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Somatic Nervous System Divisions of the PNS: Somatic Nervous System • Controls voluntary actions • Made up of the cranial and spinal nerves that go from the central nervous system to your skeletal muscles Autonomic Nervous System • Controls involuntary actions-those not under conscious control-such as your heart rate, breathing, digestion, and glandular functions Skeletal Muscles • Responsible for movement of body and all of its joints • Muscle contraction produces force that causes joint movement • Muscles also provide • protection • posture and support • produce a major portion of total body heat 2-3 Skeletal Muscles Manual of Structural Kinesiology Neuromuscular Fundamentals 2-4 Skeletal Muscles • Over 600 skeletal muscles comprise approximately 40 to 50% of body weight • 215 pairs of skeletal muscles usually work in cooperation with each other to perform opposite actions at the joints which they cross • Aggregate muscle action - muscles work in groups rather than independently to achieve a given joint motion 2-5 Muscle Tissue Properties Skeletal muscle tissue has 4 properties related to its ability to produce force & movement about joints • Irritability or Excitability - property of muscle being sensitive or responsive to chemical, electrical, or mechanical stimuli • Contractility - ability of muscle to contract & develop tension or internal force against resistance when stimulated – unique to muscle • Extensibility - ability of muscle to be passively stretched beyond it normal resting length • Elasticity - ability of muscle to return to its original length following stretching 2-6 Muscle Terminology • Action - specific movement of joint resulting from a concentric contraction of a muscle which crosses joint • Ex. biceps brachii has the action of flexion at elbow • Actions are usually caused by a group of muscles working together 2-7 Muscle Terminology • Innervation - segment of nervous system defined as being responsible for providing a stimulus to muscle fibers within a specific muscle or portion of a muscle • A muscle may be innervated by more than one nerve & a particular nerve may innervate more than one muscle or portion of a muscle 2-8 Muscle Terminology • When a particular muscle contracts • it tends to pull both ends toward the gaster • if neither of the bones to which a muscle is attached are stabilized then both bones move toward each other upon contraction • more commonly one bone is more stabilized by a variety of factors and the less stabilized bone usually moves toward the more stabilized bone upon contraction • Ex. biceps curl exercise • biceps brachii muscle in arm has its origin (least movable bone) on scapula and its insertion (most movable bone) on radius • In some movements this process can be reversed, Ex. pull-up • radius is relatively stable & scapula moves up • biceps brachii is an extrinsic muscle of elbow • brachialis is intrinsic to the elbow 2-9 Types of muscle contraction • Contraction - when tension is developed in a muscle as a result of a stimulus • Muscle “contraction” – may not necessarily mean shorten • Muscle contractions also referred to as muscle actions 2-10 Types of muscle contraction Muscle Contraction (under tension) Isometric Isotonic Concentric Eccentric 2-11 Types of muscle contraction • Isotonic contractions involve muscle developing tension to either cause or control joint movement • dynamic contractions • the varying degrees of tension in muscles result in joint angles changing • Isotonic contractions are either concentric or eccentric on basis of whether shortening or lengthening occurs Types of muscle contraction • Concentric contraction • muscle develops tension as it shortens • occurs when muscle develops enough force to overcome applied resistance • causes movement against gravity or resistance • described as being a positive contraction 2-13 Types of muscle contraction • Concentric contraction • force developed by the muscle is greater than that of the resistance • results in joint angle changing in the direction of the applied muscle force • causes body part to move against gravity or external forces 2-14 Types of muscle contraction • Eccentric contraction (muscle action) • muscle lengthens under tension • occurs when muscle gradually lessens in tension to control the descent of resistance • weight or resistance overcomes muscle contraction but not to the point that muscle cannot control descending movement 2-15 Types of muscle contraction • Eccentric contraction (muscle action) • controls movement with gravity or resistance • described as a