Nervous System Flashcards
What does the CNS and PNS include respectively?
- CNS - brain and spinal cord
- PNS - all nerves that branch off CNS
Where is the brain?
in the cranial cavity protected by the skull and meninges
What does the forebrain, hindbrain and brainstem include respectively?
- forebrain - cerebrum and diencephalon
- hindbrain - medulla oblongata, pons and cerebellum
- brainstem - midbrain, pons and medulla oblongata
Where is the spinal cord?
in the vertebral column protected by meninges and surrounded by CSF
What can neurons be morphologically?
multipolar, bipolar or pseudo-unipolar
What is the main difference between neuronal and glial cells?
neuronal cells are conducting and glial cells are non-conducting
What is the difference between projection neurons and interneurons?
- projection neurons can be efferent or afferent and are mainly excitatory
- interneurons have local connections and are mainly inhibitory
What do axons do?
conduct impulses away from the cell body
What are most axons?
long, slender processes that arise from the axon hillock in the cell body and branch at the distal (terminal) end
What does the axonal cytoplasm lack?
ribosomes, RER and Golgi apparatus
What is axon myelination?
the process of forming a myelin sheath around an axon, which increases the speed of electrical signals transmitted between neurons
What do dendrites do?
conduct impulses towards the cell body
What are most dendrites?
relatively short and highly branched; they contain all the cytoplasmic components found in the cell body except the Golgi apparatus
What does the arrival of an AP at an axon terminal cause?
Ca2+ channels to open which causes an influx of ions and increases the cytosolic Ca2+ level which then triggers exocytosis of the neurotransmitter into the synaptic cleft
What is the synaptic cleft?
a 20-40nm space separating the presynaptic and postsynaptic membranes across which a neurotransmitter diffuses
What happens at the excitatory synapse?
binding of neurotransmitter to its receptors causes opening of Na+ channels in the postsynaptic membrane which leads to depolarisation of the membrane and an AP in the postsynaptic cell
What happens at the inhibitory synapse?
neurotransmitter binding causes opening of K+ and Cl- channels in the postsynaptic membrane which leads to hyperpolarisation of the membrane and then no AP in the postsynaptic neuron
How many more glial cells are there than neuronal cells?
10x
What are the 3 types of glial cells and what is their proportion?
- oligodendrocytes - 60-80%
- astrocytes - 25%
- microglia - 5-10%
What do astrocytes have?
- numerous processes with expanded pedicles that terminate on capillaries or on the pia mater
- a tripartite synapse which allows bidirectional communication between astrocytes and neurons
What are the 2 types of astrocytes?
- fibrous - located primarily in white matter which long spindly processes with few branches
- protoplasmic - located in grey matter and have thick, lightly branched processes closely opposed to neuronal cell bodies
What are the 5 functions of astrocytes?
- regulate the composition of the intercellular environment and the entry of substances into it
- provide structural support to neurons and specifically to synapses
- metabolise neurotransmitters e.g. glutamate
- mediate the exchange of nutrients and metabolites between the blood and neurons via their end-feet (pedicles)
- forms a glial scar after injury to the CNS
What do oligodendrocytes do in white and grey matter respectively?
- white - produce the myelin sheath around myelinated fibres (Schwann cells do this in PNS)
- grey - closely associated with neuron cell bodies, functioning as satellite cells.
What is the cell marker of oligodendrocytes?
CNPase
What do oligodendrocytes express?
Nogo-A
What is Nogo-A?
a myelin associated neurite-outgrowth inhibitor; it is involved in the inhibition of axonal regeneration following injury and ischaemia in the CNS
What are microglia?
small phagocytic cells that originate from monocytes and enlarge and become mobile after injury to the CNS
What are microglia involved in?
neuroinflammation and secretion of inflammatory mediators
What does a peripheral nerve comprise?
bundles of nerve fibres surrounded by myelin sheaths or Schwann cells
What are the 3 connective tissue elements that peripheral nerves are invested with?
- epineurium - connective tissue surrounding the entire nerve
- perineurium – layer of dense connective tissue around each fascicle of nerve fibres
- endoneurium – thin, reticular layer that surrounds each individual nerve fibre and contains Schwann cells
What is the difference in axon myelination between the CNS and PNS?
- CNS - individual oligodendrocytes myelinate portions of several axons
- PNS - individual Schwann cells myelinate portions of only a single axon
What are ganglia?
encapsulated collections of neuron cell bodies, located outside the CNS that contain satellite cells, neurons and connective tissue elements
What do satellite cells do?
form a capsule of cells around neuron cell bodies located in the peripheral ganglia
What does the cerebrum consist of?
2 cerebral hemispheres separated by the longitudinal fissure
What is the cerebral cortex?
a layer of grey matter on the surface of the cerebral hemispheres
What is a gyrus and sulcus respectively?
