5th ELlition Laura K. Smith
Elizabeth L. Weiss
L. Don Lehmkuhl
Brunnstrom's Clinical Kinesiology Fifth Edition
Revised by
D, PT artment of Physical Therapy Sciences lVerslty of Texas Medical Branch eston, Texas
Elizabeth Lawrence Weiss, PhD, PT Professor, Director-New Orleans Campus Department of Physical Therapy LSU Medical Center New Orleans, Louisiana
L. Don Lehmkuhl, PhD, PT Associate Professor of Physical Medicine and Rehabilitation Baylor College of Medicine Houston, Texas
BROTH~RS P.B. No. 7193, New Delhi, India
JAYPEE
FIRST INDIAN EDITION 1998
825
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Preface to the Fifth Edition
.-
;
Signe Brunnstrom's astute analysis of muscle activity and her emphasis on palpation of living anatomy and clinical observations are continued in the fifth edition of Brunnstrom's Clinical Kinesiology. Revisions in Chapters 1 to 3, which cover kinematics, kinetics, and muscle physiology and neurophysiology, have been made to clarify concepts. Figures have been added, and material has been reorganized for reader -
,
~(. t
::>.. -
~~'
Cerebrovascular Accident (Stroke) Basal Ganglial Dysfunction Cerebellar Dysfunction
LABORATORY ACTIVITIES
Chapter 4
Muscle Activity and Strength MUSCLE ACTIVITY Recording of Contraction Terminology for Mus';n;'·.;~tll'~~stiviti;~s(Muscleso f the
r.~miti~~ap~fI~ur1k)
.... ~ri1g·an#Coughing ..
.r~R~KfA.NDIBULAR JOINTS
!y19:t~$.n~bf'theTemporomandibular Joint
fYfu·stIii·s: .
i'
[email protected]:APPLICATIONS
{;;LT~rnpbr{)mandibular Dysfunction .···';i') LAB ORATORY ACTIVITIES
•••.••
i ..•..•.•
~~}~~;lrfi~!rafgtnuf11berof degrees of freedom in a kinefri~fic\:Jlaini"'an:~dva?tage,t~sed)p"maintaiii function.The person who can.B8!..N1Ix If" "I:,~,; r~,(l.rll1C~'iaccdfu,pl!~r.haflci function by compensatory inc:~ '~~l7~9 ",f~YTI1?t~ril(m,otions. A person with a stiff ·,;~.r;-p~.fl.sa.t()~j;,rn?HGrisof;the' ankle, hip, back, or the opposi,£e .. '. p~is~fignJ however, is always at a price of increased e' 9-t ;;tpe 'same speed. Years of compensatory use J:~t.u;n~;anddysfuflctionin the compensating joint
..
.
'ViEi
~,,?no
~~r~lii;()ffr~edo~
',' . .. a , " a.. in a kinematic chain further in; as~~imp~irni~1:lt ari~'de~r~asesthe options for function. Sometimes even loss of ·;'~~~~;i~~~,~,~~~f·;:!?~~(I?mSi.lflbe,severely disabling as would occur in a finger joint of ;a.PFgr~~~~o'll(ll!;~pis,tfXY~Q1ipi~t,orbaseball pitcher.
.ARTHROKINEMATICS
Xl't~;~~l~~~a~icsjs
concerned with the movement of the articular surfaces in reli}.tionto the direction of movement of the distal extremity of the bone (osteo~inell1atics). Although human joints have been compared with geometric ~1l.i.lp'~s~F1drnechanical joints such as the hinge, pivot, plane, sphere, and cone, . t1l.eexquisite motions and capabilities of human joints exceed any joint that hu1Il3nS have made. Normally, human joints retain their functional capacities beyor d tl1~ organic life span of the human being (70 to 100 years). The phenomenal superiority of human joints as compared with man-made joints is due not only to the. physiologic capacities of biologic joints, such as low coefficient of frictiop, presence of sensation and proprioceptive feedback, and dynamic growth responses to wear and use, but also to the mechanical complexities of human joints.
