Transcript PowerPoint to accompany Hole`s Human Anatomy and Physiology

Learning Targets
Reflex Arc Lab
1-Diagram and label the path of each nerve impulse in the
reflex arc tested from sensation to response
( pupil, deep tendon, gag, eye blink, accommodation, and
plantar reflexes)
2-Reason and record (then research) the purpose for each
reflex- why does this particular reflex happen?
3-Observe, record and compare typical human reaction
times.
1
Reflex Arcs
• Reflexes are automatic, subconscious responses to stimuli within
or outside the body
• Simple reflex arc (sensory – motor)
• Most common reflex arc (sensory – association – motor)
2-neuron vs. 3-neuron reflex arc
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Sensory or
afferent neuron
Receptor
Central
Nervous
System
Motor or
efferent neuron
Effector
(muscle or gland)
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2
(a)
Reflex Arcs
3
General Components of a
Spinal Reflex
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Spinal cord
Interneuron
Dorsal
1
Receptor
3
2
Sensory neuron
Cell body
of sensory
neuron
White matter
Gray matter
4
Ventral
Motor neuron
Central
canal
5
Effector
(muscle
or gland)
(b)
4
Patellar Reflex
• Example is the knee-jerk reflex
• Simple monosynaptic reflex
• Helps maintain an upright posture & prevents overstretching
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Axon of sensory
neuron
Cell body of
sensory neuron
Spinal cord
Cell body of
motor neuron
Axon of motor
neuron
Direction of impulse
Effector (quadriceps femoris
muscle group)
Receptor associated with
dendrites of sensory neuron
Patella
Patellar ligament
5
Withdrawal Reflex
• Prevents or limits tissue damage
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cell body of sensory neuron
Axon of sensory neuron
Direction
of impulse
Dendrite of
sensory
neuron
Pain
receptor
in skin
Tack
Effector (flexor
muscle contracts
and withdraws part
being stimulated)
Interneuron
Axon of
motor neuron
Spinal cord
Cell body of
motor neuron
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Crossed Extensor Reflex
•Contralateral reflex
•Maintain balance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Interneuron
+
= Stimulation
–
= Inhibition
–
+
–
Sensory neuron
Extensor
relaxes
+
Extensor
contracts
Flexor
relaxes
Motor
neurons
Motor
neurons
Flexor contracts
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7
Some Additional Human Reflexes

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 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.
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Nervous Impulse Pathway
in a Reflex Arc
Nervous Impulse Pathway
in a Reflex Arc
Interneuron/Association Neurons



These neurons are
the vital part of the
reflex arc
They connect the
Sensory neuron to the
Motor/Effector neuron
They can be found in
the grey matter of the
spinal cord and in the
midbrain
Advantage of Reflexes


The reflex arc allows
a much quicker
response to stimuli
This is especially
important where the
stimuli is a source of
potential damage e.g.
a hot object, a sharp
pin
Inhibition of the Reflex Response
The reflex response is considerably
inhibited in several situations:
 Exposure to Noradrenalin
(Parasympathetic nervous system)
 Tiredness
 High Blood Alcohol
 Effect from Sedative Drugs (e.g.
Cannabis)

Stimulation of the Reflex Response
The speed of the reflex response can be
increase by several factors:
 Exposure to adrenaline (Sympathetic
Nervous System)
 Exposure to stimulant drugs (Caffeine,
Beta Amphetamines/Speed)

The Pupil Reflex Response
The pupil response allows the iris to
contract and dilate
 This changes the size of the pupil
 In the eye the pupil acts like an aperture
 It controls the amount of light which enters
the eye..
 … and protect the retina from
“overexposure”

Bright Light, Bright Light



When light levels are
high Circular
muscles in the iris
contract
This causes the pupil
to become smaller
This is controlled by
the parasympathetic
nervous system
In the Dark…



When light levels are
low Radial muscles
contract
This causes the pupil
to increase in size
This is caused by the
sympathetic nervous
system
Diagram of Pupil Response
Control of the Pupil Reflex: In Detail
When high levels of light strike
photoreceptors in the retina they cause
nervous impulses to be sent along the
Sensory neuron (Optic Nerve)
 These impulses are co-ordinated by relay
neurons in the Midbrain
 Signals are then sent along the
parasympathetic nervous system

Diagram of the Pupil
Reflex Arc
Atropine
Atropine is a sedative drug made from the
deadly nightshade plant (Atropa
belladonna)
 It was apparently used in the middles ages
by women to dilate there pupils
 This is the source of the word belladonna
in Latin and Belle in French

What are all the components that make a reflex happen?
stimulus  sensor
touch
 coordinator
 effector  response
 pain receptor  nervous system  muscle  movement
Looking at this sequence of steps, this is what happens when something sharp
touches you on your hand: The stimulus is touch, your pain receptor is the
sensor that senses it and relays it to the nervous system (spinal cord and brain)
which is the coordinator. The coordinator makes the decision of how to react,
and then commands the hand muscles (effector) to move the hand away
(response). Thus, we go from stimulus (touch) to response (hand movement).
Assignment during lab: Sketch out how the stimulus to response sequence for
each of the reflexes tested. Identify all the components as in the example
above.
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Reaction Times & Response Times

The time taken to respond to stimulus is the response time.
Response time = reaction time + movement time

Reaction time depends on the stimulus type:
* auditory ~ 150 ms
* visual ~ 200 ms
* touch ~ 700 ms

Movement time varies considerably,
and is dependent on age, fitness etc.

Given these variables, the time to respond (aka the
response time) to a stimulus varies among people.
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24
CN I
Olfactory
CN II
CN III
Optic
Occulomotor
Olfactory
epithelium
Retina
Midbrain
CN IV
Trochlear
Midbrain
CN V
Trigeminal
Pons
CN VI
Abducens
Pons
CN VII
Facial
Pons
CN VIII
CN IX
Vestibulocochlear
Glossopharyngeal
Pons
Medulla
CN X
Vagus
Medulla
CN XI
Accessory
Medulla
CN XII
Hypoglossal
Medulla
Smell
Vision
Eye movement;
accommodation
Eye movement
(superior oblique)
Sensation to face;
chewing
Eye movement
( lateral rectus)
Facial expression;
taste to anterior
2/3 of tongue
Hearing & balance
Salivation;
swallowing; taste
to posterior 1/3 of
tongue
Digestion; taste to
pharynx
Movement of
trapezius & SCM
Movement of
tongue
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