Question

Discuss the function of central nervous system reflexes. Describe two brain and five spinal reflexes. Be sure to include their pathway and function.

Answer 1

The basic physiology of the central nervous system, including the brain and spinal cord.

Functions of CNS reflexes:

It consists of an afferent (or sensory) nerve, usually one or more interneurons within the central nervous system, and an efferent (motor, secretory, or secreto-motor) nerve. Most reflexes have several synapses in the reflex arc. ... Probably the best-known reflex is the pupillary light reflex.

The central nervous system CNS is responsible for integrating sensory information and responding accordingly. It consists of two main components:

The spinal cord serves as a conduit for signals between the brain and the rest of the body. It also controls simple musculoskeletal reflexes without input from the brain.

The brain is responsible for integrating most sensory information and coordinating body function, both consciously and unconsciously. Complex functions such as thinking and feeling as well as regulation of homeostasis are attributable to different parts of the brain.

The medulla oblongata appears as a swelling at the upper end of the spinal cord. Besides being a conduit for fibers running between the spinal cord and higher regions of the brain, it contains control centers for involuntary functions such as blood pressure, breathing, swallowing and vomiting.

Just above the medulla are the pons and cerebellum. The pons relays information between higher regions of the brain and the cerebellum, which processes sensory information and helps coordinate movement.

The next segment, the midbrain, is primarily responsible for eye movement.

Above the midbrain lies the diencephalon, which is composed of two major parts:

The thalamus processes and integrates all sensory information going to the higher regions of the brain.

The hypothalamus is critical for homeostasis, the maintenance of the body's internal environment. It influences nervous control of all internal organs and also serves as the master regulator of endocrine function by its control over the pituitary gland.

The highest region of the brain is the cerebrum, which includes both the cerebral cortex that is visible on the outside of the brain as well as other internal structures. The cerebrum is responsible for conscious sensation and voluntary movement, as well as advanced functions such as thinking, learning and emotion.

Spinal reflexes & Function Pathways:

Myotatic reflexes

The myotatic reflexes (also known as deep tendon reflexes), provide information on the integrity of the central nervous system and peripheral nervous system. Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one. A stretch reflex is the contraction of a muscle in response to its lengthwise stretch.

• Biceps reflex (C5, C6)
• Brachioradialis reflex (C5, C6, C7)
• Extensor digitorum reflex (C6, C7)
• Triceps reflex (C6, C7, C8)
• Patellar reflex or knee-jerk reflex (L2, L3, L4)
• Ankle jerk reflex (Achilles reflex) (S1, S2)

While the reflexes above are stimulated mechanically, the term H-reflex refers to the analogous reflex stimulated electrically, and tonic vibration reflex for those stimulated to vibration.

Tendon reflex :

A tendon reflex is the contraction of a muscle in response to striking its tendon. The Golgi tendon reflex is the inverse of a stretch reflex.

Pathways:

1.Bicep reflex: Biceps reflex is a reflex test that examines the function of the C5 reflex arc and the C6 reflex arc. The test is performed by using a tendon hammer to quickly depress the biceps brachii tendon as it passes through the cubital fossa.

2. Brachioradialis reflex: The brachioradialis reflex (also known as supinator reflex ) is observed during a neurological examination by striking the brachioradialis tendon (at its insertion at the base of the wrist into the radial styloid process (radial side of wrist around 4 inches proximal to base of thumb)) directly with a reflex hammer when the patient's arm is relaxing. This reflex is carried by the radial nerve (spinal level: C5, C6).

3. Extensor digitorum reflex : The reflex arc of the extensor digitorum involves receptors (muscle spindles in the extensor digitorum), afferent fibers (α fibers), center (spinal cord C6, C7), efferent neurons (alpha motor neurons), and an effector organ (extensor digitorum muscle).

4. Triceps reflex: The triceps reflex is mediated by the C6 and C7 nerve roots, predominantly by C7. With the lower leg hanging freely off the edge of the bench, the knee jerk is tested by striking the quadriceps tendon directly with the reflex hammer.

5. Knee jerk reflex : The patellar reflex is a clinical and classic example of the monosynaptic reflex arc. There is no interneuron in the pathway leading to contraction of the quadriceps muscle. Instead, the sensory neuron synapses directly on a motor neuron in the spinal cord.