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CHP 13

Terms in this set (61)

neuronal reflexes
Reflexes are "fast, predictable, automatic responses to a particular stimulus that occur without conscious thought"
4 different ways Reflexes Can be Classified
-nervous system division
-CNS location where the reflex is integrated
-by whether reflex is inborn or learned
-number of neurons in reflex pathway
neuronal reflexes can by classified in 4 different ways
-efferent division that controls the effector
-integrating region within the central nervous system
-time at which the reflex develops
-the number of neurons in the reflex pathway
efferent division that controls the effector
somatic motor neurons control skeletal muscles
autonomic neurons control smooth and cardiac muscle glands, and adipose tissue
integrating region within the central nervous system
spinal reflexes do not require input from the brain
cranial reflexes are integrated within the brain
time at which the reflex develops
innate (inborn) reflexes are genetically determined
learned (conditioned) reflexes are acquired through experience
the number of neurons in the reflex pathway
monosynaptic reflexes have only two neurons: one afferent (sensory) and one efferent. only somatic motor reflexes can be monosynaptic
polysynaptic reflexes include one or more interneurons between the afferent and efferent neurons. all autonomic reflexes are polysynaptic because they have 3 neurons: one afferent and two efferent
reflex pathway
stimulus (activate a sensory receptor)
receptor (sensor: sends information via AP's through sensory afferent neurons)
afferent pathway (sensory neuron: either somatic or autonomic)
integrator (brain or spinal cord: evaluates information and selects response)
efferent pathway (motor neuron: either somatic or autonomic)
effector (skeletal muscle or smooth muscle, cardiac muscle or glands))
response
a monosynaptic reflex has how many synapses?
one
a monosynaptic reflexes synapses where?
between the afferent and efferent neurons
a polysynaptic reflex has how many synapses?
two or more
both polysynaptic reflex synapses synapse where?
both in the CNS
all autonomic reflexes are
polysynaptic
autonomic reflexes synapse where?
at least on synapse in the CNS and another in the autonomic ganglion
autonomic reflexes (visceral reflexes)
control of salivating, vomiting, sneezing, coughing, swallowing, gagging, heart rate, blood pressure, breathing, bladder control, maintenance of body temperature, maintenance of blood osmolarity, release of hormones, defection, blushing, piloerection, penile erection, emission and ejaculation.

many are characterized by tonic activity
tonic activity
a continuous stream of AP's that create activity in effector.
skeletal muscle (somatic) reflexes
Proprioreceptors monitor the position of our limbs in space and with respect to gravity, our movements, and the effort we exert in lifting or moving objects.
proprioceptors
receptors that detect changes in joint movements, muscle tension, muscle length and send information to CNS, which responds to:

-contracts skeletal muscle
-inhibits the contraction of skeletal muscle
3 main proprioceptors
Muscle spindles
Golgi tendon organs
various joint capsule receptors
skeletal muscle reflex components
Stimulus: varies

Receptor: proprioceptor (muscle spindle, Golgi tendon organ, or in joint capsule)

Afferent Pathway: somatic sensory neuron

Integrator-spinal cord, cerebellum, brain stem, thalamus, somatosensory cortex, primary motor cortex-perhaps pre-motor cortex and other frontal lobe planning areas

Efferent Pathway : somatic motor (alpha) neuron

Effector : skeletal muscle

Response: contracts (except for reciprocal inhibition)
reciprocal inhibition
an inhibitory interneuron is in spinal cord as part of efferent pathway, in which case, contraction is inhibited
joint receptors
are found in capsules and ligaments around all the joints.
These are stimulated by mechanical distortion that results from changes in location of bones making up the joint. They send sensory information to the areas listed above for integration.
joint receptors are stimulated by
mechanical distortion
golgi tenon organs (gto)
buried within the tendon as the muscle attaches to bone are free nerve endings that wind between connective tissue capsule (Fig 13-2a). These are sensory neurons that can be stimulated by rate of change of tension. Golgi tendon organs provide sensory information to CNS integrating centers, combines this information with feedback from muscle spindle and joint receptors for optimal motor control of posture and movement.

links the muscle and the tendon. it consists of sensory nerve endings interwoven among collagen fibers
muscle spindle (skeletal muscle)
buried within the skeletal muscle, lying parallel to normal skeletal muscle fibers, are special intrafusal muscle fibers (Fig 13-2b). Wrapped about the middle of these special intrafusal muscle fibers is a sensory neuron that is stimulated by stretch (change in muscle length). Muscle spindles are sending information that allows us to have muscle tone, adjust muscle contraction for postural changes, or to resist gravity.

are buried among the extrafusal fibers of the muscle. they send information about muscle stretch to the cns
stretch reflex
when muscle is stretched
muscle spindle
is activated and increased rate of action potentials up sensory neuron, which results in more excitatory synaptic activity within the spinal cord and increased rate of action potential down somatic motor neuron, resulting in muscle contraction. Notice: some integration can occur at just the spinal cord level!

