Neural Integration I: Sensory Pathways and the Somatic Nervous System

Transcription

1 15 Neural Integration I: Sensory Pathways and the Somatic Nervous System PowerPoint Lecture Presentations prepared by Jason LaPres Lone Star College North Harris

2 An Introduction to Sensory Pathways and the Somatic Nervous System Learning Outcomes 15-1 Specify the components of the afferent and efferent divisions of the nervous system, and explain what is meant by the somatic nervous system Explain why receptors respond to specific stimuli, and how the organization of a receptor affects its sensitivity Identify the receptors for the general senses, and describe how they function.

3 An Introduction to Sensory Pathways and the Somatic Nervous System Learning Outcomes 15-4 Identify the major sensory pathways, and explain how it is possible to distinguish among sensations that originate in different areas of the body Describe the components, processes, and functions of the somatic motor pathways, and the levels of information processing involved in motor control.

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5 An Introduction to Sensory Pathways and the Somatic Nervous System An Introduction to: Sensory receptors Sensory processing Conscious and subconscious motor functions Focusing on the general senses

6 15-1 Sensory Information Afferent Division of the Nervous System Receptors Sensory neurons Classify Afferent and Efferent as output and input Sensory pathways Efferent Division of the Nervous System Nuclei Motor tracts Motor neurons

7 Figure 15-1 An Overview of Neural Integration OVERVIEW OF NEURAL INTEGRATION CHAPTER 15 CHAPTER 16 Sensory processing centers in brain Sensory pathways Conscious and subconscious motor centers in brain Motor pathways Higher-Order Functions Memory, learning, and intelligence may influence interpretation of sensory information and nature of motor activities Somatic Nervous System (SNS) Autonomic Nervous System (ANS) General sensory receptors Skeletal muscles Visceral effectors (examples: smooth muscles, glands, cardiac muscle, adipocytes)

8 15-1 Sensory Information Sensory Receptors Specialized cells that monitor specific conditions In the body or external environment When stimulated, a receptor passes information to the CNS In the form of action potentials along the axon of a sensory neuron

9 15-1 Sensory Information Sensory Pathways Deliver somatic and visceral sensory information to their final destinations inside the CNS using: Nerves Nuclei Tracts

10 15-1 Sensory Information Somatic Motor Portion of the Efferent Division Controls peripheral effectors Somatic Motor Commands Travel from motor centers in the brain along somatic motor pathways of: Motor nuclei Tracts Nerves

11 15-1 Sensory Information Somatic Nervous System (SNS) Motor neurons and pathways that control skeletal muscles

12 15-2 Sensory Receptors General Senses Describe our sensitivity to: Temperature Pain Touch Pressure Vibration Proprioception (sense of the relative position of parts of the body)

13 15-2 Sensory Receptors Sensation The arriving information from these senses Perception Conscious awareness of a sensation In order for a sensation to become a perception, it must received by the somatosensory cortex.

14 15-2 Sensory Receptors Special Senses Olfaction (smell) Vision (sight) Gustation (taste) Equilibrium (balance) Hearing

15 15-2 Sensory Receptors The Special Senses Are provided by special sensory receptors Special Sensory Receptors Are located in sense organs such as the eye or ear Are protected by surrounding tissues

16 Compare General Senses to Special Senses Think, pair, share!

17 General versus Special Senses The general senses describe our sensitivity to temperature, touch, pressure, vibration, pain and proprioception. They involve receptors that are relatively simple in structure and distributed throughout the body. The special senses include hearing, smell, taste, vision and balance (equilibrium). These sensations are provided by receptors that are structurally more complex than those of the general senses.

18 15-2 Sensory Receptors The Detection of Stimuli Receptor specificity Each receptor has a characteristic sensitivity Receptive field Area is monitored by a single receptor cell The larger the receptive field, the more difficult it is to localize a stimulus

19 Figure 15-2 Receptors and Receptive Fields Receptive field 1 Receptive field 2

20 15-2 Sensory Receptors The Interpretation of Sensory Information Arriving stimulus reaches cortical neurons Takes many forms (modalities) Physical force (such as pressure) Dissolved chemical Sound Light Examples of sensory stimuli include touch, warmth, pain, and vibration.

21 15-2 Sensory Receptors The Interpretation of Sensory Information Sensations Taste, hearing, equilibrium, and vision provided by specialized receptor cells Communicate with sensory neurons across chemical synapses

22 15-2 Sensory Receptors Adaptation Reduction in sensitivity of a constant stimulus Your nervous system quickly adapts to stimuli that are painless and constant

23 15-2 Sensory Receptors Adaptation Stimulation of a receptor produces action potentials Along the axon of a sensory neuron The frequency and pattern of action potentials contain 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

24 15-3 Classifying Sensory Receptors General Sensory Receptors Scattered throughout the body and are simple in structure. The simplest classification divides them into 1. exteroreceptors provide information about the external environment 2. proprioreceptors report positions of skeletal muscles and joints 3. interoceptors monitor visceral organs and functions.

