anat Flashcards
neurons responsibility
□ Signal transduction within neurons: electrical (mem potential)
□ Signal transduction between neurons: biochemical (synapse)
types of neurotransmitters
Glutamate (excitatory)
□ Pyramidal neurons in neocortex (CNS)
□ Learning, memory
GABA (inhibitory)
□ Receptors are drug targets for sedatives - benzodiazepines
Acetylcholine (excitatory)
□ Nucleus basalis of Meynert
□ Excitatory at NMJ
□ Learning, arousal, reward
Dopamine (inhibitory)
□ Mem of monoamine fam (noradrenaline, adrenaline, serotonin)
□ Major source from Substantia nigra
□ Involved in motor system, reward
Ach synthesis, transporters, receptors, catabolism
- Synthesis: choline acetyltransferase
- Transporters: VAChT and SDHACU
- Receptors
a. Presynaptic = regulate - m2 muscarinic receptors
b. Postsynaptic = action (activate/ inhibit)
c. GPCR (mAChR muscarinic) and ion channels (nAChR nicotine) - Catabolism: AChE acetylcholinesterase
synaptic initiation – neurotransmitter release
- Vesicles containing neurotransmitter at cytoskeleton (away from presyn mem) by Ca2+ sensitive vesicle mem proteins (VAMPs)
- When AP reach terminal, open voltage-gated Ca2+ channels –> Ca2+ influx
- VAMPs bring vesicle from exoskeleton and facilitate vesicle docking, fuse, exocytosis from presynaptic mem
□ Release neurotransmitters
regulation of Ach release
presynaptic auto receptors (m2 muscarinic receptors)
inhibit further transmitter release via feedback inhibition
propagation // termination of neurotransmitters
- Neurotransmitters in synaptic cleft activates postsynaptic receptors
□ GPCR = 2nd messenger activation
□ Ion channels = depolarisation, propagate AP - Signal termination by catalytic enzymes/ reuptake transporters
excitatory vs inhibitory synapse
excitatory:
- presynaptic neurotransmitter release directly correlates with postsynaptic depol/ signalling
inhibitory synapse:
- presynaptic neurotransmitter release (GABA) inverse correlates with postsynaptic depolarisation/ signalling
CNS
brain + spinal cord
PNS
cranial nerves (12 pairs)
spinal nerves (31 pairs)
forebrain
- Cerebrum
◊ Largest part of brain
◊ 2 hemispheres
* Separated by longitudinal fissure - Diencephalon – hypothalamus, thalamus
Hypothalamus: lower part of lateral wall and floor of 3rd ventricle
midbrain
topmost part of the brainstem, the connection central between the brain and the spinal cord.
Connect forebrain to hindbrain
- dopamine, serotonin
midbrain
cranial nerves
nuclei assoc with
fiber tracts
- Cranial nerves (III,IV)
- Nuclei associated with
- III, IV, V
- Visual and auditory pathways
- Fiber tracts
- Ascending and descending fibers
hindbrain
medullar oblongata (most inferior of brain)
pons (superior of medulla)
cerebellum (posterior of pons and medulla)
medulla oblongata
cranial nerves
nuclei assoc with
fiber tracts
Cranial nerves
* IX, X, XI, XII
Nuclei associated with
* V, IX, X, XI, XII
* Cardiovascular and resp function
Fiber tracts
* Ascending and descending fibers
Pons
cranial nerves
nuclei assoc with
fiber tracts
- Cranial nerves
* V, VI, VII, VIII - Nuclei associated with
* V, VI, VII, VIII - Fiber tracts
* Ascending and descending fibers
4 lobes of the brain
frontal
parietal (middle)
temporal (side)
Occipital (back)
spinal cord (PNS) is connected to
Continuous with brain — foramen magnum of skull
Tapers off into — conus medullaris
brain and spinal cord is covered by
brain:
§ Located in cranial cavity. Under meninges, skull
§ surrounds brain in subarachnoid space
sc:
§ Located in vertebral column
§ Protected by
□ meninges
□ Surrounded by cerebrospinal fluid (CSF)
spinal cord grey and white matter
grey: dorsal and ventral horn (cell bodies)
white: outer region (axons)
cell types in CNS and PNS
CNS: neurons, glial cells (astrocytes, oligodendrocytes, microglia)
PNS: sensory & motor neuron, schwann cells, satellite cells
CNS cells (neurons vs glial cells)
neurons
- structural, functional
