4.1 Central Nervous System

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)
• 
• 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
• 

• 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