Anatomy of the Brain

The Central Nervous System: Brain Development

• The brain and spinal cord originate from the neural tube.

• The anterior end of the neural tube expands, forming three primary brain vesicles: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).

• The remaining caudal (posterior) part of the neural tube develops into the spinal cord.

Primary Brain Vesicles and their Derivatives

• Primary vesicles differentiate into secondary brain vesicles.

• The forebrain (prosencephalon) divides into:

  • Telencephalon (end brain)

  • Diencephalon (interbrain)

• The hindbrain (rhombencephalon) constricts, forming:

  • Metencephalon (afterbrain)

  • Myelencephalon (spinal brain)

• The midbrain (mesencephalon) remains undivided.

Five Secondary Vesicles and Adult Brain Structures

• The five secondary vesicles develop into specific adult brain structures. Telencephalon:

  • Forms the two cerebral hemispheres (cerebrum). Diencephalon forms:

    • Hypothalamus

    • Thalamus

    • Epithalamus

    • Retina of the eye

  • Mesencephalon forms the brain stem (midbrain).

  • Metencephalon forms the brain stem (pons) and cerebellum.

  • Myelencephalon forms the brain stem and medulla oblongata.

• The midbrain and hindbrain, excluding the cerebellum, form the brain stem.

Central Cavity and Brain Growth

• The central cavity of the neural tube expands in four areas, forming fluid-filled ventricles.

• Rapid brain growth causes folding due to the skull's constraints.

• The midbrain and cervical flexures shift the forebrain towards the brain stem.

• Cerebral hemispheres grow posteriorly and laterally, eventually enveloping the diencephalon and midbrain.

• Continued growth of cerebral hemispheres leads to convolutions, increasing the surface area for more neurons (around week 26).

Brain Regions

• The brain consists of four main regions:

  • Cerebral hemispheres

  • Diencephalon

  • Brain stem (midbrain, medulla oblongata, pons)

  • Cerebellum

Gray and White Matter

• Gray matter consists of short, non-myelinated neurons and neuron cell bodies.

• White matter consists of myelinated axons and some non-myelinated axons; myelin gives it the white color.

• The brain stem has additional gray matter nuclei scattered within the white matter.

• Cerebral hemispheres and the cerebellum have an outer layer of gray matter called the cortex.

Brain Ventricles

• Ventricles are continuous with the central canal of the spinal cord.

• Hollow ventricular chambers are filled with cerebrospinal fluid (CSF) and lined by ependymal cells (a type of neuroglia).

• Lateral ventricles are deep within the cerebral hemispheres and are large, C-shaped chambers that reflect cerebral growth patterns. They are separated by the septum pellucidum.

• Each lateral ventricle communicates with the third ventricle in the diencephalon via the interventricular foramen.

• The fourth ventricle is continuous with the third ventricle via the cerebral aqueduct, which runs through the midbrain.

• The fourth ventricle lies in the hindbrain, dorsal to the pons.

• Three openings mark the fourth ventricle: the lateral apertures in the sides of the walls and the median aperture in its roof.

• The ventricles connect to the subarachnoid space, a fluid-filled space surrounding the brain.

Cerebral Hemispheres

• The cerebral hemispheres are the most superior part of the brain, accounting for 83% of total brain mass.

• Gyri (singular: gyrus) are elevated ridges of tissue separated by shallow grooves called sulci.

• Fissures are deep grooves that separate large regions of the brain.

• The longitudinal fissure is the median fissure that separates the cerebral hemispheres.

• The transverse fissure separates the cerebral hemispheres from the cerebellum below.

• Sulci are important for dividing the hemispheres into five lobes.

Lobes of the Brain

• The central sulcus lies in the frontal plane and separates the frontal and parietal lobes.

• The precentral gyrus and postcentral gyrus border the central sulcus.

• The parieto-occipital sulcus, located posteriorly on the medial surface, separates the occipital lobe from the parietal lobe.

• The lateral sulcus outlines the temporal lobe and separates it from the parietal and frontal lobes.

• The insula is located deep within the lateral sulcus.

