Reflexes
1
Reflexes
Automatic responses
to stimuli
Visceral reflexes
Activate visceral
effectors
→ Smooth/cardiac
muscle
→ Glands
Somatic reflexes
Activate skeletal muscle
Reflexes
Intrinsic Reflex
Rapid,
predictable motor
esponse
Unlearned and
involuntary
Built into our
neural anatomy
Reflexes
Acquired Reflex
Reflexes
esulting from
practice or
epetition
Reflex Arc
Stimulus
Skin
Recepto
Sensory neuron
Integration cente
Motor neuron
Effecto
1
2
3
4
5
Interneuron
Spinal cord
(in cross scetion)
Reflex Arc
Recepto
Site of stimulus
Distal end of neuron
(Dendrites) or other
Sensory structure
Responds to a
specific stimulus by
producing a Graded
Potential
Reflex Arc
Sensory Neuron
Transmits afferent
impulses to CNS
Action Potential
travels along axon
to Gray Matter of
the spinal cord or
ainstem
2
Reflex Arc
Integration Cente
Point of connection
etween afferent
and efferent
pathways
Monosynaptic
→ Simplest
→ Sensory neuron
synapses with motor
neuron
Reflex Arc
Integration Cente
Point of connection
etween afferent
and efferent
pathways
Polysynaptic
→ Sensory neuron
synapses with at
least one interneuron
Reflex Arc
Motor Neuron
Conducts
efferent
impulses from
integration
center to
effector organ
Reflex Arc
Effecto
Responds to
efferent
impulse
Muscle fibers
contract
Glands secrete
Reflexes
Cranial Reflex
Integration
center resides
in the
ain
3
Reflexes
Spinal Reflexes
Integration center resides in the spinal cord
Spinal Reflexes
Integration center
esides in the
spinal cord
Effectors are
skeletal muscle
Important clinical
assessment tools
Spinal Reflexes
To smoothly coordinate skeletal
muscle nervous system must
eceive proprioceptor input
Length of muscle
→From muscle spindles
Amount of tension in muscle
→From tendon organs
Muscle Spindles
Proprioceptors
Composed of 3–
10 modified
skeletal muscle
fibers
wrapped in
connective tissue
capsule
Sensory
fibe
Tendon
Tendon organ
Capsule
(connective
tissue)
Muscle
spindle
Muscle Spindles
Bundles of
modified
skeletal muscle
fibers
Throughout
perimysium
Sensory
fibe
Tendon
Tendon organ
Capsule
(connective
tissue)
Muscle
spindle
Muscle Spindles
Noncontractile in
central regions
lack myofilaments
Stretch causes
increased rate of
impulses to spinal
cord
4
Muscle Spindles
Stimulus
Stretch causes
increased rate of
impulses to spinal
cord
Response
Contracting muscle
educes tension on
muscle spindle
How muscle stretch is detected
Muscle
spindle
Intrafusal
muscle fibe
Sensory
fibe
Extrafusal
muscle fibe
Time
Unstretched muscle.
Action potentials (APs)
are generated at a
constant rate in the
associated sensory fiber.
Muscle Spindles
Stimulus
Stretch causes
increased rate of
impulses to spinal
cord
Response
Contracting muscle
educes tension on
muscle spindle
How muscle stretch is detected
Stretched muscle.
Stretching activates the
muscle spindle, increasing
the rate of APs.
Time
Stretch Reflexes
How stretch reflex works
Stretch activates muscle spindle
Sensory neurons synapse directly with
motor neurons in spinal cord
motor neurons cause stretched muscle to
contract
All stretch reflexes are monosynaptic
Stretch Reflexes
Positive reflex reactions indicate
Sensory and motor connections between
muscle and spinal cord intact
Strength of response indicates degree of
spinal cord excitability
Hypoactive or absent if peripheral nerve
damage or ventral horn injury
Hyperactive if lesions of corticospinal
tract
Patellar ligament
Patella
Hamstrings
(flexors)
Muscle
spindle
Quadriceps
(extensors)
Spinal cord
(L2–L4)
Tapping the patellar ligament
stretches the quadriceps and
excites its muscle spindles.
The patellar (knee-jerk) reflex—an example of a stretch reflex
1
1
+
+
–
– Inhibitory synapse
+ Excitatory synapse
Patellar ligament
Patella
Hamstrings
(flexors)
Muscle
spindle
Quadriceps
(extensors)
Spinal cord
(L2–L4)
Tapping the patellar ligament
stretches the quadriceps and
excites its muscle spindles.
