Spinal reflexes

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Spinal reflexes

• The reflex arc

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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.

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A simplified reflex arc
stimulus
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A simplified reflex arc
stimulus
receptor
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A simplified reflex arc
stimulus
sensory neurone
receptor
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A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
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A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone
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A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone
motor neurone
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A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone
effector
motor neurone
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A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone
effector
response
motor neurone
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A withdrawal reflex
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A withdrawal reflex
The stimulus is the heat from the hot object
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A withdrawal reflex
The stimulus is detected by receptors in the
dermis of the skin. Since these sensory cells
respond to temperature, they are called
thermoreceptors.
The stimulus is the heat from the hot object
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A withdrawal reflex
The thermoreceptors initiate nerve impulses that
pass to the spinal cord along a sensory neurone.
The stimulus is detected by receptors in the
dermis of the skin. Since these sensory cells
respond to temperature they are called
thermoreceptors.
The stimulus is the heat from the hot object
15
A withdrawal reflex
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
The stimulus is the heat from the hot object
16
A withdrawal reflex
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.
grey matter (neurone cell bodies)
sensory neurone cell body
The stimulus is the heat from the hot object
17
A withdrawal reflex
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.
grey matter (neurone cell bodies)
sensory neurone cell body
The stimulus is the heat from the hot object
spinal cord
18
A withdrawal reflex
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.
grey matter (neurone cell bodies)
sensory neurone cell body
The stimulus is the heat from the hot object
spinal cord
white matter (neurone axons)
19
A withdrawal reflex
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.
grey matter (neurone cell bodies)
sensory neurone cell body
The stimulus is the heat from the hot object
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
20
A withdrawal reflex
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.
grey matter (neurone cell bodies)
sensory neurone cell body
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 stimulus is the heat from the hot object
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
21
A withdrawal reflex
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.
grey matter (neurone cell bodies)
sensory neurone cell body
The stimulus is the heat from the hot object
The short relay neurone forms a synapse with a
motor neurone that leaves the spinal cord via
the ventral root of the spinal cord.
spinal cord
white matter (neurone axons)
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.
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
22
A withdrawal reflex
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.
grey matter (neurone cell bodies)
sensory neurone cell body
The stimulus is the heat from the hot object
The short relay neurone forms a synapse with a
motor neurone that leaves the spinal cord via
the ventral root of the spinal cord.
spinal cord
white matter (neurone axons)
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.
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
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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 circulates.

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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.