Download Notes - Pierce College

Pierce College
Putman/Biol 241
UNIT 9 NOTES: CNS
BRAIN DEVELOPMENT
1.
2.
3.
NS derived from ectoderm under influence of notochord; notochord triggers formation of neural crest.
Neural crest is invagination of ectoderm, moves inward then fuses together, forming a hollow tube. The lumen
of the tube (dorsal hollow nerve cord) eventually develops into ventricles of brain and central canal of spinal
cord; the tube itself develops anteriorly into the brain and posteriorly into the spinal cord.
Neural tube first develops into three primary vesicles (prosencephalon, mesencephalon, rhombencephalon), that
then form five secondary vesicles:
a. Prosencephalon (= forebrain)
1) Telencephalon (secondary vesicle I): Consists of cerebral hemispheres, which form the walls of the
lateral ventricles (ventricles 1 & 2).
2) Diencephalon (secondary vesicle II): Consists of thalamus, hypothalamus & epithalamus, which form
the walls of the third ventricle
b. Mesencephalon (= midbrain)
1) Mesencephalon (secondary vesicle III): Has same name as primary vesicle, forms the walls of the
aquaduct of Sylvius.
c. Rhombencephalon (= hindbrain)
a. Metencephalon (secondary vesicle IV): Consists of the pons and cerebellum, which form the walls of
the upper portion of the fourth ventricle.
b. Myelencephalon (secondary vesicle V): Consists of the medulla oblongata, which forms the walls of
the lower portion of the fourth ventricle.
BRAIN (CNS) ANATOMY: WHITE & GREY MATTER
1.
2.
White matter is deep in brain (superficial in spinal cord).
a. Contains well-developed glial (neuroglia) & support cells including astrocytes & oligodendrocytes. The
oligodendrocytes create the myelination in the CNS.
b. No synapses in white matter, thus nerve impulses are conducted here, not transmitted from cell to cell!
Grey matter is superficial in brain (deep in spinal cord), only a couple of mm thick!
a. Glial cells are poorly represented.
b. Lots of synapses in grey matter, thus nerve impulses are transmitted from cell to cell. Note that intelligence
is a function of numbers of synapses, not brain size or number of brain cells.
c. To increase intelligence (numbers of synapses):
1) Mental stimulation & problem solving in diverse fields
2) Lean proteins or proteins with beneficial fatty acids
3) Omega-3 fatty acids, from embryonic stage through life span.
4) Kids from families who have access to (can afford) such a diet have higher IQs than kids who do not
have access to such diets.
d. Folding of grey matter increases surface area & thus numbers of synapses. Gyri are the folds in the grey
matter, sulci are the indentations between gyri.
BRAIN ANATOMY: CEREBRUM (Telencephalon)
1.
General Anatomy.
a. Largest part of brain.
b. Longitudinal fissure divides cerebrum into lateral lobes; corpus callosum joins lobes internally.
c. Lateral lobes divided into: frontal, parietal, temporal & occipital lobes.
d. Cerebral cortex: Outer layer, ~ 2-3 mm thick; composed of grey matter, folded into gyri.
e. Cerebral medulla: Inside, composed of white matter.
Putman/Pierce College Bil 241 09 notes/20150811/Page 1
2.
3.
Cerebral Cortex (Grey Matter)
a.
Divided (with general functions) into four lobes per hemisphere:
1) Frontal lobes.
a) Primary motor cortex: somatic motor function
(1) Homunculus map
b) Broca’s area, left hemisphere
(1) Prepares for speech
(2) Speech muscles
c) Advanced problem solving
d) Cognition & personality.
e) Working memory
2) Parietal lobes
a) Primary sensory cortex: General sensory processing
(1) Homunculus map
b) Reading and speech interpretation
c) Wernicke’s area (L)
(1) Reading and speech interpretation
(2) Found on both parietal & temporal lobes
3) Temporal lobes.
a) Werneke’s area (w/ parietals)
b) Primary auditory cortex
c) Primary olfactory cortex—cranial nerve I connects here
d) Gustatory cortex
e) Memory recall: Hippocampus
4) Occipital lobes.
a) Primary visual cortex
b.
