Neuroanatomy

Brain

Introduction

• The lecture will cover the brain and its various structures.
• It's a content-heavy lecture, so focused attention is required.
• A Word document titled "summary of organization and functions of the brain" is associated with the lecture and should be used as a guide.

Brain Structures

• Brain stem and its subcomponents
• Diencephalon and its subcomponents
• Cerebrum and the different lobes of the cerebrum
• Basal nuclei
• Limbic system
• Cerebellum

Superior View of the Brain

• Need to know the perspective from which the brain is being viewed to avoid confusion.
• In the image, the anterior part of the brain is on the left, and the posterior is on the right.
• The view is from the top of the head.

Key Structures

• Longitudinal Fissure: A deep, wide separation down the midline that separates the left and right cerebral hemispheres.
• Gyrus: An up folding on the surface of the brain (e.g., precentral gyrus).
• Sulcus: An enfolding on the surface of the brain, not as wide or deep as a fissure (e.g., central sulcus).

Lobes of the Brain

• Prefrontal Cortex: Located at the front of the cerebral hemispheres.
• Frontal Lobes: Separated from the parietal lobes by the central sulci.
• Parietal Lobes: Located just posterior to the frontal lobes.
• Occipital Lobes: Located posterior to the parietal lobes; there is no specific anatomic demarcation separating them; separation is based on function.

Key Cortices

• Precentral Gyrus: Contains the primary motor cortex.
• Postcentral Gyrus: Contains the primary sensory cortex.

Left Lateral Perspective

• Viewing the brain from the left side (left cerebral hemisphere).

Key Structures

• Frontal Lobe
• Central Sulcus: Separates the frontal and parietal lobes.
• Temporal Lobe: Separated from other lobes by the lateral fissure.
• Occipital Lobe
• Cerebellum: Means "little brain"; has two hemispheres.
• Brain Stem

Brain Stem Components

• Medulla: Most inferior part of the brain stem, continuous with the spinal cord; the anatomic separation between the brainstem and the spinal cord is the foramen magnum.
• Pons: Located just superior to the medulla.
• Midbrain: Located just superior to the pons.

Medial Aspect of the Right Cerebral Hemisphere

• Separating the left and right cerebral hemispheres and looking at the medial aspect.

Key Structures

• Cerebrum
• Corpus Callosum: Composed of tracts (bundles of axons and myelin sheaths) that connect the left and right sides of the brain, allowing them to act as a single unit.
• Ventricles: Contain cerebrospinal fluid.
• Cerebellar Hemisphere
• Brain Stem: Medulla, pons, midbrain.
• Diencephalon: Located above the midbrain; composed of the thalamus, hypothalamus, subthalamus, and epithalamus.

Brainstem

• Main components are the medulla, pons, and midbrain.
• Most structures of the reticular activating system are found in the brainstem.
• Viewed from anterior and posterolateral perspectives.

Medulla Oblongata

• Contains ascending and descending tracts.
• Pyramids: Located on the anterior surface.
• Pyramidal Decussation: Located on the anterior inferior surface; where the majority (~80%) of descending motor pathways cross over, resulting in the right brain controlling the left side of the body and vice versa.
• Olives: Play a role in maintaining balance; receive input from the inner ear.
• Respiratory Centers: Control rate and depth of ventilation.
• Nuclei of Origin: Where the nerve cell bodies for cranial nerves IX (glossopharyngeal), X (vagus), XI (spinal accessory), and XII (hypoglossal) are found.

Baroreceptor Reflex

• Baroreceptors: Monitor pressure in the aortic arch (cranial nerve X) and internal carotids (cranial nerve IX).
• Increased blood pressure activates sensory pathways in cranial nerves IX and X, which form the tractus solitarius and terminate in the nucleus solitarius in the medulla.
• Excitation of the nucleus solitarius excites central medullary alpha two receptors in the nucleus ambiguus (cardiovascular output center).
• Excitation of central alpha two receptors decreases sympathetic outflow and increases parasympathetic outflow, leading to decreased heart rate, stroke volume, cardiac output, and vasodilation to lower blood pressure.
• Low blood pressure results in less activation of the nucleus solitarius, less activation of central alpha two receptors, and allows sympathetic nervous system to predominate, increasing heart rate, stroke volume, cardiac output, and vasoconstriction to raise blood pressure.

