2. A few reminders!
The central grey matter contains the cell bodies of
relay and motor neurones.
The outer white matter contains myelinated axons,
which run up and down the spinal cord to and from
the brain.
In the centre of the grey matter is the spinal canal,
through which the nutritive cerebrospinal fluid
cirulates.
3. A few reminders!
Sensory neurones enter the spinal cord through the
dorsal root and the concentration of their cell bodies
forms a swelling called the dorsal root ganglion.
Motor neurones leave the spinal cord via the ventral
root.
4.
5. The Reflex Arc
An automatic, rapid response to an adverse stimulus.
Action is involuntary the brain is not involved in the
event but may be informed of it
Many reflex actions are protective
Some complex actions (swallowing, coughing and
blinking) are coordinated by reflexes.
6. Example of Neuronal Organization:
Reflexes
Reflex arcs – simple neural pathways
Responsible for reflexes
Rapid, autonomic motor responses
Can be visceral or somatic
7. Five Essential Components to the
Reflex Arc
Receptor – detects the stimulus
Afferent (sensory neuron) – transmits impulses to the
CNS
Integration center – consists of one or more
synapses in the CNS
Efferent (motor neuron) – conducts impulses from
integration center to an effector
Effector – muscle or gland cell
Responds to efferent impulses
Contraction or secretion
10. Types of Reflexes: Number of Classes
Monosynaptic reflex – simplest of all reflexes
Just one synapse
The fastest of all reflexes
Example – knee-jerk reflex
Polysynaptic reflex – more common type of reflex
Most have a single interneuron between the sensory
and motor neuron
Example – withdrawal reflexes
13. Spinal vs Cranial Reflexes
Spinal = spinal cord integration center
Ex. Knee-jerk reflex
Cranial = brain as integration center
Ex. Pupillary light reflex
14. Somatic vs Autonomic Reflexes
Somatic = motor neurons to skeletal muscles
Ex. Knee-jerk reflex
Autonomic = autonomic neurons to smooth muscle
and glands
Ex. Pupillary light reflex
15. Innate vs Learned Reflexes
Innate = born-with
Knee-jerk reflex, pupillary reflex
Learned = develops based on experiences
Pavlov’s dogs salivation in response to bell
18. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by receptors
in the dermis of the skin. Since these
sensory cells respond to temperature,
they are called thermoreceptors.
19. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve impulses
that pass to the spinal
cord along a sensory
neurone.
20. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve
impulses that pass
to the spinal cord
along a sensory
neurone.
sensory neurone cell
body
21. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve
impulses that pass
to the spinal cord
along a sensory
neurone.
sensory neurone
cell body
grey matter
(neurone
cell bodies)
22. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve
impulses that pass
to the spinal cord
along a sensory
neurone.
sensory neurone
cell body
grey matter (neurone
cell bodies)
spinal cord
23. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve
impulses that pass
to the spinal cord
along a sensory
neurone.
sensory neurone
cell body
grey matter (neurone
cell bodies)
spinal cord
white matter
(neurone
axons)
24. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve
impulses that pass
to the spinal cord
along a sensory
neurone.
sensory neurone
cell body
grey matter (neurone
cell bodies)
spinal cord
white matter (neurone
axons)
The sensory neurone enters the spinal
cord via the dorsal branch of the spinal
nerve and forms a synapse with a
relay neurone, inside the grey matter
25. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve
impulses that pass
to the spinal cord
along a sensory
neurone.
sensory neurone
cell body
grey matter (neurone
cell bodies)
spinal cord
white matter (neurone
axons)
The sensory neurone enters the spinal
cord via the dorsal branch of the spinal
nerve and forms a synapse with a
relay neurone, inside the grey matter
The short relay neurone
forms a synapse with a
motor neurone that
leaves the spinal cord via
the ventral root of the
spinal cord.
26. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by
receptors in the dermis of the
skin. Since these sensory cells
respond to temperature they are
called thermoreceptors.
The thermoreceptors
initiate nerve
impulses that pass
to the spinal cord
along a sensory
neurone.
sensory neurone
cell body
grey matter (neurone
cell bodies)
spinal cord
white matter (neurone
axons)
The sensory neurone enters the spinal
cord via the dorsal branch of the spinal
nerve and forms a synapse with a
relay neurone, inside the grey matter
The short relay
neurone forms a
synapse with a motor
neurone that leaves
the spinal cord via the
ventral root of the
spinal cord.
The motor neurone carries the
impulse to an effector, in this
case muscles in the arm,
which contract to withdraw the
hand from the hot object. This
action is known as the
response.
27. A withdrawal reflex
The stimulus is the heat
from the hot object
The stimulus is detected by receptors in
the dermis of the skin. Since these sensory
cells respond to temperature they are
called thermoreceptors.
The thermoreceptors initiate
nerve impulses that pass to the
spinal cord along a sensory
neurone.
sensory neurone
cell body
grey matter (neurone
cell bodies)
spinal cord
white matter (neurone
axons)
The sensory neurone enters the spinal
cord via the dorsal branch of the spinal
nerve and forms a synapse with a
relay neurone, inside the grey matter
The short relay neurone
forms a synapse with a
motor neurone that
leaves the spinal cord via
the ventral root of the
spinal cord.
The motor neurone carries the
impulse to an effector, in this case
muscles in the arm, which
contract to withdraw the hand
from the hot object. This action is
known as the response.
29. Other Reflexes
Stimulus Response
The aroma of your favorite
food
Salivation
A nasty odor Nausea
A bright light shining in your
eye
Pupils get smaller
An insect flying towards your
eye
Blinking