- generate/ conduct impulses, excitable
- 100 billion
glial
- non conducting
- support and protect neurons
- 1000 billion
parts of neuron
1) cell body (soma) – mitochondria, GA
2) axon – lacks ribosomes, RER, GA
3) dendrite – all cytoplasmic components except GA
- has dendritic spines, where synapse can take place
axon <–> soma transport
fast vs slow component
to: anterograde transport
from: retrograde transport
1) Fast component (50 - 400mm/day) transport cytoplasmic proteins, macromole required for metabolic and synaptic activity
2) Slow component (1 - 4mm/day) transports cytoskeletal components down axon. maintenance
synapse: Impulses transmitted from __ to __ at regions of functional apposition
- 1 neurons (PRESYNAPTIC) to another neuron (POSTSYNAPTIC)
- Neuron to effector cell (muscle)
electrical synapse vs chemical synapse
electrical: gap junction b. 2 neurons, no space in between, faster
chemical: synaptic cleft present (20 - 40nm wide), receptors for neurotransmitters found on postsynaptic cell, slower
pre vs post synaptic cells
pre: thickened region in the plasmalemma of axon terminal
- voltage gated Ca2+ channels (trigger EXOCYTOSIS)
post: thickened region in the plasmalemma of dendrite with neurotransmitter receptors
glial cells in CNS main functions
1) astrocytes (regulate environment, struc support)
2) oligodendrocytes (myelin sheath formation several axons)
3) microglia (macrophage)
glial cells in CNS makeup
astrocytes 25%
oligodendrocytes 60-80%
microglia 5-10%
astrocytes feature
largest neuroglial cells
numerous processes w/ pedicles that terminate on capillaries/ on pia mater
types of astrocytes
- Fibrous astrocytes
- White matter
- Long spindly process with few branches
- BBB formation
- Protoplasmic astrocytes
- Gray matter
- Thick, lightly branches processes —|
- Closely apposed to neuron cell bodies
- Support neuron
function of astrocytes
- BBB
- Structural support, scar formation – neurons & SYNAPSES
- metabolise neurotransmitters (glutamate shuttle – astrocytic process/ tripartite synapse)
- mediate exchange of nutrients and metabolites b. blood and neurons
- Secretion of nerve GF
- Water transport
- Excess transport (Cerebral oedema)
- regulate composition of intercellular environ and entry of sub
oligodendrocytes feature
In white matter
* Predominant type of neuroglial cells
* Produce (several axons) myelin sheath around myelinated fibers in white matter
In grey matter
* Oligodendrocytes are closely assoc with neuron cell bodies
* Function as satellite cells, support
oligo produces
- Cell marker – CNPase
- Express Nogo-A
a. Myelin associated neurite outgrowth inhibitor
b. Inhibit axonal regeneration following injury and ischemia in CNS - Satellite cells, support
microglia features
small phagocytic cells that enlarge and become mobile after CNS injury
monocyte origin
microglia function
- Brain macrophage
- Phagocytosis
- Secretion of proinflamm cytokines (neuroinflammation)
○ TNFa, IL1 b
○ Chemokines
Implicated in Alzheimer’s disease, Parkinson, cerebral ischemia (stroke) - APC (MHC II antigen)
- Immunocompetent cells of CNS
PNS composed of
- neuron processes and cell bodies located outside CNS
- neuroglial cells [schwann & satellite cells]
- nerve endings
peripheral nerve structure
3 connective tissue elements
Nerve fibers (axon) –> bundles/ (fascicles) –> nerve
1) Each nerve (axon) fiber have endoneurium myelin sheath
◊ Thin, reticular layer that surrounds each individual nerve fiber
◊ Contains Schwann cells
2) Each nerve bundle/ fascicle covered by perineurium dense connective tissue
3) Entire nerve covered by epineurium connective tissue
schwann cells
myelinate portions of only a single axon
satellite cells
- amphicytes
- Form capsule of cells around neuron cell bodies located in peripheral ganglia
ganglia (portion of PNS)
- Encapsulated collections of neuron cell bodies, located outside CNS
- Contains:
□ Satellite cells (amphicytes)
