Nervous System: CNS and PNS Overview

Study Notes

The nervous system is the organ system responsible for controlling all bodily functions through electrical and chemical signals. It consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord, while the PNS includes cranial nerves, spinal nerves, and ganglia. Both systems work together to coordinate responses to sensory information, regulate body temperature, control muscle contractions, and perform other vital functions.

Central Nervous System (CNS)

The CNS is responsible for controlling all functions necessary for survival and conscious perception. It is the command center of the body, receiving, processing, and interpreting information from the PNS. The brain's primary function is to think, feel, perceive, learn, remember, imagine, plan, and problem solve. Some key structures within the CNS include:

Brain Stem: Connected to both the cerebrum and cerebellum, this region controls essential activities such as breathing, heart rate, blood pressure, vomiting, swallowing, coughing, eye movement, facial expression, hearing, and taste sensation.
Cerebellum: Located at the base of the skull, it coordinates voluntary movements and maintains posture and balance.
Limbic System: A group of interconnected structures including the hippocampus, amygdala, thalamus, basal forebrain, hypothalamus, and prefrontal cortex. This system deals with motivation, learning, pleasure, emotion, and memory.

The human brain has approximately 86 billion nerve cells called neurons, which communicate through complex connections known as synapses. Neuron communication occurs primarily via neurotransmitters like dopamine, serotonin, norepinephrine, acetylcholine, glutamate, GABA, histamine, endorphins, and enkephalins.

Peripheral Nervous System (PNS)

The PNS receives sensory input from internal organs and external stimuli outside the brain. It also carries motor output commands from the CNS to muscles and glands. The PNS has several types of neurons: sensory, motor, and relay. Sensory neurons transmit information from receptors in the skin, muscles, tendons, joints, eyes, ears, nose, mouth, and various organs. Motor neurons activate skeletal muscles and control smooth muscle contraction. Relay neurons connect different regions of the PNS and may also have specific roles in reflex arcs.

The PNS can be further divided into the somatic nervous system (SNS), which deals with conscious control of skeletal muscles, and the autonomic nervous system (ANS), which regulates involuntary control over non-skeletal muscles, glands, and some viscera. The ANS has two divisions: the sympathetic division (also known as the "fight or flight response") and the parasympathetic division ("rest and digest response"). These divisions work together to maintain homeostasis by adjusting heart rate, blood pressure, respiration, digestion, urination, pupil dilation, and sexual arousal.

Nerve impulses travel along axons, which can be up to a meter long. Myelin, a fatty insulator, covers most of the nerve fibers except those very close to the cell body, allowing faster transmission of impulses. Axons can regenerate after injury due to their structure, but they take much longer to do so than neurons.

Description

Explore the central nervous system (CNS) and peripheral nervous system (PNS) which control essential bodily functions through electrical and chemical signals. Learn about key structures within the CNS like the brain stem, cerebellum, and limbic system, as well as the functions of the PNS in transmitting sensory input and motor output commands.