Introduction to the nervous system Flashcards
What makes up the CNS?
Brain and spinal cord
What makes up the PNS?
Cranial nerves
Spinal nerves
Give an overview of the structure of neurons.
Neurons are highly diverse.
They have dendritic trees that connect to synapses.
Their nerve impulse is generated in the axon hillock, then spread down their axon and multiple collateral axons.
Neurons can have 10,000s of neurons.
Give an overview of the neurotransmitter glutamate.
Glutamate is the main excitatory neurotransmitter in the CNS.
It has a role in memory and learning.
Give an overview of the neurotransmitter GABA.
Is the main inhibitory neurotransmitter in the CNS.
Has a calming effect
What are the different classifications of neuron?
Multipolar - most common, multiple dendrites and one axon
Bipolar - retina and olfactory mucosa, one axon and one dendrite extend from the cell body
Unipolar - not in humans
Pseudounipolar - one process extends from the body, then splits into two axons.
What are neuroglia?
Cells that provides homeostatic, metabolic and immune support to the nervous system
What are the six types of glia cells and where are they found?
CNS contains astrocytes, oligodendrocytes, microglia and ependymal cells
PNS contains satellite cells and schwann cells.
What is the function of astrocytes?
Maintain the blood brain barrier
Regulate the amount of neurotransmitter in the synapse
Regulate ion levels
Provide metabolic support
What is the function of oligodendrocytes?
Myelinate CNS axons, provide a structural framework.
What is the function of micrglial cells?
Brains immune cells remove dead cells and pathogens by phagocytosis.
What is the function of ependymal cells?
Line the brain and spinal cord.
Have a role in CSF production
What is the function of schawnn cells?
Myelinate axons and provide structural support in the PNS
What is the function of satellite cells?
Surround neuron cell bodies in the ganglia, regulate levels of neurotransmitter.
What are the two different ways the nervous system can be classified functionally?
Sensory v motor
Somatic (conscious control) v autonomic (unconscious control)
What terms are used to describe the relative position of axon tracts in the CNS?
Ipsilateral - located on the same side of the midline
Contralteral - tract crosses the midline
What axis is used in the brain?
Rostral v Caudal
Dorsal to Ventral - * note position changes as the brain is folded in on itself.
What is a ganglion?
A cluster of neuron bodies outside the CNS.
What is a nucleus?
A cluster of neuron bodies inside the CNS.
What is a sulcus and a fissure in the brain?
Sulcus is a groove or inwards dip in the brain.
A fissure is a large sulcus.
What is a gyrus in the brain?
The upwards folding on brain.
‘the hill between two sulcus (the dips)’
What are fasiculations in the brain?
A cluster of axons from different cell bodies often travelling to and from the same general direction
What is a funiculus?
A general area of white matter in the brain, made of a large group of axons containing many fasiculations.
What makes up grey matter?
Neurons
- where the mucky work is done (hence grey)
What makes up white matter?
Axons
-lines of communication
What three sections can the brain be divided into?
The cerebrum
The cerebellum
The brain stem
What makes up the brainstem?
The midbrain
The pons
The medulla
Why is the spinal cord enlarged in the cervical and lumbar regions?
Contains more cell bodies and axons.
Innervates the limbs hence has a larger neuron demand.
Give an overview of the function and structure of the meninges.
Layers covering the brain and spinal cord, from deep to superficial is the pia, the subarachnoid space filled with CSF, the arachnoid and the dura.
Support and protect the brain physically and metabollically.
Pia matter contains vasculature.
Give an overview of the dura mater
The most superficial of the meninges
Is a tough leathery structure that sits immediately deep to the skull.
It contains the meningeal arteries, supply the dura and inner periosteum of the skull.
What are dural reflextions?
When the meningeal layer of the dura folds away from the periosteal layer of the brain to fold divisions in the brain.
Falx cerebri - seperates the left and right brain
Tentorium cerebelli - seperates the cerebrum and the cerebelleum
Fax cerebelli - partial partition between the left and right cerebellum.
Diaphragma sella - upper lining on the pituitary gland.
The tentorial notch is the inner edge where the tentorium cerebelli stops creating a spaxe before the diaphragma sella starts, creates a passage for the midbrain.
What is the choroid plexus?
A heavily vascularised plexus on the inner lining of the brain ventricles that secretes CSF.