negative contraction • force developed by the muscle is less than that of the resistance 2-16 Types of muscle contraction • Eccentric contraction (muscle action) • results in the joint angle changing in the direction of the resistance or external force • controls body part to allow movement with gravity or external forces (resistance) • used to decelerate body segment movement 2-17 Types of muscle contraction • Eccentric contraction (muscle action) • Some refer to this as a muscle action instead of a contraction since the muscle is lengthening as opposed to shortening • Various exercises may use any one or all of these contraction types for muscle development 2-18 Types of muscle contraction • Isokinetics (isovelocity) - type of dynamic exercise using concentric and/or eccentric muscle contractions • speed (or velocity) of movement is constant • muscular contraction (ideally maximum contraction) occurs throughout movement • not another type of contraction, as some have described • Ex. Biodex, Cybex, Lido 2-19 Role of Muscles • Agonist muscles • cause joint motion through a specified plane of motion when contracting concentrically • known as primary or prime movers, or muscles most involved 2-20 Role of Muscles • Antagonist muscles • • • • located on opposite side of joint from agonist have the opposite concentric action known as contralateral muscles work in cooperation with agonist muscles by relaxing & allowing movement • when contracting concentrically perform the opposite joint motion of agonist • Ex. quadriceps muscles are antagonists to hamstrings in knee flexion 2-21 Role of Muscles • Stabilizers • surround joint or body part • contract to fixate or stabilize the area to enable another limb or body segment to exert force & move • known as fixators • essential in establishing a relatively firm base for the more distal joints to work from when carrying out movements • Ex. biceps curl • muscles of scapula & glenohumeral joint must contract in order to maintain shoulder complex & humerus in a relatively static position so that the biceps brachii can more effectively perform curls 2-22 Role of Muscles • Synergist • • • • • assist in action of agonists not necessarily prime movers for the action known as guiding muscles assist in refined movement & rule out undesired motions helping synergists & true synergists 2-23 Role of Muscles • Neutralizers • counteract or neutralize the action of another muscle to prevent undesirable movements such as inappropriate muscle substitutions • referred to as neutralizing • contract to resist specific actions of other muscles • Ex. when only supination action of biceps brachii is desired, the triceps brachii contracts to neutralize the flexion action of the biceps brachii 2-24 Throughout the central nervous system, the neurons involved in controlling skeletal muscles can be thought of as being organized in a hierarchical fashion, each level of the hierarchy having a certain task in motor control • Given such a highly interconnected and complicated neuroanatomical basis for the motor system, it is difficult to use the phrase voluntary movement with any real precision. • We will use it, however, to refer to those actions that have the following characteristics: • (1)The movement is accompanied by a conscious awareness of what we are doing and why we are doing it, and • (2) our attention is directed toward the action or its purpose. • The term “involuntary,” on the other hand, describes actions that do not have these characteristics. • “Unconscious,” “automatic,” and “reflex” are often taken to be synonyms for “involuntary,” although in the motor system the term “reflex” has a more precis meaning. Conceptual Motor Control Hierarchy I. The lowest level (the local level) a. Function: specifies tension of particular muscles and angle of specific joints at specific times necessary to carry out the programs and subprograms transmitted from the middle control levels. b. Structures: levels of brainstem or spinal cord from which motor neurons exit. Conceptual Motor Control Hierarchy II. The middle level a. Function: converts plans received from the highest level to a number of smaller motor programs, which determine the pattern of neural activation required to perform the movement. These programs are broken down into subprograms that determine the movements of individual joints. The programs and subprograms are transmitted through descending pathways to the lowest control level. b. Structures: sensorimotor cortex, cerebellum, parts of basal nuclei, some brainstem nuclei. Conceptual Motor Control Hierarchy III. Higher centers