Topic 6 - Coordination and Response

• Homeostasis definition


  the control / regulation of internal conditions of a cell or organism
• Examples of controlled internal conditions in homeostasis


  - water content

  - pH

  - temperature

  - blood pressure

  - blood glucose concentration
• Why is homeostasis important?


  internal conditions kept within set limits to maintain optimum conditions fro organism to function in response to internal + external changes (enzymes)
• Control of body temp in humans


  - approx 37°C

  - tightly controlled cause enzymes would stop functioning optimally

  
  

  Temp:

  body temp monitored + controlled by THERMOREGULATORY centre in brain --> blood passes through, brain can detect temp of blood cause receptors + receive messages from temp receptors in skin that send nervous impulses to thermoregulatory centre --> central nervous system can activated effectors to make sure body temp stays right

  
  

  Body water content:

  - water loss via lungs (respiration), skin (sweat), kidneys (urea)

  - detected by receptors
• Stimulus


  any change in the external or internal environment is called a stimulus (eg. change in glucose lvls in blood / body temp)
• Receptors


  these cells detect stimuli. They are in the sense organs (eyes, ears, nose, tongue, skin)
• Effectors


  Cells that bring about a response to stimuli to restore optimum levels
• How do receptors + effectors communicate and respond to stimuli?

  via the nervous system + hormonal system (endocrine system)
• Response to stimuli in plants examples


  Response to light:

  - receptors and effectors react to this stimuli by growing towards the light to maximise light absorption for photosynthesis

  
  

  Response to gravity:

  - ensure shoots grow upwards and roots grow downwards

  
  

  Response to abiotic stress (non-living):

  EG. carrots produce antifreeze proteins at low temps. Protein binds to ice crystals + lowers temp that water freezes = less ice crystals grow
• Tropisms


  Directional growth responses made by plants as a response to light + gravity are known as tropisms

  
  

  - growth TOWARDS stimulus = tropism positive

  - growth AWAY from stimulus = tropism is negative
• Auxins


  Plant hormones that control growth response. They are regulators.

  SHOOTS: auxins promote cell elongation

  ROOTS: auxins inhibit cell elongation (more auxins = less cell elongation)
• Plant response to light is ______

  Phototropism
• Plant response to gravity is ______

  Geotropism
• Shoots


  Positively phototropic:

  Shoots are positively phototropic as they grow TOWARDS the light.

  - shoot tips exposed to light = more auxins accumulated on side that is in the shade --> cells elongate faster on SHADED side so that the SHOOT is bent TOWARDS the light

  
  

  Negatively geotropic:

  - grows away from gravity, UP towards light

  - when shoot grows sideways, gravity produces unequal distribution of auxin in the tip + more auxin on lower side --> lower side to grow faster bending shoot UPWARDS
• Roots


  ROOTS INHIBITS GROWTH = MORE AUXINS BOTTOM = CELLS ON TOP ELONGATE FASTER

  
  

  Negatively phototropic:

  - grow away from the light

  - positioned horizontally so when the roots are exposed to light, more auxins accumulate on the shaded side = roots bend DOWNWARDS

  
  

  Positively geotropic:

  - roots grow downwards into soil

  - when roots are sideways, more auxins are on lower side

  - in roots, auxins inhibits growth = cells on TOP elongate faster + root bends downwards
• Roots and auxins


  auxins INHIBITS cell elongation in roots = more auxins = less cell elongation
• Central nervous system


  - Consists of brain and spinal cord

  - made up of neurones

  - info sent through nervous system as ELECTRICAL IMPULSES --> impulses travel along neurones at VERY HIGH SPEEDS = allows rapid response to stimuli

  - used to control functions that need INSTANT / RAPID responses

  - Length of effect = short (until electrical impulses stop)
• Electrical impulses


  electrical signals that pass along nerve cells (neurones)
• Endocrine system (hormonal system)


  - information sent through system as hormones

  - hormones carried by blood = can circulate around body

  - hormones provide signal that triggers a response

  - hormones = NO NEED INSTANT RESPONSE = SLOW transmission

  - length of effect = long (until hormone is broken down)

  - hormones produced by endocrine glands
• how are hormones produced

  endocrine glands
• Human nervous system structure


  - The human nervous system consists of:

  - Central nervous system (CNS) - the brain and spinal cord

  - Peripheral nervous system (PNS) - all of the nerves in the body

  - Information is sent through the nervous system as electrical impulses - these are electrical signals that pass along nerve cells known as neurones

  - A bundle of neurones is known as a nerve

  - The nerves spread out from the central nervous system to all other regions of the body + ALL SENSE ORGANS

  - The CNS, therefore, acts as a central coordinating centre for the impulses that come in from (or are sent out to) any part of the body
• Bundle of neurons is called ?

  nerve
• Types of neurones


  Sensory neurones:

  - pick up information (impulses) from the receptors (sense organs) and carry the signal into the central nervous system (CNS)

  
  

  Relay neurones:

  - just inside CNS and they relay to coordinate whats going on (make different connections/signals within the brain)

  - connect sensory + motor neurones

  - relay impulses sent from sensory neurones into brain TO motor

  
  

  Motor neurones:

  - motor = movement

  - causes effect by sending a message (impulses) to the effector (either muscle or gland) FROM the CNS
• Basic neurone structure


