Ch. 11 - Nervous System

What are the 3 divisions of the nervous system?

1. Central Nervous System (CNS)

2. Peripheral Nervous System (PNS)

3. Enteric Nervous System (ENS)

What does the central nervous system contain? Its function?

• CNS; brain and spinal cord

• Function; Information processing, integrates, coordinates sensory and motor

What does the peripheral nervous system contain?

• PNS; any nervous tissue leaving the spinal cord

What is the enteric nervous system?

• ENS; nervous controls GI tract

What are the subdivisions of the peripheral nervous system?

1. Sensory (afferent) division: brings info. to brain (CNS)

2. Motor (efferent) division; carries motor commands AWAY from CNS

   • nerve impulses toward muscles

What does the sensory (afferent) division include?

• Sensory receptors

• Special sensory organs

What are the sensory receptors?

Sensory (afferent) division

• Position, touch, pressure, pain, temperature

What are the special sensory organs?

Sensory (afferent) division

• Smell, taste, sight, balance, hearing

What does the motor (efferent) division include?

• Somatic nervous system (SNS)

• Autonomic nervous system (ANS)

What is the somatic nervous system?

Motor (efferent) Division

• Voluntary, conscious control

  • skeletal muscle

What is the autonomic nervous system?

Motor (efferent) Division

• Involuntary, automatically regulates activities

  • smooth muscle, cardiac muscle, glands, adipose

What are the main 3 regions of a neuron?

1. Dendrites

2. Cell body

3. Axon

What is the function of dendrites? What is their structure?

• Dendrites: receive stimulus/information (in CNS)

  • branched; dendritic spines

What does the cell body contain?

• Perikaryon (cytoplasm surrounds nucleus): contains organelles and synthesizes neurotransmitters/ATP

  • contains nucleus

What is the function of the axon?

• Axon: carries information AWAY/TOWARD other cells

What are the components of the axon? Their function?

1. Axon hillock: origin of axon from cell body

2. Axolemma; axon's plasma membrane

3. Axoplasm: axon’s cytoplasm

What is the telondendria?

Component of Axon

• Telondendria; fine extensions

  • end at Axon Terminals

What is a synapse?

• Synapse: a presynaptic cell connects with a post synaptic cell

What are the 3 types of synapses?

1. Synapses with another neuron; neuron + neuron

2. Neuromuscular junction; neuron + muscle fiber cell

3. Neuroglandular synapse; neuron + gland cell

What occurs when neurotransmitters are released from the presynaptic membrane?

• Neurotransmitters (like ACh); released into synaptic cleft and bind to receptors on post synaptic membrane

  • relaying AP

What are synaptic vesicles of synapses?

• Synaptic vesicles: store neurotransmitters (in presynaptic cell)

  • fuse with membrane

What are collateral branches of synapses?

• Collateral branches: allow single neuron to communicate with many cells

  • e.g. motor units

What do CNS neurons lack?

• Lack centrioles; cannot be replaced

What structures contain neural stem cells?

• Olfactory epithelium

• Retina of eye

• Hippocampus

What are the classes of neurons?

1. Anaxomic neuron

2. Bipolar neuron

3. Unipolar neuron

4. Multipolar neuron

KNOW WHAT they look like

What is an anaxomic neuron?

• Not understood

What is a bipolar neuron? Where do they occur?

• Cell body in the way

• Occur in special sense organs

What is a unipolar neuron? What is their structure?

• Cell body off one side

• Initial segment: where dendrites separate

What is a multipolar neuron? What is an example?

• Multiple dendrites and single zon

• Most common (e.g. motor neurons)

What is the function of neuroglia or glial cells? How much volume do they compromise?

• Neuroglia: cells support/protect neurons

  • compromise; half of total volume of nervous system

What are the 4 types of CNS glial cells?

1. Ependymal cells

2. Microglia

3. Astrocytes

4. Oligodendrocytes

What is the function of the ependymal cells?

• Create cerebrospinal fluid (CSF)

What do ependymal cells form? Where are they found?

• Form; Ependyma

• Found; central canal (SC) and ventrioles (brain)

What is the function of the microglia?

• Phagocytic cells that remove debris, wastes, pathogens

What is the main function of the astrocytes?

