Chapter 19

Front 1

neural circuits

Back 1

- organization of neurons
- receive sensory information
- integrate information
- control effector cells

Front 2

simple sensory motor circuit

Back 2

- sensory neuron synapsing directly on motor cell
- interneuron added = sensory interneuron motor
- can by polyneuronal

Front 3

nervous system of animals

Back 3

- networks of sensory, inerneuron, and motor neurons

Front 4

CNS

Back 4

- brain controls motor behavior
- the cerebellum and basal nuclei are the ultimate planners and coordinators of complex motor activities sending input to the primary motor cortex
- cerebral cortex is the highest level of conscious motor pathways
- thalamus is sensory relay center and is important in motor control
- motor control exerted by lover levels in involuntary and is mediated by reflex arcs and fixed action patterns or stereotypical, sequential motor actions triggered by an appropriate stimulus

Front 5

3 levels of cerebellar and basal nuclei motor control

Back 5

- segmental level
- projection level
- pre-command level
- develop a motor program for the specific voluntary task
- pull the appropriate pattern in the primary motor cortex to bring about the sequence of necessary contractions

Front 6

segmental level

Back 6

- located in cerebellum and basal nuclei
- spinal cord circuits that activate a network of anterior/ventral horn neurons to a single cord segments causing them to stimulate a specific group of muscle fibers

Front 7

organization of vertebrate CNS

Back 7

- gray matter = consists of cell bodies, synapses, and unmyelinated neural processes
- white matter = consists of tracts of myelinated axons
- segmental nerves of PNS connect to the spinal cord via sensory dorsal roots and motor ventral roots

Front 8

spinal cord tracts

Back 8

- white column = bundles of myelinated axons that carry signals up and down to and from brainstem
- 3 pairs of columns: dorsal, lateral, and anterior columns
- each column is filled with named tracts or fasciculi

Front 9

fasciculi

Back 9

- fibers with a similar origin, destination, and function

Front 10

ascending and descending tracts

Back 10

- ascending and descending tract head up or down while decussation means that the fibers cross sides
- contralateral means origin and destination are on opposite sides while ipsilateral means on same side

Front 11

central pattern generators (CPG)

Back 11

- those circuits that control locomotion and other specific, often repeated motor activities
- neural circuit in which CNS can endogenously generate a sequential patterned activation of motor neurons to antagonistic muscles that underlies a behavior pattern
- a group of neurons organized in CNS that produces a complex series of neural activity patterns responsible for motor actions
- sensory timing information can reset the CPG

Front 12

control of flight in locust

Back 12

- depressor and levator muscles show alternating bursts of muscle potentials, resulting in rhythmic wing movements
- wing-hinge stretch receptor is activated when the wing has been elevated by contraction of the levator muscle
- when the wing has be lowered by contraction of the depressor muscle, depression proprioceotors are activated

Front 13

two hypotheses for motor pattern of wing muscles

Back 13

- sensory feedback resulting from a movement triggers the next movement
- CPG produces the motor pattern without requiring moment-to-moment sensory input

Front 14

projection level

Back 14

- located in cerebellum and basal nuclei
- spinal cord is under the direct control
- consists of upper motor neurons of the motor cortex
- synapse on anterior/ventral motor horn cells that regulate fast and fine motor movements
- or brain stem nuclei that then send synapse with neurons in anterior horn = regulate muslce tone, mediate head movements used in vision, and control CPG during locomotion
- convey information to lower motor neurons and send a copy to higher command levels

Front 15

pre-command level

Back 15

- precisely start or stop movements
- control the outputs of the cortex and brain stem
- cerebellum is ultimate target of ascending motor tracts but doesn't act directly on spinal cord
- acts on brain stem and motor cortex through hypothalamus

Front 16

basal nuclei

Back 16

- receive inputs from all coritcal areas and send output to premotor and prefrontal motor cortical areas
- appear to be involved in most complex aspects of motor control

Front 17

basal ganglia/nuclei

Back 17

- inhibition of muscle tone
- coordination of slow sustained movements
- suppression of useless patterns of movement
- parkinson's disease affects the basal ganglia associated with a dopamine deficiency

Front 18

basal ganglion

Back 18

- receive output from a number of cortical areas
- these structures provide positive feedback to SMA and PMA
- may help in initiation of a behavior

Front 19

cerebellum

Back 19

- receives cortical input and provides primary motor cortex with information on the status of a behavior as well as information on its feasibility