Other Structures in the Medulla

• Components of ascending sensory pathways (nucleus cuneatus and nucleus gracilis).
• Raphe Magnus Nucleus and Reticularis Paragigantocellularis: Play a role in pain modulation.
  • Opioid receptors (mu, kappa, delta) are found in these areas, along with endogenous opioids (endorphins, enkephalins, dynorphins).
• Nuclei for autonomic reflexes (cardiovascular, swallowing, vomiting, coughing, sneezing).
• Chemoreceptor Trigger Zone: Found in the floor of the fourth ventricle; related to nausea and vomiting; located outside the blood-brain barrier; target for antiemetic drugs.

Pons

• Located superior to the medulla
• Contains ascending and descending tracts.
• Contains tracts that connect the cerebrum to the cerebellum.
• Nuclei of origin for cranial nerves V (trigeminal), VI (abducens), VII (facial), and VIII (vestibulocochlear).
• Pneumotactic Respiratory Center: Controls respirations.
• Periaqueductal Gray Matter: Plays a role in pain modulation.
• Locus Coeruleus: Part of the reticular activating system; plays a role in wakefulness, alertness, attentiveness; synthesizes and secretes norepinephrine.

Midbrain

• Also known as the mesencephalon.
• Contains nuclei of origin for cranial nerves III (oculomotor) and IV (trochlear).
• Composed of the tectum (roof) and tegmentum (floor).

Tectum

• Composed of the corpora quadrigemina (four twin bodies): two superior colliculi and two inferior colliculi.
• Superior Colliculi: Play a role in visual reflexes and tracking moving objects; receive input from the eyes, skin, and cerebral hemispheres.
• Inferior Colliculi: Synapse with neurons from the inner ear; transmit impulses to the primary auditory center; play a role in tracking where sounds come from.

Tegmentum

• Includes ascending tracts.
• Red Nuclei: Origin of rubrospinal tracts, which are extrapyramidal motor pathways (unconscious coordination of skeletal muscle movement).
• Substantia Nigra: Origin of the nigrostriatal tract; part of the basal nuclei; helps control muscle movement at the unconscious level.
• Cerebral Peduncles: Where descending tracts from the cerebrum to the spinal cord go through.

Reticular Activating System (RAS)

• Described as a cloud of nuclei distributed throughout the brainstem.
• Receives impulses from nerves that innervate the face and from ascending sensory pathways.
• Responsible for regulating alertness, state of consciousness, and sleep-wake cycle.
• Receives auditory, sensory, and visual input.
• The locus coeruleus, which secretes norepinephrine, is part of the RAS.

Control of Respirations

• Respiratory centers are found in the medulla and the pons.
  • Dorsal respiratory group = Medullary Inspiratory Center.
  • Ventral respiratory group = Medullary Expiratory Center.
  • Pontine respiratory group = Pontine Pneumotaxis Center.
• The medullary inspiratory center contains pacemaker cells that constantly generate action potentials.
  • Sends impulses to the phrenic nerve (innervates the diaphragm), causing the diaphragm to contract and increase the longitudinal size of the lungs.
  • Sends impulses to intercostal nerves that synapse with external intercostal muscles, pulling the rib cage up and out.
  • Intrapulmonary volume increases, pressure decreases, and air moves into the lungs.
• Collateral from the medullary inspiratory center synapses on the pontine pneumotaxis center, which sends inhibitory impulses to the medullary inspiratory center.
  • Inhibits the medullary inspiratory center.
    • Causes the diaphragm to relax, decreasing lung size, and the rib cage to pull down and in.
    • Intrapulmonary pressure increases, and air moves out of the lungs.
• Expiration is normally a passive process, but the medullary expiratory center is activated during forceful expiration.
  • Impulses are sent to intercostal nerves that innervate the internal intercostals, pulling the rib cage down and in even more, causing a forceful expiration.

