Chapter 12 Control of Body Movement PDF

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Chapter 12: Control of Body Movement LECTURE

UNIT 3

12.1 Overview of Motor Control Objectives:  Explain the importance of lower motor neurons.  Describe the sources of input to lower motor neurons.

Lower Motor Neurons Provide Output from the CNS to Skeletal Muscle Fibers excitatory and inhibitory signals that control all voluntary movements and some involuntary movements converge on somatic motor neurons somatic motor neurons = lower motor neurons LMN b/c their cell bodies are in lower parts of CNS (brain stem or spinal cord) from brain stem → axons of lower motor neurons extend through cranial nerves to innervate skeletal muscles of face and head from spinal cord → axons of lower motor neurons extend through spinal nerves to innervate skeletal muscles of limbs + trunk final common pathway → lower motor neurons provide output from CNS to skeletal muscle fibers (only way)

There Are 4 Sources of Input to Lower Motor Neurons  Local Circuit Neurons located close to LMN cell bodies in brain stem & spinal cord coordinate somatic reflexes major role in locomotion (walking, running)  Upper Motor Neurons an interneuron gives input to LMN & local circuit neurons cell bodies in motor processing centers of upper part of CNS upper motor neuron | local circuit neurons | LMN few synapse directly with LMNs those located in cerebral cortex and for planning and execution of voluntary movements those that originate in motor centers of brain stem (ex: reticular formation, red nucleus, vestibular nuclei, superior colliculus) regulate posture, balance, muscle tone, reflexive movement of head & trunk  Basal Nuclei assist movement by providing input to upper motor neurons interconnect with motor areas of cerebral cortex (via thalamus) and brain stem help initiate movements, suppress unwanted movements + establish normal muscle tone  Cerebellum control activity of upper motor neurons interconnect with motor areas of cerebral cortex (via thalamus) and brain stem monitor differences between intended movements and movements actually performed

issues commands to upper motor neurons to reduce errors in movement coordinates body movements + helps maintain posture and balance

CHECKPOINT why are lower motor neurons called the final common pathway? because they directly stimulate skeletal muscles what provides input to the lower motor neurons in order to control movements? vestibular nuclei superior colliculus reticular formation

12.2 Local Level of Motor Control Objectives:  Describe the importance of a somatic reflex arc.  Provide specific examples of somatic reflexes.  Discuss the functional significance of central pattern generators.

local level of motor control is coordinated by local circuit neurons LCNs) local circuit neurons receive input from somatic sensory receptors (ex: nociceptors) and muscle spindles + higher centers of the brain LCNs promote somatic reflexes and rhythmic movements of locomotion

Somatic Reflexes Allow Fast, Involuntary Contractions of Skeletal Muscle what are somatic reflexes?

fast, involuntary responses that occur when action potentials pass through a somatic reflex arc (pathway) allow skeletal muscle to contract quickly in response to certain stimuli (pain, over-stretching, excess tension)

Components of Somatic Reflex Arc

what are sensory receptors? distal end of a sensory neuron produces receptor potential types — nociceptors, muscle spindles + tendon organs what are sensory neurons? receptor potential triggers AP in axon of sensory neuron AP conveyed along axon in CNS what is the integrating center? region of GM within brain stem or spinal cord processes incoming sensory info spinal reflex → integration takes place in spinal cord

cranial reflex → integration takes place in brain stem GM consists of one or more interneurons, which may relay action potentials to other interneurons as well as to a motor neuron polysynaptic reflex arc involves more than two types of neurons and more than one CNS synapse what are motor neurons? AP triggered by integrating center propagate out of CNS along somatic motor neuron to an effector what is an effector? skeletal muscle — in somatic reflex arc