Because of alpha-gamma co-activation (Fig 13-4), the spindle continues to send action potentials, even as muscle shortens.

Even at rest, the sensory neuron is sending some tonic rate of action potentials to the spinal cord. This tonic rate of action potentials evokes a small amount of motor neuron action potentials, resulting in asynchronous contraction of motor units, resulting in "muscle tone".

are buried among the extrafusal fibers of the muscle. they send information about muscle stretch to the cns
muscle spindle pathway
-extrafusal muscle fibers at resting length
-sensory neuron is tonically active
-spinal cord integrates function
-alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles and fire continuously
-extrafusal fibers maintain a certain level of tension even at rest
stretch reflex pathway
load added to muscle
muscle and muscle

spindle stretch as arm extends. muscle spindle afferents fire more frequently

reflex contraction initiated by muscle stretch restores arm position and prevents damage from over-stretching
alpha gamma coactivation
alpha motor neuron fires and gamma motor neuron fires

muscle and intrafusal fibers both contract

stretch on centers of intrafusal fibers unchanged. firing rate of afferent neuron remains constant
stretch and flexion reflexes
myotatic unit
reciprocal inhibition
myotatic unit
collection of pathways controlling a single joint

Monosynaptic stretch reflex involves only two neurons: the sensory neuron from spindle somatic motor neuron to muscle, patellar tendon reflex
reciprocal inhibition
antagonistic muscles must relax as the prime mover muscles contract

Polysynaptic reflex pathways cause an arm or leg to be pulled away from a noxious stimulus
stretch reflex and reciprocal inhibition pathway
Stimulus : patellar tendon stretch, causes stretch on quadriceps muscle

Receptor: muscle spindles in quadriceps are stretched

Afferent Pathway : somatic sensory neuron(s) send action potentials toward the spinal cord and diverges

Integrator : in spinal cord, somatic sensory afferent neuron synapses on somatic motor efferent neuron to the quadriceps

(the same somatic sensory afferent neuron also synapses on inhibitory interneuron which synapses on somatic motor efferent neuron to the hamstring)

Efferent Pathway: somatic motor efferent neuron sends action potentials to the quadriceps

(inhibitory interneuron prevents somatic motor efferent neuron from sending action potentials to the hamstring )

Effector : quadriceps muscle contracts-extending the knee

(while simultaneously the hamstring muscle is told to stay relaxed -this process is termed reciprocal inhibition)

Response: knee jerks
crossed extensor reflex
painful stimulus activated nociceptor

primary sensory neuron enters spinal cord and diverges

one collateral activates ascending pathways for sensation (pain) and postural adjustment (shift in center of gravity)

withdrawal reflex pulls foot away from painful stimulus

crossed extensor reflex supports body as weight shifts away from painful stimulus
Flexion Reflexes Pull Limbs away from Painful Stimuli
Stimulus: right foot steps on tack
Receptor: nociceptor in right foot
Afferent Pathway : somatic sensory neuron(s) send action potentials to spinal cord and diverges
Integrator : one collateral activates ascending pathways for sensation and postural adjustment
Also in spinal cord, somatic sensory afferent neuron synapses on somatic motor efferent neuron to the right leg hamstring (the same somatic sensory neuron also synapses on inhibitory interneuron which synapses on somatic motor efferent neuron to the right leg quadriceps)
Also in spinal cord, the same somatic sensory afferent neuron synapses on interneurons that cross to other side of spinal cord and synapse on somatic motor efferent neuron to the left leg quadriceps (and also synapses on inhibitory interneuron which synapses on somatic motor efferent neuron to left leg hamstring)
Efferent Pathway: somatic motor efferent neuron sends action potentials to the right hamstring (also, inhibitory interneuron prevents somatic motor efferent neuron to send action potentials to the right quadriceps )
Also, different somatic motor efferent neuron sends action potentials to the left quadriceps (inhibitory interneuron prevents somatic motor efferent neuron to send action potentials to the left hamstring )
Effector : In right leg, hamstring contract and quadriceps relax-withdrawing the leg away from the painful stimulus. Simultaneously, in left leg, the quadriceps muscle contracts and hamstring relaxes-extending the knee, so that the leg holds the weight of the body.
Response: Withdraw right leg, extend left leg.
the CNS integrates movement
Integrated, coordinated responses require input from multiple regions of the brain

