The nervous system is anatomically divided into two parts, the Central Nervous System (the brain and the spinal cord) and the Peripheral Nervous System (ganglia, 12 pairs of cranial nerves and 31 of pair’s spinal nerves).
As a part of the feedback loop mechanism of control, the Central Nervous System (CNS) often plays a significant role as the integration center. This gives you the notion that it is for information processing, analysis and interpretation. The CNS is responsible for intricate and complex neuronal processing, with each region of the brain and spinal cord having distinct physiological functions.
The PNS can be divided into two parts, the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS). The SNS is responsible for movement of the body (soma = body), and its effector tissue is skeletal muscle. The ANS is responsible for automated responses that occur in the body (e.g., heart rate) and the effector tissues are cardiac muscle, smooth muscle and glands.
We can divide the brain into six parts in terms of physiological functions:
6. Medulla oblongata
1. Cerebrum –
This is the most developed area of brain in the human species and is considered to be the center of the highest functions. The major functions include: awareness of sensory perception; voluntary control of movement (regulation of skeletal muscle movement); language; personality traits; sophisticated mental activities such as thinking, memory, decision making, predictive ability, creativity and self-consciousness.
The 4 lobes of the cerebrum.
2. Epithalamus, Thalamus and Hypothalamus
The epithalamus contains the pineal gland, a hormone secreting endocrine structure. Under the influence of the hypothalamus, the pineal gland secretes the hormone melatonin, which prepares the body for the night-time stage of the sleep/wake cycle. The thalamus makes up about 80% of the diencephalon and is the main relay center for the various sensory and motor functions.
The Hypothalamus controls and regulates many important functions of the body, including:
Means ‘little brain’. The Cerebellum has two primary functions:
Plays a role in the regulation of the respiratory system.
Contains two ‘pontine’ respiratory centers:
1) the pneumotaxic center and
2) the apneustic center. These two centers will be discussed later in the respiratory system. The pons is not responsible for the rhythm of breathing (the medulla oblongata is) but controls the changes in depth of breathing and the fine tuning of the rhythm of breathing set by the medulla oblongata. The pons also prevents over inflation of the lungs.
6. Medulla Oblongata
The medulla oblongata is the last division of the brain. It becomes continuous with the spinal cord. It houses some very important visceral or vital centers, 1) the cardiac center – adjusts the force and rate of the heartbeat; 2) the vasomotor center – regulates the diameter of blood vessels and therefore systemic blood pressure (constriction increases and dilation decrease blood pressure); and 3) the respiratory center – for control of the basic rhythm and rate of breathing. Additional centers regulate sneezing, coughing, hiccupping, swallowing and vomiting.
The physiology of the spinal cord will be covered in the lab component of this physiology course. The basic structure of the spinal cord is that it is the downward continuation of medulla oblongata starting at the foramen magnum. It descends to about the level of the second lumbar vertebra, tapering to a structure called the conus medullaris.
The cord projects 31 pairs of spinal nerves on either side (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal) that are connected to the peripheral nerves. A cross section of the spinal cord exhibits the butterfly-shaped gray matter in the middle, surrounded by white matter. As in the cerebrum, the gray matter is composed of nerve cell bodies. The white matter consists of various ascending and descending tracts of myelinated axon fibers with specific functions.
The spinal cord serves as a passageway for the ascending (going up) and descending (going down) fiber tracts that connect the peripheral and spinal nerves with the brain. Each of the 31 spinal segments is associated with a pair of dorsal root ganglia. These contain sensory nerve cell bodies. The axons from these sensory neurons enter the posterior aspect of the spinal cord via the dorsal root. The axons from somatic and visceral motor neurons leave the anterior aspect of the spinal cord via the ventral roots. Distal to each dorsal root ganglion the sensory and motor fibers combine to form a spinal nerve – these nerves are classified as mixed nerves because they contain both afferent (sensory) and efferent (motor) fibers.