25 15-3 Classifying Sensory Receptors General Sensory Receptors Can also be divided into four types by the nature of the stimulus that excites them 1. Nociceptors (pain) 2. Thermoreceptors (temperature) 3. Mechanoreceptors (physical distortion) 4. Chemoreceptors (chemical concentration)

26 15-3 Classifying Sensory Receptors Nociceptors (Pain Receptors) Are common In the superficial portions of the skin In joint capsules Within the periostea of bones Around the walls of blood vessels

27 15-3 Classifying Sensory Receptors Nociceptors May be sensitive to: 1. Temperature extremes 2. Mechanical damage 3. Dissolved chemicals, such as chemicals released by injured cells

28 15-3 Classifying Sensory Receptors Nociceptors Are free nerve endings with large receptive fields Branching tips of dendrites Not protected by accessory structures Can be stimulated by many different stimuli sensations of fast pain, or prickling pain, such as that caused by an injection or a deep cut sensations of slow pain, or burning and aching pain

29 15-3 Classifying Sensory Receptors Thermoreceptors Also called temperature receptors (cold receptors are structurally indistinguishable from warm receptors) Cold receptors outnumber warm receptors Are free nerve endings located in: The dermis Skeletal muscles The liver The hypothalamus

30 15-3 Classifying Sensory Receptors Thermoreceptors Temperature sensations Conducted along the same pathways that carry pain sensations Sent to: The reticular formation The thalamus The primary sensory cortex (to a lesser extent)

31 15-3 Classifying Sensory Receptors Mechanoreceptors Sensitive to stimuli that distort their plasma membranes Contain mechanically gated ion channels whose gates open or close in response to: Stretching Compression Twisting Other distortions of the membrane

32 15-3 Classifying Sensory Receptors Three Classes of Mechanoreceptors 1. Tactile receptors Provide the sensations of touch, pressure, and vibration Touch sensations provide information about shape or texture Pressure sensations indicate degree of mechanical distortion Vibration sensations indicate pulsing or oscillating pressure

33 15-3 Classifying Sensory Receptors Three Classes of Mechanoreceptors 2. Baroreceptors Detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts

34 15-3 Classifying Sensory Receptors Three Classes of Mechanoreceptors 3. Proprioceptors Monitor the positions of joints and muscles The most structurally and functionally complex of general sensory receptors

35 15-3 Classifying Sensory Receptors Chemoreceptors Respond only to water-soluble and lipid-soluble substances dissolved in surrounding fluid Receptors that monitor ph, carbon dioxide, and oxygen levels in arterial blood

36 Separate pathways carry somatic sensory and visceral sensory information Afferent Neurons sensory

37 15-4 Sensory Pathways First-Order Neuron Sensory neuron delivers sensations to the CNS Cell body of a first-order general sensory neuron is located in dorsal root ganglion or cranial nerve ganglion Second-Order Neuron Axon of the sensory neuron synapses on an interneuron in the CNS May be located in the spinal cord or brain stem

38 15-4 Sensory Pathways Third-Order Neuron If the sensation is to reach our awareness, the second-order neuron synapses On a third-order neuron in the thalamus

39 15-4 Sensory Pathways Somatic Sensory Pathways Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs Three major somatic sensory pathways 1. The spinothalamic pathway 2. The posterior column pathway 3. The spinocerebellar pathway

40 Figure 15-4 Sensory Pathways and Ascending Tracts in the Spinal Cord Dorsal root Posterior column pathway Fasciculus gracilis Fasciculus cuneatus Dorsal root ganglion Spinocerebellar tracts Posterior spinocerebellar tract Anterior spinocerebellar tract Ventral root Spinothalamic tracts Lateral spinothalamic tract Anterior spinothalamic tract

41 15-4 Sensory Pathways The Spinothalamic Pathway Provides conscious sensations of poorly localized ( crude ) touch, pressure, pain, and temperature First-order neurons Axons of first-order sensory neurons enter spinal cord And synapse on second-order neurons within posterior gray horns

42 15-4 Sensory Pathways The Spinothalamic Pathway Second-order neurons Cross to the opposite side of the spinal cord before ascending Ascend within the anterior or lateral spinothalamic tracts The anterior tracts carry crude touch and pressure sensations The lateral tracts carry pain and temperature sensations

