Nervous System Flashcards
nervous system
CNS + PNS
CNS
brain + spinal cord
brain
forebrain
midbrain
hindbrain
PNS
cranial nerves
spinal nerves
peripheral ganglia
somatic + autonomic
SNS
motor + sensory
control of body wall + upper/lower extremities
ANS
visceral
motor + sensory
motor → symp. + parasymp
cells in NS
neurons: nerve cells that conduct signals
neuroglia: support cells for neurons
neuron
~ 100 billion neurons (10^11)
each one has ~ 100 000 connections with other neurons
cell body = nucleus, nucleolus, dendrites, mitochondria, Nissl bodies
1 axon leaves cell body
synapse
connections between neurons
10^15 in CNS
nerve cell bodies
nucleus: collection in CNS
ganglia: collection in PNS
Nissl bodies
specialized ribosomal bodies
specific to nerve cells
neurofibrils
intermediate filament proteins
provide support within axon hillock
axon hillock
initial segment
summation of excitatory + inhibitory input
if threshold potential is reached = fires
bipolar neuron
2 appendages = 1 dendrite + 1 axon
senses = vision, taste, olfaction
unipolar neuron
1 appendage
somatosensation (afferents)
multipolar neuron
many dendrites, one axon
efferents (motor)
pyramidal, purkinje, stellate, granule, basket cells → found in brain = different dendrite branching
satellite cells
neuroglia that surround cell bodies in ganglia (PNS)
regulate O2, CO2, nutrient, + NT levels around neurons
Schwann cells
neuroglia that surround axons in PNS
one cell wraps one section of axon + produces myelin sheath = participate in repair process after injury
oligodendrocytes
neuroglia that myelinate CNS axons
have appendages = one cell myelinates many whole axons
provides structural framework
astrocytes
neuroglia in CNS
provide structural support; regulate ion, nutrient, + dissolved gas concentrations; absorb + recycle NT; form scar tissue after injury
some maintain blood-brain barrier
ependymal cells
neuroglia in CNS
line ventricles + spinal cavity
assist in producing, circulating, and monitoring of CSF
microglia
neuroglia in CNS
circulate to remove cell debris, wasts, and pathogens by phagocytosis (substitute for blood = limited by BBB)
meninges
membranes covering CNS structures = protection
- dura mater: tough outer layer; protect from external force
- arachnoid mater: secretes CSF into subarachnoid space; covers cranial blood vessels
- pia mater: delicate covering of brain
cerebrum
higher cognitive functions
language + speech
somatic motor + sensory function
regulates emotional aspects of behaviour
cerebral cortex
outside surface
grey matter
neuronal cell bodies
cerebral medulla
inner region
white matter
axons
longitudinal fissure
interhemispheric
separates L + R hemispheres
poles of cerebrum
frontal pole
occipital pole
2 temporal poles (L+R)
sulci
central sulcus = separates pre + post central gyri
lateral sulcus = separates temporal lobe
frontal lobe
higher cognitive planning, strategy, motor
parietal lobe
perception of self in space, sensory
temporal lobe
memory, learning, social, hearing
occipital lobe
vision = most important sense
precentral gyrus
frontal lobe
primary motor cortex = initiation of motor signals
- motor homunculus - map on cortex corresponding to body
anterior to central sulcus
postcentral gyrus
parietal lobe
primary sensory cortex
- sensory homunculus - map on cortex corresponding to body
posterior to central sulcus
projection fibres
travel to and from cortex
ex. to/from spinal cord
association fibres
intrahemispheric connections
- short ex. within lobe
- long ex. between lobes → BA to WA for speech
commissural fibres
interhemispheric connections
ex. corpus callosum = largest
cerebellum
acts as a comparator = compares intended movement with evolving movement and corrects for errors → uses feedback to make adjustments
ensures movements are smooth, coordinated, and purposeful (skilled)
regulates posture + balance
cerebellar ataxia
intention tremor, lack of balance + coordination
brainstem
midbrain, pons, medulla oblongata
contains motor + sensory pathways connecting cerebral cortex + thalamus to SC
houses cranial nerve nuclei (origins of CNs)
contains RAS = arousal + consciousness
vital centres for regulating heart rate + breathing
centres for regulating swallowing + gag reflex
diencephalon
thalamus: inferior to corpus callosum; bilateral structure
