Nerves Flashcards
What are the different meninges? What are leptomeninges?
CRANIUM DURA MATER (thickest) ARACHNOID MATER PIA MATER (thinnest - strongly adhered to brain) BRAIN
Leptomeninges = arachnoid mater + pia mater
What are meninges?
Membraneous covering of the brain and spinal cord
note: meniges of spinal cord more simple than the meninges of the brain
How does CSF flow through the meninges?
Separation of layers = subarachnoid space cisterns
Occur due to dilation
- failure of arachnoid mater to adhere to pia mater
- or: failure of arachnoid mater to follow the furrows in the brain
+ blood vessels
Bleeds = CSF carries blood away = attempts to prevent hydrostatic pressure from climbing too high
What is the function of the CSF? How is it formed?
Supplies the CNS with nutrients and fluid, and carries away metabolites.
Formed by choroid plexus
What are the consequences in changes in hydrostatic pressure in the CSF?
Increase in hydrostatic pressure = restricts blood flow to the brain
Decrease in hydrostatic pressure = collapse of veins = increased bleeding
What are the membranous envelopes of cranial and spinal nerves?
Stratified squamous epithelium
Epineurium = ensheaths entire nerve
(note: interfasciular bands attach adjacent nerve fascicles)
Perineurium = ensheaths a nerve fascicle (collection of axons)
Endoneurium = ensheaths a single axon
(Oligodendrocyte/Schwann cell envelops some axons)
What are the functional units of the nervous system?
Glia (90%) = maintain homeostasis, form myelin, support and protect neurones
Neurones (10%) = electrically excitable cells that process and transmit information through electrochemical signals
What is the distinction between “heavy” and “light” connections?
Heavy = 1 nerve cells 1000s of nerve cells
Light = 1 nerve cells 1 nerve cell
What is the difference between divergence and convergence?
Divergence = output from one neurone to many
Convergence = output from many neurones to one
What are dendrites? What is the dendritic tree?
Specialisations of cell bodies which increase the surface area for conduction of impulses in the cell body
Dendritic tree = proximal dendrites (thick diameter) —> lots of distal dendrites (thin diameter)
(so there is no difference in electrical resistance at either points at synapses)
What is a dendritic spine?
Appendage of a dendrite that help transmit electrical signals, and act as an anatomical substrate for memory storage (associated with learning)
Down’s syndrome = reduced capacity to express dendritic spines = reduced learning ability
What are bipolar neurones? Give an example of where they are located.
Interneuron
1 dendrite + 1 axon
e.g. retina
What are (pseudo)unipolar neurones? Give an example of where they are located.
No dendrites + 1 axon
e.g. primary sensory neurones
What are multipolar neurones? Give an example of where multipolar neurones are located.
Multiple dendrites + 1 axon
e.g. motor neurones
What are two examples of input summation?
TEMPORAL = excitatory & inhibitory inputs summated with respect to their time of arrival on the cell body/dendrites
SPATIAL = excitatory & inhibitory inputs summated with respect to their relative spatial location on the cell body or dendrites
Outline the different components of a neurone.
INITIAL SEGMENT:
- Cell body (+ dendrites)
- Axonal hillock = “zig-zag” in initial segment where action potentials can travel back up to the cell body as well as down the axon
Axonal membrane & Internodal membrane
Myelin sheath + Nodes of Ranvier
AXONAL TERMINAL
What are the functions of axons? What are collections of axons called in the CNS and PNS, respectively?
- summates all inputs to the neurone
- initiates all-or-none action potentials
- conducts action potentials away from cell body
Collection of axons (CNS) = fibre tracts (exception: optic nerve)
Collection of axons (PNS) = nerves
What is the difference between excitatory and inhibitory neurones?
Excitatory = cause depolarisation
Neurotransmitters: glutamate, aspartate
Inhibitory = cause hyperpolarisation
Neurotransmitters: glycine, gamma-aminobutyric acid
What is the structure and function of sensory neurones?
Pseudo-unipolar (fastest conducting)
Transduces electromagnetic/mechanical energy into electrical impulses via receptors
Sensory Receptor —> Cell body —> CNS
“Afferents”
What is the structure and function of motor neurones?
Multipolar
Integrate a large array of inputs to synthesise a single output
CNS —> Cell Body —> Effector
“Efferents”
What is the structure and function of interneurones?
Multipolar
Information relay (therefore majority of neurones)
Sensory neurones —> Cell Body (brain/spinal cord) —> Motor neurones
What are the different neuroglial cells?