Ovoid and Sellar Joint Surfaces The surfaces of movable joints are not flat, cylindric, conic, or spheric; they are ovoid (egg-shaped), a shape in which the radius of curvature varies from point to point (MacConaill and Basmajian, 1969). The ovoid articular surfaces of two bones form a convex-concave paired relationship (Fig. 1-6). The concave-convex
.
,"",,,,,40 '0°,;'='~~~_ ... _.,-~-
,.
12
Brunnstrom's Clinical Kinesiology
A
B Head of humerus
Humerus
Head of radius
Ulna
c
Trapezoid Trapezium
Figure 1-6 Examples of concave-convex relationships of joint surfaces redrawn from radiographs. (A) Glenohumeral joint of the shoulder (anterior-posterior view). (B) Ulnohumeral joint of the elbow (lateral view). (C) Radiocarpal and intercarpal joints of the wrist (anterior-posterior view).
joint relationship may range from linearly planar," as in the carpal and tarsal joints, to linearly spheroid," as in the glenohumeral and hip joints. In engineering, the convex curvature is called the male component, and the concave curvature is called the female compOJ,lent. The center of rotation is in the convex component at some distance from the joint surface. Some joints have both convex and concave surfaces on each articulating bone (Fig. 1-7). These are called sellar (L., saddle) joints because they resemble the matching of a rider in a saddle (reciprocal reception). Examples of sellar joints include the carpometacarpal joint of the thumb, the elbow, the sternoclavicular joint, and the ankle (talocrural joint). In most cases, the ovoid surface of one bone in a pair is larger than its companion, as seen in the glenohumeral joint (see Fig. 1-6), the knee (Fig. 1-8), and the interphalangeal joint (Fig. 1-9). This phenomenon of the biologic joint permits a large range of motion with an economy of articular surface and reduction in the size of the joint.
Mechanical Principles: Kinematics
13
nao:tion can occur beand (3) (.irlDu.re.roJJirH~ motion such as a contacts a new and spinning, the same onltJhe mating surface. Most normal sliding, and spinning. The were only a rolling of the condyles femur would roll off the tibia and the ~etvDe:s"C)t
B
~
Figure 1-8 Movements of joint surfaces. (A) Pure rolling or hinge motion of the femur or the tibia would cause joint dislocation. (B) Normal motion of the knee demonstrates a combination of rolling, sliding, and spinning in the last 20 degrees of extension (terminal rotation of the knee).
14
Brunnstrom's Clinical Kinesiology
. Proximal phalanx
~+
A
Middle h I p a anx
t:::=(J
\~Co~cave
surface
Lconvex surface
B
,.--------+'L::==0
I
\ \ _/
"
.....
-
_---
"
Figure 1-9 Lateral view of the proximal interphalangeal joint of the index finger (A) in extension and (B,C) in flexion. When the bone with the convex joint surface moves into flexion (B), the joint surface
moves in an opposite direction to the motion of the shaft of the bone. When the bone with the concave joint surface moves into flexion (C), the joint surface moves in the same direction as the shaft of the bone.
knee would dislocate (see Fig. 1-8A). Instead, when the femur is extended on the fixed tibia, as in rising from a seated to a standing pOSition, the femoral condyles roll and slide so that they are always in contact with the tibial condyles (see Fig. 1-8B). In the last part of knee extension, the femur spins (internally rotates on the tibia). The combination of roll, slide, and spin thus permits a large range of motion while using-a small articular surface. If joints possessed only one of these motions, the range of motion would be limited or joint surfaces would need to be larger to accomplish the same range of motion.