Actively transports substances and immune cells from the blood to the CSF
How does CSF travel from the choroid plexus outwards?
Flows from the choroid plexus into the subarachnoid space and is absorbed into venous sinuses.
What are the brain ventricles?
Four spaces within the brain.
The lateral ventricles
The third ventricle
The fourth ventricle.
Four connected and communicating spaces within the brain parenchyma
What is the dentate ligament?
Found in the spinal cord, is an extension of the pia mater on both lateral sides, connects to the arachnoid mater and the dura mater.
What is the lumbar cistern and cauda aquina?
The spinal cord finishes at L1/L2
This leaves a lumbar cistern or space containing spinal nerves, these spinal nerves are called the cauda equina.
Why is the cauda equina important clincally?
Safe lumbar punctures to sample CSF or deliver antibiotics/aneasthetic (epidural)
Without the risk of injuring the spinal cord.
What are the majority of spinal nerves classified as?
Mixed nerves meaning they carry sensory and motor axons.
Give an overview of the histology of a nerve.
Endoneural fluid and connective tissue (most collagen) form endoneural bundles contained within endoneurium.
These make up nerve fasciles that are surrounded by perineurium. Nerve fascicles combine to make a nerve surrounded by a perineurium.
What should be noted about individual nerves in transverse crossection?
Nucleus is of the surrounding schwann cells majority of the time
Outer darker ring is the schwann cells, a thicker ring shows a more myelinated structure meaning faster neuron communication.
What is important to note about schwann cells and myelination?
Schwann cells can be myelinating and non-myelinating.
Can tell by looking at cross section.
1:1 ratio often indicates myelination
Multiple nerves indicates Schwann cells has a more protective that myelination role.
How are spinal nerves numbered?
Majority of spinal nerves are numbered by their superior vertebrae.
This is not true of cervical nerves.
C1 arises above the C1 vertebrae then numbered sequentially to C8 above T1 (note only seven cervical vertebrae).
What is a dermatome?
An area of skin innervated by a single nerve root.
What is shingles (varicella zosta virus)?
The same virus causes chicken pox.
Effects dermatomes
After chicken pox virus becomes dormant in the spinal ganglia, when immunity weekens the virus becomes reactive.
Multiples and spreads along the pat of the effected nerve (any spinal nerve)
Results in pain and a rash along the dermatome
What is a mytotome?
A group of muscle innervated by a single nerve root
How many cranial nerves are there and how are they classified?
There are 12 cranial nerves
Classified as sensory, motor and mixed.
What are the different sensory cranial nerves?
Olfactory (1) - smell
Optic (2) - vision
Vestibulocochlear (8) - hearing
What are the different motor cranial nerves?
Oculomotor (3) - adjust eye position
Trochlear (4) - eye movement
Abducens (6) - lateral eye movement
Accessory (11) - sternocladomastoid and scalenes muscle
Hypoglossal (12) - tongue
What is the enteric nervous system?
Part of the autonomic nervous system, allows autonomous control of gut peristalsis. Mainly by the myenteric plexus.
Has complete sensorimotor circuits that function independently of the CNs but are regulated by parasympathetic and sympathetic control.
What could be considered the control centre of the autonomic nervous system?
The hypothalamus - compares inputs to biological set points to regulate sympathetic and parasympathetic tone.
Sends signals exclusively to the brainstem and spinal cord.
What is the neural crest?
Found in the embryo.
Progenitor cells that come from the roof of the developing brain to give rise to the PNS and other structures
What are the blue rural reflections called?
Tentorium cerebelli
Tentorium notch
What are the green rural reflections called?
Flax cerebelli
What are the yellow rural reflections called?
Diaphragma sella
What are the pink dural reflections called?
Falx cerebri
What is the first cranial nerve called?
The olfactory nerve
What is the second cranial nerve called?
Optic nerve
What is the third cranial nerve called?
Oculomotor
What is the fourth cranial nerve called?
Trochlear nerve
What is the fifth cranial nerve called?
Trigeminal
What is the sixth cranial nerve called?
Abducens
What is the seventh cranial nerve called?
Facial
What is the eights cranial nerve?
Vestibularcochlear
What is the ninth cranial nerve called?
Glassopharagneal nerve
What is the tenth cranial nerve called?
The vagus nerve
What is the eleventh cranial nerve called?
Accessory nerve
What is the twelfth cranial nerve called?
Hypoglossal nerve
