central nervous system: brain and spinal cord

Anatomy. and physioloy slides on cns

1. CENTRAL NERVOUS SYSTEM

2. CENTRAL NERVOUS SYSTEM (CNS) Learning Objectives By the end of this topic, students should be able to: Describe the overall structure and role of the central nervous system (CNS). Identify the layers and functions of the meninges. Describe the structure and functions of the spinal cord. Summarize the major regions and functions of the brain. Explain the embryological development of the brain and its major divisions.

3. Introduction The central nervous system (CNS) consists of: Brain — the main control center for thoughts, emotions, memory, and coordination. Spinal cord — the communication link between brain and body, responsible for reflexes and conduction of impulses. Together, the CNS: Integrates sensory information. Coordinates voluntary and involuntary activities. Maintains homeostasis through communication with the peripheral nervous system

4. The Meninges The meninges are three protective layers (membranes) that cover the brain and spinal cord. Their main job is to protect, support, and nourish the central nervous system . They also help to keep the cerebrospinal fluid around the brain and spinal cord.

5. Layers of Meninges From the outermost to the innermost, the meninges are: 1)Dura Mater This is the outermost layer. It is thick, tough, and strong, made of dense connective tissue. It provides the main protection to the brain and spinal cord. In the brain, the dura has two layers — one attached to the skull and another covering the brain — and between them are spaces that carry venous (used) blood back to the heart. In the spinal cord, there is only one layer, and it lies separated from the bone by a space called the epidural space, which contains fat and small blood vessels.

6. 2)Arachnoid Mater This is the middle layer of the meninges. It is thin and web-lik e, resembling a spider’s web (that’s why it’s called “arachnoid”). It does not have blood vessels. Beneath this layer is a space called the subarachnoid space, which contains cerebrospinal fluid (CSF). The CSF acts like a cushion, protecting the brain and spinal cord from shocks, bumps, or sudden movements.

7. 3)Pia Mater This is the innermost layer. It is very thin and delicate, but it sticks closely to the surface of the brain and spinal cord, following all their folds and grooves. The pia mater contains many small blood vessels that supply oxygen and nutrients to the nervous tissue. It helps nourish the brain and spinal cord.

8. A ssociated spaces Epidural space: This is the space between the dura mater and the bone of the spinal column. It contains fat and connective tissue that protect the spinal cord. Doctors inject anaesthetic drugs here during childbirth (called an epidural). Subdural space: This is a thin space between the dura mater and the arachnoid mater. It has a small amount of lubricating fluid that helps the layers slide smoothly. Subarachnoid space: This is the space between the arachnoid mater and the pia mater. It contains cerebrospinal fluid , which cushions the brain and spinal cord and helps remove waste products. Blood vessels also pass through this space.

9. The Spinal Cord The spinal cord is a cylindrical structure of nervous tissue extending from the medulla oblongata (at the level of the foramen magnum) to about the L1–L2 vertebrae. it is part of the central nervous system and acts as a communication link between the brain and the rest of the body. It is protected by the vertebral column, the meninges, cerebrospinal fluid, and fat within the spinal canal.

10. External Features of spinal cord The spinal cord has several visible structures that can be seen in diagrams or models. Cervical Enlargement A wider area in the upper region of the cord (around C4 to T1). Gives rise to nerves that supply the shoulders and upper limbs. Lumbar Enlargement A second wider area in the lower region (around T9 to T12). Gives rise to nerves that control the pelvis and lower limbs. Conus Medullaris The cone-shaped end of the spinal cord found near L1–L2. Marks the point where the spinal cord itself ends.

11. Protection of the Spinal Cord The spinal cord is very delicate and must be well protected. The four main structures that provide protection include: The vertebral column – forms a hard bony wall around the cord. The meninges – three layers (dura mater, arachnoid mater, pia mater) that cover and cushion it. Cerebrospinal fluid – surrounds the cord in the subarachnoid space to absorb shocks. Epidural fat and connective tissue – in the epidural space, add extra padding and support.

