Neuroanatomy

Head and Brain + Cranial Blood Supply & Cranial Nerves + Extremity Nerves

Cranial Meninges

3 membranes encloses the brain and spinal cord

three layer:

1. Dura mater = tough mother. periosteal and meningeal

2. Arachnoid mater= spider web like

3. pia mater - pia= tender

Function of cranial meninges

1. protect brain

2. supporting framework for vessels & venous sinuses

3. enclose fluid filled space (subarachnoid) vital for normal function of brain.

• 1st layer of the cranial meninges - dura mater

• adherent to internal surface of skull

• two layered membrane

  • external periosteal layer

    • same as periosteum lining of calvaria

  • internal meningeal layer

    • strong fibrous layer

    • continuous at foramen magnum with spinal dura mater

Dura mater meningeal layer and cerebri and cerebelli

• Meningeal layer draws away from external layer to form dural infoldings

• largest is the falx cerebri which divides cranial cavity and cerebral hemispheres

• falx cerebelli separates the two hemispheres of the cerebellum

• tentorium cerebelli separates occipital lobes and cerebellum

Dura Mater Spaces

• dural infoldings spaces= sinuses

• venous drainage via sinuses

• large veins from brain drain into there sinuses

• superior sagittal sinuses lies within the falx cerebri

  • begins at crista galli and ends at occipital protuberance

  all join at confluence of sinuses

• 2nd layer of the cranial meninges - arachnoid mater

• the meningeal layer of dura mater lines on top of this

  • it is separated from dura mater. the pressure of the cerebrospinal fluid pushes the meningeal layer of dura mater and the arachnoid mater closer together

  • with no cerebrospinal fluid arachnoid layer would collapse down and stick to the pia mater

• arachnoid mater contains fibroblasts, collagen fibres, and some elastic fibres

• avascular in nature ( no blood is being supplied to the arachnoid mater. but there are blood vessels going through the arachnoid trabecula.

• held against dura mater by pressure of cerebrospinal fluid. ( not direct attachment)

• 3rd layer of the cranial meninges - pia mater

• thinner than arachnoid

• high vascularized ( lots of blood going though it)

• gives brain shiny appearance

• invests within all folds and contours of the brain

  • adds layer of protection and vascularization to the skin of brain

• hard to dissect away cause lots of folds

• everyone has a unique pattern to their cerebrum and everyone’s folds and contours are different

Meningeal spaces

• 3 spaces

  • subarachnoid

    • actual space- contains cerebral spinal fluid, arteries, and veins. healthy space

  • epidural space

    • occurs with some sort of injury

    • potential space- observed with injury

      • hematoma - blood leak from vessel in brain

  • Subdural

    • potential space with injury

what is the brain made of, parts of the brain

• cerebrum

  • various lobes and diencephalon

• cerebellum- most posterior and inferior part of the brain

• brainstem ( parts moving from superior to inferior)

  • pons

  • midbrain

  • medulla oblongata

cerebrum part of brain

• lots of lobes responsible of higher order thinking/ reasoning

• principal part of brain

• made up of various lobes divided into cerebral hemispheres

  • hemispheres separated by longitudinal fissure and joined by corpus callosum (highway of info that send info between left and right side so hemispheres talk to each other)

pic has sagittal view

Lobes of cerebrum

• frontal (most anterior lobe), parietal, (dorsal to frontal lobe) occipital (posterior and inferior to parietal), and temporal lobes (on lateral side of cerebrum)

• frontal and parietal lobes separated by central sulcus

• temporal and parietal lobes separated by lateral sulcus

functions of each of the cerebrum lobes

• frontal

  • pre-frontal area (personality) also most anterior

  • pre-central area (motor activities)

• temporal lobe

  • smell and hearing

• parietal lobe

  • sensory interpretation

• occipital lobe

  • vision

diencephalon

• core of brain and surrounds 3rd ventricle

  • Formed form right and left halves

  • joined together via intermediate mass

• composed of right and left thalamus and hypothalamus

• controls equilibrium, vison, facial sensation, hearing, phonation, respiration, salivation, swallowing, smell, taste

diencephalon is purple in pic

Midbrain

• inferior to thalamus

• first most superior part of the brainstem

• controls most autonomic functions

  • vision, hearing, alertness, temperature

• cavity forms cerebral aqueduct

  • conduct cerebrospinal fluid 3rd (other side of thalamus) to 4th ventricle (posterior to pons).

