the brain

• Human brain gross anatomy

  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe
  • Cerebellum
  • Brain stem – Pons and Medulla oblongata
• Human brain: development & structure

  1. The CNS develops from the embryonic neural tube

  2. The anterior end of the neural tube folds and swells, becoming the major divisions of the brain: forebrain, midbrain and hindbrain

  3. The remainder (posterior end) of the tube becomes the spinal cord
• Major regions of the brain

  • Forebrain (prosencephalon): cerebrum, thalamus and hypothalamus, cerebral hemisphere(s)
  • Midbrain (mesencephalon): superior & inferior colliculi (-us), the tegmentum and the cerebral peduncles
  • Hindbrain (rhombencephalon): cerebellum, pons, medulla
• Structures of the brain: forebrain

  • Cerebral hemispheres (cerebrum): two of them (right and left); involved in sensory perception, learning, memory and conscious behaviour
  • Cerebral cortex consists of an outer layer of grey matter & inner layer of white matter folding into ridges (gyri) surrounded by fissures (sulci) to give a larger surface area
  • Corpus callosum: made up of myelinated fibres connects the right & left cerebral hemispheres
• Structures of the brain: forebrain

  • Telencephalon: surrounds the diencephalon
  • Diencephalon: consists of the thalamus and hypothalamus
  • Thalamus: sensory relay centre for information going to the cerebral cortex (skeletal muscle coordination, awareness, etc)
  • Hypothalamus: Located above the pituitary gland, sends hormones controlling pituitary's function. Regulates body temperature, synchronizes sleep patterns, controls hunger and thirst, water balance, and plays a role in some aspects of memory and emotion
• Structures of the brain: midbrain & hindbrain

  • Midbrain (mesencephalon): processes auditory (inferior colliculus) and visual (superior colliculus) information
  • Brainstem made up of the midbrain, pons and medulla, which regulates breathing, circulation, some motor functions (swallowing, vomiting)
  • Hindbrain: (rhombencephalon) made up of the brainstem and cerebellum
• Cerebellum

  • A fist-sized portion of the brain located at the back of the head, below the temporal and occipital lobes and above the brainstem
  • Has two hemispheres
  • Coordinates fine voluntary muscle movements and maintains posture and balance
  • Also roles in thought, emotions and social behaviour, as well as possible involvement in addiction, autism and schizophrenia.
• Ventricles and Cerebrospinal Fluid

  • Ventricles: a communicating network of 4 cavities filled with cerebrospinal fluid (CSF) and located within the brain parenchyma. There are 2 lateral ventricles, the third ventricle, the cerebral aqueduct and the fourth ventricle: four interconnecting chambers within the hemispheres. They open into the central spinal canal and the area beneath arachnoid layer of the meninges
  • Choroid plexuses in the ventricles produce cerebrospinal fluid, or CSF, that circulates in and around the ventricles and the spinal cord, and between the meninges
  • CSF provides: Physical support of neural structures, Excretion and "sink" action, Intra-cerebral transport of biologically active substances, Control of the chemical environment of the central nervous system
• Blood supply to the brain

  • Vertebral and carotid arteries
  • external carotid arteries - extend up the side of the neck
  • internal carotid arteries - branch into the skull and circulate blood to the front of the brain
  • vertebral arteries - follow the spinal column into the skull where they join together at the brainstem to form the basilar artery which supplies blood to the rear of the brain.
  • circle of Willis - a loop of arteries connecting the anterior and posterior circulations of the brain
• 12 Cranial nerves

  • Olfactory nerve - smell
  • Optic nerve - eyesight
  • Oculomotor nerve - pupil response and eye motions
  • Trochlear nerve - eye muscles
  • Trigeminal nerve - largest and most complex - chewing
  • Abducens nerve - innervates eye muscles
  • Facial nerve - face movement, taste
  • Vestibulocochlear nerve - balance and hearing
  • Glossopharyngeal nerve - taste, ear and throat movement
  • Vagus nerve - sensory: ear and the digestive system, motor: heart, throat and digestive system
  • Accessory nerve - muscles in the head, neck and shoulder
  • Hypoglossal nerve - motor activity to the tongue
• Brain coverings: meninges (protective layers)

  • Dura mater - outer layer: thick and tough, made of two layers

  1. Periosteal layer lines the cranium
  2. Meningeal layer

  • Spaces between the layers contain veins and arteries supplying the brain.
  • Arachnoid mater: thin weblike connective tissue
  • Below the arachnoid mater is the cerebrospinal fluid (CSF)
  • Pia mater: thin membrane, in close contact with the brain surface, rich with veins and arteries
• How the brain changes with age - what declines with age?