12. Internal Structure of spinal cord Gray Matter Found in the center , shaped like the letter “H” or a butterfly. Made up of neuron cell bodies, dendrites, and unmyelinated axons. Divided into horns: Posterior (dorsal) horns — receive sensory information. Anterior (ventral) horns — send motor commands to muscles. Lateral horns — contain autonomic (involuntary) neurons in the thoracic region. White Matter Surrounds the gray matter. Made up of myelinated axons that carry nerve impulses to and from the brain. Organized into tracts or columns: Ascending tracts carry sensory information upward to the brain. Descending tracts carry motor commands downward to muscles and glands. Central Canal A small hollow channel in the center of the grey matter. Filled with cerebrospinal fluid , which helps nourish and protect the cord

13. Functions of the Spinal Cord 1. Nerve Impulse Conduction The spinal cord contains nerve tracts that act as communication paths. They carry information to and from the brain through bundles of nerve fibers located in the white matter. There are two main types of nerve tracts: Ascending tracts (sensory pathways): These carry sensory information from the body to the brain. For example: pain, touch, temperature, and body position signals travel up these tracts to the brain, where they are interpreted. Descending tracts (motor pathways): These carry motor commands from the brain to the body. For example: when you decide to move your hand, signals travel down these tracts to your arm muscles to make them contract. The spinal cord serves as a bridge — carrying sensory messages up to the brain and motor commands down from the brain. 2. Integration of Reflexes Apart from carrying messages, the spinal cord can also process information on its own — especially for quick, protective actions called reflexes. A reflex is an automatic, fast response to a specific stimulus that helps protect the body or maintain balance. These responses happen without the brain’s involvement, so they are faster.

14. Other functions include Besides conduction and reflexes, the spinal cord also: Coordinates body movements through communication between nerves. Controls muscle tone and balance. Connects the brain to the peripheral nerves , ensuring all parts of the body receive and send information properly.

15. Clinical Importance Spinal cord injury : Damage to the spinal cord can block communication between the brain and body. The result is paralysis or loss of sensation below the level of injury. For example, injury in the neck area may cause paralysis of both arms and legs (quadriplegia). Reflex testing: Doctors test reflexes (like the knee-jerk reflex) to check the health of the spinal cord and nerves. Poliomyelitis (Polio): A viral infection that destroys motor neurons in the spinal cord, leading to muscle weakness or paralysis.

16. Overview of the Brain The brain is the control center of the entire body. It receives information from all parts of the body, interprets it, and then sends out instructions. The brain also controls thinking, memory, emotions, balance, movement, speech, and heartbeat. Together with the spinal cord, the brain forms the central nervous system . It is protected by the skull bones, the meninges, and cerebrospinal fluid

17. Size and Weight: The adult brain weighs about 1.3 to 1.4 kilograms. It contains about 100 billion neurons and even more support cells called neuroglia. Although it makes up only about 2% of body weight, it uses about 20% of the body’s oxygen and glucose — showing how active it is.

18. Major Parts of the Brain The brain has four main parts: Brainstem Cerebellum Diencephalon Cerebrum Each part has special structures and functions, but they all work together.

19. 1. The Brainstem

20. The brainstem connects the spinal cord to the rest of the brain. It controls many automatic functions that keep us alive, such as breathing and heartbeat. It has three main parts — from lowest to highest: a) Medulla Oblongata Located just above the spinal cord. Contains vital control centers for: Heart rate Breathing Blood pressure Also controls reflexes such as swallowing, coughing, sneezing, and vomiting. If the medulla is severely damaged, it can cause instant death because vital functions stop.

21. b) Pons Lies above the medulla. Acts as a bridge that connects different parts of the brain. Helps control breathing rhythm and coordinates voluntary movement with the cerebellum. c) Midbrain The uppermost part of the brainstem. Connects the pons to the diencephalon. Controls eye movements, head turning in response to sights and sounds, and posture reflexes. Contains centers that relay messages related to vision and hearing.

22. 2. The Cerebellum Located behind the brainstem and below the cerebrum. It looks like a small brain with two hemispheres. The cerebellum is responsible for: Coordinating voluntary movements (so actions are smooth and balanced). Maintaining posture and balance. Fine-tuning muscle activity. It stores patterns of movement — for example, it helps you ride a bicycle or type without thinking about each motion. NB: If the cerebellum is damaged, movements become shaky and uncoordinated

23. 3. The Diencephalon The diencephalon lies above the midbrain and below the cerebrum. It includes three main structures: the thalamus, hypothalamus, and epithalamus. a) Thalamus Acts as the main relay center for sensory information going to the cerebrum. It receives signals such as pain, touch, temperature, and pressure, and sends them to the correct area of the brain. Also plays a role in emotions, learning, and memory.