a. Function: forms complex plans according to individual’s intention and communicates with the middle level via “command neurons.” b. Structures: areas involved with memory and emotions, supplementary motor area, and association cortex. All these structures receive and correlate input from many other brain structures. Neurons (nerve cells) - basic functional units of nervous system responsible for generating & transmitting impulses and consist of ALL OR NONE PRINCIPLE • When muscle contracts, contraction occurs at the muscle fiber level within a particular motor unit • Motor unit • Single motor neuron & all muscle fibers it innervates • Function as a single unit • All or None Principle - regardless of number, individual muscle fibers within a given motor unit will either fire & contract maximally or not at all 2-29 Factors affecting muscle tension development • Difference between lifting a minimal vs. maximal resistance is the number of muscle fibers recruited • The number of muscle fibers recruited may be increased by • activating those motor units containing a greater number of muscle fibers • activating more motor units • increasing the frequency of motor unit activation 2-30 Factors affecting muscle tension development • Number of muscle fibers per motor unit varies significantly • From less than 10 in muscles requiring precise and detailed such as muscles of the eye • To as many as a few thousand in large muscles that perform less complex activities such as the quadriceps 2-31 Factors affecting muscle tension development • Summation • When successive stimuli are provided before relaxation phase of first twitch has completed, subsequent twitches combine with the first to produce a sustained contraction • Generates a greater amount of tension than single contraction would produce individually • As frequency of stimuli increase, the resultant summation increases accordingly producing increasingly greater total muscle tension 2-32 Factors affecting muscle tension development • Tetanus • results if the stimuli are provided at a frequency high enough that no relaxation can occur between contractions 2-33 Interneurons • Most of the synaptic input to motor neurons from the descending pathways and afferent neurons does not go directly to motor neurons but rather to interneurons that synapse with the motor neurons. • Interneurons comprise 90 percent of spinal cord neurons, and they are of several types. • The local interneurons are important elements of the lowest level of the motor control hierarchy, integrating inputs not only from higher centers and peripheral receptors but from other interneurons as well. • They are crucial in determining which muscles are activated and when. • Moreover, interneurons can act as “switches” that enable a movement to be turned on or off under the command of higher motor centers. Proprioception & Kinesthesis • Muscle spindles & myotatic or stretch reflex 1. Rapid muscle stretch occurs 2. Impulse is sent to the CNS 3. CNS activates motor neurons of muscle and causes it to contract 2-35 Proprioception & Kinesthesis • Ex. Knee jerk or patella tendon reflex • • • • Reflex hammer strikes patella tendon Causes a quick stretch to musculotendinis unit of quadriceps In response quadriceps fires & the knee extends More sudden the tap, the more significant the reflexive contraction 2-36 Proprioception & Kinesthesis • Manual of Structural Kinesiology Ex. Knee jerk or patella tendon reflex Neuromuscular Fundamentals 2-37 Proprioception & Kinesthesis • Stretch reflex may be utilized to facilitate a greater response • • Ex. Quick short squat before attempting a jump Quick stretch placed on muscles in the squat enables the same muscles to generate more force in subsequently jumping off the floor 2-38 Proprioception & Kinesthesis • Golgi tendon organ • • • • found serially in the tendon close to muscle tendon junction sensitive to both muscle tension & active contraction much less sensitive to stretch than muscle spindles require a greater stretch to be activated 2-39 Proprioception & Kinesthesis • Tension in tendons & GTO increases as muscle contract, which activates GTO 1. GTO stretch threshold is reached 2. Impulse is sent to CNS 3. CNS causes muscle to relax 4. facilitates activation of antagonists as a protective mechanism • GTO protects us from an excessive contraction by causing its muscle to relax 2-40 Reciprocal Innervation • Sensory neuron stimulates motor neuron and interneuron. • Interneurons inhibit motor neurons of antagonistic muscles. • When limb is flexed, antagonistic extensor muscles are passively stretched. Crossed-Extensor