Nervous Tissue. Ch. 12. Overview of the Nervous System. Objectives List the structures and basic functions of the nervous system. Describe the organization of the nervous system. Structures. Nervous system Smallest and most complex system Billions of neurons Includes: Brain
CNS – Central NS
PNS – Peripheral NS
Contains brain and spinal cord (axial)
Processes sensory info
Source of thoughts, emotions, memories
Supports exercise or emergency actions
“fight or flight”
Ex: increases heart rate
“rest and digest”
Ex: decreases heart rate
Usually work in opposing actions
“brain of the gut”
Controls all activities associated with digestion and the gastrointestinal (GI) tract
What are the components of the CNS and PNS?
What kinds of problems would result from damage of sensory neurons, interneurons, and motor neurons?
What are the components and functions of the SNS, ANS, and ENS?
Which subdivisions of the PNS control voluntary actions? Involuntary actions?
Provide unique functions
Sensing, thinking, remembering, controlling muscle activity, regulating glandular secretions
Support, nourish, and protect the neurons
Maintain homeostasis in the interstitial fluid that bathes them
Synapse – site of communication between 2 neurons or a neuron and an effector cell
Synaptic end bulb – swollen end of an axon where synaptic vesicles hold neurotransmitters
Purkinje cells – cerebellum
Pyramidal cells – cerebral cortex of brain
Actively participate in nervous tissue functioning
Do not generate action potentials
Can multiply and divide – neurons cannot
Myelin sheath – multilayered lipid and protein covering around some axons
Increases speed of nerve impulse
If a cell has myelin we say that it is myelinated
Gaps in the myelin sheath are called nodes of Ranvier
Describe the parts of a neuron and the functions of each.
Give examples of the structural diversity of neurons.
Give examples of the different types of neuroglia. Where are each found? What do they do?
What is myelin?
Potential energy – energy stored in a system (the body) as a result of its position or chemical composition
Kinetic energy – energy being used for motion or force
Neurons are excitable because of a voltage difference across the membrane - potential
“Potential” will initiate an impulse that can travel through the nervous system
Graded potentials – used for short-distance communication
Action potentials – allow communication over short and long distance within the body
Gradient – difference
Electrochemical gradient – difference in charge and concentration
Positive cations move toward negative areas, negative anions move toward positive areas
Ion location can be controlled with gates that can open or close the pore
Mechanically gated channels
Define resting membrane potential.
Describe each type of ion channel.
Describe the cellular processes that create the resting membrane potential.
K+ channels open
K+ flows out of cell
Na+ channels open rapidly – Na+ rushes into the cell
Potential goes from -55 to +30 (inside is 30 more positive than the outside)
The more Na+ there is, the more channels open – this is a ____________-feedback mechanism
K+ channels open as the Na+ channels are closing
Na+ inflow slows, K+ outflow increases
Potential goes from +30 to -70
Local anesthetics – block pain and other body sensations
Novacaine or Lidocaine
Block the opening of Na+ channels
The nerve impulse can’t go past the blocked region – CNS never gets the message that there is pain
What causes a graded potential?
Describe what happens to cause an action potential.
What happens during depolarization? What does this cause?
What happens during repolarization? What does this cause?
Nerve impulse arrives
Depolarizing phase opens Ca++ channels, Ca++ flows in
Ca++ causes release of NT from vesicles
NT binds to receptors on postsynaptic neuron
Action potential continues (Na+, K+, Cl-)
What are the differences between a chemical and electrical synapse?