Cerebral Hemispheres Regions

• Superficial cerebral cortex of gray matter

• Internal white matter

• Basal nuclei: Gray matter situated deep within the white matter

Cerebral Cortex

• The cerebral cortex is where conscious awareness is found, enabling awareness of ourselves and our sensations.

• It is composed of gray matter, neuron cell bodies, dendrites, glia, blood vessels, and no fiber tracts.

• It accounts for 40% of total brain mass.

• PET scans and MRI blood flow studies show motor and sensory functions localized in discrete areas known as domains.

• The cerebral cortex contains three kinds of functional areas: motor cortex, sensory areas, and association areas.

• Neurons in the cortex are interneurons.

• Each hemisphere is concerned with sensory and motor functions of the opposite side of the body.

• The hemispheres are not equal in function; they exhibit lateralization of cortical functions.

Motor Areas of the Cortex

• Motor areas control voluntary movement.

• The primary motor cortex (primary somatic motor cortex) is located in the precentral gyrus of the frontal lobe.

• Pyramidal cells (neurons) within the gyrus allow conscious control of voluntary movements of skeletal muscles. Their long axons project along the spinal cord, forming pyramidal tracts.

• Mapping of CNS structures is called somatotopy.

• The precentral gyrus has largely control over muscles.

• Motor innervation is contralateral, meaning the left primary motor gyrus controls muscles on the right side of the body.

• Muscles are controlled by multiple cortex areas.

Premotor Cortex

• Anterior to the precentral gyrus in the frontal lobe.

• Plans movement, selects regions for complex tasks, e.g., playing an instrument.

• Controls voluntary actions that depend on sensory feedback.

• Can coordinate movement of several muscle groups simultaneously by sending impulses to the primary cortex.

• Influences motor activity more directly by supplying 15% of pyramidal tract fibers.

Broca's Area and Frontal Eye Field

• Broca's area: Anterior to the inferior part of the premotor area, also known as the motor speech area, involved in speech production.

• Frontal eye field: Superior to Broca's area, controls voluntary movement of the eyes.

• Damage to areas in the primary cortex paralyzes the body's muscle control in those areas. Only voluntary control is lost; muscles still contract reflexively.

• Damage to the premotor cortex results in loss of motor skills but does not impair muscle strength or the ability to perform discrete individual movements.

Sensory Areas

• Sensory areas provide conscious awareness of sensation.

• They are located in the parietal, insular, temporal, and occipital lobes.

• The primary somatosensory cortex resides in the postcentral gyrus of the brain.

• Neurons in this gyrus receive somatic sensory receptors from the skin and proprioceptors, located in muscles, joints, and tendons, informing the brain of the body's position.

• Spatial discrimination refers to the neurons' ability to identify the body region being stimulated.

• The amount of sensory cortex devoted to a particular body region is related to the number of sensory receptors in that area (face and lips are the most sensitive in the somatosensory homunculus).

Somatosensory Association Cortex

• Posterior to the primary somatosensory cortex.

• Its major function is to integrate sensory inputs (temperature, pressure) relayed to the primary motor cortex to produce an understanding of an object being felt.

• The primary visual cortex is located on the occipital lobe, mainly within the calcarine sulcus on the medial aspect of the occipital lobe. It is the largest cortical sensory area, receiving visual information from the retina of the eye. Damage to the primary visual cortex leads to functional blindness. Damage to the visual association area allows seeing but prevents comprehending what is being seen.

Visual and Auditory Areas

• Visual association area: Surrounds the primary visual cortex and covers most of the occipital lobe. It uses past visual experiences to interpret visual stimuli (color, form, and movement), enabling the recognition of objects or faces. "Seeing" is processed by cortical neurons.

• Auditory area: Located in the superior margin of the temporal lobe, next to the lateral sulcus. Sound energy excites hearing receptors, transmitting impulses to the primary auditory cortex, where they are interpreted as pitch, loudness, and location.

• Auditory association area allows the perception of sound stimuli. Memories of sounds heard in the past are stored here.

• Located on posterior part of insula: Vestibular cortex (Equilibrium). Part of the brain responsible for conscious awareness of balance.