Reflex • Double reciprocal innervation. • Affects muscles on the contralateral side of the cord. • Step on tack: • Foot is withdrawn by contraction of flexors and relaxation of extensors. • Contralateral leg extends to support body. motor pathways • Descending motor pathways (i.e., those descending from the cerebral cortex and brain stem) are divided among the pyramidal tract and the extrapyramidal tract. • Pyramidal tracts are corticospinal and corticobulbar tracts that pass through the medullary pyramids and descend directly onto lower motoneurons in the spinal cord. • All others are extrapyramidal tracts. The extrapyramidal tracts originate in the following structures of the brain stem: • The rubrospinal tract originates in the red nucleus and projects to motoneurons in the lateral spinal cord. • Stimulation of the red nucleus produces activation of flexor muscles and inhibition of extensor muscles. • The pontine reticulospinal tract originates in nuclei of the pons and projects to the ventromedial spinal cord. • Stimulation has a generalized activating effect on both flexor and extensor muscles, with its predominant effect on extensors. • The medullary reticulospinal tract originates in the medullary reticular formation and projects to motoneurons in the spinal cord. • Stimulation has a generalized inhibitory effect on both flexor and extensor muscles, with the predominant effect on extensors. • The lateral vestibulospinal tract originates in the lateral vestibular nucleus (Deiters' nucleus) and projects to ipsilateral motoneurons in the spinal cord. • Stimulation produces activation of extensors and inhibition of flexors. • The tectospinal tract originates in the superior colliculus (tectum or "roof" of the brain stem) and projects to the cervical spinal cord. • It is involved in control of neck muscles. • Both the pontine reticular formation and the lateral vestibular nucleus have powerful excitatory effects on extensor muscles. • Therefore, lesions of the brain stem above the pontine reticular formation and lateral vestibular nucleus, but below the midbrain, cause a dramatic increase in extensor tone, called decerebrate rigidity. • Lesions above the midbrain do not cause decerebrate rigidity. Functional subdivision of cerebellum • The cerebellum, or "little brain," regulates movement and posture and plays a role in certain kinds of motor learning. • The cerebellum helps control the rate, range, force, and direction of movements (collectively known as synergy). • Damage to the cerebellum results in lack of coordination. I- Archicerebellum It is concerned with equilibrium. It represents flocculo-nodular lobe. It has connections with vestibular & reticular nuclei of brain stem through the inferior cerebellar peduncle. Schematic drawing of cerebellum showing the relationships between the anatomical & functional divisions of cerebellum. Green =archi-cerebellum, blue=paleo-cerebellum. Pink= neo-cerebellum I- Archicerebellum It is concerned with equilibrium. It represents flocculo-nodular lobe. It has connections with vestibular & reticular nuclei of brain stem through the inferior cerebellar peduncle. Afferent vestibular Fs. Pass from vestibular nuclei in pons & medulla to the cortex of ipsilateral flocculo-nodular lobe. Efferent cortical (purkinje cell) Fs. Project to fastigial nucleus, which projects to vestibular nuclei & reticular formation. Connections of archicerebellum It affects the L.M.system bilaterally via descending vestibulo-spinal & reticulo-spinal tracts. 2- Paleo-cerebellum= (spinal part) : It is concerned with muscle tone & posture. Schematic drawing of cerebellum showing the relationships between the anatomical & functional divisions of cerebellum. Green =archi-cerebellum, blue=paleo-cerebellum. Pink= neo-cerebellum 2-Paleo-cerebellum It is concerned with muscle tone & posture. Afferents spinal Fs. consist of dorsal & ventral spino-cerebellar tract from muscle, joint & cutaneous receptors to enter the cortex of ipsilateral vermis & para vermis Via inferior & superior cerebellar peduncles . Connections of Paleocerebellum. Efferents cortical fibres pass to globose & emboliform nuclei, then Via sup. C. peduncle to contralateral red nucleus of midbrain to give rise descending rubro-spinal tract. 