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Flashcards in Nervous System Deck (56):
1

Central Nervous System

- made up of the brain and spinal cord

- integration and command center of nervous system

- receives sensory signals, interprets them and dictates motor response to them

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Afferent Signals

AKA sensory signals

- signals picked up and carried by PNS to CNS

3

Peripheral Nervous System

- all nervous tissue outside the CNS

- made up of nerves and ganglia (clusters of neuron cell bodies)

- serve as communication lines linking body to CNS

4

Efferent Signals

AKA Motor signals

- carried away from the CNS to effector organs, such as muscles and glands

5

sensory input

information gathered by the nervous system

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integration

processing and interpretation of sensory input by the CNS

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motor output

the actions performed by effector organs upon receiving an efferent signal

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Subdivisions of the PNS

Sensory (Afferent) Division
  • Somatic Sensory Receptors - outer, ie skin
  • Visceral Sensory Receptors - visceral organs

Motor (Efferent) Division

  • Somatic Nervous System - innervation of skeletal muscle, etc.
  • Autonomic Nervous System - smooth/cardiac muscle and glands

9

Somatic Sensory Perception Divisions

General Senses (widespread receptors)

  • temperature, pain, pressure, touch (via skin)
  • proprioception (joint position, postural tension, balance)

Special Senses (localized receptors)

  • Smell
  • Taste
  • Vision
  • Equilibrium & hearing

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Sympathetic Division of Autonomic Nervous System

- readies the body for activity

- "fight or flight"

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Parasympathetic Division of Autonomic Nervous System

- conserves energy and promotes digestion

- "rest and digest"

12

Neurons

- basic structural unit of nervous system that conducts electrical impulses along its plasma membrane

- each neuron can live and function for the entire lifetime of the organism

- does not undergo mitosis

- high metabolic rate

13

Neuron Properties

- Excitability - responds to changes in body and environment

- Conductivity - produce eletrical signals

- Secretion - releases neurotransmitters at synapses when eletrical signal reaches them

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purple structure at left containing nucleus

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Neuron Cell Body (AKA Soma/Perikaryon)

- contains nucleus/cytoplasm

- has the usual organelles as well as specialized neuronal organelles (Nissel granules, Neurofibrils)

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Branched purple structures coming off cell body at left

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Dendrites

- shorter than axon, but much branching

- receive signals and transmit them to cell body

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long thing cytoplasmic extension extending rightward from cell body through the yellow structures

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Axon

- one per neuron

- Sends signals away from cell body

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Nissl Granules

AKA Nissl bodies

- rER and free ribosomes within neuron cell bodies

- stain densely on microscopic slides

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Neurofibrils

- bundles of microfilaments within neurons

- similar to structure of myofibrils within muscle cells

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Ganglia

clusters of neuron cell bodies outside the CNS, along PNS nerves

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cone-shaped region of cell body where it meets the axon

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Axon Hillock

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branched ends of axon on the right

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Telodendria

- AKA axon terminals or terminal branches

- end in synaptic knobs/bulbs at dendrites of another neuron, motor end plate, etc.

22

spaces between the yellow structures on the axon

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Nodes of Ranvier

- neurofibril nodes

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yellow cells surrounding the axon

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Schwann cells

AKA neurolemmocytes

- form myelin sheath around axons in PNS only

24

the cells that appear as small dots here amongst the neurons

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Neuroglial Cells (or Neuroglia)

- outnumber neurons ~10 to 1

- insulate and support neurons

- branching processes and central cell body

25

Types of Neuroglial Cells

CNS

  • Astrocytes - star-shaped, blood vessel connections
  • Microglia - smallest, least abundant, phagocytes
  • Ependymal Cells - CS fluid producers, ciliated
  • Oligodendrocytes - myelination in CNS

 

PNS

  • Satellite Cells - surround neurons in ganglia
  • Schwann Cells - myelination in PNS

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Yellow cell here connecting capillary to neuron

