MOD 4

• Nervous control (animals)


  An animal must be able to respond to environmental stimuli
• Sensory receptors and motor effectors

  • Sensory receptors can detect the stimulus
  • Motor effectors can respond to it
• Nervous system


  Consists of neurons and supporting cells
• Types of neurons


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


  Carry impulses from sensory receptors to the central nervous system (CNS)
• Motor neurons


  Carry impulses from the CNS to effectors—muscles and glands
• Interneurons


  Located in the brain and spinal cord, help provide more complex reflexes and higher associative functions, including learning and memory
• Peripheral nervous system (PNS)

  Consists of sensory and motor neurons
• Components of the somatic nervous system

  • Motor neurons that stimulate skeletal muscles to contract
• Components of the autonomic nervous system

  • Motor neurons that regulate the activity of the smooth muscles, cardiac muscle, and glands
• Sympathetic and parasympathetic divisions

  Counterbalance each other in the regulation of many organ systems
• Structure of a typical vertebrate neuron

  • Extending from the cell body are many dendrites, which receive information and carry it to the cell body
  • A single axon transmits impulses away from the cell body
  • Many axons are encased by a myelin sheath, with multiple membrane layers that insulate the axon
  • Small gaps, called nodes of Ranvier, interrupt the sheath at regular intervals
• Schwann cells


  Form myelin sheaths in the PNS
• Oligodendrocytes


  Form myelin sheaths in the CNS
• Myelinated axons


  Form the white matter in the CNS
• Unmyelinated dendrites and cell bodies


  Form the gray matter in the CNS
• Myelinated axons in the PNS

  Bundled together, much like wires in a cable, to form nerves
• Nerve impulse transmission


  Neurons have a charged cellular membrane, and the charge can change in response to neurotransmitter molecules and environmental stimuli
• Ion channels


  Allow ions to enter or exit the neuron, have different configurations: open, closed, and inactive
• Voltage-gated ion channels


  Change their structure in response to voltage changes, regulate the relative concentrations of different ions inside and outside the cell
• Membrane potential


  The difference in total charge between the inside and outside of the cell
• Transmission of a signal between neurons

  Carried by a chemical called a neurotransmitter
• Transmission of a signal within a neuron

  Carried by a brief reversal of the resting membrane potential called an action potential
• Neurotransmitter molecules bind to receptors in a neuron's dendrites


  A change occurs in the resting membrane potential which in turn initiates action potential
• Action potential travels along the neurons up to the axon terminal


  Triggers the release of neurotransmitters
• Neurotransmitters travel across intercellular junctions known as synapses


  To reach another neuron, muscle cells or gland cells
• Axons


  Transmit neurotransmitters to another axon
• Synapses


  Intercellular junctions between neurons
• Synaptic transmission


  Generally affects only the postsynaptic cell that receives the neurotransmitter
• Hormone


  A regulatory chemical that is secreted into extracellular fluid and carried by the blood and can therefore act at a distance from its source
• Endocrine glands


  • Organs specialized to secrete hormones
• Endocrine system


  • The organs and tissues that produce hormones
• The blood carries hormones to every cell in the body


  Only target cells with the appropriate receptor for a given hormone can respond to it
• Hormone receptor proteins


  Function in a similar manner to neurotransmitter receptors, specifically bind the hormone and activate signal transduction pathways that produce a response to the hormone
• Paracrine regulators


  Molecules released and act within an organ on nearby cells, do not travel through the blood to reach their target
• Autocrine signaling


  Cells release signaling molecules that affect their own behavior
• Senses in humans


  • Olfaction (smell)
  • Gustation (taste)
  • Equilibrium (balance and body position)
  • Vision
  • Hearing
• General senses (somatosensation)


  • Temperature
  • Pain
  • Pressure
  • Vibration
• Senses related to somatosensation

  • Vestibular sensation (spatial orientation and balance)
  • Proprioception (position of bones, joints, and muscles)
  • Kinesthesia (limb movement)
• Sensory transduction


  The process of converting a stimulus (such as light, or sound, or the position of the body) into an electrical signal in the nervous system