  Long cells. Body branches off axon (main long fibre of the neurone. Have dendrites (extensions) on the ends of the body allowing many neurone connections ( to receive impulses from them)
• CNS order


  Stimulus (external or internal factor eg. temp) --> receptor detects (sense organ) --> sensory neurone --> CNS (inside it is the relay neurone) --> motor neurone --> effector (muscle or gland) --> response
• Synapses


  - when dendrites of 2 neurones meet (connection) a synapse is formed (small gap)

  - at the end of the dendrites, the electrical signal is briefly converted to a chemical signal (NEUROTRANSMITTERS)

  - the neurotransmitters are able to diffuse across the synapse (gap)

  - these chemical signals set off a new electrical signal in the next neurone (as they convert into electrical impulses)
• Synapses ensure that impulses only travel in


  ONE direction
• Simple reflex arc


  - reflexes are automatic responses to specific stimuli to reduce the chances of injury

  - INVOLUNTARY RESPONSE

  - reflex arc = pathway of a reflex response (from receptor to effector)

  
  

  1. stimulus detected by pain receptor + impulse sent to sensory neurone

  2. sensory neurone sends electrical impulses to CNS

  3. in the CNS the sensory neurone passes message to relay neurone

  4. relay neurone synapses with motor neurone

  5. motor neurone carries impulse to effector (muscle / gland) + response will occur to remove body of pain
• The Eye


  - specialised sense organ

  CORNEA - transparent lens that refracts light as it enters eye

  IRIS - controls how much light enters the pupil (no blood cells so oxygen diffuses in)

  LENS - transparent disc that changes shape to ensure light focuses on retina (controlled by ciliary muscles)

  RETINA - has light receptor cells - rods (light intensity) + cones (colour)

  OPTIC NERVE - sensory neurone that carries impulses between eye + brain (from retina)

  PUPIL - hole that allows light to enter the eye

  SCLERA - tough outer layer that protects eye

  CILIARY MUSCLES - ring of muscle that contracts + relaxes to change shape of lens

  SUSPENSORY LIGAMENTS - ligaments connecting lens to ciliary muscle

  FOVEA - region of retina that has the highest density of cones (colour detecting cells)

  CONJUNCTIVA - lubricates + protects the surface of eye
• Iris reflex in bright light


  pupils constrict to prevent too much light entering eye + damaging retina

  
  

  Radial muscles of iris relax + circular muscles of iris contract = constricted pupil (less light enters eyes)
• Iris reflex in dim light


  pupil dilate to allow as much light into the eye as possible - improve vision

  
  

  Radial muscles contract + ciliary muscles constrict = diameter of pupil wides + more light enters eye
• Iris reflex - far away objects


  ciliary muscles relax (ring of muscle increases in diameter) = suspensory ligaments contract = lens becomes thinner + less light is refracted
• Iris reflex - objects close up


  ciliary muscles contract (ring of muscle decrease in diameter) = suspensory ligaments relax = lens becomes fatter + more light is refracted
• Skin when you are cold


  Vasoconstriction of skin capillaries:

  - heat exchange occurs on surface of skin

  - decrease blood supply in skin capillaries - less heat lost to environment via radiation

  - vasoCONSTRICTION = the arterioles' (suppling capillaries with blood) walls will constrict = limiting blood volume to capillaries

  
  

  Shivering:

  - reflex action

  - muscles contract in rapid + regular manner = metabolic reaction required = increases rate of respiration - heat energy

  
  

  Erection of hair:

  - hair erector muscles contract causing hair to stand

  - forms insulating layer over skin's surface by trapping air between the hair to stop heat loss via radiation
• Skin when you are hot


  Vasodilation of skin capillaries:

  - heat exchange occurs at body's surface (where blood comes in closest proximity to the environment).

  - Increase heat loss = supply capillaries in skin with greater volume of blood = lose het via radiation to environment.

  - arterioles (connect capillaries + arteries) have muscles in their walls that control volume of blood flowing through them. During vasodilation, the walls relax causing arterioles near skin to dilate = more blood flow to capillaries

  
  

  Sweating:

  - sweat secreted by sweat glands

  - cools skin by evaporation which uses that energy from body to convert liquid water into vapour

  
  

  Relaxation of hair erector muscles (flatten):

  - no insulating layer formed = air can circulate over skin + heat can leave via radiation
• Hormones + functions (5)


  Adrenaline:

  source: adrenal glands

  role: fight or flight response = increase heart rate + breathing (ensures glucose + oxygen delivered to muscle cells at fast rate), dilation of blood vessels inside muscles (more blood can circulate)

  
  

  Insulin:

  source: pancreas

  role: control blood sugar level (too high = cells losing water by osmosis + too low = brain receiving insufficient glucose for respiration - death) = stimulates liver to turn glucose into glycogen for storage OR if levels are low stimulate liver to turn glycogen into glucose for blood

  
  

  Testosterone:

  source: male testes (male sex hormone)

  role: development of secondary sexual characteristics

  
  

  Oestrogen:

  source: female ovaries

  role: development of secondary sexual characteristics + controls menstrual cycle

  
  

  Progesterone:

  source: female ovaries

  role: maintains lining of uterus during pregnancy
• Where are auxins produced


  tips of the plant's shoots and roots