Flashcards in Lecture 6 - Basics Of The CNS Deck (16)
What is emergence?
The phenomenon where complex behaviour ‘emerges’ from the interactions of individual, relatively simple units
What comprises the CNS?
Cerebral hemispheres Brainstem and cerebellum Spinal cord
What comprises the PNS?
Dorsal and ventral roots Spinal nerves Peripheral nerves
What does the CNS arise from?
The neural tube
Is the cauda equina central or peripheral?
It is peripheral.
• The fact that it is in vertebral canal doesn’t mean it is in the CNS
What happens to the orientation of the brain as it ‘flexes’ at around the level of the midbrain?
The superior part of the hemisphere is actually dorsal.
The inferior brain is actually ventral.
Therefore, dorsal/ventral brain structures are not necessarily closest to the back/belly respectively.
Why did the frontal lobes rotate by 90º? What does this rotation now mean?
During human evolution, the frontal lobes grew massively and at the same time flexed through 90º to occupy the space above our faces.
Rostral most part of the brain is the bit closest to the nose.
Because the brain flexes, dorsal is on the top and ventral is on the bottom.
Because of the bend, can’t think about superior and inferior positions - need to think about rostral and caudal in terms of the order in which the cranial nerves emerge
What are the parts of the brainstem and what are their functions?
• Midbrain (mesencephalon)
- Eye movements and reflex responses to sound and vision/visual stimuli
- The midbrain is responsible for the unconscious reflexes we carry out when something perceived as a danger is coming towards us so we can move out of the way in time.
- the midbrain is able to do is very rapidly make an appraisal of whether a stimulus is dangerous or not
- it can mediate reflexes which have visual and auditory stimuli as well - the midbrain is also listening e.g. if we hear an explosion, most of us would reflex automatically to orientate ourselves away from the sound - the midbrain is responsible for this - it can work out if a stimulus is threatening and orientate the body towards that or move the body away from it depending on what the stimulus is.
- Sleep (sleep wake cycle)
- Cardiovascular and respiratory centres
- Contains a major motor pathway (medullary pyramids)
What are the sulci, gyri and fissures of the brain?
Which parts of the brain tend to be motor ad which sensory?
• Sulcus (pl. sulci): A ‘groove or furrow’ in the brain separating adjacent gyri
• Gyrus (pl. gyri): A ‘ridge or fold’ in the brain
• Fissure: A large ‘crack’ or ‘split’ between adjacent large areas of the brain
• If a structure in the CNS is ventral/anterior to the central sulcus it tends to be motor
• If a structure is dorsal/posterior to the central sulcus it tends to be sensory
• Precentral gyrus drives the muscles - major motor part
• Postcentral - sensory gyrus
What are the lobes of the brain and what are their roles?
Frontal lobe: Higher cognition, personality, problem-solving, motor function, speech
Parietal lobe: Sensation, spatial awareness - there are px that don’t acknowledge the left half of the world, for example - this can arise from parietal lobe damage
Temporal lobe: Memory, smell, hearing - without this lobe, we can’t learn new things or retrieve memories, we can’t smell or hear
Occipital lobe: Vision (visual cortex - it is far away from the eyes because the other lobes developed so much - in other animals, it is closer to the eyes because their lobes aren’t as developed)
Cerebellum: - ‘little brain’ (motor) Co-ordination and motor learning, (cognition and higher through processes)
What is the optic chiasm?
A site where fibres in the visual system cross over
What is the uncus?
Part of the temporal lobe that can herniate, compressing the midbrain
In brain tumours, the uncus can squash adjacent midbrain nerve.
1 million axons in optic nerves and medullary pyramids
What are the medullary pyramids?
Location of descending motor fibres (each has around 1 million axons!)
What is the corpus callosum?
Fibres connecting the two cerebral hemispheres
if it is damaged based on left hand not knowing what right hand is doing - alien hand syndrome.
• Corpus callosum is white matter - axis - callosum means callous
• Women have a bigger corpus callosum than men
What is the thalamus?
Thalamus: Sensory relay station projecting to sensory cortex
main role is to relay sensory information that comes up the brainstem out to the cortex.