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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

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overview of the nervous system
Overview of the Nervous System
  • Objectives
    • List the structures and basic functions of the nervous system.
    • Describe the organization of the nervous system.
  • Nervous system
    • Smallest and most complex system
    • Billions of neurons
    • Includes:
      • Brain
      • Cranial nerves
      • Nerves – bundle of axons
      • Spinal cord – connects to brain
      • Spinal nerves
  • Sensory – detect internal and external stimuli
    • Sensory neurons carry information to brain
  • Integrative – analyzes and stores information; makes appropriate responses
    • Perception – conscious awareness of sensory stimuli
    • Interneurons – participate in integration
  • Motor – causes movement or gland secretion in response to stimuli
    • Motor neurons – carry information to muscle or gland (effectors)
nervous system
Nervous System

CNS – Central NS

PNS – Peripheral NS

Contains brain and spinal cord (axial)

Processes sensory info

Source of thoughts, emotions, memories

  • All tissue outside the CNS (appendicular)
  • Includes cranial nerves, branches, spinal nerves, sensory receptors
  • Divided further
    • SNS – somatic NS (body)
    • ANS – autonomic NS (self)
    • ENS – enteric NS (intestines)
peripheral ns branches
Peripheral NS Branches
  • Somatic NS – voluntary
    • Consists of:
      • Sensory neurons in head, body, limbs, vision, hearing, taste, and smell that send messages to CNS
      • Motor neurons that conduct messages from CNS to skeletal musclesonly
  • Autonomic NS – involuntary
    • Consists of:
      • Sensory neurons in organs that send messages to CNS
      • Motor neurons that conduct messages from CNS to smooth muscle, cardiac muscle, and glands
ans branches
ANS Branches

Sympathetic division

Parasympathetic division

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?

histology of nervous tissue
Histology of Nervous Tissue
  • Objectives
    • Contrast the histological characteristics and the functions of neurons.
    • Contrast the functions of neuroglia.
neurons vs neuroglia
Neurons vs. Neuroglia



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

  • Vocabulary:
    • Neuron – nerve cell
    • Electrical excitability
      • the ability to respond to a stimulus and convert it into an action potential
    • Stimulus
      • any change in the environment that is strong enough to initiate an action potential
    • Action potential – nerve impulse
      • An electrical signal that propogates (travels) along the surface of the membrane of a neuron
      • Can travel up to 280 mph
parts of a neuron
Parts of a Neuron
  • Three parts
    • Cell body
      • Main part of the cell
      • Includes organelles, nucleus, and cytoplasm
    • Dendrites
      • Receiving parts of the neuron
      • Short, tapered, and highly branched
    • Axon
      • Transmitting parts of the neuron
      • Long, thin, cylindrical
parts of a neuron2
Parts of a Neuron

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

neural diversity
Neural Diversity
  • Multipolar neurons
    • Several dendrites, one axon
    • Found in brain and spinal cord
  • Bipolar neurons
    • One main dendrite, one axon
    • Eye, ear, olfactory of brain
  • Unipolar neurons
    • Axon and dendrite fuse at beginning and then branch
    • Occurs as an embryo

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

types of neuroglia
Types of Neuroglia
  • CNS
    • Astrocytes – create blood-brain barrier, strength
    • Oligodendrocytes – create myelin sheath around CNS axons
    • Microglia – remove cellular debris during neural development
    • Ependymal cells – assist with circulation of cerebrospinal fluid
  • PNS
    • Schwann cells – create myelin sheath around PNS axons
    • Satellite cells – support, regulate exchange of materials

Myelin sheath – multilayered lipid and protein covering around some axons

Provides insulation

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?

electrical signals in neurons
Electrical Signals in Neurons
  • Objectives
    • Describe the cellular properties that permit communication among neurons and effectors.
    • Compare the basic type of ion channels, and explain how they relate to action potentials and graded potentials.
    • Describe the factors that maintain a resting membrane potential.
mini physics lesson
Mini-Physics Lesson

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

physics to anatomy
Physics to Anatomy

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

  • Membrane potential – electrical voltage difference across the membrane
  • Resting membrane potential – membrane potential in an excitable cell
    • Like voltage stored in a battery
    • If + and – ends connect, electrons flow in a current
  • Current
    • Flow of charged particles
    • For the body – these are ions instead of elecrons
ion channels
Ion Channels