Joint Axes Because of the incongruity of joint surfaces and the motions of roll, slide, and spin, animal joint axes are complex. The axis does not remain stationary, as in a mechanical hinge joint, but moves as the joint position changes, usually following a curved path (see Fig. 9-3). The largest movement of the axes occurs in the knee, elbow, and wrist. In addition, the joint axes are seldom exactly perpendicular to the long axes of the bones but are frequently oblique. This is particularly notiCeable when the little finger is flexed into the palm. The tip of the finger points to the base of the thumb rather than to the base of the fifth metacarpal. Wh~n the elbow is extended from full flexion with the forearm in supination, the forearm laterally deviates 0 to 20 degrees. This is called the carrying angle and is usually larger in women than in men (see Fig. 5-1). These oblique axes and changing positions of the joint centers create problems and necessitate compromise when mechanical appliances and joints are applied to the body, as in goniometry, orthotics, and exercise eqUipment. Mechani-
Mechanical Principles: Kinematics
15
cal appliances usually have a fixed axis of motion that is perpendicular to the moving,pilTt. When the mechanical and anatomic parts are coupled, perfect aligTlmenjcan occur at only one point in the range of motion. At other points intA~,ratige of motion, th~, mechanical appliance may bind and cause pressure 9~'v~~~d?8Bx.part!'9ritmayforcethe human joint in abnormal directions. Thus, i,F~~RI~;r~fi8H~~i6s,i ,. , 'oJ~me~roi'i()int ':_> .su'ifac~s ,"__ .'.'.:_ . rel~tive _,_ _ ;to the movement of the ,e--~;_,:yernent, and4) impaired muscle function perpetuates and may cause de(erlofatfon'in abnormal joints."
;:-~i~,' -~~h
;, ",;
~~li~j2~i.~g~'ic~tid~~: '> :,'; .: ./:;.,- ',: :,:;:': : .:'.: /:;L:.,:,.: - _'_i',: 'i, ~_, _?':,: .:? ::./«::;,:"':':::':":.'; r;:':),__
'f
. '_::--;: '::,
i:i:,:,,( ·;': ....;' . :,"::::.'i-, : ,
.:,:~g'jil7'~.S:)'J.ry a person with t~S~.~;Je~i,6ij,p1(libe.'IJ),ade by .:'" , .. ;~s'~:a~t.ic:~~a.tlp;ns.·" ' . ' e;..~f£J)gr~~9cewheh,motion of the '>'ii>bXhi?f~,asti:rrioiion.If,for example, in/Ii~~~;'IJ),ar;, 9fc:pr:withscar tissue formation of n~s);tl1enormaldownward movement of the ";~~~$?>~S~1199~9c:c~i(se~Fig; 1':'9C). When the concave ,'tmove down, a force applied distally on the phalanx ?;il~f;~()glestJ:1lc~resareoverstretched and others are com,';" ,,' d/ ,.".?,~,iA:~p:g~iI'lingdownward movement of the phalanx by applying "'tl1e'Jdrc~ 2-4A) the forearm is represented in isolation
Witll.~l simp~~J~n~gQ;I~w
Figure 2-5 Vector representation of forces developed by (A) th~ biceps brachialis, (El) the brachialis, and (e) a combination of the brachioradialis, extensor carpi radialis longus, and extensor carpi '. radialis brevis muscles when the subject lifts an exercise weight 'with the hand and forearm.
graphic composition of forces (drawing the force vectors to scale) or by algebraic composition of forces (see Fig. 2-6D) using the formula that the resultant force (R) is equal to the sum of the individual forces (R = H). In both methods, the resultant force is the same and has the same effect on the femur as the three original forces do together. In this problem, the resultant is equal and opposite to the forces of the joint ligaments, fascia, and capsule. Simililr procedures can be used to find the resultant force in a linear force system when the forces act in opposite directions, as occurs when applying a 25-lb (1IIN) traction force to the cervical structures with the subject sitting upright (Fig. 2-7). In this case, the upward force on the cervical spine is only 15 lb (67 N).
