Neuroanatomy Flashcards
anatomical position
- standard reference point
- body erect
- feet on ground
- eyes and palms face forwards
- thumbs point away from the body
directional terms
1) cranial (head, rostral) vs caudal (tail)
2) posterior/dorsal (back) vs anterior/ventral (front
3) superior (head) vs inferior (feet)
4) proximal (nearer to center of body or attachment) vs distal (farther) = tubes or limbs only!
5) medial, lateral, intermediate
6) superficial vs deep
planes and sections
1) frontal/coronal: separates into anterior and posterior
2) transverse: separates into superior and inferior
3) sagittal: separates into L/R
articulations
- aka joints
- union between 2 or more bones
- classified by structure (how they are connected) and function (i.e. how much they move)
types of structural joints
1) fibrous
2) cartilaginous
3) synovial (majority)
types of functional joints
1) synarthroses: immoveable
2) amphiarthroses: slightly moveable
3) diarthroses: freely moveable (most)
some types of joints
1) fibrous synarthroses
2) fibrous amphiarthroses
3) cartilaginous synarthroses
4) cartilaginous amphiarthroses
5) synovial joints (all diarthroses)
fibrous synarthroses
- joined by dense irregular CT
- ex. sutures: connect skull bones
- ex. gomphosis: tooth to bony jaw
fibrous amphiarthroses
- joined by dense irregular CT
- ex. syndesmoses: articulation between forearm and leg bones
cartilaginous synarthroses
- joined by cartilage
- ex. synchondroses: epiphyseal plates in growing bone and 1st sternocostal joint
cartilaginous amphiarthroses
- joined by cartilage
- ex. symphysis: pubic symphysis and joints of vertebral bodies (intervertebral discs)
synovial joint general anatomy
1) articular capsule (aka joint capsule): two layers (fibrous for strength and synovial membrane), creates joint cavity
*distinguishing feature
2) synovial fluid: produced by membrane for lubrication, nourishment of articular cartilage, shock absorption
3) articular cartilage: covers articular surfaces where there is no synovial membrane (covering bone)
4) ligaments: connect bone to bone, reinforce articular capsule (provide stability and limit movement)
accessory structures of synovial joints
1) bursae: fibrous, saclike structures filled with synovial fluid to alleviate friction (ex. lots in knee)
2) fat pads: supportive material found around joint, often fill spaces that form during movement
2) tendons: muscle to bone connection, provides stability around joint
classification of synovial joints
- based on shape of articulating surfaces and movements permitted
1) pivot: uniaxial
2) hinge: uniaxial
3) saddle: biaxial
4) ball and socket: multiaxial
5) condyloid: biaxial
6) plane: uniaxial
types of movements at synovial joints
1) gliding: opposing surfaces glide back and forth
2) angular: flexion/extension in sagittal plane, abduction/adduction in frontal plane
3) rotation: medial/lateral rotation in transverse plane (R/L for vertebral column)
4) special movements
flexion vs extension
flexion = joint angle decreases, extension = increases
abduction vs adduction
abduction = away from midline, adduction = towards
lateral vs medial rotation
lateral = rotates away from midline, medial = towards midline
axial vs appendicular skeleton
- axial = skull, vertebral column and bony thorax (ribs and sternum)
- appendicular = pectoral and pelvic girdles, upper and lower limb bones
vertebral column
- fetus & infant: 33 separate bones
- 9 fuse to form two composite bones (sacrum and coccyx)
- complete ossification occurs between 25-30
- adult: 24 unfused irregular bones
division of vertebral column bones
1) cervical (1-7)
2) thoracic (1-12)
3) lumbar (1-5)
4) sacrum (5 fused)
5) coccyx (3-4 fused)
shape of vertebral column
- looks straight from anterior/posterior view
- curvature in lateral view (single curve in fetus –> multiple)
curvature of vertebral column
1) cervical: secondary curvature (develops after, not the same) develops with ability to hold head up
2) thoracic: primary
3) lumbar: secondary, develops with ability to stand upright
4) sacrum + coccyx: primary
kyphosis
exaggerated curvature in thoracic region
lordosis
exaggerated curvature in lumbar region
typical vertebra
1) weight bearing vertebral body (anterior)
2) vertebral foramen (for spinal cord, line up to form vertebral canal)
3) 2 x transverse process (lateral)
4) 1 x spinous process (posterior)
5) 2 x lamina (connecting processes)
6) 2 x pedicle (connecting transverse process to body)
*5/6 form vertebral arch
7) 2 x superior articular process
8) 2x inferior articular facet
*7/8 articulate to form facet joints
9) superior/inferior vertebral notch
10) notches form intervertebral foramen (between two vertebrae, for spinal nerve)
11) intervertebral disc
facet joint
- connecting superior and inferior articular processes of adjacent vertebrae
- plane synovial joint (gliding)
general regional variation in vertebrae
from cranial to caudal:
1) size of vertebral bodies increase as load increases
2) diameter of vertebral canal decreases as diameter of spinal chords decreases
3) process change shape and orientation to reflect differences in function and movement
4) some unique features
features of C3-C7
- bifid spinous processes
- transverse foramina for vertebral vessels (blood for brain)
- articular processes allow a range of movements
features of C1 (atlas)
- articulates with skull (superior articular facets articulate with occipital condyles) –> permits “yes” movement
- no body or spinous processes (anterior arch instead)
- larger posterior arch
features of C2 (axis)
- dens is unique part, everything else is the same
- articulations between C1/C2 permit “no” movement (C1 rotates round dens)
transverse ligament of atlas
holds dens in place, running from one side of anterior arch to the other
features of T1-T12
- articulate with ribs using transverse costal facets (two)
- spinous process are long, point inferiorly
- orientation of articular facets inhibits flexion and extension, but permits gliding
features of L1-L5
- enhanced weigh bearing function = large, kidney bean body
- spinous processes are short and point posteriorly
- orientation of articular processes allow for flexion and extension
features of sacrum
- five fused vertebrae (remnants of spinal processes form medial and lateral (2) sacral crest)
- 4 anterior and posterior sacral foramina
- wide part = base, tip = apex
- sacral promontory at top of base
- sacral hiatus at apex (posterior side)
- sacral canal in the middle
- 2 x ala: “wing” on each side of base (anterior side)
features of coccyx
- no unique features
- 3-4 fuse vertebrae
- at apex of sacrum
intervertebral discs function and location
- permit movement between vertebrae
- shock absorption
- located everywhere except C1-C2
parts of intervertebral disc
1) nucleus pulposus: inner gelatinous part
2) anulus fibrosus: outer stronger collar of collagen fibers and fibrocartilage (thicker anteriorly than posteriorly for strength)
supporting ligaments in vertebral column
1) ligamentum flavum: between vertebrae
2) posterior longitudinal ligament: continuous along portion of canal
3) anterior longitudinal ligament: continuous along column
joints of vertebral bodies
- contain intervertebral disc
vertebral column movement limitations
1) orientation of facet joints
2) attachment of bony thorax
3) bulk of surrounding tissue (more bulk = less movement)
types of movement in vertebral column
- flexion: bend forward
- extension: bend backward
- lateral flexion: vertebrae slide past each other
- rotation of head and neck (around neck area)
- rotation of upper trunk, neck and head (around waist area)
herniated disc
- rupture of anulus fibrosus, leading to leakage of nucleus pulposus
- puts pressure on spinal cord and nerves = pain
- usually occurs in posterolateral (anulus fibrosus thinner)
division of skull bones
1) cranial (neurocranium, brain case)
2) facial (viscerocranium, facial skeleton)
how are skull bones united?
- majority by fibrous sutures: synarthrotic fibrous joints
- exception: jaw (temporal mandibular joint) is synovial joint capsule
why aren’t sutures completely fused at birth?
