Principles of Anatomy and Physiology

Sensory, Motor, and Integrative Systems CHAPTER 16 Introduction Now that you know the organization of the NS we can explore sensation along with somatic sensory and motor pathways. Not every stimulation elicits a response thus many stimuli, along with stored information are integrated. Two complex integrative functions:

Wakefulness Learning and sleep and memory Sensation Recepto r Nerve Impulse s Spinal Cord Brain Stem Cerebral Cortex Sensor

y Info CN S Reflexes Complex Autonomic Reflexes Aware of stimuli (pain, hearing, taste etc) Sensation Conscious or subconscious awareness of environmental (int or ext) changes. Perception: conscious interpretation

of sensation If sensory info doesnt reach the cerebral cortex = no perception (BP) Sensory Modality = each unique type of sensation (ex. Retina, cochlea) Senses 5 basic In anatomy perceived senses

are: General: visceral Special Somatic vs Process of Sensation Stimulation 1. Stimulus in receptive field Transduction 2.

Transduce stimulus to graded potential Conduction 3. GP threshold nerve impulse conducted Translation 4. CNS translates impulse into sensation Graded Potential vs. Action Potential Graded

Vary in magnitude Vary in duration Decay with distance Dendrites and cell body (direction can vary) Variety of ion channels open and close to create potential No refractory period Generator potential Create an action potential Receptor potentials neurotransmitter release

Action All or none principle Same duration Long distances Axons (hillock one way direction) Voltage-gated ion channels cause potential Absolute or relative refractory periods possible Graded Potential Types of Sensory Receptors

Microscopic Structure Free nerve endings Encapsulated nerve endings Separate cells Location Exteroceptors Interoceptors Proprioceptors Type of Stimulus Mechanoreceptors Thermoreceptors Nociceptors Photoreceptors Chemoreceptors Osmoreceptors Adaptation in Sensory Receptors Rapidly adapting receptors Slowly

adapting receptors Somatic Sensations 1. Tactile Sensations 2. Thermal Sensations 3. Proprioceptive Sensations 4. Pain Sensations Fig. 16.2 Tactile and Thermal Sensations

Fig. 16.4 Proprioceptiv e Sensations: muscle spindle and tendon organ Proprioception Kinesthesia Perception Weight of motion Discrimination Ability

to assess object weight Stereognosis Perception Usually of 3D depth perception of solid objects by touch Pain Sensations Protective Nociceptors Many stimuli (pressure, temp, chem ex. Histamine, bradykinin) Slowly

2 adapting major Sensory pathways Fast, slow, referred Fig. 16.3 Distribution of referred pain Somatic Sensory Pathways Relay sensory info from somatic receptors primary somatosensory area of cerebral cortex and cerebellum

Key Characteristics: Decussation Relay Sensory pathways cerebral cortex contain thousands of sets of 3 neurons First-order neuron Second-order Third-order Symmetry Somatotopy neuron neuron

Spinal Cord Review Note that the illustration does not demonstrate symmetry: only right-sided sensory pathways and left-sided motor pathways are depicted. Table 16.3: Major Somatic Sensory Tracts and Pathways RIGHT SIDE OF BODY Posterior columnmedial lemniscus

Primary pathway somatosensory area of cerebral THIRD-ORDER cortex NEURONS Thalamu s Medial lemniscus Gracile nucleus Cuneate nucleus FIRST-ORDER SECOND-ORDER NEURONS

Midbrain NEURONS Posterior root ganglion Receptors for touch and proprioception in the upper limbs, upper trunk, neck, and posterior head Medulla POSTERIOR COLUMN: Gracile fasciculus Cuneate fasciculus Cervical spinal cord Lumbar spinal cord Spinal nerve

Receptors for touch and proprioception in the lower limbs and lower trunk LEFT SIDE OF BODY RIGHT SIDE OF BODY Anterolateral (spinothalamic) pathways Primary somatosensory area of cerebral cortex THIRD-ORDER

