area

• 4. Frontal Eye Field
• 

-Large pyramidal cells (large neurons) of the precentral gyrus

-Long axons--> pyramidal (corticospinal) tracts

-Allows conscious control of precise, skilled, coluntary movements

• -Motor homunculi: upside-down caricatures representing the motor innervation of body regions
• 

-Anterior ot the precentral gyrus

-Controls learned, repetitious, or patterns motor skills (such as typing)

-Coordinated simultaneous or sequential actions

-Involved in the planning of movments that depend on sensory feedback

-Anterior to the inferior region of the premotor area

-Present in one hemisphere (usually the left)

-A motor speech area that directs the muscles of the tongue

-Is active as one prepares to speak

Anterior ot the premotor cortex and superior to Broca's Area

Controls coluntary eye movments

*Conscious awareness of sensation

• -Primary somatosensory cortex
• -Somatosensory association cortex
• -Visual Areas
• -Auditory Areas
• -Olfactory cortex
• -Gustatory Cortex
• -Visceral Sensory Area
• -Vestibular Cortex
• 

-In the postcentral gyri

-Recieves sensory information from the skin, skeletal muscles, and joints

-Capable of spatial discrimitation: identification of the body region being stimualted

Posterior to the primary somatosensory cortex

Integrates sensory input (such as pressure, temp, etc) from the primary somatosensory cortex

Determines size, texture, and relationship of parts of objects being felt (based soley on touch, not sight)

• Primary visual (striate) cortex
• -extreme posterior tip of the occipital lobe
• -most of it is buried in the calcarine sulcus
• -receives visual information from the retinas

• Visual Association Area
• -surround the primary visual cortex
• -uses past visual experiences to interpret visual stimuli (ex: color, form, and mvoement)
• -complex processing involves entore posterior half of the hemispheres

• Primary Auditory Cortex
• -superior margin of the temporal lobes
• -interprets infomration from inner ear as pitch, loudness, and location

• Auditory Association area
• -located posterior to the primary auditory cortex
• -stores memories of sounds and permits the perception of souns

Medial Aspect of temporal lobes (in piriform lobes)

• Part of the primative rhinencephalon, along wotj tje p;factpry bulb and tracts
• -remainder of the rhinencephalon in humans is part of the limbic system

Region of concious awareness of odors

In the Insula (just deep to the temporal lobe)

• Involved in the perception of taste
• 

Posterior to the gustary cortex

Concious perception of visceral snesation (such as an upset stomache or a full bladder)

Posterior part of the insula nad adjacent parietal cortex

responsible for conscious awareness of balance (position of the head in space)

-recieves input from multiple sensory areas

-sends output to multiple areas, including the premotor cortex

-allows us to give meaning to information received, store it as memory, compare it to previous experiences, and decide on what actions to take

• Three parts:
• 1. Anterior association area (prefrontal cortex)
• 2. Posterior association area
• 3. Limbic Association Area

-Most complicated cortical region

-involved with intellect, cognition, recall, and personality

-Contains working memory needed for judgement, reasoning, persistence, and conscience

-development depends on feedback from social enviornment

Large region in temporal, parietal, and occipital lobes

Plays a role in recognizing patterns and face and localizing us in space

Involved in understanding written and spoken language (Wernicke's area)

Part of the limbic system

Provides emotional impact that helps establish memories

• 1. Neural plate form from ectoderm
• 2. Neural Plate invaginates to form a neural groove and neural folds
• 3. Neural groove fuses dorsally to form the neural tube
• 4. The neural tube gives rise to the brain and spinal cord
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• Anterior end of the neural tube gives rise to three primary brain vesicles
• 1. Proencephalon- forebrain
• 2. Mesencephalon- midbrain
• 3. Rhombencenphalon- hindbrain

• These primary vesicles give rise to 5 secondary vesicles
• 1. Telencephalon and diencephalon arise from the forebrain
• 2. Mesencephalon remains undivided
• 3. Metencephalon and myelencephalone arise from the hindbrain
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• Telencephalon--> cerebrum (2 hemispheres with cortex, white matter, and basal nuclei)
• Diencephalon--> thalamas, hypothalamus, epithalamus, and retina
• Mesencephalon-->Brain stem (mid brain)
• Metenchephalon--> brain stem (pons) and cerebellum
• Myelencephalon--> brain stem (medulla)

Central Canal of the neural tube enlarges to form fluid filled ventricles

-Midbrain flexure and cervical flexure cause forebrain to move toward the brain stem

- Cerebral hemispheres grow posteriorly and laterally

-cerebral hemisphere surgaces crease and fold into convolutions

Laterlization: division of labor between hemispheres

Cerebral dominance: designates the hemispheres dominant for language (left hemispheres in 90% of people because most people are right handed)

• Left hemisphere:
• controls language, math, logic

• Right Hemisphere:
• insight, visual spatial skills, intuition, and artistic skills

Right and Left hemispheres communicate bia fiber tracts in the cerebal white matter

-Myelinated fober and their tracts

• Responsible for communication
• -Commisures (in corpis collosum)-- connect gray matter of two hemispheres
• -Associated fibers- connect different parts of the same hemisphere
• - Projection fibers (corona radiata)- connect the hemispheres with lower brain or spinal cord
• 

Subcortical nuclei

• consists of corpius striatus
• -caudal nucleus
• -lentiform nucleus (putamen + globus Pallidus)

• Functionally associated with the subhtalamic nuclei (diencephalon) and the substantia nigra (midbrain)
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Though someone elusive, the folloiwng are though to be function of basal nuclei:

• 1. influence muscular control
• 2. help regulate attention and cognition
• 3. regulate intensity of slow or sterotyped movement (too much movement, huntingtons. too little movement- parkinsons)
• 4. Inhibit antagonistic and unnecessary movments

