anat Flashcards
what does grey matter consist of
cell bodies of neurons
what does the forebrain include
- cerebrum (folds of the brain)
- diencephalon *where hypothalamus is at
what does the hindbrain include
- medulla oblongata
- pons
- cerebellum
what does the brainstem include
- midbrain
- pons
- medulla oblongata
what are the nerves in the PNS
- cranial nerves (12 pairs)
- spinal nerves (31 pairs)
features of the cerebrum
- largest part of the brain
- consists of 2 cerebral hemispheres separated by LONGITUDINAL FISSURE
- CEREBRAL CORTEX: layer of GREY matter on the surface of hemispheres
- GYRI & SULCI (grooves on surface of brain)
- CENTRAL sulcus
- LATERAL sulcus
- PARIETO-OCCIPITAL sulcus
what are the lobes of the brain (and location relative to sulcus/ fissure/ other lobes)
- Frontal lobe: anterior to CENTRAL sulcus & superior to LATERAL FISSURE
- Parietal lobe: posterior to CENTRAL sulcus & superior to LATERAL FISSURE
- Temporal lobe: inferior to LATERAL FISSURE
- Occipital lobe: Posterior to PARIETAL & TEMPORAL lobes (separated by parieto-occipital sulcus)
Features of diencephalon
HYPOTHALAMUS: forms lower part of lateral wall & floor of THIRD ventricle (CSF)
What are the structures associated with the midbrain
- CRANIAL NERVES (III,IV)
- NUCLEI associated with: 3,4,5, visual & auditory pathways
- FIBER TRACTS: ascending & descending fibers
features of PONS
appearance: bulge-like
location: in HINDBRAIN; inferior to midbrain
superior to medulla oblongata
structures associated:
- CRANIAL NERVES 5,6,7,8
- NUCLEI associated with 5,6,7,8
- FIBER TRACTS (ascending & descending)
feature of MEDULLA OBLONGATA
location: in HINDBRAIN; MOST INFERIOR portion of the brain
structures associated:
- CRANIAL NERVES 9,10,11,12
- NUCLEI associated with 5, 9,10,11,12, cardiovascular & respiratory function
- FIBER TRACTS (Ascending & descending)
features of CEREBELLUM
location: POSTERIOR to pons & medulla oblongata
appearance: consists of a midline portion (VERMIS) & 2 hemispheres
- connected to the brainstem
features of SPINAL CORD
structure:
- continuous with brain at FORAMEN MAGNUM of skull
- tapers off into the CONUS MEDULLARIS
structures associated:
- Spinal nerves
- Grey matter
- Fiber tracts
types of cells in the brain
- neurons: structural & functional unit of nervous system
- generate/ conduct impulses, excitable - non-neuronal cells (glial cells)
*NON-CONDUCTING
- supports, protects neurons
- 10x no. of neurons
structure of a normal neuron
- cell body: SOMA
- contains nucleus, cytoplasmic organelles, cytoskeletal elements, inclusions
*golgi complex located NEAR nucleus; mitochondria THROUGHOUT cytoplasm - AXONS
- LONG, slender processes that arise from the axon hillock in the cell body; branch at the distal (terminal) end
- conduct impulses AWAY from cell body
*axonal cytoplasm (Axoplasm) has NO ribosomes, RER, Golgi apparatus -> lacks components for synthesising new proteins/ degrading old ones -> materials are TRANSPORTED back & forth between cell body & terminus (anterograde transport: cell body -> axon terminal VS retrograde transport: axon terminal -> cell body)
** FAST component (50-400mm/day): cytoplasmic proteins, macromolecules [metabolic, synaptic activity]
SLOW component (1-4mm/day): cytoskeletal components
ANTEROGRADE (forward) transport: cell body -> axon
RETROGRADE (backward) transport: axon -> cell body - DENDRITES: conduct impulses TOWARDS cell body
- relatively short & highly branched (contains all cytoplasmic components EXCEPT Golgi apparatus)
*dendritic spines -> increases surface area -> receive more information
Features of synapse
Definition: Regions of functional apposition where impulses are transmitted from 1 neuron (presynaptic) to another neuron (postsynaptic) OR from one neuron to an effector cell (muscle)
Types of synapse:
1. CHEMICAL
*presynaptic axon terminal: small, knoblike termination (End-foot) of the transmitting neuron
- contains SYNAPTIC VESICLES filled with neurotransmitter
*PREsynaptic membrane: thickened region in the plasmalemma of the presynaptic axon terminal
- contains voltage-gated Ca2+ CHANNELS
