Chapter 13: Integrative Physiology I: Control of Body Movement

What are the three phases of voluntary movement?

(1) decision-making and planning (2) initiating the movement (3) executing the movement

What three levels of the nervous system control movement?

(1) the spinal cord, which integrates spinal reflexes and contains central pattern generators (2) the brain stem and cerebellum, which control postural reflexes and hand and eye movements (3) the cerebral cortex and basal ganglia, which are responsible for voluntary movements

Name and briefly describe the three categories of movement.

1) *Reflex movements* are the least complex and are integrated primarily in the spinal cord. However, like other spinal reflexes, reflex movements can be modulated by input from higher brain centers. 2) *Voluntary movements* are the most complex type of movement. They require integration at the cerebral cortex, and they can be initiated at will without external stimuli. Learned voluntary movements improve with practice, and some even become involuntary, like reflexes (muscle memory) 3) *Rhythmic movements*, such as walking or running, are a combination of reflex movements and voluntary movements. Rhythmic movements are initiated and terminated by input from the cerebral cortex, but once activated, networks of CNS interneurons called central pattern generators (CPGs) maintain the spontaneous repetitive activity

Describe the stretch reflex using the standard steps of a reflex. What is the protective purpose of the stretch reflex?

1) Load added to muscle 2) Muscle and muscle spindle stretch as arm extends. Muscle spindle afferents fire more frequently 3) Reflex contraction initiated by muscle stretch restores arm position and prevents damage from overstretching

Stretch Reflexes and Reciprocal Inhibition Control __________ around a Joint

1) Movement

What are central pattern generators (CPGs), and what role do they play in movement?

1) Networks of CNS neurons that function spontaneously to control certain rhythmic muscle movements 2) maintain the spontaneous repetitive activity. (unconscious rhythm of quiet breathing.) The ability of central pattern generators to sustain rhythmic movement without continued sensory input has proved important for research on spinal cord injuries

Movement Can Be Classified as ___1_____, ___2_______, or ___3_______

1) Reflex 2) Voluntary 3) Rhythmic

Integration of muscle reflexes

1) Sensory input from receptors goes to spinal cord, cerebral cortex, and cerebellum. Signals from the vestibular apparatus go directly to the cerebellum 2) Postural and spinal reflexes do not require integration in the cortex. Output signals initiate movement without higher input

List the components of skeletal muscle reflexes.

1) Sensory receptors (proprioceptors). The input signal from proprioceptors goes to the CNS through sensory neurons. 2) The central nervous system integrates the input signal using networks and pathways of excitatory and inhibitory interneurons. In a reflex, sensory information is integrated and acted on subconsciously. However, some sensory information may be integrated in the cerebral cortex and become perception, and some reflexes can be modulated by conscious input. 3) Somatic motor neurons carry the output signal. 4) The effectors are contractile skeletal muscle fibers, also known as extrafusal muscle fibers.

Golgi Tendon Organs Respond to Muscle ___1_____

1) Tension

The presence of gamma motor neurons in a normal muscle keeps the muscle spindles __1_____, no matter what the muscle ___2______ is.

1) active 2) length

Neural Reflexes List the steps in a neural reflex.

1) begin with a stimulus that activates a sensory receptor. 2) The sensor sends information in the form of action potentials through sensory afferent neurons to the CNS. 3) The CNS is the integrating center that evaluates all incoming information and selects an appropriate response. 4) It then initiates action potentials in efferent neurons to direct the response of muscles and glands—the targets (5)

Note in Figure 13.6 how the one sensory neuron synapses on multiple ___1______. ____2________ of the sensory signal permits a single stimulus to control two sets of antagonistic muscle groups as well as to send sensory information to the ____3_____. This type of complex reflex with multiple neuron interactions is more ___4______ of our reflexes than the simple monosynaptic knee jerk stretch reflex.

1) interneurons 2) Divergence 3) brain 4) typical

Explain Alpha-Gamma-Coactivation When alpha motor neurons fire, the muscle ___1____, releasing tension on the muscle spindle capsule. To keep the spindle functioning normally, gamma motor neurons innervating the __2______ ends of the muscle spindle also fire at the same __3____. The gamma motor neurons cause the spindle intrafusal fibers to __4_____ and shorten. This contraction pulls on the central region of the spindle and maintains ___5______ on the sensory nerve endings. As a result, the spindle remains ____6____ even when the muscle contracts

1) shortens 2) contractile 3) time 4) contract 5) stretch 6) active

Explain and give an example of a feedforward postural reflex.

As the pitcher begins the pitch, feedforward postural reflexes adjust the body position, shifting weight slightly in anticipation of the changes about to occur (Fig. 13.11). Through the appropriate divergent pathways, action potentials race to the somatic motor neurons that control the muscles used for pitching: some are excited, others are inhibited. The neural circuitry allows precise control over antagonistic muscle groups as the pitcher flexes and retracts his right arm. His weight shifts onto his right foot as his right arm moves back.

Symptoms of Parkinson's Disease Reflect _________ __________ Function

Basal Ganglia

What is a myotatic unit?

