Brain structure and function

• What is bio psychology?

  The scientific study of the biology of behaviour
• What is neuroanatomy and neurophysiology?

  NEUROANATOMY - the study of the structure of the nervous system

  NEUROPHYSIOLOGY - the study of the functions and activities of the nervous system
• The brain

  pinkish grey mass of tissue, weighs around 1.5 kg

  the most complex object

  —>enables humans to be the dominant creature. 100 billion neurones, each projecting to 5000-10000 other neurones.

  houses human mind etc.

  capable of self-reflection, consciousness and free-will

  Uses 20% of body’s energy

  Brain research benefits us all, helps understand human afflictions and to improve treatment.
• History of bio psychology

  PLATO (429-348BC) - Ancient Greece. First to suggest the brain is the organ of reasoning

  GALEN (AD130-200) - Roman Empire. proposed theory of brain function based on ventricles (fluid filled cavities)

  LEONARDO DE VINCI (late 15th century) - first drawings of the brain.
• RENÉ DESCARTES (1596-1650)

  “cognito; ergo sum” —> i think; therefore i am

  proposed mind and body interacted in pineal gland

  realised much behaviour was mechanical, mental processes not required

  developed concept of automatic reflexes - the basis of our modern understanding of sensory nerves conveying messages to the brain

  some behaviour reflexive, mind not involved

  paved the way for scientific and non-secular approach of understanding human psychology
• Divisions of the nervous system

  Two subdivisions that have further divisions

  meant to be autonomic

  
• Central nervous system

  made up of brain and spinal cord
• Peripheral nervous system

  all the nerves in the body that communicate with the brain and spinal cord
• Autonomic nervous system

  Communicates with internal glands and organs
• Somatic nervous system

  communicates with sense organs and voluntary muscles
• Afferent and Efferent

  found in both ANS & SNS

  SNS - afferent = sensory input, efferent = motor output
• ANS VS SNS

  ANS - some actions involuntary and unconscious

  SNS - voluntary movements
• Subdivisions of ANS

  has two types of efferent nerves, projecting from CNS to internal organs.

  Sympathetic mobilises energy

  Parasympathetic conserves energy

  they work in opposition to each other
• Directional terms in neuroanatomy

  described in relation to the orientation of the neuroaxis - the direction in which the CNS lies in relation to the spinal cord
• Directional terms in animals

  In the head, there is MEDIAL (towards midline) and LATERAL (away from midline)

  
• Humans

  MEDIAL & LATERAL

  PROXIMAL - close to CNS e.g. shoulders

  DISTAL - far from CNS e.g. hands

  
• Directional terms in the head

  IPSILATERAL - on the same side of the body or head

  BILATERAL - on both sides of the body or head

  CONTRALATERAL - on opposite sides of the body or head

  
• Combined terms in the brain

  1 = DORSOMEDIAL (top, midline)

  2 = DORSOLATERAL (top, away)

  3 = VENTROLATERAL (bottom, away)

  4 = VENTROMEDIAL (bottom, midline)

  
• Types of brain sections

  CORONAL - slices from front to back

  SAGGITAL - slices from side to side

  HORIZONTAL - slices from top to bottom

  
• Protection of the brain

  Meninges

  brain and spinal cord well protected by bone and 3 protective membranes

  
• Cerebrospinal fluid (CSF)

  fills the subspace and surrounds spinal cord

  fills ventricles of the brain

  provides cushioning, draining it can lead to headaches

  Excess CSF continually absorbed into subarachnoid space, and sinuses which run through dura mata and drains in jugular vein

  if obstructed (e.g. tumour between ventricles), CSF can build up in ventricles and cause brain to expand. A condition called hydrocephalus (water head)
• Blood-brain barrier (BBB)

  a semi-permeable membrane which separates blood from CSF and prevents entrance of many toxins

  ll blood vessels lined with endothelial cells that are rallying close together. allowing only certain molecules to pass e.g. H2O, O2, some fat soluble sub (caffeine, alcohol). glucose passes with help of certain proteins.

  causes a problem for medicine. struggle to find good treatments for neurological conditions (alzheimers, strokes and brain cancer)

  the degree to which drugs (therapeutic and recreational) work depends on the ease with which they can cross the BBB
• Major structures of brain

  5 divisions evident in brain from embryonic development to adulthood

  TELENCEPHALON - cerebral cortex, limbic system & basal ganglia

  DIENCEPHALON - thalamus & hypothalamus

  MESENCEPHALON - tectum & tegmentum

  METENCEPHALON - pons & cerebellum

  MYELENCEPHALON - medulla, largely compromises tracts between brain and spinal cord

