14 Brain

the brain contributes to homeostasis by (4)

receiving sensory input
integrating new and stored information
making decisions
executing responses through motor activities

major parts of the brain

brain stem, cerebellum, diencephalon, cerebrum

brainstem includes

midbrain, pons, medulla oblongata

Diencephalon includes

thalamus, hypothalamus, epithalamus

the brain is protected by (2)

cranial bones and cranial meninges

What is continuous with the spinal meninges?

cranial meninges

unlike the spinal dura mater, the cranial dura mater \_____--

has 2 layers
-periosteal layer (external)
-meningeal layer (internal)

what are the 2 layers of the cranial dura mater?

-periosteal layer (external)
-meningeal layer (internal)

the 2 layers of the cranial dura mater are fused together except where

they separate to enclose venous sinuses (drain blood and CSF)

no \________ space around brain

epidural

\_____ extensions of dura mater separate parts of the brain

3

3 extensions of dura mater (cranial)

falx cerebri, falx cerebelli, tentorium cerebelli

falx cerebri

separates the cerebrum hemispheres

falx cerebelli

separates the cerebellum hemispheres

tentorium cerebelli

separates the cerebrum from cerebellum

blood flow to brain

internal carotid and vertebral arteries

blood flow away from brain to heart

dural venous sinuses drain into internal jugular veins

when activity of neurons and neuroglia increases in a region of the brain -\> blood flow to that area \_____

also increases

brain circulation is measured by

functional magnetic resonance imaging (fMRI)

why does the brain have such high blood demands

brain tissue needs oxygen and nutrients, specifically glucose, to generate ATP to maintain action potentials and maintain Na+/K+ pump

blood-brain barrier

protects brain cells from harmful substances by preventing substance from blood entering blood tissue

what forms the BBB? (3)

-tight junctions seal endothelial cells of brain capillaries
-thick basement membrane surrounds endothelial cells
-astrocytes press up against capillaries -secrete substances that selectively allow/inhibit substances to pass from blood to neurons

What type of substances cross the BBB easily?

lipid-soluble substances (oxygen, carbon dioxide, alcohol, nicotine, caffeine, and most anesthetic agents)

in BBB, water soluble substances may be \____

transported(glucose)

At what speed do other substances (ions) transport across the BBB?

very slowly

What are some big molecules that do not enter BBB?

antibiotics and proteins

Why are some therapeutics delivered in high concentration of sugar solution?

creates a hypertonic environment (b/c of osmosis) which sends water out, shrinking the cell-\> creates gaps in the tight junctions allowing the drugs to enter through the gaps

cerebrospinal fluid

colourless liquid composed mainly of water that bathes the CNS

what is CSF mainly composed of?

water

What does CSF contain?

contains small amounts of oxygen, glucose, proteins, ions and some WBC

CSF total volume in adults

~80-150 mL

Functions of CSF

mechanical protection
chemical protection
circulation

CSF: mechanical protection

absorbs shock and protects the delicate tissues of the CNS from jolts
-buoys the brain so it doesnt float in the cranium

What buoys the brain so it doesn't float in the cranium?

mechanical protection

CSF: chemical protection

optimal chemical environment for neuronal signalling

CSF: circulation

medium for exchange of nutrients and waste products between blood and nervous tissue

"little cavities" refer to

4 CSF filled ventricles

in each hemisphere, there is 2 \______ ventricles

CSF filled lateral

2 paired ventricles in CSF separated by

septum pellucidum

Third ventricle

along midline superior to hypothalamus and between right and left halves of thalamus

Fourth ventricle

between brain stem and cerebellum

Where is CSF produced?

choroid plexus

Choroid plexus

produces CSF
-capillaries covered by ependymal cells found in the walls of the ventricles

How do ependymal cells secrete CSF?

via filtration of the blood plasma

\___________ secretion controlled by ependymal cells (CSF)

bidirectional

\`ependymal cells are joined by \_______ junctions to make a \_______ barrier

tight
blood-CSF

Where is CSF reabsorbed?