Collection of synergistic and antagonistic muscles that act in a coordinated fashion to control a single joint ( Sensory neurons from muscle receptors and efferent motor neurons that control the muscle are linked by diverging and converging pathways of interneurons within the spinal cord.)

What are extrafusal muscle fibers?

Contractile skeletal muscle fibers (AKA effectors) . Action potentials in alpha motor neurons cause extrafusal fibers to contract

convergent pathway

Convergence integrates the input from multiple sources to modify the response.

Sketch a muscle spindle. Identify the intrafusal fibers, gamma motor neurons, and capsule.

Each muscle spindle consists of a connective tissue capsule that encloses a group of small muscle fibers known as intrafusal fibers (lacks myofibrils) The contractile ends of the intrafusal fibers have their own innervation from gamma motor neurons (Small neuron that innervates intrafusal fibers within the muscle spindle)

What roles do feedforward reflexes and feedback mechanisms play in voluntary movement?

Feedforward reflexes allow the body to prepare for a voluntary movement, and feedback mechanisms are used to create a smooth, continuous motion. Coordination of movement requires cooperation from many parts of the brain.

Describe the role of the corticospinal tract in controlling voluntary movement. (Fig. 13.11)

Group of interneurons controlling voluntary movement that run from the motor cortex to the spinal cord, where they synapse directly onto somatic motor neurons. Most of these descending pathways cross to the opposite side of the body in a region of the medulla known as the pyramids. Consequently, this pathway is sometimes called the pyramidal tract.

13.2 Autonomic Reflexes List locations where autonomic reflex integration centers can be found

In the spinal cord or in the brain, primarily in the hypothalamus, thalamus, and brain stem

polysynaptic reflex

Include one or more interneurons between afferent and efferent neurons. All autonomic reflexes are polysynaptic because they have three neurons: one afferent and two efferent. The modification in polysynaptic pathways may involve excitation or inhibition

Neural Reflexes Distinguish between negative feedback and feedforward responses.

Negative: Feedback signals from muscle and joint receptors keep the CNS continuously informed of changing body position Feedforward: allows the body to anticipate a stimulus and begin the response. Bracing yourself in anticipation of a collision is an example of a feedforward response.

Sketch a Golgi tendon organ and describe its function.

Primarily provide sensory information to CNS integrating centers. The sensory information from GTOs combines with feedback from muscle spindles and joint receptors to allow optimal motor control of posture and movement. When a muscle contracts, its tendons act as a series elastic element during the isometric phase of the contraction. Muscle contraction pulls on collagen fibers within the GTO, pinching sensory endings of the afferent neurons and causing them to fire.

somatic reflexes

Reflexes that involve somatic motor neurons and skeletal muscles

autonomic reflexes

Reflexes whose responses are controlled by autonomic neurons, cardiac muscle, glands, and adipose tissue

Describe the role of the following in planning and executing movement: (Figs. 13.8, 13.9, 13.10; Tbl. 13.3) thalamus

Role: Contains relay nuclie that modulate and pass messages to cerebral cortex Recieves input from: Basal ganglia, cerebellum, and spinal cord Sends integrative Output to: Cerebral cortex

Describe the role of the following in planning and executing movement: (Figs. 13.8, 13.9, 13.10; Tbl. 13.3) basal ganglia

Role: Monitor planning (planning movement) Recieves input from: Cerebral cortex Sends integrative Output to: Cerebral cortex and brain stem

Describe the role of the following in planning and executing movement: (Figs. 13.8, 13.9, 13.10; Tbl. 13.3) cerebellum

Role: Monitors output signals from motor areas and adjusts movements (Planning movement + executing movement) Recieves input from: spinal cord (sensory), cerebral cortex (commands) Sends integrative Output to: Brain stem, cerebral cortex (all output in inhibitory)

Describe the role of the following in planning and executing movement: (Figs. 13.8, 13.9, 13.10; Tbl. 13.3) cerebral cortex

Role: Planning and coordinating complex movements (initiating movement) Recieves input from: thalamus Sends integrative Output to: Brain stem, spinal cord (Corticospinal tract), cerebellum, basal ganglia

Describe the role of the following in planning and executing movement: (Figs. 13.8, 13.9, 13.10; Tbl. 13.3) brain stem

Role: Posture and hand/eye movement (fine tuning movement) Recieves input from: cerebellum, visual and vestibular sensory receptors (information about motion, equilibrium, and spatial orientation - found in ear) Sends integrative Output to: spinal cord

Describe the role of the following in planning and executing movement: (Figs. 13.8, 13.9, 13.10; Tbl. 13.3) spinal cord

Role: Spinal reflexes and locomotor pattern generators Recieves input from: Sensory receptors and brain Sends integrative Output to: Brain stem, cerebelluum, thalamus/cerebral cortex

What functions of the basal ganglia were discovered through research into Parkinson's?

Scientists have learned that the basal ganglia play a role in cognitive function and memory as well as in the coordination of movement.

What are proprioceptors? What are the three types found in the body?