Regulation of Ventilation Rate

• Conscious thoughts from the cerebrum can increase or decrease ventilation rate.
• Central medullary chemoreceptors in the medulla primarily monitor the pH of the central spinal fluid.
  • As $CO_2$ levels rise, central medullary chemoreceptors are activated to increase ventilation rate.
• Peripheral chemoreceptors in the aortic arch and bifurcation of the carotids primarily monitor $PaO_2$.
  • When $PaO_2$ gets below about 60 millimeters of mercury (especially below 50), the medullary inspiratory center's activity increases.
• Stretch receptors in the lungs prevent overinflation (Hering-Breuer reflex).
• Skeletal muscle activity increases ventilation rate.
• Pain increases ventilation rate.

Diencephalon

• Composed of four structures: thalamus, subthalamus, epithalamus, and hypothalamus.
  • Located below the lateral ventricle and above the midbrain.

Thalamus

• Largest part of the diencephalon.

• The third ventricle of the brain is located between the two lobes of the thalamus.

• The thalamus serves as a relay center for virtually all ascending sensory pathways.

• Lateral geniculate bodies: Visual input from the cranial nerve || synape here before transmission back in the primary visual vortex.

• Cranial nerve VIII (auditory) pathways synapse in the medial geniculate bodies before being transmitted to the primary auditory cortex.

• Other nuclei (ventral, posterior, medial) relay other sensory input to higher brain centers.

Subthalamus

• A component of the basal nuclei.

Epithalamus

• Composed of two structures: habenular nucleus and pineal body.

• Habenular Nucleus: Part of the limbic system; involved in emotional and visceral responses to odors; receives input from olfactory pathways.

• Pineal Body: Secretes melatonin; possibly related to the onset of puberty; melatonin is produced in darkness, suppressed by light, helps induce sleep, and may play a role in depression.

Hypothalamus

• Composed of nuclei with many different functions.

• The hypothalamus is connected to the anterior pituitary gland via the hypothalamo-hypophyseal portal system.

• Portal System: Two capillary networks that are connected by a vein.

• hormones from the hypothalamus are transported down the portal system and bind to receptors in the anterior pituitary, which regulates synthesis and secretion. Hypothalamic hormones regulates the synthesis and secretion of anterior pituitary hormones.

Hypothalamic Hormones

*Growth hormone releasing hormone:
* stimulates growth hormone synthesis and release from anterior pituitary

• Growth hormone inhibiting hormone (somatostatin):
  • inhibits GHRH synthesis.
• Thyroid stimulating hormone releasing hormone:
  • stimulates release of TSH.
• Adrenocortico hormone releasing hormone:
  • stimulates release of ACTH.
• Gonadotropin releasing hormone :
  • stimulates release of follicle stimulating hormone and luteinizing hormone
• Prolactin releasing hormone
  • Anterior pituitary synthesis of prolactin.
• prolactin inhibitory hormone.
  • inhibits synthesis and secretion of prolactin.

Posterior Pituitary Hormones

• Connected to the hypothalamus via the hypothalamo-hypophyseal tract (bundles of axons and myelin sheaths).
• There are two posterior pituitary hormones: ADH and oxytocin.

ADH

• Synthesized in the supraoptic and periventricular nuclei in the hypothalamus.

• Transported via axonal streaming down the axons through the hypothalamo-hypophyseal tract, and stored in secretory vesicles in the posterior pituitary.

• Hypovolemic osmoreceptors monitor osmolality of body fluids (normal ~300 milliosmols).

