Nervous Tissue

Compare and contrast the various types of sensory receptors

• Special sensory receptors - monitor smell, taste, vision, balance, hearing

• Visceral sensory receptors - monitor internal organs

• Somatic sensory receptors - monitor skeletal muscles, joints, and skin surface

Define soma

The cell body

Define perikaryon

Cytoplasm of the neuron where organelles supplying energy and organic material/neurotransmitters is

Define neurofibrils

Bundles of neurofilaments that extend into the dendrites and axon, providing internal support/prevent the cell from tearing during tensile forces

neurofilaments parallel intermediate filaments in other cells

Define dendrites

Receptive region where information is received from the internal or external environment

Dendritic spines are specialized projections that form synapses with other neurons

Define axon

Impulse generative and conducting region going away from cell

• each neuron only has one

• begins at axon hillock - trigger zone

• lack RER and golgi apparatus so depends on the cell body to transport proteins and membrane components

Define telodendria

The terminal branches of the axon - secretory structures

Define Nissl bodies

Clusters of RER and free ribosomes in the perikaryon that stain dark purple

make up gray color of gray matter

What direction is anterograde axonal transport? What substances/components are involved?

Away from the cell body

• Mitochondria

• cytoskeletal elements

• Membrane components for the axon plasma membrane

• Enzymes needed for certain neurotransmitters

What direction is retrograde transport? What substances/components are involved?

On axon back toward cell body

• organelles returning to the cell body to be degraded or recycled

• For intracellular communication to let soma know about conditions at axon terminals

What are the 4 types of neuroglia in the CNS?

Astrocytes, microglia, ependymal cells, and oligodendrocytes

Major role for astrocytes

• create BBB; determine capillary permeability

• guide migration of young neurons and formation of synapses between neurons

• mop up leaked K+; recapture and recycle neurotransmitters

Major role for microglia

Smallest and least common

• phagocytic; immune roles

Major role for ependymal cells

• line central canals and ventricles to produce and monitor CSF

• help circulate CSF

Major role for oligodendrocytes

• form myelin sheath along axons (can do for multiple)

What are the two major types of neuroglia in the PNS? What are their roles

• Schwann cells - myelinate PNS

• satellite cells - monitor CO2, similar to astrocytes

What are nerve fibers?

Bundles of axons that carry sensory info and motor commands in the PNS

What are the anatomical divisions of the nervous system?

What are the major types of ion channels that influence a neuron’s membrane potential? Their roles?

Where are the different types of ion channels distributed along a neuron and how does their distribution contribute to specialized functions?

Gated

• Chemical -

  • @ soma and dendrites

• Voltage

  • axons - Na and K

  • axon terminals - Ca+

• Mechanically gated

Leaky

• 
  

What are the relative concentrations of Na+ and K+ inside and outside a neuron at rest?

• a higher concentration of K+ in the cell

  • stabilized by anionic proteins

• a lower concentration of Na+ outside of the cell

  • stabilized by Cl- ions extracellularly

Which ion channels contribute to the resting membrane potential?

• Na+/K+ ATPase pumps → -5mV

  • stabilizing/maintains concentrations

• Leaky K+ ion channels → -90 mV

• Leaky Na+ ion channel → -70mV

Resting = -70mV because internal is negative

• Difference in ionic composition of internal and external

• Differences in permeability of plasma membrane to ions

  • K+ is much more able to diffuse out of the cell than for Na+ to diffuse into the cell (making inside more negative, thought Na+ also helps prevent getting to negative to some extent)

What maintains the resting membrane potential over time?