The patellar (knee-jerk) reflex—an example of a stretch reflex
1
2
1
+
+
–
2
– Inhibitory synapse
+ Excitatory synapse
Afferent impulses travel to the
spinal cord, where synapses occur
with motor neurons and
interneurons.
5
Patellar ligament
Patella
Hamstrings
(flexors)
Muscle
spindle
Quadriceps
(extensors)
Spinal cord
(L2–L4)
Tapping the patellar ligament
stretches the quadriceps and
excites its muscle spindles.
Afferent impulses (blue) travel to
the spinal cord, where synapses
occur with motor neurons and
interneurons.
The motor neurons send
activating impulses to the
quadriceps causing it to contract,
extending the knee.
The patellar (knee-jerk) reflex—an example of a stretch reflex
1
2
3a
1
+
+
–
2
3a
– Inhibitory synapse
+ Excitatory synapse
Patellar ligament
Patella
Hamstrings
(flexors)
Muscle
spindle
Quadriceps
(extensors)
Spinal cord
(L2–L4)
Tapping the patellar ligament
stretches the quadriceps and
excites its muscle spindles.
Afferent impulses (blue) travel to
the spinal cord, where synapses
occur with motor neurons and
interneurons.
The motor neurons (red) send
activating impulses to the
quadriceps causing it to contract,
extending the knee.
The interneurons make inhibitory
synapses with ventral horn neurons
that prevent the antagonist muscles
(hamstrings) from resisting the
contraction of the quadriceps.
The patellar (knee-jerk) reflex—an example of a stretch reflex
1
2
3a
3b 3
1
+
+
–
2
3a
3
– Inhibitory synapse
+ Excitatory synapse
Tendon Organs
Propriocepto
Located in tendons,
close to skeletal
muscle
Small bundles of
collagen fibers
Sensory terminals
coil between and
around collagen
Tendon Organs
Muscle contraction
stretches the tendon
fibers
Nerve fiber is
compressed
Reflex reaction is
triggered
→ Muscle relaxes
Quadriceps strongly contracts.
Tendon organs are activated.
Interneurons
Spinal cord
Quadriceps
(extensors)
Tendon organ
Hamstrings
(flexors)
+
+
+–
+ Excitatory synapse
– Inhibitory synapse
1 Quadriceps strongly contracts.
Tendon organs are activated.
Afferent fibers synapse with
interneurons in the spinal cord.
Interneurons
Spinal cord
Quadriceps
(extensors)
Tendon organ
Hamstrings
(flexors)
+
+
+–
+ Excitatory synapse
– Inhibitory synapse
21
6
Quadriceps strongly contracts.
Tendon organs are activated.
Afferent fibers synapse with
interneurons in the spinal cord.
Interneurons
Spinal cord
Quadriceps
(extensors)
Tendon organ
Hamstrings
(flexors)
Efferent
impulses to muscle
with stretched
tendon are damped.
Muscle relaxes,
educing tension.
+
+
+–
+ Excitatory synapse
– Inhibitory synapse
3a
21 Quadriceps strongly contracts.
Tendon organs are activated.
Afferent fibers synapse with
interneurons in the spinal cord.
Interneurons
Spinal cord
Quadriceps
(extensors)
Tendon organ
Hamstrings
(flexors)
Efferent
impulses to muscle
with stretched
tendon are damped.
Muscle relaxes,
educing tension.
Efferent impulses
to antagonist muscle
cause it to contract.
3
+
+
+–
+ Excitatory synapse
– Inhibitory synapse
3a
21
Flexor & Crossed-Extensor Reflexes
Flexor reflex
Initiated by painful
stimulus
Causes automatic
withdrawal of
threatened body part
Protective &
important
Brain can ove
ide
Flexor & Crossed-Extensor Reflexes
Crossed-Extensor reflex
Occurs with flexor
eflexes in weight-
earing limbs
maintains balance
+ Excitatory synapse
– Inhibitory synapse
Afferent
fibe
Efferent
fibers
Arm movements
Extenso
inhibited
Flexo
stimulated
Interneurons
Efferent
fibers
Flexo
inhibited
Extenso
stimulated
Site of reciprocal
activation: At the
same time, the
extensor muscles
on the opposite
side are activated.
Site of stimulus:
A noxious stimulus
causes a flexo
eflex on the same
side, withdrawing
that limb.
