Pathways: movement and sensation Pedro Amarante Andrade, PhD

LEARNING OUTCOMES Learn the cross-sectional anatomy of the spinal cord Be able to explain the types of connections between and within the CNS and PNS Understand the basic functions of the brainstem and how it relates to the spinal cord pathways

MOVEMENT

MOVEMENT OVERVIEW Complex and incompletely understood Planned in sensorimotor areas of the cortex Is effected by pathways of descending neurons, under the control of the cerebellum and the basal ganglia Control is achieved through sensory feedback from muscles/joints And information from the eyes and ears (vision and balance) also influences the motor pathways

MOVEMENT OVERVIEW

MOVEMENT OVERVIEW Biological Psychology: An introduction to Behavioural, Cognitive, and Clinical Neuroscience. S. Marc Breedlove, Simon Watson

LOCATION OF THE BASAL GANGLIA http://antranik.org/cerebral-white-matter-and-gray-matter-and-basal-ganglia/ https://kin450-neurophysiology.wikispaces.com/Basal+Ganglia+II

CONTROL CIRCUITS The CEREBELLUM: coordinates motor and sensory information Gets info from the cortex about what muscles SHOULD be doing, and compares this with what is ACTUALLY happening The basal ganglia: involved in control of background movement, and initiation of movement patterns Biological Psychology: An introduction to Behavioural, Cognitive, and Clinical Neuroscience.S. Marc Breedlove, Simon Watson

VOLUNTARY MOVEMENT Although skeletal movement is under our voluntary control, much of it is automatic Speech, chewing, swallowing comes under the heading of automatic movements that can be altered voluntarily Can be affected by developmental abnormalities or acquired brain injury

CORTICAL ANATOMY OF THE MOTOR SYSTEM http://www.sofiatopia.org/equiaeon/ibrain12.jpg

CORTICAL ANATOMY OF THE MOTOR SYSTEM http://www.sofiatopia.org/equiaeon/ibrain12.jpg Blood flow to this region increases prior to movement actually occurring suggesting a role in planning the movement flow

HOMUNCULI

SOMATOTOPIC CORTEX The primary motor and sensory cortices are somatotopically arranged in the precentral and postcentral gyri with the body represented upside down and individual areas represented out of proportion to their actual size Note that disproportionately more cortex devoted to the movements of the muscles involved in speech

THE PATHWAYS A neural pathway connects one part of the nervous system with another via a bundle of axons Motor Efferent Sensory Afferent

THE PATHWAYS The motor pathways The sensory pathways The white matter pathways The grey matter pathways

MOTOR PATHWAY Neurons

CORTICAL ANATOMY OF THE MOTOR SYSTEM

FUNCTIONAL DIVISIONS OF THE MOTOR SYSTEM DIRECT activation pathway (pyramidal tracts): Upper Motor Neurons: corticobulbar and corticospinal tracts INDIRECT activation pathway (extrapyramidal tracts): Upper Motor Neurons: corticorubral, corticoreticular, rubrospinal, reticulospinal, vestibulospinal and related tracts Final common pathway (FCP): LMNs: generates activity in skeletal muscles

FUNCTIONAL DIVISIONS - MOTOR SYS. SYSTEMS TRACTS ORIGIN CONNECT TO PYRAMIDAL Corticobulbar Cortex Cranial nerves (Brainstem) Corticospinal Spinal cord EXTRAPYRAMIDAL Rubrospinal Red nucleus Pontine reticulospinal Reticular formation Medullary reticulospinal Lateral vestibulospinal Vestibular nuclei Tectospinal Midbrain tectum

THE DIRECT PATHWAYS PYRAMIDAL PYRAMIDAL CELLS

THE DIRECT PATHWAYS PYRAMIDAL PYRAMIDAL CELLS www.studyblue.com

Wikicommons. Polarlys and Mikael Häggström. MOTOR TRACTS Wikicommons. Polarlys and Mikael Häggström. Sensory and motor neuros travel by different tracts within the spinal cord

THE DIRECT ACTIVATION PATHWAY Summary Originates in the (predominantly) frontal cortex of each hemisphere Directly connects this cortex to the lower motor neurons The upper motor neurons synapse on: anterior horn cells (corticospinal tract) cranial nerve nuclei (corticobulbar tract) The lower motor neurons emerge at the spinal and bulbar levels, and activate skeletal muscle Activity leads to finely controlled, skilled and discrete movements The ‘express’ route

THE INDIRECT PATHWAYS EXTRAPYRAMIDAL The axons of the UMNs follow the same path as those of the corticospinal tract until they reach the brainstem, there some cross over, others remain uncrossed The UMNs terminate in the nuclei of CN III IV V VI VII IX X XI and XII