Force Acting at Angles The resultant force of vector forces in the same plane acting at angles to each other cannot be found by simple addition or subtraction but must be found graphically or trigonometrically. If two forces are pulling from the same point, the resultant force can be found graphically by constructing a parallelogram (Fig. 2-8).
L
B
R
W
Figure2~ 'Forces acting at the knee joint when the .subject is sitting' .vithan exercise boot arid weight on the foot. (A) Anatomic diagram. (E) Free body diagram of the forces on the femur. (e) G'raphic composition 0f the resultant force. (D) Algebrail composition of the resultant, forc"e (negative sign indicates that the direction of the force is down).' .
'--
.
A
c
B
I
lib.
D
R = IF
R= -L -B-W R -6.1bs. -3 Ibs. "" 10 Ibs. R -19Ibs.
=
=
L = weight of leg and foot = 6lbs. B = weight-of bdot = 3 Ibs. weights 10 Ibs. W R resultant force 19 Ibs.
= =
=
=
Mechanical Principles: Kinetics
29
B Ibs.
R LF R=+T-H R = 251bs. - 10 Ibs. R = 151bs.
A
1--1
61bs.
, "'..........,
, R" 241bs.
Figure 2-8 Parallelogram method of finding the resultant traction force on the leg. (A) The force vectors acting on the leg are drawn to scale. (B) Lines are drawn- parallel to each force vector from the arrowhead of the other vector to form a parallelogram. (C) The resultant force is the diagonal from the origin of the forces. The magnitudecan be found by measuring the length of the action line.
30
Brunnstrom's Clinical Kinesiology
A
B
I----l
5lbs.
c
Figure 2..,.9 (A) Polygon method for composition of forces using Russell traction, which applies a distraction force on the femur. (A) Fifteen pounds of weight are suspended on the weight carrier. The leg, foot, and footpiece weigh 8 lb. (E) Scale diagram of the forces acting on the femur. (e) The force vectors are connected serially, according to their angle and direction. The open side of the polygon is the single resultant force. In this case, the traction force on the femur is 26 lb and is acting at a 30-degree angle from the long axis of the femur. Realignment of the pulleys is needed to bring the resultant force in line with the long axis of the femur.
The resultant force is the diagonal of the parallelogram, not the sum of the two forces, Note that, as the angle between the two forces increases, the resultant force decreases, reaching a minimum when the forces are on the same line and acting in opposite directions, when the angle becomes 180 degrees. Conversely, as the angle between the forces becomes smaller, the resultant force increases. When the angle becomes zero, the forces are on the same line, and the resultant force is the sum of the two forces., Thus, in the leg traction example, if the patient moves to-
Mechcmical Principles: Kinetics
31
ward the head of the bed, the angle betwee~1 the ropes becomes smaller, and the traction force increases. If the patient moves toward the foot of the bed, the angle en the ropes becomes larger, and the traction force decreases. The same efoccur if someone moves the fixed pulleys on the bedpost farther apart or together. Other examples of forces acting at angles to each other occur in muscles parts may have different lines of pull. Examples include contraction of the and lower trapezius to result in adduction of the scapula, and contraction of wo heads of the gastrocnemius with a resultant force on the tendon of lles. hen more than two forces are acting, the resultant force can be obtained ically by forming a polygon. One force vector is drawn to scale and placed in rop rection. Subsequent vectors are drawn in the same manner, and the f ea ecto is placed at the tip of the previous vector (Fig. 2-9). This process n on one side. The resultant force closes the polygon. and the angle of the resultant force shows the sinfor two forces is a special case of the am, one could draw the second gie forms the resultant force. AlgIe and polygon can be found
