01. Brain Structure

What do psychobiologists do?

Aim to understand how the brain’s composition and chemistry give rise to human thought and behaviour

Plato (429-348 BC)

Ancient Greece, the brain is the organ of reasoning

Galen (AD 130-200)

Physician of the Roman Empire, proposed theory of brain function based on ventricles through observing cattle and Oxon

Leonardo Da Vinci (15th Century)

First drawings of the brain

René Descartes (1596-1650)

French philosopher and mathematician, ‘he thought, therefore he was’.

What did René Descartes propose?

The mind and body interacted with the pineal gland

Much behaviour was mechanical, not requiring mental processing

The concept of the automatic reflex

The automatic reflex

The basis of modern understanding of sensory nerves conveying messages to the brain.

Some behaviour is reflexive, the mind is not involved or the cause of behaviour

Central nervous system

Brain and spinal cord

Peripheral nervous system is made up of…

Autonomic and somatic NS

The autonomic nervous system

Communicates with internal organs and glands

The somatic nervous system

Communicates with sense organs and voluntary muscles

Divisions of the autonomic system

Sympathetic (arousing) and parasympathetic (calming)

Divisions of the somatic system

Sensory/afferent system (sensory input) and motor/efferent system (motor output)

The three axes of the body

Anterior - posterior; dorsal - ventral; medial - lateral

Anterior - Posterior Axis

• Anterior: towards the front end of the body (nose)

• Posterior: towards the tail/feet

Dorsal - Ventral Axis

• Dorsal: toward the back of the body or the top of the head

• Ventral: toward the front (belly) of the body or the bottom of the head

Medial - Lateral Axis

• Medial: toward the midline

• Lateral: away from the midline

Types of sections

• Coronal: slices from front to back

• Saggital: vertical slices from top to bottom

• Horizontal: horizontal slices from right to left

• Cross section: a slice taken at right angles to the neuraxis

• Transverse planes: divides the body into superior and inferior halves

• Missagital plane: through the neuraxis perpendicular to the ground, divides brain in two symmetrical halves

Membrane

Selective barrier, allows some things to pass but not others

Dura mata

Thick connective tissue that lies directly underneath the skull

Subarachnoid space

Where cerebrospinal fluid flows through

Cerebrospinal fluid

Fills the subarachnoid space and provides cushioning and support for the brain

Blood-brain barrier (BBB)

A semi-permeable membrane, which separates blood from CSF, providing a barrier that prevents toxins from entering the brain via the bloodstream

The 5 major structures of the brain

1. Myelencephalon

2. Metencephalon

3. Mesencephalon

4. Diencephalon

5. Telencephalon

The Myelencephalon

• Part of the hindbrain

• Oldest part controls breathing, heart rate, salivation, vomiting.

• Damage is fatal

The metencephalon

• Part of hindbrain, contains pons and cerebellum

• Pons - enlargement of medulla

• Cerebellum - little brain, important for sensorimotor control, decision making and language

The mesencephalon

• Part of the midbrain, two divisions - tectum and tegmentum

• Tectum - dorsal of midbrain, auditory and visual-motor functioning

• Tegmentum - contains PAG (primary control centre for descending pain modulation)

Functions of the PAG

• Area of grey matter found in the midbrain, surrounds the cerebral aqueduct.

• Regulation of heart rate and blood pressure

• Management of autonomic processes

• Production of vocalisations, fearful and defensive reactions

• Role in pain reduction

The Diencephalon

• Forebrain, covers and surrounds the older ‘tubular’ brain to add complexity and new structures - hypothalamus and thalamus

• 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, sex)

Telencephalon

Everything else, mediates most of the brain’s complex functions - voluntary movement, sensory input, cognitive processes

Contains cerebral cortex and subcortical structures

The cerebral cortex

• Composed of small unmyelinated neurons to make grey matter

• Contains convolutions that serve to increase surface area

• Longitudinal fissures separate hemispheres

• Contains the neocortex and subcortical structures

Fissures

Large convolutions

Sulci

Small convolutions

Gyri

Ridges between fissures and sulci

Subcortical structures

• Hippocampus

• Limbic system

• Basal Ganglia

The Hippocampus

• 3 major layers

• Major role in memory and spatial location memory

Limbic system

• Circuit of midline structures that circle the thalamus

• Regulation of motivated behaviours

Basal Ganglia

• Motor system, important for motor function

• Coordination of automated, smooth and fluent movement

The Neocortex

• Largest and newest part of the cerebral cortex

• Six layers

• Divided into 4 lobes

The 4 lobes

• Frontal Lobe: motor cortex, cognitive functions, frontal cortex, precentral gyrus

• Parietal Lobe: somatic sensations (e.g. touch), orientation, location of objects, post central gyrus

• Temporal Lobe: hearing, language, complex visual patterns and memory

• Occipital Lobe: visual processing