• Increased body fluid osmolality activates the supraoptic paraventricular nuclei, which send action potentials down the hypoaldalinal hypophyseal tract, causing secretion of ADH from the posterior pituitary.

• ADH has two receptors: V1 and V2.

  • V1 receptors are found in vascular smooth muscle and cause vasoconstriction.
  • V2 receptors are found in the kidneys; increase permeability of medullary collecting ducts to water, increasing water reabsorption.

Oxytocin

*Synthesized in the superoptic paraventricular nuclei:
* transported in vesicles and the hypophsel tract for storage and release later at pituitary.
* Stimulation of secretion = uterine contraction of nipple stimulation.

• Once secreted = increased uterine contractions for delivering of fetus.
• Addition cause smooth contractions of the mammary glands to promote milk expression.
• Prolactin: promotes production of the milk.
• Oxytocin favors expression of the milk.
• Oxytocin: Recently describe as the trust hormone (mother/child relationship)

Other Hypothalamic Functions

• Autonomic centers (swallowing center).
• Temperature regulation.
• Hunger and satiety centers.
• Coordinates with the reticular activating system in regulating sleep-wake cycles.

Cerebral Hemispheres

• Reasonably symmetrical.

• Key Structures

• Longitudinal fissure (separation between hemispheres)

• Precentral gyrus (primary motor cortex)

• Postcentral gyrus (primary sensory cortex)

• Central sulcus (separates frontal and parietal lobes)

Lobes of the Brain

*Frontol
* Located at the very front of the head.
* prefrontal at the very anterior surface of the head

• parietal

• occipital (all the way in the back)

• Central sulcus. (separation).

  • Seperates the frontal lobe from teh parietal lobes.

Functions of the Cerebral Lobes

• Frontal lobes: Key location on preccesntral gyrus == motor cortex.

• There is no anatomic seperation between parietial and occiptal loabes == functional. * Lateral Fissure: Separates temporal lobe from rest of brain.

  • Functional Coding: Based on function, MRIs are used to better understand function of all areas of brain

Frontal Lobes

• Prefrontal lobes are larger in humans than any other animal.

  • Key in play for complex behaviors.

• Subcomponents of the Frontal Lobe:

  • Broca area Premotor area at frontal (location primary motor cortex)

• Perfroantal Areas:

  • Larger in humans other for any other animal on heart.

  • key for personality. Decission mkain,

  • Social behavior moderated. Ppl whoa re damage can no make moderal behavior

Premotor Dominance

• Left prefrontal dominance:

  • very well oraganized high maths
  • type a ocd.

• Right prefrontal Dominance

  • Artsy farts. People who make us laugh.
  • Make movies with lots of abstract thibnkaoing. Not well organized at times.

• Those with damage cannot moderate social behavior.

Primary Motor Cotex

• Found In fromntal lobe (pre-central gyurs.)

  • Sub coponent is the motor speeach area. called BOCA area.

• Primanry motor cortex.

  • Oring of our descending motor pathwasy. (inncerationskeltla msucles.)
  • Also origi of hte uppder motor nuruons.
  • Upper motor neurions travles dpown spinal cors and synpses with lwoer motor nuerons to eventaully ivvervate ske,tlaal msucles.

Primary Motor Cortex vs Premotor

• Premotor Area:
  *Muscles mvoemnts are. Pre planned ore segquenced.

• If somthing ot oick it u = then premotor area preserquecne hte msucles mvoemnt order and send infor ot pirmay otcro cortex.

• Muscle mvoment is pre planned per ognaized and pre sequenced. and then sen to priamrto cortex and sketal muslces move

• Primary mortot cortex: left will control hte muscles mvoemnt on the side of hte body
  Because of th esprmidial ducations. at nteero inferior pat of medula

Mortor HOminculas (Sepration hsemisher )

• ooking at elft hsmishet and off to primay motor cortex, l. Anteeiro paat and precentra gyriss.
  • Later = ouer lateral of cereval
    medial == longitudal fisure.