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Astrocyte

- most abundant neuroglia in CNS

- star-shaped

- connect blood vessels to neurons

- contribute to BBB

- regulate ion balance and brain tissue fluid

- take up neurotransmitters from synapses

- replace damaged neurons

27

phagocytotic glial cell

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Microglia

- smallest, least abundant CNS neuroglia

- engulfs invading microorganisms and dead neurons

- derived from monocytes

28

cuboidal, ciliated CNS neuroglia shown here as row of darker cells

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Ependymal Cell

- line brain and spinal cord cavities

- produce cerebrospinal fluid

- ciliated to help circulate fluid

29

round central structure

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oligodendrocyte

- CNS neuroglial cell with few branches

- one cell myelinates multiple axons of CNS

30

unlabeled structures surrounding the neuron body

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Satellite Cells

- surround neuron bodies within ganglia of the PNS

31

Protective lipoprotein around axons

Myelin

- 20% protein, 80% lipid

- forms myelin sheath, concentric layers of plasma membrane of supporting cells (Schwann in PNS, Oligodendrocytes in CNS)

- insulates axon and increases speed of conduction

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cytoplasm within the axon of a neuron

Axoplasm

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Plasma membrane of an axon

Axolemma

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Outermost layer of Schwann cells around axons

Neurilemma

- outermost layer where nucleus of Schwann cell resides

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Unmyelinated Neurons

- thick axons are myelinated

- thin axons are unmyelinated, meaning surrounded and supported by Schwann cells, but not wrapped

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What kind of neuron?

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Multipolar

- more than 2 processes, many dendrites & 1 axon

- muscle innervation

37

What kind of neuron?

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Bipolar

- 2 processes, dendrites on one, axon on other

- rare neurons in sensory organs (ex: retina)

38

What kind of neuron?

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unipolar neuron

- pseudounipolar

- has one short single process connecting the body to the receptive and transmissive endings of the axon

39

Function Classification of Neurons

  1. Sensory (afferent) Neurons - detect changes in body and environment
  2. Motor (efferent) Neurons - send signals to muscles and glands (effectors)
  3. Interneurons (association neurons) - between sensory and motor (CNS only), make up 99% of neurons, process, store and retrieve info

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CT around each nerve fiber (axon)

Endoneurium

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dense irregular CT around each nerve fascicle

Perineurium

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dense irregular CT around entire nerve, binding fascicles

epineurium

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nerve fascicles

a group of nerve fibers (axons) bound into bundles, surrounded by perineurium

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sites at which neurons communicate

synapse

- signals pass in one direction only

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cell that conducts a signal toward a synapse

presynaptic neuron

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cell that transmits a signal away from a synapse

postsynaptic neuron

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types of synapses

Axosomatic - axon to cell body

Axodendritic - axon to dendrites

Axoaxonic - axon to axon, signal acts on axon terminals only, regulating synapse function

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functional junction between a neuron and another cell in which communication is transmitted via ions passing through gap junctions

electrical synapse

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junction between a neuron and another cell in which neurotransmitters carry a signal across a space between the cells

chemical synapse

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mebrane-bound sacs in a presynaptic neuron that contain neurotransmitters

synaptic vesicles

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space between the axon terminal of one neuron and the dendrites of another

synaptic cleft

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neuronal regeneration overview

-  None in CNS

- Axons regenerate slowly (1-5 mm/day) in PNS, but not cell bodies

Dependent on:

  • extent of damage
  • Schwann cells' secretion of Nerve Growth Factor
  • distance from damage to organ being innervated (closer = better)

53

Neuronal Regeneration Steps

  1. axon is severed
  2. proximal end of severed axon seals off/swells, distal end degenerates
  3. distal Schwann cells form "regeneration tube"
  4. axon regenerates and threads through tube
  5. effector is reinnervated

54

Rapid, autonomic motor response to stimuli

Reflex

- predictable and involuntary

55

A simple chain of neurons responsible for a reflex

reflex arc

- made up of:

  • Receptor - takes in stimulus
  • Sensory neuron - transmits afferent signal
  • Integration Center - 1+ synapses in CNS
  • Motor neuron - conducts efferent signal
  • Effector - muscle/gland which acts

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Two Types of Reflexes

Monosynaptic Reflex:

  • fastest
  • contains no CNS interneurons
  • less common

Polysynaptic Reflex:

  • most common
  • contains at least 1 CNS interneuron