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

ion channels1
Ion Channels

Leakage channels

Voltage-gated channels

Ligand-gated channels

Mechanically gated channels

ion channels2
Ion Channels
  • Leakage channels
    • Randomly open and close
    • most cells leak more potassium (K+) than sodium (Na+)
  • voltage-gated channels
    • Opens in response to a change in voltage (membrane potential)
    • Generate and conduct action potentials
ion channels3
Ion Channels
  • Ligand-gated channels
    • Opens and closes in response to chemical stimulus (nts, hormones, other ions – ligand molecule)
    • Ex: Ach opens channels that allow Na+ and Ca2+ to go in and K+ to go out
    • Work in 2 ways
      • ligand molecule can open or close the channel itself by binding
      • Ligand molecule activates another chemical messenger to open the channel
ion chanenls
Ion Chanenls
  • Mechanically gated
    • Opens or closes in response to stimulation by:
      • Vibration: sound waves
      • Pressure: touch
      • Tissue stretching
    • The channel is physically disrupted and opens
resting membrane potential
Resting Membrane Potential
  • Exists due to negative ions in cytosol (ICF) and equal positive ions in ECF
  • The greater the difference in charge, the larger the potential
  • Example:
    • 5 Na+ on outside, 4 Cl- on inside – small potential
    • 25 Na+ on outside, 4 Cl- on insdie – great potential
  • Most cells have potential between -40 to -90 mV; typical is -70mV
  • Minus sign means the cell is negative – not negative potential!
  • Any cell with potential is polarized
    • The potential varies between +5 to -100 mV
how does the potential get there
How does the potential get there?
  • ECF
    • Rich in Na+ and Cl-
  • ICF
    • Rich in K+
    • Also has P-, amino acids,
  • Ion interaction
    • There are many K+ leakage channels, so K+ diffuse out
    • + ions exit, inside becomes more negative
    • - ions can’t leave because they are bound to molecules
    • - charges attract the K+ back in toward the cell
    • Few Na+ ions leak inward
    • This would destroy the membrane potential, so there are pumps that take care of this
na k pump
Na+/K+ pump
  • To keep the RMP
    • Pump out Na+ as it leaks in
    • Pump in K+ as it leaks out
    • 3 Na+ for each 2 K+ - this still maintains a negative charge in the cell

Define resting membrane potential.

Describe each type of ion channel.

Describe the cellular processes that create the resting membrane potential.

  • Objectives
    • Describe what causes a graded potential.
    • Understand the process for creating an action potential.
    • Explain depolarization and repolarization, including the relationship between them.
graded potentials
Graded Potentials
  • When a stimulus causes a channel to open or close in an excitable cell
  • Causes more polarization (more - inside)
  • Causes less polarization (less – inside)
  • Hyperpolarized (much more – inside)
  • Depolarized (much less – inside)
  • Graded signals – vary in size
    • Spread out along plasma membrane and die out
    • Only used for short distance communication
generation of action potentials
Generation of Action Potentials
  • Action potential (AP) or impulse – sequence of rapidly occurring events that take place in two phases
    • Depolarizing phase – negative membrane potential becomes
      • Less negative
      • Reaches 0
      • positive
    • Repolarizing phase – membrane potential is
      • Restored to the resting state of -70 mV
depol vs repol
Depol. vs. Repol.
  • Na+ channels open
  • Na+ rushes into cell
  • All or none principle
    • when depolarization reaches the threshold, the AP occurs
    • AP is always the same size
    • Like dominos – no matter how hard you push the first domino they will all fall or they won’t – same goes for the AP

K+ channels open

K+ flows out of cell

depolarizing phase
Depolarizing Phase

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

repolarizing phase
Repolarizing Phase

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?

signal transmission synapses
Signal Transmission Synapses
  • Objectives
    • Explain the events of signal transmission at a chemical synapse.
synaptic vocabulary
Synaptic vocabulary
  • Presynaptic neuron – the one sending the signal
  • Postsynaptic neuron – the one receiving the signal
  • 3 types
    • Axodendritic – axon to dendrite
    • Axosomatic – axon to body cell
    • Axoaxonic – axon to axon
electrical synapse
Electrical Synapse
  • Action potentials conduct between cells through gap junctions
    • Tunnels connect the two cells together and the electrical impulse can pass
  • places:
    • Smooth muscle, cardiac muscle, developing embryo
  • advantages:
    • Faster – don’t have to “jump the gap”
    • Synchronization – allows groups of cell’s to work together – heart beating
chemical synapse
Chemical Synapse
  • Pre- and post-synapses do not touch – separated by synaptic cleft
  • Transfer of signal must occur
    • Pre-synaptic neuron turns electrical signal into chemical signal (neurotransmitter)
    • Post-synaptic neuron turns chemical signal into electrical signal
  • this transfer takes more time than electrical signals
chemical synapse1
Chemical Synapse

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?