*POSTsynaptic membrane: thickened region in plasmalemma of a receiving dendrite, containing neurotransmitter receptors
-> MOA: arrival of an action potential at an axon terminal -> opening of Ca2+ channels -> influx of Ca2+ ions -> rise in cytosolic Ca2+ levels -> depolarisation => TRIGGERS EXOCYTOSIS of neurotransmitter into synaptic cleft
** Synaptic cleft: 20-40nm wide space separating presynaptic & postsynaptic membranes across which neurotransmitter diffuses
*POSTsynaptic membrane: thickened region in plasmalemma of a receiving dendrite, containing neurotransmitter receptors
-> MOA
[EXCITATORY synapse] binding of neurotransmitters to its receptors -> OPENING of Na+ channels in the postsynaptic membrane -> DEPOLARISATION of the membrane + ACTION POTENTIAL in postsynaptic cell
[INHIBITORY synapse] neurotransmitter binding -> opening of K+ OR Cl- channels in postsynaptic membrane -> HYPERPOLARISATION of membrane -> NO action potential in postsynaptic neuron
Features of glial cells in CNS
Glial cells - supportive structures in CNS
- ~10x more in number than neurons
- Oligodendrocytes (60-80%) – MYELIN SHEATH FORMATION in CNS (PNS: Schwann cells)
- WHITE matter: predominant neuroglial cell -> produce MYELIN SHEATH around myelinated fibers
- GRAY matter: closely associated with neuron cell bodies; functioning as satelitte cells (supportive function)
*myelin sheath: increases speed of impulse down axon (minimise channels needed to open up during transmission of signal)
> Cell marker (CNPase)
> a few processes
> Express Nogo-A (myelin associated neurite-outgrowth inhibitor)
*myelin-producing cells:
CNS - individual oligodendrocytes myelinate portions of SEVERAL axons
PNS - individual Schwann cells myelinate portions of only a SINGLE axon
- Astrocytes (25%) [BBB formation, STRUCTURAL support, scar formation, secretion of nerve growth factors, water transport, excess transport (cerebral edema)]
- LARGEST neuroglial cells
- have numerous processes with expanded end-feet (PEDICLES) that terminate on capillaries/ on the pia mater
(a) FIBROUS astrocytes: located primarily in WHITE matter; long, spindly processes with FEW branches
(b) PROTOPLASMIC astrocytes: located in GRAY matter; THICK, lightly branched processes; closely apposed to neuron cell bodies
- [Function] REGULATE composition of intercellular environment & entry of substances into it; provide STRUCTURAL SUPPORT to neurons + synapses; METABOLISE neurotransmitters (eg. glutamate glutamine shuttle) –> REGULATE HOMEOSTATSIS OF GLUTAMATE; mediate EXCHANGE of nutrients & metabolites between blood & neurons
**TRIPARTITE SYNAPSE (axon; dendritic spine; ASTROCYTIC PROCESS: takes up EXCESS neurotransmitters + metabolise + transports it to presynaptic terminal) - Microglia (5-10%) *immunocompetent cells of CNS (brain macrophage) [phagocytosis, secretion of proinflammatory cytokines (TNF-alpha, IL1beta), chemokines, antigen-presentation function (MHCII antigen)]
- Small phagocytic cells that enlarge & become mobile after injury to the CNS
> Marker: Lectin, OX42 (complement type 3 receptor)
> Monocyte origin
> Brain macrophages, immunocompetent cells
> Neuroinflammation -> secrete proinflammatory mediators (TNF-alpha, IL-1beta)
**implicated in Alzheimer’s disease/ Parkinson’s disease/ cerebral ischemia
PNS features (structure, cells)
Structure of peripheral nerve
- Cranial nerves: 12 pairs
- Spinal nerves: 31 pairs
Cells in peripheral nervous system
- Neuron processes & cell bodies located outside CNS
- Neuroglial cells [Schwann cells & satellite cells]
*ganglia: collections of neuron cell bodies, located OUTSIDE CNS -> contain SATELITTE CELLS (Amphicytes; form a CAPSULE of cells around neuron cell bodies located in the peripheral ganglia) & CONNECTIVE TISSUE ELEMENTS along with neurons
- Nerve endings
Peripheral nerve structure: bundles (FASCICLES) of nerve fibers (axons) surrounded by myelin sheaths (formed by Schwann cells)
*invested with THREE connective tissue elements;
(1) EPIneurium: connective tissue surround the ENTIRE nerve
(2) PERIneurium: layer of dense connective tissue around EACH fascicle of nerve fibers
