General anatomy of the brain Flashcards
Cerebrum
- has 4 major lobes ( frontal, temporal, parietal and occipital lobes)
- lobar surface is heavily folded forming sulci (valleys) and gyri (ridges)
- Primary (major) sulci are more invariant in their appearance than the secondary (minor sulci)
Central sulcus
-divides frontal lobe from the parietal lobe
Precentral gyrus
- primary motor cortex
- part of the frontal lobe
- homunculus represents the different parts of the body
Post-central gyrus
- part of the parietal lobe
- the primary somatosensory cortex with a similar homunculus representation
Lateral sulcus
- Sylvian fissure
- divides frontal lobe from the temporal lobe
Insula
- a structure sometimes regarded as the 5th lobe of the cerebrum
- located deep in the Sylvian fissure
- where primary gustatory cortex is found
Dorsolateral prefrontal cortex
- in between the superior and inferior frontal sulci is the middle frontal gyrus and this has the dorsolateral prefrontal cortex in it
- executive functions of the human brain
Cingulate sulcus
- on the medial side of the frontal lobe
- the anterior portion of the adjoining cingulate gyrus is considered to be the seat of motivation
Orbitofrontal cortex
- olfactory and orbital sulci are on the inferior surface of the frontal lobe
- the orbitofrontal cortex is often considered to be the seat of associative learning and decision-making
Primary auditory cortex
-is in the superior temporal sulcus ( in lateral sulcus)
Inferior parietal lobe
- made of the angular gyrus and supramarginal gyrus
- is considered to be important for visuospatial attention
- interparietal sulcus separates suiperior and inferior parietal lobes
Primary visual (striate) cortex
-in the calcarine sulcus in the medial occipital cortex
Left temporal cortex
language comprehension
Right hemisphere
language prosody (tonal modulation of speech)
Dominant hemisphere
- hemisphere contralateral to the dominant hand is the dominant hemisphere
- mediates language and speech functions
- dominance can be tested using Annette’s handedness scale or Edinburgh handedness inventory
- handedness is not always same as dominance
- in 10% right handed people, the right hemisphere is dominant
- left-handed people only 20% are right hemisphere dominant, 64% are left hemisphere dominant and 16% show bilateral dominance
Planum temporale
- triangular region in the upper surface of the superior temporal gyrus
- important for language learning
- larger on the left than the right hemisphere in 65% brains
- it can be very asymmetrical
- reduced or reversed asymmetry in schizophrenia
Left Hemisphere Lesion
- aphasia
- right-left disorientation
- finger agnosia
- dysgraphia (aphasic)
- dyscalculia (number alexia)
- limb apraxia
- facial recognition
Right Hemisphere lesions
- visuospatial deficits
- anosognosia
- finger neglect
- dysgraphia (spatial, neglect)
- dyscalculia (spatial)
- constructional apraxia
- dressing apraxia
- facial recognition
Papez circuit
Limbic structures involved in emotional processing
hippocampus=> fornix==>mamilliary bodies==>mammillothalamic tract==>anterior thalamic nucleus==>genu of the internal capsule==>cingulate gyrus==> parahippocampal gyrus==> entorhinal cortex==> perforant pathway==>back to hippocampus
Limbic system
- described by Broca, Papez and Maclean
- after Papez circuit, this was expanded to include amygdala, septum, basal forebrain, nucleus accumbens and orbitofrontal cortex
- involved in mediation of emotional responses, influencing neuroendocrine responses and reward system regulation
- evolutionarily older than the higher cortical centres
Medial temporal structures
- include the hippocampus, amygdala, entorhinal and parahippocampal cortex
- plays role in memory processes
- few areas where the continuous production of new neurons is noted even in adult life
- amygdala appears crucial for fear conditioning and emotional regulation
Basal ganglia
- basal ganglia are a group of gray matter nuclei forming the largest subcortical structure in the brain
- they are involved in planning an dprogramming of movement and also have a role in the processes by which an abstract thought is converted into voluntary action
