Forebrain: Cerebrum, Thalamus and Hypothalamus
முன்மூளை: பெருமூளை, தலாமஸ், ஹைப்போதலாமஸ்
The hypothalamus — not the cerebrum, not the medulla — controls body temperature, hunger and thirst. Together with the limbic system (amygdala, hippocampus) it also drives emotions like fear, rage and pleasure.
The idea
The brain is the central information processing organ of our body and acts as the 'command and control system'. It controls voluntary movements, balance of the body, functioning of vital involuntary organs (lungs, heart, kidneys etc.), thermoregulation, hunger and thirst, circadian rhythms, activities of several endocrine glands and human behaviour; it is also the site for processing vision, hearing, speech, memory, intelligence, emotions and thoughts. The human brain is well protected by the skull and covered by cranial meninges consisting of an outer dura mater, a very thin middle arachnoid and an inner pia mater in contact with the brain tissue. The brain is divided into forebrain, midbrain and hindbrain. The forebrain consists of the cerebrum, thalamus and hypothalamus. The cerebrum forms the major part of the brain; a deep cleft divides it longitudinally into two halves, the left and right cerebral hemispheres, connected by a tract of nerve fibres called the corpus callosum. The layer of cells covering the cerebral hemispheres is the cerebral cortex, thrown into prominent folds; it is referred to as grey matter due to its greyish appearance, as neuron cell bodies are concentrated here. The cerebral cortex contains motor areas, sensory areas and large regions that are neither clearly sensory nor motor — the association areas, responsible for complex functions like intersensory associations, memory and communication. Fibres of the tracts are covered with myelin sheath and constitute the inner part of the cerebral hemisphere, giving an opaque white appearance — the white matter. The cerebrum wraps around a structure called the thalamus, a major coordinating centre for sensory and motor signalling. Another very important part of the brain, the hypothalamus, lies at the base of the thalamus; it contains a number of centres which control body temperature and the urge for eating and drinking, and several groups of neurosecretory cells which secrete hormones called hypothalamic hormones. The inner parts of the cerebral hemispheres and a group of associated deep structures like the amygdala and hippocampus form a complex structure called the limbic lobe or limbic system; along with the hypothalamus it is involved in the regulation of sexual behaviour, expression of emotional reactions (e.g. excitement, pleasure, rage and fear) and motivation.
Why it matters
The forebrain integrates everything we sense with memory and emotion, and the hypothalamus links that brain activity to the body's internal state and hormones.
NEET lens
Key pairs: corpus callosum connects the two cerebral hemispheres; cerebral cortex = grey matter (cell bodies), inner tracts = white matter (myelinated); association areas — intersensory associations, memory, communication; thalamus — major coordinating centre for sensory and motor signalling; hypothalamus — body temperature, eating and drinking, neurosecretory cells (hypothalamic hormones); limbic system = amygdala + hippocampus (with hypothalamus: sexual behaviour, emotions, motivation). Meninges: dura mater, arachnoid, pia mater.
Clinical significance
Fever is the hypothalamus resetting the body's thermostat to a higher temperature in response to infection. Damage to the hippocampus, as in Alzheimer's disease, impairs the formation of new memories.
Introduction
The forebrain — cerebrum, thalamus and hypothalamus — is the largest part of the brain and the seat of thinking, sensation, emotion and many body controls.
Core concept
Meninges: dura mater (outer), arachnoid (thin, middle), pia mater (inner, on brain tissue). Brain = forebrain + midbrain + hindbrain. Cerebrum: two hemispheres joined by corpus callosum; cerebral cortex = grey matter, folded; motor areas, sensory areas, association areas (intersensory associations, memory, communication); white matter = myelinated tracts inside. Thalamus: cerebrum wraps around it; major coordinating centre for sensory and motor signalling. Hypothalamus: at base of thalamus; centres for body temperature (thermoregulation), eating and drinking; neurosecretory cells → hypothalamic hormones. Limbic system: inner parts of hemispheres + amygdala, hippocampus; with hypothalamus → sexual behaviour, emotional reactions (excitement, pleasure, rage, fear), motivation.
Go deeper
Grey matter is grey because neuron cell bodies are concentrated there; white matter is white because of the myelin around the fibres.
From Class 10
Class 10 introduced the forebrain as the thinking part of the brain and the hypothalamus as a link to hormones. NEET goes into its parts and their specific jobs.