nervous system = communication network and control centre of body

central nervous system (CNS) = brain and spinal cord, where incoming messages are processed and outgoing messages are initiated

peripheral nervous system (PNS) = nerves that connect CNS w/ receptors, muscles and glands

Protection of CNS

• bone

• membranes called meninges

• cerebrospinal fluid

1. Cranium and vertebrae

• cranium = part of skull that houses the brain

• vertebral canal = opening in the vertebrae through which the spinal cord passes

2. Meninges

• three layers of connective tissue forming membranes

  • outer: dura mater, tough and fibrous, sticks closely to bones of skull, texture similar to household rubber glove

  • middle: arachnoid mater, loose mesh of fibres

  • inner: pia mater, delicate, contains blood vessels and sticks closely to surface of brain and spinal cord

3. Cerebrospinal fluid (CSF)

• fluid produced in cavities of the brain; fills brain cavities and surrounds the brain and spinal cord

• clear, watery fluid containing a few cells and glucose, protein, urea and salts

• functions:

  1. Protection: acts as shock absorber, cushioning any blows or shocks to CNS

  2. Support: brain is suspended inside cranium and floats in fluid that surrounds it

  3. Transport: formed from the blood and circulates around and through CNS before re-entering blood capillaries - during this, it takes nutrients to the cells of the brain and spinal cord and carries away wastes

The brain

• works as an integrated whole

Cerebrum

• largest part of the brain; made up of left and right hemispheres

• cerebral cortex: outer later, made up of grey matter

• below cortex is white matter = myelinated axons

• fatty nature of myelin gives white matter its colour and texture

• basal ganglia: masses of grey matter inside each cerebral hemisphere

Cerebral cortex

• folded in patterns that increase SA

• cortex contains 70% of all the neurons in CNS

• convolution: upward fold of the cerebral cortex of the brain; also called gyrus

• sulci: shallow downfolds between convolutions of the cerebral cortex → deep down fold = fissure

• longitudinal fissure: longest fissure in brain; almost separates cerebrum into 2 halves (cerebral hemisphere: one of the 2 halves)

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• fissures and sulci further subdivide each hemisphere into 4 lobes: frontal, temporal, occipital and parietal lobes

  • insula: part of cerebrum that is buried deep inside brain; 5 lobe. of each cerebral hemisphere

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• cortex divided into 3 functional areas:

1. sensory: receive and process nerve impulses from senses

2. motor: send impulses to muscles, especially for voluntary movement

3. association: interpret info from senses and make it useful

Corpus callosum

• bundle of nerve fibres that link the 2 cerebral hemisphere - allow them to communicate

Cerebellum

• part of brain behind and below cerebrum; concerned with coordination of movement

• recieves sensory info from ear about posture and balance and stretch receptors in skeletal muscles for info about length of muscles

• we can still move w/o it but it would be jerky and uncontrolled

• outer folded part is grey matter, inside is white matter where it branches like a tree

• fine motor control

Hypothalamus

• lies below thalamus; helps maintain a constant internal environment by regulating heart rate, blood pressure, digestion, temp, water intake and emotions

Medulla oblongata

• joins to spinal cord

• cardiac centre: regulates heartbeat

• respiratory centres: regulates breathing rate

• vasomotor centre: regulates diameter of blood vessels

Brain diagram

Spinal cord

• never cord that extends from brain to about waist level; enclosed in the vertebrae

• contains myelinated fibres that take impulses towards the brain in the ascending tracts (sensory axons) and away from the brain in the descending tracts (motor axons)

• bundles of nerve fibres = tracts, outside CNS = nerves

Structure and functions of main areas of CNS