- consists of the striatum (made up of the caudate nucleus and putamen) and pallidum ( globus pallidus)
- putamen and globus pallidus are sometimes called lenticular/ lentiform nucleus
Striatum
- made of caudate nucleus and putamen
- part of the basal ganglia
Lenticular/lentiform nucleus
-putamen and globus pallidus
Subthalamic nuclei and the substantia nigra
-functionally related to the basal ganglia but are not considered part of the basal ganglia
Corticostriatal projection
-basal ganglia receives crucial inputs from the glutamategic corticostriatal projection
Circuits involving the basal ganglia
- described by Alexander
- motor circuit
- oculomotor circuit
- dorsolateral prefrontal circuit (executive)
- anterior cingulate circuit (motivation)
- lateral orbitofrontal circuit (social intelligence)
OCD
-basal ganglia dysfunction: volumetric changes and higher blood flow to the caudate nuclei. Increased caudate metabolism in untreated subjects reduces after effective treatment
Tourette’s syndrome
-basal ganglia dysfunction: striatal dopaminergic dysfunction
Huntington chorea
-basal ganglia dysfunction: degeneration of the striatum (mainly caudate nucleus) and selective loss of GABAergic neurons
Wilson’s disease
-basal ganglia dysfunction: copper deposits in the lenticular nuclei
CO poisoning
-basal ganglia dysfunction: acute bilateral anoxic damage to basal ganglia
Hemiballismus
- basal ganglia dysfunction: subthalamic nucleus damage (especially in infarction)
- flailing limb movements
Parkinsonism
- depigmentation of substantia nigra
- Lewy bodies are seen
- Striatal overactivity associated with bradykinesia
Fahr’s disease
- ‘Fahr too much ccalcium in the basal ganglia’
- progressive calcium desposition in the basal ganglia
- early onset cases present with schizophreniform psychoses and caratonia
- later onset cases exhibit dementia and choreoathetosis
Thalamus
- large oval mass of grey matter nuclei in the subcortical region, relaying all types of sensory information onto cortex (except olfaction)
- it also relays cerebellar and basal ganglia imputs to the cerebral cortex
- plays a crucial role in the filtering of sensory information in preparation for cortical processing
Anterior thalamus
- part of the limbic system
- receives the mamillothalamic tract and fornix and connects to the cingulate cortex
- thus it relays information from hypothalamus and hippocampus onto the frontal cortex
Pulvinar
- associated with visual attention
- sleep spindles are generated in the reticular nucleus f the thalamus
Hypothalamus
- regulates physiological functions such as eating, drinking, sleeping and temperature regulation
- hypothalamus has chemoreceptors that respond to variations in glucose levels, osmolarity, acid balance etc
- it plays a major role in neuroendocrine control
Ventromedial hypthalamus
- acts as the satiety centre
- animals with a lesion of the ventromedial hypothalamus hyperphagia and obesity are noted
Lateral hypothalamus
-the feeding centre
Cerebellum
- important role of preparing a motor plan and predicting balance needed between muscle groups to carry out the intended action smoothly
- cerebellar lesions produce ataxia and coarse intentional tremors along with hypotonia, past pointing and pendular knee jerk
- may have a cognitive role
Cognitive dysmetria
- Andreasen
- refers to the difficulty in coordinating and monitoring the process of receiving, processing and expressing information that could result from disrupted cortico-cerebellar circuitry in schizophrenia
Brainstem
- midbrain, pons and medulla
- 9 out of 12 cranial nerves enter or exit the brain from the brainstem
Midbrain
-consists of superior (conjugate gaze control) and inferior colliculi (auditory source localisation)
Substantia nigra
- also located in the midbrain along with the periaqueducal grey matter
- important role in vocalisation and freezing response to threat and in pain suppression
Pons
-positioned beneath the cerebellum and surrounds the upper half of the 4th ventricle
Medulla
-surrounds the inferior part of the 4th ventricle and is continuous with the spinal cord
