Nervous system, reflexes
and reaction time
◼ Reflexes
◼ Voluntary action
◼ Autonomous reflex
Nervous system
Central NS – brain, spinal cord
Peripheral NS – spinocerebral nerves
◼ Somatic NS
 somatic sensory and somatic motor
system; somatic reflexes
 Affects skeletal muscle tissue
◼ Autonomic NS
 Involuntary; visceral reflexes
 sympaticus/parasympaticus
 Viscelar system: affects cardiac
muscle, smooth muscles, exocrine
glands
Reflexes
A reflex, or reflex action, is an involuntary and nearly
instantaneous movement in response to stimulus
◼ Fast, stereotypic, automatic reaction of NS, without direct
involvement of the brain
Reflex arc:
1. Somatic receptor (e.g. heat receptor or
muscle spindle = stretch receptors of
muscles)
2. Afferent nerve fibers (muscles → dorsal
horn of the spinal cord)
3. Integrating center (gray matter of the
spinal cord or brainstem)
4. Efferent nerve fibres (ventral horn of the
spinal cord → muscles)
5. Effector (e.g. Neuromuscular junction of
skeletal muscle)
Reflexes
◼ Innate lifelong reflexes - an automatic
instinctive unlearned reaction to a stimulus
 protective reflexes – sneezing, coughing,
corneal, pharyngeal, blink, withdrawal reflex,...
 Posture reflexes – tendon reflexes (patellar
reflex), stretch reflexes, ...
◼ Special infant reflexes – crawl, grasp, suck,
moro, ... video
◼ Conditional reflexes – type of a learning
procedure in which a biologically potent
stimulus (e.g. food) is paired with a previously
neutral stimulus (e.g. a bell); temporary
 I. P. Pavlov – dogs: sallivation + sound
 Taste aversion (nausea + food)
Taste aversion
Somatic (motoric) control system
◼ 1. Reflexes
 Maintaining posture and balance by
muscle tone
 Myotatic reflexes – strecth reflexes,
tendon reflexes (e.g. knee jerk reflex)
 Association with cerebellum, inner ear
 Reaction time 20 – 40 msec
◼ 2. Voluntary action and motorics
 Somatic system of voluntary action
 Cerebral cortex, basal ganglia and other
centres
skeletal muscles control - CNS + peripheral nerves;
cooperation and coordination (↑↑ chemical
synapses)
◼ Exteroreceptor → Sensoric pathway → brain processing
through the sensoric centre of the brain and motoric centre of
the brain → motoric pathway → muscles
◼ Reaction time of voluntary action ≥100ms
Voluntary action
Experiment 1 - Reaction time comparison
 Electrodes on the calf muscle, special hammer,
software
 Monosynaptic reflex (achilles reflex) - tap on
Achilles tendon with special hammer → reflexive
calf muscle locomotion
A sudden stretch, tapping the Achilles' tendon, causes a reflex
contraction in the muscle as the spindles sense the stretch and send
an action potential to the motor neurons which then cause the
muscle to contract; this particular reflex causes a contraction in the
group of muscles.
T = 20-40ms
 Voluntary action – voluntary locomotion of calf
muscle after the tap of hammer on shoulder
T ≥ 100ms
Web task reaction time or here
Experiment 2
Reaction time of voluntary action
Autonomous reflexes
 Visceral, involuntary
 Under the control of hypothalamus
 Sympaticus + parasympaticus
 Connection with limbic system and amygdala –
emotions: breath frequency, heart beat, sweating,
salivating, ...
 Much slower than motoric reflexes
◼ Crucial for smooth muscle, glands and heart
functions
Rest & digest systemFight-or-flight reaction antagonists
Polygraph (lie
detector test)
◼ Stress caused by lying → cerebral cortex + hypothalamus
+ limbic system → sympaticus → hand sweating (etc.)
→ higher conductivity → higher graph amplitude on
record
◼ In most European jurisdictions, polygraphs are generally
not considered reliable evidence and are not generally
used by law enforcement.
EXPERIMENT 3
Polygraph experiment
1. Put the electrodes on palms (do not moisture),
keep eyes closed, keep calm and think about
one particular number from 1 to 5
2. Audience question about numbers in random
order
3. After being asked, say No to every single
question
Do not forget: Autonomous reflexes are
much slower, therefore be patient about
physiological response