□ Connective tissue elements
□ Neurons - dorsal – sensory neuron (to dorsal horn)
BLOOD SUPPLY of brain
GO READDDD from the slides
1) Common carotid artery in neck –> INTERNAL CAROTID (L,R) –> middle & anterior cerebral
2) subclavian artery in neck –> VERTEBROBASILAR (L,R) –> posterior cerebral
circle of willis
Anastomosis between left and right arteries supplying the brain b. vertebral and internal carotid arteries
□ Located at base of brain
- Anterior communicating artery
a. Connects anterior cerebral arteries of both sides - Posterior communicating artery
a. Connects middle cerebral artery with posterior cerebral artery
circle of willis and slow occlusion in 1 artery
□ Communicating arteries have time to enlarge and accommodate to incr blood flow
□ Blood can still pass around the other way to reach affected area – collateral circulation
** Not if sudden occlusion
Haemorrhagic stroke
Circle of Willis freq site of aneurysms
Abnormal out-pocketing of wall of a blood vessel
esp at junction where basilar artery splits into posterior cerebral arteries
venous drainage of brain
Blood from brain drains into venous sinuses –> empty into internal jugular vein
READ FROM SLIDES (split into superior, inferior, central part of brain)
ventricles in brain
lateral
3rd
4th
central canal
patho of brain venous drainage — Subdural hemorrhage
- Rupture of cerebral vein (occur b. superior cerebral veins) as it drains –> superior sagittal sinus
- Low venous pressure in brain
□ Slow seepage
-Wks ltr after blow has been forgotten
-Slow expanding hematoma press on brain
□ Sx: dizzy, headache, apathy, falling, confusion, drowsiness
BBB and capillaries
1) found where?
2) formed by?
3) function?
- TIGHT JUNCTIONS b. endothelial cells, form BBB
- Formed by astrocytes
- Prevent random entry of water soluble sub into brain parenchyma
intracranial pressure (ICP)
generally measured as CSF pressure (cerebrospinal fluid)
reflects change in volume of IC contents
CSF produced in
choroid plexus (80%) by ependymal cells
rest is secreted in interstitial spaces of brain
reabsorbed through arachnoid granulation and dural sinus
CSF surrounds __
ventricles and central canal
bathes brain and spinal cord in sub-arachnoid space
sub-arachnoid space
space b. 2 meninges (arachnoid mater & pia mater – below)
function of CSF
- shock absorber to protect brain
- clear waste (remove metabolites from brain, since no lymphatic system)
- distribution of material via CSF
- buoyancy of brain (decr brain weight)
skull made up 3 major components
85% brain
7% blood
7% CSF
frontal lobes
sensation and perception
voluntary control of movement (somatomotor cortex)
personality traits
learning and memory
LANGUAGE: left hemi
left side of body: right cortex
broca’s area
expressing language, speak
wernicke’s area
○ comprehend language
parietal lobe
○ Sensory info from body
○ 1* somatosensory cortex: sense of touch
(frontal) sensorimotor cortex: coordination and balance
- execution of movements of the contralateral side of the body
- TOPOGRAPHIC representation
somatosensory cortex vs somatomotor cortex
sensory: Parietal. processing sensations from various parts of the body.
motor: precentral gyrus of the frontal lobe. Processing movements of those bodyparts
occipital lobe
Visual info processed
temporal lobe
auditory info
limbic structures
thalamus, hippocampus, hypothalamus, amygdala
add memory and emotions to sensory experiences
declarative memory: recollection by hippocampus
non-declarative memory: recollection through actions
amygdala
recognition of facial expression
emotion and emotional memory, fight or flight
brainstem and cortex
execution of behaviours
sends long axons from site of origin to spinal cord
basal ganglia
midbrain region
- initiation
- selection of motor program
- degeneration of dopamine neurons in basal ganglia: parkinson’s disease
- (disorder of movement - bradykinesia, tremor, disorder of posture - rigid)
