Chapter 15: Neural Integration I: Sensory Pathways and the Somatic Nervous System

1. Chapter 15: Neural Integration I: Sensory Pathways and the Somatic Nervous System

2. Neural Integration

3. Afferent Division of the Nervous System • Receptors • Sensory neurons • Sensory pathways

4. Afferent Division • Sensory receptors  sensory pathway  • Somatic Sensory info • Sensory cortex of cerebrum • Cerebellum • Visceral Sensory info • Reflex centers in brainstem • Reflex centers in diencephalon

5. Sensory Receptors • Specialized cells that monitor specific conditions in the body or external environment • General Senses: • Temp, pain, touch, pressure, vibration, proprioception • Simple receptors located anywhere on body • Special Senses: • Are located in sense organs such as the eye or ear • Olfaction, vision, gustation, hearing, equilibrium • Complex receptors located in specialized sense organs

6. Sensory Receptors • Sensation – the sense info; action potentials • Taste, hearing, equilibrium, and vision provided by specialized receptor cells • Communicate with sensory neurons across chemical synapses • Perception – conscious awareness of sensation

7. Sensory Receptors • Transduction – conversion of environmental stimulus into action potential by sensory receptor • Action potential: • When stimulated, a receptor passes information to the CNS in the form of action potentials along the axon of a sensory neuron • Receptors specific for particular type of stimulus • Specificity is due to structure of receptor • Simplest receptors are dendrites (free nerve endings), least specific

8. Free Nerve Endings • Branching tips of dendrites • Not protected by accessory structures • Can be stimulated by many different stimuli

9. Sensory Receptors • Receptive field • area monitored by single receptor (e.g. touch: arm vs. fingertip) • Area is monitored by a single receptor cell • The larger the receptive field, the more difficult it is to localize a stimulus

10. Sensory Receptors • Labeled line • Link between receptor and processing site in CNS • Stimulation anywhere on labeled line will produce the same perception (e.g. phantom limb) • Stimulus -> receptor -> transduction -> action potential -> sensation ->-> CNS perception

11. Sensory Pathways • Deliver somatic and visceral sensory information to their final destinations inside the CNS using: • nerves • nuclei • tracts

12. Sensory Receptors • Tonic Receptors: • Always active • Signal at different rate when stimulated • Monitor background levels • Phasic Receptors: • Activated by stimulus • Become active for a short time whenever a change occurs • Monitor intensity and rate of change of stimulus

13. Sensory Receptors • Adaptation • Reduced sensitivity to a constant stimulus • Peripheral Adaptation: • Reduction in receptor activity • Phasic fast adapting • Tonic  slow or non adapting • Remind you of an injury long after the initial damage has occurred • Central Adaptation: • Inhibition of nuclei along labeled line • Not all pathways will adapt

14. Four types of General Sensory Receptors • Pain: nociceptor • Temperature: thermoreceptor • Physical: mechanoreceptor • Chemicals: chemoreceptors • All can be found in both somatic (exteroceptors) and visceral (interoceptors) locations except: • Proprioceptors (a mechanoreceptor) are somatic only • report the positions of skeletal muscles and joints

15. 1. Pain Receptors: Nociceptors • Detect Pain • Are common in the: • superficial portions of the skin • joint capsules • within the periosteum of bones • around the walls of blood vessels • Rare in deep tissue and visceral organs • Consist of free nerve endings with large receptor fields Figure 15–2

16. 1. Pain Receptors: Nociceptors • Mode of Action: • Injured cells release arachidonic acid • Arachidonic acid is converted into prostaglandins by the interstitial enzyme cyclo-oxygenase • Prostaglandins activate nociceptors • Many pain medications like aspirin function to inhibit cyclo-oxygenase

17. 1. Pain Receptors: Nociceptors • Once transduced pain sensations are carried on either type A and type C fibers/axons: • Type A: • Fast pain; stab or cut; triggers defensive reflexes • Type C: • Slow pain; aching pain • Tonic receptors with no peripheral adaptation • Pain levels are modulated by endorphins which inhibit CNS function

18. 2. Thermoreceptors • Detect temperature • Found in skin, skeletal muscle, liver, and hypothalamus • Consist of free nerve endings • Phasic receptors that adapt easily

19. 3. Mechanoreceptors **Detect membrane distortion Three receptor types: • Tactile Receptors • Proprioceptors • Baroreceptors

20. 3. Mechanoreceptors • Tactile Receptors • Detect touch, pressure and vibration on skin • Free nerve endings • Detect touch on skin • Tonic receptors with small receptor fields • Root hair plexus nerve endings • Detect hair movement • Phasic receptors, adapt rapidly • Tactile discs/Merkel’s discs • Detect fine touch • Extremely sensitive • Whole cell tonic receptors

21. 3. Mechanoreceptors • Tactile Receptors • Tactile corpuscles/Meissner’s corpuscles • Detect fine touch and vibration • Larger receptor structure • Phasic receptors, adapt rapidly • Lamellated corpuscles/Pacinian corpuscles • Detect deep pressure • Larger multi-layer receptors • Phasic receptor, adapt rapidly • Ruffini corpuscles • Detect pressure and distortion • Large tonic receptors, no adaptation

