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Essay Question for exam 3
Describe how action potentials are generated and propagated along
neurons. Include in your description how intracellular voltage changes
during the action potential by labeling the action potential tracing (shown
below) and describing what is occurring at that particular time.
The answer to this question can be found early in Chapt. 11
Points to include. Certainly may include more:
Presynaptic axon:
Action potential
Axon terminal
Ca++ influx via VGCa++ channels
Synaptic Cleft
Postsynaptic Dendrite:
ACh receptors
Na/K channels
Threshold potential
Graded potential
VGNa Channel
Action Potential
Unmyelinated Action Potential
Cell Body
Axon Hillock
Action Potential and myelination (Saltatory conduction vs. conduction along unmyelinated sheath)
Axon terminal
Ca++ influx
Ohm’s Law: V = I x R
Know the neurotransmitters
Structural features of a neuron
Saltatory conduction
Na/K pump
• Neural support cells
• Neuron Classification structure: uni, bi,
• Neuron Classification function:
– Sensory (afferent): transmit impulses from sensory receptors in
the skin or internal organs toward or into the CNS
• All are unipolar
• Cell bodies are located in sensory ganglia outside of the CNS
• Only most distal parts act as receptor sites, with long peripheral
processes (e.g. again, the great toe)
– Motor (efferent): carry impulses away from the CNS to the
effector organs (e.g. muscles, glands)
• Multipolar
• Cell bodies are located in the CNS
– Interneurons (association neurons): lie between sensory & motor
neurons in neural pathways
• Confined to the CNS
• 99% of neurons in the body
• multipolar
Types of plasma membrane ion
– Passive, or leakage, channels – always open
but selective to the ion they let in
– Chemically gated/ligand gated channels –
open with binding of a specific chemical
– Voltage-gated channels – open and close in
response to changes in membrane potential
– Mechanically gated channels – open and close
in response to physical deformation of
receptors (e.g. touch or pressure receptors)
InterActive Physiology ®:
Nervous System I: Ion Channels
• Membrane potentials: what are they and
where do they come from
• Graded potentials
• Action potentials
Propagation of an Action Potential
(Time = 0ms)
Figure 11.13a
Propagation of an Action
(Time = 2ms)
• Ions of the extracellular fluid move toward
the area of greatest negative charge
• A current is created that depolarizes the
adjacent membrane in a forward direction
• The impulse propagates away from its
point of origin
Propagation of an Action
(Time = 2ms)
Figure 11.13b
Propagation of an Action
(Time = 4ms)
• The action potential moves away from the
• Where sodium gates are closing,
potassium gates are open and create a
current flow
Propagation of an Action
(Time = 4ms)
Figure 11.13c
Threshold and Action Potentials
• Threshold – membrane is depolarized by 15 to
20 mV
• Established by the total amount of current
flowing through the membrane
• Weak (subthreshold) stimuli are not relayed into
action potentials
• Strong (threshold) stimuli are relayed into action
• All-or-none phenomenon – action potentials
either happen completely, or not at all
Brain structure
Brain ventricles
Structures of cerebral hemispheres
Grey cortex, white matter, basal nuclei
Lobes of the brain
Primary (somatic) motor cortex
Premotor cortex
Broca’s area
Frontal eye field
Primary somatosensory cortex
Somatosensory association cortex
Visual and auditory areas
Olfactory, gustatory, and vestibular
• Location/function/etc.
Cerebral White Matter
Basal Nuclei
• Midbrain
• Cerebellum
• Brainstem
• Consists of three regions – midbrain, pons, and
medulla oblongata
• Brainwaves
• Sleep
• Memory
• Protection of the brain
• bone, meninges, cerebrospinal fluid, blood-brain
Spinal cord
Gray & white matter and spinal roots
Ascending pathways: specific and
• Descending pathways: direct and indirect
Receptor Classification by Stimulus Type
Receptor Class by Location
Receptor Classification by Structural
• Organization of the Somatosensory
System: receptor level, circuit level,
perceptual level
• Classification of nerves
Sensory and motor divisions
Sensory (afferent) – carry impulse to the CNS
Motor (efferent) – carry impulses from CNS
Mixed – sensory and motor fibers carry impulses to
and from CNS; most common type of nerve
• Ganglia: a collection of neuron cell bodies
associated with nerves in the PNS
• Regeneration of nerves
• The cranial nerves
• The spinal nerves
Spinal Nerves: Roots
• Ventral roots: motor (efferent) fibers
• Dorsal roots: sensory (afferent) fibers
• They unite to form a spinal nerve before emerging from the
vertebral column via a intervertebral foramina
• After emerging, from foramina, spinal nerve divides into small
dorsal, ventral rami and menigeal branch (that re enters the
vertebral column
Innervation of Specific Body Regions
Rami and plexuses
Skin (dermatomes)
Innervation of Visceral Muscle and Glands
Hierarchy of motor control
• ANS Versus Somatic Nervous System
Sympathetic vs. parasympathetic
• Parasympathetic Division Outflow
• Sympathetic Division Outflow
• Neurotransmitters and receptors
• Acetylcholine (ACh) and norepinephrine (NE)
are the two major neurotransmitters of the ANS
• ACh is released by:
• 1) All preganglionic axons
• 2) All parasympathetic postganglionic axons
• Cholinergic fibers – ACh-releasing fibers
• Adrenergic fibers – sympathetic postganglionic
axons that release NE
• Neurotransmitter effects can be excitatory or
inhibitory depending upon the receptor type