Pons next inferior part of brain stem

• part of brainstem between midbrain and medulla oblongata

• forms superior part of 4th ventricle

• control sleep and arousal

• midbrain is superior to the pons

• inferior to that is the medulla oblongata

Medulla oblongata-most inferior part of the brain stem

• inferior to pons

• continuous spinal cord

• controls autonomic functions (breathing and heartbeat)

Cerebellum

• a mini brain

• dorsal to pons and medulla oblongata

• controls fine motor coordination

  • fine tunes motion like throwing a ball or catching

• arbor vitae (tree of life)

  • tree like configuration seen in a sagittal section of cerebellum

  • relays sensory information

• pic is sagittal section of cerebellum

ventricles of the brain

• filled with cerebrospinal fluid

• consisted of

  • lateral ventricle

    • sit on cerebrum on each side. there’s a left lateral ventricle and a right

    • also called the 1st and second ventricle

  • third ventricle (sit in between thalama and same shape)

  • cerebral aqueduct

  • fourth ventricle

pic has frontal plane and sagittal plane

Lateral ventricles

• also called 1st and 2nd ventricles. doesn’t matter if left or right is the first

• largest cavities

• separated by septum pellucidum (separates each ventricle so each one has its own space) which sits inferior to corpus callosum (corpus callosum is a mass that communicated between left and right?)

3rd and 4th ventricles

• 3rd ventricle is between the two halves of the diencephalon

  • intermediate mass lies within

• 3rd and 4th connected via cerebral aqueduct so cerebrospinal fluid can also pass through there

• 4th ventricle is posterior to pons and medulla oblongata

  • continuous with central canal of spinal cord

Septum pellucidum

Septum pellucidum separates the two lateral ventricles - roof is corpus callosum

intermediate mass lies within 3rd ventricle - lateral borders are diencephalon

Cerebrospinal fluid

• produced by choroid plexus found within each ventricle and travels throughout brain

• circulates throughout central nervous system

• old cerebrospinal fluid and fluid that is used up is absorbed into venous system through heart after by sinuses

• functions:

  • protection

  • buoyancy

  • excretion of waste products

  • endocrine medium for the brain

Cerebrospinal fluid flow

CRANIAL BLOOD SUPPLY AND CRANIAL NERVES BELOW

The two main blood vessels

arteries - take oxygenated blood away from heart to its destination

veins- take deoxygenated blood ( venous blood) from muscle, brain, bone etc back towards heart so it can get oxygen

brain receives arterial blood ( oxygenated blood) from heart via 2 sources:

• internal carotid arteries

  • branches off heart with the brachiocephalic trunk and then splits into external carotid which goes to outer part of face and the internal carotid artery which goes through the carotid canal and then to cerebralarterial circle

• vertebral arteries

  • go up brachiocephalic trunk then go up the subclavian axillary then to the vertebral arteries

  • vertebral arteries tied into our axial skeleton cuz these are the ones that go thru the transverse forename in the transverse processes of the cervical vertebrae. then goes to cerebralaterial circle/circle of Willis

in diagram we want to from heart ( behind sternum) and go up towards the brain so it has oxygenated blood and then the venous blood can go back towards heart

Cerebralarterial Circle/ Circle of Willis

pic also the same as below pic

• where arterial blood is distributed to areas within the brain

• ICA (3) branch into anterior (2) and middle (8) cerebral arteries

• anterior cerebral arteries connected via anterior communication artery (1)

• vertebral arteries (7) join to form basilar artery (6)

• basilar splits to form posterior cerebral arteries (5)

• posterior cerebral arteries joined to circle via posterior communicating arteries (4)

to get to temporal lobe it’ll go through middle cerebral arteries (8)

frontal lobe would be anterior cerebral arteries (2)

Cerebral Venous blood return

pic is the same as below

• once oxygenated blood is received by the brain, the brain will then discard deoxygenated blood so we can go back to heart

• cerebral venous blood return refers to veins that are taking deoxygenated blood away

• venous blood drained via dural venous sinuses

• they drain into internal jugular veins (IJV). This then drains back into heart

Cranial nerves

• emerge from foramina in the cranium and go out of skull

• contain sensory or motor fibres or combination of both

  • whether they’re responsible of sensation only or motor only or a combination of both

• twelve pairs

  • Goes anterior to posterior to inferior as we make our way down the brainstem

12 pairs of cranial nerves

• CNI- olfactory (sensory)

• CN II - optic (sensory)

• CN III - oculomotor (motor)

• CN IV - Trochlear (motor)

• CN V - Trigeminal (both sensory and motor)

• CN VI abducens (motor)

• CN VII - facial (both sensory and motor)

• CNVIII - Auditory/ Vestibulocochlear (sensory)

• CN IX - Glossopharyngeal (both sensory and motor)

• CN XI - accessory (motor)

• CN XII hypoglossal (motor)

CN I - olfactory

• olfactory bulb rests on cribriform plate

• pure sensory nerve ( only function is sensory)

