Central Nervous System (CNS)

• Components: The Central Nervous System (CNS) consists of the brain and spinal cord, which play crucial roles in processing information and coordinating bodily functions.

• Brain Areas:

  • Cerebrum: The largest part of the brain, responsible for higher cognitive functions such as thinking, reasoning, and learning. It is divided into two hemispheres, with specific areas dedicated to sensory perception, voluntary muscle movement, and executive functions, is 2- 4 mm thick. Deep inside the cerebrum is additional grey matter (lacking myelinated fibres – fatty protein coating providing insulation to the nerve cell, allowing electrical impulses to transmit more quickly and efficiently) this inner grey matter is called the basal ganglia. – Convolutions (gyri) are round ridges. They are separated by shallow downfolds called sulci or deep downfolds called fissures. Longitudinal fissures separate the cerebrum into the left and right cerebral hemispheres. Function: thinking, reasoning, learning, intelligence, memory, also concerned with initiation and control of voluntary muscle contraction, perception of senses.

    • Cerebral Cortex: This outer layer of the cerebrum is made of grey matter, consisting of unmyelinated cell bodies. It is intricately folded into convolutions, allowing for a greater surface area to accommodate the large number of neurons. Below the cortex is white matter (myelinated axons). Nearly all impulses from our sense organs are carried to the cerebral cortex, which then has all relevant information about the environment and can initiate responses accordingly.

  • Cerebellum: second largest part of the brain. Second largest part of the brain, its surface is folded into a series of parallel ridges, grey matter forms the outer folded part of the cerebellum. White matter forms the inside and branches to all parts of the cerebellum. Located at the back of the brain, it is involved in subconscious control of posture, balance, and coordination of fine movements, it stops movements from being spasmodic, jerky and uncontrolled, allows smooth coordinated movements such as those required for writing, playing a musical instrument or using a computer keyboard. It receives sensory information from inner ear (posture + balance, stretch receptors in skeletal muscles. It integrates sensory inputs to fine-tune motor activity.

  • Medulla Oblongata: A vital structure that regulates autonomic functions such as breathing, heart rate, and blood pressure. It acts as a communication pathway between the brain and spinal cord.

Cerebral Lobes:

• Frontal Lobe:

  • Located at the front of the brain, responsible for higher cognitive functions such as decision-making, problem-solving, planning, and emotional regulation.

  • Contains the primary motor cortex, which is crucial for voluntary muscle movements.

• Parietal Lobe:

  • Positioned behind the frontal lobe, it processes sensory information such as touch, temperature, and pain.

  • Houses the primary somatosensory cortex, which is instrumental in perceiving and interpreting sensory inputs from various body parts.

• Temporal Lobe:

  • Located beneath the lateral fissure, associated with auditory processing and is important for memory formation and emotional responses.

  • Contains structures such as the hippocampus and amygdala, which are essential for memory and emotional regulation.

• Occipital Lobe:

  • Found at the rear of the brain, dedicated to visual processing and interpreting visual stimuli.

  • The primary visual cortex receives input from the eyes and processes visual information, allowing for the recognition of shapes, colours, and motion.

• Insula Lobe:  The insula, located deep within the lateral sulcus, is hidden beneath the brain’s surface. It plays a key role in sensing internal bodily states (like heart rate, hunger, and pain), emotional processing, empathy, and self-awareness. It also helps regulate taste, autonomic functions, and overall bodily balance (homeostasis).

Cerebrum structure tracts: between cerebral cortex + basal ganglia is white matter composed of bundles of nerve fibres covered in myelin. In CNS called tracts; outside of CNS called nerves

types of tracts in the white matter: Tracts that connect various areas of cortex withing same area. Tracts that carry impulses between left and right hemispheres, and tracts that connect the cortex to other parts of the brain or spinal cord

basal ganglia consists of groups of nerve cell bodies associated with control of skeletal muscles. Role – initiating wanted movements and inhibiting unwanted movements.

• Spinal Cord:

  • A long cylindrical structure that serves as a major conduit for neural signals between the brain and the rest of the body. Usually around 44cm long. Extends from the foramen magnum to the second lumbar vertebra (waist level), it has a cylindrical structure with a central canal running down its length. This canal contains cerebrospinal fluid.

  • It contains both ascending and descending tracts that transmit sensory information to the brain and motor commands to peripheral structures. Additionally, it hosts neural circuits responsible for reflex actions, allowing for immediate responses without processing in the brain.

• Protection: The CNS is encased in protective structures, including the skull and vertebrae. Furthermore, it is safeguarded by the meninges—three layers of connective tissues, the dura matter is not attached to the bone, instead a space containing far connective tissue and blood vessels, pad around the spinal cord allows the cord to bend when the spine is bent. The centre of the spinal cord is made up of grey matter, surrounded by white matter this is the reverse of the brain. The white matter – myelinated fibres – for ascending and descending tracts. — and the cerebrospinal fluid (CSF) that cushions and supports the brain and spinal cord, preventing damage during movement or trauma.