Sensory receptors ( monitor the position of our limbs in space, our movements, and the effort we exert in lifting objects. The input signal from proprioceptors goes to the CNS through sensory neurons) 1) *Joint receptors:* are found in the capsules and ligaments around joints in the body. 2) Golgi tendon organs - Info about contracting muscle (tension) 3) Muscle spindles - Info about stretching muscle

Control of Movement in Visceral Muscles: How does reflex control of visceral muscles differ from reflex control of skeletal muscles?

Skeletal muscles are controlled only by the nervous system, but in many types of visceral muscle, hormones are important in regulating contraction. In addition, some visceral muscle cells are connected to one another by gap junctions that allow electrical signals to pass directly from cell to cell.

Now describe the crossed extensor reflex that would accompany this flexion reflex. (Fig. 13.7)

The crossed extensor reflex is a postural reflex that helps maintain balance when one foot is lifted from the ground. The quick withdrawal of the right foot from a painful stimulus (a tack) is matched by extension of the left leg so that it can support the sudden shift in weight. The extensors contract in the supporting left leg and relax in the withdrawing right leg, while the opposite occurs in the flexor muscles.

learned reflexes (conditioned reflexes)

The example of Pavlov's dogs salivating upon hearing a bell is the classic example of a learned reflex, also referred to as a conditioned reflex.

How can a single stimulus, transmitted through a single sensory neuron, create two opposing responses?

The sensory fibers branch upon entering the spinal cord. Some of the branches activate motor neurons innervating the quadriceps, while the other branches synapse on inhibitory interneurons.

Describe reciprocal inhibition in the knee jerk reflex using the standard steps of a reflex.

The single stimulus of the tap to the tendon accomplishes both contraction of the quadriceps muscle and reciprocal inhibition of the hamstrings. The sensory fibers branch upon entering the spinal cord (integrating center). Some of the branches activate motor neurons innervating the quadriceps (efferent path 1), while the other branches synapse on inhibitory interneurons (efferent path 2). The inhibitory interneurons suppress activity in the motor neurons controlling the hamstrings (a polysynaptic reflex). The result is a relaxation of the hamstrings that allows contraction of the quadriceps to proceed unopposed. (response)

What are alpha motor neurons?

The somatic motor neurons that innervate skeletal muscle contractile fibers are called alpha motor neurons

Why does the crossed extensor reflex take longer than the knee jerk reflex?

This type of reflex requires more time than a stretch reflex (such as the knee jerk reflex) because it is a polysynaptic rather than a monosynaptic reflex.

13.2 Autonomic Reflexes Describe the influences that emotions and higher brain centers can have on autonomic reflexes.

Urination may be voluntarily initiated by conscious thought. Or it may be inhibited by emotion or a stressful situation, such as the presence of other people (a syndrome known as "bashful bladder"). Often, the higher control of a spinal reflex is a learned response. The toilet training we master as toddlers is an example of a learned reflex that the CNS uses to modulate the simple spinal reflex of urination.

Describe the flexion reflex in Figure 13.6 using the standard steps of a reflex.

When the foot contacts the point of the tack, nociceptors (pain receptors) in the foot send sensory information to the spinal cord. Here the signal diverges, activating multiple excitatory interneurons. Some of these interneurons excite alpha motor neurons, leading to contraction of the flexor muscles of the stimulated limb. Other interneurons simultaneously activate inhibitory interneurons that cause relaxation of the antagonistic muscle groups. Because of this reciprocal inhibition, the limb is flexed, withdrawing it from the painful stimulus.

Describe a monosynaptic stretch reflex, the knee jerk (patellar tendon) reflex, using the standard steps of a reflex.

When the patellar tendon below the kneecap is tapped (stuimulus) with a small rubber hammer, the tap stretches the quadriceps muscle (receptor), which runs up the front of the thigh (afferent path). This stretching activates muscle spindles and sends action potentials via the sensory fibers to the spinal cord (integrating center). The sensory neurons synapse directly onto the motor neurons (efferent path) that control contraction of the quadriceps muscle (a monosynaptic reflex). Excitation of the motor neurons causes motor units in the quadriceps to contract, and the lower leg swings forward. (response)

What is muscle tone? (Fig. 13.3a)

continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state

13.2 Autonomic Reflexes Autonomic reflexes are always _________________

polysynaptic

cranial reflexes

reflexes integrated in the brain

As a response to a stimulus, what is the only way to achieve skeletal muscle relaxation?

relaxation results from the absence of excitatory input by the somatic motor neuron. Inhibition and excitation of somatic motor neurons and their associated skeletal muscles must occur at synapses within the CNS. ATP-driven pumps will move Ca++ out of the sarcoplasm back into the SR. This results in the "reshielding" of the actin-binding sites on the thin filaments caused by a lack of excitatory inputs (meanig less ACh in released at the synapse)

monosynaptic reflex

single synapse between the two neurons in the pathway: a sensory afferent neuron (often just called a sensory afferent) and an efferent somatic motor neuron (only somatic motor reflexes can be monosynaptic)