Neurons:
The Nerve
Cells
Our Goals Today
• Identify and give functions for each of the
following: dendrite, cell body, axon, axoplasm,
and axomembrane
• Differentiate among sensory, motor, and
interneurons with respect to structure and
function
• Relate the structure of a myelinated nerve fibre to
the speed of impulse conduction, with reference
to myelin sheath, Schwann cell, node of Ranvier,
and saltatory transmission
• Describe the structure of a reflex arc (receptor,
sensory neuron, interneuron, motor neuron, and
effector) and relate its structureto how it functions
Neuron
• Dendrite: conducts impulses towards a cell
body
• Cell Body: contains the nucleus (maintains the
cell)
• Axon: conducts impulses away from a cell body
• Axomembrane: cell membrane surrounding the
axon
• Axoplasm: cytoplasm inside the axon
• Within each neuron the impulse travels in the
following sequence:
• Dendrite → Cell Body → Axon
Neuron
Types of Neurons
• Sensory Neurons
• Association or
Interneurons
• Motor Neurons
Sensory Neurons
• Long dendrite, short axon
• Cell body and dendrite are located
outside the spinal cord
• Conduct impulses to the spinal cord
Motor Neurons
• Short dendrite , long axon
• Long axon between the cell body and
an effector (muscle or gland)
• Axon is located outside of the spinal
cord
• Dendrite and cell body are located
within the spinal cord
Interneurons
• Interconnect nerve cells
– Sensory neurons with motor neurons
• Entirely in the CNS
Nerves
• Grouping of nerve cells (neurons)
• Mixed nerves: dendrites of sensory neurons and
axons of motors neurons located in the same
nerve
• May contain hundreds of long fibers
• Covered with a myelin sheath
– Fatty tissue
– Composed of Schwann cells wrapped around each
nerve fiber
– Areas between Schwann cells are called nodes of
Ranvier
• Myelin sheath has two functions
– Prevents cross-communication between neurons
– Allows impulses to travel faster
Nerves
Spinal Nerves: connected to the CNS at either the dorsal or
ventral side of the spinal cord (mixed nerves)
Sensory Nerves
• Connected through a
dorsal root
• Sensory neurons - cell
bodies are located in
the dorsal root
ganglion
Motor Nerves
• Connected through a
ventral root
• Motor neurons - cell
bodies are located in the
spinal cord
• Cell bodies of motor
neurons along with
interneurons makes inner
part of the spinal cord
dark in colour (grey
matter)
White Matter: outer regions of the spinal cord
Reflex Arc
• No thought required, protective mechanism
• Involves all 3 types of neurons
1) Receptor (eg. Pain receptor) detects a
stimuli that exceeds the threshold and
initiates an impulse
2) Impulse travels through a sensory neuron
3) To an interneuron
4) To a motor neuron
5) Axon of the motor neuron sends the impulse
to the effector
– Muscle (to cause movement)
– Gland (cause a secretion)
• Synapse: connections between 2 nerve cells
• Brain will be alerted by other interneurons that
reflex took place
Reflexive Arc
Remember Our Goals...
• Identify and give functions for each of the
following: dendrite, cell body, axon, axoplasm,
and axomembrane
• Differentiate among sensory, motor, and
interneurons with respect to structure and
function
• Relate the structure of a myelinated nerve fibre to
the speed of impulse conduction, with reference
to myelin sheath, Schwann cell, node of Ranvier,
and saltatory transmission
• Describe the structure of a reflex arc (receptor,
sensory neuron, interneuron, motor neuron, and
effector) and relate its structureto how it functions