13.7-13.9 Notes


EXTRA: Sensory fibers are on dorsal horn.

Motor fibers are on ventral horn.


13.7 Notes: Three levels of motor control

  • Cerebral Cortex - conscious motor pathways


    Segmental level - lowest level

    • reflexes and spinal cord circuits

    • controls autonomic movement

  • central pattern generators - neural circuits within the nervous system that can produce rhythmic motor patterns like walking, breathing, or swimming, even without sensory input or specific commands from the brain

Projection Level - middle level

  • Upper motor neurons - direct voluntary movements (pyramidal)

  • Brain Stem motor nuclei - Indirect pathways - control reflexes

  • Internal feedback - specific mechanism by which the body detects changes within itself and responds to maintain that stable state; essentially, internal feedback is a key process that allows homeostasis to occur.


The Precommand Level - highest level

  • basal nuclei - "gatekeeper" for movement by selecting which actions to allow and which to inhibit. - located in cerebral cortex

    • gets input from ALL areas of cerebral cortex then sends it to premotor and prefrontal cortex

    • complex motor control

    • unconscious planning of movement

  • Precommand areas - control the outputs of the cerebral cortex and brain stem motor centers

    • controls motor cortex

  • Cerebellum - sensory & motor integration control

    • motor pathways through projection areas

    • unconscious planning of movement


13.8 Notes: Reflex arcs

  • inborn or intrinsic reflexes - rapid and predictable response it is unlearned and involuntary.

    • the same movement every time

  • Learned or acquired reflex - reflect from repitition or practice

    • Ex: driving a car


COMPONENTS of a Reflex Atc

1) Receptor: Site where the stimulus is received

2) Sensory neuron: Transmits sensory impulses to the Brain and Spinal cord

3) Integration Center: within the CNS

  • Monosynaptic reflex - Simple reflex arcs will have a single synapse between sensory and motor neurons

  • Polysynaptic reflex - complex reflex arcs synapse with multiple interneurons

4) Motor neuron: Conducts motor impulses form integration center to specific body part

5) Effector: Muscle fiber or gland cells that responds to motor impulses


  • Somatic Reflexes - reflexes that activate skeletal muscles

  • Autonomic reflexes - visceral reflexes that activate smooth or cardiac muscles or glands


13.9 Notes: Spinal reflexes

  • Spinal reflexes - involuntary, automatic responses to sensory stimuli that are processed and initiated within the spinal cord, without the involvement of the brain

Stretch and Tendon Reflexes

Two tympes of info about current muscle state that are required by CNS is

  • Length of muscles

    • muscle spindles - specialized sensory receptors located within skeletal muscles

  • Amount of tension in the muscle and its tendons

    • sensory receptors that detect changes in muscle tension

Functional Anatomy of Muscle Spindles

  • Intrafusal muscle fiber - muscle fibers withing muscle spindles - sensory receptors

  • Extrafusal muscle fibers - effector muscle fibers - muscle fibers that produce the majority of muscle tension during movement

    Two different sensory ending that send inputs to CNS

  • Annulospiral endings - primary sensory ending within a muscle spindle, responsible for rapid responses to muscle stretch

    • stimulated by rate and degree of stretch

  • Flower spray endings - secondary ending formed by small axons that supply to the spindle ends

    • stimulated by degree of stretch

  • Gamma efferent fibers - motor nerve fibers that regulate the sensitivity of muscle spindles

    • innervate muscle spindles

    • Also known as (y motor neurons)

    • Contractile regions - areas of cells that can generate force to contract, divide, or move

  • (a) alpha motor neurons - innervate and stimulate extrafusal muscle fibers to contract

    Muscle spindle is excited in two ways

  • External stretch - external force

  • Internal stretch - stimulation of y motor neurons and intrafusal fibers

  • a-y coactivation - motor fiber pathways will synapse with both a & y motor fibers so stimulus will happen at the same time

    Stretch Reflex

  • Stretch reflex - muscle contraction that occurs as a response to stretching a muscle

  • Patellar (knee-jerk) reflex - a muscle contraction that occurs when the patellar tendon is tapped

    • helps maintain posture and balance, allowing to keep one's balance with little effort or conscious thought

    • helps maintain muscle tone

  • reciprocal inhibition - a neurological process where when one muscle contracts, the opposing muscle group automatically relaxes, allowing for smooth and coordinated movement at a joint

  • Reflex arc - neural pathway, a specific sequence that allows for a reflex to happen

    ALL Reflexes are either Monosynaptic or Ipslateral

  • Monosynaptic - reflex arc with only one synapse

  • Ipsilateral - on the same side of the body as another structure or point. For example, the left arm is ipsilateral to the left leg

Adjusting Muscle spindle activity:

  • brain can control the gamma motor neurons controlling the muscle spindles

  • why athletes stretch before running and other vigorous movement that requires degree of motion

    The Tendon Reflex:

  • The tendon reflexes allows and muscles relax and lengthen instead of contract and length

  • Reciprocal activation - the simultaneous activation of antagonist muscles after the agonist muscles are activated

The Flexor and Crossed-Extensor Reflexes

  • Flexor/Withdrawl reflex - a protective response that moves a body part away from a painful or harmful stimulus

    • polysynaptic and ipsilateral

    • brain can override flexor reflex

  • Crossed - Extensor reflex - a reflex that occurs when one limb withdraws from a painful stimulus, while the opposite limb extends to support the body's weight

    • ipslateral response lifts injured limb

    • contralateral response then extends other limb to hold your weight

    Superficial Reflexes

  • Superficial reflex - an involuntary motor response to a gentle touch or scratch on the skin

    • Plantar reflex: Stimulated by scraping the sole of the foot

      a) Babinski’s sign - abnormal response a reflex that occurs when the big toe moves upward and the other toes fan out after the bottom of the foot is stroked

    • Abdominal reflex: Stimulated by stroking the abdomen

      a) absence of reflex can be caused by corticospinal lesions

    • Cremasteric reflex: Stimulated by stroking the inner thigh in males

    • Geigel reflex: Stimulated by stroking the upper part of the inguinal ligament in females

    • Anal wink: A superficial reflex