- allows body to squeeze through birth canal more easily
- flexibility allows for growth
fontanels
- areas of unossified mesenchyme
- two major:
1) anterior fontanel: diamond shape, closes ~9-18 months after birth
2) posterior fontanel: triangular, closes ~1-2 months after birth
function of cranial bones
1) protect brain
2) stabilize position of brain and provide attachment points for brain
3) attachment site for muscles
cranial bones
eight bones:
1) 2 x parietal: largest superior aspect of skull
2) 2x: temporal
3) occipital: wraps under to form skull base and support brain
4) frontal: forms shelf to support brain
5) sphenoid
6) ethmoid
cranial sutures
1) coronal: along coronal plane, joins parietal and frontal
2) squamous: lateral plane, joins parietal and temporal
3) lambdoid: joins parietal and occipital
4) sagittal: joins two parietal
5) zygomaticofrontal suture: zygomatic and frontal
6) sphenosquamosal suture: sphenoid and temporal
temporal bony features
1) internal/external acoustic meatus: for ear canal
2) mastoid process: attachment of neck muscles
3) styloid process: attaches to soft tissue
4) mandibular fossa: helps form temporal mandibular joint
5) zygomatic process: forms prominence of cheek
6) squamous part: flat part of bone
7) pterion: articulation of parietal, temporal, frontal and sphenoid bones (weakest area of skull)
8) interior petrous (“rough”) part
bregma
where frontal and two parietal bones meet (used to be anterior fontanel)
lambda
where occipital and two parietal bones meet (used to be posterior fontanel)
features of frontal bone
1) supraorbital foramen: hole for small nerve to supply forehead
2) squamous part
3) supraorbital margin: edge of shelf created by…
4) orbital part
5) frontal sinus: makes skull lighter, connects into nose
features of sphenoid
- expands width of skull
- articulates with all cranial bones
- has sphenoid sinus
- butterfly shape with lesser (closer to frontal bone) and greater wing on each side
- lateral and medial pterygoid plates: muscle attachments for chewing with jaw
- pterygoid hamulus: hook-like structure at the end of medial plate
- sella turcica (aka hypophyseal fossa): “turkish saddle” where pituitary gland sits and is protected
features of ethmoid
- located inside nose, between orbits
- extends to form nasal septum (perpendicular plate attaches to vomer) and medial part of orbit
- crista galli: “rooster cone” that points up
- lateral mass: contains air cells (makes bone lighter) and form ethmoid sinuses
- middle nasal concha (2): divide nasal airway
- cribriform plate on either side of crista galli containing olfactory foramina (for smell nerves)
suture bones
- tiny bones inside suture
- only present in some skulls
occipital bone features
1) external occipital protuberance
2) occipital condyles (2): hang down to flank foramen magnum, where C1 articulates
3) foramen magnum: where spinal chord passes through
cranial base
- formed by portions of all cranial bones
- sphenoid is keystone
cranial fossae
- three different to support parts of brain
1) anterior: frontal, ethmoid, sphenoid bones - houses frontal lobes
2) middle: sphenoid, temporal and parietal - houses temporal lobes
3) posterior: occipital, temporal, parietal - houses cerebellum
facial bones function
1) supply framework for face, sense organs and teeth
2) provide openings for passage of air and food
3) anchor facial muscles
facial bones
14 total:
1) 2 x lacrimal: hole for tears to pass through
2) 2 x zygomatic: form prominence of cheek
3) 2 x palatine bones: form roof of mouth
4) 2 x nasal
5) ONE vomer
6) 2 x inferior nasal concha
7) 2 x maxillae
8) ONE mandible
features of maxillae
- form part of orbit
- infraorbital foramen: hole for nerve
- alveolar process of maxilla: where teeth attach
- joined by suture
- palatine process: roof of mouth, attaches to palatine bones
features of mandible
- alveolar process of mandible: where teeth attach
- mandibular foramen (2): nerve for sensation of lower jaw
- coronoid process: helps form joint for chewing
- condylar process: articulates with mandibular fossa for temporomandibular joint
- ramus (between angle and coronoid process)
- angle (jawline)
- body
- mental foramen (2) for nerve to chin
- super strong
features of palatine bones
- horizontal plate (bottom): L-shape, goes up into nasal cavity, attaches to perpendicular plate (ethmoid) and vomer
zygomatic arch
1) temporal process of zygomatic bone
2) zygomatic process of temporal bone
nasal complex
- bones and cartilage enclose nasal cavity and paranasal sinuses
- nasal septum (formed by cartilage at the tip: septal hyaline cartilage) divides cavity into two chambers = perpendicular plate of ethmoid bone and vomer
paranasal sinuses functions
- all connected and continuous with nasal cavity
- lined with mucous membranes (grabs particles to prevent entry into lungs, warms air)
- lighten skull mass and increase surface area of nasal mucosa
paranasal sinuses
one on each side, within bones:
1) frontal
2) sphenoidal
3) ethmoid cells of ethmoid sinus
4) maxillary sinus
(portion of temporal bone has mastoid air cells but not connected to sinuses)
associated bones of skull
1) auditory ossicles: in petrous part of temporal bone (malleus, incus, stapes)
2) hyoid bone: in anterior neck at C3 (curved shape, doesn’t articulate with other bones but instead held in place by muscles and cartilage)
additional foramen, fissures and canals in the cranium
foramen:
1) rotundum: maxillary nerve
2) ovale: mandibular nerve
3) spinosum: middle meningeal artery/vein, meningeal branch of mandibular nerve
4) lacerum: greater petrosal nerve (pre-ganglionic PNS), deep petrosal nerve (post-ganglionic SNS)
5) stylomastoid: facial nerve
6) incisive: greater palatine arteries, sphenopalatine
7) greater palatine
8) lesser palatine
canals:
1) hypoglossal: motor innervation for tongue
2) carotid: internal carotid artery, nerves to heart
central nervous system
- brain in cranium + spinal cord in vertebral column
- nuclei = cell bodies
- tracts = nerve fibers
peripheral nervous system
- cranial nerves from brain/brainstem + spinal nerves from spinal cord
- ganglia = cell bodies
- nerves = never fibers
spinal cord
- continuation of brain stem
- extends through foramen magnum and vertebral canal, ending at inferior border of L1
- conduit for tracts to and from higher centers
- contains neural circuits (reflex arcs)
cervical and lumbosacral enlargements
- increased number of neurons in these regions for upper and lower limbs
(caudal) conus medullaris
- inferior end of spinal cord (vertebral level L2)
division of spinal cord
- 31 spinal segments with a pair (R/L) of spinal nerves for each
- C1-8, T1-12, L1-5, S1-5, C0 (coccygeal)
- do not match up exactly with vertebrae of same name
- C1-C7: spinal nerves superior
- C7: spinal nerve C8 emerges below
- T1 onwards: spinal nerves below associated vertebra
cell bodies in spinal cord
- axons within a nerve come from bodies at a prescribed level or segment
- leads to predictable patterns for locating pathologiesc
cauda equina
- collective mass of nerves below vertebral level L2
- spinal cord stops growing shortly after birth, but bones continue to
meninges of spinal cord
- extensions of brain meningeal coverings
1) pia mater: adheres tightly to spinal cord, outgrowths form denticulate ligaments and filum terminale
2) arachnoid mater
3) dura mater: thick single layer for stability, extends between adjacent vertebrae to fuse with CT layers surrounding spinal nerves
spaces in spinal cord meninges
1) subarachnoid space: between arachnoid and pia, contains CSF
2) subdural space: POTENTIAL space between dura and arachnoid
3) epidural space: between dura and periosteum, contains areolar CT, BVs and adipose tissue (cushions spinal cord)
denticulate ligament
- suspend and anchors cord laterally to dura mater
- preventing side to side movement
- looks like mesh/cobweb
dural sac
