functional components of a reflex. Reflexes & homeostasis.

Stretch Reflex: 5. Effector (ame muscle) contracts

-Acetylcholine released by nerve impulses at the NMJs triggers one or more muscle action potentials in the stretched muscle (effector), and the muscle contracts. -muscle stretch is followed by muscle contraction, which relieves the stretching.

flexor/withdrawal reflex: 5. effectors (flexor muscles)

-Acetylcholine released by the motor neurons causes the flexor muscles in the thigh (effectors) to contract, producing withdrawal of the leg. -This reflex is protective because contraction of flexor muscles moves a limb away from the source of a possibly damaging stimulus.

Tendon Reflex: 1. increased tension stimulates sensory receptor

-As the tension applied to a tendon increases, the tendon organ (sensory receptor) is stimulated (depolarized to threshold).

Stretch Reflex: 4. Motor Neuron excited

-If the excitation is strong enough, one or more nerve impulses arise in the motor neuron and propagate along its axon, which extends from the spinal cord into the anterior root and through peripheral nerves to the stimulated muscle. -The axon terminals of the motor neuron form neuromuscular junctions (NMJs) with skeletal muscle fibers of the stretched muscle.

Stretch Reflex: 2.Sensory Neuron becomes excited

-In response to being stretched, a muscle spindle generates one or more nerve impulses that propagate along a somatic sensory neuron through the posterior root of the spinal nerve and into the spinal cord.

Stretch Reflex: 3. Within the Integrating center

-In the spinal cord (integrating center), the sensory neuron makes an excitatory synapse with and thereby activates a motor neuron in the anterior gray horn.

Reflex Arc: Integrating center

-One or more regions of gray matter within the CNS act as an integrating center. -In the simplest type of reflex, the integrating center is a single synapse between a sensory neuron and a motor neuron. -monosynaptic reflex arc: A reflex pathway having only one synapse in the CNS. -polysynaptic reflex arc: involves more than two types of neurons and more than one CNS synapse. -More often, the integrating center consists of one or more interneurons, which may relay impulses to other interneurons as well as to a motor neuron.

Stretch Reflex: 1.Stretching stimulates muscle receptor

-Slight stretching of a muscle stimulates sensory receptors in the muscle called muscle spindles -The spindles monitor changes in the length of the muscle.

Reflex Arc: Sensory receptor

-The distal end of a sensory neuron (dendrite) or an associated sensory structure serves as a sensory receptor. -responds to a specific stimulus—a change in the internal or external environment—by producing a graded potential called a generator (or receptor) potential. -If a generator potential reaches the threshold level of depolarization, it will trigger one or more nerve impulses in the sensory neuron.

flexor/withdrawal reflex: 4. Motor Neurons excited

-The interneurons activate motor neurons in several spinal cord segments. -As a result, the motor neurons generate nerve impulses, which propagate toward the axon terminals.

Reflex arc

-The most basic conduction pathway through the nervous system. -nerve impulses propagating into, through, and out of the CNS follow specific pathways, depending on the kind of information, its origin, and its destination. -connecting a receptor and an effector and consisting of a receptor, a sensory neuron, an integrating center in the central nervous system, a motor neuron, and an effector.

Reflex Arc: Sensory neuron

-The nerve impulses propagate from the sensory receptor along the axon of the sensory neuron to the axon terminals, which are located in the gray matter of the spinal cord or brain stem. -relay neurons send nerve impulses to the area of the brain that allows conscious awareness that the reflex has occurred.

Reflex Arc: Effector

-The part of the body that responds to the motor nerve impulse, such as a muscle or gland. -Its action is called a reflex.

How do reflexes contribute to homeostasis?

-The second way the spinal cord promotes homeostasis. -the spinal cord serves as an integrating center for some reflexes.

tendon (Golgi tendon) organs

-The sensory receptors for the tendon reflex. -lie within a tendon near its junction with a muscle. -In contrast to muscle spindles, which are sensitive to changes in muscle length, tendon organs detect and respond to changes in muscle tension that are caused by passive stretch or muscular contraction.

spinal reflex

-When integration takes place in the spinal cord gray matter. -example: the familiar patellar reflex (knee jerk).

Reflex

-a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus. -Some reflexes are inborn, such as pulling your hand away from a hot surface before you even feel that it is hot. Other reflexes are learned or acquired.

a polysynaptic reflex arc

-a polysynaptic reflex arc to the antagonistic muscles operates at the same time. -This arc involves three neurons and two synapses.

cranial reflex

-an integration that occurs in the brain stem rather than the spinal cord. -example: the tracking movements of your eyes as you read this sentence.

