Anatomy of the Nervous System Flashcards
The thalamus acts as a sensory relay centre. Virtually all sensation passes through the thalamus on its way to the cortex. There are exceptions though. What is the exception?
Smell (the olfactory nerve), because it arises through the telencephalon (which creates the forebrain).
Identify the location of the cervical enlargement and the lumbosacral enlargement of the spinal cord.
What is the purpose of the enlargements of the spinal cord?
- Has two enlargements in cervical region and lumbosacral region.
- These enlargements correspond to an increase in lower motor neurones to the limbs (so there’s a lot more information coming out of these regions to the limbs, hence there’s an enlargement).
- The spinal cord and brain are covered by meningeal coverings - Pia, arachnoid (arachnoid is linked to pia but cling-filmy like) and the dura (which is a tough, fibrous canvasy type membrane).
Describe the anatomy of the spinal cord
- 42-45 cm
- Upper 2/3 of vertebral column
- Foreamen magnum - L1/L2
- Cervical and lumbosacral enlargements (increase in lower motor neurons to the limbs)
- Meningeal coverings (pia, arachnoid and dura).
What type of nerves would you find in the dorsal root?
- Dorsal root is purely sensory.
Segment = a piece of spinal cord which is bound front and back by rootlets of a single spinal nerve.
What type of nerves would you find in the ventral root?
Ventral root = purely motor (efferent).
Is epidural space found in the spine or the meninges?
Spine
Where does the spinal cord end at?
L1
Explain the development of the spinal cord from a foetus to an infant.
- At birth, the bottom end of the spinal cord is about L2/L3, but in infant adult it is at L1.
- Essentially when you are born, the roots are pulled down by the vertebral column as you’re growing.
Identify the filum terminale, cauda equina and conus medullaris of the spinal cord.
Also where do you find spinal nerves?
- Spinal nerve is found in its corresponding vertebral foreamen.
- L5 spinal nerve is found in intervertebral foreamen between L5 and S1.
- They are long nerves.
- But as you go higher the roots get shorter because they get more transverse.
What is a sistern?
A collection of CSF where there isn’t much tissue.
Where would you take CSF from the spinal cord?
L3, L4, L5
Identify the anterior white commissure of the spinal cord.
Commisures = fibres which cross the mid-line.
Identify the anterior median fissure
Identify the central canal of the spinal cord
Identify the posterior (sensory ) and anterior (motor) horns
What are the ascending tracts of the spinal cord?
Ascending tract neurons are categorised into 3 groups:
- 1st oder neurons - pick up stimuli from external receptor, run through the dorsal roots of the spinal nerves, and their cell bodies are found within the dorsal root ganglions. So part of this neuron is in the peripheral nervous system but its central projection goes into the central nervous system.
- 2nd order neurons - neurons which take information from wherever it is in the spinal cord or brainstem, and takes it into the thalamus. That exists purely within the CNS.
- 3rd order neurons - neurons from the thalamus to the cerebral cortex where the higher functions take place.
The thalamus acts as a sensory relay centre. Virtually all sensation passes through the thalamus on its way to the cortex. There are exceptions though.
What is the dorsal colum?
The posterior column (dorsal column) refers to the area of white matter in the middle to posterior side of the spinal cord. It is made up of the gracile fasciculus and cuneate fasciculus and itself is part of the posterior funiculus.
It receieves several types of sensory information from the body including fine touch, propriioception and vibration. It is involved in conscious perception.
What is the spinothalamic tract?
The spinothalamic tract is a sensory pathway from the skin to the thalamus.
From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upwards to the somatosensory cortext of the postcentral gyrus.
What is the ascending tract / dorsal column?
- The dorsal column is a major route for administrative aspects of fine touch (tactile) and proprioceptive sensation.
- Just remember, the nerve decasates towards the opposite side of the brain to its origin in the spinal cord.
- Major route for discriminative aspects of tactile and proprioceptive sensation.
- Two point discriminiation (fine touch), pressure, vibration & conscious proprioception (position sense).
- Sensory ataxia.
How does the ascending spinothalamic tract articulate?
- Decussates (crosses the midline) but runs ventrolateral to ventral horns.
- Runs ipsilaterally 1-2 segments as the dorsolateral fasciculus
- Decussates and ascends contralaterally ventrolateral to ventral horns.
- Spinal leminiscus in brainstem.
How do the ascending spinothalamic tracts articulate?
- Ripse ipsilaterally 1-2 segments as the dorsolateral fasciculus (of Lissauer)
- Decussate and ascend contralaterally ventrolateral to ventral horns.
- Spinal leminiscus in brainstem
- 2 order neurons of lateral pinothalamic joined in brainstem by trigeminothalamic tract
- 2 order collateral neurons project to reticular formation (wakefulness and consciousness).
What sensations are carried in the ascending spinothalamic tracts?
- carries primarily pain, temperature and crude touch.
- Sharp pain, temperature, crudely localised touch.
- Anterior spinothalamic - crude touch.
- Lateral spinothalamic - pain & temperature.
- Sensory level 2 segments distal to cordotomy.
Describe the ascending tract - spinocerebellar tract
- Unconscious proprioception for posture & movement coordination.
- Consits of 2 ascending pathways:
1. Dorsal spinocerebellar tract
- Muscle spindles, golgi tendon organs, touch and pressure receptors.
- Enter at T1-L2-2nd order neurons of nucleus dorsalis (of Clarke)
- Ipsilateral ascent - inferior cerebellar peduncle
- Ipsilateral propioception.
2. Ventral spinocerebellar tract
- Movement control
- Decussate
- Contralateral ascent.
Identify the tracts in the spinocereballar and anterolateral pathways, as well as the fasciculus gracillis and fasciculus cuneatus.
The most medial fibres in the fasiculus gracile come from the…
…lowest part of the body.
The most lateral fibres come from the most…
superior parts of the body.
(so you can see how well organised the whole thing is)