43 15-4 Sensory Pathways The Spinothalamic Pathway Third-order neurons Synapse in the thalamus After the sensations have been sorted and processed, they are relayed to primary sensory cortex

44 Figure 15-5 Somatic Sensory Pathways SPINOTHALAMIC PATHWAY KEY Axon of firstorder neuron Second-order neuron Third-order neuron Third-order neurons synapse in the thalamus and after the sensations have been sorted and processed, they are relayed to primary sensory cortex Midbrain Axons of first-order sensory neurons enter spinal cord and synapse on secondorder neurons within The anterior spinothalamic tracts of the spinothalamic pathway carry crude touch and pressure sensations. Medulla oblongata Anterior spinothalamic tract Second-order neurons cross to the opposite side of the spinal cord before ascending (going up towards the brain) posterior gray horns Crude touch and pressure sensations from right side of body

45 15-4 Sensory Pathways Posterior Column Pathway Carries sensations of highly localized ( fine ) touch, pressure, vibration, and proprioception

46 15-4 Sensory Pathways The Spinocerebellar Pathway Cerebellum receives proprioceptive information about position of: Skeletal muscles Tendons Joints

47 15-4 Sensory Pathways Sensory Information Most somatic sensory information Is relayed to the thalamus for processing A small fraction of the arriving information Is projected to the cerebral cortex and reaches our awareness

48 15-4 Sensory Pathways Visceral Sensory Pathways Collected by interoceptors monitoring visceral tissues and organs, primarily within the thoracic and abdominopelvic cavities These interoceptors are not as numerous as in somatic tissues

49 15-4 Sensory Pathways Visceral Sensory Pathways Interoceptors include: Nociceptors Thermoreceptors Tactile receptors Baroreceptors Chemoreceptors

50 15-4 Sensory Pathways Visceral Sensory Pathways Cranial Nerves V, VII, IX, and X Carry visceral sensory information from mouth, palate, pharynx, larynx, trachea, esophagus, and associated vessels and glands

51 15-4 Sensory Pathways Visceral Sensory Pathways medulla oblongata Major processing and sorting center for visceral sensory information Extensive connections with the various cardiovascular and respiratory centers, reticular formation

52 15-5 Somatic Motor Pathways Efferent Neurons Motor Neurons The Somatic Nervous System (SNS) The Autonomic Nervous System (ANS)

53 15-5 Somatic Motor Pathways The Somatic Nervous System (SNS) Also called the somatic motor system Controls contractions of skeletal muscles (discussed next) The Autonomic Nervous System (ANS) Also called the visceral motor system Controls visceral effectors, such as smooth muscle, cardiac muscle, and glands (Ch. 16)

54 15-5 Somatic Motor Pathways Somatic Motor Pathways Always involve at least two motor neurons 1. Upper motor neuron 2. Lower motor neuron

55 15-5 Somatic Motor Pathways Upper Motor Neuron Cell body lies in a CNS processing center Synapses on the lower motor neuron Innervates a single motor unit in a skeletal muscle Activity in upper motor neuron may facilitate or inhibit lower motor neuron

56 15-5 Somatic Motor Pathways Lower Motor Neuron Cell body lies in a nucleus of the brain stem or spinal cord Triggers a contraction in innervated muscle Only axon of lower motor neuron extends outside CNS Destruction of or damage to lower motor neuron eliminates voluntary and reflex control over innervated motor unit

57 Figure 15-8 The Corticospinal Pathway KEY Axon of upper motor neuron Motor homunculus on primary motor cortex of left cerebral hemisphere Lower motor neuron To skeletal muscles To skeletal muscles Decussation of pyarmids Corticobulbar tract Motor nuclei of cranial nerves Motor nuclei of cranial nerves Cerebral peduncle Midbrain Medulla oblongata Pyramids Lateral corticospinal tract To skeletal muscles Anterior corticospinal tract Spinal cord

58 15-5 Somatic Motor Pathways Conscious and Subconscious Motor Commands Control skeletal muscles by traveling over three integrated motor pathways 1. Corticospinal pathway conscious motor control of skeletal muscles 2. Medial pathway subconscious regulation of balance and muscle tone subconscious regulation of eye, head, neck, and upper limb position in resonse to visual and auditory smell subconscious regulation of reflex activity 3. Lateral pathway subconscious regulation of upper limb muscle tone and movement

59 15-5 Somatic Motor Pathways Levels of Processing and Motor Control All sensory and motor pathways involve a series of synapses, one after the other General pattern Spinal and cranial reflexes provide rapid, involuntary, preprogrammed responses that preserve homeostasis over short term

60 15-5 Somatic Motor Pathways Levels of Processing and Motor Control Cranial and spinal reflexes Control the most basic motor activities