+
+
+
–
–
+
Autonomic Nervous System
Involuntary nervous
system
General visceral motor
system
Make adjustments to
ensure optimal
support for body
activities
Operate via
subconscious
control
7
Autonomic Nervous System
Involuntary nervous
system
General visceral motor
system
Consists of motor
neurons that
innervate smooth
and cardiac muscle,
and glands
Central nervous system (CNS) Peripheral nervous system (PNS)
Sensory (afferent)
division
Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Somatic versus Autonomic
Both have motor fibers
Differ in
Effectors
Efferent pathways and ganglia
Target organ responses to
neurotransmitters
Somatic Nervous System
Effecto
Skeletal muscle
Cell body in CNS
thick, myelinated
fiber extends in
spinal or cranial
nerve to skeletal
muscle
Somatic Nervous System
Somatic nervous system
All somatic motor neurons release
acetylcholine (ACh)
Effects always stimulatory
Cell bodies in central
nervous system Peripheral nervous system
Neurotransmitte
at effecto
Effecto
organs Effect
S
O
M
A
T
IC
N
E
R
V
O
U
S
S
Y
S
T
E
M
Single neuron from CNS to effector organs
ACh
Skeletal muscle
Stimulatory
+
Heavily myelinated axon
Autonomic Nervous System
ANS pathway uses two-neuron chain
1. Preganglionic neuron (in CNS) has a
thin, lightly myelinated preganglionic
axon.
2. Postganglionic (ganglionic) neuron in
autonomic ganglion outside CNS has
nonmyelinated postganglionic axon that
extends to effector organ
8
Autonomic Nervous System
Two-neuron chain from CNS to effector organs
Ganglion
Nonmyelinated
postganglionic axon
Epinephrine and
norepinephrine
Adrenal medulla Blood vessel
Ganglion
Nonmyelinated
postganglionic
axon ACh Smooth muscle
(e.g., in gut),
glands,
cardiac muscle
Stimulatory
or
inhibitory,
depending
on neuro-
transmitte
and
eceptors
on effecto
organs
NE
+ –
S
Y
M
P
A
T
H
E
T
I
C
P
A
R
A
S
Y
M
P
A
T
H
E
T
I
C
Divisions of the ANS
1. Sympathetic division
2. Parasympathetic division
Dual innervation
~ All visceral organs served by both divisions,
ut cause opposite effects
Dynamic antagonism between two
divisions maintains homeostasis
Parasympathetic Division
Rest & Digest
Blood pressure, heart
ate, and respiratory
ates are low
Gastrointestinal tract
activity high
Pupils constricted;
lenses accommodated
for close vision
Sympathetic Division
Fight or Flight
Exercise,
excitement,
emergency,
emba
assment
Increased heart
ate; dry mouth;
cold, sweaty skin;
dilated pupils
Sympathetic Division
Fight or Flight
During vigorous
physical activity
Shunts blood to
skeletal muscles and
heart
Dilates
onchioles
Causes liver to
elease glucose
9
Parasympathetic Sympathetic
Eye Eye
Salivary
glands
Brain stem
Cranial
Sympathetic
ganglia
Salivary
glands
Heart Cervical
Lungs
T1
Lungs
Heart
Stomach
Thoracic
PancreasStomach
Pancreas
Live
and gall-
ladderL1
Liver and
gall-
ladde
Lumba
Adrenal
gland
Bladder Bladde
Genitals Sacral Genitals
Skin*
Cranial part of Parasympathetic
Cell bodies in
ain
stem
Preganglionic fibers
in oculomotor, facial,
glossopharyngeal,
and vagus nerves
CN III
CN VII
CN IX
CN X
CN III
Ciliary
ganglion
Eye
Lacrimal
glandPterygo-
palatine
ganglion
Nasal
mucosa
Submandibula
ganglion
Submandibula
and sublingual
glandsOtic ganglion
Parotid gland
Heart
Cardiac
and
pulmonary
plexuses
Lung
CN VII
CN IX
CN X
Preganglionic
Postganglionic
CN Cranial nerve
S Sacral nerve
Cranial part of Parasympathetic
Ciliary Ganglia
Preganglionic axons
Within CN III
CN III
CN VII
CN IX
CN X
CN III
Ciliary
ganglion
Eye
Lacrimal
glandPterygo-
palatine
ganglion
Nasal
mucosa
Submandibula
ganglion
Submandibula
and sublingual
glandsOtic ganglion
Parotid gland
Heart
Cardiac
and
pulmonary
plexuses
Lung
CN VII
CN IX
CN X
Preganglionic
Postganglionic
CN Cranial nerve
S Sacral nerve
Cranial part of Parasympathetic
Ciliary Ganglia