Spinal reflexes 9-

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Spinal reflexes 9-

  1. 1. Spinal reflexes The reflex arc SMS 1084 Dr. Mohanad R. Alwan
  2. 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. 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. 4. 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.
  5. 5. Example of Neuronal Organization: Reflexes Reflex arcs – simple neural pathways Responsible for reflexes  Rapid, autonomic motor responses Can be visceral or somatic
  6. 6. 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
  7. 7. Example of the Five Components to the Reflex Arc
  8. 8. Reflex Classification Monosynaptic or polysynaptic Spinal or cranial Somatic or autonomic Innate or learned
  9. 9. 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
  10. 10. Monosynaptic Reflex
  11. 11. Polysynaptic Reflex
  12. 12. Spinal vs Cranial Reflexes Spinal = spinal cord integration center Ex. Knee-jerk reflex Cranial = brain as integration center Ex. Pupillary light reflex
  13. 13. 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
  14. 14. 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
  15. 15. A withdrawal reflex
  16. 16. A withdrawal reflex The stimulus is the heat from the hot object
  17. 17. 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.
  18. 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. The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory neurone.
  19. 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. sensory neurone cell body
  20. 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 grey matter (neurone cell bodies)
  21. 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) spinal cord
  22. 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 white matter (neurone axons)
  23. 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) 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
  24. 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 The short relay neurone forms a synapse with a motor neurone that leaves the spinal cord via the ventral root of the spinal cord.
  25. 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. 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.
  26. 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. 27. Review of reflex arc.
  28. 28. 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

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