• Maintain Blood Brain Barrier (BBB); isolates CNS from chemicals and hormones in blood

What do the astrocytes and BBB regulate?

• Regulate; ion, nutrient, gas concentration in interstitial fluid

  • shared fluid of neurons

What do astrocytes do with the neurotransmitters?

• Absorbs/recycles neurotransmitters (after being used)

What is the function of oligodendrocytes?

• Provide CNS framework and produce myelin

What do the oligodendrocytes do to the axon?

• Wraps axon with layers of myelin and plasma membrane: myelin sheath

What is the difference between oligodendrocytes (CNS) and schwann cells (PNS)?

• Oligodendrocytes; one cell product myelin for multiple internodes (areas of axon)

• Schwann cells; singe cell wraps around internode

What are myelinated axons?

• Axons with myelin sheaths (appear white)

What is CNS white matter?

• Many myelinated axons

What are internodes?

• Internodes: myelin wrapped areas

What are nodes?

• Nodes: gaps between internodes (nodes of Ranvier)

What are unmyelinated axons?

• Unmyelinated axons: axons without myelin sheath

What is CNS gray matter?

• Most cell bodies and unmyelineated axons

What are the two types of Neuroglia in the PNS?

1. Schwann cells

2. Satellite cells

What is the function of schwann cells? Found?

• Axon repair and forms myelin sheath of axon

• Found; cover peripheral axons

What is neurilemma?

• Plasma membrane of schwann cells in PNS

What is membrane potential?

• Unequal charge distribution across a membrane

  • inside of cell; negative

  • outside of cell; positive

What is the charge inside of a cell?

• - 70 mV

What is resting membrane potential?

• Undisturbed, starting point

  • has energy, holding back

What is the graded potential?

• Temporary, localized change in resting potential

  • determine if stimulus is enough (“grades”); Na+ moving in

What is action potential? What is it triggered by?

• Electric impulse spreading from axon surface to axon terminals

  • Triggered by sufficiently large graded potential; enough Na+ entering

What is an example of a cell that has reached synaptic acitivity?

• Neuromuscular junction

  • simplest form of information processing

What the general steps of synaptic activity?

1. Presynaptic cell releasing neurotransmitters

2. Neurotransmitters binds to receptors on postsynaptic cell membrane changing permeambility

3. Produces graded potentials in postsynaptic membrane; depends on action

What is the sodium potassium pump?

• Pumps 3 Na+ OUT of cell to ECF

• Pumps 2 K+ INSIDE of cell

  • active transport; requires ATP

What is the function of the sodium potassium pump?

• Maintain stable resting potential (-70 mV)

  • occurring at resting potential

What are the leaky channels?

• Passive membrane channels always open

  • create membrane potential (-70 mV)

What are the potassium leak channels? Their purpose?

• K+ leak channels; K+ LEAVING cell

  • rush out when cell is too positive

What are the sodium leak channels? Their purpose?

• Na+ leak channels; Na+ ENTERING cell

  • rush in when cell is too negative

How does the ECF and cytosol contribute to resting membrane potential?

• ECF; high conc. of Na+ and Cl- (pos.)

• Cytosol (inside of cell); high conc. of K+ and negatively charged proteins (neg.)

What is essentially a nerve impulse?

Contributors of Resting Membrane Potential

• Nerve (AP): movement of Na+ and K+ going in and out

What do proteins and ions have to use to move?

Contributors of Resting Membrane Potential

• Proteins/Ions; CANNOT move freely, have to use active transport or passive membrane channels

What are the general steps of the changes in membrane potential?

1. Stimulus

2. Depolarization; Na+ ions in

3. Repolarization; K+ ions OUT

4. Hyperpolarization

5. Resting state

What is the first step of a change in membrane potential?

1. Graded potential; enough of a stimulus reaches threshold (-55 mV)

What is the second step of a change in membrane potential?

2. Triggers AP/depolarization; rushing in Na+ ions to cells

What is the third step of a change in membrane potential?

3. Hits +40; Repolarization: rushing K+ OUT of cell

   • to restore/repolarize to negative cell

What is the fourth step of a change in membrane potential?

4. Hyperpolarization; overshoot of K+ ions out of cell activates sodium potassium pump

What is the fifth step of a change in membrane potential?

5. Sodium potassium pump restores resting state