Olfactory and Gustatory Areas

• Olfactory Cortex: (Primary Olfactory Cortex) lies on medial aspect of temporal lobe in a smaller reigon called "Piriform lobe" dominated by Uncus. Afferent fibers from smell receptors in the superior nasal cavity send impulses to the olfactory cortex and relayed to olfactory cortices, which brings awarness of different odours. It is part of the primitive Rhinencephalon located on temporal lobe medial aspect.

• Rhiencephalon ("Nose brain"): Includes all parts of cerebrum that receive olfactory signals. Orbit: frontal cortex, uncus, & regions on medial aspects of temporal lobes protrude olfactory tracts and bulbs that extend the nose. "Old" Rhinencephalon takes on new functions & becomes part of the "limbic System". Explain why certain Smells cause memories w/ memory & emotions.

• Gustatory Cortex (taste): Region located in the insula, involved in receiving taste stimuli.

• Visceral Sensory Area: Involved mainly with our visceral sensations such as discomfort & pain. Including upset stomach. Stimulus such as full bladder, or feeling of lungs being full.

Multimodal Association Areas

• These areas connect all cortex regions, receive inputs from multiple senses, and output to many areas. They allow for giving meaning to information received, storing it in memory, tying it to past experiences, and deciding what action to take.

• The multimodal association cortex is where our sensations, thoughts, and emotions become conscious. Decisions are relayed to our premotor cortex, which communicates to our motor cortex.

• Information flow: Sensory receptors > primary sensory cortex > sensory association cortex > multimodal association cortex.

• Multimodal association cortex is divided into anterior, posterior, and limbic association areas.

Anterior Association Area (Prefrontal Cortex)

• Located in the frontal lobe and is the most complicated region.

• Involves intellect, complex learning abilities (cognition), recall, and personality.

• Contains working memory, abstract ideas, judgment, reasoning, persistence, and planning.

• These abilities develop slowly in children.

• The prefrontal cortex matures slowly and depends heavily on feedback from the social environment.

Posterior Association Area

• Large region encompassing the temporal, parietal, and occipital lobes.

• Recognizes patterns, faces, and localizes us and our surrounding space.

• Awareness from all our senses originates here.

• Also involved in understanding written and spoken languages.
  Limbic Association Area: Provides emotional impact that matches a Sense important to US.
  Involves our Hippocampus, Cingulate gyrus, parahippocampal gyrus and Hippocampus allows for us to memorize incidents.

• Tumors or lesions to the anterior dissociation cause personality disorder, loss of judgment, attentiveness, & inhibiton.

• Lesions in posterior association cause self in space disorientation

Lateralization of Cortical Functioning

• Each hemisphere is divided in labor and abilities are not completely shared.

• Cerebral dominance designates the dominance for language in the hemisphere.

• In about 90% of people, the left hemisphere has dominance over language, math, and logic. Important when composing sentences, numbers, and memorizing lists.

• The right hemisphere is more free-spirited and involved with skills, emotions, and musical ability.

• Most with left cerebral dominance are right-handed; 10% are left-handed, in whom the roles of the hemispheres are shared or reversed. Some have cerebral cortex that function bilaterally are ambidextrous.
  Two hemispheres communicate via connecting fiber tracts.

• The two hemispheres have instantaneous communication via connecting fiber tracts and complete functional integration. Neither is better at everything.

Cerebral White Matter

• Deep to the cortical gray matter and responsible for communication between cerebral areas, the cerebral cortex, and lower CNS centers.

• White matter consists of myelinated fiber bundles into large tracts and are classified by the direction they run.

Association Fibers

• Connect different parts of the same hemisphere.

• Short association fibers connect adjacent gyri; long association fibers are bundled into tracts and connect different cortical lobes.

Commissural Fibers

• Connect corresponding gray areas of the two hemispheres to function as a coordinated whole.

• The largest commissure is the corpus callosum, which lies superior to the lateral ventricles deep within the longitudinal fissure.

• Less prominent commissures are the anterior and posterior commissures.

Projection Fibers

• Enter the cerebral cortex from lower brain areas or descend from the cortex to lower areas.

