Lectures 7 & 8 (ANS + brain protection & vasculature) Flashcards
Purpose of the autonomic nervous system
Maintain Homeostasis
controls glands and involuntary muscles (heart + smooth muscle)
also has a sensory element: referred & visceral pain + interoception
- also called visceral nervous system
Nervous system divisions
- Somatic and autonomic sensory divisions
- Peripheral nervous system (loop with central NS)
- Motor division
- autonomic –> parasympathetic (rest, relaxation, rumination) OR sympathetic (fight, flight, fright)
*each organ has a dominant branch - somatic
- autonomic –> parasympathetic (rest, relaxation, rumination) OR sympathetic (fight, flight, fright)
Somatic vs Autonomic motor system (neuron type + name, axon traits)
Somatic:
- one neuron: lower motor neuron from spinal cord to muscle (myelinated)
Autonomic:
- two neurons: autonomic ganglia from spinal cord to destination
- preganglionic (myelinated) –> postganglionic (unmyelinated)
What happens if all ANS to the heart is stopped
heart rate would increase and force of contractions would increase (heart has built in pacemaker that is normally slowed by PMS)
Organs with only one ANS input (and which input)
- sweat glands (SMS)
- visceral arterioles, smallest arteries (SMS almost only)
- iris sphincter, constricts pupil (PMS)
- radial muscle of the iris, dilates pupil (SMS)
*Dominant ANS in organs
- heart: PMS
- blood vessels: SMS
- gastrointestinal tract: PMS
Sympathetic vs Parasympathetic autonomic ganglia (major diffs, receptors, neurotransmitters)
S: short preganglionic n. –> nicotinic cholinergic receptors –> adrenergic receptors (NE & E used on effector)
P: long preganglionic n. –> nicotinic cholinergic receptors –> muscarinic cholinergic receptors (ACh used on effector)
Purposes of Parasympathetic MS and ganglia locations
SLUDD
Salivation
Lacrimation (tears)
Urination
Digestion
Defecation
- ganglia close to effectors so each action can be done separately (myelination of preganglionic ns. insulates signals)
Purposes of Sympathetic MS and ganglia locations
3Fs
Fight
Flight
Fright
- all ganglia are far from effectors to broadcast message through entire SMS at once
- most ganglia are connected to form a chain: sympathetic trunk ganglia
Receptor activation time due to acetylcholine (ACh) vs norepinephrine and epinephrine
- short activation: ACh breaks down fast because of anticholinesterase on postsynaptic neuron/effector
- long activation: NE and E breakdown/get removed slowly in comparison
adrenergic receptors (subtypes, purpose)
x-adrenoceptors
alpha 1: contract smooth muscle, mostly blood vessels
alpha 2: dont care
beta 1: tachycardia (increase HR)
beta 2: relaxes bronchioles + uterus
beta 3: dont care
Adrenergic drugs
beta blockers: slow heart + constrict bronchioles unless B1 specific
beta agonists: dilate bronchioles for asthma + speed heart unless B2 specific
3 classes of neurons in terms of signalling (name + basic purpose)
- afferent: deliver sensory info (up to brain)
- efferent: deliver message to effectors (down from brain)
- interneuron: all in CNS, connect neural pathways
Afferent neuron signal path (location of neuron structures + order)
sensory/visceral receptors –> peripheral axon –> cell body (in dorsal root ganglion) –> central axon (dorsal root) –> axon terminal (spinal cord) –> interneuron
Efferent neuron signal path (location of neuron structures + order)
interneuron –> cell body (spinal cord) –> axon (ventral root) –> effector
Cell types in CNS
Grey matter:
- ependymal cells (stem cells, make CSF)
- astrocytes (blood-brain barrier)
- neurons (signals)
White matter:
- microglia (immune)
- oligodendrocytes (myelinate CNS neurons)
Myelination (in CNS vs PNS)
CNS - oligodendrocytes: form several myelin sheaths on one or multiple axons
PNS - schwann cell: one myelin sheath on one axon
NS regeneration
CNS - extremely limited
- neurons degenerate when injured
- glia inhibit axon growth
PNS - 1mm/day
- distal neuron degenerates
- schwann cells proliferate for support
- macrophages remove debris
- axon regenerates + remyelinates
Brain CNS protection (layers + in between)
Superficial
- skull
* meningeal arteries + nerves
- periosteal dura mater (attaches to skull)
- meningeal dura mater (separates compartments)
* bridging veins
- arachnoid mater
* sub arachnoid space (CSF, cerebral vessels inside)
- pia mater
Deep
meninges: dura, arachnoid and pia mater
Structures formed by dura mater + purpose
- falx cerebri: separates L & R cerebral hemispheres
- tentorium cerebelli: separates cerebrum & cerebellum
*formed by specifically meningeal DM
Hematomas in CNS (name, location, BV damaged, appearance)
- epidural h. (skull + dura) meningeal artery, dent shape
- subdural h. (dura + arachnoid) bridging veins, crescent shape
- subarachnoid h. (arachnoid + pia) circle of willis + branches, spider web shape
- intracerebral (cerebrum) BV in brain, hole shape
what innervates the meningeal nerves?
CN V - trigeminal n.
Spinal cord CNS protection (layers + in between)
Superficial
- vertebrae
* epidural space (fat + veins)
- dura
- arachnoid
- pia
Deep
Lumbar punctures (names + location)
- Epidural: collect epidural fat from epidural space
- Spinal tap: collect CSF from subarachnoid space, done below L1/L2 at cauda equina
Ventricles (in order of CSF flow)
- *lateral ventricles
- intraventricular foramina
- *third ventricle
- cerebral aqueduct
- *fourth ventricle
- central canal (in spinal cord) OR subarachnoid space
*CSF produced here
(replace all CSF every 6-8 hours)
Anatomy of the lateral ventricles
anterior horn, posterior horn, inferior horn
Production of CSF
produced in lateral, third and fourth ventricles by ependymal cells of the choroid plexus
drainage of CSF
arachnoid granulations/villi transfer CSF from subarachnoid space to:
- superior or inferior sagittal sinus to
- transverse sinus to
- sigmoid sinus to
- internal jugular veins
- heart (superior vena cava)
CSF composition
essentially filtered blood
- ions (high Na, Cl, K, Ca, proteins…)
- 2/3 glucose
- very few white blood cells (*no red blood cells)
CSF flow pathology
Hydrocephalus: rate of CSF production is higher than CSF drainage, ventricles enlarge
*stenosis (narrowing) somewhere in the cycle
blood supply to brain (below cerebrum)
leaves heart
- common carotid
- internal carotid (to circle of willis)
- external carotid (to meninges)
- vertebral arteries R & L (to circle of willis)
Aneurysm (explanation, vessels with highest risk)
localized enlargement of artery caused by weakening of arterial wall
- 85% occur in circle of willis
- highest risk: anterior communicating artery
- second high risk: posterior communicating artery
Stroke (explanation + types)
blood stops flowing properly
- hemorrhagic stroke: hemorrhage in BG, blood leaks into brain
- ischemic stroke: blood clot stops blood supply, area of brain dies
Blood brain barrier
capillaries in brain lined by:
- endothelial cells (no gaps)
- astrocytes (cover cell)
*barrier starts to decline with age
