12-4: The Brain - overview and the brainstem

Question 1

What elements form the protection of the brain?

Answer 1

cranium (bony case around the brain, made of 8 cranial bones); 
meninges (three membranes that surround the brain and spinal cord); 
cerebrospinal fluid (circulates through the CNS in the subarachnoid space)

Question 2

CSF is formed by ___ from clusters of capillaries called ___, found in the four hollow chambers of the brain, called ____.

Answer 2

filtration (high > low pressure); choroid plexuses; ventricles

Question 3

How is CSF formed?

Answer 3

Choriod plexus of the lateral ventricles >

drains through the interventricular foramen into the third ventricle, where more CSF is added >

flows down the third ventral down the cerebral aqueduct into the fourth ventricle, where more is added >

flows out three openings in the fourth ventricle into the subarachnoid space, around the back of the brain and down the back of the spinal cord >

returns up the front of the cord and around the front of the brain >

reabsorbed into veins, especially the superior sagittal sinus

Question 4

hydrocephalus

Answer 4

an obstruction (tumor, birth defect) interferes with drainage of CSF, causing it to accumulate in ventricles. Intracranial pressure rises (and head enlarges if fontanelles are still present). A shunt may be inserted.

Question 5

The brain makes up __% of body weight but uses __% of the body’s O2 supply

Answer 5

2; 20; metabolically the most active organ

Question 6

circle of willis

Answer 6

loop of vessels around the base of the brain allowing a continuous supply of O2 and glucose

Question 7

What feeds the circle of willis?

Answer 7

the basilar artery

Question 8

If blood flow is interrupted for 1 minute: ____; 5 minutes: ___.

Answer 8

unconscious; brain damage

Question 9

blood brain barrier

Answer 9

brain capillaries are the least permeable in the body, allowing some substances to cross from blood to brain cells (O2, glucose), but preventing the movement of many things (toxins, drugs, proteins, creatinine)

Question 10

The blood brain barrier is not effective against ___ molecules. Eg. ____.

Answer 10

fat-soluble molecules (diffuse easily through plasma membranes); eg. alcohol, nicotine, anesthesia

Question 11

The blood brain barrier ___ brain cells from ___ in the blood.

Answer 11

protects; harmful substances

Question 12

What may cause the blood brain barrier to be absent?

Answer 12

brain injury may cause a local breakdown

Some areas do not have a blood brain barrier, such as the vomitting center and hypothalamus

Question 13

What are the four main regions of the brain?

Answer 13

Brainstem
>medulla oblongata
>pons
>midbrain

Diencephalon
>thalamus
>hypothalamus

Cerebrum
>cerebral cortex
>lobes
>grey and white matter
>sensory and motor areas

Cerebellum

Question 14

brainstem

Answer 14

the stalk at the base of the brain that connects it to the spinal cord, consists of the medulla oblongata, pons, and midbrain

Question 15

medulla oblongata

Answer 15

most inferior part of the brain, a continuation of the spainl cord above the foramen magum (about an inch long)

Question 16

The medulla contains all of the ____ that communicate between the spinal cord and higher brain.

Answer 16

ascending (sensory) and descending (motor) tracts

Question 17

pyramids

Answer 17

two triangular ridges on the ventral surface of the medulla

Question 18

Most motor tracts cross over at a point called ____, which is why the right side of the brain controls ____.

Answer 18

decussation of pyramids; movement of the left side of the body

Question 19

What are the autonomic reflex centers found in the medulla?

Answer 19

cardiac center - controls the force and rate of heartbeat

respiratory center - controls the force and rate of breathing

vasomotor center - controls the diameter of blood vessels and blood pressure

Also has centers that regulate vomiting, hiccupping, swallowing, coughing, sneezing, etc.

Question 20

A blow to the base of the skull is often ___, because ___.

Answer 20

fata; the medulla is responsible for many vital activities that maintain homeostasis

Question 21

pons

Answer 21

“bridge”; one inch over swelling above the medulla and in front of the cerebellum. Longitudinal fibers connect the spinal cord to the higher brain and transverse fibers connect the cerebellum with the rest of the brain

Question 22

midbrain

Answer 22

one inch region above the pons, at the top of the brainstem; the cerebral aqueduct passes through here and connects the third and fourth ventricles

Question 23

corpora quadrigemina

Answer 23

4 round bumps round on the dorsal wall of the midbrain

Question 24

superior colliculi

Answer 24

upper pair of the corpora quadrigemina; reflex center for movement of eyes and head in response to visual stimuli

Question 25

inferior colliculi

Answer 25

lower pair of the corpora quadrigemina; reflex center for movement of the head in response to unexpected auditory stimuli (“startle response”)

Question 26

reticular formation

Answer 26

a network of neurons extending through the center of the brainstem, regulating sensory input to the cortex and governing arousal of the brain

Question 27

How does the reticular formation regulate sensory input?

Answer 27

filters all input and ignores 99% of incoming stimuli as unimportant (preventing “sensory overload”) - LSD removes this filter - one becomes aware of all sensory input at once

Question 28

How does the reticular formation govern arousal of the brain?

Answer 28

its neurons connect with other parts of the brain and keep the cortex in an alert, conscious state (RAS - reticular activating system). The RAS is inhibited by alcohol, tranquilizers and the sleep center in the hypothalamus

Question 29

Nuclei of which cranial nerves are associated with the brainstem?

Answer 29

medulla - 8-12
pons - 5-7
midbrain - 3-4

1 and 2 do not have nuclei associated with the brainstem