Front 20

preparing for movement

Back 20

- conscious decision to move info is relayed from frontal lobes to supplemental motor association areas
- supplemental motor association areas then relay info to the cerebellum and basal nuclei
- at same time, cerebellum receives info from proprioceptors and visual and equilibrium pathways
- cerebellar cortex calculates best way to coordinate force, direction, extent of muscle contraction
- cerebellum send to the cerebral motor cortex its blueprint of coordination
- cerebellum send to the brain stem information that influence motor neurons of the spinal cord

Front 21

interaction of brain areas in the planning, execution, and control of voluntary movement

Back 21

- two loops from the association cortex are involved in pre-programming a movement
- basal ganglia involved in selection and initiation
- cerebrocerebellum involved in initial programming
- information passes to the primary motor cortex for executing the movement
- sensory information from the spinal cord and the cerebellum gives integrated feedback information to the primary motor cortex

Front 22

performing a movement

Back 22

- as the movement begins the supplemental motor association areas send instructions to the primary motor cortex
- feedback from the cerebellum and basal nuclei modify those commands
- outputs directs involuntary adjustments in position and muscle tone

Front 23

spinal cord

Back 23

- relays information to and from the brain
- central pattern generators
- ascending and descending paths in the spinal cord
- reflexes
- not merely a pathway for sensory and motor connections between the brain and peripheral nervous system
- responsible for sensory-motor coordination particularly reflex arcs

Front 24

spinal reflex/reflex arc

Back 24

- simple automatic response to a sensory stimulus

Front 25

spinal reflexes

Back 25

- receptors in skin, muscles, tendons, and joint synapse with dorsal root ganglia fibers/afferent fibers through the dorsal root ganglia
- action potential travels afferent fiber to the dorsal root of the spinal cord
- afferent fiber synapses with interneurons
- interneurons synapse with motor neurons in the ventral horn and neurons in higher centers of the CNS
- motor fibers/efferent fibers leave the CNS through the ventral horn
- motor fibers synapse with effector

Front 26

stretch reflex, myotactic reflex

Back 26

- essential for posture and coordination of movements
- involves muscle spindles
- absent in people with chronic diabetes, neurosyphilis, and injury to the 2,3,4 lumbar segments

Front 27

characteristics of knee jerk reflex

Back 27

- ipsilateral = response on the same side of the body
- intrasegmental = only one segment of the spinal cord is involved
- monosynaptic = one synapse within the spinal cord

Front 28

muscle spindle

Back 28

- an internal mechanoreceptor associated with the musculoskeletal system
- monitors length of skeletal muscles
- in parallel to muscle fibers
- embedded along with the muscle fibers
- associated with the 1 afferent sensory fiber-1a which is largest and fastest conducting sensory fiber in the body
- 1a axon enters spinal cord and makes direct excitatory synaptic contact with motor neurons to the same muscle

Front 29

vertebrate muscle spindle stretch receptors

Back 29

- at resting length, 1a afferent fiber generates tonic activity
- stretch of muscle increases 1a afferent activity
- shortening of muscle during contraction decreases 1a afferent activity

Front 30

stretch reflex mediates load compensation in voluntary movement

Back 30

- simplest manifestation of stretch reflex involves only a 1a fiber and a motor neuron
- stretch muscle spindle
- action potential along 1a fiber
- synapse with alpha motor neuron in the ventral horn that controls same muscle fiber as muscle spindle
- motor neuron output EPSPs to extrafusal muscle fiber
- contraction

Front 31

reciprocity

Back 31

- neural circuit of stretch reflex
- muscles tend to be arranged in antagonist pairs that oppose each other
- extensor = muscle that increases the angle between two articulating bones
- flexor = muscle that decreases the angle between two articulating bones

Front 32

principle of reciprocity

Back 32

- any signal that activates movement is sent to a pair of muscle-agonist and the antagonist
- causing the agonist to contract and the antagonist to relax
- reciprocal inhibition prevents muscles from working against each other

Front 33

stretch reflex

Back 33

- stretching of a leg extensor muscle activates a muscle spindle stretch receptor
- sensory neuron of the stretch receptor synapses on motor neurons (E) to the same muscle
- stretch receptor sensory neuron also activates inhibitory interneurons that inhibit the motor neurons (F) to antagonistic muscle fibers

Front 34

reflex pathway

Back 34

Front 35

renshaw cell

Back 35

- interneuron that inhibits or prevents prolonged motor neuron activity in an inhibitory feedback loop

