Cerebrum

• Basal Ganglia

  Consist of 5 large subcortical nuclei- caudate nucleus, putamen, globus pallidus, subthalamic nuclei and substantia nigra. All of these participate in the control of movement.
• Basal Ganglia function

  Receive input from and project to the cortex via the thalamus
• Components of the Basal Ganglia

  • Caudate nucleus
  • Putamen
  • Globus pallidus
  • Subthalamic nuclei
  • Substantia nigra
• Striatum

  The caudate and putamen nuclei together
• Striatum

  • Constitutes the "input side" of the basal ganglia
  • Major inputs: the cerebral cortex
  • Outputs: project mainly to the globus pallidus
  • Involved in motor and cognitive planning
• Globus Pallidus

  • An "output" nucleus of the basal ganglia
  • Receives input from the caudate and putamen
  • Projects to the thalamus, specifically to the ventral anterior and ventral lateral nuclei
  • Basal ganglia exert some control over movement by acting through descending pathways originating in the cerebral cortex
• Basal Ganglia

  • Involved in the initiation and direction of voluntary movement
  • Balance (inhibitory)
  • Postural reflexes
  • Part of extra-pyramidal system: regulation of automatic/ voluntary movement
• Components of the Basal Ganglia

  • Caudate
  • Putamen
  • Nucleus accumbens
  • Globus pallidus
  • Substantia nigra
  • Subthalamic nucleus
• Claustrum

  A thin, irregular, sheet of neurons that is attached to the underside of the neocortex in the centre of the brain
• Claustrum

  • May be involved in widespread coordination of the cerebral cortex, synchronising neuronal activity so that a seamless common percept is achieved between the two cortical hemispheres or between cortical regions within the same hemisphere
• Basal Ganglia and Frontal Lobe

  The frontal lobe plans the action and sends information to basal ganglia so that this cortical-basal ganglia-cortical loop is involved with higher order cognitive aspects of motor control
• Basal Ganglia

  Also involved in emotion via the limbic system
• Substantia Nigra

  • Can be divided into two parts: the substantia nigra pars compacta (SNpc) and the substantia nigra pars reticulata (SNpr)
  • SNpc (dopaminergic pathway) receives input from the caudate and putamen, and sends information right back
  • SNpr receives input from the caudate and putamen, but sends it outside the basal ganglia to control head and eye movements
• Globus Pallidus

  • Can be divided into two parts: the globus pallidus externa (GPe) and the globus pallidus interna (GPi)
  • Both receive input from the caudate and putamen, and both are in communication with the subthalamic nucleus
  • GPi sends the major inhibitory output from the basal ganglia back to thalamus
  • GPi also sends a few projections to an area of midbrain (the pedunculopontine area or PPA), presumably to assist in postural control
• Limbic System

  • Consists of limbic lobe and deep lying structures
  • Primitive cortical tissue encircling the upper brain stem
• Components of the Limbic System

  • Parahippocampal gyrus
  • Cingulate gyrus
  • Subcallosal gyrus
  • Hippocampal formation (hippocampus, dentate gyrus and subiculum)
  • Amygdala
• Olfactory System

  • Begins in the roof of the nasal cavity
  • Olfactory receptors are ciliated epithelial cells with an array of receptors capable of detecting thousands of different odours
• Olfactory Bulb

  • Recognizes smell and associates it with memories
  • Discriminate odours
  • Filter background odours
• Hypothalamus and Limbic System

  • The hypothalamus is tightly integrated with the limbic system and it makes up the deep limbic system along with all limbic structures
  • Functions of the deep limbic system: sets the emotional tone of the mind, filters external events through internal states (emotional colouring), tags events as internally important, stores highly charged emotional memories, modulates motivation, controls appetite and sleep cycles, promotes bonding and modulates libido
• Papez's Proposed Limbic Circuit

  Cortex ➤cingulate gyrus ➤ hippocampal formation ➤ mamillary bodies of hypothalamus (via the fornix) ➤ anterior thalamic nuclei ➤ cingulate gyrus ➤ cortex
• Amygdala

  An almond-shaped neural structure involved in producing and responding to non-verbal signs of anger, avoidance, defensiveness, and fear
• Amygdala

