control & coordination

• your nervous system sends ELECTRICAL messages along your nerves to and from different parts of your body
• your endocrine system sends CHEMICAL messages around your body to target an organ in the blood
• your nervous system contains 2 parts:

  1. CNS (central nervous system) = brain and spinal cord
  2. PNS (peripheral nervous system) = sensory and motor neuron
• The central nervous system and the peripheral nerves are made up of nerve cells, called neurons.
• 3 types of neurons:

  1. motor: carry impulses from the CNS to the muscles & glands
  2. sensory: carry impulses from sense organs to CNS
  3. relay: neurons located in spinal cord that link sensory neurons to motor neurons
• stimuli are the changes in the external or internal environment of the organism
• receptors detect the changes
• effectors bring about the response
• each neuron consists of:

  1. cell body (cytoplasm, nucleus, dendrites)
  2. axon (nerve fiber covered by insulating sheath)
• cell bodies of the neurons are mostly located in the brain or spinal cord
• a reflex response is a rapid response to a stimulus without the need for a thought or decision
• The sequence of events in a simple reflex arc is:

  1. stimulus
  2. receptor
  3. sensory neuron
  4. relay neurons in spinal cord
  5. motor neuron
  6. effector
  7. response
• voluntary actions are controlled by the brain and are consciously done
• involuntary actions are done subconsciously and are controlled by the brain
• reflex action is a involuntary action in response to a stimulus
• sensory neuron

  
• relay neuron

  
• motor neuron

  
• synapses are the junctions between 2 nerve cells or a nerve cell & an effector that ensure the nerve impulses are travelling in one direction only
• synaptic cleft is the gap between the presynaptic neurons & post synaptic neurons across which a nerve impulse is transmitted thru neurotransmitters
• synaptic vesicles are secretory vesicles that are located in the presynaptic neuron and store neurotransmitters & release them in the synaptic cleft on the arrival of a nerve impulse
• when an impulse arrives at the presynaptic neuron the vesicles fuse with membrane thus releasing neurotransmitters into the synaptic cleft
• How is an impulse transmitted between two neurons?

  1. impulse reaches the end of one neuron
  2. vesicles release neurotransmitters in the synaptic cleft
  3. neurotransmitter diffuses across the gap binding to the receptor
• sense organs are a group of organs that detect change in the environment
• sense organs are specialized receptors
• eye structure:

  • cornea is a clear layer that coats the iris, it refracts light into the eye
  • iris is the colored section of the eye controlling the amount of light entering the eye by diluting & contracting the pupil
  • pupil is a hole in the center of the iris which lets light enter into the rest of the eye
  • lens is a transparent structure held in by a ring of fibers (suspensory ligaments) / positioned behind iris / changes shape to focus the image on retina
• eye structure 2:

  • retina is the internal lining at the back of the eye it contains rod and cone cells which are sensitive to light (photoreceptors)
  • rod cells respond to dim light thus helping with night vision / located around the periphery of the retina
  • cone cells detect color & respond to light of high intensity / found in fovea
  • fovea is a section in the middle of the retina containing large amount of cone cells providing the clearest image
• eye structure 3:

  • optic nerve, each photoreceptor cell is attached to a neuron, they group to form optic nerve which carry impulses to the brain
  • blind spot is area at back of the eye where optic nerve exits the eye, it lacks receptor cells so it cant detect an image
  • ciliary muscle is a ring of smooth muscle which controls the shape of the lens
  • radial muscle is muscle of the iris that are involved in pupil reflex action, in dim light radial muscle contract to dilute the pupil so more light enters the eye
• the pupil reflex:

  • in bright light circular muscle contract / parasympathetic nerve radial muscle relax / pupil contracts
  • in dim light circular muscle relax / sympathetic nerve radial muscle contract / pupil dilates
• the circular & radial muscles act antagonistically
• how eye focuses on distant objects:

  1. ciliary muscle relax & suspensory ligaments tighten
  2. lens becomes thinner
  3. light is refracted less
• endocrine glands are a network of hormone secreted glanding which make up the endocrine system
• endocrine system helps in growth, metabolism, and homeostasis
• endocrine glands are sometimes called ductless glands
• a hormone is a chemical substance that is produced by a gland & carried by the blood altering the activity of one or more targetted organs
• endocrine system:

  1. transmission of chemicals
  2. transmission via blood
  3. slow transmission
  4. hormones dispersed throughout body
  5. long term effects
• nervous system:

  1. transmission of electrical impulses
  2. transmission in nerves
  3. rapid transmission
  4. impulse sent directly to target organs
  5. short lived effects
• adrenaline helps the body in action by:

  1. heart rate increases so more oxygen & glucose reach to the muscles for energy released
  2. bronchioles widen so more air can reach to the lungs
  3. blood vessels to the gut & other organs narrow allowing the blood to reach to more life saving organs
• homeostasis is the maintenance of a constant internal environment within set limits despite external change
• specialized pigment cells in the basal layer and epidermis produce a black pigment, melanin, which gives the skin its color, the more melanin, the darker is the skin.