hypothalamus: inferior to thalamus
midbrain
substantia nigra + red nucleus
relay centres for visual and auditory pathways (reflexive orientation)
CNs III + IV attached
substantia nigra
regulates motor activity
neuronal degeneration = Parkinson’s disease
red nucleus
regulates motor activity
active controller of flexors of upper extremities
controlled by descending inhibition
pons
bridge between cerebrum + cerebellum
CNs V, VI, VII, VIII attached
medulla oblongata
contains vital cardio-respiratory regulatory centres
nuclei for CNs IX, X, XI, XII
ventricles
lumen of neural tube during development
fluid from capillary beds = CSF → circulates within brain
lateral ventricles
have anterior + posterior horns
connect to 3rd ventricle
3rd ventricle
separates L + R thalamus
feeds into cerebral aqueduct = connects to 4th ventricle
4th ventricle
between pons and cerebellum
feeds into central canal within SC
internal carotid arteries
paired
ascend carotid canals
divide into anterior + middle cerebral arteries
vertebral arteries
branch from subclavian arteries
ascends through foramen magnum
L+R join at pons → basilar artery → posterior cerebral arteries
anterior cerebral artery
branches from internal carotid, forms anterior of Circle of Willis
supplies medial + dorsal brain
anterior communicating artery
bridges L+R anterior cerebral arteries
middle cerebral artery
from internal carotid, extends laterally
supplies lateral brain
posterior cerebral artery
from basilar, extends laterally
forms posterior of Circle of Willis
supplies posterior and ventral brain
posterior communicating arteries
connects posterior + middle cerebral arteries (2; one on each side)
forms sides of Circle of Willis
spinal cord
within vertebral column
projection pathway to/from cerebral cortex; extends from medulla at foramen magnum
ends as conus medullaris at L1-2 intervertebral disc
bulges in lower cervical (brachial plexus) + lumbar (lumbosacral plexus) segments = roots of spinal nerves for upper/lower extremities
central canal
within SC; passes through centre of grey matter
continuous with ventricles of brain
cauda equina
nerve roots extending from SC; lie inferior
growth to maintain attachment between SC and vertebral column during development (VC grows faster)
filum terminale
pia matter continues past SC
attaches cord to coccyx = stabilizing
ends at S2 vertebral level
spinal cord organization
inner grey matter
- dorsal (sensory) horn → dorsal root
- ventral (motor) horn → ventral root
outer white matter = axon tracts
dorsal + ventral roots join = spinal nerve
posterior median sulcus; anterior median fissure
sensory + motor info
continuous flow between brain, SC, peripheral nerves + organ systems
millions of neurons deliver incoming + outgoing info
pathways between CNS + PNS
ascending + descending
consists of a chain of neurons + associated cell bodies (nuclei or ganglia)
somatic sensory pathways
dorsal column/medial lemniscal
spinothalamic
spinocerebellar
dorsal columns
proprioception + discriminant touch
receptor → 1st order neuron ascends ipsilaterally → medulla = synapse on 2nd order neuron → crosses in brainstem
fasciculus cuneatus
upper dorsal column
formed by upper extremities + trunk
corresponds to nucleus cuneatus in midbrain
fasciculus gracilis
lower dorsal column
formed by lower extremities + trunk
corresponds to nucleus gracilis in midbrain
medial lemniscus
2nd order neuron ascends from brainstem through midbrain to thalamus (ipsilaterally)
synapses on 3rd order neuron in ventral nuclei of thalamus
thalamocortical projections
3rd order neurons project from thalamus to S1 (homotopic = cortex mapped according to receptor region)
spinothalamic pathway
pain + temp; deep touch
receptor → 1st order neuron enters dorsal horn = synapse on 2nd order neuron → crosses in SC + ascends → thalamus
anterior spinothalamic tract
deep touch (crude - non-discriminative)
= itch, pressure
2nd order neuron crosses midline of SC from dorsal horn to anterior (white matter)
lateral spinothalamic tract
pain + temp
2nd order neuron crosses midline of SC from dorsal horn to lateral (white matter)
spinocerebellar pathway
unconscious proprioception
from trunk + extremities
receptor → 1st order neuron enters dorsal horn = synapses on two 2nd order neurons → anterior + posterior tracts
posterior spinocerebellar tract