The Stretch Reflex monosynaptic reflex arc

ipsilateral

activation of single sensory neuron that forms one synapse in CNS with single motor neuron ex: patellar (knee jerk) reflex — extension of the leg at the knee joint by contraction of the quadriceps femoris muscle of the thigh in response to tapping the patellar ligament

 slight stretching of muscle stimulates muscle spindles (type of sensory receptor) — which monitor length of muscle  muscle spindle generates receptor potential if reaches threshold, it triggers one or more AP that propagate along somatic sensory neuron through dorsal root of spinal nerves into spinal cord  in spinal cord (integrating center), sensory neuron makes excitatory synapse and activates motor neuron in ventral gray horn An axon collateral (branch) from the muscle spindle sensory neuron also synapses with an inhibitory interneuron in the integrating center when the stretched muscle contracts during a stretch reflex, antagonistic muscles that oppose the contraction relax  one or more AP arise in motor neuron and propagate along its axon, extends from spinal cord into ventral root and through peripheral nerves to stimulated muscle axon terminals of motor neuron form neuromuscular junctions NMJs) with skeletal muscle fibers of stretched muscle  ACh released by AP at NMJs triggers one or more AP in stretched muscle (effector) → muscle contracts

what is an ipsilateral reflex? sensory input enters spinal cord on same side from which motor output leaves ALL monosynaptic reflexes are ipsilateral

By adjusting how vigorously a muscle spindle responds to stretching, the brain sets an overall level of muscle tone

what is reciprocal innervation?

type of arrangement, in which the components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonists

The Tendon Reflex

feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn ipsilateral sensory receptors → tendon organs Golgi tendon organs) — lie within tendon near its junction w/ muscle

tendon organs detect and respond to changes in muscle tension that are caused by passive stretch or muscular contraction

 tension on tendon increases → tendon organ (sensory receptor) is stimulated (depolarized to threshold)  AP arise and propagate into spinal cord (integrating center) along sensory neuron  sensory neuron activates an inhibitory interneuron that synapses with motor neuron sensory neuron from the tendon organ also synapses with an excitatory interneuron in the spinal cord excitatory interneuron in turn synapses with motor neurons controlling antagonistic muscle reciprocal innervation → while the tendon reflex brings about relaxation of the muscle attached to the tendon organ, it also triggers contraction of antagonists  inhibitory NT hyperpolarizes motor neuron, which generates fewer APs  muscle relaxes and relieves tension

The Flexor Withdrawal) Reflex causes flexion of limb in order to withdraw from painful stimulus ipstilateral → the incoming and outgoing action potentials propagate into and out of the same side of the spinal cord polysynaptic reflex arc → several motor neurons must simultaneously convey action potentials to several limb muscles intersegmental reflex arc → action potentials from one sensory neuron ascend and descend in the spinal cord and activate interneurons in several segments of the spinal cord

a single sensory neuron can activate several motor neurons more than one effector

stimulating

 stimulus (ex: stepping on tack) stimulates dendrites (sensory receptor) of pain-sensitive neuron  generates AP, which propagates into spinal cord (integrating center)  sensory neuron activates interneurons that extend to several spinal cord segments  interneurons activate motor neurons that generate AP and propagate toward axon terminals  ACh released by motor neurons causes flexor muscles in thigh (effector) to contract — producing withdrawal of leg

The Crossed Extensor Reflex causes extension of the opposite limb to help maintain balance synchronizes the extension of the contralateral limb with the withdrawal (flexion) of the stimulated limb contralateral reflex arc → sensory input enters one side of the spinal cord and motor output exits on the opposite side

 stepping on tack stimulates sensory receptor of pain-sensitive neuron in RIGHT foot  sensory neuron generates AP, which propagates to spinal cord (integrating center)  sensory neuron activates interneurons that synapse with motor neuron on LEFT side of spinal cord in several spinal cord segments incoming pain signals cross to the opposite side through interneurons (@ point of entry into spinal cord)

 interneurons excite motor neurons in several spinal cord segments that innervate extensor muscles — motor neurons generate more AP that propagate toward axon terminals  ACh released by motor neurons causes extensor in thigh (effector) of unstimulated LEFT limb to contract → producing extension weight can be placed on the foot that must now support the entire body

Central Pattern Generators Are Responsible for Locomotion lumbar spinal cord contains networks of local circuit neurons called central pattern generators CPGs) CPGs responsible for the rhythmic movements (alternating flexion and extension) of the limbs that occur during locomotion coordinate the output of the lower motor neurons that control the muscles of the limbs while the body is walking or running sustain limb movements on their own without any additional input from higher centers in the brain

