Control of Movement Chap 13 (exam 3)

***Differentiate between extrafusal and intrafusal fibers and alpha and gamma motor neurons. *** a little sketch on this one

Alpha motor neurons are the same things as somatic motor neurons. They carry output signal to effector (muscle fiber). The muscle fibers that receive this are extrafusal fibers. The intrafusal fibers are innervated by an efferent neuron known as the gamma motor neuron. Within a muscle spindle, there are several small, specialized muscle fibers known as intrafusal fibers.

****Compare autonomic reflexes with somatic. Note whether or not the brain is involved. Give examples of each.

Autonomic reflexes (visceral) - smooth muscle, cardiac, glands. These are polysynaptic reflexes because they involve one or more interneurons. Somatic reflexes - These are monosynaptic. Just one afferent and one efferent neuron. Note: somatic and autonomic reflexes can be either cranial or spinal reflexes. And even if they are spinal, its possible that the stimuli is still modulated by the brain at some point (integrated). Example of autonomic: Also known as visceral. Heart rate, blood pressure, breathing. Examples of somatic: knee jerk, gag reflex.

1 thing in common between somatic and autonomic reflexes?

Both have one afferent neuron

What are muscle spindles? ALPHA GAMMA COACTIVATION AND STRETCH REFLEX PATHWAY.

Each muscle spindle contains intrafusal fibers which are sensory receptors that send info to the spinal cord about stretching of the muscle. As the intrafusal fibers detect stretching in the muscle they will be activated to also stretch through gamma motorneurons (their stretch comes from that instead of alpha motor neurons). Now that the muscle spindle ends have stretched, they will sense it is time to contract to protect the muscle. They will then send info to the spinal cord. The spinal cord will then respond through alpha motor neurons which innervate the extrafusal fibers to contract as a response to the stretching that happened. This mechanism prevents damage from overstretching. The more change there is in stretch, the more firing intrafusal fibers will do. THIS MECHANISM IS CALLED THE STRETCH REFLEX Extrafusal fibers are just the normal muscle fibers that are innervated by alpha motor neurons The presence of gamma motor neurons in a muscle keep the muscle spindles active no matter what the muscle length is. Remember that in the stretch reflex, when alpha motor neurons activated the extrafusal muscle fibers, the muscle contracts and this causes tension on muscle spindle. To keep the spindle functioning normally, gamma motor neurons fire at the same time to make intrafusal fibers contract and shorten (this will cause the tension created from extrafusal fibers to not affect the center of muscle spindles size which is in charge of firing to the spinal cord). This process ensures that even when muscle contracts, muscle spindle can keep their constant rate of afferent neuron firing constant and this process is called ALPHA GAMMA COACTIVATION!

**Diagram a stretch reflex with alphagamma coactivation in the muscle spindle. *** it would be nice to have a better explanation of this

Excitation of gamma motor neurons and alpha motor neurons at the same time is a process known as alpha-gamma coactivation. Alpha-gamma coactivation maintains spindle function when muscle contracts. Avoid release of tension on intrafusal fibers When alpha motor neurons fire after a muscle stretch, the muscle shortens and this causes tension on the muscle spindle. To keep the spindle functioning normally , gamma motor neurons also fire which make the spindle contract and shorten. This makes the spindle remain active even when the muscle contracts.

**Diagram a flexion reflex and its associated crossed extensor reflex.

Flexion reflex: 1. Painful stimulus (stepping on a nail with a foot). 2. Primary sensory neuron takes stimulus to spinal cord. 3. At spinal cord, the stimulus will diverge into several interneurons. These will synapse with alpha motor neurons. Some of these will take stimulus to brain for sensation of pain and postural adjustment. Some of them will cause a withdrawal reflex to pull foot away from stimulus. Some of them will cause a crossed extensor reflex (supports body as weight shifts from painful stimulus). The divergence of the one sensory neuron makes it possible for the body to quickly send all these types of information.

Autonomic and Skeletal muscle reflex. How many synapses in each reflex?

In the skeletal muscle reflexes there can be monosynaptic (no interneuron) and polysnaptic pathways . In ANS, there can ONLY be polysynaptic pathways.

***Explain the function and location of muscle spindles and Golgi tendon organs.

Muscle spindles - Muscle spindles are sensory receptors. Send info to CNS about muscle stretch. They are parallel with the main muscle fibers within skeletal muscle. Every skeletal muscle in the body has many muscle spindles. Prevent injuries from overstretching. Firing increases as the muscle stretches. They are buried among extrafusal fibers. Golgi Tendon organs- Found at the junction of tendons and muscle fibers. Responds to tension that is placed on the tendon by the contraction of extrafusal fibers. This prevents overstretching and injuries. It sends info to the CNS to relax and relieve tension. Both of these main function is to send sensory info to CNS.

***Diagram the steps of a skeletal muscle stretch reflex, including the terms: alpha motor neuron, proprioceptor, extrafusal fibers, muscle tone.

Muscle stretches (stimulus) -> each person has different muscle tones (resistance to stretching), this causes extrafusal fibers to stretch (they are the effectors) -> This causes proprioceptors (which in this case would be muscle spindles) to sense that contraction and send that information to the CNS -> CNS will then respond by increased firing of alpha motor neurons (which are efferent neurons). This will cause the muscle to contract to avoid injury. Now that it is contracted, firing of muscle spindles will decrease and therefore we see a negative feedback cycle.

****Define proprioceptor and list 3 examples.

Proprioceptors are sensory receptors located in skeletal muscles, joints and ligaments. The input signal then goes to CNS through sensory neurons. 1. Muscle spindle 2. Golgi tendon organ 3.Joint receptors.

**Explain the purpose of reflex testing in a clinical setting.

Provides an assessment of the function and interplay of both sensory and motor pathways. With the results of these tests, doctors can potentially locate an injury based on where the test indicates a normal or abnormal reaction. Reflex tests are performed as part of a neurological exam