• Sensory information reaches the motor cortex, and motor output leaves it through these projections.

• Ties the cortex to the rest of the nervous system. Projection fibers run vertically.

• At the top of the brain stem, projection fibers form a band on each side, the internal capsule, and pass through the thalamus and basal nuclei. Superiorly, fibers fan out to the cerebral white matter to Cortes, called the corona radiata.

Basal Nuclei (Basal Ganglia)

• Located deep within the cerebral white matter.

• Primarily involved in the control of movement.

• Each basal nucleus includes the caudate nucleus, putamen, and globus pallidus.

• The caudate nucleus arches superiorly over the diencephalon. With the putamen, it forms the striatum due to fibers running through them, creating a stripped appearance.

• The putamen and globus pallidus form a lens-shaped mass called the lentiform nucleus, functioning separately.

• Basal nuclei are associated with the subthalamic nuclei (located on the lateral floor) and the substantia nigra of the midbrain.

• Basal nuclei receive input from the entire cerebral cortex and other subcortical nuclei.

• Via relays through the thalamus, the output nuclei of the basal nuclei and substantia nigra project to the premotor and prefrontal cortex, influencing muscle movement directed by the primary motor cortex.

• Basal nuclei have no direct access to motor pathways.

• The precise role of basal nuclei is undetermined but play a role in cognition and emotion. They filter out incorrect or inappropriate responses, only passing the best response to the cortex.

• They inhibit antagonistic or unnecessary movements.

• Disorders of the basal nuclei include Huntington's disease and Parkinson's disease.

Diencephalon

• Consists largely of the thalamus, hypothalamus, and epithalamus. These gray matter areas enclose the third ventricle.

Thalamus

• Forms the superolateral walls of the third ventricle and makes up 80% of the diencephalon.

• Known for relaying information coming into the cerebral cortex.

• Within the thalamus, there are numerous nuclei, mostly named after their location. Each nucleus has specific functions and projection fibers to receive fibers.

• Afferent impulses from all senses and parts of the body converge on the thalamus and synapse with at least one nuclei.

• Within the thalamus, information is sorted out and edited. Impulses are relayed as a group through the internal capsule to the appropriate area.

• When afferent impulses reach the thalamus, we recognize them as pleasant or unpleasant. Spatial discrimination occurs in the cerebral cortex.

Inputs funnel through Thalamic Nuclei

• Inputs that help regulate emotion and visceral functions from hypo (via antiflor nuclish)

• Instructions that help direct activity of motor cortices from the Cerebellum & Basal nuclei (via mental lateral & anterior nuclei)

• Inputs of memory or Sensory Intergration (via pulvinar, lateral dorsal, & lateral posterior pucjei).

• Thalamus paly in role in mediating Senation, motoractivites, cortial arousal, learning,and memory.

Hypothalamus

• Caps the brain stem and forms the inferolateral walls of the third ventricle.

• Merges into the midbrain inferiorly and extends from the optic chiasma to the posterior margin of the mammillary bodies.

• Mammillary bodies are paired nuclei that form bulges on the hypothalamus and relay stations in olfactory pathways.

• The infundibulum is a stalk of tissue between the optic chiasma and mammillary bodies that connects the pituitary gland to the base of the hypothalamus.

• It is the main visceral control center of the body, maintains body homeostasis.

Functions of the Hypothalamus

• Controls the autonomic nervous system (ANS) by regulating activity in centers of the brain and spinal cord. Influences blood pressure, heart rate and force, digestive tract motility, and eye pupil size.

• Initiates physical responses to emotions. It is the heart of the limbic system and contains nuclei involved in perceiving pain, fear, pleasure, and rage (sex drive).

• The hypothalamus acts through ANS pathways to initiate most physical expressions of emotions.

• Regulates body temperature. The body's thermostat is in the hypothalamus. Hypothalamic neurons monitor blood temperature and receive input from thermostatic receptors. It initiates cooling or heat-generating actions (sweating and shivering) to maintain body temperature.

More Functions of the Hypothalamus

• Regulates food intake: It regulates feelings of hunger and satiety via glucose, amino acids, or hormones.

