Nervous system
The nervous system is composed of a central nervous system (CNS), brain and spinal cord, and the peripheral nervous system (PNS), cranial nerves and spinal nerves. The CNS is located within the dorsal cavity, and the PNS extends through the ventral cavity. The central nervous system provides control and coordination of all eleven body systems and utilizes the endocrine system to form hormone chemical messengers that transport through the blood to influence the activity of individual cells of the body and their associated tissues, organs and systems.
The CNS receives sensory (afferent) input from the PNS and directs the flow of information to association neurons (interneurons), located in the grey matter of the spinal cord and brain to create chemical synapse responses which in turn cause the formation of motor (efferent nerve) responses to stimulus.
The CNS is protected by the cranium, vertebral column, meninges, cerebrospinal fluid. The spinal cord, which is an extension of the brain, and brain stem are joined at the base of the cranium at the foramen magnum. Most of the functions of the head and neck are directly influenced by the brain and transmitted to the PNS via the cranial nerves and spinal nerves of the cervical portion of the spine.
The PNS has two subdivisions
- somatic nervous system (SNS). The SNS is associated with the voluntary control of body movements through the action of skeletal muscles, and also reception of external stimuli.
- the autonomic nervous system (ANS). The ANS is divided into subsystems: the sympathetic nervous system (SNS) and the parasympathetic (PNS) nervous systems. The SNS and PNS often have opposing effects in the same organs or physiological systems, and the ANS is a major factor in maintaining homeostasis.
Spinal nerves
The spinal nerves arise from the spinal column. The top section of the spine is the cervical section, which contains nerves that innervate muscles of the head, neck and thoracic cavity, as well as transmit sensory information to the CNS.
The cervical spine section contains seven vertabrae, C-1 through C-7, and eight nerve pairs, C-1 through C-8.
There is the formation of an extensive network of nerve groups or tracts attaching to the spinal cord in arrangements called rami or plexus.
The sensory branches of spinal nerves include: lesser occipital, C-2, great auricular, (C-2 and C-3); transverse cervical, C-2 and C-3; and supraclavicular, C-3 and C-4. These nerve groups transmit afferent (sensory) information from the scalp, neck, and shoulders to the brain.
The motor branches of spinal nerves include: ansa cervicalis, dividing into a superior root, C-1, and an inferior root, C-2 and C-3, and the phrenic nerve, C-3 to C-5, the segmental nerve branches, C-1 to C-5. These nerve groups transmit efferent nerve (motor) information from the brain to muscle groups of the scalp, neck, diaphragm (anatomy), and shoulders.
Additionally there are: (C5-C8, and T1) Brachial plexus, providing the entire nerve supply of the shoulder and upper limb; and includes supraclavicular branches (dorsal scapular, suprascapular, long thoracic) lateral cord (musculocutaneous, lateral antibrachial cutaneous, lateral head of median nerve), medial cord (ulnar, medial head of median nerve, medial antibrachial cutaneous, medial brachial cutaneous), posterior cord (axillary, radial), controlling the arm.
Note: Damage to the spinal cord above C-5 may result in respiratory arrest and death if not medically treated.
Endocrine system
The endocrine system is under the direct supervision of the nervous system, using the negative feedback principal of homeostasis, to create hormones which act as chemical instant messengers. The hypothalamus connects directly to the pituitary gland, both through the circulatory system and by direct connection of neurons. Also, within the cranium, the pineal gland, which attaches to the thalamus, controls the body's 24 hour rhythms circadian rhythm through the release of melatonin. Endocrine indicates that the secretion is used within the body. Endocrine glands are termed as ductless and release their secretions directly into the blood.
The pituitary gland is also called hypophysis, or master gland. It secretes hormones that directly impact the body as well as hormones that indirectly control body functions because they activate other endocrine glands, such as the adrenal cortex (ACTH) and the thyroid gland (TSH). These two glands when stimulated by pituitary hormones then release their own hormones. The pituitary gland has two lobes, the anterior lobe and the posterior lobe. The anterior lobe secretes: growth hormone (GH), Luteinizing hormone (LH), Follicle stimulating hormone (FSH), Adrenocorticotropic hormone (ACTH), Thyroid-stimulating hormone (TSH), Prolactin (PRL), and the posterior lobe secretes: Antidieuretic hormone (ADH), and Oxytocin (OT). There is an intermediate lobe, in adult humans it is just a thin layer of cells between the anterior and posterior pituitary, nearly indistinguishable from the anterior lobe. The intermediate lobe produces melanocyte-stimulating hormone (MSH).
In the neck are the thyroid and parathyroid glands, that secrete hormones that control metabolism and blood calcium levels. The four parathyroid glands are situated upon the dorsal (back) surface of the thyroid gland.
Respiratory system
The respiratory System involves:
- (1) the nasal cavity for filtering, moistening, and warming the air
- (2) the pharynx or throat which is the combining point for respiratory and digestive system
- (3) larynx or voice box containing the epiglottis
- (4) trachea, or windpipe
- (5) bronchus breathing tubes of the lungs
- (6) lungs primary organs of respiration
- (7) the respiratory membranes consisting of the alveoli and surrounding capillary network of the pulmonary loop of the circulatory system
The critical pathway between the respiratory and digestive systems is the cartilage flap epiglottis which shuts during swallowing to prevent aspiration. The epiglottis is normally open to support respiration and shuts during swallowing to prevent food and fluids from enterng the trachea, activating the gag reflex or initiates the choking mechanism.
The respiratory system is involved in ventilation (physiology) and cellular respiration. Its functioning during oral procedures and surgery is essential to good patient care. If the patient stops breathing, heart failure will result within four to six minutes. The use of cardiopulmonary resuscitation (CPR) and rescue breathing may be required to revive the patient.
Other illnesses that may present a concern to the health care professional include: influenza, pulmonary embolism, cystic fibrosis, and respiratory distress syndrome, ARDS.