NEURON Thalamus Midbrain FIRST-ORDER NEURON Posterior root ganglion Receptors for pain, temp, itch from limbs, trunk, neck and posterior head LEFT SIDE OF BODY Medulla SECOND-ORDER NEURON Posterior gray horn

LATERAL SPINOTHALAMIC TRACT Spinal nerve Spinal cord ANTERIOR SPINOTHALAMIC TRACT Sensations carried Beginning of pathway End of pathway # neurons in pathway Neuron crosses over Crossover location Axon

Cell body Axon Cell body Posterior Column-Medial Spinothalamic Pathway Lemniscus Pathway Pressure, vibration, touch, Pain, temperature, itch, conscious proprioception tickle Sensory receptors in: Limbs, trunk, neck, posterior head Cerebral cortex 3 Second-order neuron Medulla oblongata Spinal cord First order neuron Posterior column of spinal cord Posterior gray horn SC

Posterior root ganglion of spinal nerve Second order neuron Gracile fasiculus Gray commissure ventral posterior nucleus of thalamus Gracile nucleus or cuneate Posterior gray horn of nucleus of medulla oblongata spinal cord RIGHT SIDE OF BODY Trigenminothalamic pathways LEFT SIDE OF BODY Primary somatosensory

area of cerebral THIRD-ORDER cortex NEURON Thalamus SECOND-ORDER NEURON FIRST-ORDER NEURON Receptors for touch, pain, and temperature in the face, nasal cavity, oral cavity, and teeth Midbrain Pons Medulla

TRIGEMINOTHALAMIC TRACT Trigeminal ganglion Trigeminal (V) nerve SECOND-ORDER NEURON Homunculus Mapping the Primary Somatosensory Area Primary somatosenso ry area Primary motor area Somatic Motor Pathways Conduct

motor information from cerebral cortex and brain stem to skeletal muscle. Key Characteristics: Decussation Relay. The pathways consist of a chain of 2 neurons Upper motor neurons. Direct somatic motor pathways

Indirect Lower somatic motor pathways motor neurons. Synapse Symmetry Somatotopy with skeletal muscles Somatic motor pathways coordination and control of LMNs receive input mvmt

directly from: 1. Local circuit neurons (purple) 2. UMNs in the cerebral cortex and brain stem (green) Neural circuits involving basal nuclei and cerebellar neurons (3 & 4) regulate activity of upper

motor neurons (red) RIGHT SIDE OF BODY LEFT SIDE OF BODY Primary motor area of cerebral cortex Internal capsule The lateral corticospina l pathway Midbrain Cerebral peduncle UPPER MOTOR

NEURON Pons Medulla Pyramid Decussation (crossing) in medulla LATERAL CORTICOSPINAL TRACT Spinal cord Spinal nerve Spinal cord LOWER MOTOR NEURON To skeletal muscles in the distal parts of the limbs (voluntary mvmt of limbs and trunk) RIGHT SIDE OF BODY

LEFT SIDE OF BODY Primary motor area of cerebral cortex Internal capsule The anterior corticospinal pathway Midbrain UPPER MOTOR NEURON Cerebral peduncle Pons Medulla Pyramid

ANTERIOR CORTICOSPINAL TRACT Spinal cord LOWER MOTOR NEURON Spinal nerve Spinal cord To skeletal muscles in the trunk and proximal parts of the limbs RIGHT SIDE OF BODY LEFT SIDE OF BODY Primary motor area of cerebral

cortex Internal capsule UPPER MOTOR NEURON The corticobulba r pathway CORTICOBULBAR TRACT Cerebral peduncle Facial (VII) nerve Midbrain Pons Hypoglossal (XII) nerve LOWER MOTOR NEURON

To skeletal muscles of facial expression LOWER MOTOR NEURON Medulla To skeletal muscles of the tongue

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