The brain

The human brain weighs around 1.4kg and is comprised of 200 billion neurons with >100 trillion connections in the cortex alone.

Brain orientation: Coronal = frontal (vertical) section. Mid-sagittal = medial section. Horizontal = horizontal section. Dorsal = from the top

We have more wrinkles or convolutions than most other species such as the mouse or howler monkey. However, dolphins have even more convolutions than humans - brain size is partly related to body size. Gyri = bulges in the brain surface. Sulci = shallow folds in the brain surface. Fissures = deep folds in the brain

The brain is divided into 2 cerebral hemispheres. It also has 4 different lobes. The frontal lobe encompasses the front of the brain. The parietal lobe encompasses the mid upper section, the temporal lobe is the mid lower section. The occipital lobe is the back section of the brain.

The visible lower structures just underneath the bulk of the brain are the brainstem and cerebellum.

Four main arteries that supply to the brain are: the middle cerebral arteries, supplying mainly the temporal and parietal lobes. The posterior cerebral arteries irrigate mainly the occipital lobe. The anterior cerebral arteries irrigate the medial regions of the the frontal lobes. The basilar artery irrigates the brainstem.

If the brain is dissected along the longitudinal fissure, it becomes immediately clear that there are lots of inner complex structures

The hindbrain covers the areas of the cerebellum, pons, medulla and reticular formation. It is the phylogenetically oldest part of the brain. It controls many essential functions such as breathing, heart-rate, blood pressure, sleep-wake cycles, hunger, and thirst. The medulla oblongata helps control breathing, heart-rate, vomiting, salivation, coughing, and sneezing. The pons is a bridge which allows axons to cross from one side to the other. It plays a role in sleep, respiration, swallowing, bladder control, hearing, taste, eye movements, facial expressions and sensations, and posture. The cerebellum is comprised of 2 lobes. It is important for motor control

The midbrain consists of the superior and inferior colliculus, and the substantia nigra. The midbrain is associated with vision, hearing, motor control, sleep/wake cycle, arousal, and temperature regulation. There are 2 major parts: the tectum and tegmentum. The tectum contains the superior (part of visual system) and inferior (part of auditory system) colliculus. The tegmentum is made up of periaqueductual grey matter (controls sequences of movements), substantia nigra, and red nucleus (important components of the motor system)

The forebrain is the bulk of the brain, made up of the cerebrum (cortex, lateral ventricles, basal ganglia, hippocampus and amygdala), and the diencephalon (thalamus and hypothalamus). The hypothalamus is a complex structure, containing many nuclei and tracts. It controls the autonomic nervous system and the endocrine system, with direct links to the pituitary gland. The thalamus sits on top of the brainstem. It functions as a gateway to higher cortical regions. Most sensory information, except smell, passes through the hypothalamus. It also plays a major role in sleep and wakefulness. The hippocampus surrounds the thalamus, and is at the heart of our spatial memory.

The limbic system  is a set of brain structures located on both sides of the thalamus, immediately beneath the cerebrum. Papez (1937): set of interconnected brain structures that formed a circuit whose primary function was motivation and emotion. It includes: the olfactory bulbs, hippocampus, hypothalamus, amygdala, and fornix (among other structures).

It's associated with the "four Fs of survival" fleeing, fighting, feeding, and reproduction. The limbic system supports a variety of functions including emotion, behaviour, motivation, long-term memory, and olfaction. Many limbic structures are believed to be partly responsible for the rewarding effects of psychoactive drugs. 

The basal ganglia is a group of subcortical nuclei, which are situated at the base of the forebrain. Basal ganglia nuclei are strongly interconnected with the cerebral cortex, thalamus, and brainstemm as well as several other brain areas.

The basal ganglia are associated with a variety of functions including: control of voluntary motor movements, procedural learning, routine behaviours such as eye movements and cognition, and emotion. They do not initiate movements, but are involved in a loop of modulation with the cortex that's constantly active.

They are involved in monitorying the force to be applied to a task and gross postural adjustments. They don't project directly to the cortex, but to the thalamus.

Malfunction of the basal ganglia can lead to Parkinson's disease, and Huntington's disease. Parkinson's is associated with a reduction in dopamine activity in the basal ganglia, while Huntington's is associated with basal ganglia degeneration.