- dura and arachnoid mater
- extends to S2 (past end of spinal cord)
filum terminale
- outgrowth of pia that anchors spinal cord, preventing vertical movement
1) internum: extends from conus medularis to caudal end of dural sac - internum takes on layers of dura/arachnoid as it passes through and out of the dural sac to become:
2) externum (coccygeal ligament): extends through sacral hiatus to coccyx
lumbar cistern
- expanded subarachnoid space between L2-S2
- more CSF circulating around
lumbar puncture
- clinical procedure to sample CSF
- passes through: skin, back muscles, ligamentum flavum (pop because of CT resistance), epidural space, dura, arachnoid, subarachnoid space
epidural
- needle stops at epidural space
external surface of spinal cord
- contains 2 longitudinal depressions:
1) anterior median fissure: contains anterior spinal artery (veins run next to artery outside of the fissure)
2) posterior median sulcus - fissure deeper than sulcus
- extends along entire spinal cord
posterior rootlets
- pass through intervertebral foramen
- nerves for afferent sensory info
spinal cord white matter characteristics
- longitudinally along length of cord, external to grey matter
- fissures and sulci partition into columns and funiculi
- ascending tracts/columns = sensory info
- descending = motor
spinal cord white matter division
two sides connected by white commissure, each side has:
1) posterior column
- separated by: posterolateral sulcus, where posterior rootlets enter
2) lateral column
- separated by anterolateral sulcus, where anterior rootlets exit
3) anterior column
1 = ascending tracts
2 = descending tracts
spinal cord grey matter characteristics
- continuous column along length of cord
- contains nuclei
- butterfly shape
spinal cord grey matter divisions
1) posterior horn: sensory neurons and interneuron cell bodies
2) lateral horn (only T1-L2): visceral motor neurons
3) anterior horn (larger than posterior): somatic motor neurons
- R/L sides connected by grey commissure
central canal
- middle of spinal cord
- continuous with ventricles, contains CSF
regional variations in anterior horns
- enlarged at cervical (C5-T1) and lumbar (L2-S2) levels for somatic motor neurons of upper/lower limbs
regional variation in lateral horns
- T1-L2: visceral motor neurons, SNS preganglionic neurons
- S2-S4: no distinct lateral horns present because of large anterior horns, contain visceral motor neurons, PNS preganglionic neurons
regional variation in white matter
- decreases in cranial to caudal direction
- cord size in general decreases
spinal nerve
- posterior root and anterior root united
- anterior roots convey both somatic and visceral motor info
- posterior roots convey sensory input
anterior root lesions
- manifest motor signs in myotomal distribution
- myotome: group of muscles supplied by given spinal level
- ex. knee extension requires L3 myotome
dorsal root ganglion
- contains cell bodies of sensory neurons
posterior root lesions
- manifest sensory signs in dermatomal distribution
- dermatome: region of skin innervated by the sensory component of a given spinal level
anterior and posterior rami
- after leaving intervertebral foramen, spinal nerve splits into these
- posterior ramus: to back of body
- anterior ramus: to front of body
spinal nerve lesions
- manifest both sensory and motor signs
- location of signs helps to localize pathology
nerve plexus
- network of axons from anterior rami on R/L sides of body interweave fibers to form plexuses
- give information different routes to travel (if blocked in one path, can retain function by alternative route)
- four associated with spinal cord:
1) cervical: C1-4
2) brachial: C5-T1
3) lumbar: T12-L4
4) sacral: L4-S4
compound nerve
- anterior rami of some spinal nerves merge to form compound nerves
- carry axons from 2 or more spinal segment
- therefore, a muscle innervated by a compound nerve is controlled by >1 spinal segment
- ex. radial nerve for upper limb
brachial plexus palsy
- nerve trauma during birth leads to tearing of upper anterior rami
- loss of shoulder sensation and movement
- preservation of forearm and hand function because lower anterior rami are intact
reflexes
- involuntary motor response of muscles or glands evoked by specific stimulus to maintain homeostasis through rapid adjustments
- can be monosynaptic
components of a (non-visceral) reflex arc
1) stimulus activates sensory receptor
2) impulse travels through sensory neuron to CNS
3) motor neuron transmits impulse to effector (no interneuron)
4) effector responds
ipsilateral vs contralateral
- ipsi: stimulus/effect on same side of body
- contra: opposite sides
visceral reflexes
- autonomic reflexes initiated in viscera
- ex. bladder stretch when full
- all are polysynaptic
visceral reflex arc
1) stimulus activates sensory receptor
(2) nerve impulse travels through sensory neuron to CNS, but not to brain = long reflex)
*if skipped = short reflex
3) info processed in integration center by interneurons
4) motor neurons transmit impulse to effector
5) effector responds
parts of adult brain
1) forebrain: cerebral hemispheres and deep structures (diencephalon)
2) midbrain
3) hindbrain: includes cerebellum
*2/3 form brainstem
brainstem
- passageway for sensory/motor info, involuntary functions
- integrates body (spinal chord), cerebellum, cerebrum
- midbrain, pons, medulla
cerebrum function
conscious thought processes and intellectual functions
transverse fissure
- separates cerebellum from rest of brain
brain development
- starts as hollow neural tube
- disproportionate growth rates in different regions
1) 4 weeks to primary vesicles
2) 5 weeks to secondary vesicles
3) adult
primary vesicles in brain development
1) prosencephalon (forebrain)
2) mesencephalon (mid)
3) rhombencephalon (hind)
secondary vesicles in brain development
- prosencephalon divides into:
1) telencephalon (folds over to form cerebral hemisphere)
2) diencephalon - 3) mesencephalon (mid)
- rhombencephalon divides into:
4) metencephalon (pons, cerebellum
5) myelencephalon (medulla)
cerebrum structure
- paired cerebral hemispheres and deep structures
- surface called cerebral cortex
- covered by meninges
cerebral hemispheres
- same anatomy, different function
- separated by longitudinal fissure
cerebral cortex folding
- grey matter
- highly folded into gyri (bumps) and sulci (grooves)
cerebral cortex lobes
frontal, parietal, occipital, temporal, insula
division of lobes in cerebral cortex
1) central sulcus divides frontal and parietal loves
2) lateral fissure (very deep): divides temporal and frontal, insula lies within lateral fissure
3) parieto-occipital sulcus: divides parietal and occipital
4) cingulate sulcus: divides frontal and cingulate gyrus
5) calcarine sulcus: goes through occipital lobe
6) transverse fissure
precentral gyrus
- posterior part of frontal love
- contains primary motor area
postcentral gyrus
- anterior part of parietal lobe
- contains primary somatosensory area
limbic lobe
- not a discrete lobe, associated with other lobes
- formed by:
1) cingulate gyrus: frontal and parietal
2) parahippocampal gyrus: temporal
protective coverings of brain
1) cranium (skull bones)
2) cranial meninges
3) CSF (floating brain, nutrients)
4) blood-brain barrier: microscopic structure
brain cranial meninges function
- enclose and protect blood vessels
- contain and circulate CSF
brain cranial meninges structure
1) dura mater: thick (can’t see gyri/sulci), external, consists of TWO layers (periosteal adhered directly to bone and sutures, meningeal attached to arachnoid)
2) arachnoid: thin, avascular, lines meningeal layer of dura, trabeculae extend to pia (direct attachment), goes on top of sulci
3) pia: direct attachment to brain and spinal cord
potential spaces in cranial meninges
- above and below dura
- some normal spaces in specific locations
subarachnoid space in cranium
- between arachnoid and pia
- real space
