chapter 14: cranial nerves Flashcards
what are the main parts of the brain and what do they consist of
- Brainstem ◦ Medulla oblongata, pons, and
midbrain - Diencephalon ◦ Thalamus, hypothalamus,
epithalamus - Cerebrum
- Cerebellum
what are is the brain protected by and how does they spinal meninges differ from the cranial meninges
- Cranial bones
- Cranial meninges
- dura, arachnoid, and pia maters.
▪ Unlike the spinal dura mater, the cranial
dura mater has 2 layers – periosteal layer
(external) and meningeal layer (internal)
▪ Two layers are fused together except
where they separate to enclose venous
sinuses (drain blood and CSF)
▪ No epidural space around brain
what are the 3 dura mater extentions
◦ Falx cerebri – separates the cerebrum
hemispheres. It attaches to the crista
galli of the ethmoid bone
◦ Falx cerebelli – separates the
cerebellum hemispheres
◦ Tentorium cerebelli – separates the
cerebrum from cerebellum
why are oxygen and glucose so important for the brain
20% of oxygen & glucose in blood gets used by brain
Good supply of O2
and glucose is vital to brain function
◦ no glucose stores in brain
◦ low level of O2 or glucose in blood leads to confusion,
dizziness, unconsciousness
◦ 1–2-minute interruption leads to impaired function
◦ > 4 minutes = permanent damage
brief slowing can cause disorientation or lack of consciousness
which ways does blood in the brain flow. what makes blood flow increase
lood 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 → flow to
that area also increases
what does the blood brain barrier do and what are the 3 things that form the blood brain barrier
Protects brain cells from harmful substances
by preventing substances from blood entering
brain tissue
Three things form the BBB:
1. Tight junctions seal endothelial cells of
brain capillaries
2. A thick basement membrane surrounds
endothelial cells
3. Astrocytes press up against capillaries –
secrete substances that selectively
allow/inhibit substances to pass from
blood to neurons
what substances can and can not cross the blood brain barrier
Lipid-soluble substances cross easily (i.e. oxygen,
carbon dioxide, alcohol, nicotine, caffeine, and
most anesthetic agents)
Water-soluble substances may be transported
(i.e. glucose)
Other substances are transported across very
slowly (i.e. most ions)
Big molecules (antibiotic drugs, proteins) do not
enter at all
what is cerebrospinal fluid and what is it’s function in the brain
Clear liquid containing glucose & O2
and other chemicals essential to neurons
and neuroglia
Functions
◦ mechanical protection
◦ softens contact/impact with skull, and makes brain float (reducing weight)
◦ chemical protection
◦ regulation of pH and other ions concentration
◦ circulation
◦ Clearance of waste products into the bloodstream
where is CSF contained in the brain
2 lateral ventricles (one of each cerebral hemisphere)
interventricular forman, third ventricle alond midline between right and left halves of thalamus
cerebral aqueduct and fourth ventricle between brainstem and cerebellum
what is the choroid plexus
a network of capillaries in walls of ventricles covered by ependymal cells
ependymal cells make the CFS by filtration of blood plasma
Ependymal cells are joined by
tight junctions, so substances
from blood MUST go through
cells before they enter the
brain ventricles
describe circulation of CFS
- flows from lateral ventricles to 3rd ventricle via interventricular foramina
- next through cerebral aqueduct to 4th ventricle (through midbrain)
- then into subarachnoid space through median and 2 lateral apertures in 4th ventrcile
- into the central canal of the spinal cord and subarachnoid space of the cord and brain (purple arrows)
hydrocephalus
when CSF production exceeds reabsorption
◦ accumulation of fluid in brain (swelling)
◦ in newborn or fetus, fontanels allow expansion of skull
◦ implantation of shunt can redirect CFS to veins
◦ in adults, skull can’t expand so swelling can lead to rapid death
Cerebral spinal fluid is produced in which
structure(s)?