2nd order neuron stays ipsilateral → projects through pons to cerebellum
anterior spinocerebellar tract
2nd order neuron crosses in SC → projects to pons = crosses over back to ipsilateral pons → cerebellum
somatic motor systems
CNS sends motor commands → distributed to body by PNS
effect contraction of skeletal muscle
pathways involve at least 2 motor neurons: upper + lower
upper motor neuron
cell body is in CNS processing centres (M1)
influences LMN: sends descending signal to excitatory/inhibitory synapse
lower motor neuron
cell body is in ventral horn of SC or motor CN nucleus in brainstem
axon extends to skeletal muscle = Common Final Pathway
UMN lesion
cannot pass signal
if inhibitory synapse = disinhibition of LMN
= spastic paralysis (continuous, uncontrolled firing leads to rigidity)
LMN lesion
signal cannot reach periphery
no response = flaccid paralysis → tone cannot be monitored (no feedback)
motor pathways
corticospinal pathway (pyramidal)
corticonuclear pathway (corticobulbar)
corticospinal pathway
UMNs descend from cerebral cortex (M1 + S1) through crus cerebri (midbrain) and pyramids (anterior medulla) → SC
= synapse on LMN in ventral horn (somatic motor nuclei) → muscles in limbs + trunk
bundle of fibres (~1m) originating from pyramidal neurons in cortex from 3 main areas: M1, PMC + SMA, S1
regulates distal limb muscles → precise, skilled, learned movements
corticonuclear pathway
UMNs extend from cerebral cortex (M1) → motor CN nuclei in brainstem
= synapse on LMN → head + neck muscles
extrapyramidal pathways
subsidiary descending pathways
important as backup systems
basal ganglia + cerebellum pathways
modulate + modify activity in corticospinal tract to ensure smooth, coordinated, purposeful movement
central motor program
production of voluntary movements
- incoming sensory info is conveyed to posterior parietal cortex via association fibres
- posterior parietal cortex = process info to identify + localize targets in space
- PMC + SMA = formulation of plan of action
- M1 = execution of movement through desc pathways
simple finger flexion
activates:
- M1 = effect movement
- S1 = receive feedback about movement
finger movement sequence (performance)
activates:
- M1 + S1
- premotor + supplementary motor area = activity prior to movement + during (planning sequence)
finger movement sequence (mental rehearsal)
activates:
- only premotor + supplementary motor area
lateral corticospinal pathway
85% of UMN axons cross at pyramids in inferior medulla = contralateral path to SC
anterior corticospinal pathway
15% of UMN axons stay ipsilateral at pyramids in medulla
cross midline in SC (at level they leave to periphery)
internal capsule
area of bundled axons of corticospinal path in brain
supplied by small arteries
UMN lesion ex. corticospinal pathway
- middle cerebral artery stroke or injury to internal capsule = lose all corticospinal input
- brainstem lesion = decorticate or decerebrate posture
- spinal cord injury = lose UMN output
= spastic paralysis in contralateral limb
decorticate posture
no inhibitory control of upper extremity muscles = flexion
lesion above level of red nucleus
stiff, legs out straight, arms flexed across chest
decerebrate posture
inhibitory control is present to prevent flexion = extensor muscles are active
lesion below level of red nucleus
all limbs extended and held stiff
LMN lesion ex. corticospinal pathway
spinal nerve injury → lost downstream flow
= flaccid paralysis
SNS
supplies body wall structures (skin, muscle, bone, parietal membranes)
motor functions: skeletal muscle = voluntary control (exception: reflex arc)
sensory functions: pain, temp, touch, proprioception
ANS
supplies viscera (glands, smooth muscle, cardiac muscle, visceral membranes) → involuntary control
motor functions: symp + parasym → balance
sensory functions: visceral afferents → pain (indirect or referred)
spinal nerves
emerge from SC → out to periphery = supply peripheral structures
31 pairs: 8C, 12T, 5L, 5S, 1C
dorsal + ventral root together
bifurcates into ventral + dorsal primary rami (end of SN)
cervical spinal nerves
nerve emerges superior to respective vertebrae (C8 n. = inferior to C7 vertebrae)
all downstream nerves (T-Coccygeal) emerge inferior to respective vertebrae
general afferents
carry sensory info to SC
