Ch 14 Brain Control and Movement

Reticular Formation

The reticulospinal tracts arise mainly from here of the brain stem. It can be divided into two parts that give rise to two different descending tracts: the pontine (medial) reticulospinal tract and the medullary (lateral) reticulospinal tract.

Vermis

This is the midline region (worm) and it separates the two lateral cerebellar hemispheres from each other

Lowers motor Neurons

Those originating in the brain stem control speech and swallowing(bulbar motor neurons) and those originating in the spinal cord control limb and respiratory muscles

Ataxia

a cerebellar lesion that deals with movements becoming uncoordinated and inaccurate

Pyramidal Tract

a tract running along the ventral medulla that carries corticospinal axons.

Parkinson's Disease

affects about 1% of all people over age 50 is characterized by hypokinesia. Symptoms include slowness of movement difficulty in initiating willed movements, increased muscle tone and tremors of the hands and jaw, which are most prominent at rest.

Ventromedial Pathways

axons from brain descend and are involved in the control of posture and locomotion and are under brain stem control.

Lateral Pathways

axons from brain descend and are involved in voluntary movement of the distal musculature and are under direct cortical control.

Spinal cord

based on commands received from the motor cortex and the brainstem, lower motor neurons send signals to the muscles -during the movement, sensory information from the limb is acquired and transmitted back to the cortex. *Reflex pathways ensure stability of the limb

Spasticity

characterized by tight or stiff muscles and in inability to control those muscles. *symptoms: increase muscle tone causes flexion, overactive reflexes, involuntary movements, may include spasms (brisk and or sustained involuntary muscle contraction) and clonus (series of fast involuntary contractions) -affects posture -pain *upper motor neuron signs

Hemiballismus

characterized by violent flinging movements of the extremities. -when symptoms usually occur on one side of the body

supplementary motor cortex

conception and initiation of movement -especially involved in internally generated movement ex dance -neurons project directly to the spinal cord so they can play a role in the direct control of movement -postural stabilization of the body coordination of both sides of the body, bimanual action -control of sequences of movements *lesions cause deficits in voluntary movement or speech

Globus Pallidus

consists within the Basal ganglia and is the source of the output to the thalamus

Substantia nigra

consists within the basal ganglia

Pyramidal system and disorders

controls volitional movement -paralysis on contralateral side of body -weakness

Cerebellum

coordinates multi-joint movements, learning of movements and maintenance of postural stability. *output excitatory

Hyperkinesia

decreased basal ganglia output, an excess of movement

Pontine Reticulospinal Tracts

enhances the anti gravity reflexes of the spinal cord. Activity in this pathway facilitates the extensors of the lower limbs, helps maintain a standing posture by resisting the effects of gravity. -motor control -the activity of the ventral horn maintains muscle length and tension

Lateral pathway lesions

fractionated movements of arms and hands -Damage of corticospinal tract -paralysis on contralateral side -difficulties moving multiple muscle groups (e.g. shoulders elbows wrists and fingers) independently -could grasp of small objects but only using all fingers at once

Hypokinesia

increased inhibition of the thalamus by the basal ganglia, a paucity of movement

Huntington's disease

is a hereditary, progressive, inevitably fatal syndrome characterized by hyperkinesia and dyskinesias, abnormal movements; dementia impaired cognitive abilities and a disorder of personality. *effects later in life

Areas 5

is a target of inputs from the primary somatosensory cortical areas 3, 1 and 2

M1

is located in the precentral gyrus and at the primary motor cortex

Areas 6

lies just anterior to area 4 contains two somatotopically organized motor maps in the lateral region is premotor are (PMA) and the medial region (SMA). *Play an important role in the planning of movement especially complex movement sequences of the distal musculature -'go'

Premotor area

located in area 6 in a lateral region and connects primarily with reticulospinal neurons that innervate proximal motor units

Supplementary motor area

located in area 6 in the medial region and sends axons that innervate distal motor units directly

Upper motor Neurons

located in primary motor cortex (Brain) and send signals to neurons in the ventral spinal cord -corticospinal tracts to the spinal cord -synapse in the anterior horn the spinal cord with lower motor neurons

Hypotonia

low muscle tone (the amount of tension or resistance to stretch in a muscle -often includes reduced muscle strength -disruption of afferent input from stretch receptors and/or lack of the cerebellum's facilitatory afferent influence and may disappear *lower motor disorder

Striatum

made up of the caudate and the putamen which is the target of the cortical input to the basal ganglia

Lateral Corticospinal Tract

most important pathway of the lateral pathway. -controls coordinated movements of joints, speed precision -passes through *internal capsule, midbrain and *pons axons join together in the medulla oblongata to form a dense bundle of nerve fibers-*pyramidal tract -90% of fibers cross over to synapse with motor neurons innervating contralateral distal muscles. 10% innervate axial muscles, bilaterally -Two-thirds of the axons in the tract originate in areas 4 and 6 of the frontal lobe.

