How Does the Brain Produce Movement?

1 PThe Hierarchical Control of MovementThe Forebrain and movement InitiationThe Brainstem and Species-Typical MovementFocus on Disorders: AutismThe Spinal Cord and movement ExecutionFocus on Disorders: ParaplegiaThe Organization of the Motor SystemThe Motor CortexThe Corticospinal TractsThe Motor NeuronsThe Control of MusclesThe Motor Cortex and SkilledMovementsInvestigating Neural Control of Skilled MovementsThe Control of Skilled Movements in Other SpeciesHow Motor Cortex Damage Affects Skilled MovementsThe Basal Ganglia and the CerebellumThe Basal Ganglia and movement ForceFocus on Disorders.

2 Tourette s SyndromeThe Cerebellum and movement SkillThe Organization of theSomatosensory SystemSomatosensory Receptors and Sensory PerceptionDorsal-Root Ganglion NeuronsThe Somatosensory Pathways to the BrainSpinal-Cord Responses to Somatosensory InputThe Vestibular System and BalanceExploring the SomatosensorySystemThe Somatosensory HomunculusThe Effects of Damage to the Somatosensory CortexThe Somatosensory Cortex and Complex Movement354 How does the BrainProduce Movement? CHAPTER10 Kevork Djansezian/AP PhotoMicrograph: Dr.

3 David Scott/PhototakepKamala is a female Indian elephant that lives at the zoo in Calgary, Canada. Her trunk, which is really just a greatly extended upper lip and nose, con-sists of about 2000 fused muscles . A pair of nostrils runs itslength and fingerlike projections are located at its tip. Theskin of the trunk is soft and supple and is covered sparselywith sensory hairs. Like all elephants, Kamala uses hertrunk for many purposes. It can gather food, scratch an ear,rub an itchy eye, or caress a baby.

4 It can also be used to ex-plore. Kamala raises it to sniff the wind, lowers it to exam-ine the ground for scents, and sometimes even pokes it intoanother elephant s mouth to investigate the food there. She,like other elephants, can inhale as much as 4 liters of waterinto her trunk, which she can then place in her mouth todrink or squirt over her body to bathe. She can also inhaledust or mud for bathing. Kamala s trunk is a potentialweapon, too. She can flick it as a threat, lash out with it inaggression, and throw missiles with it.

5 Her trunk is bothimmensely strong and very agile. With it, Kamala can liftobjects as large as an elephant calf, sometimes uprootingentire trees, yet this same trunk can grasp a single peanutfrom the palm of a proffered one way, however, Kamala uses this versatile trunkvery unusually for an elephant (Onodera & Hicks, 1999).She is one of only a few elephants in the world that paintswith its trunk (Figure 10-1). Like many artists, she paintswhen it suits her, but nevertheless she has commemoratedmany important zoo events, such as the arrival of newspecies to the zoo.

6 An elephant artist is not as far-fetched asthe idea may at first seem. Other elephants, both in thewild and in captivity, pick up small stones and sticks anddraw in the dust with them. But Kamala has gone well be-yond this simple doodling. When given paints and a brush,she began to Produce works of art, many of which havebeen sold to art collectors. Kamala, in fact, has achieved aninternational reputation as an defining feature of animals is their ability to the example of Kamala illustrates, even very skilledmovements are not limited to humans.

7 Although we hu-mans display the most skilled motor control of all animals,members of many species have highly dexterous move-ments. This chapter explores how the Brain producesmovement. We begin by considering how the control ofmovement is organized. Then, we examine the variouscontributions of the neocortex, the brainstem, andthe spinal cord to movement . Of particular interestis how neurons of the motor cortex take part in pro-ducing skilled movements. Next, we investigatehow the basal ganglia and the cerebellum help tofine-tune our control of movement .

8 Finally, we turnto the role of the somatosensory system. Althoughother senses, such as vision, play a part in enablingmovement, body senses play a special role, as youwill soon discover. Figure 10-1 Kamala (her name means lotus flower ) was born in 1975 in SriLanka s Yala National Park and orphaned shortly thereafter. Shewas adopted by the Calgary, Alberta, Zoological Society. Elephantswere first observed to paint with sticks or rocks in the dust, andsome have become accomplished artists when given paints and abrush.

9 Kamala began painting as part of an environmentalenrichment program and her paintings are widely sold tocollectors. 355 The Calgary Zoological SocietyThe Calgary Zoological SocietyTHE HIERARCHICAL CONTROL OF MOVEMENTWhen Kamala paints a picture, her behaviors are sequentially organized. First, she looksat her canvas and her selection of paints; then, she considers what she wants to paint;and, finally, she executes her painting. These sequentially organized behaviors are dic-tated by the hierarchical organization of Kamala s nervous system.

10 The major compo-nents of this nervous system hierarchy are the neocortex, the brainstem, and the spinalcord. All contribute to controlling the behaviors required to Produce her the same way, your hierarchically organized nervous system controls everymovement that you make. Figure 10-2 shows the sequences of steps taken when thehuman nervous system directs a hand to pick up a coffee mug. The visual system mustfirst inspect the cup to determine what part of it should be grasped.