Homunculas chart

• What is lcoated at pre central guirs and primay motor cortes
• We know w hichat area of hte pyrtmraial cortext inveravtesvarious tissue.
  * The greated number the of muscel goruo re om in the prmydaial cotrtex == the mt finely cntroled movemnet eh parts of the obydy can acgievied. == phranyzs lots of romm becaue se cplex movements.
  * Lrge tonyu can do ots of thing in terums fo chwin an spreakind and cconmtucaintign.
• Medial: Lower hallof the body.hipknee anukes feet and hoes. upperbody latral faceandd hand

Cerebral Movement Sequence. Complex

*Anterior front lobes. inititlal pLaniin motivation for ehough
* the sneds to premotor area. desciess hwich muscles to conract and roder. in whihc they will contaft
* the snes messages to the mototr cortex
* descnetding pota ways and smesucls mvoemvnt .

Pariteal Lobpes

*Senesations up to prmaueseny cotrtex that itialiterpreat and lciseal whate is sensated.
*Seneses area cpomses snes with previouos. and see it simpotant and reopsnes.
*Comparsion with exprecieces adjust based on importnacse whtehr pay attneion iot.

Sensory Homonuclas. (parati lobes)

*Looking at post central gyus pariatr lobe
*Anatietrior perspectiv
* Laeral medial * the more senrseopto the odbyo the mor spacne n prmoary sesonr otxet.
* pParitcualry hte lips ehteteh and gumsm lots of receoto. so lots fo spacew.
Highly protecerdt medially. = geanitls.

Occipital Lobes

*Lcotation on most posteerio aspect of cortx
* The primary visual cortex locatied at back of ocptipla lobe, and anterio to it is teh visual association area.

• No specaifiic aanotmoic demcarstion just based on function and fmis
  Prmay visual cotexp and inotilaitl sent innput.

• Cranial enver 2. send imput from rods and cones and images een but not intpreted or underts.

• It goes toe visaul asociatin aera, and campred it wiht previous. and determins importacne and treansit otrh areas.

. sequence ot eent sto ing awod understanndting it, eht en spreakenig it. (to read).

Seeing the Imaged and Understandning it sequence:.

• image prpted onrods and cones, and snes cranual nrver 2
  • priam visual otc tex where it is see.
  • visual assocation ater = it an word and eht sneds tot werntikes .
    *Weerntkes arae.
  • Paretal lobes.wher inovidla wirs are intered adned and sequeceod so can understand ogcal thought.
    Choss eh words youre gnon to spraek.
  • Seuence ot eh worees toue gonn say and snedt to broac area..
    Bora acrae.
  • Subo mpopnte of premotr arae. Pre sequences and organizaes and plane muscles mvomnets and send to motr cortex an dinervated by muscles.
  • Lateral aspect of cerebral cortext is where hte msucles involved will be at and not medial
    infactiaong worntkes.
  • receptive or express aphasa and htou ahve ehte express and treceptov are ehte receoptve eht wored and suenng.
    boarc area. can pre seqcuece motpr mvomnest will be jumblied and uniintelbgbal.

Tempora lobesaudtory.

Audotry Crottex

*Lacte hte rpimay auldtory cot rex and audorty assiicato are withal
Primay aldtory cot cex. sound throguh cranenrve 8 orinitlat setn.
* Detmiens the oitc and otlum,
Ausotry asiacat areacpmpesound iwht orevuis and othe pat and what the rspone shoud be.
See a word undernd and then. skprk owordds.
sound it traesnted cranal nerve eiht a sounds are sent and voluime
*audoat ry
* Ah word i an gone and ssen t to Wernkcs arai i. idendnfy sequeence and spraek ot sent or brocat anfd broacr ot ptmoarty otcotex. and ot skelto msucles.

Basa Nucli

• Ol term = bassla ganglia is incorrect bdcau eanglia 8a peitohreal strucut.