There are 4 ventricles (CSF filled chambers) in the brain. Two large lateral ventricles are in the forebrain, 1 (thrid) central ventricle below and between them, and 1 (fourth) ventricle just behind the medulla and pons. The ventricular system is continuous with the central canal of the spinal cord, allowing for the flow of CSF to circulate.

Hydrocephalus: a condition in which ventricles are enlarged by overfilling with CSF. In most cases, it's associated with cogntive deficits.

Cerebral cortex: most evolutionary recent part of the brain. A highly folded layerered sheet of neurons form the outer surface of the cerebral hemispheres. It is brownish grey matter that covers the white matter. Grey matter is the cortex, white matter is the axons that connect the cortex to other regions of the brain. The cortex makes up about 76% of human brain volume. About 2/3 of the cortex is found in the folds. There are 3 phylogenetic categories of cerebral cortex:

• Archicortex: oldest, composed of 3 layers of neuronal cell bodies found mostly in olfactory cortex and hippocampus
• Paleocortex (piriform lobe): old, 3 layers, olfaction related
• Neocortex: it is only present in mammalia brains. It is the 2-4mm thick top level of the cerebral hemisphere. It's comprised of 6 distinct laminae (or layers), and makes up nearly all of cortical matter in humans. Associated with higher brain functions, i.e memory, attention, and language.

Occipital lobe

• Nerve signals related to vision are relayed by the thalamus to the occipital lobe
• Visual processing centre - contains most of the anatomical region of the visual cortex
• If you become blind by damage to the eyes, you continue to experience visual imagery. However, if you become blind due to occipital lobe damage, you lost the capacity for visual imagery and cease to have visual dreams
• It is the smallest lobe

Temporal lobe

• Includes the primary auditory cortex. Contains areas for high-level visual processing, such as object and facial recognition. Left hemisphere of most right-handed people contains Wernicke's area (language comprehension)
• The temporal lobe is involved in processing sensory input into derived meanings for the appropriate retention of visual memory, language comprehension, and emotion association

Parietal lobe

• It is positioned above the occipital lobe and behind the frontal lobe and central sulcus
• Integrates sensory information among various modalities, including spacial sense and navigation, the main sensory receptive area for the sense of touch (mechanoreception) in the somatosensory cortex, and the dorsal stream of the visual system
• The major sensory inputs from the skin (touch, temperature, and pain receptors), relay through the thalamus to the parietal lobe

Frontal lobe

• The frontal lobe is located at the front of each cerebral hemisphere and positioned in front of the parietal lobe, and above in front of the temporal lobe
• Contains most of the dopamine-sensitive neurons in the cerebral cortex. The dopamine system is associated with attention, short-term memory tasks, planning, and motivation
• Includes the primary motor cortex, premotor cortex, and prefrontal lobe. The motor cortex is involved in the planning and execution of voluntary movements.

Premotor cortex: the cytoarchitecture of the motor and premotor areas differ and are referred to as Brodman areas 4 and 6, respectively. Premotor area seems to be involved in directly controlling the trunk muscles of the body and in the sensory and spatial guidance of movement.

Prefrontal cortex: believed to control the planning of complex behaviour, decision making, personality, and social inhibition. It was the region in Phineas Gage's brain that was damaged. It is the region affected by prefrontal lobotomies. Prefrontal lesions in some cases may produce environmnetal dependency syndrome.

Although we map the areas of the cortex into discrete areas, function is never concentrated in one area. One region may become more activated than others, but activation is always distributed across the cortex and often other parts of the brain.

The cortex receives signals from the subcortical structures and sends signals within itself and back down via the axons of nerve cells. Association fibres connect areas within the same hemisphere. Commissural fibres connect equivalent areas in the 2 hemispheres.

Disruption of cortical development: Agenesis of the corpus callosum is when it fails to develop normally. It is either partly or completely missing. Fibres may be present, but don't cross the inter-hemispheric fissure. Can result in severe disability or no symptoms.

Split-brain patients: A treatment for life-threatening epilepsy is to surgically cut the corpus callosum. This reduces the connections between the 2 hemispheres.

Fibres of projection unite the cortex with the lower parts of the brain. They often send signals up via the thalamus and down through the internal capusle.