- somatic afferents (GSA) = PTTP from body wall
- visceral afferents (GVA) = pain, distention, chemical from visceral structures
general efferents
emerge from SC + carry motor info away
- somatic efferents (GSE) = motor neurons in ventral horn projecting to skeletal muscles
- visceral efferents (GVE) = autonomic fibres innervating smooth muscle, cardiac muscle, glands
intermediate zone
lateral horn (grey matter) in sc at levels T1-L2 = symp. preG cell bodies
autonomic
dorsal primary ramus
feeds through muscle
supply muscle + reach subcutaneous space → posterior cutaneous branch = sensation to skin
only back (stops at scapula)
ventral primary ramus
continues all around body wall
lies between muscles that form wall
supplies all body wall muscle (all plexi)
lateral cutaneous branch: formed by branching at mid-axillary line
anterior cutaneous branch: formed by branching at midline
dermatome
innervation of entire strip of skin around body wall by spinal nerve
= segmented pattern along body (on all 4s)
VPR follows extremities
T4 = nipples
T10 = umbilicus
intervertebral foramen
opening between vertebrae
where spinal nerve emerges
vertebral canal
down middle of spinal column
where spinal cord is
nerve
covered by epineurium
contains fascicles + blood vessels
grow slowly
fascicles
bundle of axons going to area of body
individually covered by perineurium (membrane)
nerve axons
covered by endoneurium = integrity
make up fascicles
reflex arc
short circuit information pathway
1. stimulus = activation of receptor
2. activation of sensory neuron
3. info processing in CNS (interneuron)
4. activation of motor neuron
5. response by effector
info still travels to brain
somatic nerve plexuses
formed by ventral spinal rami
- at thoracic level → follows ribs
- above + below thoracic → nerves aggregate to form plexus
brachial plexus
supplies upper extremities
VPR of SNs C5, C6, C7, C8, T1
→ 5 main nerves: axillary, median, musculocutaneous, radial, ulnar
lumbar plexus
lower anterior abdominal wall
medial + anterior thigh
inguinal region (groin)
VPR of SNs L1, L2, L3, L4
→ 6 main nerves: iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, obturator
cremasteric reflex arc
formed by ilioinguinal + genitofemoral nerves
(lumbar plexus)
lumbosacral plexus
gluteal region
lower extremities (except ant. med. thigh)
perineal region + genitals
VPR of SNs L4, L5, S1, S2, S3
→ 6 main nerves: tibial, common peroneal, superior gluteal, inferior gluteal, pudendal, posterior femoral cutaneous
autonomic motor system
controlled by hypothalamus → output to pons + medulla
neurons synapse in periphery before target site (next to vertebral column) = 2 neuron system
- preG fibre: from CNS → autonomic ganglion
- postG fibre: from ganglion → effector site
sympathetic autonomic motor nerves
GVEs
thoracolumbar (SC levels)
T1-L2 (lateral horn in grey matter = symp preG nerve cell bodies → synapse in symp ganglion on post G fibre)
fight or flight + fright
parasympathetic autonomic motor nerves
GVEs
craniosacral
- CN III, VII, IX, X
- S2, S3, S4
preG neurons extend from CNS to ganglion near target
rest, relax, regenerate
sympathetic NS
SNs (T1-L2)→ symp. ganglia → symp. nerves → targets
sympathetic chain ganglia
secondary pathway
collection of ganglia linked together by axons passing between
distribute symp. info up + down for postG supply to supradiaphragmatic organs
break at T5
splanchnic nerve
preG fibres pass through symp. ganglia without synapsing and join to form nerve
nerve extends to prevertebral ganglia = close to visceral targets → synapse with postG fibres
supply visceral organs (subdiaphragmatic)
sympathetic actions
eye: pupil dilation
salivary glands: thick viscid secretion
trachea + bronchioles: dilation
heart: ↑ rate + contractility
ureters + bladder: relax detrusor m. (wall of bladder) + contract trigone + sphincter
gastrointestinal: ↓ motility + tone; contract sphincter
genitalia: ejaculation + relaxation of uterus
blood vessels: dilation in skeletal muscle; constriction in viscera
parasympathetic NS
no control to the skin
CNs III, VII, IX, X → preG to terminal ganglia = synapse on postG → targets
pelvic splanchnic nerves → preG to targets = synapse on postG → effect
parasympathetic actions
eye: pupil constriction; accomodation reflex
lacrimal gland: stimulate tears