arachnoid villi

arachnoid villi

grapelike clusters of arachnoid that penetrate dural venous sinus

reabsorption rate of CSF

~20mL/hour

reabsorption rate of CSF \= \____ rate

production

Describe the circulation of CSF

CSF produced in choroid plexus -\> lateral ventricles -\> through intervertebral foramen -\> third ventricle (CSF also comes from choroid plexus of third) -\> through cerebral aqueduct -\> fourth ventricle (CSF also comes from choroid plexus of fourth) -\> central canal of spinal cord OR through lateral and medial apertures -\> subarachnoid space -\> arachnoid villi (CSF reabsorbed) -\> heart and lungs

hydrocephalus

blockage of drainage of CSF (tumour, inflammation, developmental malformation, meningitis, hemmorrhage, or injury)

Hydrocephalus: continued production causes an increase in CSF pressure -\>

hydrocephalus

hydrocephalus: in newborns or fetus, the \_________ allow this internal pressure to cause expansion of the skull

fontanels

if hydrocephalus not treated quickly,

fluid buildup compresses and damages nervous tissue

How is hydrocephalus treated?

neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen

brainstem located between

diencephalon and spinal cord

3 sections of brainstem

midbrain, pons, medulla oblongata

brainstem has interspersed \____

reticular formation

medulla oblongata is a continuation of \_____

spinal cord

medulla oblongata contains

ascending sensory tracts
descending motor tracts
nuclei

Nuclei in the medulla oblongata are

integrating centers
send info in and out of cerebellum

Pyramids

ventral surface bulge in medulla oblongata

Pyramids contains

large motor tracts that pass from cerebrum to spinal cord (corticospinal tracts)

Pyramids controls

voluntary movement of limbs and trunk

medulla oblongata: \_________-(crossing) of pyramids

decussation

what is the functional consequence of decussation of the pyramids?

right hand movement is controlled by left brain

Lateral to each pyramid is an oval shaped swelling called \_____

olive

Olive

lateral to pyramids in medulla oblongata
-oval shaped swelling

Olive contains

inferior olivary nucleus

Olive receives input from

cerebral cortex, midbrain and spinal cord

Olive sends input to \____ which \___(2)

-cerebellum
-controls proprioceptive signals
-give precision to movements

medulla oblongata controls many vital body functions (3)

cardiovascular center
respiratory center
reflex centers

cardiovascular center

controls force and rate of heart beat and diameter of blood vessels

respiratory center

sets basic rhythm of breathing(rhythmicity)

reflex centers

coughing, sneezing, swallowing, vomiting, hiccuping

the other nuclei of the medulla (~6)

gracile and cuneate nuclei
gustatory, cochlear, vestibular
nuclei for cranial nerves (viii-xii)

gracile and cuneate nuclei

associated with somatic sensations ( touch, pressure, vibration, conscious proprioception)

gracile and cuneate nuclei synapse with

axons in the ascending tracts in the spinal cord

Gustatory

taste

cochlear

hearing

vestibular

equilibrium

Pons location

superior to the medulla

pons consists of

nuclei and tracts

pons "bridge" connects

the parts of brain with each other via tracts

pons connects right and left sides of \___

cerebellum

pons relays nerve impulses related to \______ from the \____ to the \_____ (both sensory and motor tracts)

voluntary skeletal movements
-cerebral cortex
-cerebellum

pons plays a role in \___ (pontine respiratory group)

breathing

pons contains nuclei from \_____

cranial nerve (V-Viii)

midbrain location

extends from the pons to the diencephalon

midbrain also called

mesencephalon

midbrain contains __which connect 3rd and 4th ventricle

cerebral aqueduct

cerebral aqueduct

connects 3rd ventricle above to 4th ventricle

midbrain contains \____ tracts, \_____ tracts and \______

sensory
motor
nuclei

the nuclei in the midbrain contain \___ and \____ info

sensory and auditory

anterior midbrain

cerebral peduncles

cerebral peduncles contain (midbrain)

anterior
-contain corticospinal, corticopontine and corticobulbar motor axons
-sensory axons that extend from medulla to thalamus

cerebral peduncles contain sensory axons that extend from

medulla to thalamus

Posterior midbrain contains

tectum, substantia nigra, red nuclei, nuclei for cranial nerves (iii and iv)

tectum composed of

4 rounded elevations