020 an introduction to neuroanatomy Flashcards
where are olfactory sensory neurons?
- live in the olfactory epithelium
- have axons run through cribiform plate of ethmoid bone in the nasal cavity
- they synapse in the olfactory bulb in the brain (just above the cribriform plates
what is special about olfactory sensory neurons?
- they are replaced by stem cells throughout their life as they are vulnerable as they are exposed to the environment
- this means preferences of smells change throughout our life
- olfactory nerves contain special glial cells
why olfaction relevant clinically?
- loss of sense of smell is often one of the first symptoms of many diseases such as Parkinson’s and covid-19
what is the evolution of olfactory epithelium?
- animals have much larger olfactory epitheliums than humans as many are colourblind, so rely on smell more
- as humans have better eyesight than most animals, we rely on smell less so have a smaller olfactory epithelium
what is unique about cranial nerve 2 pathway?
- optic nerve
- nasal side axons in the retina cross the midline in the brain in the optic chiasm (contralateral)
- temporal side axons stay on the same side and don’t cross over in the optic chiasm (ipsilateral)
what is clinically important about the structure/insualtion of optic nerves?
- their axons are covered with CNS myelin (oligodendrocytes) which can thus be affected by multiple sclerosis
- the optic nerves are also covered by meninges (dura mater) that attach to the eyeball and are surrounded by CSF
- so raised intracranial pressure will be transmitted through CSF to optic disc and lead to papilloedema
what is the myelination of axons in the CNS vs PNS?
- CNS = oligodendrocytes (microscope can see layers of cell wrapping round)
- PNS = Schwann cells
what are peripheral nerves surrounded by?
outer to inner:
- epineurium
- perineurium
- endoneurium
what are peripheral unmyelinated axons embedded in?
- embedded in Schwann cells
what is grey matter in the spinal cord divided into?
laminae of Rexed (layers dividing function of neurons)
- 10 in total
- 1 starts in dorsal horn (back)
what lamina are nociception neurons found?
- lamina 1 and 2 and maybe 5
describe function of lamina 1 of spinal cord
- receives noxious and thermal stimuli
- sends information to brain via lateral spinothalamic tract
- corresponds to marginal zone of spinal cord
describe function of lamina 2 of spinal cord
- involved in the reception of all sensory stimuli (noxious and non-noxious) and moderates perception/interpretation of pain
- sends information to lamina 3 and 4
- corresponds to substantia gelatinosa of spinal cord
describe function of lamina 3 of spinal cord
- involved in proprioception and discriminatory/light touch
- connected to laminas 4,5,6
- corresponds to nucleus proprius in spinal cord
describe the function of lamina 4 of spinal cord
- involved in non-noxious sensory reception and processing and distribution
- connected to lamina 2
- corresponds to nucleus proprius in spinal cord
describe the function of lamina 5 of spinal cord
- relays all sensory information, including nociception, to the brain via lateral spinothalamic and contralateral tracts
- also receives descending information from the corticospinal and rubrospinal tracts
- e.g. moving arm away from flame
describe the function of lamina 6 of spinal cord
- only present in the cervical and lumbosacral enlargements
- contains many small interneurons that are involved in the modulation of spinal reflexes and reception of sensory information from muscle spindles, (involved with proprioception)
- Sends information to the brain via the ipsilateral spinocerebellar pathways
- This lamina does not correspond with any spinal nuclei.
describe the function of lamina 7 of the spinal cord
- along with Lamina IX, form the middle region between the dorsal and ventral roots, medial to the position of the lateral gray horns
- changes configuration based on the level of the vertebral column observed
- receives information directly from Lamina 2 to 6, and from viscera
- relays motor information back to the viscera
- gives rise to cells that are involved in the autonomic nervous system
- corresponds to the dorsal nucleus of Clarke and the lateral and medial motor neurons.
describe the function of lamina 8 of the spinal cord
- varies in configuration based on the level of the spinal cord
- It is most prominent in the cervical and lumbar vertebral levels
- involved in the modulation of motor output to skeletal muscles
- corresponds to the lateral and medial motor neurons
describe the function of lamina 9 of the spinal cord
- composed of clusters of large alpha motor neurons that innervate striated muscles, and small gamma motor neurons that innervate the elements of muscle spindles that are responsible for contraction. (The axons of both alpha and gamma motor neurons emerge via the ventral roots.)
- varies in configuration based on the vertebral level on which it occurs.
- It distributes motor information to skeletal muscles
- corresponds to the lateral and medial motor neurons
describe the function of lamina 10 of the spinal cord
- surrounds the central canal of the spinal cord and is known as the grey commissure
- This is where axons decussate from one side of the midline of the spinal cord to the other
- corresponds with the spinal cord nucleus, the interomediolateral nucleus
where do preganglionic sympathetic neurons have their cell bodies?
- in the lateral horn of the spinal cord, part of lamina 7 in the thoracic and upper lumbar cord
what happens when a peripheral nerve is damaged?
- cell body may die if the injury is close enough
- if the injury is further away from the cell body then the axon regenerates from the injury distally
- axons regenerate along course of pre-existing fibre, looking for something to innervate
how can peripheral nerves be surgically repaired?
- suture proximal end surrounding connective tissue/membrane connected to the spinal cord back to distal stump membrane
- axon regenerates under suture
what is a lower motor neuron lesion?
lesion which affects nerve fibers traveling from the anterior horn of the spinal cord to the associated muscle
give some examples of upper motor neuron lesion signs
- Weakness – the extensors are weaker than the flexors in the arms, but the reverse is true in the legs
- Muscle wasting is absent or slight
- Hyperreflexia with clonus
- Spasticity paralysis
- No fasciculation’s
- Babinski sign positive – extended hallux and flaring of remaining digits
- Hoffmann’s sign is positive if flexion and sudden release of the terminal phalanx of the middle finger result in reflex flexion of all the digits
- Pronator drift – Patient is asked to hold fully extended arms straight out in front with palms facing upward. If a lesion is present when the patient is asked to close his/her eyes the arm on the affected side pronates due to the difference in muscular tone between pronators and supinators
what is the Babinski sign and what is is it adults and babies?
- stroking the sole of foot from heal to big toe
- in healthy adults, the toe reflexes and curls down = negative Babinski sign
- positive Babinski sign = toes curl up = either upper motor lesion or in babies
- babies will show a positive Babinski sign until their corticospinal tracts are myelinated
what are descending spinal cord tracts?
- spinal nerve tracts that arise in the brain and carry information down the spinal cord –> to motor neurons
what is the function of corticospinal tracts?
- controls voluntary movement
- carries information from the brain, down the spinal cord to motor neurons to initiate movement
what is the pathway of corticospinal tracts?
- origin = arise from neurons in the cerebral cortex
- then pass down the brainstem near its ventral/anterior surface
- then crosses the midline at the lowest part of the medulla
- then carries down the spinal cord on the contralateral side
where in the brain is this section from?
oblique slide through the upper part of the midbrain
what is A?
- superior colliculus (part of tectum)
what is b?
cerebral aqueduct
what is c?
periaqueductal
what is d?
-corticospinal tract
what is e?
substantia nigra
what is f?
red nucleus
what is a?
4th ventricle
what is b?
cerebellum
what is c?
middle cerebellar peduncle
what is d?
corticospinal fibres
what is e?
ascending sensory tracts
what artery supplies the pons?
basilar artery
