Anatomy Week 12 (Brain and Meninges, Cranial Nerves, Skull and Cranium)

What are the different parts of the brain?

- Cerebrum (executive functions, conscious thought and memory)

- Diencephalon (thalamus and hypothalamus)

- Mesencephalon

- Pons

- Medulla oblongata

- Cerebellum (coordination of movement)

What are the various lobes of the brain?

Frontal, temporal, parietal, occipital

What is the function of the cerebrum?

Largest part of the brain associated with higher brain function (thought and action)

Also big memory storehouse, integration and processing of sensory data and initiation of motor activities

What is the function of the thalamus?

Final processor for sensory information, relays information to other areas of the brain

What is the function of the hypothalamus?

Autonomic functions (regulates hunger, thirst, hormone production, etc.)

What is the function of the cerebellum?

Coordinates movement and balance

What is the importance of the jaw's proximity to the cerebellum?

Jaw will be used a lot when doing various movements

What is a good way to remember the functions of the limbic system?

Limbic system takes you HOME

Homeostasis

Olfaction

Memory

Emotions

Signals that originate anterior to the central sulcus are:

Efferent (motor) signals

Signals that originate posterior to the central sulcus are:

Afferent (sensory) signals

What are the pre-central and post-central gyrus?

Pre-central gyrus = motor cortex

Post-central gyrus = sensory cortex

What is Wernicke's area? What would a deficiency in this area result in?

Area of the brain that involves understanding language and words

Wernicke's aphasia: person is able to say words but they do not make any sense

What is Broca's area? What would a deficiency in this area result in?

Area of the brain responsible for formulating spoken language --> enables the movement of muscles to let you say the word aloud

Broca's aphasia: person has issues forming a word

Who was Phineas Gage and what did his injury teach us about the brain?

Phineas Gage suffered an accident where an iron rod went through his skull --> destroyed most of the front and left part of his brain

Sx following the injury:

- No reaction to emotional events

- Unable to make personal or social decisions

- Unable to plan (even a few hours ahead)

His injury damaged the emotion centers of the brain, which subsequently affected his powers of reasoning --> proves the two are interconnected

What is a transorbital lobotomy?

Surgical disconnection of the prefrontal cortex from the rest of the brain by pushing a stylus through the eye socket

Used as early psychiatric tx --> often left a pt apathetic and childlike

What is the function of the frontal lobe of the cerebral cortex?

Primary motor cortex

Conscious control of skeletal muscles

What is the function of the parietal lobe of the cerebral cortex?

Primary sensory cortex

Conscious perception of touch, pressure, vibration, pain, temperature and taste

What is the function of the occipital lobe of the cerebral cortex?

Visual cortex

Conscious perception of visual stimuli

What is the function of the temporal lobe of the cerebral cortex?

Auditory cortex and olfactory cortex

Conscious perception of auditory and olfactory stimuli

What is Alzheimer's disease and how does it affect the brain?

Most common type of dementia, affects memory, thinking, and behavior

Has massive loss of cortical tissue in the brain, also can have the development of plaques that cause atrophy and decreased levels of ACh in the brain

What is a potential treatment for early Alzheimer's?

Cholinesterase inhibitor to raise levels of ACh (will just slow down the progressive nature of the disease, not reverse it)

What is CTE and why is it important?

Chronic traumatic encephalopathy -- result of repetitive concussion or mild traumatic brain injury (usually 17% of individuals)

Important in contact sports such as football where players are exposed to repeated collisions in the head

What are common presenting symptoms of CTE?

- Memory loss

- Irritability

- Outburts of aggressive or violent behavior

- Confusion

- Speech abnormalities

- Cognitive decline

- Gait abnormalities

- Unsteadiness

- Headaches

- Slurred speech

- Parkinsonism

*Head injuries, like CTE or concussions, can present with emotional deficits*

What are some physical signs of a cerebral concussion?

- Impaired conscious state or brief loss of consciousness

- Confusion

- Vacant stare/glassy eyed

- Amnesia (retrograde or anterograde)

- Slow to answer questions or follow directions, easily distracted/poor concentration

- Personality change, inappropriate emotion (laughing/crying)

- Slurred speech

What are some somatic symptoms of a cerebral concussion?

- Headache

- Nausea

- Vomiting

- Dizziness

- Sensitivity to light

- Numbness/tingling

- Blurred vision/diplopia/flashing

- Tinnitus

What can we observe in a mid-sagittal cut of the brain?

- Central sulcus

- Pre and post central gyrus

- Corpus callosum

- Pituitary gland

- Sella turcica

- Cerebellum

- Brain stem

- Foramen magnum

- Spinal cord

What is Parkinson's disease and how is the brain affected?

Movement disorder caused by the death of cells that generate dopamine in the substantia nigra (will see a diminished substantia nigra in the brain of Parkinson's pts)

Characterized by resting tremor, slowed movement, rigidity of facial muscles, and shuffling gait

How would lesions of the cerebellum present?

Ataxia and "drunken" gait (shuffle and lean, typically to the side of the lesion)

How can we test for functioning of the cerebellum?