  
• Myelencephalon (hind)

  Most posterior part of brain

  Oldest part = medulla oblongata (long marrow), controls breathing, heart rate, salivation, vomiting

  Damage to medulla is fatal

  Contains reticular formation -> sleep, attention, movement and cardiac circulatory and respiratory reflexes
• Metencephalon (hind)

  most posterior

  contains pons and cerebellum

  pons (bridge), enlargement of medulla. contains pontine nuclei also coeruleus and dorsal raphe -> origin of noradrenergic and serotonergic contsining fibres in forebrain

  Cerebellum (little brain), sensory motor control. damage can cause problems with decision making and language
• Mesencephalon (mid)

  Two divisions:

  TECTUM - dorsal of mid brain. Inferior colliculi (auditory function), superior colliculi (visuo-motor function)

  TEGMENTUM - periaqueductal gray -> primary control centre for descending pain modulation which contains enkephalins (endogenous opioids)

  Substantia nigra, important component of sensory motor system
• Function of periaqueductal gray (PAG)

  Area of gray matter in midbrain

  Surrounds cerebral aqueduct

  Regulation of heart rate and blood pressure, management of autonomic processes (e.g. bladder control), production of vocalisation, fearful and defensive reactions

  Best known for its role in analgesia (pain reduction)
• Pathway for PAG pain inhibition

  stimulation of PAG inhibits pain. mechanisms are not completely understood

  Midbrain, PAG -> Medulla, Raphe nuclei (serotonin producing neurones) -> Spinal cord, Dorsal horn (inhibits neurones that transmit pain signals)

  This inhibits pain naturally
• Diencephalon (fore)

  mushrooms out and surround older ‘tubular’ brain. adds greater complexity and new structures

  THALAMUS - relays sensory signals from skin to prepare motor signals to cerebral cortex. involved in sleep consciousness and alertness

  HYPOTHALAMUS - important for motivated behaviours (eating, sleeping and sexual behaviour)
• Telencephalon (fore)

  mediates most of brains complex functions -> voluntary movements, sensory input, cognitive processes (learning, speaking, problem solving)
• Cerebral cortex

  composed of small unmyenlated neurones -> grey matter on surface

  convolutions (wrinkles) serve to increase surface area

  large con. = fissure small con. = sulci

  ridges between fissures and sulci = gyri

  longitudinal fissures separating hemispheres (remains connected by cerebral commissure inc. corpus callosum

  Contains neocortex (on surface of brain) and subcortical structures
• Subcortical structures

  HIPPOCAMPUS

  LIMBIC SYSTEM

  BASAL GANGLIA
• Hippocampus

  3 major layers

  located in medial edge of cerebral cortex, folds back on itself in the medial temporal lobe

  means seahorse

  major role in memory (spatial location, autobiography)
• Limbic system

  circuit of midline structures that circle the thalamus

  regulation of motivated behaviours -> consists of mammillary bodies, hippocampus, amygdala, fornix, singular, septum
• Basal ganglia

  motor system

  consists of amygdala, striatum (caudate nucleus + putamen), globus pallidus

  extrapyramidal motor system (output fibres dont cross pyramidal regions of medulla)

  degeneration of nigral-striatal pathway causes religiosity, tremor and slow movement in Parkinson’s

  coordination of automated (w/o thinking) smooth, fluent movement
• Neocortex

  6 layers, most developed

  90% of cerebral cortex (largest), remaining is allocortex which contains hippocampus

  Humans have large neocortex ratio -> correlates with complexity og behaviour. Brain must evolve in size to support this

  central and lateral fissures divide each hemisphere into 4 lobes

  Lobes arent functional units
• 4 lobes

  FRONTAL -> motor cortex (pre central gyrus). complex cognitive function - frontal cortex

  PARIETAL -> somatic sensations e.g. touch (post central gyrus) orientation in the back

  TEMPORAL - hearing and language. complex visual patterns, memory -> bottom

  OCCIPTAL -> visual processing
• Amnesiac effects of bilateral medial temporal lobectomy

  Patient HM

  epileptic, part of temporal lobes removed as surgeons identified seizures were coming from foci both sides

  hippocampus and amygdala removed

  after -> could not form any LTM
• Phineas Gage

  Damage to frontal cortex = loss of social inhibitions

  Provided evidence that frontal cortex involved in personality and behaviour