3- Neo-cerebellum= (cerebral part) : It is concerned with muscular coordination. controls the planning and initiation of movements Schematic drawing of cerebellum showing the relationships between the anatomical & functional divisions of cerebellum. Green =archi-cerebellum, blue=paleo-cerebellum. Pink= neo-cerebellum 3- Neo-cerebellum It is concerned with muscular coordination. controls the planning and initiation of movements It receives afferents from cerebral cortex involved in planning of movement- to pontine nuclei ,cross to opposite side Via middle Cerebellar peduncle to end in lateral parts of cerebellum (cerebro-pontocerebellar tract). Neo-cerebellar efferents project to dendate nucleus,which in turn projects to contra-lateral red nucleus & ventral lateral nucleus of thalamus ,then to motor cortex of frontal lobe, giving rise descending cortico-spinal & cortico-bulbar pathways. Connections of Neo-cerebellum. Efferents of dentate nucleus form a major part of superior C. peduncle. BASAL GANGLIA The basal ganglia are the deep nuclei of the telencephalon: • caudate nucleus, • putamen, • globus pallidus, and • amygdala. There also are associated nuclei, including • the ventral anterior and ventral lateral nuclei of the thalamus, • the subthalamic nucleus of the diencephalon, and • the substantia nigra of the midbrain. The main function of the basal ganglia is to influence the motor cortex via pathways through the thalamus. The role of the basal ganglia is to aid in planning and execution of smooth movements. The basal ganglia also contribute to affective and cognitive functions. Cerebral Cortex Corticospinal tract and Corticobulbar projections Brainstem and Spinal Cord Cerebral Cortex Striatum Glutamate Brainstem and Spinal Cord Cerebral Cortex Striatum Glutamate D1 D2 Dopamine Substantai Nigra compacta Brainstem and Spinal Cord Cerebral Cortex Striatum Glutamate Glutamate D1 GABA-dyn DA Direct Pathway Thalamus SNc GABA Brainstem and Spinal Cord Globus pallidus interna/Substantia Nigra reticulata Cerebral Cortex Glutamate Striatum D2 GABA-enk Globus Pallidus externa D1 GABA-dyn Thalamus DA Subthalamic Nucleus SNc Glutamate Brainstem and Spinal Cord Glutamate GABA Gpi/SNr The outputs of the indirect and direct pathways from the basal ganglia to the motor cortex are opposite and carefully balanced: The indirect path is inhibitory, and the direct path is excitatory. Cerebral Cortex Glutamate Indirect Pathway Striatum D2 GABA-enk Globus Pallidus externa Subthala mic Nucleus Brainstem and Spinal Cord Gluta mate D1 GABAdyn DA Direct Pathway Thalamus A disturbance in one of the pathways SNc will upset this balance of motor control, with either an increase or a decrease in motor activity. GABA Glutamate Such an imbalance is characteristic of Globus pallidus interna/Substantia Nigra reticulata diseases of the basal ganglia. MOTOR CORTEX • Voluntary movements are directed by the motor cortex, via descending pathways. • The motivation and ideas necessary to produce voluntary motor activity are first organized in multiple associative areas of the cerebral cortex and then transmitted to the supplementary motor and premotor cortices for the development of a motor plan. • The motor plan will identify the specific muscles that need to contract, how much they need to contract, and in what sequence. • The plan then is transmitted to upper motoneurons in the primary motor cortex, which send it through descending pathways to lower motoneurons in the spinal cord. • The planning and execution stages of the plan are also influenced by motor control systems in the cerebellum and basal ganglia. • The motor cortex consists of three areas: • primary motor cortex, • supplementary motor cortex, and • premotor cortex. • Premotor cortex and supplementary motor cortex (area 6) are the regions of the motor cortex responsible for generating a plan of movement, which then is transferred to the primary motor cortex for execution. • The supplementary motor cortex programs complex motor sequences and is active during "mental rehearsal" of a movement, even in the absence of movement. • Primary motor cortex (area 4) is the region of the motor cortex responsible for execution of a movement. • Programmed patterns of motoneurons are activated from the primary motor cortex. • As upper motoneurons in the motor cortex are excited, this activity is transmitted to the brain stem and spinal cord, where lower motoneurons are activated and produce coordinated contraction of the appropriate muscles (i.e., the voluntary movement). • The primary motor cortex is topographically organized and is described as the motor homunculus. • This topographic organization is dramatically illustrated in jacksonian seizures, which are epileptic events originating in the primary motor cortex. • The epileptic event usually begins in the fingers of one hand, progresses to the hand and arms, and eventually spreads over the entire body (i.e., the "jacksonian march").