• Regulates water balance and thirst:

  • Osmoreceptors become activated when body fluid becomes too concentrated.

  • They excite hypothalamic nuclei and trigger the release of antidiuretic hormone (ADH) from the posterior pituitary. ADH causes the kidneys to retain water and also stimulates the thirst center.

• Regulates sleep-wake cycles: The suprachiasmatic nucleus (our biological clock system) sets the timing of the sleep cycle, primarily from daylight-darkness cues from visual pathways.

• Controls endocrine system functions:

  • Releases and inhibits hormonal control over the secretion of the pituitary gland.

  • Supraoptic and paraventricular nuclei produce antidiuretic hormone (ADH) and oxytocin.

Epithalamus

• The most dorsal portion of the diencephalon, forming the roof of the third ventricle.

• The pineal gland extends from it and secretes melatonin, helping regulate the sleep-wake cycle.

• The brain stem consists of the midbrain, pons, and medulla oblongata.

• Consists of only 2.5% of total brain mass.

• Has nuclei of gray matter surrounded by white matter fiber tracts, unlike the spinal cord.

• Programmed for automatic behaviors of survival.

Midbrain

• Located between the diencephalon and pons.

• Cerebral peduncles form vertical pillars holding up the cerebrum.

• The crus cerebri ("leg of cerebrum") contains pyramidal motor tracts descending down to the spinal cord.

• Superior cerebellar peduncles are fiber tracts that connect the midbrain to the cerebellum.

• The cerebral aqueduct runs through the midbrain, connecting the third and fourth ventricles.

• Periaqueductal gray matter is involved in pain suppression and controls fight-or-flight responses. It also includes the control of oculomotor and trochlear nuclei.

• The corpora quadrigemina, the largest nuclei of the midbrain, consists of the superior and inferior colliculi.

• Superior colliculi: visual relay centers coordinate head and eye movement.

• Inferior colliculi: auditory relay centers that initiate the startle reflex (head turn).

Substantia Nigra and Red Nucleus

• Substantia nigra: Embedded in the midbrain white matter, located deep to the cerebral peduncle. Its black color reflects melanin, a precursor of the neurotransmitter dopamine, which is released by these neurons and linked to the basal nuclei.

• Degeneration of dopamine-releasing neurons is the ultimate cause of Parkinson's disease.

• Red nucleus: Deep in the substantia nigra, red in color due to its blood supply and iron content. It relays nuclei of descending motor pathways that cause limb flexion.

Pons

• Located between the midbrain and medulla oblongata. The fourth ventricle separates it from the cerebellum.

• Composed of two different tracts:

  • Deep projection fibers run longitudinally between higher brain centers and the spinal cord.

  • More superficial fibers are transverse and dorsal, forming the middle cerebellar peduncles and connecting the pons bilaterally to the cerebellum. These fibers issue from numerous pontine nuclei, which relay conversations between the motor cortex and cerebellum.

• The pons includes the trigeminal, abducens, and facial nerves.

• Helps the medulla oblongata maintain normal breathing.

Medulla Oblongata

• The most inferior part of the brain stem.

• The central canal of the spinal cord continues into the medulla to form the fourth ventricle.

• Longitudinal ridges (pyramids) are tracts descending from the motor cortex; most fibers cross over to the opposite side before continuing to the spinal cord. This crossover point is known as the decussation of pyramids. This crossover results in the cerebral hemisphere controlling voluntary movement of the opposite side of the body.

• Inferior olivary nuclei relay sensory information on the degree of stretch in muscles and joints to the cerebellum.

• Cranial nerves associated:

  • Glossopharyngeal & Vagus

  • Vestibulocochlear nerves synapse with cochlear nuclei and numerous Vestibular nuclei in pons & medulla. Which respond to maintain equilibrium.

• The medulla also contains ascending sensory tracts.

• Nucleus gracilis & nucleus cuneatus Sensory function to Spinal Cortex and Somatosensory cortex.

• The medulla is an autonomic reflex center involved in maintaining homeostasis. Maintains important visceral motor nuclei such as the cardiovascular, cardiac center and Respritory autonomic reflex center controls: vomiting, hicaping, swallowing, coughing & sneezing.

