Human Anatomy & PhysiologyNinth Edition

C H A P T E R

© 2013 Pearson Education, Inc.© Annie Leibovitz/Contact Press Images

The CentralNervous System:Part 3 –CSF, BBB, CVA

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Brain Video

• Neurotransmitters – Noradrenalin, serotonin, dopamine and endorphins

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Cerebrospinal Fluid (CSF)

• Composition– Watery solution formed from blood plasma

• Less protein and different ion concentrations than plasma

– Constant volume

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Cerebrospinal Fluid (CSF)

• Functions– Gives buoyancy to CNS structures

• Reduces weight by 97%

– Protects CNS from blows and other trauma– Nourishes brain and carries chemical signals

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Choroid Plexuses

• Hang from roof of each ventricle; produce CSF at constant rate; keep in motion – Clusters of capillaries enclosed by pia mater

and layer of ependymal cells

• Ependymal cells use ion pumps to control composition of CSF and help cleanse CSF by removing wastes

• Normal volume ~ 150 ml; replaced every 8 hours

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Figure 12.24b Formation, location, and circulation of CSF.

Ependymal cellsCapillary

Connectivetissue ofpia mater

Sectionof choroidplexus

Wastes and unnecessarysolutes absorbed

Cavity ofventricle

CSF forms as a filtratecontaining glucose, oxygen, vitamins, and ions(Na+, Cl–, Mg2+, etc.)CSF formation by choroid plexuses

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Figure 12.24a Formation, location, and circulation of CSF. Slide 1

Superiorsagittal sinus

Choroid plexus

InterventricularforamenThird ventricle

Cerebral aqueductLateral apertureFourth ventricleMedian aperture

Central canalof spinal cord

(a) CSF circulation

1 The choroid plexus of each Ventricle produces CSF.

2 CSF flows through the ventriclesand into the subarachnoid space via the median and lateral apertures.

3 CSF flows through the subarachnoid space.

4 CSF is absorbed into the dural venous sinuses via the arachnoid villi.

Arachnoid villus

Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater

Right lateral ventricle(deep to cut)

Choroid plexusof fourth ventricle

1

4

2

3

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Figure 12.25 Hydrocephalus in a newborn.

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Blood Brain Barrier

• Helps maintain stable environment for brain

• Separates neurons from some bloodborne substances

• Composition– Continuous endothelium of capillary walls– Thick basal lamina around capillaries– Feet of astrocytes

• Provide signal to endothelium for formation of tight junctions

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Figure 11.3a Neuroglia.

Capillary

Neuron

Astrocyte

Astrocytes are the most abundant CNS neuroglia.

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Blood Brain Barrier: Functions

• Selective barrier– Allows nutrients to move by facilitated diffusion– Metabolic wastes, proteins, toxins, most drugs, small

nonessential amino acids, K+ denied– Allows any fat-soluble substances to pass, including

alcohol, nicotine, and anesthetics

• Absent in some areas, e.g., vomiting center and hypothalamus, where necessary to monitor chemical composition of blood

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Homeostatic Imbalances of the Brain

• Traumatic brain injuries– Concussion—temporary alteration in function– Contusion—permanent damage– Subdural or subarachnoid hemorrhage—

may force brain stem through foramen magnum, resulting in death

– Cerebral edema—swelling of brain associated with traumatic head injury

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Blood Flow to the Brain

• Brain requires more blood flow and oxygen

• Receives 15 – 20% of body’s blood flow

• Uses 15 – 20% of body’s oxygen

• Superficial temporal artery• Maxillary artery• Occipital artery• Facial artery• Lingual artery• Superior thyroid artery

Ophthalmic artery

Larynx

Thyroid gland(overlying trachea)Clavicle (cut)

BrachiocephalictrunkInternal thoracicartery

Basilar artery

Vertebral artery

Internalcarotid artery

SubclavianarteryAxillaryartery

(b) Arteries of the head and neck, right aspect

Externalcarotid arteryCommoncarotid artery

ThyrocervicaltrunkCostocervicaltrunk

Branches ofthe external carotid artery

Figure 19.22b Arteries of the head, neck, and brain.

Figure 19.22d Arteries of the head, neck, and brain.Frontal lobe

Optic chiasma

Middlecerebral artery

Internalcarotid arteryMammillarybody

Temporallobe

Occipital lobe

Cerebral arterialcircle (circle of Willis)

• Posterior cerebral arteryBasilar artery

Vertebral artery

Cerebellum

• Posterior communicating artery

(d) Major arteries serving the brain (inferior view, right side of cerebellum and part of right temporal lobe removed)

Pons

• Anterior cerebral artery

• Anterior communicating artery

Posterior

Anterior

Figure 19.22c Arteries of the head, neck, and brain.

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Homeostatic Imbalances of the Brain

• Cerebrovascular accidents (CVAs or strokes)– Ischemia

• Tissue deprived of blood supply; brain tissue dies, e.g., blockage of cerebral artery by blood clot

– Hypoxia• condition in which inadequate oxygen is available to tissues

– Hemiplegia (paralysis on one side), or sensory and speech deficits

– Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia

– Tissue plasminogen activator (TPA) is only approved treatment for stroke

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Homeostatic Imbalances of the Brain

• Degenerative brain disorders– Alzheimer's disease (AD): a progressive

degenerative disease of brain that results in dementia

• Memory loss, short attention span, disorientation, eventual language loss, irritable, moody, confused, hallucinations

• Plaques of beta-amyloid peptide form in brain– Toxic effects may involve prion proteins

• Neurofibrillary tangles inside neurons kill them• Brain shrinks

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Homeostatic Imbalances of the Brain

• Parkinson's disease– Degeneration of dopamine-releasing neurons

of substantia nigra– Basal nuclei deprived of dopamine become

overactive tremors at rest– Cause unknown

• Mitochondrial abnormalities or protein degradation pathways?

– Treatment with L-dopa; deep brain stimulation; gene therapy; research into stem cell transplants promising

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Homeostatic Imbalances of the Brain

• Huntington's disease– Fatal hereditary disorder– Caused by accumulation of protein huntingtin

• Leads to degeneration of basal nuclei and cerebral cortex

• Initial symptoms wild, jerky "flapping" movements

• Later marked mental deterioration• Treated with drugs that block dopamine effects• Stem cell implant research promising

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Brain Video

• Shows effects of stroke and repair

• Formation of new synapses

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Physiology of Addiction

• Definition

• Psychological or Physiological?

• Kinds of addictions?

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Day in the Life of Nicotine Junkie• 1 st Cigarette/chew of

the day– Nicotine = ACh– Stimulates release of

hormones Epi and NE– Lasts 30 min

• 2nd, 3rd, 4th cig/chew– Stimulates release of

hormone cortisol– Then NT dopamine

and glutamate– Lasts 30 min

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Why is Nicotine Addictive?

• ↓ ACh

• ↑ # Nicotinic of Receptors

• So what?

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Physiology of Depression

• Definition

• Psychological or Physiological?

• Causes?– Environmental and neurotransmitters

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Physiology of Depression• ↓ in NE and/or

Serotonin• Due to?????• Treatment – dual

approaches – MAO Inhibitors

(monoamine oxidase)– Tricyclic

antidepressants– SSRI (serotonin

specific reuptake inhibitors)

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What about anxiety?

• What system creates anxiety?

• Treatment– Valium (diazepam), Ativan (lorazepan), Xanax

• Rohypnol – date rape drug is in the same family of drugs as Valium, Ativan

• Barbiturates (penobarbital) bind to GABA receptor – opens chloride channels which cause hyperpolarization

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