yr9 biology

• Stimulus


  Any change in the environment of an organism that is detected by a receptor and provokes a response in the organism
• Receptor

  Sense organs that supply the brain with information to keep us in touch with the world around us. They are able to absorb different types of energy from the environment and transform it into nerve impulses.
• Effector


  A muscle, organ or gland that produces a response to a stimulus
• Response


  A reaction or change in an organism, either physiological or behavioural, as a result of a stimulus
• Types of receptors

  • Mechanoreceptors
  • Chemoreceptors
  • Thermoreceptors
  • Photoreceptors
• Reflex arc


  A pre-programmed response initiated directly from the spinal cord, without requiring the brain for decision-making
• Regular stimulus-response model


  Requires the incoming message to travel to the brain and for a decision to be made regarding an appropriate response
• Advantages of reflexes


  • Quick response to prevent harm/avoid danger
  • They don't require any learning. We are born with them.
• Central Nervous System (CNS)


  Brain and spinal cord
• Peripheral Nervous System (PNS)


  All nerves outside the brain and spinal cord, including sensory and motor nerves
• Components of PNS

  • Somatic nervous system
  • Autonomic nervous system
• Somatic nervous system


  Includes all sensory nerve cells and motor nerve cells connecting to skeletal muscles
• Autonomic nervous system


  Includes motor nerve cells connecting to internal organs, regulates internal processes without our awareness
• Neuron


  Nerve cell that carries messages in the form of electrical impulses
• Main types of neurons

  • Sensory (afferent) neurons
  • Interneurons
  • Motor (efferent) neurons
• Sensory neurons

  Neurons that receive information from sensory receptors (senses) and send this sensory information as impulses towards the central nervous system
• Interneurons


  Found entirely within the central nervous system, they process and integrate incoming information, and relay outgoing motor information. They send information between sensory neurons and motor neurons
• Motor (efferent) neurons


  Send information away from the central nervous system to effector muscles, glands and other organs (effectors)
• Dendrites


  Short, branching terminals that receive nerve impulses from other neurons or sensory receptors, and relay the impulse TOWARD the cell body
• Soma (cell body)


  Processes input from the dendrites. If the input received is large enough, the cell body relays it to the axon, where an impulse is initiated. The soma contains the nucleus
• Axon

  The long, threadlike part of a neuron which conducts impulses AWAY from the soma (cell body)
• Myelin


  A white, fatty substance that encases (surrounds) the axon and insulates it, called a myelin sheath. This helps messages to be transmitted quickly
• Axon terminals

  The terminal end of an axon branches into many fibres called axon terminals. Each axon terminal finishes in a swollen knob, sometimes called a terminal button or synaptic knob
• Synapse


  A junction between two neurons or a junction between neurons and receptor or effector cells. The membranes of the neurons are separated by a narrow gap called a synaptic cleft or synapse
• Transmission of messages across a synapse


  1. Messages are passed across the synapse in the form of chemicals called neurotransmitters. Neurotransmitters always pass in the same direction

  2. When an impulse arrives at the end of a neuron, the impulse causes sacs that contain neurotransmitters to fuse with the membranes of the axon. These sacs, called vesicles, release their contents into the synaptic cleft. The neurotransmitters then diffuse across the synapse, taking less than 1 millisecond to reach the dendrites of the next neuron, or the cell membrane of the effector
• Cerebrum

  Comprises nearly 90 percent of the brain tissue and is associated with higher function, such as thought and action. There are two hemispheres or halves (right and left) and four sections or lobes
• Functions of the cerebral lobes

  • Frontal lobe - voluntary movement, speech, intelligence and behaviour
  • Temporal lobe - hearing, smell, language, taste, memory and understanding speech
  • Parietal lobe - sensation, artistic and scientific ability
  • Occipital lobe - processing incoming visual information and storing visual memories
• Cerebellum


  Located at the back of the brain, controls movement, balance and muscle coordination. Helps in learning and remembering motor skills
• Brain stem


  The lower extension of the brain that connects the brain to the spinal cord and controls involuntary functions. Connects the peripheral nervous system to the cerebrum, and the transfer of information between the PNS and higher brain regions is one of its most important functions
• Hypothalamus


  Maintains homeostasis, integrating the nervous and endocrine systems. Located slightly in front of the centre of the brain and regulates most endocrine activity. Contains the body's thermostat, as well as centres for regulating body temperature, water balance, hunger and thirst
• Pituitary gland

  Under the control of the hypothalamus, produces, stores and releases a set of hormones which regulate many of the body's functions
• The brain is surrounded by a bony cranium
• Grooves of the brain

  • Provide increased surface area for the cerebral cortex
  • Allow for more neurons to fit in the skull
• White matter


  Made of myelin, which insulates axons and allows for faster transmission of nerve impulses
• Corpus callosum


  Connects the two hemispheres of the cerebrum and allows for communication and integration of information between the two sides of the brain
• Reflexes are generated at the top of the spinal cord and don't need to go to the brain for processing, so the response is faster than a normal response
• Types of receptors

  • Thermoreceptors
  • Chemoreceptors
  • Mechanoreceptors
  • Photoreceptors
• Motor neurons carry messages from the CNS to effectors
• Dendrites relay nerve impulses towards the cell body
• Neurotransmitters


  Chemicals that transfer a nerve message across a synapse