principle of a rigid bar being acted on by forces its pivot point is called a lever. In biomechanics, used to visualize the more complex system of forces the body. By reducing these forces to their simplest orces, approximate magnitudes of forces and displaces can be found, and the basis for therapeutic manipulation of er understood. thr rces of the mechanical lever are the axis A (or pivot), the weight W (or resistance R), and the moving (or holding) force F (Fig. 2-10). The perpendicular distance from the pivot point (or center of rotation) to the linf of action of the weight is called the weight arm. The perpendicular distance frorl: the holding force to the axis is called the force arm. Mechanical advantage (MA) of the lever refers to the ratio between the lenoth o of the force arm and the length of the weight arm. The equation is: MA :::
Force Arm Length Weight Arm Length
The ratios for the lever systems shown in Figure 2-10 would be: I = I, II = 2, and III = 0.5. The higher the number, the greater the mechanical advantage. An increase in the length of the force arm or a decrease in the length of the weight arm (or resistance arm) results in greater mechanical advantage, thus facilitating the task to be performed. In angular motions or postures of the body, the bone or segment is the lever,
32
Brunnstrom's Clinical Kinesiology
III
II
i
F
w
F t----
F
A
A
r.--a-l
a~1
I-b-I
I'
b----·I
I-b-l
a
I'
-,
Figure 2-10 Veetordiagrams of the first-class, second-class, and third-class levers. Classification is according to the positions of the weight and force in relation to the axis. A = axis or fulcrum; W = weight or resistance; F = moving or holding force; a = force arm distance; b = weight or resistance arm distance.
and the axis is usually ,at the joint. Muscle contraction is the holding or moving force, and the resistance is the weight of the part, body segments, or applied resistances (Fig. 2-11). Different positions of these forces on the lever arm give different advantages for motion and work. The operation of levers provides either force or excursion advantages.
First-Class Lever First-class levers, such as the seesaw or balance scale, may be used to gain either force or distance, depending on the relative lengths of the force arm and the weight arm. This principle is used in the forearm trough of the ball-bearing feeder III
\I
150,bs.
w
W M
= body weight = soleus muscle
J
= jointforce
R
I50'bs.
J
W
= weight of head. trunk, and arms
J l = joint force (left) J R = joint force (right)
= =
R resistance weight M = elbow flexor muscles J joint force
Figure 2-11 Anatomic examples of the three lever systems. (1) Forces at the ankle when standing on one foot. (If) Forces on the pelvis when standing on both feet. (Ill) Forces on the forearm when holding a weight in the hand (weight of forearm is neglected). The break in vectors (J and M in [III]) indicates that their magnitude is not drawn to scale.
33
Force arm
,~B9"L ea~T~ proximally or distally. In the body, the first-class s.. ~q\J.~n,tlyused for maintaining postures or balance (see Fig. 2-11 I). .. ts:fOund at the atlanto-occipital joint (axis), where the head (weight) s b~lanced by-neck extensor muscle force. The same principle occurs at the inter.. ;-!·Y~~R.~~!;jR~~l~in,sitting or standing, where the weight of the trunk is balanced by .>j;ii.!t~~~r~9tPclYr(lndreaches the maximum at 90 degrees of shoulder elydecreas es again as shoulder fle~on continues. Only when force is perpendicular to the lever arm is the distance the = 20° Find: M= J = a =
o o
- 380 Ibs. (0.342) + 30 Ibs. (0.866) - 130 Ibs. + 26 Ibs.
Jr
= 1041bs.
J sin a sin a
[
1041bs.
3501bs. 0.297
a = 17°
Figure 2-24 Trigonometric solution for the magnitude of the muscle and joint forces as well as the angle of the joint force when the 'seated subject is holding a 30-lb weight on the foot and the knee is at 30 degrees of t1exion (see Fig. 2-19). Force vectors are placed on the coordinate system and resolved into components, as in Figure 2-21. Angles and distances are determined and labeled. The problem is solved by using the two equilibrium formulas and trigonometric ratio. The angle and the distance of the patellar tendon attachment were measured from radiographs. The angle of knee t1exion and the distance of the weight from the joint center were measured on the subject. (This simplified equation introduces a 7-lb error in the value of J. A more aC!;:!lJ:.iJ1j;~quation requires finding 1x as well as Jr and then using the Pythagorean theorem to find J = "\IJ/ + J/.