- contains CSF
epidural hematoma
- torn branch of middle meningeal artery (under pterion)
- blood pools between periosteal dura and skull bone
- epidural space
- dura adheres to sutures, blood will not cross sutures –> biconcave lens shape
subdural hematoma
- tearing of cerebral veins
- skull does not break
- thrashing injuries, ex. whiplash
- blood accumulates between dura and arachnoid
- subdural space
- crescent shape, can freely move in cranial cavity
dural reflections
- meningeal layer of dura peels away from periosteal and folds back on itself
- hard CT plates that separate parts of the brain
major dural reflections
1) falx cerebri: biggest, separates R/L hemispheres, sits in superior longitudinal fissure
2) tentorium cerebelli: overlies cerebellum, sits in transverse fissure
3) diaphragma sellae: small, forms roof over sella turcica (sphenoid bone) and stabilizes pituitary gland
tentorial notch
opening created by tentorium cerebelli
venous sinuses
- created by (enclosed within) dural reflections
- drain blood from brain mainly to L/R internal jugular veins
- ex. superior sagittal sinus enclosed by falx cerebri
major venous sinuses (one on each side)
1) superior sagittal sinus: drains superficial cerebral veins of cortex
2) inferior sagittal sinus: drains floor of longitudinal fissure
3) straight sinus: drains internal structures and underside of brain
*1-3 meet at the confluence of sinuses (posterior), then pass through 4/5
4) transverse sinus: occipital bone
5) sigmoid sinus: passes through jugular foramen to connect to jugular vein
6) cavernous sinus: receives ophthalmic veins from orbit and rest of face, drains into 7/8
7) superior petrosal sinus: temporal bone
8) inferior petrosal sinus: temporal bone
brain ventricles
- cavities derived from lumen of neural tube
- filled with CSF produced by choroid plexus
- continuous with each other and spinal cord central canal
division of ventricles
1) 2 x lateral ventricles
- connected to 2) by interventricular foramen
2) 3rd ventricle: in diencephalon, between grey matter in midline
- connected to 3) by cerebral aqueduct
3) 4th ventricle: between pons/medulla and cerebellum
4th ventricle continuous with…
- subarachnoid space
- medial aperture
- 2 x lateral aperture (extend into cerebellum)
structure of lateral ventricles
1) anterior horn
2) body
3) posterior horn
4) inferior horn
- get further apart moving anterior to posterior
- separated by septum pellucidum
3rd ventricle structure
lateral walls formed by thalamus and hypothalamus
grey matter in brain
cerebral cortex and basal nuclei (deep)
cerebrospinal fluid
- formed by blood plasma pumped out of capillaries through ependymal cells into ventricles
- found in all ventricles
- supports/cushions brain, preventing it from getting sucked through foramen magnum
- transports nutrients to brain
- removes waste from brain
- continuous exchange between brain parenchyma and CSF
choroid plexus
- ependymal cells
- fenestrate capillaries that lie within pia matter
CSF circulation
- circulates through ventricles
- enters subarachnoid space via median/lateral apertures of 4th ventricle
- excess CSF drains into dural venous sinuses via arachnoid granulations (collection of villi mostly in superior sagittal sinus)
hydrocephalus
- “water on the brain”
- can be congenital or acquired
- increased CSF volume, enlargement of one or more ventricles, leading to intracranial pressure
causes of hydrocephalus
1) obstructive: blockage in ventricular system (localized increase in fluid)
2) non-obstructive: inadequate removal of CSF from brain (global increase in fluid)
blood brain barrier
- regulates what substances can enter interstitial fluid of brain
- perivascular feet of astrocytes and capillary endothelial cells (continuous: tight junctions block movement of molecules paracellularly)
white matter tracts
- carry info towards or away from neuronal cell bodies of cerebral cortex
- connect different parts of brain
groups of white matter tracts
1) commissural fibers: correct corresponding lobes between hemispheres
2) projection fibers: cerebral cortex to sub-cortical structures (ex. thalamus, spinal cord)
3) association fibers: interconnect cortical regions within same hemisphere
types of association fibers
- short: connect adjacent gyri
- long: connect lobes within same hemisphere
major association fibers
short:
1) arcuate fibers
long:
2) cingulum
3) inferior longitudinal fasciculus (temporal to occipital)
4) occipitofrontal fasciculus
5) superior longitudinal fasciculus: frontal to occipital, temporal
6) uncinate fasciculus: frontal to temporal
fasciculus
collection of white matter tracts
major commissural fibers
1) corpus callosum: largest, connects L/R hemispheres to coordinate cortical activities
2) anterior commissure: connects temporal lobes and olfactory bulbs to unify emotional responses
parts of corpus callosum
- anterior to posterior: genu, body, splenium
- forceps minor: genu in midsagittal view
- forceps major: splenium in midsagittal view
major projection fibers
1) corona radiata: fanning fibers from internal capsule
2) internal capsule: transfers sensory/motor info between cortex and subcortical structures
other structures to know location of
caudate nucleus, insula, putamen, globus pallidus, thalamus
parts of internal capsule
1) anterior limb: to and from frontal lobe
2) genu
3) posterior limb: descending motor and ascending sensory pathways
types of functional areas of cerebral cortex
1) primary cortical areas: receive info from peripheral receptors, little interpretation of meaning
2) association areas: receive info from primary area for higher order processing, integration and interpretation
uni vs heteromodal
- unimodal: association area that processes single sensor or motor modality
- heteromodal: processing and integration of information across more than one modality
sensory functional areas
1) primary somatosensory area (post central gyrus): contralateral touch, proprioception, pain and temperature
2) somatosensory association area (unimodal): interprets significance of sensory info
3) parietal association area (heteromodal): overlaps with 2)
right vs left brain
- primary cortical and association areas relatively symmetrical, lateralization is specific areas and specific tasks
- dominant = language, usually left side
- dominant hemisphere directs to prevent confusion and coordinate motor response
motor function areas
1) primary motor area (precentral gyrus): contralateral
2) supplementary motor complex: premotor and supplementary areas, controlling postural muscles, coordinated limb movement, higher order processing and integration of motor areas
motor homunculus
- size of neuron pool supplying musculature of that part of body
- feet most medial, then hands, then face
motor area lesions
1) primary motor area: weakness/paralysis, hypertonia, hyperreflexia on contralateral part of body
2) supplementary motor complex: apraxia, deficit in skilled motor activity, overall gross movement still intact
sensory homunculus
- size of cortical representation correlated with tactile acuity
- medial: foot, then hand, than face
sensory area lesions
1) primary somatosensory: “anesthesia” = less awareness of sensory input, poor localization
2) somatosensory association: inability to recognize complex objects by feel and difficulty reaching out for objects
cortical plasticity
- cortical representation can change in response to input or lack of input from a body region
- ex. limb amputation: portion for limb taken over by others
- ex. reading Braille: increased cortex association for hand
auditory function areas
1) primary auditory area: mainly contralateral, receives hearing from both ears
2) auditory association area: integrates complex auditory features
auditory lesions
1) primary auditory: decreased sound perception from contralateral ear
2) auditory association: difficulty interpreting pitch, timing, etc.
