The Nervous
System
PNS: Nerves, Senses, and Responses
Peripheral Nervous System
Form & Function
 Two major jobs:
 Carries signals between the
CNS and the rest of the body
 Regulates involuntary body
functions and responses
 4 major groups of nerves,
organized by spinal cord:
 Cervical
 Thoracic
 Lumbar
 Sacral
 Both are involuntary
 Sympathetic:
 “arousing” reactions
 Ex. Heartbeat increase, digestion inhibition,
Autonomic NS:
Parasympathetic
vs Sympathetic
pupils dilate, epinephrine released
 Parasympathetic:
 “calming” reactions
 Ex. Heartbeat slows, digestion stimulated,
saliva produced
 Together they’re responsible for
“fight/flight/freeze” responses and their
opposites
 Two-way pathways between sensory input and
motor responses
 Afferent (sensory) pathway: sensory organ 
Somatic NS:
Sensory and
Motor
CNS
 Efferent (motor) pathway: CNS 
muscle/motor response
 Both voluntary and involuntary
 Voluntary: See a penny, pick it up
 Involuntary: Reflexes
See cat…
…must pet
Reflexes
 Reflex arc
 simple path, only
includes a few neurons
(involuntary,
instantaneous)
 Knee-jerk reflex
 maintains uprightness
 Withdrawal reflex
 avoidance of painful
stimuli
 acoustic reflex - In response to high sound intensities,
contraction of the stapedius and tensor tympani
muscles in the middle ear.
 blushing - A reddening of the face caused by
Some more
human reflexes
embarrassment, shame or modesty.
 corneal reflex - Blinking of both eyes when the cornea
of either eye is touched.
 rooting reflex - Turning of an infant's head toward
anything that strokes the cheek or mouth.
 shivering - Shaking of the body in response to early
hypothermia in warm-blooded animals.
 vestibulo-ocular reflex - Movement of the eyes to the
right when the head is rotated to the left, and vice versa.
Neurons!
Synapse
Cell Body
Dendrite
Axon
Neuron
Structure
 Neurons - masses of nerve cells that transmit
information
 Each neuron is connected in long chains
 They don’t actually touch! Space between = synapse
 Cell Body - contains the nucleus and two extensions
 Dendrites – extend from the cell body and receive
information
 Axons - long section, transmits impulses
 Myelin - insulation surrounding axons
 Protects and speeds up signals – think like an insulated wire!
 Multiple sclerosis = degradation of myelin (immune)
 Nodes of Ranvier - gaps in the insulation
 Signals “jump” between nodes = super speedy!
Neuron
Structure
White vs. Grey matter
 White matter – myelinated axons
 Grey matter – unmyelinated
 Why might one be more myelinated
than the other?
Longevity – can live and function for a lifetime
Do not divide – fetal neurons lose their ability
to undergo mitosis; neural stem cells are an
exception
Neuron Facts!
High metabolic rate – require abundant
oxygen and glucose
The nerve fibers of newborns are unmyelinated
- this causes their responses to stimuli to be
coarse and sometimes involve the whole
body. Try surprising a baby!
Neurotransmitters
 To complete the signal, a
NEUROTRANSMITTER is
released at the gap to signal
the next neuron.
 Receptors on the dendrite
receive the chemical
message
Types of neurotransmitters
 Over 100 different kinds
 Acetylcholine - stimulates muscle
contraction
 Monoamines - Norepinephrine &
Dopamine (sense of feeling good,
low levels = depression)
 Serotonin - sleepiness and mood
 Endorphins - reduction of pain,
good mood
Neurotransmitters
Weak point of nervous system
Any substance that affects neurotransmitters
or mimics them affects nerve function
• gases: nitrous oxide, carbon monoxide
• mood altering drugs
• Stimulants: amphetamines, caffeine, nicotine
• Depressants: alcohol
• hallucinogenic drugs
• poisons
 Curare - poison made from frog skin and
causes paralysis by blocking Ach receptors at
the neuromuscular junction.
 Uses: indigenous weapons
 Botulinum toxin – produced by bacteria
Neurotoxins
Clostridium botulinum, inhibits Ach release.
“Food poisoning”
 Uses: BOTOX
Brain plasticity
 "I Listen to Color" - Neil Harbisson
Reflex activity!
 Pupillary Response Exercise
 Perform this exercise with a partner.
 Dim the room lights. After a few minutes, look at the eyes of your
partner and note the pupil sizes (the black center spots in the middle
of the eyes).
 Turn on the room lights. Check the pupil sizes again. The pupils should
now be smaller.
 This is called the pupillary reflex response. This reflex
“automatically” keeps out excessive light that may damage the eyes,
and thus protects your eyes for you!