Coordination and Response

• The human nervous system consists of:

  • Central nervous system (CNS): the brain and the spinal cord
  • Peripheral nervous system (PNS): all of the nerves in the body
• The nervous system allows us to:

  • Make sense of our surroundings and respond to them
  • Coordinate and regulate body functions
• Information is sent through the nervous system as nerve impulses, which are electrical signals that pass along nerve cells known as neurons (nerves)
• • Sensory neurons carry impulses from sense organs to the CNS (brain or spinal cord)
  • Relay neurons are found inside the CNS and connect sensory and motor neurons
  • Motor neurons carry impulses from the CNS to effectors (muscles or glands)
• Label diagram

  A) sensory neurone

  B) relay neurone

  C) motor neurone

  D) receptor cell

  E) dendrite

  F) cell body

  
• Reflex Arc

  • An involuntary (or reflex) response does not involve brain as the coordinator of the reaction
  • an automatic and rapid response
  • A reflex action is a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)
• Reflex Pathway

  Stimulus → Receptor → Sensory Neuron → Relay neuron → Motor neuron → Effector → Response
• 1. Stimulus is detected by receptor in skin
  2. Sensory neurons send electrical impulse to spinal cord
  3. Electrical impulse passed to relay neuron in spinal cord
  4. Relay neuron connects to motor neuron and passed impulse on
  5. Motor neuron carries impulse to a muscle (effector)
  6. Muscle will contract/perform appropriate response (response)
• Synapses

  A junction between two neurons. Only travels in one direction to avoid confusion within the nervous system
• Label diagram

  A) neurotransmitters

  B) synaptic gap

  C) receptor proteins

  
• Events at synapse:

  1.  An impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap
  2. The neurotransmitter molecules diffuse across the gap 
  3. Neurotransmitter molecules bind with receptor proteins on the next neuron
  4. An impulse is then stimulated in the next neuron
  5. The neurotransmitters are then destroyed to prevent continued stimulation of the second neuron which would cause repeated impulses to be sent
• Sense organs are groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals.
• Label diagram

  A) suspensory ligament

  B) cornea

  C) iris

  D) pupil

  E) lens

  F) ciliary muscle

  G) retina

  H) fovea

  I) optic nerve

  
• Cornea - Refracts light as it enters eye

  Iris - Controls how much light enters pupil

  Lens - Changes shape to focus light onto retina

  Retina - Contains light receptor cells

  Optic nerve - Sensory neurone that carries impulses between eye and brain

  Pupil - Allows light to enter eye
• The Blind Spot

  • At the point where the optic nerve joins the retina, there are no light-sensitive rod and cone cells on that part of the retina
  • Light falling onto that part of the retina will not result in an image being detected
  • The brain fills in from surrounding light so we don't see a black hole where no light has fallen
  • This causes a blind spot, where cannot detect an object in our peripheral vision even if it is there
• The Pupil Reflex

  Carried out to protect the retina from damage in bright light and protect us from not seeing objects in dim light.
• In dim light: 

  Photoreceptors detect change in environment, the pupil dilates to allow as much light into the eye as possible, radial muscle contract, circular muscles relax
• In bright light:

  Photoreceptors detect change in environment, pupil constricts and less light enters eye, radial muscles relax, circular muscle contract
• Accommodation 

  When an object is close:

  • Ciliary muscles contract
  • Suspensory ligaments slack
  • Lens thicken
  • Light is refracted more
• Accommodation 

  When an object is far:

  • Ciliary muscles relax
  • Suspensory ligaments taut
  • Lens become thinner
  • Light is refracted less
• Rod Cells - Greater sensitivity of rods for night vision 

  COne Cells - Three different kinds of cones, absorbing light of different colours, for colour vision
• The Fovea is an area on the retina where almost all of the cone cells are found 

  Rod Cells are found all over the retina, other than the area where the optic nerve nerve attaches to the retina - there are no light-sensitive cells at all in this area, and so it is known as the blind spot 
• Hormones

  A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs. The glands that produce hormones in animals are known collectively as the endocrine system.
• Adrenal Glands - Secrete adrenaline

  Adrenaline is the hormone secreted in ‘fight or flight’ situations. It:

  • increases breathing rate and heart rate 
  • (Supply more oxygen and glucose to brain and muscles more quickly, respiration increases, energy for action increases)
  • increases pupil diameter 
  • (allow more light to enter eyes for better vision)
  • increases the blood glucose concentration
• Pancreas - Secrete insulin and glucagon

  • Insulin decreases blood glucose concentration by converting glucose to glycogen
  • Glucagon increases blood glucose concentration by converting glycogen to glucose
• Ovary - Secrete oestrogen

  Testes - Secrete testosterone
• What is homeostasis?

  Homeostasis is the maintenance of a constant internal environment
• Insulin is secreted into blood at times when blood glucose levels are high (mostly after a meal). To avoid this, insulin temporarily converts excess glucose into glycogen in the liver and muscles, which reduces blood glucose concentration. The glycogen is converted back to glucose several hours later when blood glucose levels have dipped due to respiration in all tissues.
• Type 1 diabetes is a condition where the blood glucose levels are not able to be regulated as the insulin-secreting cells in the pancreas are not able to produce insulin
• Negative feedback occurs when conditions change from ideal or set point and returns conditions to a set point. Regulation is controlled by the brain which contains receptors sensitive to the temperature of blood.
• Label the diagram.

  A) hair

  B) receptors

  C) sensory neurone

  D) fatty tissue

  E) hair effector muscle

  F) sweat gland

  G) blood vessels

  
• When we are hot:

  1. Sweating

  • Sweat is secreted by sweat glands, cools skin by evaporation
  • Heat energy from the body is lost as liquid water in sweat becomes water vapour

  2. Vasodilation

  3. Heat is more easily lost from the blood.

  • Hairs lie flat allows air to freely circulate

  Increases transfer of heat to environment by radiation
• Vasodilation:

  • Shunt vessels constrict, arterioles dilate
  • More blood flows through the capillaries nearer to the surface of the skin.
• When we are cold:

  1. Skeletal muscles contract rapidly and we shiver

  • These involuntary muscle contractions need energy from respiration and some of this is released as heat.

  1. Vasoconstriction
  2. Hair erector muscle contract (hair stands up)

  • Trap a layer of air around the skin which acts an an insulation
• Vasoconstriction:

  • Shunt vessels dilate, arterioles constrict
  • Less blood flows through the capillaries in the surface of the skin
  • Heat is less easily lost
• Gravitropism is a response in which parts of a plant grow towards or away from gravity  
• Phototropism is a response in which parts of a plant grow towards or away from the direction of the light source.
• Shoots: Phototropism positive but gravitropism negative

  Roots: Phototropism negative but gravitropism positive
• Advantages of shoot growing toward light:

  • Trap more light for photosynthesis

  Advantages of shoot growing: away from gravity:

  • Shoot of germinating seed grows out of soil
  • More chances for pollination and seed dispersal
• Advantages of root growing towards from gravity:

  • Anchors plant
  • Search for water
  • Ensures root always grows downwards