48
Brunnstrom's Clinical Kinesiology
Mr x s M r = 1: m -'- S M r = 520 in-lb -'- 4 in
To find the force in the muscle (M), the rotary component M r must first be found, To find the magnitude of the rotary component of the muscle (M r ), use the formula for torque:
1: m =
Mr
To find the muscle force (M), use trigonometric functions of the right triangle:
=
1301b
sin 20°
= Mr M = Mr
-'-
M
-'-
sin 20°
M = 130 Ib -'- 0.342 M = 380 Ib
To find the approximate magnitude of the joint force U), use the equilibrium formula:
To find the angle of application for J, one of the components of J must be found. If, at equilibrium, the sum of the forces is zero, then the sum of the rectangular components must also be zero. To find the magnitude of J component, use the equilibrium formula 2:Fx = 0 or H y = O. To find the angle of the joint force, use trigonometric functions and find the degree of the angle in a table of sines and cosines.
H=O -J+M-W=O - J = -380 Ib + 30lb J = 350 lb
H
-Jr +
y
=
0
Mr - W r = 0 -Jr = -M r + W r
-Jr Jr
= =
sin ex = sin ex = sin ex = ex =
-130 lb + 26lb 104lb
Jr -'- J '104 lb -'- 350 lb 0.297 17°
If this problem were repeated with the knee in full extension, the rotary component of the weight (Wr ) would be larger, thus increasing the torque of the weight (1:w) as well as the torque of the muscle (1:m ), the muscle force (M), and the joint force U) .. Conversely, if the angle between the horizontal and the tibia were increased to 60 degrees, the values of W" 1:w , 1:m , M and J would all be less. Note that the weight of the leg and foot was omitted in this problem (see Fig. 2-23). The weight of the leg and foot (w) is approXimately 9 lb acting at its center of gravity 8 inches from the origin of the coordinate system in a vertical direction. When this force is added, the corrected equilibrium equations are: A.
B.
2:1: =
30 lb (0.866) 20 in + 9 lb (0.866) 8 in - M (0.342) 4 in = M = 2:F = - J + 425 lb - 30 lb - 9 lb =
J=
0
0 425 lb 0 0 386 lb
The vector equation 2:F = 0 has been used to simplify equations for finding the joint forces U) and introduces a 2 percent error into this problem. The correct equation requires finding both of the components of J and then using the Pythagorean theorem: J = YJx 2 + Jy 2 . When this is done, J is found to be 357 lb when the weight of the leg is neglected and 396 lb when the weight of the leg is included.
50
Brunnstrom's Clinical Kinesiology
Fischer, 1984), or approximately 55 percent of a person's height (Hellebrandt et ai, 1938), The horizontal plane through this point can be found experimentally using a long board supported at one end by a bathroom scale and supported at the other end by blocks (Fig, 2-25). Triangular strips of wood are placed between the plank and the supports to act as "knife edges." The distance between the edges is measured. Then the subject, who has been preViously weighed, lies down on the board with all of the body positioned between the knife edges to form a second-class lever system. The values for (1) the scale reading, (2) the subject's weight, and (3) the distance between the knife edges can be entered into the equilibrium formula L't = 0 to find the distance from the axis (A) that the weight is centered. The distance is the center of gravity in the horizontal plane and can be marked on the subject with chalk before the subject moves from the board. The center-of-gravity mark usually falls near the level of the anterior-superior spines of the ilium. Variations in body proportions and weight distribution cause
1\
....
)
Scale yaxis I
I I
I
~I
l+·--------------d
a~s:t--------~-------------------------r:I I I
W
IT
'.