CHECKPOINT what are components of a somatic reflex arc? sensory receptors sensory neuron integrating center motor neuron effector what type of reflex prevents muscles from over stressing tendons? tendon reflex what reflex is typically polysynaptic and contralateral?

cross extensor reflex small diameter motor neurons are known as ____ motor neurons. gamma what is responsible for rhythmic movements like walking? central pattern generators CPGs)

12.3 Control of Movement by the Cerebral Cortex Objectives:  Discuss the functions of the motor areas of the cerebral cortex.  Describe the roles of the corticospinal and corticobulbar tracts.

what 2 areas in cerebral cortex play important roles in motor control?  primary motor cortex  premotor cortex

The Premotor Cortex Creates a Motor Plan the idea/desire to move is generates in one or more cortical association area info is sent to basal nuclei, which processes the info and sends to thalamus → premotor cortex association area → basal nuclei → thalamus → premotor cortex motor plan is developed in the premotor cortex

what is the motor plan? This plan identifies which muscles should contract, how much they need to contract, and in what order

premotor cortex → primary motor cortex → movement the premotor cortex stores info about learned motor activities premotor cortex activates appropriate neurons in primary motor cortex causing specific groups of muscle to contract in specific sequence

The Primary Motor Cortex Controls the Execution of Voluntary Movements Electrical stimulation of any point in the primary motor cortex causes contraction of specific muscles on the opposite side of the body controls muscles by forming descending pathways that extend to the spinal cord and brain stem Different muscles are represented unequally in the primary motor cortex More cortical area is devoted to those muscles involved in skilled, complex, or delicate movement (ex: fingers, lips, tongue)

The Primary Motor Cortex Gives Rise to the Direct Motor Pathways Direct motor pathways provide input to lower motor neurons via axons that extend directly from the cerebral cortex AKA pyramidal pathways consists of axons that descend from pyramidal cells of primary motor cortex and premotor cortex

The Corticospinal Pathways conduct action potentials for voluntary control of skeletal muscles of the limbs and trunk

axons of upper motor neurons in cerebral cortex form corticospinal tracts which descend from cerebral cortex to spinal cord pass through medulla oblongata, forming ventral bulges (pyramids) 90% of corticospinal axons cross over in medulla then descend into spinal cord

LATERAL CORTICOSPINAL TRACT axons synapse with lower motor neurons that supply skeletal muscles in the distal parts of the limbs distal muscles are responsible for precise, agile, and highly skilled movements of the hands and feet

VENTRAL CORTICOSPINAL TRACT the 10% of corticospinal axons that do not cross over in medulla — cross over in spinal cord synapse with lower motor neurons that supply skeletal muscles in the trunk and proximal parts of the limbs trunk = muscles located in the chest, back, and abdomen proximal muscles = upper parts of limbs

The Corticobulbar Pathway conducts APs for voluntary control of skeletal muscles in the head axons of upper motor neurons from cerebral cortex form corticobulbar tract which descends from cerebral cortex to brain stem synapse with lower motor neurons associated with nine pairs of cranial nerves oculomotor trochlear trigeminal

abducens facial glossopharyngeal vagus accessory hypoglossal control facial expression, chewing, speech, and movements of the eyes, tongue + neck

CHECKPOINT where in the cerebral cortex is the idea or thought to move generated? premotor cortex which tract from the cerebral cortex allows you to tie your shoes lateral corticospinal tract the _______ ________ is the motor area of the cerebral cortex responsible for developing a motor plan and storing learned motor info premotor cortex

12.4 Control of Movement by the Brain Stem Objectives:  Identify the motor centers of the brain stem.  Explain the functions of the various tracts of the indirect motor pathways.

brain stem is important to motor control

what are the 4 major motor centers that help regulate body movements in the brain stem?  vestibular nuclei — in medulla & pons  reticular formation  superior colliculus — in midbrain  red nucleus — in midbrain

Brain Stem Motor Centers Give Rise to the Indirect Motor Pathways Indirect motor pathways provide input to lower motor neurons from motor centers in the brain stem AKA extrapyramidal pathways convey APs from brain stem to cause involuntary movements and regulate posture, balance, muscle tone, and reflexive movements of head + trunk