A stretch reflex

-causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle. -occurs via a monosynaptic reflex arc. -can occur by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron. -can be elicited by tapping on tendons attached to muscles at the elbow, wrist, knee, and ankle joints. -an example of a stretch reflex is the patellar reflex (knee jerk)

autonomic (visceral) reflexes

-generally are not consciously perceived. -involve responses of smooth muscle, cardiac muscle, and glands.

somatic reflexes

-involve contraction of skeletal muscles.

flexor/withdrawal reflex

-involving a polysynaptic reflex arc results when, for instance, you step on a tack. -In response to such a painful stimulus, you immediately withdraw your leg.

tendon reflex

-operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn. -less sensitive than the stretch reflex. -it can override the stretch reflex when tension is great, making you drop a very heavy weight. -like the stretch reflex, the tendon reflex is ipsilateral.

crossed extensor reflex

-reflex to help you maintain your balance; it operates as follows

muscle spindles

-sensory receptors in the muscle. -The spindles monitor changes in the length of the muscle.

reciprocal innervation

-the components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonists -prevents conflict between opposing muscles and is vital in coordinating body movements.

contralateral reflex arc

-the crossed extensor reflex involves a contralateral reflex arc. -Sensory impulses enter one side of the spinal cord and motor impulses exit on the opposite side. -synchronizes the extension of the contralateral limb with the withdrawal (flexion) of the stimulated limb. -Reciprocal innervation also occurs in both the flexor reflex and the crossed extensor reflex. - In the flexor reflex, when the flexor muscles of a painfully stimulated lower limb are contracting, the extensor muscles of the same limb are relaxing to some degree. -If both sets of muscles contracted at the same time, the two sets of muscles would pull on the bones in opposite directions, which might immobilize the limb. -one set of muscles contracts while the other relaxes.

muscle tone

-the small degree of contraction present while the muscle is at rest. - By adjusting how vigorously a muscle spindle responds to stretching, the brain sets an overall level of muscle tone.

monosynaptic

-the stretch reflex pathway itself is monosynaptic. -two neurons and one synapse

What initiates a nerve impulse in a sensory neuron? Which branch of the nervous system includes all integrating centers for reflexes?

A sensory receptor produces a generator potential, which triggers a nerve impulse if the generator potential reaches threshold. Reflex integrating centers are in the CNS.

Reflex Arc: Motor neuron

Impulses triggered by the integrating center propagate out of the CNS along a motor neuron to the part of the body that will respond.

What makes this an ipsilateral reflex?

In an ipsilateral reflex, the sensory and motor neurons are on the same side of the spinal cord.

Tendon Reflex: 2. Sensory Neuron Excited

Nerve impulses arise and propagate into the spinal cord along a sensory neuron.

Ipsilateral

On the same side, affecting the same side of the body.

flexor/withdrawal reflex: 1. Stepping on tack stimulates sensory receptors

Stepping on a tack stimulates the dendrites (sensory receptor) of a pain‐sensitive neuron.

Why is the flexor reflex classified as an intersegmental reflex arc?

The flexor reflex is intersegmental because impulses go out over motor neurons located in several spinal nerves, each arising from a different segment of the spinal cord.

Tendon Reflex: 4. Motor Neuron inhibited

The inhibitory neurotransmitter inhibits (hyperpolarizes) the motor neuron, which then generates fewer nerve impulses.

Tendon Reflex: 5. Effector (muscle attached to same tendon)

The muscle relaxes and relieves excess tension.

flexor/withdrawal reflex: 2. Sensory neuron excited

This sensory neuron then generates nerve impulses, which propagate into the spinal cord.

Tendon Reflex: 3. Within Integrating Center (spinal cord)

Within the spinal cord (integrating center), the sensory neuron activates an inhibitory interneuron that synapses with a motor neuron.

flexor/withdrawal reflex: 3. within integrating center (spinal cord)

Within the spinal cord (integrating center), the sensory neuron activates interneurons that extend to several spinal cord segments.

If the effector is skeletal muscle, then what is the reflex?

the reflex is a somatic reflex.

If the effector is smooth muscle,cardiac muscle, or a gland, then what is the reflex?

the reflex is an autonomic (visceral) reflex.