Test for antagonistic muscle coordination

Ask pt to perform a specific movement against resistance (i.e., flex their elbow against resistance), then abruptly stop resistance

If cerebellum is working properly, the antagonistic muscle should contract once resistance is stopped to minimize movement

If the cerebellum is not working properly, the antagonistic muscle will not contract, the movement will be unopposed

What inhibits the cerebellum?

Alcohol

What are the different meninges of the brain?

Dura mater, arachnoid mater, pia mater

What is meningitis?

Inflammation/infection of the meninges caused by viral or bacterial infection

Can be caused by fungi, chemical irritation, or drug allergies and tumors

What is Kernig's sign?

Indicates meningitis

Passively flexing the neck puts tension on the dura --> will cause reflexive recoil and "kick" of the leg as well as pain

What is the tentorium cerebelli?

Extension of the dura mater that separates the cerebellum from the cerebrum

One of the diaphragms of the body

Where do the dural venous sinuses drain to?

Internal jugular vein

What are the different dural venous sinuses?

- Superior sagittal sinus

- Inferior sagittal sinus

- Straight sinus

- Transverse sinus

- Superior petrosal sinus

- Sigmoid sinus

- Inferior petrosal sinus

- Cavernous sinus

- Facial and ophthalmic vein

- Great cerebral vein

What is the dangerous area of the face?

A triangular space on the face that, if infected, can spread to the cavernous sinus via the pterygoid plexus

What is cavernous sinus thrombosis?

Blood clot within the cavernous sinus

What is the function of the choroid plexus?

Produces CSF

What would happen if the internal jugular vein is blocked?

Dural venous blood cannot drain --> will expand cranial cavity

As a result, CSF cannot return through foramen magnum --> will result in an increase in lumbar CSF pressure

What is hydrocephalus?

Enlargement of the ventricles of the brain due to fluid within the brain

How can issues with CSF sometimes present?

As dementia --> be mindful of nose and ear discharge (can be indicative of CSF leak)

Describe CSF flow

Lateral Ventricle -> 3rd Ventricle -> 4th Ventricle

What are the 12 cranial nerves?

CN I - Olfactory

CN II - Ophthalmic

CN III - Oculomotor

CN IV - Trochlear

CN V - Trigeminal

CN VI - Abducens

CN VII - Facial

CN VIII - Vestibulocochlear

CN IX - Glossopharyngeal

CN X - Vagus

CN XI - Accessory

CN XII - Hypoglossal

"Oh oh oh, to touch and feel very good velvet, ah heaven"

Do cranial nerves belong to the CNS or PNS? Which is the exception?

Belong to the PNS

EXCEPT CN II (along with retina) which are part of the CNS

Where do incoming sensory cranial nerves synapse?

In nuclei in the brain (NOT spinal cord like spinal nerves)

What are cranial nerve nuclei?

Cell groups that either receive incoming messages to the brain or send outgoing messages of cranial nerves

Where do incoming motor cranial nerves synapse?

Nuclei in the brainstem (EXCEPT CN XI)

Which cranial nerves are purely sensory?

CN I (olfactory), CN II (optic), CN VIII (vestibulocochlear)

Which cranial nerves are purely motor?

CN III (oculomotor), CN IV (trochlear), CN VI (abducens), CN XI (spinal accessory), CN XII (hypoglossal)

Which cranial nerves are a mix of sensory and motor?

CN V (trigeminal), CN VII (facial), CN IX (glossopharyngeal), CN X (vagus)

What is the parasympathetic innervation of CN III (oculomotor)?

- Parasympathetic to sphincter pupillae to constrict pupil

- Parasympathetic to ciliary muscle to focus lens for near vision (accommodation)

What is the parasympathetic innervation of CN VII (facial)?

Parasympathetic to salivary glands, lacrimal glands, and mucous membranes

What is the parasympathetic innervation of CN IX (glossopharyngeal)?

Parasympathetic to parotid salivary gland (helps with ability to salivate)

What is the parasympathetic innervation of CN X (vagus)?

Parasympathetic to all organs of the chest and abdomen

What is the mnemonic to remember the cranial nerve modalities?

Some (CN I sensory)

Say (CN II sensory)

Marry (CN III motor)

Money (CN IV motor)

But (CN V both)

My (CN VI motor)

Brother (CN VII both)

Says (CN VIII sensory)

Big (CN IX both)

Brains (CN X both)

Matter (CN XI motor)

Most (CN XII motor)

What are the different functional components of cranial nerves (5)?

- General somatic afferent (GSA)

- General somatic efferent (GSE)

- General visceral afferent (GVA)

- General visceral efferent (GVE)

- Special sensory afferent (SSA)

What are general somatic afferent fibers?

Axons that carry sensory information about perception of touch, pain, temperature, vibration, and proprioception from the periphery to the CNS

PURELY SENSORY

What are general somatic efferent fibers?

Axons that carry motor innervation to skeletal (voluntary) muscles

PURELY MOTOR

What are general visceral afferent fibers?

