L11 Cerebral Hemispheres Flashcards
What is the neocortex and where is it found?
Also called the cortex.
- Thin sheet of neurons lying just beneath the pia mater of the cerebral hemispheres
- Associated with higher level functions
- Only found in mammals and the most developed primates
Describe the structure of the neocortex.
- Highly folded to increase SA
- Ridges called gyri occupy 2/3rds of the cortex area
- Grooves called sulci occupy 1/3rd of the cortex area
Name the cortical lobes.
- Frontal lobe
- Parietal lobes
- Occipial lobes
- Temporal lobes
Describe the funciton of the neocortex.
- Recieves sensory info associated with the primary cortical areas
- Info sent to sensory association cortical areas which integrates info
- Info then relayed to primary and secondary motor areas where we plan and command voluntary movements
- At the frontal lobe association cortex we formulate desires, intentions, beliefs and decision making
How many layers is the neocortex composed of?
6 layers.
Describe layer I.
- The molecular layer
- Closest to the pia mater
- Contains very few neurons or cell bodies
Describe layer II.
- Contains small neuron soma and intra-hemisphere cortical circuits
Describe layer III.
- Contains small pyramidal neurons connected to other cortical areas (intra and inter hemisphere connections)
Describe layer IV.
- Contains small neurons which recieve input from the thalamus
Describe layer V.
- Contains large pyramidal neurons with large axons projecting to areas outside of the neocortex
Describe layer VI.
- Small spindle like neurons which make efferent connections to the thalamus, and intra-cortical connections to other cortical layers
What percentage of cortical connections are intra cortical and what percentage are sub-cortical?
- 99% of cortical connections are intra-cortical, both intra and inter hemisphere.
- 1% of cortical connections are to sub-cortical areas.
What are the 4 primary cortices?
- Primary motor cortex in the frontal lobe (M1)
- Primary somatosensory cortex in the parietal lobe (S1)
- Primary visual cortex in the occipital lobe (V1)
- Primary auditory cortex found on top of the temporal lobe
How have researchers been able to assign functions to specific cortical areas?
Non-invasive imaging e.g. MRI, fMRI, CT, PET.
Historical records of patients with traumatic brain injuries.
The cortex is divided into…
Functional columns
Functional columns make up a cortical map of the body called…
A somatotopic map
Describe the somatotopic map.
- A map which displays the spatial organisation of body parts correspongin to the mammalian primary somatosensory cortex and innervation
- Higher density fof sensory innervation = larger erea of somatotopic map occupied
- Lips and oral cavity highly innervated = large
When sensory info is recieved by the primary sensory cortices (e.g. visual and auditory) where is it sent to?
The sensory association areas, integrated and processed, allowing us to form a perception of the outside world
Where is info sent from the sensory association areas?
Sent to the primary motor cortex which executes voluntary movement.
Or sent to supplementary second motor areas.
What is the internal capsule?
A white matter structure containing the axons which comprise the principle fibre tracts to and from the cortex.
Describe the stucture of the internal capsule.
- V-shaped
- Anterior limb, posterior limb and apex called the genu
What are the 3 major axon types found in the internal capsule?
- Extrapyramidal motor neurons
- Thalamo-cortical fibres
- Corico-spinal and cortico-bulbar fibres
What structure connects the two cerberal hemispheres?
The corpus callosum
Which hemisphere is dominant in right handed people?
The left hemisphere