Cerebellum

• Accounts for 11% of brain mass and occurs subconsciously.

• Has a thin gray matter cortex, internal gray matter, and masses of dendrite nuclei.

• Purkinje cells are branched dendrites that send axons through white matter to synapse with central nuclei of the cerebellum, resembling a tree known as the arbor vitae.

Coordinate of Body Movements

• The medial portion influences motor activities of the trunk and girdle muscles.

• The intermediate part infivuence the plan and role in movement of limbs.

• Flocculonodular receives input from equilibrium to adjust posture to maintain posture.

• All Fibers entering and leaving cerebellum are ipsilateral.

Cerebellar Peduncles

• Connect the cerebellum to the brain stem.

  • Superior cerebellar peduncles carry instructions from neurons in deep cerebellar nuclei to the cerebral cortex via the thalamic cortex.

  • The cerebellum has no direct connection to the cerebral cortex.

  • Middle cerebellar peduncles carry one-way communication to the cerebellum, advising the cerebellum of voluntary motor activities.

  • Inferior cerebellar peduncles connect the medulla oblongata to the cerebellum.

  Cerebellum Processing.

  1) motor areas of cerebral cortex relay nuclei in brain stem, notify cerebellum to initiate voluntary muscle contraction by:
  2) Receives info, enables to evaluate body position and momentum.
  3) calculates best way to coordinate, force, direction and extent muscle contraction
  4) Cerabellum dispatches to cerebral motor cortex For
  5) Cerebellar injury result in loss of muscle tone & Clumsyness.
  6) Cchalbellum allso play important role in cognative functions such as thinking, learning, and emotions.

Limbic System and Reticular Formation

• Limbic system include Amy daloid body and in main part of diencephalon and Limbic structures the hypothalamus and anterior thalamic nuclei.

• Fornix link limbic system together. It's the emotionl visceral. system brain.

• The amygdaloid body is critical for responding to perceived threats.

• The cingulate gyrus expresses our emotions with gestures and can trigger emotional reactions to smells.

Reticular Formation

• Composed of loosely clustered neurons (white matter).

• The reticular activating system (RAS) sends a stream of impulses to the cerebral cortex, keeping the cortex alert.

• It also filters floods of sensory inputs, disregarding 99% of all sensory input.

• The RAS is depressed by alcohol, sleep-inducing drugs, and tranquilizers.

Language and Memory

• Language is associated with Broca's and Wernicke's areas, which produce a single language implementation system that analyzes incoming and outgoing word sounds and grammatical structures.

• Broca's area: difficulty Speaking but Understand language.

• Wernicke's area: able to speak but produced as nonsense.

• The right (non-language) hemisphere is involved in body language and allows the areas to lift or raise tone and gestures as we speak.

• Memory: Declarative, Procedural, Motor, and emotional which Declarative memory involves short term & long term memory.STM- Worthing memory only can memorize short info whereas Long term (LTM) has limiless capacity.

• Hippo Campus plays major role in memory consolidation by communicating thalamus to prefrontal cortex.

Brain Waves

• Brain waves reflect electrical activity.

• EEG (Electroencephalogram) records aspects of activity and is used for diagnosing epilepsy & sleep disorders and determining brain death.

• Brain waves are patterns of neuronal electrical activity generated by synaptic activity at the surface ad cortex.

  • Alpha waves are associated with a relaxed state of wakefulness.

  • Beta waves indicate mental alertness.
    Thera waves are common in Children when awake adults but Delta waves occur When reticular system is supressed. Those two indicate brain damage.

• Consciousness is a continuum that grades behavior:

  • Alertness, drowsiness, stupor, and coma.

  • Sleep non- rapid eye movement (NREM) and Rapid eye movement (REM)

• Before waking up, hypothalamic neurons release peptides called orexins, which are walk-up chemicals.

Meninges

• Three connective tissue membranes that lie external to the CNS.

• They cover & protect the CNS, protect blood vessels and enclose venous sinuses, contain cerebral fluid, and form partitions of the skull.