Axons that carry sensory input from viscera (organs, this includes blood vessels) to the CNS

What are general visceral efferent fibers?

Axons that carry motor innervations to smooth muscle, heart muscle, and smooth muscle in glands

What are special sensory afferent fibers?

Axons that carry information about the special senses of smell, taste, vision, hearing, and balance

Which cranial nerves carry parasympathetic (GVE) fibers?

III, VII, IX, X

Where are the preganglionic neurons of parasympathetic cranial nerves located?

Nuclei in brain stem

Where are the ganglionic neurons of CN III located? What are its target organs?

Ganglionic neurons: ciliary ganglion

Target organs: intrinsic eye muscles (pupils and lens shape)

Where are the ganglionic neurons of CN VII located? What are its target organs?

Ganglionic neurons: pterygopalatine and submandibular ganglia

Target organs: nasal glands, tear glands, and salivary glands

Where are the ganglionic neurons of CN IX located? What are its target organs?

Ganglionic neurons: otic ganglion

Target organs: parotid salivary gland

Where are the ganglionic neurons of CN X located? What are its target organs?

Ganglionic neuron: intramural ganglia

Target organs: visceral organs of neck, thoracic cavity, and most of the abdominal cavity

Does CN V carry any parasympathetic signals?

Technically, yes

Even though CN V itself does not have parasympathetic/GVE fibers, a branch of CN V will act as a distributor of parasympathetic signals from CNs III, VII, IX and X

Where do postganglionic neurons of the parasympathetic cranial nerve fibers originate?

Superior cervical ganglion --> will then follow blood vessels to pass through the ganglion and eventually reach the target for innervation

What innervates the parotid gland?

CN IX via the auriculotemporal nerve (branch of CN V3)

What is the auriculotemporal nerve?

Branch of CN V3 --> will carry some parasympathetic signals

Describe the signaling path of CN IX starting with its preganglionic neuron.

Preganglionic neuron in brain sends signal, will synapse on otic ganglion

Postganglionic neuron will exit and jump on branch of V3 to get to parotid gland

What are the 4 ganglion of parasympathetic cranial nerves?

- Ciliary ganglion (CN III)

- Pterygopalatine/submandibular ganglion (CN VII)

- Otic ganglion (CN IX)

- Intramural ganglion (CN X)

Through which foramen does CN I exit through?

Cribiform plate

Through which foramen does CN II exit through?

Optic canal

Through which foramen does CN III exit through?

Superior orbital fissure

Through which foramen does CN IV exit through?

Superior orbital fissure

Through which foramen does CN V exit through?

V1: superior orbital fissure

V2: foramen rotunda

V3: foramen ovale

Through which foramen does CN VI exit through?

Superior orbital fissure

Through which foramen does CN VII exit through?

Internal acoustic meatus

Through which foramen does CN VIII exit through?

Internal acoustic meatus

Through which foramen does CN IX exit through?

Jugular foramen

Through which foramen does CN X exit through?

Jugular foramen

Through which foramen does CN XI exit through?

Jugular foramen

Through which foramen does CN XII exit through?

Hypoglossal canal

What kind of sensory fibers does CN I have?

SSA fibers --> sense of smell

Has ability to bypass thalamus -- has direct connection to the brain

What would damage to CN I result in?

Impaired sense of smell (anosmia - loss of smell or hyperosmia - heightened sense of smell)

How do olfactory signals get received by CN I?

Olfactory cells from the bulb will travel down through cribiform plate and synapse on olfactory epithelium --> will give us our sense of smell

What kind of sensory fibers does CN II have?

SSA fibers --> vision

What would damage to CN II result in?

Blindness in visual field

How can we test for CN II function?

Visual acuity tests (Snellen chart)

What kind of fibers does CN III have?

GSE --> motor to some extraocular muscles and levator palpebrae superioris

What are some functions of CN III?

- Turns eye up, down, and medially (due to EOM)

- Opening of eyelid (via levator palpebrae superioris)

- Constriction of pupil (iris sphincter)

- Focusing and accommodation of pupil (ciliary muscle)

What 4 EOM are innervated by CN III?

- Inferior oblique

- Superior rectus

- Medial rectus

- Inferior rectus

SO4LR6,3

What movement does the superior oblique extraocular muscle perform?

Will pull eye down and in into intorsion (towards nose)

What movement does the inferior oblique extraocular muscle perform?

Will pull eye up and out into extorsion

What would happen if there was damage to CN III?

Paralysis of CN III would lose 4 of the EOMs --> would only be able to abduct and bring the eye down (will be stuck in this position)

Will also have eyelid ptosis (due to loss of levator palpebrae superioris), and loss of direct and consensual light response

What kind of fibers does CN IV have?

GSE --> motor into the superior oblique muscle

Will be able to perform intorsion of the eye (depression and adduction)

What would occur as a result of damage to CN IV?

- Double vision (diplopia)

- Eye will drift up and out (due to unopposed motion)

- Head tilt to unaffected side in an effort to compensate for diplopia