Central Nervous System: Structures and Functions (Chapter 11, Lecture 3)

Central Nervous System Overview

Major Structures and Their Functions

The central nervous system (CNS) consists of the brain and spinal cord, which coordinate sensory information, motor output, and higher cognitive functions. Several key structures within the brain play specialized roles in processing information and regulating bodily functions.

• Cerebrum: Responsible for higher brain functions such as thought, reasoning, and voluntary movement.

• Cerebellum: Coordinates voluntary movements, balance, and posture.

• Corpus Callosum: A large bundle of nerve fibers connecting the left and right cerebral hemispheres, allowing communication between them.

• Pons and Medulla: Structures in the brainstem that regulate vital functions such as breathing, heart rate, and sleep cycles.

Corpus Callosum

The corpus callosum is essential for integrating motor, sensory, and cognitive performances between the two hemispheres of the brain.

• Gray Matter vs. White Matter: The corpus callosum is primarily composed of white matter (myelinated axons), which facilitates rapid communication between hemispheres.

• Function: Enables coordinated actions and unified perception by sharing information across hemispheres.

Thalamus and Hypothalamus

The thalamus and hypothalamus are critical relay and regulatory centers in the brain.

• Thalamus: Acts as a relay station for sensory information, directing signals to appropriate areas of the cerebrum.

• Hypothalamus: Regulates homeostasis, including temperature, hunger, thirst, and endocrine functions via the pituitary gland.

Cerebellum

The cerebellum is involved in the coordination of voluntary movements and maintenance of balance and posture.

• Trauma Effects: Damage to the cerebellum can result in loss of coordination, balance issues, and difficulty with fine motor tasks.

Autonomic Nervous System (ANS)

Structure and Function

The autonomic nervous system (ANS) regulates involuntary physiological processes, including heart rate, digestion, and respiratory rate. It is divided into two main branches:

• Sympathetic Nervous System: Prepares the body for 'fight or flight' responses.

• Parasympathetic Nervous System: Promotes 'rest and digest' activities.

ANS Neurotransmitters

• Acetylcholine: Main neurotransmitter of the parasympathetic system.

• Norepinephrine: Main neurotransmitter of the sympathetic system.

These neurotransmitters help regulate stress responses and maintain homeostasis.

ANS Responses and Stress Regulation

• Sympathetic Response: Increases heart rate, dilates pupils, inhibits digestion.

• Parasympathetic Response: Decreases heart rate, stimulates digestion, promotes relaxation.

• Regulation of Stress: The body balances these responses to adapt to changing environments and maintain internal stability.

Reticular Activating System (RAS)

Main Function and Role

The reticular activating system (RAS) is a network of neurons in the brainstem that regulates wakefulness and attention.

• Information Overload Regulation: The RAS filters incoming sensory information, preventing the brain from being overwhelmed.

• Role in Consciousness: Maintains alertness and helps focus attention on relevant stimuli.

Effects of Drugs on the Nervous System

Stimulants vs. Depressants

• Stimulants: Increase neuronal activity, leading to heightened alertness and energy (e.g., caffeine, amphetamines).

• Depressants: Decrease neuronal activity, resulting in relaxation and reduced anxiety (e.g., alcohol, benzodiazepines).

• Mechanism: Stimulants often increase neurotransmitter release or block reuptake, while depressants enhance inhibitory neurotransmitter effects.

Alzheimer's Disease

Impact on the Brain

Alzheimer's disease is a progressive neurodegenerative disorder that impairs memory, cognition, and behavior.

• Pathology: Characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain.

• Effects: Leads to loss of neurons and synapses, especially in the hippocampus and cortex, crippling memory and cognitive function.

Key Vocabulary Table

Term	Definition
Alzheimer's Disease	Progressive brain disorder causing memory loss and cognitive decline
Autonomic Nervous System	Regulates involuntary bodily functions
Cerebellum	Coordinates movement and balance
Corpus Callosum	Connects left and right cerebral hemispheres
Depressants	Drugs that decrease neuronal activity
Hypothalamus	Regulates homeostasis and endocrine functions
Parasympathetic Nervous System	Promotes rest and digest responses
Pituitary Gland	Master endocrine gland controlling other glands
Pons	Brainstem structure involved in sleep and respiration
Reticular Activating System	Regulates wakefulness and attention
Spinal Cord	Transmits signals between brain and body
Stimulants	Drugs that increase neuronal activity
Sympathetic Nervous System	Prepares body for fight or flight
Thalamus	Relay station for sensory information

Additional info:

• Some context and definitions were inferred from standard Anatomy & Physiology curriculum.

• Equations are not directly relevant to this topic, but if needed, the Nernst equation for neuronal membrane potential is: $E = \frac{RT}{zF} \ln \frac{[\text{ion outside}]}{[\text{ion inside}]}$