  • Committing new information to memory and recalling names and numbers
  • Declarative memory - autobiographical memory of life events and accumulated knowledge of learned facts and information
  • Working memory — the ability to hold a piece of information in mind, e.g. phone number, password. Starts as early as age 30
  • Processing speed and problem-solving
  • Selective attention: the ability to tune out distractions and focus on a particular stimulus
  • Divided attention. Splitting focus between two tasks – like holding a conversation whilst driving
• How the brain changes with age - Stays the same

  • Procedural memory e.g. remembering how to ride a bike remain largely intact
  • Learning new tasks
• How the brain changes with age - Improves

  • Verbal abilities, spatial reasoning, maths, and abstract reasoning
• How the brain changes with age - Structural change

  • By the age of 6, the size of the brain is about 90% of its adult volume
  • The brain starts to shrinks and cerebral cortex thins from 30s
  • The frontal lobe and hippocampus - responsible for cognitive functions - shrink more than other areas
  • Cortical density: thinning of the outer surface of the brain due to decreasing synaptic connections is particularly pronounced in the frontal lobes and parts of the temporal lobe
  • White matter: myelinated nerve fibres shrinks with age, slowing down processing and reducing cognitive function
  • Neurotransmitter systems: Levels of chemicals that affect neurotransmitters and protein production decrease leading to a decline in cognitive function
• How the brain changes with age - Neuronal and chemical changes

  • less neurotransmitters are produced: less dopamine, and serotonin and fewer receptors
  • decrease in number of synapses between brain cells drops, affecting learning and memory
  • Dendrites shrink, and branching become less complex in the prefrontal cortex and hippocampus
  • Loss dendritic spines: in rhesus monkeys, ageing targets thin spines: small, slender protuberances which are highly plastic structures, extending and retracting more rapidly than the larger "mushroom" spines
  • Neurogenesis also declines with age
• Homunculus

  • Comes from the Latin for little man, or miniature human.
  • Is a distorted representation of the human body onto the brain (parietal lobe).
  • Is based on a neurological "map" of the areas and proportions of the brain dedicated to processing motor or sensory functions of the different parts of the body.
• Sensory homunculus

  • Each cerebral hemisphere has somatosensory cortex just behind the central sulcus (Brodmann's area 1,2 and 3)
  • The map of the homunculus represents the tactile representation of the opposite side of the brain
  • The density of receptors for various parts of the body are not the same which is why the homunculus has different body parts
  • The surface area of the anatomical body part reflects the density of tactile receptors dedicated to that body part. So, the lips make up a small surface area compared to other body parts but have a greater density of receptors compared to the shoulder or forearm.
• Motor homunculus

  Primary motor cortex that is located just in front of the central sulcus Brodmann's Area 4. Again it is contralateral so the primary cortex in the right cerebral hemisphere represents motor activity on the left side of the body and vice-versa.
• Handedness

  • Handedness is influenced by genetics and environment
  • In Western countries, 85 to 90 percent of people are right-handed and 10 to 15 percent of people are left-handed
  • Ambidextrousness is rarer
  • Hand preference becomes apparent in early childhood
  • Probably arises as part of the developmental process that differentiates right and left sides of the body (called right-left asymmetry)
  • Initially thought that a single gene controlled handedness
  • Recent studies suggest that up to 40 contribute
  • Other factors contribute to handedness, including prenatal environment and cultural influences
• Children of left-handed parents are more likely to be left-handed than are children of right-handed parents. However, because the overall chance of being left-handed is relatively low, most children of left-handed parents are right-handed.
• Mirror image twins

  Mirror image twins are a form of monozygotic twins. The twins, when facing each other, appear as matching reflections, e.g. if one twin is right-handed the other twin may be left-handed. In MZ twins at some time during the first two weeks after conception, the developing embryo splits into two identical parts. If the split occurs later than usual in the embryo's development, it already has a right side and a left side. The twins that form in this situation are mirror image twins. About 25% of MZ twins fit this description.
• function of the brain

  frontal lobe - speech, smell, problem-solving, planning, motor control

  parietal lobe - taste, touch and pressure, body awareness, language

  temporal lobe - hearing, facial recognition, reading

  occipital lobe - vision

  cerebellum - coordination

  
• pituitary gland

  • pea-sized structure, regulates the flow of hormones from the thyroid, adrenals, ovaries and testes. 
  • Receives regulating hormones from the hypothalamus through its stalk and blood supply.
• Amygdala

  • Small, almond-shaped structures, located under each hemisphere of the brain.
  • Included in the limbic system, regulates emotion and memory and associated with the brain’s reward system, stress, and the “fight or flight” response
• Hippocampus

  • A curved seahorse-shaped organ on the underside of each temporal lobe, part of a the hippocampal formation. 
  • Supports memory, learning, navigation and perception of space.  
  • Receives input from the cerebral cortex and may play a role in Alzheimer’s disease.
• Pineal Gland

  •  Attached by a stalk to the top of the third ventricle.  
  • Responds to light and dark and secretes melatonin, which regulates circadian rhythms and the sleep-wake cycle.
• comparative anatomy

  brain structure of different animals

  
• sensory homunculus

  • Each cerebral hemisphere has a somatosensory cortex just behind the central sulcus (Brodmann's area 1,2 and 3)
  • The map of the homunculus represents the tactile representation of the opposite side of the brain
  • The density of receptors for various parts of the body are not the same which is why the homunculus has different body parts
  • The surface area of the anatomical body part reflects the density of tactile receptors dedicated to that body part.