visual functional areas
1) primary visual area: either side of calcarine sulcus, receives fibers from contralateral half of visual field
2) visual association area: meaning and interpretation
visual lesions
1) primary visual: blindness in contralateral half
2) visual association: complex visual deficits, ex. object identification
insular cortex
- deep to lateral fissure
- contains gustatory cortex (taste)
- also involved in consciousness, emotion, self-awareness and cognition
cortical representation for smell
- interior surface and medial surfaces of the brain
non-contralateral senses
taste, smell
language centers in brain
- not bilateral! in dominant hemisphere (most left)
1) motor speech area (Broca): production of spoken, written and signed language)
2) sensory speech area (Wernicke): comprehension of spoken and signed language - two areas connected by arcuate fasciculus (subset of superior longitudinal fasciculus)
- two areas bilaterally connected to other parts of the cortex
Broca aphasia
- aka expressive or productive aphasia
- difficulty speaking/writing (difficulty initiating speech, not fluent, broken-up)
- comprehension preserved
Wernicke aphasia
- aka receptive or sensory aphasia
- inability to understand language and formulate thoughts for communication
- inappropriate word substitutions
basal nuclei (basal ganglia)
- deep within each cerebral hemisphere
1) caudate nucleus: parallel to lateral ventricles
2) putamen - 1+2 = striatum (striped appearance because of white matter in between)
3) globus pallidus - 2+3 = lentiform nucleus
4) subthalamic nuclei
5) substantia niagra
function of basal nuclei
- communicate with cortex to refine normal voluntary movement:
1) decision to move
2) direction
3) amplitude of movement
4) motor expression of emotions
parts of caudate nucleus
anterior to posterior:
1) head (bulbous)
2) tail (curved)
substantia nigra function
- regulates motor output from basal nuclei
- produces dopamine
- part of brainstem (midbrain)
- neurons are pigmented
parkinson’s disease
- motor disorder
- resting tremor, bradykinesia, postural instability
- degeneration of dopaminergic neurons (difficulty initiating movement
structures of diencephalon
1) thalamus: surrounds third ventricle
2) hypothalamus: forms walls of inferior 3rd ventricle, connected to pituitary gland
3) epithalamus: forms part of roof of 3rd ventricle, contains pineal gland
function of diencephalon parts
1) thalamus: process and relay sensory and motor info to cortex and basal nuclei, gateway to consciousness
2) hypothalamus: regulatory influences on homeostasis, endocrine system, ANS, limbic system
3) epithalamus: pineal gland secretes melatonin
thalamus structure
- paired mass of grey matter, each contains several groups of nuclei:
1) motor: movement planning and control - ventral anterior, ventral lateral
2) sensory: vision, hearing, taste, somatic sensation, proprioception - ventral posterior, lateral geniculate nucleus, medial geniculate nucleus
- interthalamic adhesion connects L/R but no function or cross-communication
thalamus nuclei groups
1) anterior
2) ventral: ventral anterior, lateral and posterior
3) lateral
4) posterior
5) medial
limbic system components
1) limbic lobe (cingulate gyrus + parahippocampal gyrus)
2) hippocampus
3) hypothalamus
4) amygdala
5) thalamus
“hippo with a HAT”
limbic system function
- regulates emotions, learning and memory
- strong connection between emotions and memory
fornix
tract of white matter connecting hippocampus with hypothalamus
mammillary body
- involved in memory and controls reflex movements associated with eating
hippocampus specific function
- learning and memory storage
- one portion closely associated with lateral ventricle
amygdala specific function
- emotional learning and memory
- loss of stimulation causes mellowing effects
- lots of stimulation = anger/anxiety
CNS pathways
- communication with body structures through sensory and motor pathways
- all are paired
- most decussate
sensory pathways
- conduct info about position sense, touch, temp, pressure and pain to brain
- three neuron pathway
3 neurons of sensory pathway
1) cell body in dorsal root ganglia OR sensory ganglia of cranial nerves
2) cell body in posterior horn of spinal cord OR brain stem nucleus, DECUSSATES (except olfaction) and projects to contralateral thalamus
3) cell body in thalamus, projects to primary sensory cortex via posterior limb of internal capsule
specific receptors of sensory pathways
1) exteroceptors: external body, ex. touch, temp, pressure, pain, vision, hearing
2) proprioceptors: within body, ex. muscle, tendons, joints
3) enteroreceptors: within the body, ex. viscera
what mediates conscious awareness of stimuli?
- sensory input reaching cortex
proprioceptors in skeletal muscle
1) muscle spindle: deep, detects changes in length
2) tendon organ: detects tension
ascending sensory pathways
- bundled according to modality
1) posterior column-medial lemniscus pathway (PCML): discriminative touch, vibration, pressure, proprioception
2) anterolateral pathway: pain, temperature, non-discriminative touch
3) spinocerebellar pathway: unconscious proprioception to cerebellum for fine adjustments of body movements
PCML pathway primary sensory neurons
- enter spinal cord and pass directly to ipsilateral posterior column
- fasciculus cuneatus: upper body, above T6
- fasciculus gracilis: lower body, below T6
PCML lower body pathway
1) cell body in DRG, axons form fasciculus gracilis
2) cell body in nucleus gracilis (medulla), decussates, axons form medial lemniscus and project to thalamus
3) cell body in ventral posterior nucleus (VPN), project to primary somatosensory cortex in postcentral gyrus via posterior limb of internal capsule
PCML upper body
1) cell body in DRG, axons = fasciculus cuneatus
2) cell body in nucleus cuneatus (medulla), decussates, axons = medial lemniscus, project to thalamus
3) cell body in VPN, project to primary somatosensory cortex in postcentral gyrus via posterior limb of internal capsule
somatotopy of posterior funiculi
- ascending: axons are added to the anterolateral column laterally
- sacral/coccygeal most medial
anterolateral pathway
- several tracts
- majority in spinothalamic tract
spinothalamic tract
1) cell body in DRG, synapse with 2) in spinal cord
2) cell body in posterior horn, axons decussate (immediately) in anterior white commissure and ascend in anterolateral column, becomes spinal lemniscus in brainstem
3) cell body in VPN of thalamus, project to primary somatosensory cortex in postcentral gyrus via posterior limb of internal capsule
anterolateral somatotopy
- axons added from medial aspect
- cervical most medial
spinocerebellar tracts
1) cell body in DRG
2) cell body in posterior horn inter neurons, some axons decussate and others do not, project to cerebellum
*NO tertiary neuron
motor pathways
- control skeletal muscle
- 2 neurons
- upper and lower motor systems
upper vs lower motor neurons
1) upper: arise in primary motor cortex and brainstem, 90% axons decussate in caudal medulla
2) lower: arise in motor nuclei of cranial nerves and anterior horn of spinal cord, have direct control over skeletal muscles, influenced by reflexes
descending motor pathways
1) lateral motor system: lateral corticospinal tract, rubrospinal tract
2) medial motor system: anterior corticospinal tract, reticulospinal, vestibulospinal, tectospinal
lateral motor system control
- LMNs that innervate proximal and distal limbs
- skilled voluntary movements
medial motor system control
- LMNs that innervate trunk (core of body) and proximal limbs
- influences posture, balance, stance (not fine motor movements)
lateral corticospinal tract
- UMN fibers cross midline in caudal medulla
- descend in lateral column
- target LMNs that innervate distal limb muscles
- cervical and lumbrosacral levels only
anterior corticospinal tract
- UMN fibers descend in anterior column
- some cross the midline in the spinal cord at the level where they stop (others do not, bilateral control)
- target LMNs controlling trunk and proximal muscles
- all spinal levels
corticospinal tracts in the brainstem
1) cerebral peduncles: hold up cerebrum, contain descending corticospinal tracts that pass along anterior surface of midbrain
2) pyramids: shapes formed by corticospinal tracts in medulla
3) decussation of pyramids: location where majority of corticospinal tracts cross to contralateral side
clinical signs of LMN lesions
- damage limited to muscles innervated by affected LMNs
- loss of input: weakness/paralysis, hypotonia, hyporeflexia
- spontaneous discharge of LMNs: fasciculations (muscle twitches) = early effect
- denervation: atrophy = later effect
clinical signs of UMN lesions
- damage typically involves entire limbs
- contralateral effects
- loss of input to LMN: weakness/paralysis, Babinski sign
- loss of LMN regulation: spasticity (hypertonia, hyperreflexia, clonus)
Babinski sign
- touching sole of foot causes toes to flail (no curling reflex)
clonus
- tapping tendon causes shaking
other pathways involved in movement
1) basal nuclei: decision, direction, amplitude, emotion
2) cerebellum: proprioception, vestibular info, environmental cues
*these communicate with UMN system
cranial nerves in brainstem
III-XII + associated nuclei
brainstem gray matter arrangement
- bilateral nuclei: distinct regions, not columns
1) sensor: somatic, visceral, special
2) motor: somatic, visceral/parasympathetic
brainstem nuclei function
- maintenance of vital functions (CV/respiratory) and consciousness
- of note: reticular formation
pons and ventricles
- part of pons forms 4th ventricle
midbrain structure
1) cerebral peduncles containing descending motor tracts (corticospinal)
2) superior cerebellar peduncles: connect cerebellum to midbrain
3) superior colliculi (2): vision
4) inferior colliculi (2): hearing
midbrain cranial nerves
III: oculomotor
IV: trochlear (from posterior of brainstem)
tectum
formed by colliculi in brainstem
transverse section of midbrain
1) substantia nigra: darker
2) red nucleus
3) tectum
pons structure
- bulging anterior region of brainstem
- middle cerebellar peduncles connect to cerebellum
pons cranial nerves
V: trigeminal (lateral, one of the largest)
VI: abducens (anterior)
VII: facial (anterior)
VIII: vestibulocochlear (anterior)
medulla structure
1) pyramids: contain corticospinal tracts
2) olives: contain gray matter
3) inferior cerebellar peduncles: connect medulla to cerebellum
4) nucleus cuneatus and gracilis
medulla cranial nerves
IX: glossopharyngeal
X: vagus
XI: spinal (accessory)
XII: hypoglossal
why is XI sometimes not considered a true cranial nerve?