A W S d s
= axis
+ Ws - Sd
= body weight (150 Ibs.) = scale reading (80 Ibs.) = distance between supports (76 in.) = distance of center of gravity from axis
s s s
=0 =0 = -Sd W x 76 in. = 80 Ibs. 1501bs. = 40.5 in.
Figure 2-25 Experimental method for finding the center of gravity in the horizontal plane when the subject is in the. anatomic position. The vector diagram is placed on the coordinate system with the axis (A) at the origin and the board on the x axis. The weight of the board is eliminated from the equation by placing the scale on zero before the subject lies down.
51
found to be slightly higher in shoulders, while women ;:)hove-~:nE'e amputations will have a high a conventional wheelchair l1'"
a
applied forces, yvhich may occur with manual resistance, exercise crutch-walking, propelling a wheelchair, or opening a door, do not act in "o.·.. r'.. direction as do weights attached to the body. Instead, the forces exert efthat vary according to their particular angle of application and have either distracting or stabilizing components. In pulley systems, the angle of application chamg,es in different parts of the range of motion (Fig. 2-33). Each change in the angle (or direction) of the force causes a change in the magnitude of the rotary component of the force. Consequently, the resistance torque will vary at different points of the range of motion. LAlL. muscles become elbow flexors.
'j.. rv1e(~h(mll::;al Disadvantage of Muscles /"'l\tfulsclle attachments and action lines lie close to joint axes, and most muscle tenattach to bones at an acute angle. Consequently, muscles have short force distances and a mechanical disadvantage relative to the more distally placed /:;;::Di"Vi/ i'j·esilstcmy
releasing small ." '. e.i'nilJ}?es,.ciluse dealq~/ainel1rol.1 upon
'ftfil~t",jI,lhibitory ~Fi~l)/o~i the postodinactive.. Action 9Hitatory' impulses exy,IJ.~I?Jicending of an in~apticmembrane rather f..)ieurotransmitters is found
'"
.~ct~~:i/6f~~~~le
fibers by sending control sig-
?~~9~~lstConversion of a nerve impulse to a muscle
ufs .o~ghac8mplicatedprocess. The nerve fiber branches rW".amotpr~nd"plate,'Nhich adheres tightly to the muscle fiber but , . ....,§t,:lie;:~~tfiinthemuscle fiber membrane (see Fig. 3-4C). The junc~iof1ff .d i?a:]YIW' of synapse referred to as the myoneural (Gr. mye, muscle) ·!i;>jp~~~~9n~fh~!~Bq-Pla.~~ofthemotorneuron contains mitochondria that synthe'sJze;(milril,lf~ctllr~).·aneurQtransmitter, a cetylcholine. Molecules of acetylcholine •.. ille.storedjnsm
>'
progra~s : .:.
Muscles
Figure 3-21 Block diagram of the spinal and supraspinal motor centers and their important connections, Sensory inputs are summarized on the le{t, while the right column indicates the chief role played by structures in the middle of the diagram during the performance of movements, Note that motor cortex is assignee! to the transition between programs and execution of movement. (From Schmidt, RF red]: Fundamentals ofNellruphysiology, ed 2, Springer-Verlag, New York, 1978, p 176, with permission,)
Aspects of Muscle Physiology and Neurophysiology
111
Npte,however, that voluntary motor commands may be superimposed upon nvoiuntary motor commands to achieve a particular posture or movement. basal ganglia participate in the conversion of plans for movement reh;arisein the supplementary motor cortex) into programs for movement. ~iei,.of the basal ganglia are particularly significant with respect to the initia· )ii;and execution of slow movements. The basal ganglia are adjacent. to the Ia,IIlus,an important sensory relay center in the brain (see Fig. 3-19). c>Th:e.cerebellum is interconnected with all levels of the CNS and functions as '¢:V:eriiLlIcoordinator" of motor activities. The cerebellum is responsible primal'programming rapid movements, correcting the course of rapid moveeIlts;;and correlating posture and movement (see Fig. 3-18). Thus, the cerebel