23. 3. Mechanoreceptors • Proprioceptors: • Detect positions of joints and muscles • Tonic receptors, do not adapt, complex • Muscle spindles • Modified skeletal muscle cell • Monitor skeletal muscle length • Golgi tendon organs • Dendrites around collagen fibers at the muscle-tendon junction • Monitor skeletal muscle tension • Joint capsule receptors - Monitor pressure, tension and movement in the joint

25. 3. Mechanoreceptors • Baroreceptors • Detect pressure changes • Found in elastic tissue of blood vessels and organs of digestive, reproductive and urinary tracts • Consists of free nerve endings • Phasic receptors, adapt rapidly

27. 4. Chemoreceptors • Detect change in concentration of specific chemicals or compounds • E.g. pH, CO2 • Found in respiratory centers of the brain and in large arteries • Phasic receptors, adapt rapidly

29. KEY CONCEPT • Stimulation of a receptor produces action potentials along the axon of a sensory neuron • The frequency and pattern of action potentials contains information about the strength, duration, and variation of the stimulus • Your perception of the nature of that stimulus depends on the path it takes inside the CNS

30. Somatic Sensory Pathways • Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs

31. Somatic Sensory Pathways • Consist of two or three neurons: • First Order Neuron: • Sensory neuron • Connects from receptor to CNS • Cell body is in dorsal root ganglion/cranial nerve ganglion • Second Order Neuron: • Interneuron (stimulated by first order) • Located in spinal cord or brain stem • Subconscious processing of info • Third Order Neuron: • Located in thalamus • Relays info to primary somatosensory cortex of cerebrum for conscious awareness (perception)

32. Only ~1% of somatic sensory info reaches cerebrum (major changes only, “background” in filtered) • LSD interferes with sensory damping/filtering = sensory overload • All sensory info undergoes decussation in spine before reaching target in CNS

33. 3 Major Somatic Sensory Pathways Figure 15–4

34. Posterior Column Pathway • Carries sensations of highly localized (“fine”) touch, pressure, vibration, and proprioception Figure 15–5a

35. Visceral Sensory Pathways • Interoceptors transmit info to solitary nucleus of medulla oblongata for relay to visceral centers in brainstem and diencephalon • No perception • Two neurons: 1st and 2nd order

36. Efferent Division • Conscious and subconscious motor centers in brain -> motor pathways -> • Somatic Nervous System  skeletal muscle • Autonomic Nervous System  visceral effectors - Smooth and cardiac muscle, glands, and adipose

37. Somatic Nervous System • Motor control of skeletal muscle • Consists of two neurons: • Upper motor neuron • Has soma in CNS processing center: • Primary motor cortex of cerebrum - voluntary control • Cerebrum, diencephalon, and brain stem - subconscious control:reflex • Basal nuclei of cerebrum and cerebellum - coordination, balance, fine tuning • Lower motor neuron • Soma in brain stem or spinal cord • Links to skeletal muscle motor unit

38. Motor Homunculus

39. Sensory HomunculusFunctional map of the primary sensory cortex Figure 15–5a, b

40. Processing in the Thalamus • Determines whether you perceive a given sensation as fine touch, as pressure, or as vibration

41. Motor Related Disorder • Parkinson’s Disease • Jittery movements: lack of fine tuning of motor • Results from degeneration of dopamine neurons of substantia nigra • Inhibits basal nuclei • Overactive basal nuclei = “ticks” • Amylotrophic Lateral Sclerosis • Degeneration of motor neurons in CNS • Causes muscle atrophy and death

42. Motor Related Disorder 3. Epilepsy • 1/25 people • Wide range in condition: • Absence seizures (blank) to grand mal seizures (convulsions, unconscious) • Uncontrolled/chaotic neuron activity in brain: blocks normal messages

43. When the nociceptors in your hand are stimulated, what sensation do you perceive? • pain • heat • vibration • pressure

44. What would happen to you if the information from proprioceptors in your legs were blocked from reaching the CNS? • no pain sensations from the legs • uncontrolled blood pressure in the legs • uncoordinated movements and inability to walk • no tactile sensations in the legs

45. Chapter 16: Neural Integration II: The Autonomic Nervous System and Higher-Order Functions

47. Autonomic Nervous System(ANS) • Operates without conscious instruction • Coordinates systems functions: • cardiovascular • respiratory • digestive • urinary • reproductive

48. Autonomic Nervous System • Motor control of visceral effectors • Involves three neurons: • Visceral motor nuclei in hypothalamus to autonomic nuclei in CNS • Autonomic nuclei to autonomic ganglia in PNS • Autonomic ganglia to visceral effector **Nuclei = in CNS, a center with a visible boundary **Ganglia = in PNS, collection of somas together in one place

49. Autonomic Nervous System

50. Two subdivisions • Sympathetic: “fight or flight” • Parasympathetic: “rest and digest” • Typically oppose each other on same effector • Some effectors innervated by only one: • Blood vessels/sweat glands –> sympathetic only • Smooth muscle of eye –> parasympathetic only