Monday, 10 June 2013

Brain and Nervous system

The cerebrum - what makes us human

  • this is the largest part of the brain
  • it is divided into two cerebral hemispheres, left and right
  • these are joined by corpus callosum
  • the outermost layer has a surface area of 2.5m^2 and it is folded
  • it consists of a thin layer of nerve cell bodies known as cerebral cortex
  • this area is highly developed in humans than in any other orgnisms
  • The cerebrum contols the higher brain functions such as
    • concious thoughts and emotional responses
    • the ability to override some reflexes
    • features associated with intelligence, such as reasoning and judgement

  • Two areas of the brain (most found in the left cerebral hemisphere) are associated with understanding language and speaking
  • these a Broca's area and Wernicke's area. Damage to these cause problems with understanding language.
    • damage to Bronca's area will result with an inability to speak
    • damage to Wenicke's area causes trouble understanding language.
    • they are connected by a bundle of neurones
    • if broke - unable to speak but understand the language
  • visual sensory and association - Wernicke's area
  • hearing sensory area - Broca's area

The cerebellum - movement and postures
  • the concious decision to move voluntary muscle is initiated by the cerebral hemispheres
  • the fine control of muscular movements requires a significant level of non-concious operation and involves the cerebellum e.g. walking and riding a bike
  • examples - responding to changes in the body position to remain balanced and upright
    • judging the position of objects and limbs
    • tensioning of muscles in order to manipulate tools effectively
    • feedback information on muscle position, tension and fine movement
  • Neurones in cerebellum carry impulses to the motor areas so that motor output the effectors can be adjusted appropriately
  • often feels like we are on 'auto-pilot' some activties become programmed into the cerebellum e.g. catching  a ball
  • the cerebellum contains over half of the nerve cells in the brain
Key role in balance and fine movement
  • the cerebellum processes sensory information from
    • the retina
    • balance organs in the inner ear
    • joints
    • specialised fires in muscles called spindle fibres which relay information about muscle tension
Hypothalamus
  • controls the body's homoeostatic mechanisms
  • temperature regulations - input from thermoreceptors
  • osmoregulation - input from osmoreceptors
  • controls much of the endocrine function because it regulates pituitary gland
Medulla oblongata
  • controls non-skeletal muscle eg. cardiac muscle, smooth muscle of the gut
  • effectively in control of autonomic nervous system
  • contains regulatory centres such as cardiac centre and the respiratory centre
  • contains reflex centres for vomiting, coughing sneezing and swallowing

RESPONDING TO THE ENVIRONMENT
  • The CNS (central nervous system) is a way of connecting sensors with effectors
  • this is significant if living things are to escape predation, control balance and regulate temperature
  • the nervous system is made up of the CNS and peripheral nervous system
CNS
  • the central nervous system is made up of the brain and spinal cord
  • it is made up of grey matter and white matter
  • grey matter has billions on non-myelinated nerve cells
  • white matter has longer, myelinated axons and dendrons
Peripheral nervous system
  • relays impulses from sensors to the CNS
  • it then relays impulses from CNS to effectors (motor neurones)
  • this peripheral nervous system is divided into sensory and motor systems
Motor system
  • the motor system is divided into
    • somatic motor neurones - impulses from the CNS to skeletal muscle which are under voluntary concious control
    • autonomic motor neurones - impulses from the CNS to cardiac muscle, smooth muscle in the gut to glands, involuntary (subconscious) control
Somatic v Autonomic
  • Autonomic neurones are non-myelinated
  • Somatic neurones are myelinated
  • Autonomic connections to effectors consists of two neurones (connect at a ganglion)
  • somatic connections to effectors consist of one
  • autonomic
    • independent of concious control
    • controles homoeostatic mechanisms
    • autonomic motor neurones occur in 2 types
      • sympathetic
        • dilates pupils
        • no effects on tears glands
        • accelerates heart, constrict arterioles
        • dilates bronchi
        • relaxes bladder
          • most active in times of stress
          • the neurones of a pathway are linked at a ganglion just outside the spinal cord. pre-ganglionic neurones are very short
          • post-gaglionic neurones secrete noradrenaline t the end of the synapse etween neurone and effector 
      • parasympathetic
        • constricts pupil
        • stimulates tear glands
        • inhibits heart, dilates arterioles
        • constricts bronchi
        • contracts bladder
          • most active in sleep and relaxation
          • the neurones of a pathway are linked at a ganglion within the target tissue. pre-ganglionic neurones carry considerable in length
          • post-ganglionic neurones secrete acetyl-choline at the synapses between neurone and effector

No comments:

Post a Comment