Brain structure and function

Biopsychology

The scientific study of the biology of behaviour

Neuroanatomy

The study of the structure of the nervous system

Neurophysiology

The study of the functions and activities of the nervous system

Neurochemistry

The study of the chemical basis of neural activity

Neuroendocrinology

The study of interactions between the nervous system and the endocrine system

Neuropathology

The study of the nervous system disorders

Neuropharmacology

The study of the effects of drugs on neural activity

How much does the brain weigh

1.5kg

How many neurons are in the brain

100 billion, each projecting to 5000-10000 other neurons

Plato

(429-348 BC): The brain is the organ of reasoning

Galen

(AD 130-200): Proposed theory of brain function based on ventricles through observations on Cattle and Oxon

Rene Descartes

(1596-1650): “Cognito; ergo sum” proposed that the mind and body interacted in the pineal gland and developed the concept of automatic reflex where sensory nerves convey messages to the brain

Central nervous system

Brain and spinal cord

Peripheral nervous system

Made up of the autonomic nervous system and somatic nervous system

Autonomic nervous system

• communicates with internal organs and glands

• subdivisions: sympathetic division and parasympathetic division

Somatic nervous system

• communicates with sense organs and voluntary muscles

• sensory (afferent): nerve senses hot flame on skin and send rapid messages to the spinal cord

• motor (efferent): nerves respond by sending signal from CNS to muscles, to move hand away from the flame

Sympathetic division and examples

• Autonomic motor nerves that prepare us for action (fight or flight) and mobilises energy

• Dilates pupil

• Inhibits saliva

• Heart rate increasing

• Inhibits secretion

• Secretion of adrenaline

• inhibits bladder contraction

Parasympathetic division

• Autonomic motor nerves that prepare us to relax this conserves energy

• constricts pupils

• slows heartbeat

• stimulates secretion

• contracts bladder e

• ‘feed, breed and rest’

Afferent

Going towards the CNS

Efferent

going away from the CNS

Directional terms

In relation to the orientation of the neuraxis (where CNS lies in relation to the spinal cord)

Dorsal

Towards the back of the body, or top of the head

Ventral

Towards the front (belly) or towards the bottom of the head

Rostral/ frontal

Towards the nose

Caudal/posterior

Towards the feet/ or in animals the tail

Proximal

Close to the CNS (shoulders)

Distal

Far from the CNS (fingers)

Lateral

Away from the midline

Medial

Towards the midline

Bilateral

On both sides of the body or head

Ipsilateral

On the same side of the body or head

Contralateral

On the opposite side of the body or head

Ventromedial

Towards the front and midline of the brain or body.

Dorsolateral

Towards the top and sides of the brain or body (upper and outer)

Ventrolateral

Towards the front and sides of the body or brain (bottom and outer)

Dorsomedial

Towards the top and towards the midline of the brain or body

Coronal sections

Divides the body/brain into front and back halves

Sagittal sections

Divides the body into left and right halves

Horizontal sections

Divides the body into top and bottom halves

Cross section

A slice taken at right angles to the neuraxis

Midsagittal plane

The plane through the neuraxis perpendicular to the ground; divides the brain into two symmetrical halves

Meninges

Three thin layers of tissue that cover and protect the brain, made up of:

• Duramater: connecting tissue

• arachnoid membrane

• Subarachnoid space: blood vessel and cerebrospinal fluid

Cerebrospinal fluid

• fills the subarachnoid space, spinal cord and ventricles of the brain

• provides cushioning and support for the brain

• If drained suffer headaches

• Excess in continually absorbed into the subarachnoid space, and sinuses which run through dura matter and drains into jugular vein

• if obstructed can build up ventricles leading the brain to expand (Hydrocephalus/water head)

Blood-brain barrier

A semi-permeable membrane which separates blood from the CSF providing a barrier that prevents many toxins from entering the brain from the bloodstream. They can effect the degree to which drugs work

The 5 major structures of the brain

• Myelencephalon

• Metencephalon

• Mesencephalon

• Diencephalon

• Telencephalon

Myelencephalon

• part of the hindbrain

• medulla (oldest part): tracts between brain and spinal cord which controls breathing, heart rate, salivation, vomiting

• contains the reticular formation

• involves in sleep, attention movement, cardiac, circulatory and respiratory reflexes

Metencephalon

• part of the hindbrain

• contains pons and cerebellum

Pons (bridge)

Enlargement of medulla, containing the pontine nuclei, coeruleus and dorsal raphe

Cerebellum (little brain)

Important for sensorimotor control (movements) but damage can also cause problems with decision making and language

Mesencephalon

• part of the midbrain

• two divisions: Tectum and Tegmentum

• substantia nigra; important component of sensory motor system

Tectum

Dorsal of the midbrain, containing inferior colliculi (auditory function) and superior colliculi (visual-motor function)

Tegmentum

Contains PAG, the primary control centre for descending pain modulation (contains enkephalins)

functions of the PAG

Regulation of heart rate and blood pressure, automatic control, produces vocalisations and fearful reactions

Diencephalon

Forebrain mushrooms out surrounding the older ‘tubular’ brain, adding greater complexity and new structures: Hypothalamus and Thalamus

Thalamus (inner chamber)

Relays sensory signals from skin to prepare motor signals to cerebral cortex. Is also involved in sleep, consciousness and alertness

Hypothalamus

Important for motivated behaviours such as: eating, sleeping and sexual behaviour

Telencephalon

• the largest division of the human brain

• mediates most of the brains complex functions: voluntary movement, sensory input, cognitive processes like learning, speaking and problem solving

• contains cerebral cortex, subcortical structures and fibre bundles

Cerebral cortex

• composed of small unmyelinated neurons

• grey matter

• convulsions serve to increase surface area: large convulsions = fissures and small convulsions = sulci

• ridges between fissures and sulci- gyri

• longitudinal fissures separates hemispheres- connected by cerebral commissure/ corpus callosum contains the neocortex and subcortical structures: hippocampus, limbic system and basal ganglia

Hippocampus

• 3 major layers

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

• major role in memory (spatial location)

Limbic system

• circuit of midline structures that circle the thalamus

• regulation of motivated behaviours

• consists of mamillary bodies, hippocampus, amygdala, fornix, cingulate, septum

Basal ganglia

• motor system

• consists of amygdala, striatum,, globus pallidus

• extrapyramidal motor system

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

• coordination of automated, smooth, fluent movement

Neocortex

• newest part of the cerebral cortex to evolve

• largest part of the cerebral cortex (90%) other part is allocortex

• has 6 layers

• central and lateral fissure divide each hemisphere into 4 lobes (frontal, parietal, temporal and occipital

4 lobes of the cerebral cortex/ neocortex

frontal, parietal, temporal and occipital

Frontal lobe

• motor cortex (precentral gyrus)

• frontal cortex: complex cognitive functions

Parietal lobe

somatic sensations (post central gyrus)

Temporal lobe

Hearing and language

Occipital lobe

Visual processing

The case of HM

• Epileptic who had his temporal lobes removed including hippocampus and amygdala

• Had one generalised seizure per week, and several focal seizures per day

• EEG suggested seizures arose from foci in both left and right temporal lobes

• From this his seizures stopped and with normal perceptual and motor ability

• memories for events predating surgery were intact as well as STM but inability to form new LTM

Phineas Gage

• Tamping iron went through his head

• Despite this within minutes was conscious and recounting what had happened

• But ‘no longer gage’ according to friends and acquaintances

• The damage to Gage’s frontal cortex resulted in a loss of social inhibitions

• Provided evidence that the frontal cortex was involved in personality and behaviour