- arises partially from spinal cord
cerebellum connection to brainstem
cerebellar peduncles (superior, middle, inferior)
cerebellum structure
- left and right cerebellar hemispheres separated by vermis
- 3 lobes: anterior, posterior, flocculonodular (can only see from caudal view)
- 3 regions: cortical gray matter, subcortical white matter, deep cerebellar nuclei
- folia: ridges (tighter than gyri)
cerebellum function
- coordination and prediction of movement (planning more lateral, movement more medial)
- posture and balance (flocculonodular and vermis)
cerebellum lesions
- lead to ataxias
- ex. F/V lesion = trunk instability
cerebellum sensory inputs
1) vestibulocerebellar input from inner ear: position and acceleration of head –> CN VIII and inferior colliculi
2) spinocerebellar input: proprioceptive info (body position and muscle tone) from limbs –> inferior
3) tectocerebellar input: vision and auditory info from tectum –> superior + inferior
4) corticopontocerebellar input: movement planning from frontal cortex via pons –> middle
*not necessarily conscious info
cerebellum outputs
1) corticospinal tract: directs communicated signal to LMN
2) cerebrocerebellar output: to motor cortex via ventrolateral nucleus (thalamus)
*only output from superior peduncle
cerebellum lesion side
- double cross over, so ipsilateral effects
cranial nerve categories
1) special sensory: I, II, VIII
2) motor: III, IV, VI, XI, XII
3) both: V, VII, IX, X
some say money matters, but my brother says big brains matter more
cranial nerve crossover?
- none, so lesions have ipsilateral effects
- all are bilateral
cranial nerve names
I: olfactory
II: optic
III: oculomotor
IV: trochlear
V: trigeminal
VI: abducens
VII: facial
VIII: vestibulocochlear
IX: glossopharyngeal
X: vagus
XI: (spinal) accessory
XII: hypoglossal
oh once one takes the anatomy final very good vacations are heavenly
olfactory nerve (I)
- smell from olfactory epithelium (nasal cavity)
- enters via olfactory foramina in cribriform plate (ethmoid bone)
optic nerve (II)
- visual input from retina
- enters via optic canal
vestibulocochlear (VIII)
- vestibular: equilibrium from vestibular apparatus
- cochlear: auditory sensation from cochlea
- enters via internal acoustic meatus
oculomotor (III)
- 4/6 extraocular muscles
- levator palpebrae superioris: upper eyelid muscle
- preganglionic parasympathetic fibers to lens of eye (ciliary ganglion)
- superior orbital fissure
trochlear (IV)
- superior oblique muscle
- superior orbital fissure
abducens (VI)
- lateral rectus muscles
- superior orbital fissure
strabismus
- misaligned eye
- CN III, IV, or VI
diplopia
- double vision
- CN III, IV, or VI
ptosis
- droopy eye
- CN III
mydriasis
- dilated pupil
accessory (spinal) (XI)
- rootlets from upper cervical spinal segments
- enters skull through foramen magnum
- exits skull through jugular foramen
- trapezius and sternocleidomastoid (SCM) muscles
trapezius
- elevates ipsilateral shoulder
SCM
- rotates head to contralateral shoulder
hypoglossal (XII)
- hypoglossal canal
- intrinsic and extrinsic tongue muscles
hypoglossal lesion
- tongue deviates to same side when stuck out
- dysarthria: difficulty speaking
- dysphagia: difficulty swallowing
trigeminal (V)
- somatic sensation from head
- three divisions from trigeminal ganglion (pseudounipolar primary somatic sensory neuron cell bodies)
1) V1 opthalmic: superior orbital fissure –> forehead to tip of nose
2) V2 maxillary: foramen rotundum –> posterior to eye, cheek and upper lip
3) V3 mandibular: foramen ovale –> jaw to temple - V3 also contains motor fibers for muscles of mastication
facial (VII)
- internal acoustic meatus, then other openings
1) somatic sensation from around ear opening
2) special visceral sensation from anterior 2/3 tongue (taste)
3) motor fibers (5 major branches) via stylomastoid foramen for facial expression muscles
4) preganglionic parasympathetic fibers to submandibular, sublingual and lacrimal glands
facial nerve ganglions
pterygopalatine, geniculate, submandibular
glossopharyngeal (IX)
- jugular foramen
- somatic sensation from posterior 1/3 of tongue, pharynx and soft palate (gag reflex)
- special visceral sensation from posterior 1/3 tongue (taste), common carotid artery: carotid sinus (baroreceptor) and body (chemoreceptor)
- motor fibers for 1 muscle in pharynx (swallowing)
- preganglionic parasympathetic fibers to parotid gland (otic ganglion), carotid body and sinus
parotid gland
largest salivary gland
vagus (X)
- jugular foramen
- somatic sensation and motor fibers for pharynx and larynx (swallowing, speaking)
- visceral sensory from larynx, trachea, esophagus, thoracic and abdominal viscera, stretch receptors in aortic arch
- preganglionic parasympathetic fibers to intramural ganglia of thoracic and abdominal viscera
autonomic nervous system functions
1) maintain homeostasis
2) regulate body temp via sweat glands and vascular smooth muscle
3) coordination of cardiovascular, respiratory, excretory and reproductive functions
CNS structures in ANS
1) hypothalamus: integration and command center
2) brainstem: reflex centers
3) spinal cord: reflex centers
ANS vs somatic NS
somatic NS:
- single LMN extending from CNS
- all myelinated
- innervates skeletal muscle
ANS:
- two LMNs extending from CNS
- only preganglionic myelinated
- innervates smooth and cardiac muscle and glands
can somatic and ANS share nerve?
yes, can share same peripheral nerve
ANS divisions and differences
PyNS:
- craniosacral division (brainstem + sacral)
- rest and digest
- decrease heartrate, increase digestion
- long pre, short post
- autonomic ganglion close to or within effector organ (wall)
SyNS:
- thoracolumbar division
- fight or flight
- increase heart rate, decrease digestion
- short pre, long post
- preganglionic branching (widespread effects)
- autonomic ganglion close to vertebral column
SyNS and PSyNS innervation
- most structures have both
- SyNS alone controls most vascular smooth muscle + all smooth muscle in limbs and body wall (BVs, erector pili, glands)
anatomical differences between PSyNS and SyNS
1) location of preganglionic neuron cell bodies
2) length of pre/post
3) # of preganglionic branches
4) location of ganglia
PSyNS craniosacral division
- preganglionic arise in CN III, VII, IX, X and S2-S4
- postganglionic in intramural pr terminal ganglia near or in effector organ
SyNS thoracolumbar division
- preganglionic arise in T1-L2
- post either in sympathetic chain ganglia (paired) or collateral ganglia (unpaired)
preganglionic neuron synapse with…
- can synapse with several postganglionic neurons in the ganglion
PSyNS neurotransmitters
- pre: synthesize and release Ach, acting on nicotinic receptors (ligand-gated ion channels), always excitatory
- post: synthesize and release Ach, acting on muscarinic receptors (secondary messenger), effects depend on receptor and tissue type
- ex. excite GI tract, constrict (inhibit) pupil
SyNS neurotransmitters
- pre: synthesize and secrete Ach, nicotinic receptor, always excitatory
- post: most use NE, adrenergic receptor effect depends on tissue ex. excites (dilates) pupil, inhibits GI tract
- sweat glands and BV of skeletal muscle: release Ach onto muscarinic receptor
- adrenal medulla releases 80% E, 20% NE
PSyNS nerve distribution
CN III, VII, IX = viscera of face
CN X = viscera of thorax and most of abdomen
pelvic splanchnic (visceral nerves) = viscera of distal abdomen and pelvis
pelvic splanchnic nerves
- preganglionic S2-S4
- terminal ganglia in walls of colon, ureters, bladder and reproductive organs
- do NOT join anterior rami of spinal nerves
SyNS targets
1) smooth muscle of limbs and body wall
2) viscera of head and thorax
3) viscera of abdomen and pelvis
paired sympathetic chain (paraverterbral) ganglia targets
1) smooth muscle of limbs and body wall
2) viscera of head and thorax
unpaired collateral (prevertebal) ganglia targets
1) viscera of abdomen and pelvis
rami communicantes
- connect spinal nerves to each sympathetic chain
- contains gray and white rami
sympathetic innervation to smooth muscle of limbs and body wall
- preganglionic goes through white ramus (myelinated) –> these can ascend or descend within the chain before synapsing: distributes innervation above T1 and below L2
