B6: Brain and Mind

Reflexes
1. living organisms can detect and respond to a stimulus such as the environment where there is a change in light/temperature etc.
  1. Receptors are stimulated by the stimulus and produce a rapid involuntary response. this means that it is automatic - organism responds without thinking - a simple reflex
    1. the simplest animals rely on reflex actions for much of their behaviour. all movement and reactions are simple reflex responses. the reflex actions ensure that the animal will respond in a way that is most likely to result in its survival
    2. a simpple reflex response to chemicals can lead to an organism finding food quickly. a change in light level could indicate the presence of a predator and so the organism will move away quickly.
2. Simple Reflexes
  1. newborn refelxes
    1. Stepping Reflex
      1. when held under its arms in an upright position with feet firmly on the floor, a baby will make walikng movements with its legs
    2. Grasping Reflex
      1. a baby tightly grasps the finger put into its hand
    3. Sucking Reflex
      1. a baby sucks on a finger or the nipple when put into ots mouth
    4. Stratle Reflex
      1. a baby shoots out its arms and legs when stratled - by a sudden loud noise
    5. Rooting Reflex
      1. a baby turns its head and opens its mouth ready to feed when its cheek is stroked
    6. Adult Reflexes - for potentially dangerous events
      1. knee jerk
        when the knee is struck below the kneecap, the leg will kick out.
      2. pupil reflex
        bright light causes muscles in the eye to contract so the retina is not damaged
        light landing in the retina sends impulses along the optic nerve. impulses from the brain are are passed along a nerve to the iris, causing it to increase or decrease the size of the pupil
        bright light = pupil size decreases so less light is let in
        radial muscles relax and circular muscles contract
      3. dropping hot object reflex
        the response is to throw it away so you don't damage yor hand
  2. newborns cannot think for themselves. they exhibit a range of simple reflexes for a short time after birth. the absence of these or their failure to disappear could indicate that the nervous system hasn't developed properly
3. sending Signals
  1. electrical impulses through long wire like cells called neurons (nerve cells) - quick and short lived
    1. sensory neurons carry nervous impulses (electrical signals) from receptors to the central nervous system (impulse travels towards cell body) and motor neurons carry impulses from the central nervous system to effectors (impulse travels away from cell body
  2. the other is via hormones which are chemical signals.an example is insulin which control blood sugar levels and oestrigen - the female sex hormone which are secreted into the blood. chemical signals ae slower than electrical impulses and they move to target organs but their effects last longer
  3. the nervous and hormonal communication systems are present in large complex organisms - a result of evolution of multicellular organisms
Detecting Changes
1. nervous coordination requires the presence of one or more receptors that are different to detect stimuli
  1. light - detected by receptors in the eyes
  2. sound - detected by receptors in the ears
  3. changes of position - detected by receptors for balance in the inner ear
  4. taste - detected by receptors on the tongue
  5. smell - detected by receptors in the nose
  6. pressure - detected by receptors for pressure in the skin
  7. temperature - detected by receptors temperature in skin
2. Coordinating the Response
  1. the receptors are connected to a processing centre by sensory neurons
    1. with simple reflexes, the processing centre is the spinal cord; the brain isnt involved. the processing centre coordinates a response by sending back a message electrically via motor neurons to the effector, which carries out the response. THIS IS THE SPINAL REFLEX ARC
  2. A SPINAL REFLEX ARC
    1. 1) A receptor is stimulated by the stimulus (drawing pin)
      1. 2) this causes the impu;ses to pass along a sensory neuron into the spinal cord
        3) the sensory neuron synapses with a relay neuron, by-passing the brain
        4) the relay neuron synapses with a motor neuron sending impulses down it
        5) then it goes down it tp the muscles (effectors) causing them to contrcat in response to the sharp drawing pin
      2. Receptors and Effectors - form part of very complex organs
        Muscle cells in Muscle Tissue
        the specialised cells that make up muscles tissues are effectors. Impulses travel along motor neurons and terminate at the muscle cells
        these impulses cause the muscle cells to contract
        Light Receptors in the Retina of the Eye
        the eye is a complex sense organ. the lens focuses light onto receptor cells in the retina - sensitive to light.
        the receptor cells are then stimulated and send electrical impulses along the sensory neurons to the brain
        Hormone Secreting Cells in a Gland
        the hormone secreting cells in glands are effectors
        they are activated by an impulse which travels along a motor neuron from the central nervous system and terminates at the gland
        the impulse triggers the release of te hormone into the bloodstream which transports it to the sites where it is required
    2. the arrangement of neurons into a fixed pathway in a spinal reflex arc means that the responses are automatic and therefore very rapid because no processing is required
      1. if the signal had to travel to the brain and be processed before action was taken, then, by the time the response arrived, it may be too late
Neurons
1. neurons are especially adapted cells that can carry electrical signals (nerve impulses). they are elongated to make connections from one part of the body to another
  1. they have branched endings which allow a singe neuron to act on many other neurons or effectors - muscle fibres e.g.
2. in motor neurons, the cytoplasm forms a long fibre surrounded by a cell membrane called an AXON
  1. Some axons are also surrounded by a fatty sheath which insulates the neuron from neighbouring cells (like plastic coating on a copper electrical wire). it increases the speed at which the nerve impulse is transmitted
central nervous system
1. information from neurons is coordinated overall by the central nervous system. in animals/vertebrates, the CNS is the brian and spinal cord. the pathway for receiving information and then acting upion it is shown here:
  1. Nervous System
    1. Receptor
      1. Sensory Neurons
        Relay Neurons
        SPINAL CORD
        BRAIN
        SPINAL CORD
        motor neurons
        Effector
  2. the CNS is connected to the body via sensory and motor neurons which make up the PERIPHERAL NERVOUS SYSTEM (PNS)
    1. The PNS is the second majour division of the nervous system, its sensory and motor neurons transmit messages all over the body - to limbs and organs. they also transmit messages to and from the central nervous system
2. DRUGS
  1. Ecstasy/beta blockers/prozac cause changes to the speed at which nerve impulses travel to the brain - speeding up/slowing down and sometimes false signals are sent
  2. drugs can prevent impulses from travelling acros synapses or they can cause the nervous system to become overloaded with too many impulses
synapses
1. GAPS BETWEEN ADJACENT CELLS
2. they allow the brain to form inerconnected neural circuits
  1. adult brain contains 100-500 trillion synapses.
    1. children have 1000 trillion but they decrease as they age, stabilising by adulthood
3. when an impulse reaches the end of a sensory neuron, it triggers the release of chemicals called transmitter substances into the synapse
  1. they diffuse across the synapse and then bind with specific receptor molecules on the membrane of a relay neuron
    1. the receptor molecules will only bind with specific chemicals to initiate a nerve impulse in the relay neuron so the signal can continue on its way. meanwhile the transmiter substance is reabsobed back into the sensory neuron to be used again.
4. sequence is as follows
  1. 1) Electrical signal (nerve impulse) moves through sensory neuron
    1. 2) transmitter substances are released into the synapse
      1. 3) transmitter substances bind with receptors on the motor neuron
        4) Electrical signal (nerve impulse) is now sent through motor neuron

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B6: Brain and Mind

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	Created by pv7137 about 10 years ago