(3) ENDOneurium: thin, reticular layer that surround each INDIVIDUAL nerve fiber + contains Schwann cells
*myelin-producing cells:
CNS - individual oligodendrocytes myelinate portions of SEVERAL axons
PNS - individual Schwann cells myelinate portions of only a SINGLE axon
Arterial supply of blood to brain (systems, Circle of Willis)
*brain only 2% of total body weight BUT uses 15-20% of total cardiac output
- L/R INTERNAL CAROTID arteries & L/R VERTEBRAL arteries
Vertebrobasilar arterial system
- Vertebral artery: originates from SUBCLAVIAN artery in neck -> enters skull through FORAMEN MAGNUM (hole @ base of skull) -> branches to supply spinal cord/ medulla oblongata/ cerebellum [Anterior/Posterior spinal artery, Posterior Inferior cerebellar artery]
- 2 vertebral arteries join to form BASILAR artery (Single artery in the MIDLINE) -> branches to supply pons/ cerebellum/ inner ear [Anterior inferior cerebellar artery/ Pontine branches/ Labyrinthine artery/ Superior cerebellar artery]
- basilar artery ends by dividing into 2 POSTERIOR CEREBRAL arteries, supplies Midbrain/ Medial aspect of Occipital lobe/ Base of Temporal & Occipital lobe
Carotid arterial system
- Internal carotid artery: from COMMON CAROTID ARTERY (neck) -> enters skull through CAROTID CANALS (situated within cavernous sinus)
- internal carotid artery ends by dividing into the ANTERIOR CEREBRAL artery & the MIDDLE CEREBRAL artery -> passes FORWARD into the medial longitudinal fissure, then sweeps back into the parieto-occipital sulcus -> pass LATERALLY between temporal & frontal lobes -> emerge at LATERAL FISSURE, fans out to supply most of the LATERAL SURFACE of the hemisphere (frontal/ parietal/ temporal/ occipital)
Circle of Willis: anastomosis (connection) between L&R arteries supplying the brain
may help to supply blood to the OPPOSITE side in cases of SLOW occlusion of an artery on one side (communicating arteries have time to ENLARGE -> accommodate increased blood flow)
- ANTERIOR COMMUNICATING ARTERY: connects anterior cerebral arteries of both sides
- POSTERIOR COMMUNICATING ARTERY: connects MIDDLE cerebral artery with POSTERIOR cerebral artery
**Anastomotic ring: between vertebral & internal carotid arteries – located at the BASE of the brain
**only helps in the event of SLOW OCCLUSION (collateral circulation: blood passes the other way to reach the affected area)
** Circle of Willis as frequent site of ANEURYSMS -> hemorrhagic stroke
Venous drainage of brain (general/ common drainage, superficial, inferior, centre)
SUMMARY: Blood from SUPERFICIAL & DEEP parts of brain -> drain into VENOUS sinus -> internal jugular vein
SUPERFICIAL part of superior aspect of brain -> drain into SUPERIOR SAGITTAL sinus; SSS & STRAIGHT sinus flow into TRANSVERSE sinus -> SIGMOID sinus -> INTERNAL JUGULAR vein
INFERIOR part of brain -> drain into TRANSVERSE sinus + SUPERFICIAL MIDDLE CEREBRAL VEIN -> drain into cavernous sinus (closely related to cranial nerves 3/4/5/6 + part of INTERNAL CAROTID ARTERY)
CENTRE OF BRAIN -> drain into DEEP CEREBRAL veins -> drain into venous sinus (straight)
what is subdural hemorrhage (pathophysiology, what + how symptoms arise)
Rupture of a cerebral vein (between one of the SUPERIOR cerebral veins) as it drains into the superior sagittal sinus
*LOW venous pressure -> SLOW seepage -> slowly expanding hematoma
Symptoms (due to hematoma pressing onto brain):
- Dizziness
- Headache
- Confusion
- Apathy
- Falling
- Drowsiness
Blood brain barrier structure/features
Capillaries has TIGHT JUNCTIONS between endothelial cells -> BBB
- prevents random entry of water soluble substances into brain parenchyma
Cerebrospinal fluid (CSF) feature/ composition
CSF: CLEAR fluid that acts as a protective “liquid cushion” around the brain & spinal cord by ABSORBING SHOCK WAVES from blows & falls
Functions: remove metabolites from the brain
*brain has NO lympathic channels
Where CSF is produced: by CHOROID PLEXUS (delicate, lacelike structure in cerebral ventricles)
Flow of CSF: from lateral ventricle to 3rd (via cerebral aqueduct) -> 4th -> into brain & spinal cord
*CSF absorbed into superior sagittal sinus by ARACHNOID GRANULATIONS
