1. Spinal reflexes
The reflex arc

2. 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.

3. A simplified reflex arc
stimulus

4. A simplified reflex arc
stimulus
receptor

5. A simplified reflex arc
stimulus
sensory neurone
receptor

6. A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system

7. A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone

8. A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone
motor neurone

9. A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone
effector
motor neurone

10. A simplified reflex arc
stimulus
sensory neurone
receptor
spinal cord of central nervous system
relay neurone
effector
response
motor neurone

11. A withdrawal reflex

12. A withdrawal reflex
The stimulus is the heat from the hot object

13. 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

14. 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 sensory neurone cell body
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 grey matter (neurone cell bodies)
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 spinal cord
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 white matter (neurone axons)
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

23. 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.

24. 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.