• sense of smell and induce visceral response (salivation)

• most anterior nerve

• combination of olfactory nerve and nerve fibres

• all the olfactory nerves are coming through the ethmoid bone

• CN II - optic (sensory)

• formed from axons of retina ganglion cells from eyeballs

• fibres from each nerve run from to each hemispheres at optic chiasm then make its way back to occipital love

  • allow for 3D vision (sensory)

CN III - oculomotor

• motor nerve to 4 of 6 extraocular muscles and upper eye lid

• parasympathetic nerve to sphincter of pupil

  • pupil changing sizes due to light

CN IV Trochlear

motor nerve to one extraocular muscle. its the 5th of the 6th extraocular muscle

trochlear= Latin for pulley

trochlear nerve innovates into the superior oblique muscle and has a pulley system. it pulls on posterior side of eyeball. if u want to lower ur eyeball downwards u pull up on pulley and u can look down

• CN V - Trigeminal

• sensory and motor nerve

• general sensory nerve for cornea, skin of forehead, scalp, nose, nasal cavity, lips, teeth, and tongue

• motor nerve for muscles of mastication (chewing)

• three branched nerve to 3 diff regions:

  • ophthalmic- forehead and eye

  • maxillary - in maxilla region in upper jaw

  • mandibular - low jaw or mandible

depending on region it goes to it’ll act as either a sensory or motor nerve. all three branches have sensation though.

• CN VI abducens

• motor nerve to the final or 6th extraocular eye muscle

• abducens is going to the muscle that will abduct your eye

• if u look to left, right eye will abduct. if u look to right, left eye will abduct. all due to abducens

CN VII - facial

• motor nerve to facial muscles of expression and to scalp

• motor and sensory

  • motor aspect- allows for facial muscles of expression in the scalp. ex a big smile, frowning, surprise

  • sensory aspect-

• taste from anterior 2/3 of tongue, floor of mouth and palate

• sensation from outer ear

• parasympathetic innervation to submandibular, sublingual, and lacrimal glands and glands of nose and palate

CN VIII - auditory / vestibulocochlear

• sensory nerve form inner ear related to position and movement of head

• also associated with hearing

• balance

CN IX Glossopharyngeal

• motor and sensory

• motor nerve for swallowing

• parasympathetic nerve to parotid gland ( gland in cheek)

• visceral (organ) sensation to carotid body and carotid sinus, pharynx and middle ear. give info about blood pressure

• sense of taste from posterior 1/3 of tongue

• glossal= tongue

• pharynx= throat

CN X - Vagus

• visceral motor function- it will innervate the pharynx, larynx, superior 2/3 esophagus,, cardiac muscle, and most organs

  • you don’t have control of the organs but it controls them with smooth muscles motor activity

• visceral sensory function from most organs and many others

  • coughing, sneezing, swallowing, speaking, digestion, secretions from the glands of stomach, sensation of hungry

CN XI - Accessory

motor nerve - helps innervates for movement of the muscles of the upper shoulders, head, neck, larynx, and pharynx

CN XII - Hypoglossal

motor nerve for muscle of tongue. allows for movement of tongue so u can talk, speak, move ur tongue when u eat, etc

hypo=above

glossal= tongue

EXTREMITY NERVES BELOW

Brachial Plexus

• most nerves in upper limb arise from this collection of nerves

• R - roots C5-T1

  • cervical nerve 5 to thoracic nerve 1

• T - sup, mid, inferior trunks

  • Trunks then branch off into divisions

• D - ant, posterior divisions

• C - lat, med, posterior cords

  • anterior divisions are lat and med cords and posterior division is posterior cord. the posterior cord is an extension of the divison

• B - terminal branches or nerves

  • innervate muscles in upper extremities

brachial is made of 5 sections RTDCB above

Finding brachial plexus

Find elusive “M” and then work backwards

musculocutaneous, median, and ulnar n.

all arise form anterior division and from either lateral or medical cords

posterior division (cord) is axillary n. and radial n.

posterior division has an elusive “Y”

pic is brachial plexus

Notes in brachial plexus:

there are 7 cervical vertebrae and 8 cervical nerves why?

there is a cervical nerve one 1 sitting on top of the atlas and cervical nerve 2 under the atlas. there is an extra nerve on top of the atlas essentially

lumbar nerves, thoracic all do not have a mismatch with nerve and bone

Describe the boxed red

median nerve- cuz running midline of the 3 nerve bundle

musculocutaneous- towards upper arm muscles

ulnar nerve- running down ulnar side so most medial of the 3 nerves in the anterior division and it is coming of the medical cord

in posterior division it branches off into the auxiliary nerve- right into the armpit and into shoulder

radial nerve- running down posterior side of the arm and the forearm

Brachial Plexus - anterior division in detail

• musculocutaneous nerve

  • pierces coracobrachialis muscle

  • innervates all muscles on anterior brachium ( responsible for elbow function)

  • most lateral nerve

• ulnar nerve- most medial nerve or the branch

  • medial humerus, medial epicondyle

  • innervates 1 ½ forearm flexors then goes hypothenar eminence. innervates 5th digit and half of 4th.