Hemisphere Lateralization
1) Right & left hemispheres are not functionally symmetrical!
a) Results from PET/PET
2) Right Hemisphere Functions: “The arts & senses”
a) Somatic sensory input from left side of body
b) Somatic motor output to left side of body.
c) Music & art abilities/perceptions, including space & pattern perception.
d) Emotion, including the recognition of emotions on faces & association of emotion with language.
e) Facial discrimination & recognition.
f) Mental imaging
g) Odor discrimination & identification.
h) Handedness?
3) Left Hemisphere Functions: “Analysis & language”
a) Somatic sensory input from right side of body.
b) Somatic motor output to left side of body.
c) Reasoning & logic.
d) Analytical skills; mathematics.
e) Language—spoken, written & sign language.
f) Handedness?
Cerebral White Matter (Cerebral Medulla)
a. Composed of tracts = axon bundles in CNS (equivalent to nerves in PNS). Tracts make up most of brain.
1) Association Tracts. Connect gyri to same hemisphere.
2) Commissural Tracts. Connect gyri between the two lateral lobes:
a) Corpus callosum (the major commissural tract)
b) anterior commissure (a minor tract) and
c) posterior commissure (a minor tract).
4) Projection Tracts. Connect gyri with lower parts of brain or spinal cord.
Putman/Pierce College Bil 241 09 notes/20150811/Page 2
a) Corona radiata is a crown-like structure formed from vertical divergence of projection tracts out to
cerebral cortex.
b.
Basal Nuclei (Basal Ganglia). System of nuclei deep within cerebral hemispheres.
1) Include
a) Lentiform nucleus, which is the putamen (lateral) and globus pallidus (medial to putamen),
b) Caudate nucleus, which is long and tadpole-shaped, and
c) Amygdala (amygdaloid nucleus), which is functionally part of the limbic system.
2) Connections. Basal nuclei connected to one another; receive input from cortex (which surrounds
structure); sends output to motor control regions of cortex through the thalamus (which is located
medial to basal nuclei).
3) Function.
a) Beginning and ending of muscle movements and some cognitive functions (memory, attention,
planning).
b) Regulates rhythmic movement.
c) Inhibits unnecessary movement.
d) Begins/ends some cognition
e) With limbic system to control emotions.
BRAIN ANATOMY: DIENCEPHALON
1.
2.
3.
The diencephalon is the central part of forebrain (prosencephalon);
a) Connects the cerebrum to midbrain and consists of the hypothalamus, thalamus, and epithalamus.
THALAMUS
a. Anatomy: Makes up most of diencephalon. Consists of two lateral lobes of grey matter connected by the
interthalmic adhesion (intermediate mass). Cranial nerve II connects to thalamus.
b. Functions:
a) Relay center to and from cerebrum and between L & R cerebral hemispheres—allows for
communication between two sides of cerebrum.
b) Control functions. Nuclei exist in the thalamus that
1) Integrate & evaluate all sensory input into cerebrum—sensory input may be passed on or
terminated
2) Regulates mood & emotion, in association with limbic system & hypothalamus
HYPOTHALAMUS
a) Located on top of the midbrain; “caps” the midbrain
1) Connects cerebrum to midbrain
2) Infundibulum of the pituitary attaches to hypothalamus inferiorly.
b. Contains 12 nuclei, the most obvious of which are the paired mammillary bodies. The mammillary bodies
are olfactory reflex sites. The primary function of the nuclei is the control of the visceral regions of the
body. Specific functions of hypothalmic nuclei include:
1) Control of ANS. Axons connect hypothalmic nuclei to brain stem & spinal cord, regulating
sympathetic and parasympathetic activities.
2) Control of Endocrine System.
a) Two hypothalmic nuclei have axon bulbs in posterior pituitary where they release two hormones:
oxytocin and antidiuretic hormone (vasopressin).
b) Hypothalmic nuclei secrete releasing hormones into hypothalmic-hypophyseal portal, a direct
blood route to the anterior pituitary, where they control the release of anterior pituitary hormones.
3) Regulation of Emotion Perception & Response. Nuclei in hypothalamus, in association with the lymbic
system, perceive emotions (pleasure, fear, anger, rage, etc.), and respond to emotions through the
ANS—for instance, the emotion of fear elicits sympathetic responses.
4) Regulation of Circadian Rhythms. The timing of the sleep cycle, as cued by daylight/night cycles, is
set by hypothalmic nuclei.
5) Temperature Homeostasis. Blood thermoreceptors exist throughout body & in hypothalamus itself. If
it’s too cold, the hypothalamus triggers shivering; if it’s too hot, the hypothalamus triggers sweating.
