Anatomical Divisions of the brain week 7

MBB1

Navigating neural space

• Rostral (anterior) – ‘toward the beak’

• Caudal (posterior) – ‘toward the tail’ § Dorsal (superior) – ‘toward the back’

• Ventral (inferior) – ‘toward the belly’

• Human neural axis bends because the head is perpendicular to the back

• Lateral - toward the side

• Medial - toward the midline

• Ipsilateral – on same side of midline

• Contralateral – on opposite side of midline

Corpus callosum

• Consists of large bundle of axons that connect two hemispheres

• Green & Blue represent contralateral connections

• Homotopic connects complementary region of other hemisphere

• Heterotopic communicates to a different brain regions

• Ipsilateral is on the the same side

• Callosotomy - procedure to cut the corpus collosum to stop severe epileptic seizures

• Prevents communication between hemispheres

Anatomical Subdivisions of the brain

• Forebrain

  • telencephalon

    • cerebral cortex

    • basil ganglia

    • limbic system

  • diencephalon

    • thalamus

    • hypothalamus

• Midbrain

  • mesencephalon

    • tectum/tegmentum

• Hindbrain

  • metencephalon

    • cerebellum

    • pons

  • myelencephalon

    • medulla oblongata

Telencephalon – Cerebral Cortex

• Telencephalon is a subdivision of the forebrain & consists of the limbic system, Basal Ganglia and Cerebral Cortex

• Cerebral cortex - largest structure of human brain

• Divided into two cerebral hemispheres

• Inner “white matter” is pale because it has a high proportion of axon fibres covered in fatty myelin layer.

• Outer “grey matter” where the neurons synapse and connect together

Telencephalon – Basal ganglia

• the nuclei of the basal ganglia (including caudate nucleus & Putamen) are responsible for controlling involuntary movement, particular aspects that are highly automatised or involuntary (such as walking).

• The basal ganglia are dysfunctional in patients with Parkinson’s disease which leads to weakness, tremors, limb rigidity, poor balance and difficulty initiating movements

Telencephalon – Limbic System

• 1937 James Papez first proposed an emotion circuit in the brain

• The “limbic system” includes the hypothalamus, thalamus, cingulate gyrus, fornix, hippocampus, amygdala & orbitofrontal cortex and some nuclei of the basal ganglia and was previously thought to be the emotion circuit

• Concept of Limbic system still used today, however, the understanding of the role of different brain structures has been refined.

• While the amygdala plays a crucial role in emotion, it is now known the hippocampus & parts of surrounding cortex are involved in learning & memory

Diencephalon - thalamus & hypothalamus

• Thalamus:

  • Major relay station for sensory inputs to cerebral cortex

  • Divided into several nuclei

• Hypothalamus:

  • Controls autonomic nervous system and endocrine (hormone) system

  • Regulates survival behaviours (fighting, feeding, fleeing, mating)

Midbrain – Mesencephalon

• The midbrain (and hindbrain) are located within the brainstem.

• The midbrain (or mesencephalon) is at topmost region of brainstem and sits directly above the hindbrain.

• It connects the pons and cerebellum with the forebrain.

• plays an important role in motor movement particularly movement of the eye, and in auditory and visual processing.

Hindbrain - Metencephalon

• Includes the cerebellum (‘little brain’) which receives information from visual, auditory, somatosensory & vestibular (balance) systems helps coordination of movement. Damage to the cerebellum causes problems with walking and leads to jerky, poorly coordinated movements and problems maintaining balance.

• The pons lies on the ventral surface of the brainstem. It contains several nuclei important in regulating sleep and arousal; it also relays information from the cerebral cortex to the cerebellum.

Hindbrain - Myelencephalon

• The myelencephalon is more commonly called the Medulla oblongata (or Medulla) and links the hindbrain to the spinal cord and contains neurons important for autonomic functions like respiration and hear rate.

Lobes of the cerebral cortex

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Primary visual cortex

• Occupies medial and lateral parts of the occipital cortex/lobe at the back/posterior of the brain.

• Receives sensory information from retina.

• The left and right visual field are each projected to the contralateral hemisphere.

• Light stimulus from the external environment from both visual fields stimulate the corresponding area of the retina within each eye.

• Different regions of the retina are represented by different areas within the primary visual cortex.

• areas further out in peripheral vision are processed by areas of the visual cortex that extend into the calcarine fissure

• Within the primary visual cortex neurons show “orientation selectivity”

• Hubel and Wiesel won the Nobel prize in 1981 for this work.

Parietal Lobe / Parietal Cortex

• Involved in attention and spatial awareness.

• sits on the dorsal surface of the cortex and is referred to as part of the dorsal stream and the “where” pathway – named for its role in spatial localisation

Temporal Lobe / Temporal Cortex

• Important in auditory processing.

• Also involved in more complex visual processing (faces & complex object recognition).

• sits on the ventral surface of the cortex and is part of the ventral stream and the “what” pathway – named for its role in complex object recognition

Primary auditory cortex

• Occupies superior part of the temporal cortex, as well as a patch of cortex that is buried within the Sylvian fissure. It receives auditory sensory information from the cochlea (part of the inner ear concerned with hearing).

• Sounds of different frequencies (e.g., low versus high tones) are represented by different areas within the primary auditory cortex, forming a tonotopic map.

Primary somatosensory cortex

• Located immediately posterior to the central sulcus (large grove between the frontal & parietal lobe)

• Receives sensory information from the skin (temperature, touch & pain).

• Different regions of skin surface represented by different areas along the strip of cortex, forming a somatotopic map (face & hands overrepresented)

Primary motor cortex

• Located on the precentral gyrus immediately anterior to central sulcus.

• Different parts of primary motor cortex send signals that control different groups of voluntary muscles (e.g., hands, feet, lips).

• Like the primary sensory cortices, the primary motor cortex controls muscles on the opposite (contralateral) side of the body

Frontal Lobe

• Human frontal cortex is different from other animals

  • relatively larger than non primates

  • a higher level of connectivity with rest of the brain (compared to other apes)

• “higher order” functions of the frontal lobes

  • Voluntary, controlled behaviour

  • Impulse control & emotional regulation

  • Abstract reasoning & planning

  • Social cognition

  • Language

• Phineas Gage – Classic case of altered “executive functioning” with frontal lobe damage

• railway foreman in Cavendish, Virginia accident involving ‘tamping iron’ (1848)

• survived profound damage to frontal lobe behavioural changes (‘no longer Gage’ )

  • personality changed profoundly

  • angry, impatient, obstinate, capricious

  • unable to plan for the future.

  • not employable in old job, (only held jobs where he did not make decisions)