The Vestibular Nuclei Help Control Posture in Response to Changes in Balance

postural reflexes keep the body in an upright and balanced position

what are the 3 sources of input for postural reflexes?  the eyes — visual info about position of body in space  the vestibular apparatus of the inner ear — info about position of head  proprioceptors in muscles and joints — info about position of limbs

sensory input → upper motor neurons (brain stem) → lower motor neurons → appropriate postural muscles contract

posture also maintained by stretch and crossed extensor reflexes — regulated by reflex centers in spinal cord

vestibular nuclei receive neural input form vestibulocochlear VIII nerve regarding state of equilibrium of body + neural input form cerebellum generate AP along axons of vestibulospinal tract → convey signal to skeletal muscle of trunk + proximal limbs → contraction to maintain posture

The Superior Colliculus Promotes Reflexive Movements of the Head and Trunk and Saccadic Eye Movements superior colliculus located in tectum (roof) of midbrain receives visual input from eyes + auditory input from ears

sudden, unexpected input → superior colliculus produces AP along tectospinal tract → activate skeletal muscles in head and trunk

allows body to turn in direction of sudden visual or auditory stimulus

superior colliculus is integrating center for saccades what are saccades? small, rapid jerking movements of the eyes that occur as a person looks at different points in the visual field

CHECKPOINT which tracts from the brain stem help regulate posture? vestibulospinal tracts which tract allows the body to turn in the direction of sudden visual or auditory stimuli? tectospinal tract these tracts control precise movements lateral corticospinal tract rubrospinal tract

12.5 The Basal Nuclei and Motor Control Objectives:  Describe the functions of the basal nuclei

WHAT ARE THE FUNCTIONS OF THE BASAL NUCLEI/GANGLIA?  Initiation of Movements INPUT: sensory association & motor areas of cerebral cortex OUTPUT: basal nuclei → thalamus → premotor cortex → primary motor cortex (upper motor neurons) → activate corticospinal and corticobulbar tracts → promotes movement

 Suppression of Unwanted Movements tonically inhibiting the neurons of the thalamus that affect the activity of the upper motor neurons in the motor cortex particular movement desired — remove inhibition of thalamic neurons to activate appropriate upper motor neurons in motor cortex  Regulation of Muscle Tone neurons of basal nuclei send AP to reticular formation to reduce muscle tone via medial and lateral reticulospinal tracts  Regulation of Non-motor Processes Non-motor aspects of cortical function = sensory, limbic, cognitive, and linguistic functions help initiate and terminate some cognitive processes, such as attention, memory, and planning act with the limbic system to regulate emotional behaviors

CHECKPOINT the basal nuclei initiate movements or suppress unwanted movements by acting on neuron in what structure? thalamus what are non-motor functions of the basal nuclei? initiate cognitive processes regulate emotional behaviors regulate some sensory functions

12.6 Modulation of Movement by the Cerebellum  Describe how the cerebellum controls body movements.

cerebellum exerts influence body movements by acting on upper motor neurons helps maintain proper posture and balance active in learning and performing rapid, coordinated, highly skilled movements

4 ACTIVITIES OF CEREBELLAR FUNCTION  Monitoring Intentions for Movement receives input from the motor cortex and basal nuclei via pontine nuclei in the pons regarding what movements are planned  Monitoring Actual Movement receive input from proprioceptors in joint and muscles that reveals what is actually happening AP travel along ventral & dorsal spinocerebellar tracts AP from vestibular apparatus (inner ear) and from eyes also enter cerebellum  Comparing Command Signals with Sensory Information compares intentions for movement with actual movement performed → comparator function  Sending Out Corrective Feedback nuclei deep within the cerebellum send out corrective feedback signals to upper motor neurons in the cerebral cortex (via the thalamus) and in brain stem motor centers upper motor neurons alter movements accordingly via direct and indirect motor pathways cerebellum continuously provides error corrections to upper motor neurons, which decreases errors and smoothes the motion

CHECKPOINT what is used to send input to the cerebellum about intentions for movement? pontine nuclei monitoring movements by receiving input from proprioceptors is done by way of ...? spinocerebellar tracts Learning and performing rapid, coordinated, highly skilled movements is a function of ...? cerebellar nuclei

CHAPTER REVIEW 12.1 Overview of Motor Control  All excitatory and inhibitory sig...