movement can be reflex or voluntary or rhythmic
reflex
least complex, integrated at the spinal cord or brain stem
voluntary
most complex, integrated in cerebral cortex

Voluntary movements require coordination between the cerebral cortex, cerebellum, and basal ganglia.

Travel from cortex to spinal cord through the corticospinal tract
rhythmic
intermediate complexity; integrated in spinal cord with higher center input required
parkinson's disease
a progressive neurological disorder

Characterized by abnormal movements, tremors at rest, speech difficulties, and cognitive changes

Loss of basal ganglia neurons that release dopamine

Treatment: L-Dopa Why? because it can cross the blood brain barrier because dopamine can not
types of movement
reflex
voluntary
rhythmic
reflex
stimulus that initiates movement: primarily external via sensory receptors; minimally voluntary
example: knee jerk, cough, postural reflexes
complexity: least complex; integrated at level of spinal cord or brain stem with higher center modulation
comments: inherent, rapid
voluntary
stimulus that initiates movement: external stimuli or at will
example: playing piano
complexity: most complex; integrated in cerebral cortex
comments: learned movements that improve with practice; once learned, may become subconscious (muscle memory)
rhythmic
stimulus that initiates movement: initiation and termination voluntary
example: walking, running
complexity: intermediate complexity; integrated in spinal cord with higher center input required
comments: spinal circuses act as pattern generators; activation of these pathways requires input from brain stem
voluntary movements have 3 steps
1. decision making and planning
2. initiating the movement
3. executing the movement
decision making and planning of voluntary movement
Sensory info ( how is body positioned before making movement)
Cerebral Cortex-prefrontal cortex, pre-motor cortex, primary motor cortex
Basal Nuclei ( info about posture, balance and gait) and Thalamus
initiating the movement of voluntary movement
Cerebral Cortex-primary motor cortex
Brain stem
Spinal cord ( somatic motor efferent neurons)
executing the movement of voluntary movement
Sensory info from proprioceptors goes to cerebellum, thalamus and somatosensory cortex (parietal). From there, it goes to primary motor cortex and other control areas.
voluntary movement is divided into 3 phases
planning
initiating
execution
sensory feedback allows the brain to correct for any deviation be
...
control of voluntary movements pathway
sensory input
planning and decision making
coordination and timing: cebellar input
execution: corticospinal tract to skeletal muscles
execution: extrapyramidal influence on posture, balance, and gait
continuous feedback
Feedforward postural reflexes
adjust body position, shifting weight slightly in anticipation of changes about to occur.
neural control of movement
spinal cord
brain stem
motor areas of cerebral cortex
cerebellum
thalamus
basal gangla
spinal cord
role: spinal reflexes; locomotor pattern generators
receives input from: sensory receptors and brain
sends integrative output to: brain stem, cerebellum, thalamus/cerebral cortex
brain stem
role: posture, hand and eye movements
receives input from: cerebellum, visual and vestibular sensory receptors
sends integrative output to: spinal cord
motor areas of cerebral cortex
role: planning and coordinating complex movement
receives input from: thalamus
sends integrative output to: brain stem, spinal cord (corticospinal tract), cerebellum, basal glands
cerebellum
role: monitors output signals from motor areas and adjusts movements
receives input from: spinal cord (sensory), cerebral cortex (commands)
sends integrative output to: brain stem, cerebral cortex, (all output is inhibitory)
thalamus
role: contains relay nuclei that modulate and pass messages to cerebral cortex
receives input from: basal ganglia, cerebellum, spinal cord
sends integrative output to: cerebral cortex
basal ganglia
role: motor planning
receives input from: cerebral cortex
sends integrative output to: cerebral cortex, brain stem
control of movement in visceral muscles
contraction in smooth and cardiac muscles
-Spontaneously depolarizing muscle fibers (pacemakers)
-Control by hormones or autonomic division of the nervous system
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