- post ganglionic goes through gray ramus, splits into posterior and anterior
sympathetic innervation to viscera of head and thorax
- preganglionic from T1-T5
- post ganglionic do NOT leave through gray ramus
- instead, extend medially from sympathetic chain and project directly to the effector (contribute to autonomic plexuses
sympathetic innervation to viscera of the HEAD
- postganglionic neurons form autonomic plexuses that ravel along blood vessels to target tissues
- ex. carotid plexus travels along carotid artery
sympathetic innervation to viscera of the THORAX
- postganglionic neurons form splanchnic (visceral) nerves
- these contribute to autonomic plexuses that innervate targets in the thorax
- ex. cardiac nerve forms cardiac plexus
sympathetic innervation to viscera of abdomen and pelvis
- preganglionic fibers from inferior thoracic and upper lumbar segments –> these do NOT synapse in sympathetic chain
- instead, converge to form splanchnic nerves (greater, lesser, least, lumbar)
- splanchnic nerves terminate in collateral ganglia, where they synapse with postganglionic –> connection occurs around roots of major arteries that branch from aorta
- postganglionic contribute to autonomic plexuses that travel with blood vessels to reach their targets
collateral ganglia
1) celiac ganglion: greater thoracic splanchnic nerve
2) superior mesenteric ganglion: lesser and least
3) inferior mesenteric ganglion: lumbar
adrenal medulla pathway
1) preganglionic sympathetic neurons from T5-T8
2) medullary cells = modified postganglionic neurons, release E and NE directly into blood for systemic distribution (thus, effects last longer)
dual innervation
- most vital organs receive both PSyNS and SyNS
- plexus: sympathetic postganglionic axons, parasympathetic preganglionic axons, visceral sensory axons
plexus examples
1) cardiac
2) pulmonary
3) esophageal
4) celiac, superior, inferior mesenteric: abdominal viscera
5) hypogastric: digestive, urinary, reproductive organs
visceral afferents
- bring info from body’s core to CNS, most are unconscious
- nociceptors, mechanoreceptors (fullness), specialized receptors (chemical, physical environment)
how do visceral afferents travel?
- with visceral efferent fibers
1) for pain: travel with sympathetic efferent fibers
2) homeostatic sensory info: parasympathetic efferent fibers
referred pain
- pain perceived at location other than site of painful stimulus
- afferent pain fibers enter posterior horn and travel with anterolateral system on contralateral side
- ex. cardiac pain (ex. ischemia) refers to dermatomes associated with chest, armpit and arm
somatic pain vs referred visceral pain
somatic:
- conducted to CNS via spinothalamic tract
visceral:
- travel with (not same fiber!) sympathetic efferent fibers
- visceral sensory fibers overlap (same secondary neuron) with somatic, CNS cannot differentiate source = referred pain
major arteries
from arch of aorta:
1) brachiocephalic
2) left common carotid
3) left subclavian
from brachiocephalic:
4) right common carotid
5) right subclavian
major veins
from superior vena cava:
1) 2x brachiocephalic
from brachiocephalic
2) L/R subclavian
3) L/R internal jugular
blood supply to spinal cord
- vertebral-basilar system and segmental arteries
- vertebral arteries give rise to unpaired anterior spinal artery and paired posterior spinal arteries
anterior/posterior spinal arteries
- anterior: supplies anterior and lateral columns of white matter, anterior gray horns
- posterior: posterior white columns and gray horns
segmental arteries (types and where from)
1) cervical region from branches of vertebral arteries
2) thoracic from intercostal arteries
3) lumbar from lumbar
blood supply to brain
pairs of:
1) vertebral arteries
- vertebral arteries merge to form basilar artery
2) internal carotid
vertebral artery
each vertebral artery has three branches
1) anterior spinal
2) posterior spinal
3) posterior inferior cerebellar
basilar artery
- overlies pons
- supplies brainstem and cerebrum
- three branches:
1) pontine arteries
2) anterior inferior cerebellar artery
3) superior cerebellar artery - bifurcates to form L/R posterior cerebral arteries
posterior inferior cerebellar artery
- goes to inferior aspect of cerebellum (posterior lobe)
internal carotid artery
4 branches:
1) middle cerebral artery: along lateral fissure to supply lateral cortex
2) anterior cerebral artery
3) posterior communicating artery: connects to posterior cerebral artery
4) ophthalamic artery
anterior communicating artery
- connects both anterior cerebral arteries
common locations for aneurysms/strokes
- posterior and anterior communicating arteries
cerebral arterial circle
- aka circle of willis
- creates collateral flow (redundancies)
- protective in event when one part of the system is compromised
perfusion areas of cerebral arteries
- anterior: medial and 1-2cm of lateral surface of frontal/parietal
- middle: majority of lateral surface of cortex
- posterior: occipital lobe, medial and inferior temporal lobes
orbit shape and location
- pyramidal space
- base located anterior
- apex posteriormedially at optic canal
bones of the orbit
1) frontal = superior
2) zygomatic = lateral
3) sphenoid = superior, lateral
4) ethmoid = medial
5) maxilla = floor
6) lacrimal = floor
foramens and fissures in orbit
1) supraorbital foramen
2) optic canal
3) superior orbital fissure
4) inferior orbital fissure
5) infraorbital foramen
6) lacrimal foramen
eye accessory structures
1) hairs: eyebrow, eyelashes
2) eyelid
3) superficial epithelium
4) lacrimal apparatus
palpebral fissure
eye opening
lacrimal caruncle
- soft tissue on medial side
- contains glands
eyelid components
1) fibrous CT tarsal plates (2)
2) tarsal glands
3) palpebral part of orbicularis oculi
4) levator palpebrae superioris: elevates superior part of eyelid (CN III)
orbicularis oculi
muscle around eye (sphincter)
conjunctiva
- layer of epithelium covering inner surface of eyelids and outer surface of eye
- internal surface of eyelid: specialized stratified columnar epithelium (BV rich) and goblet cells (secretions)
lacrimal apparatus function
- produces and removes tears
- tears reduce friction, remove debris, prevent infection and nourish epithelium
lacrimal apparatus components (flow of tears)
1) CN VII (PSyNS) or sympathetic trunk stimulates lacrimal gland to produce tears
2) lacrimal ducts conduct to eye
3) blinking moves tears lateral to medial
4) lacrimal canaliculi drains fluid into lacrimal sac
5) nasolacrimal duct transports fluid to nasal cavity
6) nasal meati = small openings that lead into nose
eye anatomy
- hallow
- two cavities separated by lens
- wall has three layers
1) fibrous (most superficial)
2) vascular
3) inner
eye cavities
1) anterior: anterior/posterior chambers filled with aqueous humour
2) posterior: contains vitreous body (maintains shape of eye)
fibrous layer (eye)
- strong, dense fibrous CT containing collagen and elastic fibers
- sclera and cornea
cornea
- outer clear, curved structure
- avascular
- regularly spaced collagen fibers
- function: curved surface to refract incoming light
sclera
- visible white part of eye
- provides shape, protects inner parts and is attachment point for muscles
extraocular muscles
- control eye movement and elevate eyelid
- attach to sclera
- surrounded by periorbital fat
- oriented along long axis of orbit and arise from common tendinous ring
axis of orbit and visual axis
not lined up normally
major actions of extraocular muscles
y-axis:
- superior rectus: elevate abducted eye
- inferior rectus: depress abducted eye
x-axis:
- lateral rectus: abduct
- medial rectus: adduct
z and y-axis:
- superior oblique: intorsion and depression of adducted eye
- inferior oblique: extorsion and elevation of adducted eye
other:
- levator palpebrae superioris
extraocular muscle innervation
LR6
SO4
others = 3
vascular layer of eye
- blood vessels, lymphatics and intrinsic eye muscle
1) choroid
2) ciliary body
3) iris
choroid (eye)
highly vascularized, contains melanocytes (melanin absorbs extraneous light)
iris
- blood vessels, pigment cells, smooth muscle cells that regulate pupil size
ciliary body
- ciliary muscles: alter shape of lens