6) Osmoregulation of Blood. Osmoreceptors in the hypothalamus detect blood osmotic levels. If blood is
too concentrated (too salty, not enough water), antidiuretic hormone is secreted (from posterior
Putman/Pierce College Bil 241 09 notes/20150811/Page 3
pituitary) causing kidneys to retain water; the thirst center in the hypothalamus is also triggered,
causing desire to drink water.
7) Hypothalmic nuclei monitor blood levels of nutrients (eg. glucose, amino acids); low nutrient levels
trigger hunger response.
4.
EPITHALAMUS
a. Dorsal-most part of diencephalon; forms roof of third ventricle.
b. Pineal Gland in posterior epithalamus. Pineal secretes melatonin, which triggers sleepiness. Together,
hypothalamus & pineal gland trigger sleep.
BRAIN ANATOMY: THE BRAIN STEM
1.
2.
3.
Consists of the medulla oblongata, pons and midbrain (cerebellum is functionally considered apart).
Most primitive/fundamental part of brain; all basic life support controlled here.
Relay center: Connects spinal cord with diencephalon
4.
MIDBRAIN
a. Connects to pons & diencephalon; cranial nerves III & IV come from midbrain.
b. Relay center.
c. Control centers
1) Corpora Quadragemina. Located on posterior aspect of midbrain (not in a ventricle). Consists of four
bodies.
a) The two superior colliculi contain nuclei coordinating head & eye movements associated with
scanning stationary objects & tracking moving objects.
b) The two inferior colliculi contain startle reflex nuclei, nuclei that cause your head to jerk when
you hear a loud noise. It also relays signals from hearing receptors of ear to thalamus.
2) Substantia Nigra. Contain nuclei that are involved in maintaining muscle tone & coordination via
dopamine secretion. Parkinson’s disease linked to degeneration of the dopamine-secreting nuclei of the
substantia nigra.
3) Red Nuclei. Contain nuclei controlling unconscious motor activities.
5.
PONS
a. Between medulla & midbrain.
b. Mostly a relay center.
c. Control functions work with medulla to help control breathing.
Note: Cranial nerves V to VIII attach to pons. (CN VIII attaches to both pons & medulla)
6.
MEDULLA OBLONGATA
1) Connected to spinal cord inferiorly and pons superiorly.
2) Relay center function. White matter. All sensory tracts from spinal cord go through here to rest of brain and
all motor tracts from brain to spinal cord go through here.
5) Pyramids of Medulla Oblongata. Anterior bulges formed from largest motor tracts.
6) Decussation of Pyramids—where 90% of motor tracts cross just superior to spinal cord; explains why
left brain controls right side of body and visa-versa.
7) Olives of Medulla Oblongata. Lateral to pyramids, relay proprioception from muscles & joints to
cerebellum.
c. Autonomic control function. Occurs in “centers” formed from neuron nuclei. Nuclei are groups of nerve
cell bodies (ganglia).
1) Cardiovascular Center: Nuclei controlling heart rate and force of heart beating, and BP via
vasoconstriction/vasodilation.
2) Respiratory Center: Nuclei controlling breathing rate, depth and rhythmicity. Rhythmicity is controlled
in conjuction with the pons.
3) Other centers in medulla contain nuclei controlling coughing, sneezing, hiccuping, swallowing,
vomitting.
Note: The hypothalamus initiates many of the above autonomic responses; the medulla oblongata carries them
out.
Putman/Pierce College Bil 241 09 notes/20150811/Page 4
Note: Cranial nerves VIII to XII attach to medulla.
7.
BRAIN ANATOMY: CEREBELLUM
a.
Ipselateral connections to midbrain via
1) Cerebellar peduncles connect cerebellum to brain stem and have relay function only. Note that
they are ipsilateral connections (not contralateral), meaning the nerve tracts entering the cerebellum
don’t cross! Right side of cerebellum controls right side of body, etc.
a. Flocculonodular lobe. Found on inferior surface; contains nuclei regulating posture, equilibrium & balance.
Receives input from semicircular canals, utricle & saccule.
b. Arbor vitae: Cerebellar medulla. Mylenated tracts shaped like a tree.
c. Folia: Cerebellar cortex. Outside, grey matter, deeply ridged into folia.
d. Cerebellar Processing: “Advise and concent.”