• subasta nigra:
  Is origin of nigrosty trail . synapeses hte audate ucleus.
  also compto the globes.

• corpus striaut.
  Lentrifomr ncuelus copmes ot global palidusd e the butamen

How Brain Movement is coordinated,

• pirmay mott cotrex: skeltal msucles e th eucnosious lever.
  • to prpovide smooth ocrdinted mvomknet.

Three pathways the brain uses

nigrot stratral trat from substata nigrt. to audtae. the transerter relea.sed at udtae nculeus rorm negrtor stratial tac is dopamibe .
Dopamine. idnerty to the audit acleus
glabau paridrus to audtear nues. the nrsoteo rtnsamr is glulitmtae.
*gltatmte i xeiatoty to hte cauidate ncule.
primnar torot cortex. to auide ncoleus aettlyone. acethyholcine the exiatorty to to eh udtae acleus
cauidate nuesus receivng. Exiatatory r mpuses.
Delicate baclanee. btw. ex iatoty
Impules the adedlatice balance. betw exito atotry an. Indityo tprovice smoth cdianrted movemnts otlse of ere is imalce and can lead tmovemng.

Parlinsons diseseaa

Themisn gin domapine or rpcoet no the cautdatee nuclues are nor resoninng.

• We hv eto gave the. lo dpoat t ecdacue i cpassaes. blood barrar bais and cpverted to the dmpamieb
  And restorer e bacnale becs of the pyramdel derussaiton.
  l dpt cross the barrir and convetes ot dopamiek to restore bachlanec btw exiatoatoy d and m
• tremrs at re st nintenaiuon termrks,
  pill roiling acterint gopnatation snd supinanot of hand s.

lrts agtes go td o sothetningt ehte tor goes ahay. . stoop pdosotoure e unstead gait
moer and woirse beddden d and subocunt

Limbicl stystwm (emotions) (Long term membrps)

Afects the emotioonal rspes to to htereinvorndent
* role in mtivation l term mer.morem. but not areed po. strucut.
soturt

Limbicl system Sub Structure.
Singuita gyi
* sitting ov er croop caloso,. corpuse allosums: ttcaks ocnting
hopcompuas:
* play. trole term memory memors storred all ng the embes iunved in embess
tel peotple stydying. be hapo o. adn evryting becase it rintsg ckakc.
anteterio
habenucleurs nucleus involved 8nemoti al dn visceral responsesd to ordrs.l
memmilleary boise: plynumanseulity (mammrlaru boiss
olflaroy bulb and the cortx the fonix .

OVerall LImbicl system Functions

The limibcl sistr == detrmines the emoitional repsone.
Detmines emotioal visceral rspne
detrmines. moitivaton moud
Appetiote. anget a los of abiloty toget angerr (wont gt amnger0 and fear(won be afraid of anything).

Carebellum == The LTitlle brarin

A play importatnntr trole in otor cotol (ucnicuss lveel )
payl and lator the ucunsoui. slves skeletla msucles

: is ressnolay suymmtaitcla. cerebllum. doesit ivoatred mvoem,mten = controntteso coordinat and acraic and accuagte timing

serves as acomaoactr and cpmayres the

Key Steps For Function

• motor cortx primary = actiuatrs th ehdssnendinnmototr
  and nmotr
  send all

  • spinal crod

• e. sends collateral fro ot cerebellum. toknow hte obydy wanna dp
  infmrs cerebullma for desriee dmsucle movem,nt
  pht to gogi etnoo body = seds poprio to cerebellum.

a alpha iberrd.
What hte anin wated too with. what th euscles s auclly did based pootpri
l and try iger connrruance d d cporot smotl mtvomnemnte

a a 1 red nuculeuse:
activate rubro spinal trac (cat).

• send emssasgtehtrlmuls tpo primo motro otxex os rto braom tpo make atjust,
  cerebral lesions = iteneitntor trmoaes (brain telling and msucels.not dping0