• Three paired structures:
• 1. Thalamus
• 2. Hypothalamus
• 3. Epithalamus

Diencephalon enlocses the third ventricle

80% of diencephalon

Superplateral walls of third ventricle

Connected by teh interthalamic adhesion (intermediate mass)

Contains several nuclei, named for their location

Nuclei project and recieve fibers from the cerebal cortex

Gateway to the cerebral cortex

• Sorts, eduts, and relays information
• -afferent impulses from all senses and all parts of body
• -impulses from the hypothalamus for regulation of emotion and visceral function
• *impulses from the cerebullum and basal nuclei to help direct motor cortices

Mediates snesation, motor activities, cortical arousal, learning, and memory

Caps the brain stem, posterior and inferior to thalamus

*lies at the heart of the limbic system

Forms the inferolateral walls of the third ventricle

• Contains many nuclei
• -Example: mammilary bodies (paired anterior nuclei)-olfactory relay stations

Infundibulum-- stalk that connects the pituitary gland to the hypothalamus

Autonomic control center for many visceral functions (main visceral control center) such as blood pressure, rate and force of heartbeat, digestive tract motility

Center for emotional response: involved in perception of pleasure, fear, and rage and in biologicial rythms and drives

Regulates body temperature, food intake, water balance, and thirst

regulates sleep and the sleep cycle

controls release of hormones by the anterior pituitary

produces posterior pituitary hormones (ADH, Oxycotin)

Most dorsal portion of the diencephalon; forms the roof of the third ventricle

Pineal gland--extends from the posterior border and secretes melatonin (helps regulate the sleep-wake cycle)

each about 1 inch long-->Midbrain, pons, medulla oblongata

Similar structure to spinal cord byt contains embedded nuclei (deep gray matter surrounded by whtie matter, but also nuclei of gray matter embedded in white matter)

controld automatic behaviors necessary for survival

Contains fiver tracts connecting higher and lower neural centers

Associated with 10 of the 12 pairs of cranial nerves

located between the diencephalon and the pons

Cerebral peducles (little verticle pillars seemingly holding up the cerebrum)

Contain pyramidial motor tracts (descending toward the spinal cord)

• Cerebral aqueduct
• -channel between the third and fourth ventricles (surrounded by gray matter, involved in pain suppression and fight or flight response)

Nuclei that control cranial nerves III (oculomotor) and IV (trochlear)

• Corpora Quadrigemina - domelike dorsal protrusions
• -superior colliculi: visual reflex centers
• -inferior colliculi: auditory relay centers (also "startle" relex)

Substantia nigra- functionally linked tot he basal nuclei (deep the cerebral peducle, dark in color, releases dopamine)

• red nucleus- relay nuclei for some descending motor pathways and part of the reticular fomation (red dur to rich blood supply )
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Forms part of the anterior wall of the fourth ventricle

• Fibers of the pons
• -connect higher brain centers and the spinal cord
• -relay impuses between the motor cortex and the cerebellum

Origin of CN V (trigeminal), VI (abducens) and VII (facial)

Some nuclei of the reticular formation

Nuclei that help maintain normal rythm of breathing

Joins the spinal cord and the foramen magnum

Forms part of the ventral wall of the forth ventricle

Contains a choroid plexus of the fourt ventricle

Pyramids--two ventral longitudinal ridged formed by the pyramidal tracts

Decussation of the pyramids-- crossover and othe corticospinal tracts (how the hemisphere controld hte opposite side of the body)

Inferior olivary nuclei- relay sensory information from msucles and joints to cerebellum

CN VIII, X, and VII are associated with medulla

Vestibular nuclear complex- mediates responses that maintain equilibrium

Several nuclei (such as nucleus cuneatus and nucleus gracilis) relay sensory information

**Medulla and Hypothalamus have many similar functions. This is b/c hypothalamus relays its instructions through the medulary reticular centers, which carry them out in the body**

Autonomic Reflex centers

• Cardiovasulcar Center
• -cardiac center adjusts force and rate of heart contraction
• -Vasomotor centers adjusts blood vessel diameter for blood pressure regulation

• Respiratory Centers:
• -generate respiratory rhytm
• -control rate and depth of breathing, with pontine centers

• Additional centers regulate
• -vomiting
• -hiccuping
• -swallowing
• -coughing
• -sneezing

11% of brain mass

Dorsal to the pons and the medulla (protrudes under occipital lobe)

Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction

Two hemispheres connected by vermis ((bilaterally symmetrical)

• Each hemisphere has 3 lobs (divided by deep fissures)
• 1. Anterior (both anterior and posterior coordinate body movemnets)
• 2. Posterior
• 3. Flocculonodular (maintains balance)

Folia- transversely oriented gyri

• Arbor vitae- distinctive treelike pattern of cerebellar white matter
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All fibers in the cerebellum are ipsilateral (to the same side of the body)

• Three paired fiber tracts connect the cerebellum to the brain stem
• 1. Superior peduncles connect the cerebellum to the midbrain
• 2. Middle peduncles connecet the pons to the cerebellum (one way communication)
• 3. Inferior peduncles connectt he medulla to the cerebellum (convey sensory information from muscle sensors, vestibular nucleu of the brain stem concerned with balance)

Cerebellum recieves impulses from the cerebal cortex of the intent to initiate voluntary muscle contraction

signals from proprioceptors and visual and equilibrium pathways continuously "inform" the cerebellum of the bodys position and momentum

cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction

a "blue print" of coordinated movment is sent to the cerebal motor cortex and to the brain stem nuclei via superior peduncles

Recognizes and predicts sequences of events during complex movments

Plays a role in nonmotor functions such as word association and puzzle solving