Nervous Tissue

Nervous Tissue

1. Nervous Systems

   • Central Nervous system - Contrains only the Brain and Spinal Cord
   • Periphereal Nervous System - Everything that is not your brain or spinal cord! Contains axons, bundles of nerve fibers, also called nerves.
     • Efferent - carries motor commands from the CNS from muscles, glands and adipose tissue
       • Effectors - do something
       • Somatic Nervous System - controls skeletal muscle contractions
       • Autonomic Nervous System - automatically regulates smooth muscle, cardiac muscle, galndular secreations and adipose tissue
     • Afferent - brings information from PNS to CNS
       • Receptors - sensory structures that either detect changes in the environment or respond to specific stimuli. Information goes TO the CNS
         • Sensory Structure

2. Neurons

   • Perikaryon
     • Axon Hillock - how the axon is attached to the cell body
     • Axoplasm - cytoplasm of the axon
   • Structural Classification
     • Multipolar - motr than two processes with one axon and multiple dendrites
     • Bipolar - two distinct processes. One dendrite and one axon.
     • Unipolar - single elongated process with cell body off the the side.
     • Anaxonic - axons are not obvious.
   • Motor - carry instructions from CNS to PNS
   • Sensory - carry instructions from PNS TO CNS

3. Nueroglia - separate and protect neurons, provide a supportive framwork for nervous tissue, act as phagocytes and help regulate the composition of the interstitial fluid.

   • Astrocytes - largest and most numerous in the CNS
   • Microglia - least numerous and smallest neuron are found in stem cells
   • Oligodendrocytes - forms myosheath for the axon
   • Ependymal - line the central canal and ventricles, where they form a simple cuboidal to columnar epithelium.
   • Cells
     • Satellite - surround the neuron cell bodies in ganglia. They regulat interstitial fluid around the neurons.
     • Schwann - form a thick myelin sheath or indented folds of plasma membranes around axons in all parts of the PNS
   • Wallerian Degeneration - repairs damaged nerves.

4. Ions, Concentrations and Memrane Permeability

   • Ion Channels
     • Passive - always open
     • Active - open/close in response to specific stimuli
   • Mechanical Channels
     • Chemical
     • Volted
   • Gradient Potential
     • Depolarization - helps send the message through
     • Hyperpolarization - stops the message

5. Potential

   • Action - "nerve impulses" are changes in the membrane potential that, once intiated, affect and entire excitable membrane.
   • Presynaptic
     • Inhibition - the release of GABA inhibits the opening of voltage-gated calcium ion channels in the axon terminal.
     • Facilitation - the activity at an axoaxonic synapse increase the amount of neurotransmitter released when an action potential arrives at the axon terminal. prolongs the effects of the neurotransmitter on the postsynaptic membrane.
   • Postsynaptic
     • Inhibitory - cause hyperpolarization and suppress the generation of action potentials.
     • Excitatory - cause depolarization and promotes the generation of action potential.

6. Neurotransmitter

   • Inhibitory - graded hyperpolarization of the posynaptic membrane.
   • Excitatory - graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane. Results from the opening of the chemically gated ion channels in the PM that lead to membrane depolarization.

7. Synapses - site of intercellular communication

   • Presynaptic - sends a message
   • Postsynaptic - receives a message
   • Chemical - far more common than electrical. moves communication from Pre to Postsynaptic.
   • Electrical - occur in the CNS and PNS but they are rare.