Front 36

patellar tendon reflex arc

Back 36

- extensor muscle stretched
- muscle spindle stimulated
- primary afferent neuron excited
- primary afferent neuron stimulates alpha motor neuron to extensor muscle
- alpha motor neuron stimulates extensor muscle to contract
- primary afferent neuron stimulates inhibitory interneuron
- interneuron inhibits alpha motor neuron to flexor muscle
- flexor muscle (antagonist) reflexes

Front 37

gamma motor neurons

Back 37

- small motor neurons that innervate intrafusal muscle fibers
- activation of the gamma motor neurons excites 1a sensory neuron by contracting the contractile end of the intrafusal fiber
- 2 ways to increase muscle spindle receptor activity: passive stretch of the muscle and gamma motor neuron activity

Front 38

stretch reflex mediates load compensation in a voluntary movement

Back 38

- CNS estimates the force necessary to pick up a load
- descending command co-activates the alpha and gamma motor neurons

Front 39

no load present

Back 39

- extrafusal fibers shorten to flex the arm
- intrafusal shorten due to gamma signal
- intrafusal fiber shortening decreases its tension and lessens the activation of the stretch receptor

Front 40

load present

Back 40

- prevents muscle from shortening
- coactivation of alpha and gamma fiber
- extrafusal fibers don't shorten because the load is to great
- intrafusal fiber shortens due to gamma activation
- creating an error signal that activates the alpha motor neuron = train of action potentials
- adds to proportional excitation and tension in the muscle to help overcome the load
- creates a load-compensating servo loop (failure to shorten-more force)

Front 41

circuit diagram of ventral horn of mammalian spinal cord

Back 41

- motor neurons are activated primarily by CNS input rather that spinal reflexes
- motor output neurons of spinal cord are alpha motor neurons to flexor and extensor muscles and gamma motor neurons to the intrafusal fibers of muscle spindle
- input pathways to motor neurons and interneurons from the ventral horn include
- descending pathways from the brain = green
-1a afferent excitatory neuron = blue
- 1a inhibitory inter neuron/inhibitory pathways from the muscle spindle = black

Front 42

additional proprioceptors of vertebrates

Back 42

- golgi tendon organs
- joint receptors

Front 43

golgi tendon organ

Back 43

- collects information about differences in tension among tendons
- relay data to the CNS where they are processed
- help to coordinate fine muscular contractions
- in series with working muscle fibers

Front 44

golgi tendon reflex

Back 44

- 1mm long
- encapsulated nerve bundle
- excessive tension on tendon inhibits motor neuron = muscle contraction decreased
- functions when muscle contracts unevenly

Front 45

joint receptors

Back 45

- embedded in connective tissue at the joint
- respond over certain range of joint positions and movments

Front 46

flexor reflex

Back 46

- reflex afferents have endings in skin muscles and joints
- make excitatory synapses with interneurons in the CNS that excite motor neurons in flexor muscles = not direct connections as seen in stretch reflex
- occur along with cross extensor reflex
- polysynaptic reflex = 3 or more neurons are involved
- ipsilateral = response on same side of body
- intersegmental = involves more than one segment

Front 47

flexor withdrawal reflexes

Back 47

- occurs during withdrawal of foot from pain
- polysnaptic reflex arc
- neural circuitry in spinal cord controls sequence and duration of muscle contractons

Front 48

cross extension reflex

Back 48

- contralateral reflex
- uses commissional, interneurons in spinal cord to relay information to opposite side
- painful stimulus to left foot can elicit withdrawal of the left and extension of the right to support body

Front 49

neural circuit of flexion reflex and crossed extension reflex

Back 49

- noxious stimulation of skin excites flexion reflex afferent neurons
- afferent neurons excite interneurons to synaptically excite flexor motor neurons and inhibit extensor motor neurons on the stimulated side
- flexion-reflex afferents also synapse onto interneurons that cross the midline of the spinal cord and indirectly stimulate extension of the opposite leg

Front 50

crossed extensor reflexes

Back 50

- maintains balance by extending other leg
-intersegmental reflex extends up and down spinal cord
- contralateral reflex arcs explained by pain at one foot causes muscle contraction in other leg

Front 51

flexor reflex and crossed extension reflex

Back 51

- stepping on glass stimulates pain receptors in foot
- sensory neuron activates multiple interneurons
- ipsilateral motor neurons to flexor excited
- ipsilateral flexor contracts
- contralateral motor neurons to extensor excited
- contralateral extensor contracts