a) Choroid plexuses
b) Cerebral aqueduct
c) Arachnoid villi
d) Median aperture
e) All the above
a) choroid plexus
Which of the following statements is true about the
blood-brain barrier and blood-CSF barrier?
a) Both involve astrocytes
b) Both involve tight junctions
c) Both involve ependymal cells
d) A and B
e) B and C
b) both invlove tight junctions
what is the brainstem and what are the 3 sections
The brainstem is the part of the brain between the diencephalon and the spinal
cord
3 sections:
◦ Medulla oblongata
◦ Pons
◦ Midbrain
describe the medulla oblongata of the brain stem
A continuation of spinal cord containing:
◦ Ascending sensory tracts
◦ Descending motor tracts
◦ Nuclei
◦ Integrating centers
◦ Send information in and out of cerebellum
describe the white matter of the medulla
composed of ascending sensory tracts and motor descending tracts
the anterior portion of the medulla bulges out; theses are called the pyramids and are composed of motor tracts
about 90% of pyramidal tracts on left cross to right, and vice versa; called decussation (meaning crossing)
what does the decussation of pyramids cause
due to the decussation of pyramids, the left side of the brain controls the right side of the body and vice versa
The term “decussation” means?
a) To split in half
b) Control of movement
c) A form of sensory input
d) Crossing of axons
e) Leaping of axons
d) crossing of axons
A common site of decussation for motor tracts is
a) In the pyramids of the medulla
b) In the anterior area of the medulla
c) In the pons
d) In the midbrain
e) a and b
e
describe the grey matter of the medulla
the medulla contains many nuclei that act as integration centers or relay centers
what are inferior olivary nucleus and where are the found
lateral to each pyramid is an oval-shaped swelling called an olive
◦ Contains inferior olivary nucleus
◦ Receives input from cerebral
cortex, midbrain and spinal cord
◦ Sends input to cerebellum
→Controls proprioceptive signals
→Gives precision to movements
what do the nuclei of the medulla do and what do the other nuclei of the medulla do?
Control many vital body functions
◦ Cardiovascular center
-Controls force and rate of heartbeat, diameter of blood vessels
◦ Respiratory center
◦ Sets basic rhythm of breathing
◦ Reflex centers for coughing, sneezing, swallowing, vomiting, hiccupping
Other nuclei of the medulla:
Gracile and cuneate nuclei: Associated with somatic sensations (touch, pressure,
vibration, conscious proprioception)
Gustatory (taste), cochlear (hearing), and vestibular (equilibrium) nuclei
Nuclei for cranial nerves (VIII-XII)
describe the pons
Located superior to the medulla
Consists of both nuclei and tracts
The pons (“bridge”) connects the parts of brain with each
other via tracts
◦ Connects right and left sides of cerebellum
◦ Relays nerve impulses related to voluntary skeletal
movements from the cerebral cortex to the cerebellum
(both sensory and motor tracts)
what do the nuclei of the pons do
Nuclei in the Pons control aspects of breathing, sleep, swallowing, bladder
control, hearing and equilibrium, as well as taste and facial expressions.
The Pons contains nuclei for cranial nerves V-VIII
describe the midbrain
Extends from pons to diencephalon
Contains cerebral aqueduct, which connects 3rd ventricle above to 4th ventricle
below
Contains sensory tracts, motor tracts and nuclei (visual and auditory info)
describe the white matter of the midbrain
The anterior midbrain contains the cerebral peduncles. These contain tracts
of motor neurons leading to different parts of the CNS from the cerebrum;
they also contain sensory tracts leading up from medulla to thalamus
grey matter of the midbrain: what does the superior colliculi do?
In the posterior midbrain, the superior
colliculi (nuclei) deal with visual reflexes
* tracking
* direct movement of head, neck and eyes
in response to visual stimuli
gray matter of the midbrain: what does the inferior colliculi do?
the inferior colliculi (nuclei)deal with auditory reflexes
* direct movement of head, neck and eyes in response
to sudden/loud auditory stimuli (startle reflex)
the gray matter of the midbrain: what does the substantial nigra do?