  • funny bone cause very exposed

• median nerve

  • deep humerus, cubital fossa, anterior antebrachium (forearm)

  • innervates most of forearm flexors, thenar eminence (around the thumb). innervates digits 1, 2,3 and half of the 4th

  • runs down middle of ulnar and musculocutaneous nerve

  • doesn’t touch muscles of anterior brachium just like ulnar nerve

Brachial Plexus - posterior division in detail

• axillary nerve

  • 1st branch of posterior division

  • wraps around humeral head

  • innervates deltoid (any shoulder muscle movement including extension, abduction, adduction, etc.)

• radial nerve

  • posterior humerus, lateral epicondyle, posterior antebrachium

  • triceps brachii, forearm extensors

Anatomy of upper extremities summarized

Lower extremities- Lumbar and sacral plexuses

• start from lumbar and sacral vertebrae and branch off into diff parts of the lower extremity.

Full view of lower extremity

• femoral and obturator come out of lumbar and sacral plexuses

  • responsible for anterior thigh and medial thigh

  • obturator nerve travels through framing and then innervates into medial thigh specifically

• posterior side coming from sacral plexus is sciatic

  • sciatic= bundle of 2 fibres. common fibular/ common peroneal nerve or tibial nerves

• fibular nerve also runs on posterior side of calf

• superficial peroneal innervates superficial part of the leg

anterior side of nerves for the femoral nerves, look for femoral triangle

triangular space in the superoanterior top 1/3 of thigh.

space borders inguinal ligament ( most superior border), sartorius muscle ( lateral border), and adductor longus (medial border) at the border

contains:

femoral nerve

femoral artery

femoral vein ( with great saphenous vein)

blue in pic is femoral vein ( most medial). femoral nerve in yellow (most lateral). red artery

Trick to find femoral triangle

VAN from medial to lateral ( VAN out; VAN outwards from medial to lateral)

femoral sheath holds femoral artert and femoral veins together

greater saphenous veins enters inferior to femoral sheath via saphenous opening

Iliacus sheath holds femoral nerve

Femoral nerve

• passes under inguinal ligament

• starts from branch of lumbosacral plexus (L2,3,4)

• Follows same course as femoral artery and veins

• supplies anterior thigh muscles

Posterior side - Sciatic nerve

• branch coming from lumbosacral plexus (L4-S3)

• posterior thigh

• largest nerve in the body

• through greater and less sciatic nerve

• supplies no structures in gluteal region but most of lower extremity

• tibial and common peroneal portions loosely bound together

• obturator nerve also formed from this plexus (L2,3,4). goes to medial thigh

• Largest nerve in body cuz its technically made up of two nerves ( sciatic nerve made up of common fibular and tibial)

Sciatic nerve

• coming from the lumbosacral plexus, meeting at the notches, it is going to pass through posterior side of thigh and exit inferior to piriformis

• anterior to gluteus maximus

• tibial branch supplies flexor muscles of lower leg

• common peroneal branch supplies extensor muscles of lower leg

• damage to sciatic nerve causes a lot of pain since it innervates so much of leg and foot

• tibial nerve runs in deep posterior compartment with posterior tibial artery

  • innervates posterior side of leg/shank

• common peroneal nerve divides into superficial and deep peroneal nerves

  • superficial runs laterally and hits/innervates all peroneal/fibular muscles on posterior side

  • deep runs run through trough fossa btw fibular and tibialar. fossa = opening for deep peroneal/ fibular nerve to run through and go to anterior side of lower leg

• superficial peroneal nerve runs in lateral compartment

• deep peroneal nerve runs in anterior compartment with anterior tibial artery and vein

Popliteal fossa ( back of knee)

• diamond shaped depression on posterior aspect of thigh

• borders consist of the two heads (medial and lateral head ) of gastrocnemius and hamstrings

• floor is popliteus muscle

• roof is skin

• top part of diamond is hamstring muscles. bottom half is gastrocnemius

Popliteal fossa

• from medial to lateral the popliteal fossa contains:

  • popliteal arteries

  • popliteal veins

  • tibial nerves

  • common peroneal nerves/ common fibular nerve (runs laterally)

SUMMARY OF WHAT EVERYTHING INNERVATES