THE INDIRECT PATHWAYS EXTRAPYRAMIDAL www.eyesthetica.com

ALL PATHWAYS http://humanphysiology.academy/Neurosciences%202015/Chapter%205/A.5p%20Cerebellar%20Pathways.html

INDIRECT ACTIVATION PATHWAYS Sometimes called extrapyramidal pathway Complex and incompletely understood (especially with regard to speech pathways) Originates in motor, premotor and sensory cortex, and brainstem Composed of numerous short pathways and interconnected structures (so are polysynaptic) involving the motor cortex, the basal ganglia, the limbic system, the thalamus, the cerebellum, the reticular formation AND nuclei in the brainstem

INDIRECT ACTIVATION PATHWAYS UMNs synapse Helps regulate reflexes & mediates subconscious automatic muscle activities e.g. posture and tone Many of its activities are inhibitory (i.e. prevent too much tone/movement) The ‘local’ route

EXAMPLES OF INDIRECT PATHWAYS Rubrospinal - large muscle movement as well as fine motor control. Terminates cervical spinal cord. Facilitates flexion in the upper extremities Reticulospinal - descends from reticular formation in two tracts to act on the motor neurons supplying the trunk and proximal limb muscles. Involved mainly in locomotion and postural control Tectospinal - coordinates head and eye movements. Connects midbrain tectum and spinal cord. Mediates reflex postural movements of head in response to visual and auditory stimuli

EXAMPLES OF INDIRECT PATHWAYS Vestibulospinal – Vestibular nuclei receive information through vestibulocochlear nerve about changes in orientation of head. The nuclei relay motor commands through the vestibulospinal tract. Function of these motors commands = to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head.

SUMMARY OF DIRECT AND INDIRECT ACTIVATION PATHWAYS Both pathways end on LMNs These LMNs receive both excitatory and inhibitory stimulation from both pathways The sum of this input determines the final response of an individual neuron in the pathway The indirect pathway provides the framework (muscle tone, posture, regulation of reflex activity) The direct pathway accomplishes the skilled, discrete muscle actions The LMNs are referred to as the final common pathways or FCP

SENSORY SYSTEM

STRUCTURAL CLASSIFICATION OF NEURONS

SENSORY SYSTEM 3 or more neurons CNS – Thalamus Organ CNS –Cortex CNS – Spinal cord Organ Ganglion 3 or more neurons

SENSORY FASCICULI TRACT ORIGIN CONNECT TO Spinocortical Cuneatus (upper limbs) -Gracilis (lower limbs) Spinal cord Cortex Spinocerebellar Cerebellum Spinothalamic Thalamus Spino-olivary Olivary complex

Wikicommons. Polarlys and Mikael Häggström. MOTOR & SENSORY TRACTS Wikicommons. Polarlys and Mikael Häggström.

WHITE MATTER PATHWAYS There are three types of white matter pathway: Commissural Association Projection

COMMISSURAL WHITE MATTER PATHWAYS Commissural white matter pathways connect the 2 hemispheres. The largest is the corpus callosum, with its posterior splenium, central body or trunk, anterior genu, and ventrally directed rostrum. Besides the corpus callosum, commissural white matter pathways include the anterior commissure which connects the olfactory & temporal regions, and the posterior commissure

ASSOCIATION WHITE MATTER PATHWAYS Connect cerebral areas within each hemisphere (generally bidirectional) Contain short association fibres known as "U" or arcuate fibres that link adjacent cortical gyri Long association fibres, all of which terminate in the frontal lobe are: the cingulate, the arcuate fasciculus, the superior occipitofrontal fasciculus, the inferior occipitofrontal fasciculus, and the uncinate fasciculus

PROJECTION WHITE MATTER PATHWAYS White matter projections consist of long tracts which connect the cortex with the brainstem and spinal cord These long tracts both ascend and descend. The corona radiata consists of projection tracts running to and from the cortex The projections converge at the internal capsule

www.leonidzhukov.ru

STUDY THE STRETCH REFLEX Revise the structure and function of the muscle spindle (see lecture 3, Nerves, Muscles and How They Work) Watch the video or review the pathways involved in the stretch reflex: http://www.youtube.com/watch?v=HfuhVWK8C0U

NOTE THE TERMS: Agonist/antagonist Interneuron Reciprocal innervation If you are unfamiliar with these terms through your reading, then look them up and write some definitions now

PARTICULAR RELEVANCE TO SLT To perform accurate movements, information re the range, rate and force of contraction, and position of the muscles, is essential. Muscle spindle actions are involved in controlling the rapid and fine muscle movements required for speech. Sensory nerves from muscle spindles send out a continuous stream of impulses to the CNS Muscle tone is maintained via these feedback mechanisms

PARALYSED MAN WALKS AGAIN

Amyotrophic Lateral Sclerosis