  • A primeval arousal centre, originating in early fishes, which is central to the expression of negative emotions in man
  • Inputs: association areas of visual, auditory, and somatosensory cortices
  • Outputs: to the hypothalamus and brainstem autonomic centers, including the vagal nuclei and the sympathetic neurons
  • Also interconnected with frontal cortex, mediodorsal thalamus, and the medial striatum
• Hippocampus

  Absolutely necessary to form memory - both long-term and short-term but it is crucial to the consolidation of the former
• Hippocampus

  • Appears to be directly affected by oestrogen - the more the oestrogen the greater the synaptic density
  • Involved in 3 types of memory: Working Memory, Declarative Memory, Procedural memory
• Alzheimer's disease

  Affects the hippocampus first and severely, before other parts of the cortex (later, the frontal lobes too)
• Hippocampus

  • Involved in severe mental illnesses like schizophrenia and some severe depressions
  • Appears to shrink in these conditions
  • Shrinkage can be prevented in people with depression if they are taking antidepressants
• Hippocampus

  Directly affected by oestrogen, the more the oestrogen the greater the synaptic density
• Hippocampus

  Involved in memory, including working memory, declarative memory, and procedural memory
• Cerebral White Matter

  • Association fibres interconnect both nearby and distant parts of the cerebral cortex on one side
  • Projection fibres project information into the cerebral cortex from subcortical structures, and out of the cerebral cortex to subcortical structures on the same side
  • Commissural fibres interconnect the cerebral cortices of the two sides
• Internal Capsule

  • Separates the caudate nucleus and the thalamus from the lenticular nucleus
  • Contains both ascending and descending axons
  • Consists of corticobulbar, frontopontine and thalamocortical fibres
• External Capsule

  • A series of white matter fiber tracts in the brain
  • Runs between the most lateral segment of the lentiform nucleus and the claustrum
  • A route for cholinergic fibers from the basal ganglia to the cerebral cortex
  • Eventually joins the internal capsule around the lenticular nucleus
• Cerebral Cortex

  • Functionally divided into numbered areas first proposed by Brodmann in 1909
  • Brodmann's areas were described based on cytoarchitecture and later found to be functionally significant
• Primary Somatosensory Area (Areas 1,2,3)

  • Somatotopically organized
  • Areas of cortex proportional to sensory discrimination of the area not to amount of surface area
  • Stimulation produces contralateral tingling or numbness but never pain
  • Lesions cause contralateral loss of tactile discrimination and position sense but no relief of pain
• Primary Visual Area

  • Occipital lobe, mostly in and around calcarine fissure
  • Primary visual cortex=V1=Brodmann area 17
  • Other visual areas V1-V5
  • Topographic (retinotopic) maps
  • Map is distorted
  • Necessary for conscious visual sensation
  • Lesion causes scotoma
  • Roughly 20 areas devoted to vision, each has retinotopic map, about 1/3 of cortex' area
• Primary Auditory Cortex (Areas 41 & 42)

  • Transverse temporal gyrus
  • Tonotopic organization, high frequency postero-medial and low freq anterolateral
  • Lesion causes difficulty in recognizing distance and direction of sound, especially when the sound comes from the contralateral side
• Primary Gustatory Cortex (Area 43)

  • Anterior part of parietal operculum
  • Lesion results in contralateral (mostly) ageusia
• Frontal Lobe

  • Makes up 1/3 of all cerebral cortex
  • Contains primary motor, premotor, frontal eye field, supplementary motor, prefrontal, and Broca's area
• Primary Motor Cortex (Area 4)

  • Somatotopic/somatomotor organization
  • Size of areas is proportional to the degree of skill involved with movement
  • Lesions result in paralysis/paresis of contralateral body area
• Premotor Area (Area 6)

  • Contains programming for movements
  • Electrical stimulation produces slower movements of larger groups of muscles compared to area 4
  • Lesion produces apraxia - inability to perform voluntary movement in the absence of paralysis
• Frontal Eye Field (Inferior part of Area 8)

  • Stimulation produces conjugate eye movement to contralateral side
  • Lesions produce transient deviation of eyes to ipsilateral side and paralysis of contralateral gaze