In a typical functional loop, the Peripheral Nervous System sends messages to the spinal cord, which then relays those messages to the brain for processing.
The Peripheral Nervous System (PNS)
The PNS consists of all the nerves that lie outside the CNS. Its job is to connect the central command center to the rest of the body. The PNS is further subdivided into two functional systems:
- The Somatic Nervous System: This system conveys information into and out of the CNS and is responsible for controlling the voluntary movements of our skeletal muscles.
- The Autonomic Nervous System: This system carries involuntary and automatic commands that control internal organs, glands, and blood vessels.
Study Tip: To distinguish between the two, remember that "Somatic" relates to the body you can control (voluntary muscles), while "Autonomic" relates to the body functions that run on "autopilot" (involuntary organs).
The Autonomic Nervous System: Balance and Response
The Autonomic Nervous System is essential for maintaining homeostasis. It is divided into two branches that work together to manage our body's internal state:
- The Sympathetic Nervous System: Known as the "arousing" system, it is responsible for the "fight or flight" response. It helps us respond to life-threatening situations by preparing the body for action.
- The Parasympathetic Nervous System: Known as the "calming" system, it is responsible for returning the body to its normal, resting state after a period of arousal.
Exploring the Brain
The brain is the most complex part of the nervous system. It is organized into several distinct regions, each serving specific functions.
The Hindbrain
The hindbrain is responsible for several fundamental survival functions. A helpful mnemonic to remember its components is RCMP:
- Reticular Formation: Regulates sleep/wake cycles, arousal, attention, and vital functions like cardiac and respiratory function.
- Cerebellum: Crucial for motor coordination.
- Medulla: Manages basic bodily functions.
- Pons: Acts as a bridge between the medulla and other brain areas; it also contains the Locus Coeruleus, which influences much of the CNS.
The Midbrain
The midbrain is a smaller, more central region. You can remember its parts using the mnemonic Teensy – Tiny: Tegmentum and Tectum:
- Tegmentum: Involved in movement, arousal, and orienting the organism toward sensory stimuli.
- Tectum: Responsible for orienting the organism within its environment.
The Forebrain
The forebrain is the most highly developed part of the brain and is organized both across hemispheres and within them.
Hemispheric Organization: The brain is divided into a Left Hemisphere and a Right Hemisphere. These exhibit contralateral control, meaning each hemisphere controls the functions on the opposite side of the body. Each hemisphere is further divided into four lobes: the occipital, parietal, temporal, and frontal lobes.
Subcortical Structures: Deep within the forebrain lie several critical structures, often remembered by the mnemonic BELT:
- B - Basal Ganglia: A set of structures that direct intentional movements.
- E - Endocrine System: A network of glands that secrete hormones into the bloodstream to influence metabolism, growth, and development.
- L - Limbic System: Includes the amygdala (central to emotional processes and emotional memories) and the hippocampus (critical for creating and storing new memories).
- T - Thalamus & Hypothalamus: The thalamus acts as a relay station, filtering sensory information and sending it to the cerebral cortex. The hypothalamus regulates vital drives such as hunger, thirst, body temperature, and sexual behavior.