The substantia nigra is the site
of Dopamine production
* helps control subconscious
muscle activity
* involved in rewards and
addiction
also the one that has issues when people have parkinsons
Grey matter of midbrain: what does the red nuclei do?
axons from the cortex and the
cerebellum synapse in the Red
nuclei to assess and coordinate
upper limb movements and
overall muscle tone
where are the nuclei for cranial nerves III and IV found
in the midbrain
Parkinson disease results from
a) a decrease in the size of the midbrain
b) a decrease in neurons from the substantia nigra
c) a decrease in the release of serotonin
d) a decrease in neurons from the pyramids
e) b and c
b)
b
Excessive hiccupping could indicate
dysfunction in which part of the brain?
a) Midbrain
b) Medulla oblongatta
c) Pons
d) RAS
e) Mesencephalon
c) pons
Where are the cerebral peduncles found?
a) Midbrain
b) Medulla oblongatta
c) Pons
d) RAS
e) Cerebrum
a) midbrain
what is the reticular formation and what does it do
The Reticular formation is a series of scattered nuclei located in the brain stem. They are
involved in:
* maintaining posture and muscle tone
* relaying pain and analgesic information
* sleep, alertness and consciousness (via the Reticular activating system - RAS)
* differentiate between meaningless stimuli (e.g., background noise) and meaningful ones
Which part of the brain has failed this student?
a) Midbrain
b) Medulla oblongatta
c) Pons
d) RAS
e) Mesencephalon
d) RAS
what does te cerebellum do
~10% of weight of
the brain, but 50%
of the neurons
- Evaluate how well movements initiated by motor
areas in the cerebrum are being carried out - Adjusts postural muscles to maintain balance
- Programs and fine tunes both voluntary and
involuntary movements - Stores memories of learned movements
what are the different parts of the cerebellum
Cerebellar hemispheres (left and right) each consist of
anterior and posterior lobes separated by fissures
Flocculonodular lobe
Cerebellar peduncles (superior, middle, inferior)
what does the superior part of the cerebellum do?
involved in regulating subconscious aspects of skeletal muscle movements
what does the cerebellar peduncles do in the cerebellum?
attach the cerebellum to the brain stem, they contain tracts that link the cerebellum to other parts of the brain
what does the flocculodonular lobe do in the cerebellum
involved in balance/ equilibrium
what can happen when the cerebellum is damaged? what can cause it?
Damage to the cerebellum can cause ataxia = loss of ability to coordinate
movements
No sense of proprioception
Uncoordinated speech muscles and abnormal walking (like a drunk person –
alcohol affects cerebellar functions)
Can also be result of side effect of certain diseases or medication
Which statement about the cerebellum is true?
a) The cerebellar peduncles attach it to the cerebrum
b) The cerebellar lobes are also called tentorium cerebelli
c) Its main function is to ‘fine tune’ motor function
d) Its main function is to initiate motor function
c
where is the diencephalon found in the brain?
- Between the top of the brain stem
and the bottom of the cerebrum - Wraps around the third ventricle
describe the diencephalon/thalamus
Think structure
- the thalamus forms ~80% of the diencephalon
- it is mainly a mass of gray matter – nuclei with interspersed tracts
- two egg-shaped halves, connected by the intermediate mass,
surrounding 3rd ventricle
what sensory functions does the thalamus have?
The thalamus mainly acts as a relay station for sensory and motor functions:
Sensory functions:
◦ sensory info from spinal cord and brain stem goes through thalamus to
cerebral cortex
◦ pain, temperature, pressure, hearing…
◦ the thalamus acts as a filter, passing on to the cerebral cortex only a small
portion of the sensory information it receives
◦ each region of the thalamus contains nuclei that connect to specific regions of
the cerebral cortex
describe and locate major anatomical featues of the cerebrum
only need to know 12