- ciliary processes: secrete aqueous humour, attachment for suspensory ligaments (that attach to lens)
pupillary constriction vs dilation
- constriction = sphincter pupillae contract = PSyNS
- dilation = dilator pupillae (radial) contract = SyNS
inner (retina) layer of eye
two layers:
1) pigmented: absorbs light, has important biochemical interactions with photoreceptors
2) neural: photoreceptors and associated neurons, responds to light and processes visual info
ora serrata
margin between neural and pigmented layer that continues anteriorly
neural layer organization
1) photoreceptors (rods/cones) detect light, transduce into membrane potential, synapse with bipolar neurons
2) bipolar, horizontal and amacrine cells process visual info
3) ganglion cell axons form optic nerve going to optic disc
optic disc
where optic nerve exits, no photoreceptors so blind spot
macula
- contains fovea centralis
- highest concentration of cones = highest visual acuity
cones vs rods
- cones = high intensity light and colour vision
- rods = dim light
- more rods than cones
lens
- divides internal eye into two cavities
- focuses images on photoreceptors by changing shape
lens in distant vision
- PSyNS
- ciliary muscles relax
- ciliary body moves posteriorly
- suspensory ligaments tense
- lens flattens
lens in near vision
- ciliary muscles contract
- ciliary body moves anteriorly
- suspensory ligaments loosen
- lens becomes round
visual pathway
- each eye receives from both left and right visual fields
- projection onto retina is reversed and inverted
- primary neurons = bipolar
- optic nerves carry info from ipsilateral eye
- medial region cross at optic chiasm
- optic tracts contain fibers from both eyes, majority extend to LGN and synapse with tertiary neurons that extend to visual cortex (contralateral visual field processed)
optic nerve lesion
- ipsilateral eye complete loss of vision
optic chiasm lesion
- temporal fields lost
- common ex. in pituitary tumour
ear divisions
1) external ear: auricle, external auditory canal, ceruminous and sebaceous glands (produce cerumen), elastic cartilage
- separation: tympanic membrane
2) middle ear: ossicles, tympanic cavity, surrounded by bone
3) inner ear: auditory tube, cochlea, vestibular complex
ear division functions
1) external: direct sound into ear, protect tympanic membrane
2) middle: ossicles connect tympanic membrane to receptor complex of inner ear
3) sensory receptors for equilibrium and hearing
middle ear connections
1) communicates with nasopharynx via auditory tube
2) mastoid cells through numerous small connections
tympanic membrane
- converts sound waves into mechanical movements
- transfers them to ossicles to amplify sound
ossicles
1) malleus (hammer)
2) incus (anvil)
3) stapes (stirrup)
protection against loud noises
muscles that contract to modulate sound and protect from violent movements:
1) tensor tympani (CN V): decreases range of movement of tympanic membrane
2) stapedius (CN VII): decreases movement of stapes
hyperacusis
- normal noises perceived as sharp or painful
- can arise from paralysis (ex. CN lesion) of tensor tympani or stapedius
inner ear bony labyrinth
- fluid-filled (perilymph)
- three regions:
1) semicircular canals (anterior, posterior and lateral): houses semicircular ducts
2) vestibule: houses utricle and saccule
3) cochlea: houses cochlear duct
inner ear membranous labyrinth
- fluid-filled (endolymph)
- suspended in and protected by bony labyrinth
- contains sensory receptors for equilibrium and hearing (connected to CN VIII
endolymph
- higher in K, lower in Na
perilymph
- similar to CSF
- suspends and protects membranous labyrinth from bony
vestibular apparatus
- formed by utricle, saccule and semicircular ducts
- sensory receptors for equlibrium
utricle and saccule
- detect head position during static equilibrium and linear acceleration
- contain sensory receptors in area called macula: contains hair cells and support cells
- tips of stereocilia embedded in otolithic membrane (jelly-like, contains otoliths = calcium carbonate crystals)
- otolithic membrane has higher specific gravity than surrounding endolymph, responds differently to gravity
semicircular ducts
- detect angular acceleration (rotation) of the head
- ampulla filled with endolymph
- cupula embeds kinocilia and stereocilia in gelatinous dome in the middle of ambula
- crista (ampularis): expanded area containing sensory receptors (hair cells) and supporting cells
hair cell structure
- many stiff stereocilia
- one very tall kinocilium that detects movement
utricle/saccule equilibrium mechanism
- movement shifts otolithic membrane, causing bending of stereocilia and kinocilium
- changes amount/rate of NT release to sensory nerve
- utricle: horizontal linear movement and head tilt, otolithic membrane in horizontal orientation
- saccule: vertical movement, otolithic membrane in vertical orientation (gravity, kinocilium distorted)
semicircular ducts equilibrium mechanism
- rotation of head causes endolymph to push against cupula (same S.G) (ex. move head to the right = canals move to right but endolymph resists motion due to inertia, opposite flow)
- bending of stereocilia results in altered NT release from hair cells, changes AP traffic along nerve
- ducts do not behave in the same way in each ear!
vestibular pathway
- information used to coordinate head movements with eye, neck, trunk and limb movements
1) semicircular canals
2) vestibular ganglion
3) vestibular nerve
4) joins with cochlear = CN VIII
5) vestibular nucleus projects to several areas: cerebellum, vestibulospinal tracts, XI, VI, III, IV, red nucleus, superior colliculus to cerebral cortex
motion sickness
conflict between vestibular complex and visual references
cochlea
- houses hearing organs
- wraps 2.5x around spongy bone axis (modiolus)
- membranous cochlear duct suspended inside (contains space called scala media, filled with endolymph)
cochlear duct
- roof: vestibular membrane
- floor: basilar membrane
- divides cochlear space into:
1) scala vestibuli
2) scala tympani
(both filled with perilymph)
spiral organ
- sensory structure for hearing
- protected within membranous cochlear duct
- located on basilar membrane
- thick sensory epithelium with hair cells and supporting cells
- stereocilia and kinocilium in gelatinous tectorial membrane (extends over spiral organ)
inner vs outer hair cells in spiral organ
- inner: closer to modiolus, solo, sensory receptors for hearing
- outer: columns of 3, amplify movement of basilar membrane during low intensity sounds
nerves in spiral organ
- spiral ganglion: cell bodies of sensory afferent
- afferent nerve fiber: monitors hair cells
- both contribute to cochlear part of vestibulocochlear nerve
helicotrema
- where tympanic and vestibular duct become continuous with each other (apex)
what happens when you hear a sound?
1) vibration of tympanic membrane moves ossicles
2) stapes moves in and out of the oval window like piston
3) pressure waves initiated in perilymph of vestibular duct
4) vestibular and basilar membrane vibrate in response to pressure waves = sensory cells create electrical signal
5) remaining pressure waves transferred to tympanic duct, exit at round window
how do ossicles amplify sound?
large SA to small
how is frequency (pitch) interpreted?
- pressure waves displace different parts of the basilar membrane
- base: narrow, stiff, high frequency
- apex: wide, floppy, low frequency
how is intensity (loudness) perceived?
- hits basilar membrane at same spot according to frequency, but moves it more
auditory pathway
- project bilaterally to primary auditory cortex
- four neurons:
1) vestibular cochlear nerve to cochlear nucleus in medulla
2) two pathways: - directly to inferior colliculi
- pass through superior olivary nucleus first
3) to medial geniculate nucleus (thalamus)
4) to auditory cortex
frequency in auditory cortex
high = medial, low = lateral
conduction hearing loss
- obstruction of conduction of sound energy
- external and middle ear involved
sensorineural hearing loss
- problem in inner ear
- can involved hair cells or cochlear nerve
which hearing loss do hearing aids target?
- conduction deafness
- amplify sound into ear