salivary glands: copious watery secretion
trachea + bronchioles: constrict; ↑ secretion
heart: ↓ rate + contractility
ureters + bladder: contract detrusor m.; relax trigone + sphincter
gastrointestinal: ↑ motility + tone
genitalia: stimulates erection
subcutaneous structures
supply to skin
from SN, enters symp. chain via white ramus → synapse on postG → leave through grey ramus back to SN
supradiaphragmatic organs
preG lateral horn (T1-T5)
ventral root → SN → ganglion → up/down symp. chain
synapse on different postG → goes straight to organ
- heart = cardiac nerve
- lungs = pulmonary nerve
subdiaphragmatic organs
preG fibre leaves SN via white ramus to ganglion but doesn’t synapse → pass through symp. ganglion = forms splanchic nerves
→ synapse in prevertebral (collateral) ganglion associated with abdominal aorta where branch comes off
postG follows blood vessel
general visceral afferents
autonomic sensory info
follows same pathway as motor info
ex. splanchic n. → symp. ganglion → white ramus → SN → dorsal root ganglion
referred pain
pain in visceral structures → referred to body wall through dermatomes
ex. appendix
- T10 symp. level → swelling = interpreted as pain at T10
cranial nerves
emerge from area of brainstem
12 pairs
(exception of X) run functions of head + neck
arise from + interact with nuclei in brainstem
cell bodies of sensory neurons = in CN ganglia
CN I
olfactory nerve
pure sensory = olfaction
olfactory nerve path
receptors on roof of nasal cavity → olf. epithelium = supplied by olf. nerve filaments → pass through cribiform plate, terminate in olf. bulb → olf. tract → primary olf. cortex in temporal lobe (bypass thalamus)
damage to olfactory nerve
hyposmia / anosmia = ↓ sense of smell
CN II
optic nerve
pure sensory = vision
optic nerve path
retinal receptors → bipolar → amacrine → ganglion cells = axons → optic nerve
optic nerve → optic chiasm → tract → LGN → V1
VFs projected onto V1 inverted + reversed
V1 = medial occipital, along calcarine fissure
damage to optic nerve
visual field defects
CN III
oculomotor nerve
from midbrain
mixed nerve
- somatic motor → extraocular muscles
- parasymp. → pupillary constriction + accomodation (ciliary ganglion)
oculomotor nerve path
superior division:
- superior rectus + levator palpebrae mm.
inferior division:
- medial rectus + inferior rectus + inferior oblique mm.
- carries preG parasymp. info to ciliary ganglion → pupillary constrictor + ciliary + medial rectus mm.
damage to oculomotor nerve
pupillary dilation
ophthalmoplegia (weakened eye movements)
CN IV
trochlear nerve
from midbrain (posterior)
smallest CN; longest intracranial path
pure motor = superior oblique m.
damage to trochlear nerve
isolated = uncommon
protected by double layer of dura
CN VI
abducens nerve
pure motor = lateral rectus m. (abduction of eye)
at ponto-medullary junction (anterior surface of pons)
damage to abducens nerve
vulnerable to injury in head trauma/ ↑ intracranial pressure
damage = paralysis of muscle → deviation of eye medially (strabismus) = double vision (diplopia)
CN V
trigeminal nerve
chief sensory nerve to face
3 branches from trigeminal ganglion
mixed nerve = sensory + motor
conduit for parasymp. functions of CNs III, VII, IX
damage to trigeminal nerve
mainly V2, V3
trigeminal neuralgia (tic Douloureux)
very painful
V1
ophthalmic nerve
eye = pure sensory
→ supraorbital nerves
ciliary ganglion = parasymp. relay from CN III
supplies superior corner of eye towards lambdic suture
sensation to frontal + ethmoidal paranasal air sinuses
sensory innervation (general sensation) to nasal cavity
sensation to upper eyelid, side of nose, forehead + scalp
V2
maxillary nerve
cheek = pure sensory
→ infraorbital nerves
pterygopalatine ganglion = parasymp. relay for CN VII
enters floor of orbit through inferior orbital fissure
supplies corner of eye to corner of mouth
sensation to: maxillary air sinus, nasal cavity, lower eyelid, skin of cheek, upper lip, maxillary teeth + gums
V3
mandibular nerve
mandible
somatic motor:
→ muscles of mastication
sensory:
→ lingual nerve (submandibular ganglion = CN VII)
→ inferior alveolar nerve → mental nerve
otic ganglion = parasymp. relay for CN IX
V3 functions
motor
- muscles of mastication (4)
sensory
- lower lip, skin of mandible
- mandibular teeth + gums (i.a. n.)
