The nervous system is a complex network of cells that coordinates our body's functions. The central nervous system, consisting of the brain and spinal cord, processes information and controls our actions. It works in tandem with the peripheral nervous system, which connects our body to the outside world.
The peripheral nervous system is divided into two main parts: somatic and autonomic. The somatic system controls voluntary movements, while the autonomic system regulates involuntary functions. Understanding these systems helps us grasp how our body responds to various stimuli and maintains balance.
Central Nervous System Components
Brain Structures and Functions
- Central nervous system (CNS) consists of the brain and spinal cord, which process and integrate sensory information and coordinate motor responses
- Brain is the main control center of the CNS located in the skull, responsible for higher cognitive functions, sensory processing, and motor control
- Cerebral cortex is the outermost layer of the brain involved in conscious thought, perception, memory, and decision making (frontal lobe, parietal lobe, temporal lobe, occipital lobe)
- Brainstem connects the brain to the spinal cord and regulates vital functions such as breathing, heart rate, and sleep-wake cycles (midbrain, pons, medulla oblongata)
- Cerebellum is located at the back of the brain, coordinates muscle movements, maintains balance and posture, and is involved in motor learning and fine motor control
Spinal Cord Structure and Function
- Spinal cord is a long, thin bundle of nervous tissue that extends from the brainstem down the back, serving as a conduit for sensory and motor information between the brain and body
- Spinal cord is protected by the vertebral column and is divided into cervical, thoracic, lumbar, and sacral regions based on the level of the vertebrae
- Spinal cord contains white matter (myelinated nerve fibers) on the outside and gray matter (cell bodies and unmyelinated fibers) on the inside, organized into sensory and motor pathways
- Spinal cord receives sensory input from the body, processes reflexes, and relays information to and from the brain to control voluntary movements
Peripheral Nervous System Components
Somatic Nervous System
- Peripheral nervous system (PNS) consists of all the nerves and ganglia outside the brain and spinal cord, connecting the CNS to the rest of the body
- Somatic nervous system is part of the PNS that controls voluntary movements and receives sensory information from the skin, muscles, and joints
- Somatic nervous system includes sensory neurons that detect stimuli (touch, pain, temperature) and motor neurons that innervate skeletal muscles for conscious control of movement
- Examples of somatic nervous system functions include moving your arm to reach for an object, feeling the texture of a surface, and sensing the position of your limbs in space (proprioception)
Autonomic Nervous System
- Autonomic nervous system is part of the PNS that regulates involuntary functions of internal organs and glands, such as heart rate, digestion, and secretion of hormones
- Autonomic nervous system operates largely unconsciously and is divided into the sympathetic and parasympathetic divisions, which often have opposing effects on target organs
- Autonomic nervous system uses two types of neurons: preganglionic neurons (originate in the CNS) and postganglionic neurons (located in autonomic ganglia outside the CNS)
- Examples of autonomic nervous system functions include increasing heart rate during exercise (sympathetic), stimulating digestion after a meal (parasympathetic), and regulating blood pressure (both divisions)
Autonomic Nervous System Divisions
Sympathetic Nervous System
- Sympathetic nervous system is one of the two divisions of the autonomic nervous system, often referred to as the "fight or flight" response
- Sympathetic nervous system prepares the body for stressful or emergency situations by increasing heart rate, dilating pupils, diverting blood flow to muscles, and releasing glucose from the liver
- Sympathetic nervous system originates in the thoracic and lumbar regions of the spinal cord (T1-L2) and has relatively short preganglionic fibers and long postganglionic fibers
- Examples of sympathetic nervous system activation include increased alertness and arousal during a threatening situation, sweating and trembling during public speaking, and increased blood pressure during exercise
Parasympathetic Nervous System
- Parasympathetic nervous system is the other division of the autonomic nervous system, often referred to as the "rest and digest" response
- Parasympathetic nervous system promotes relaxation and energy conservation by slowing heart rate, constricting pupils, stimulating digestion, and promoting urination and defecation
- Parasympathetic nervous system originates in the brainstem (cranial nerves III, VII, IX, X) and sacral region of the spinal cord (S2-S4), with long preganglionic fibers and short postganglionic fibers
- Examples of parasympathetic nervous system activation include slowing of heart rate during sleep, increased salivation and peristalsis during a meal, and constriction of bronchioles in the lungs