• The ascending tracts are sensory axons that carry impulses toward the brain, descending tracts are motor axons that conduct impulses away from the brain. Functions: spinal cord carries sensory impulses up to  the brain and motor impulses away from the brain, integrates fast automatic responses – reflexes.

Meninges

• Definition: The meninges are protective coverings of the brain and spinal cord, consisting of three layers:

  1. Dura Mater: The tough, outermost layer that provides strength and protection; it is firmly attached to the skull and loosely envelops the vertebrae.

  2. Arachnoid Mater: The middle layer, characterized by its web-like appearance, encapsulates the sub-arachnoid space that is filled with cerebrospinal fluid (CSF) to absorb shocks.

  3. Pia Mater: The delicate innermost layer that intimately follows the contours of the brain and spinal cord while harboring blood vessels that supply nutrients and oxygen.

Cerebrospinal Fluid (CSF)

• Composition: A clear, colorless liquid composed of water, glucose, proteins, urea, electrolytes, and a few white blood cells. Its unique chemical composition helps maintain ionic balance critical for neuron function.

• Functions:

  • Provides support to the CNS, acting as a cushion to protect against sudden impacts.

  • Serves as a shock absorber for the brain and spinal cord, thus preventing mechanical injuries.

  • Facilitates the transportation of nutrients to and waste products away from the brain's cells, playing a key role in maintaining homeostasis.

  • CSF circulates within the sub-arachnoid space surrounding the brain, the central canal of the spinal cord, and the brain's ventricles, contributing to nutrient delivery and waste disposal.

• Production: Generated by the choroid plexus, specialized structures located in the brain's ventricles that filter blood to produce CSF.

The Brain

• Major Parts of the Brain:

  • Cerebrum: Largest part; involved in complex functions including decision-making, emotional regulation, and voluntary motor control.

  • Cerebellum: Coordinates fine motor control and balance, integrating sensory information from the body to optimize movement.

  • Hypothalamus: Regulates a variety of homeostatic functions, such as temperature control, hunger, thirst, homeostatic control, patterins of waking and sleeping, contraction of urinary bladder, ensuring the body maintains a stable internal environment. Responsible for many vital functions of the body and most concerned with homeostasis. Regulates heart rate, blood pressure, digestive juices, alimentary canal, diameter of pupil of the eye. Also responsible for emotional responses; fear, anger, aggression, pleasure, contentment. Also monitors secretion of hormones, coordinates part of the endocrine system, regulates metabolism and growth production, coordinated body’s response to stress, using the pituitary glands.

  • Medulla Oblongata: Functions as a critical linkage between the brain and spinal cord, regulating many involuntary actions essential for survival, including reflex actions involving breathing and heart rate. 3cm long, the continuation of the spinal cord. Extends just above the point where the spinal cord enters the skull, consists of nerve fibres from brain to body, and from body to brain. Important role in automatically adjusting body functions, medulla oblongata contains; the cardia centre regulates the rate and force of heartbeat, the respiratory centres control rate and depth of breathing, the vasomotor centre regulated the diameter of blood vessels. Also regulates, swallowing, sneezing, coughing, vomiting. All centres of the medulla oblongata are controlled by hypothalamus.

Functional Areas of the Cerebral Cortex

• Types:

  • Sensory Areas: Responsible for processing sensory information, including touch, temperature, and pain from the body. They interpret impulses from receptors.

  • Motor Areas: Control voluntary muscle movements. The basal ganglia, a group of nuclei within the brain, are involved in movement regulation, ensuring smooth and coordinated motions. They consist of groups of nerve cell bodies.

  • Association Areas: Integrate information from various sensory modalities and are crucial for functions such as memory, language, and emotion processing.

Cerebral Hemispheres

• The cerebrum is divided into two hemispheres, with distinct specialized functions:

  • Left Hemisphere: Dominant for language abilities, analytical thinking, and calculation.

  • Right Hemisphere: Involved in musical and artistic abilities, as well as spatial abilities. Each hemisphere also controls movements and sensations on opposite sides of the body.

Spinal Cord Structure and Function

• Structure: Approximately 44 cm long; encased in protective meninges within the vertebral canal, consisting of cervical, thoracic, lumbar, sacral, and coccygeal regions.

• Function:

  • Conducts sensory impulses towards the brain and motor impulses away from the brain. These impulses travel along ascending (sensory) and descending (motor) tracts.

  • Integrates reflex actions for rapid responses, enabling immediate reactions to stimuli, often bypassing conscious brain processing.

Summary of CNS Functions

• Cerebrum: Engages in higher-order functions such as problem-solving, reasoning, and planning, as well as emotional responses.

• Hypothalamus: Ensures homeostasis and regulates endocrine functions, appetite, and emotional responses.

• Medulla Oblongata: Monitors and regulates autonomic functions such as heart rate and respiration, crucial for sustaining life.

• Cerebellum: Coordinates voluntary movements, posture, and balance, contributing to physical dexterity.

• Spinal Cord: Acts as a pathway for communication between the brain and peripheral nervous system, facilitating both voluntary and involuntary responses, while also containing circuits for reflex actions.