• From external to internal, the meninges are:

  • Dura mater

  • Arachnoid mater

  • Pia mater

Layers of the Meninges

• Dura mater surrounds the brain as a two-layered sheet of fibrous connective tissue.

• Arachnoid mater forms a loose brain covering separated by the subdural space containing film fluid.

• Beneath is the subarachnoid space, which is filled with Cerebrall fluid & blood vessels serving the brain.

• Pia mater is composed of delaccate connective tissue containing many small blood vessels.

Cerebrospinal Fluid (CSF)

• Found in the brain and spinal cord

• CSF carries chemical impulses, contains less protein & Na+, Cl- & H+ than blood plasma.

• Choroid plexuses hang from the roof of each ventricle and form CSF.

• Their thin capillaries are enclosed by a layer of ependymal cells held together by tight junctions, having ion pumps to filtrate certain ions to the CSF pool.

• It is important due to CSF mixing with extracellular fluid.
  Ionic pumps set up ion gradient causing water to diffuse into ventricles.
  1) CSF volume is 150 ML replaced every 8 hrs
  2) 500 formed Doily
  3)The Choroid plexuses cleanses by removing Waste & unnecessary solutes.
  Long cilid of ependymal cells help CSF in constant motion.

Hydrocephaws

• CSF bathes cutter lining of Brain & spinal cord.

• Condition when CSF is large in children where brain enlargies.

  Blood Brain Barrier

• A protective mechanism that maintains the brain's environment.
  Tight junctions between endothelia cells
  The cells Smooth muscles cells Called pericytes regulate the endothelial cells. Surrounding endothelid cells are astrocytes
  Transcytosis moves larger substances
  Instead it passes through plasma membrane.

Functions of the Blood Brain Barrier

• They form tight junctions to prevent molecules to move from endothelial cells from blood to brain.
  Fatty acids, oxygen, carbon dioxide & lipid
  Solubles are diffused easily into plasma

• Nutrients glucose, amino acid are passively by facilitated diffusion.
  Metabolic waste, proteins, & certain toxins are denied entry:
  Amino acids and Potassium ions are prevented.from entering brain.

Spinal Cord:

• Lateral horns consist of cell bodies in the autonomic system and ventral contain both somatic and autonomic system efferent fibers.

• Dorsal root: afferent fibers carring impulses fan out and enter spinal cord

• Dorsal root gagnlion: enlarged reagion of the dorsal root that contains the cell bodies of sensory neurons.

• Spinal gray matter has four zones: Somatic sensory, visceral sensory, viseral motor and somatic motor,

White matter :

• composed of nonmyelinated and mylinated nerve fibers: fiber run in three main directions: ascending (to the brain), descending (from the brain), and transverse (across the cord).

• White matter is divided into funiculi which contain several fiber tracts made up of axons

Neuronal Pathway

• Relay : pathway consist of two or three neurons that contribute successive tracts

• Somatotopy: oderly mapping the body

• Symmetry: align with the brain or spinal cord

Functional Organization: pathways are grouped by their role in sensory or motor functions, allowing for efficient information processing.

Ascending Pathways to the brain: conduct pathway sensory impulses upward:

• 1st order neurons body reside in the ganglion and conduct impulses to the skin and from propioceptos to the spinal cord.

• 2nd order neruons reside in the dorsal horn and transmit impulses to the thalamus to the cerebellum where they synapse

• 3rd oder neurons have cell bodies in the thalamus they relay impulses to the cerebrum

Spinothalmic pathway is responsible for transmitting pain and temperature sensations from the body to the brain, specifically utilizing the first, second, and third order neurons for effective communication of sensory information. Pathways from dorsal and lateral horns

Spinocerebellar pathways contribute to skeletal muscle activity:

Direct pathways: Pyramidal pathways: These pathways originate in the cerebral cortex and descend directly to the spinal cord, controlling voluntary movement by influencing lower motor neurons.

Indirectpathways: involved in regulating axial muscle balance and posture, muscle controlling , and head and neck movements through the activation of various brainstem nuclei and spinal cord circuits, ensuring coordinated muscular responses and stability during dynamic activities.