1) Cerebrum sends signal to cerebellum that cerebrum wants to effect some sort of an action involving
skeletal muscles.
2) Cerebellum also receives sensory input from proprioceptors, retina and utricle/saccule, semicircular
canals of inner ear.
3) Cerebellar cortex evaluates information and determines which muscles to contract/relax and extent of
contraction/relaxation to achieve goal.
4) Cerebellum sends recommendation on how to proceed to cerebrum via superior cerebellar peduncle.
Note: Cerebellum sensory & motor map, “homunculus map,” is identical to that of cerebrum.
Note: Recent studies suggest cerebellum may be involved in some cognitive activities such as language use &
solving problems.
BRAIN SYSTEMS
1.
Limbic System. Integrated group of commissures & nuclei, medial to each cerebral hemisphere.
a. Includes diencephalon structures (both thalmic and hypothalmic nuclei—mammillary body, for instance).
1) Connections:
a) Input from lower & higher brain regions.
b) Output through hypothalamus.
2) Functions:
a) Recognition & generation of emotions. Ex. Amygdala recognizes facial expressions exhibiting
anger & fear & generates rage & fear responses.
b) Memory. Specific smells trigger specific memories associated with those smells. Regarding
general memory, the hippocampus accesses memory, the amygdala associates memory with
specific emotions.
c) Psychosomatic Illnesses. Since the output of the limbic system is through the hypothalamus,
emotional stress triggers ANS sympathetic responses.
d) Emotion vs. Logic. Since the limbic system is heavily integrated with the cerebral cortex,
sometimes emotions override logic in decision making, and logic stops us from expressing
emotions at inappropriate times!
2.
RETICULAR FORMATIONS
b. Tracts of mixed myelinated axons and unmyelinated cell bodies; called reticular due to net-like appearance.
c. Extend from diencephalon to spinal cord.
d. Function: forms RAS (Reticular Activating System)
2) Relay center
3) Arousal from sleep
4) Consciousness
5) Filters sensory input that is repetitive or familiar; prevents overloading brain.
Putman/Pierce College Bil 241 09 notes/20150811/Page 5
MENINGES
1.
2.
3.
Meninges are the tissues that surround & protect the CNS (both brain & spinal cord).
There are three meninges:
a.
Dura Mater. Deep to periosteum lining bone of CNS.
1) Epidural space found between periosteum & dura mater. It’s well-developed in the spinal cord,
containing connective tissues including fat that affords protection for spinal cord. Note that this space
is considerably less developed in brain, without connective tissue.
2) Toughest meningeal layer, made of dense-irregular CT.
3) Forms dural sinuses. These are areas where the dura splits, forming cavities or sinuses. The sinuses
drain blood from the skull, join together, and empty into the internal jugular vein. Arachnoid villi
project into the dural sinuses.
4) Extensions of dura mater that separate the lobes of the brain, thus helping to protect them: a) Falx
cerebri—separates cerebral hemispheres, b) falx cerebelli—separates cerebellar hemispheres, and c)
tentorium cerebelli, separates cerebrum from cerebellum.
5) Subdural space exists deep to the dura mater. It contains interstitial fluid.
b.
Arachnoid Mater: Deep to subdural space.
1) Delicate, spider web-like tissue, made of collagen & elastin fibers.
2) Subarachnoid space is deep to arachnoid mater; subarachnoid space contains cerebrospinal fluid
(CSF).
3) Arachnoid villi: Extensions of arachnoid & subarachnoid space (with CSF) into dural sinuses.
c.
Pia Mater: Deep to subarachnoid space; covers brain & spinal cord directly.
1) Thin & delicate tissue, made of collagen & elastin fibers.
2) Denticulate ligaments are lateral extensions of the pia mater, found only in spinal cord. They fuse with
arachnoid & dura, suspending the spinal cord securely in center of spinal column, acting as a shockabsorber.
Recap of cushioning/protection of CNS:
a. Brain protected by
1) Skull bones
2) Meninges, including extensions (falx cerebri, falx cerebelli and tentorium cerebelli)
3) CSF
b. Spinal Cord protected by
1) Vertebrae
2) Meninges, including epidural fat layer and denticulate ligaments.
3) CSF
CEREBROSPINAL FLUID (CSF): FORMATION, FLOW & REABSORPTION
1.
2.
Secreted continually by ependymal cells lining the ventricles & central canal, especially at regions of high
vascularization called choroid plexi.