Premotor

motor coordination-involved in programming movements that require coordinated action different muscles of an appendage, especially when motor occurs in relation to external stimulus -lesions cause impairments in stability of stance, gait and hand coordination -uses info on location of the cup with respect to hand, computes trajectory, sequence and forces that are necessary to move the arm

Fasciculations

muscle twitch is small, local, involuntary muscle contractions -spontaneous depolarization of lower motor neurons -will cease with voluntary movement

Hemiparesis

one half of the body has less marked weakness -common with stroke

Vestibulospinal Tract

originate in the vestibular nuclei of the medulla which relay sensory information from the vestibular labyrinth in the inner ear. *ventromedial pathways

Tectospinal Tract

originates in the superior colliculus of the midbrain, which receives direct input from the retina. *ventromedial pathway

Hyperreflexia

overactive or over responsive reflexes indicative of upper motor neuron disease lessening or loss of control ordinarily exerted by higher brain centers of lower neural pathways (disinhibition) -could also be due to spinal injury

Hemiplegia

paralysis of the arm, leg and trunk on the same side of the body -common with stroke *upper motor neuron lesion

Parietal

processes information of body position in space based on vision hearing, and proprioception and somatic sensation -visual and proprioceptive information essential to compute location of the cup with respect to the hand -sends information to motor cortex

Sensorimotor System

provides feedback to make necessary adjustments -Proper function of motor hierarchy contingent on sensory information -sensory information used to generate mental image of body and its relationship to the environment -Tactical decisions based on memory of sensory information from past movements -used to maintain posture, muscling, and tension, before and after each voluntary movement

Anterior corticospinal tract

responsible for the control of proximal musculature -part of 10% of corticospinal fibers that does not crossover in the medulla -cross over in the spinal cord near motor neurons they innervate *ventromedial pathways

Brainstem

sends commands to the spinal cord to maintain the body's balance during the reaching movement -Activation of motor neurons must be timed precisely to produce coordinated movement -mediates simultaneous postural corrections and adjustment to spinal cord

Malleable motor map

studies the changes with experience

Ventral Lateral Nucleus:VLo

the major subcortical input to area 6 arises in a nucleus of the dorsal thalamus

Motor loop

through Basal Ganglia originates with an excititory connection from the cortex to cells in the putamen

Babinski Sign

when sole of the foot has been firmly stroked produces plantar reflex-downward response of the hallux -if absent or if response is an upward response (extension) of the hallux-big toes moves upward or toward the top surface of the foot. The other toes fan out -may signal damage t corticospinal tract, pyramidal tract -normal in young babies *upper motor neuron sign

Areas 7

which is targets of higher order visual cortical areas such as MT

Red nucleus

within the lateral pathways is the rubrospinal tract located in the the mid brain. Axons decussate to the pons and join the corticospinal tract in the lateral column of the spinal cord tract.

Premotor & Supplementary areas

"Set"

Parietal and Frontal lobes

"ready"

Clonus

-Greek for violent, confused motion -involuntary, rhythmic muscular contractions and relaxations -sign of upper motor neuron lesions involving descending motor pathways -often accompanied by spasticity

Medullary Reticulospinal Tract

-influences proximal muscles important for maintaining balance and posture Pontine: innervates extensor muscles of the lower limb helping us to stand up, antigravity muscles (posture) -Medullary: inhibits motor neurons at all levels *ventromedial pathway

Corticobulbar tract

-innervates the head -most fibers terminate in reticular formation near cranial nerve nuclei

Basal ganglia

A collection of associated cell groups in the basal forebrain, including the caudate nucleus, putamen, globus pallidus and subthalamus -mediates learning of movements, stability of movements, initiation of movements, emotional and motivational aspects of movements *output inhibitory

Anterior Frontal lobes

Abstract thought, decision making and anticipating consequences of action -initiates goal evaluates contingencies possible obstacles (taking info from parietal lobe), prepares plan of action -options fed forward to basal ganglia and back to cortex -Decisions made based on multiple factors including experience (memory)

Frontal cortex: Anterior Frontal lobes

Area 6: Actions converted into signals specifying how actions will be preformed

Goal-directed Behavior

Associated with activation of many cortical areas -parietal cortex, somatosensory, frontal cortex and visual cortex

Pontine nuclei

Axons arising from layer V pyramidal cells in the sensorimotor cortex-frontal areas 4 and 6 somatosensory areas on the postcentral gyrus and the posterior parietal areas form a massive projection to clusters of cells in the pons and feeds into the cerebellum

Lower motor neuron damage

Damage in spinal cord afferents control limbs and respiratory muscles -damage in brain stem results in loss of control speech and swallowing (bubar motor neurons) Paralysis, Fasciculations, Hypotonia, Hyporeflexia, weakness, wasting

Areas 4

Lies within motor cortex just anterior to the central sulcus on the precentral gyrus and is primary motor cortex or M1 can be innervated by electrical stimulation creates a twitch

Atrophy/wasting

Loss of muscle mass, poor nourishment, poor circulation, loss of nerve supply to target organ, excessive amount of apoptosis of cells disuse or lack of exercise due to disease. *lower motor neuron damage.

Motor cortex

Low level-execution -generates signals that control the execution of movements -longest and one of the largest central nervous system tracks 1,000,000 axons -commands send to the brainstem and the spinal cord -also sent to basal ganglia and cerebellum which coordinate movement -Area 4=Primary motor cortex or M1 in precentral gyrus

Prefrontal cortex

Motor Planning, decision-making and goal invitation generally is taken place here

Upper motor neuron disorders

Motor palsy, Babinski sign, Hyperreflexia, spasticity-increase muscle tone and clonus

Premotor and Supplementary motor area

Movement Selection

Primary Motor Cortex

Movement initiation -somatotopic organization

Betz cells

Pyramidal cells in cortical layer 5 and the two sources are cortical areas and thalamus

Rubrospinal Tracts

Smaller part of lateral pathway, originating in red nucleus of the midbrain -Crosses over immediately -an older pathway that has been supplanted by the corticospinal tract in humans -can compensate for to corticospinal tract innervates UE flexors reaching movements-fine motor