Exam 3

• Synapse


  Site where action potentials in one cell cause action potentials in another cell
• Components of a synapse


  • Presynaptic: cell that transmits signal toward the synapse
  • Postsynaptic: target cell receiving the signal
• Electrical synapse


  Gap junctions that allow graded current to flow between adjacent cells
• Connexons


  Protein tubes in cell membrane
• Electrical synapses are found where contractions are important: cardiac muscle and many types of smooth muscle
• Chemical synapse


  Neurotransmitters released by action potentials in presynaptic terminal
• Chemical synapse


  1. Synaptic vesicles: action potential causes Ca2+ to enter cell that causes neurotransmitter to be released from vesicles

  2. Diffusion of neurotransmitter across synapse

  3. Postsynaptic membrane: when neurotransmitter binds to receptor, ligand-gated ion channels open
• Components of a chemical synapse


  • Presynaptic terminal
  • Synaptic cleft
  • Postsynaptic membrane
• Neurotransmitters


  Chemical messengers secreted by neurons. Neurons can secrete more than one type
• Neurotransmitters


  • Fits in one receptor
  • Affects only the cells with receptors for that neurotransmitter
  • Excitatory in some cells and inhibitory in others
  • Some neurotransmitters (for example, norepinephrine) can also attach to the presynaptic terminal and modulate its own release
• Norepinephrine


  1. Recycled within presynaptic neuron or diffuses away from synapse

  2. Enzyme monoamine oxidase (MAO) breaks it down

  3. Absorbed into circulation, broken down in liver
• ACh


  1. Acetylcholinesterase splits ACh into acetic acid and choline

  2. Choline recycled within presynaptic neuron
• Excitatory postsynaptic potential (EPSP)

  • Depolarization occurs and response is stimulatory
  • Depolarization might reach threshold producing an action potential and cell response
  • Goes towards threshold
• Inhibitory postsynaptic potential (IPSP)


  • Hyperpolarization and response is inhibitory
  • Decrease likelihood of action potential by moving membrane potential farther from threshold
  • Goes away threshold
• Neuromodulators


  Influence likelihood of an AP being produced in postsynaptic cell
• Axoaxonic synapses


  Axon of one neuron synapses with the presynaptic terminal (axon) of another. Common in CNS
• Presynaptic inhibition


  Reduction in amount of neurotransmitter released from presynaptic terminal. Endorphins can inhibit pain sensation
• Presynaptic facilitation


  Amount of neurotransmitter released from presynaptic terminal increases. Glutamate facilitating nitric oxide production
• Spatial and Temporal Summation


  1. Many postsynaptic potentials combine in summation at the trigger zone. If threshold is reached, and action potential is triggered

  2. Spatial – Space [go through as many dendrites as possible- A.P going down more than one dendrite]

  3. Temporal – Time/tempo [goes down one dendrite – another A.P (action potential) follows it after]
• Spatial and temporal happen at the same time, it's never just the one
• Convergent pathways


  Synthesis of data in brain
• Divergent pathways


  Important information can be transmitted to many parts of the brain
• Reverberating circuit


  Rhythmic activities such as breathing or heart beating
• Parallel after-discharge circuit


  Complex data processing within the brain
• Spinal cord is a crucial component of the central nervous system (CNS), serving as a relay and processing center for sensory and motor information
• Gray Matter


  Consists of nerve cell bodies, dendrites, and unmyelinated axons. The gray matter is where integration and processing of sensory and motor signals occur
• White Matter


  Consists mainly of myelinated axons bundled into tracts. Tracts facilitate communication between different levels of the spinal cord and between the spinal cord and the brain
• Spinal Nerves


  Thirty-one pairs of spinal nerves emerge from the spinal cord. Each spinal nerve is formed by the fusion of a dorsal root (sensory) and a ventral root (motor)
• Meninges


  The spinal cord is enveloped by three layers of protective membranes called meninges: the dura mater (outer layer), arachnoid mater (middle layer), and pia mater (inner layer)
• Sensory Function


  Sensory neurons convey information from sensory receptors in the body to the spinal cord and then to the brain for processing
• Motor Function


  Motor neurons transmit signals from the brain and spinal cord to muscles and glands, controlling movement and secretion, respectively
• Reflexes


  The spinal cord is capable of generating reflex responses to certain stimuli without input from the brain
• Segments of the spinal cord

  • Cervical
  • Thoracic
  • Lumbar
  • Sacral
• The spinal cord extends from foramen magnum to second lumbar vertebra
• Two enlargements: Cervical and Lumbar
• Conus Medullaris


  It's like the end point of the main wire. It tells the spinal cord where to stop
• Cauda Equina


  Help make sure your lower body gets the messages it needs; it looks like a horse tail. They're like the branches of a tree spreading out to reach different parts of your legs and lower back
• Nerve numbers


  • Cervical (8)
  • Thoracic (12)
  • Lumbar (5)
  • Sacral (5)
  • Coccygeal (1)
• Dura Mater


  • Meaning: Dura mater means "tough mother" in Latin, and it lives up to its name
  • Description: The dura mater is a tough, fibrous membrane that surrounds and protects the spinal cord
  • Function: The dura mater provides strong protection for the delicate structures of the spinal cord, shielding it from injury
• Arachnoid Mater


  • Meaning: Arachnoid mater gets its name from its spiderweb-like appearance
  • Description: This membrane lies just beneath the dura mater and is separated from it by the subdural space
  • Function: The arachnoid mater helps cushion and protect the spinal cord, acting as a barrier between the dura mater and the innermost layer, the pia mater