Ependyma = line ventricles and central canal of spinal cord for circulation of CSF
Astrocytes = transfer nutrients/waste between neurone and blood
- blood brain barrier
- phagocytic functions
- physical support for neurones
Oligodendrocytes = myelination (CNS)
Schwann cells = myelination (PNS)
Myelination insulates neurones, allowing faster saltatory conduction
Microglia = immunity & inflammation
Satellite cells = physical support of neurones in PNS
What are ganglia? What is the equivalent in the CNS?
Collections of neuronal cell bodies in the PNS (swellings)
CNS = collections of neuronal cell bodies = nuclei
How many cranial & spinal nerves are there in the PNS?
Cranial nerve axons = 10
Spinal nerve axons = 31
Outline the structure of grey and white matter in the nervous system.
Grey matter = butterfly/H-shape (post-ganglionic neurones; unmyelinated)
White matter = surrounds grey matter (pre-ganglionic neurones; myelinated)
Posterior grey matter = dorsal horn = receives sensory input
Anterior grey matter = ventral horn = stimulates motor neurones
Central canal (lined by ependyma)
Either side = lateral horn
What is the structure of somatic efferents?
Active or inactive (inactive during REM sleep)
Voluntary control
Single neurone
Neurotransmitter = acetylcholine
Effector = skeletal muscle
What is the structure of parasympathetic nerves?
Long pre-ganglionic neurone (myelinated), short post-ganglionic neurone
Synapse between neurones = Acetylcholine, nAChR
End plate synapse = Acetylcholine, mAChR
What is the structure of sympathetic nerves?
Short pre-ganglionic neurone (myelinated), long post-ganglionic neurone
Synapse between neurones: ACh, nAChR
End plate:
1) Noradrenaline one alpha/beta receptor
2) Direct release of adrenaline/noradrenaline from pre-ganglionic neurone from adrenal medulla into bloodstream
Give some examples of effector organs in the autonomic nervous system. Give some examples of organs not innervated by either the parasympathetic or sympathetic nervous system.
Visceral organs e.g. cardiac muscle
Smooth muscle e.g. airways, GI, blood vessels
Secretory glands e.g. serous/mucous secretions
Exceptions:
- sweat glands
- ejaculatory mechanisms
What does an overactive parasympathetic nervous system cause? What does an overactive sympathetic nervous system cause?
Overactive parasympathetic = dilated blood vessels —> shortage of substrates to the brain —> faints
Overactive sympathetic = constricted blood vessels —> shortage of substrates to tissues —> tissue necrosis of peripheries
Outline the functions and anatomy of sympathetic neurones.
Fight-or-flight response
- Diversion of blood to muscles and heart
- Increase in heart rate/force of contraction
- Increase in blood pressure
- Reduced blood flow to GI & skin
- Hyperventilation
Thoracolumbar (all 12 thoracic & first 2 lumbar segments)
Pre-ganglionic = cholinergic
Post-ganglionic = nicotinic receptors, noradrenergic/adrenergic (adrenal medulla)
Effector organs = alpha and beta receptors
Outline the functions and anatomy of parasympathetic neurones.
Rest-and-digest
- Promotes digestion
- Decrease in heart rate/force of contraction
- Promote sleep and bladder emptying
- Increased bloodflow to GI & skin
Craniosacral (cranial/cervical + 2-4 sacral segments)
Pre-ganglionic: ACh
Post-ganglionic: nAChR, cholinergic
Effector organs: muscarinic receptors
What are some examples of cranial nerves?
- occulomotor nerve = constricts pupil
- facial nerve = serous secretions (nasal, lacrimal)
- glossopharangeal = serous secretions (submandibular & sublingual)
- vagal = slowing of activity e.g. heart rate
What is the sympathetic chain?
Base of skull to sacrum
Bundles of ganglia
Retroparavertebral position
What is Horner’s syndrome?
Lesion in sympathetic trunk of neck/cancer in apex of lung
—> compression of cervical nerves
- pupil constriction (unilateral mitosis)
- partial ptosis (drooping of upper eyelid)
- anhydrosis of one side of the face
- enophtalmos (eye looks sunken)
What is the pathology of a demyelinating disease? Give an example of a demyelinating disease.
Damage to the myelin sheath, so conduction velocity is slower
S&S:
- blurred vision
- weakness/fatigue
- lack of coordination
- difficulty controlling bowel movements/urination
e.g. Multiple sclerosis (autoimmune destruction of myelin)
What are the types of glial cells and their functions?
Astrocytes (CNS) = blood-brain barrier (transfer of nutrients and waste)
Oligodendrocytes (CNS) = myelination
Microglia (both) = immune & inflammatory functions
Schwann cell (PNS) = myelination
Satellite cells = physical support of peripheral neurones
