Lecture 3: Peripheral and central afferent pathways PDF

Peripheral and central afferent pathways KIN 255 – Fundamentals of Neuroscience  Outline – Peripheral and Central Afferent Pathways KIN 255 – Fundamentals of Neuroscience 1. Afferent neurons – fibre types, propert...

Peripheral and central afferent pathways KIN 255 – Fundamentals of Neuroscience  Outline – Peripheral and Central Afferent Pathways KIN 255 – Fundamentals of Neuroscience 1. Afferent neurons – fibre types, properties, conduction velocities 2. Spatial mapping of sensory information 3. Visual afferent pathways 4. Vestibular afferent pathways 5. Somatosensory afferent pathways  Peripheral and central afferent pathways KIN 255 – Fundamentals of Neuroscience 3 Why do you think proprioceptive afferent neurons are the fastest conducting afferent neurons? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways KIN 255 – Fundamentals of Neuroscience 4 Why do you think nociceptive afferent neurons are among the slowest conducting afferent neurons? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 5 Overview: Sensory systems KIN 255 – Fundamentals of Neuroscience receptor Stimulus sensory neuron motoneuron Central nervous system Transform stimulus Pathways Pathways to action potential in the PNS and processing in the CNS Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 6 The afferent neuron: Somatosensory In the somatosensory system, mechanoreceptors are specialized cells that KIN 255 – Fundamentals of Neuroscience project to an afferent neuron or are actually part of the afferent neuron itself Receptor Receptor Receptors To spinal cord To spinal cord K. Booker, Principles of Sensory Transduction Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 7 Insulated protected by a non- The afferent neuron: Somatosensory conducting material that prevents the passage of electrical current How fast the afferent information reaches the central nervous system KIN 255 – Fundamentals of Neuroscience (CNS) depends on ❖ The amount of insulation around the axon of the afferent neuron ▪ Insulation prevents ions from leaking out of the axon and forces ions to move along the axon ❖ The diameter of the axon of the afferent neuron ▪ A larger diameter provides more room for ions to flow unobstructed along the axon Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 8 The afferent neuron: Somatosensory Proprioceptive afferent neurons are the quickest transmitters of afferent KIN 255 – Fundamentals of Neuroscience information Receptor type Afferent fibre classification Cutaneous mechanoreceptors Group II A-beta Muscle spindles Dynamic Group Ia A-alpha Static Group II A-beta Golgi tendon organs Group Ib A-alpha Joint receptors Group II A -beta Free nerve endings Group III A-delta Group IV C-fibre Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 9 Overview of sensory systems KIN 255 – Fundamentals of Neuroscience receptor Stimulus sensory neuron motoneuron Central nervous system Transform stimulus Pathways Pathways to action potential in the PNS and processing in the CNS Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 10 Afferent projections to the CNS Afferent projections travel to Action KIN 255 – Fundamentals of Neuroscience specific gray matter regions in “How” the CNS that are specific for one sensory system ❖ Sensory information from multiple systems eventually converges in association areas to generate a unified percept Perception or action “What” Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 11 Key Terms: Convergence and divergence Divergence – the same input KIN 255 – Fundamentals of Neuroscience separates/disperses to multiple locations Convergence – multiple inputs project to a common location Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 12 Key Terms: Spatial mapping in the CNS Topographic - Ordered projection of a sensory Topography is found KIN 255 – Fundamentals of Neuroscience throughout all levels of the surface, like the retina or the skin, within nuclei CNS. (neurons) in the central nervous system. Ipsilateral - belonging to or occurring from the SAME side of the body Most sensory and motor control pathways cross the Contralateral – belonging to or occurring for the body midline at some point. OPPOSITE of the body Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 13 Peripheral and central pathways: Visual system The location of the The optic nerve projects to two parallel stimulus on the pathways: retina is preserved KIN 255 – Fundamentals of Neuroscience with high affinity ❖ Geniculostriate visual system (90% of fibers) from the retina to primary visual ▪ The primary visual pathway cortex (retinotopic maps). ▪ Retina → Lateral geniculate (LGN) thalamic nucleus → Primary visual (V1) cortex ❖ Tectopulvinar visual system (10% of fibers) Retinotopic maps are still present in ▪ The secondary visual pathway secondary visual cortex and ▪ Retina → Superior colliculus (midbrain) association cortex -- → Pulvinar nucleus of the thalamus - they are just more abstract Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 14 Peripheral and central pathways: Visual system Retinotopic Organization KIN 255 – Fundamentals of Neuroscience Both eyes capture most of the visual The location of the stimulus field. on the retina is preserved with high affinity from the retina to However, information from the primary visual cortex contralateral visual field cross the (retinotopic maps). midline at the optic chiasm. Retinotopic maps are still ▪ Left hemifield = Right thalamus/V1 present in secondary visual ▪ Right hemifield = left thalamus/V1 cortex and association cortex --- they are just more abstract Note: V1 is a mirror of the visual environment Visual field the part of the visual environment that can ▪ The upper visual field is be detected by both eyes represented in the inferior part of Hemifield the left or right half the cortex of the visual field Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Lecture 3: Peripheral and central afferent pathways 15 Monocular hemianopia is the complete loss of vision in one eye due to damage of the ipsilateral optic nerve KIN 255 – Fundamentals of Neuroscience Exercise: How would your perception of the visual world change if: a) you had a lesion of the right optic nerve b) you had a lesion of the optic chiasm c) you suffered a lesion to the right optic tract Optic tract the bundle of nerves relaying visual information from the optic chiasm to the LGN thalamic nucleus Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 16 Peripheral and central pathways: Visual system The dorsal stream visual areas Two visual cortical pathways relate the visual environment KIN 255 – Fundamentals of Neuroscience (spatial location, motion) to the body. Therefore, it is thought of as vision for action. The ventral stream visual areas emphasize object recognition and classification. Therefore, it is often thought of as vision for perception. Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 17 Prosopagnosia is a disorder characterized by the inability to recognize faces. KIN 255 – Fundamentals of Neuroscience Prosopagnosia is associated with damage to which cortical visual pathway? The dorsal stream or the ventral stream? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 18 Peripheral and central pathways: Vestibular Remember, cranial nerves do not run through the spinal cord The vestibular axons forming the vestibular nerve (Cranial nerve VIII) KIN 255 – Fundamentals of Neuroscience directly projects to: ❖ The ipsilateral vestibular nuclei (located in pons and medulla) ▪ 4 nuclei that make up the vestibular nuclear complex ❖ The ipsilateral cerebellum The vestibular nuclei relay vestibular signals to the cerebellum, cortex (via the thalamus) and brainstem nuclei that send efferent signals to the eye muscles Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 19 Overview: Sensory systems KIN 255 – Fundamentals of Neuroscience receptor Stimulus sensory neuron motoneuron Central nervous system Transform stimulus Pathways Pathways to action potential in the PNS and processing in the CNS Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 20 The afferent neuron: Somatosensory In the somatosensory system, mechanoreceptors are specialized cells that KIN 255 – Fundamentals of Neuroscience project to an afferent neuron or are actually part of the afferent neuron itself Receptor Receptor Receptors To spinal cord To spinal cord K. Booker, Principles of Sensory Transduction Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 21 Peripheral and central pathways: Somatosensory Somatosensory nerves (except those from the head) enter the spinal cord KIN 255 – Fundamentals of Neuroscience via the dorsal horn ❖ The nerves from the head form the trigeminal nerve (cranial nerve V) Somatosensory nerves layer to form the ascending pathways, but also have many divergent projections in the spinal cord Remember, The cell bodies of motor ❖ Divergent projections facilitate neurons are inside the spinal cord. reflexes and coordination among The cell bodies of sensory neurons are outside the spinal cord (in the muscle groups dorsal root ganglion) Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 22 Peripheral and central pathways: Somatosensory (Posterior Column) Pathways or tracts are often named The nerves that bundle in the posterior column pathway according to their origin and convey fine touch, vibration and proprioceptive afferent KIN 255 – Fundamentals of Neuroscience terminus. For example, the spinocerebellar pathway originates in information the spinal cord and terminates in the cerebellum Third order neuron – Axon that projects from the thalamic nuclei to the primary somatosensory cortex Second order neuron – Axon that crosses the body midline in the medulla and projects to the thalamic nucleus First order neuron - Axon that projects from the receptor to the medulla Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 23 Peripheral and central pathways: Somatosensory (Spinothalamic) The spinothalamic pathway is divided into two parts KIN 255 – Fundamentals of Neuroscience 1. Anterior spinothalamic tract ▪ The more anterior-medial part of the spinothalamic tract ▪ Crude, poorly localized, information about touch 2. Lateral spinothalamic tract ▪ The more lateral part of the spinothalamic pathway Note how the nerves making up the ▪ Information about noxious stimuli and spinothalamic pathway cross the midline temperature immediately after enter the spinal cord Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways KIN 255 – Fundamentals of Neuroscience 24 A patient reports the concurrent loss of touch from their right hand and pain from their left hand. Which somatosensory pathways have been damaged and at what level might this damage have occurred? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Peripheral and central afferent pathways 25 Peripheral and central pathways: Somatosensory (Spinocerebellar) The spinocerebellar pathway is divided into three parts Peduncle a thick stock (or bundle) of axons. 1. Dorsal spinocerebellar tract (DSCT) KIN 255 – Fundamentals of Neuroscience ▪ Projects to the inferior peduncle of the cerebellum ▪ Proprioceptive information from the lower limbs (Spindle fibers via Ia afferent neurons) 2. Rostral spinocerebellar tract (RSCT) ▪ Projects to the inferior peduncle of the cerebellum ▪ Proprioceptive information from the upper limbs 3. Ventral spinocerebellar tract (VSCT) ▪ Projects to the superior peduncle of the cerebellum ▪ Proprioceptive information from the lower limbs (Golgi tendon organs via Ib afferent neurons) Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Summary – Peripheral and Central Afferent Pathways KIN 255 – Fundamentals of Neuroscience 1. Afferent neurons – fibre types, properties, conduction velocities 2. Spatial mapping of sensory information - common properties across systems 3. Visual afferent pathways – dorsal / ventral streams 4. Vestibular afferent pathways – ipsilateral cerebellar connections 5. Somatosensory afferent pathways – 2 pathways - posterior column and spinothalamic