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 and sleep Learning and memory

Sensation Receptor Nerve Impulses Sensory Info CNS Spinal Cord Brain Stem Cerebral Cortex 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 doesn’t 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: Special General: Somatic vs visceral Special

Process of Sensation Stimulation Transduction Conduction Translation Stimulus in receptive field Transduction Transduce stimulus to graded potential Conduction GP – threshold – nerve impulse - conducted Translation CNS translates impulse into sensation

Graded Potential vs. Action Potential Vary in magnitude All or none principle Vary in duration Same duration Decay with distance Long distances Dendrites and cell body (direction can vary) Axons (hillock – one way direction) Variety of ion channels open and close to create potential Voltage-gated ion channels cause potential No refractory period Absolute or relative refractory periods possible Generator potential  Create an action potential Receptor potentials  neurotransmitter release

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

Cold stimulus (temp)  Free nerve ending  exteroreceptor  thermoreceptor (generator potential) Pressure stimulus  encapsulated nerve ending  exteroreceptor  mechanoreceptor (generator potential) Taste stimulus  Separate cells (gustatory cell)  triggers release of neurotransmitters  synapses with exteroreceptor  chemoreceptor (Receptor potential)

Adaptation in Sensory Receptors Rapidly adapting receptors Slowly adapting receptors

Somatic Sensations Tactile Sensations Thermal Sensations Proprioceptive Sensations Pain Sensations

Fig. 16.2 Tactile and Thermal Sensations

Fig. 16.4 Proprioceptive Sensations: muscle spindle and tendon organ

Proprioception Kinesthesia Weight Discrimination Stereognosis Perception of motion Weight Discrimination Ability to assess object weight Stereognosis Perception of 3D depth Usually perception of solid objects by touch

Pain Sensations Protective Nociceptors Slowly adapting Many stimuli (pressure, temp, chem ex. Histamine, bradykinin) Slowly adapting 2 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 neuron Third-order neuron Symmetry Somatotopy

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

Posterior column–medial lemniscus pathway RIGHT SIDE OF BODY Posterior column–medial lemniscus pathway LEFT SIDE OF BODY Primary somatosensory area of cerebral cortex THIRD-ORDER NEURONS Thalamus Medial lemniscus Midbrain SECOND-ORDER NEURONS Gracile nucleus Cuneate nucleus FIRST-ORDER NEURONS POSTERIOR COLUMN: Medulla Posterior root ganglion Gracile fasciculus Cuneate fasciculus Receptors for touch and proprioception in the upper limbs, upper trunk, neck, and posterior head Spinal nerve Cervical spinal cord Receptors for touch and proprioception in the lower limbs and lower trunk Lumbar spinal cord

Anterolateral (spinothalamic) pathways RIGHT SIDE OF BODY Anterolateral (spinothalamic) pathways LEFT SIDE OF BODY Primary somatosensory area of cerebral cortex THIRD-ORDER NEURON Thalamus Midbrain SECOND-ORDER NEURON Posterior gray horn FIRST-ORDER NEURON Medulla LATERAL SPINOTHALAMIC TRACT Posterior root ganglion Spinal nerve Receptors for pain, temp, itch from limbs, trunk, neck and posterior head Spinal cord ANTERIOR SPINOTHALAMIC TRACT

Posterior Column-Medial Lemniscus Pathway Spinothalamic Pathway   Posterior Column-Medial Lemniscus Pathway Spinothalamic Pathway Sensations carried Pressure, vibration, touch, conscious proprioception Pain, temperature, itch, tickle  Beginning of pathway Sensory receptors in: Limbs, trunk, neck, posterior head End of pathway Cerebral cortex # neurons in pathway 3 Neuron crosses over Second-order neuron Crossover location Medulla oblongata Spinal cord First order neuron Axon Posterior column of spinal cord Posterior gray horn SC Cell body Posterior root ganglion of spinal nerve Second order neuron Gracile fasiculus Gray commissure  ventral posterior nucleus of thalamus Gracile nucleus or cuneate nucleus of medulla oblongata Posterior gray horn of spinal cord Third order neuron Primary somatosensory area of cerebral cortex in the parietal lobe Thalamus 

Trigenminothalamic pathways RIGHT SIDE OF BODY Trigenminothalamic pathways LEFT SIDE OF BODY Primary somatosensory area of cerebral cortex THIRD-ORDER NEURON Thalamus SECOND-ORDER NEURON TRIGEMINOTHALAMIC TRACT FIRST-ORDER NEURON Midbrain Receptors for touch, pain, and temperature in the face, nasal cavity, oral cavity, and teeth Pons Trigeminal ganglion Trigeminal (V) nerve SECOND-ORDER NEURON Medulla

Homunculus – Mapping the Primary Somatosensory Area

Primary somatosensory 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 somatic motor pathways Lower motor neurons. Synapse with skeletal muscles Symmetry Somatotopy

Somatic motor pathways - coordination and control of mvmt LMNs receive input directly from: Local circuit neurons (purple) 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)

The lateral corticospinal pathway RIGHT SIDE OF BODY LEFT SIDE OF BODY Primary motor area of cerebral cortex The lateral corticospinal pathway Internal capsule Midbrain Cerebral peduncle UPPER MOTOR NEURON Pons Medulla Pyramid Decussation (crossing) in medulla LATERAL CORTICOSPINAL TRACT Spinal cord Spinal nerve LOWER MOTOR NEURON To skeletal muscles in the distal parts of the limbs (voluntary mvmt of limbs and trunk) Spinal cord

The anterior corticospinal pathway RIGHT SIDE OF BODY LEFT SIDE OF BODY Primary motor area of cerebral cortex Internal capsule The anterior corticospinal pathway Midbrain Cerebral peduncle UPPER MOTOR NEURON Pons Medulla Pyramid Spinal cord ANTERIOR CORTICOSPINAL TRACT LOWER MOTOR NEURON Spinal nerve Spinal cord To skeletal muscles in the trunk and proximal parts of the limbs

The corticobulbar pathway RIGHT SIDE OF BODY LEFT SIDE OF BODY Primary motor area of cerebral cortex Internal capsule UPPER MOTOR NEURON The corticobulbar pathway CORTICOBULBAR TRACT Cerebral peduncle Facial (VII) nerve Midbrain LOWER MOTOR NEURON To skeletal muscles of facial expression Pons Hypoglossal (XII) nerve LOWER MOTOR NEURON To skeletal muscles of the tongue Medulla