B10 Nervous system

• • the nervous system enables humans to react to their surroundings and coordinate their behaviour
• Stimulus > receptor > coordinator > effector > response
• • Information from receptors passes along neuron's as electrical impulses to the central nervous system
  • the CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones
• The brain is the main control centre, it receives information from sensory organs and sends out instructions via motor nerves to other parts of the body.
• Reflex a rapid, automatic response to a stimulus that does not involve the conscious part of the brain therefore protecting the body
• Sensory neurons carry messages towards the CNS (afferent) Motor neurons carry messages away from the CNS (efferent)
• Stimulus is a change in the environment that causes a response in the organism.
• 1. Stimulus detected by receptor cells, converts them into electrical signals
  2. electrical impulse pass from receptor along a sensory neuron to the CNS
  3. then passes along the relay neuron by transmitting electrical signals through a gap where electrical signals diffuse (synapse)
  4. the electrical impulse passes through the motor neuron from the CNS to the effector
  5. the effector triggers a response
• Stimulus > receptor > sensory neurone > relay neurone > motor neurone > effector > response
• What is reaction time?

  The time it takes for a person to respond to a stimulus.
• Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• The brain controls complex behaviour. it is made of billions of interconnected neurons and has different regions that carry out different functions
• Cerebral cortex is the outer layer of the brain, responsible for consciousness, intelligence, language and memory
• cerebellum is found at the back of the brain, controls our balance and co-ordinates our movements
• medulla is at the base of the brain and at the top of the spinal cord, it controls heart rate, digestion and breathing rate (unconscious activity)
• The hypothalamus is the control center of the endocrine system.
• the pituitary gland produces hormones which regulate growth, metabolism and reproduction
• Ways to investigate the brain:

  • studying patients with brain damage
  • Eclectically stimulating different parts of the brain
  • MRI scans
• The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult
• The cornea is the transparent front of the eye which start the focussing of the light rays
• The iris is the coloured part of the eye that regulates how much light enters the pupil
• The lens is a transparent structure that changes shape to focus light onto the retina.
• The retina contains photoreceptor cells called rods and cones which detect light and send electrical signals along optic nerve fibres to the brain
• The optic nerves carry impulses from the eyes to the brain where they are interpreted as images
• the Sclera is the white part of the eye which protects the eye
• Accommodation is the process of changing the shape of the lens to focus on near or distant objects.
• To focus on near object;

  • the ciliary muscles contract
  • the suspensory ligaments loosen
  • the lens is then thicker and refracts light rays strongly
• To focus on distant objects:

  • the ciliary muscles relax
  • the suspensory ligaments are pulled tight
  • the lens is then pulled thin and only slightly refracts light rays
• Two common defects of the eyes are myopia(short sightedness) and hypopia(long sightedness) in which light rays do not focus on the retina
• hyperopia can be treated by using glasses with convex lenses
• Myopia can be treated using glasses with concave lenses
• The eye is a sense organ containing receptors sensitive to light intensity and colour