Na+/K+ ATPase

Define depolarization

Any shift away from resting membrane potential toward a less negative potential (closer to 0 or positive)

• will be greater if the size of stimulus is greater (bc est. number of open Na+ channels)

Define repolarization

Process of restoring the normal resting membrane potential after depolarization

• via chennels and pumps

Define hyperpolarization

An increase in the negativity of the resting membrane potential (more negative)

• if gated K+ ion channels open then interior loses more K+ and become -

Define threshold

The membrane potential at which an action potential is initiated (-60mV to -55mV)

Define all-or-none response

For all excitable membranes:

• size and speed of action potential are independent of the stimulus strength; either stimulus causes threshold for action potential is reached or not

Compare continuous vs saltatory propogation

How AP travel along an axon

• continuous - on unmyelinated axons

  • relatively slow, sequential activation of VG channels each step along axon

• saltatory - on myelinated axons

  • myelin increases resistance and allows local current to skip internodes

  • uses less energy because less SA and Na+ ions being pumped

How are axon fiber types classified

• Axon Type A Fiber- largest myelinated axons, diameters from 4-20um, fastest

  • Critical sensory info: position, balance, delicate touch & pressure of skin surface

• Axon Type B Fiber- smaller myelinated axons, diameters from 2-4um, intermediate speed

  • Temp, pain, general touch/pressure, to effectors

• Axon Type C Fiber- smallest and unmyelinated, diameter < 2um, slowest

  • Temp, pain, general touch/pressure, CNS to effectors

What are the major differences between channel-linked and g-protein-linked receptors

Channel-linked- aka ionotropic are quicker as binding directly opens an ion channel

GPCRs- aka metabotropic are slower as effector enzymes must be activated to yield an intracellular cascade of responses

• longer lasting

Compare temporal vs spatial summation

Spatial- simultaneous arrival of stimuli from different locations

Temporal- successive arrival of stimuli from the same location (at different times)

Why can’t neurons divide?

They lack centrioles, key to organizing the cytoskeleton and chromosomes during mitosis .

Only parts that can regenerate are the olfactory receptors and in the hippocampus (limbic system)

How are axons called in the CNS versus PNS?

CNS - Tracts

PNS - Nerves

How are neurons classified structurally?

• Anaxonic - many small dendrites, sense organs

• Bipolar - 1 axon, 1 dendrite with many processes, special sense organs

• Unipolar - dendrites and axon are continuous with the cell body to the side - most sensory organs in PNS

• Mulipolar - 2+ dendrites, 1 axon - motor neurons & most common

How are neurons classified functionally?

• Sensory - afferent division of PNS; cell bodies in DRG; between sensory receptor and CNS (somatic and visceral) - unipolar

• Motor - Away from CNS to effector organs - multipolar

• Interneuron - most neurons, multipolar; do integration; between motor and sensory

Generally what are neuroglia?

nerve glue; can divide

• separates and protects neurons

• provides supportive FW

• Phagocytes

• regulate interstitial fluid

How is a change in membrane potential produced?

Anything that alters ion concentration on the two sides of the membrane

Anything that changes membrane permeability

Compare graded potentials versus action potentials

• Graded - (usu.) incoming signals over a short distance (cannot go far from site of stimulation ~1mm)

  • Hyper or depol

  • Depolarization weakens with distance

  • no threshold

  • cytosol resists ion movement

  • summation can occur

  • EPSP and IPSP

• action - long distance signals of axons

  • Depol only

  • has threshold before AP

  • no summation

  • no decrease in strength over tie=me

Compare the 2 types of refractory period

• Absolute refractory period: First part of refractory period where all voltage-gated Na channels are either open or inactive

• Relative refractory period: from whenever Na+ ions regain resting condition until membrane potential goes back to resting

  • Second depolarization can occur if larger-than-norm stimulus

Classify synapses - sites of communication between neurons and other cell/neuron

• Electrical - has direct physical contact using connexons; potential of one cell produces local current that can affect other; fast

• Chemical - more common; neurotransmitter into synaptic cleft via synaptic vesicles

e.g.

• axodendritic

• axosomatic

• axoaxonal

• dendrodendritic

• somatodendritic

How are neurotransmitters functionally classified?

Effects - excit/inhib

mode of action - direct/indirect