- general sensation to anterior 2/3 of tongue (l. n.)
- ends as mental n.
- carries proprioceptive info from muscles of mastication to brainstem = force of bite
CN VII
facial nerve
mixed nerve = somatic motor + sensory, parasympathetic
attached to pons
geniculate ganglion
facial nerve path
pons → geniculate ganglion
- main branch = 5 → muscles of facial expression
(temporal, zygomatic, buccal, mandibular, and cervical branches)
- chorda tympani n. → submandibular ganglion
- posterior auricular n.
- greater petrosal n. → pterygopalatine ganglion
damage to facial nerve
partial taste, salivation, or lacrimation loss
Bell’s palsy = hemi-facial paralysis
facial nerve functions
motor
- muscles of facial expression (5 branches)
sensory
- taste to anterior 2/3 of tongue (chorda tympani n.)
- some sensory to skin around ear
parasympathetic
- lacrimal gland via pterygopalatine (V2)
- submandibular + sublingual salivary glands via submandibular ganglion (V3)
CN VIII
vestibulocochlear nerve
pure sensory
- cochlear branch → organ of Corti
- vestibular branch → vestibular apparatus
vestibular branch CN VIII
supplies vestibular apparatus (semicircular canals + vestibule)
= balance and equilibrium
disease: Meniere’s syndrome (vertigo, nausea, vomiting)
cochlear branch CN VIII
supplies organ of Corti in cochlear = hearing
bilateral central pathway in brainstem carries info to temporal lobe → primary auditory cortex
damage: difficulty in localizing sound
CN IX
glossopharyngeal nerve
mixed nerve = somatic motor + sensory, parasympathetic
attached to medulla
supplies tongue + pharynx; mediated gag reflex
main branch → carotid sinus + pharyngeal branches + lingual branches
branch → otic ganglion → parotid gland
damage to glossopharyngeal nerve
difficulty swallowing, loss of gag reflex (protection of airway)
glossopharyngeal nerve functions
motor
- one muscle = stylopharyngeus (elevates pharynx) through lingual branch
sensory (general)
- posterior tongue, pharynx, palatine tonsils, carotid sinus + body
sensory (special)
- taste to posterior 1/3 of tongue
parasympathetic
- supplies parotid gland via otic ganglion (V3)
carotid sinus reflex
carotid stimulation
= induce response to ↓ bp and pulse rate
monitors bp + blood chemistry → feedback
CN X
vagus nerve
mixed nerve = motor, sensory, parasymp.
attached to medulla
damage: difficulty in speech + swallowing
vagus nerve functions
motor
- muscles of palate, pharynx, larynx (CN XI)
sensory
- muscles of palate, pharynx, larynx
- sensory to eardrum
- baroreceptor to hollow organs
- carries visceral afferents from organs to CNS
parasymp.
- nerve for viscera
- motor to smooth muscle in thoracic + abdominal organs up to distal transverse colon
- regulates heart rate (↓)
CN XI
spinal accessory nerve
motor only
attached to medulla + upper SC
damage = weakness when shrugging shoulders, turning head to side against resistance
cranial - spinal accessory nerve
extends from accessory root → accessory branch
distributed by CN X to palate, pharynx, larynx
(CN X sensory functions)
spinal - spinal accessory nerve
extends from spinal root → spinal branch
supplies trapezius and sternocleidomastoid muscles in neck
CN XII
hypoglossal nerve
pure motor
attached to medulla
supplies muscles of tongue (except stylopharyngeus)
damage: inability to protrude tongue symmetrically