- gyrus - raised tissue layer of cerebrum
- sulcus - groove between gyri
Where is the frontal lobe?
anterior to the central sulcus and superior to the lateral fissure
Where is the parietal lobe?
posterior to the central sulcus and superior to the lateral fissure
Where is the temporal lobe?
inferior to the lateral fissure
Where is the occipital lobe?
posterior to the parietal and temporal lobes
What separates the parietal and temporal lobes from the occipital lobe?
the parieto-occipital sulcus
Where is the hippocampus and what is it essential for?
rolled in part of the cerebral cortex essential for formation of new memories
What is the hippocampus particularly vulnerable to?
damage during global ischaemia and AD
What is the thalamus?
a large mass of grey matter on either side of the third ventricle in the dorsal part of the diencephalon
Where is the hypothalamus?
below the thalamus (separated by hypothalamic sulcus) that forms the lower part of the lateral wall and floor of the third ventricle
Where is the midbrain?
between the forebrain and hindbrain
Where is the pons?
inferior to the midbrain and superior to medulla oblongata
What is the most inferior portion of the brain?
medulla oblongata
Where is the cerebellum?
posterior to the pons and medulla oblongata
What does the cerebellum consist of?
a midline portion (vermis) and two hemispheres connected to the brainstem
Describe the pathway of the spinal cord
attaches to the brainstem at the foramen magnum and tapers off into the conus medullaris
What does a cross section of the spinal cord show?
spinal nerves, grey matter and fibre tracts
What is the PNS split into?
somatic and autonomic nervous systems
What is the hypothalamus?
the control and integrative centre for the ANS
What does the hypothalamus do?
- influence the secretion of hormones from the pituitary gland, which in turn affects other endocrine glands
- discharges the impulses down the cord to the sympathetic or parasympathetic preganglionic neurons in the brainstem and spinal cord
What 3 tissue types does the ANS stimulate?
- cardiac muscle
- smooth muscle
- glands
What happens under sympathetic control?
muscles work harder, need more oxygen and use more energy; one breathes faster, and the bronchi and bronchioles open up for quicker and greater passage of air
What are the 10 main functions of the sympathetic NS?
- heart beats stronger and faster to increase CO and BP
- arteries to the heart and voluntary muscles dilate
- arteries to the skin and peripheral areas constrict
- liver secretes glycogen for quick energy supply
- peristalsis in the GIT slows down
- cells in the adrenal medulla produce adrenaline
- ejaculation in males
- uterine contraction in non-pregnant females
- pupils dilate
- increased sweating
What are the 8 main functions of the parasympathetic NS?
- heart beats slower and respiratory rate is reduced
- coronary arteries constrict
- peristalsis and other digestive functions
- pupils constrict
- detrusor muscle contraction in the bladder for micturition
- erection in males
- clitoral engorgement in females
What does the vagus nerve do?
innervate the heart, lungs and all the abdominal viscera up to the left colic flexure (up to the proximal 2/3 of the transverse colon)
What is the vagus nerve supply to the lungs?
- motor to the smooth muscle of the bronchial tree (bronchoconstrictor)
- secretory to the glands of the bronchial tree (secretomotor)
What are the 2 pairs of arteries that supply blood to the brain?
- left and right vertebral arteries
- left and right internal carotid arteries
Where does the vertebral artery originate from and where does it enter the skull?
originates from the subclavian artery in the neck and enters the skull through the foramen magnum
What does the vertebral artery supply?
spinal cord, medulla oblongata and cerebellum
What are the 3 branches given off by the vertebral artery?
- anterior spinal artery
- posterior spinal artery
- posterior inferior cerebellar artery
What do the 2 vertebral arteries join to form?
the basilar artery
What does the basilar artery give off branches to supply?
the pons, cerebellum and inner ear
How does the basilar artery end?
by dividing into the 2 posterior cerebral arteries
What does the posterior cerebral artery supply?
the midbrain, medial aspect of the occipital lobe and the base of the temporal and occipital lobes
Where does the internal carotid artery originate from and where does it enter the skull?
originates from the common carotid artery in the neck and enters the skull through the carotid canals situated within the cavernous sinus
How does the internal carotid artery end?
by dividing into the anterior cerebral artery and middle cerebral artery
What is the pathway of the anterior cerebral artery?
it passes forward into the medial longitudinal fissure and then sweeps back to the parieto-occipital sulcus
What does the anterior cerebral artery supply?
most of the medial surface of the hemisphere, except the medial aspect of the occipital lobe
What is the pathway of the middle cerebral artery?
it passes laterally between the temporal and frontal lobes then emerges at the lateral fissure and fans out
What does the middle cerebral artery supply?
most of the lateral surface of the hemisphere
What is the circle of Willis?
an anastomosis between the left and right arteries supplying the brain
What does the circle of Willis help to do?
supply blood to the opposite side in cases of slow occlusion of an artery on one side; the communicating arteries have time to enlarge to accommodate the increased blood flow
Where does blood from the brain drain?
into venous sinuses, which eventually empty into the internal jugular vein
Where does blood from the superior part of the brain drain into?
the superior sagittal sinus
Where does blood from the inferior part of the brain drain into?
the transverse sinus and superficial middle cerebral vein
Where does blood from the centre of the brain drain?
into the deep cerebral veins which then drain into the straight (venous) sinus
Where do the superior sagittal and straight sinuses flow?
transverse sinus → sigmoid sinus → internal jugular vein of the neck