Choroid plexi
a. Highly vascularized, associations of capillaries & ependymal cells formed into choroid papilli; filtrate
comes from blood through endothelium of capillaries, into interstitial fluid, then into and through
ependymal cells, thus forming a blood-CSF barrier, as there is selection as to what gets into the CSF. (Not
the same as the blood-brain barrier.)
b. Located in ventricles, not in spinal cord.
1) Lateral ventricles (ventricles 1 & 2) are enclosed by the walls of the cerebrum and are separated by the
septum pellucidum. The lateral ventricles are connected to the third ventricle by the interventricular
foramina. The choroid plexus of the lateral ventricles is located at the base of the septum pellucidum,
and extends down through the interventricular foramina on both sides into the roof of the third
ventricle.
Putman/Pierce College Bil 241 09 notes/20150811/Page 6
2) Third ventricle is enclosed by the walls of the diencephalon (thalamus & hypothalamus) and is
connected inferiorly to the aquaduct of Sylvius, also called the cerebral aquaduct. The choroid
plexus is in the superior wall (roof).
3) Aquaduct of Sylvius (= cerebral aquaduct). Enclosed by walls of the mesencephalon (midbrain),
connects inferiorly to the fourth ventricle.
4) Fourth Ventricle. Enclosed by walls of the rhombencephalon (medulla, cerebellum & pons).
Connections: a) Superiorly, connects to aquaduct of Sylvius. b) Inferiorly, connects to the central
canal of the spinal cord. c) Laterally, connects to the lateral apertures and d) posteriorly, connects
to the medial aperture; both the lateral apertures and the medial aperture are the exits for the CSF
into the subarachnoid space.
3.
CSF propelled mainly by systolic pressure waves—induction flow from the cardiovascular system, with minor
contributions by the cilia of the ependymal cells.
a. Flow continues posteriorly down and around subarachnoid space and down through central canal of spinal
cord, to end of spinal cord. Central canal empties into cauda equina region.
b. Anteriorly, flow is brought up, around brain, into the the arachnoid villi, which project into the dural
sinuses. In the arachnoid villi the CSF is reabsorbed back into the blood.
4.
CSF secretion rates must equal reabsorption rates; if not, CSF pressure builds, which can damage CNS tissue.
One result in newborn babies is hydrocephalus—CSF pressure canses skull to expand as skull bone plates have
not fused together yet.
BLOOD BRAIN BARRIER
1.
Physiology.
a. CNS capillaries are most impermeable capillaries in body; very tightly sealed.
b. Astrocyte foot processes wrap around capillaries, secrete substances that regulate permeability of
endothelial cells, thus regulate the composition of the interstitial fluid surrounding brain cells.
2.
Permeability.
a. Size. The basement membrane of endothelium doesn’t let substances > 5000 molecular weight pass; thus,
no proteins, antibiotics, antibodies, many drugs can enter through blood brain barrier.
b. Lipid solubles can pass. These include respiratory gases (oxygen, carbon dioxide), vitamins, fats & fatty
acids, alcohol, nicotine, anesthetic agents, etc.
c. Can pass by facilitated diffusion (via transport proteins and ion channels, all with gradient): glucose,
essential amino acids, most ions (not potassium!).
d. Actively transported out: potassium & nonessential amino acids
e. Prevented from entering: Generally, nitrogenous wastes and things that can be metabolized to form
nitrogenous wastes, as they are highly toxic to brain tissue! These include uirea, uric acid, ammonia,
creatine, nonessential amino acids, and proteins.
CNS ENERGY ISSUES
1.
2.
Brain does not metabolize amino acids/proteins for energy as they produce very toxic nitrogenous compounds.
Glucose is the main energy source, ketones secondary
a. Crosses blood-brain barrier by facilitated transport.
b. Required high levels of oxygen to fully utilize glucose. Aerobic respiration is preferred, as lactate buildup
(anaerobic respiration) makes brain hypertonic; this attracts water, causing brain to swell.
c. High vascularization is required to keep brain supplied with oxygen, to keep brain aerobic. Any blockage to
cerebral arteries causes brain to go anaerobic, creating swelling from lactate buildup. For instance, a loss of
CSF allows brain to settle, compressing arteries—brain goes anaerobic & swells.
Putman/Pierce College Bil 241 09 notes/20150811/Page 7