24. b) Hypothalamus Lies below the thalamus and is very small but powerful. It controls many automatic body functions, including: Body temperature Hunger and thirst Sleep and wake cycles Hormone production Emotional behavior The hypothalamus connects the nervous system to the endocrine system through the pituitary gland, which it controls. c) Epithalamus The smallest part of the diencephalon. Contains the pineal gland, which produces the hormone melatonin that regulates sleep and wake patterns. Also helps control emotional and visceral (organ-related) responses.

25. 4. The Cerebrum The cerebrum is the largest and most developed part of the brain. It makes up about 80% of the brain’s weight and is responsible for intelligence, thought, memory, and voluntary movement. Structure Divided into right and left hemispheres, separated by a deep groove called the longitudinal fissure. The two hemispheres communicate through a thick band of nerve fibers called the corpus callosum. The outer layer of the cerebrum is the cerebral cortex, made up of gray matter (cell bodies). The inner part is made of white matter (myelinated nerve fibers ).

26. The hemispheres

27. The left hemisphere is associated with language functions, such as formulating grammar and vocabulary and containing different language centers The right hemisphere is associated with more visuospatial functions such as visualization, depth perception, and spatial navigation. These left and right functions are the case in most people, especially those who are right-handed.

28. Lobes of the Cerebrum

29. Each hemisphere of the cerebrum is divided into four main lobes, each with specific functions: Frontal Lobe: Controls reasoning, planning, problem-solving, and voluntary movements. Contains Broca’s area (controls speech production). Parietal Lobe: Processes touch, temperature, pain, and pressure sensations. Helps with body position and spatial awareness. Temporal Lobe: Responsible for hearing, memory, and smell. Contains Wernicke’s area, which helps in understanding speech. Occipital Lobe: Located at the back of the brain. Handles vision and visual recognition.

30. Functions of the Cerebrum Controls voluntary body movements. Handles thinking, reasoning, and problem-solving. Stores and recalls memories. Interprets sensory input (what we see, hear, touch, taste, smell). Produces speech and language. Manages emotions and personality.

31. Protection of the Brain Cranial bones – form a hard outer covering. Meninges – three membranes (dura mater, arachnoid mater, pia mater). Cerebrospinal fluid (CSF) – surrounds the brain and acts as a shock absorber. Blood-brain barrier – controls what substances can enter brain tissue from the blood.

32. Ventricles and Cerebrospinal Fluid Within the brain, there are fluid-filled interconnected cavities called  ventricles , which are extensions of the spinal cord. These are filled with a substance called cerebrospinal fluid, which is a clear and colorless liquid. The ventricles produce cerebrospinal fluid and transport and remove this fluid. The ventricles do not have a unique function, but they provide cushioning to the brain and are useful for determining the locations of other brain regions. Cerebrospinal fluid circulates through the brain and spinal cord and functions to cushion the brain within the skull. If damage occurs to the skull, the cerebrospinal fluid will act as a shock absorber to help protect the brain from injury.

33. Clinical Importance Stroke (Cerebrovascular Accident): Blood supply to part of the brain is blocked, causing tissue death and loss of function. Meningitis: Inflammation of the meninges; may cause headache, fever, and stiffness. Parkinson’s Disease: A brain disorder affecting movement due to loss of dopamine in the midbrain. Alzheimer’s Disease: Gradual loss of memory and thinking ability due to neuron damage in the cerebrum. Brain Tumor : Abnormal growth that can increase pressure inside the skull and affect brain function.

34. summary The brain is the main control center of the body. It has four main parts : brainstem, cerebellum, diencephalon, and cerebrum. The brainstem controls vital body functions like breathing and heartbeat. The cerebellum coordinates movement and balance. The diencephalon regulates internal body processes like temperature and hormones. The cerebrum handles thinking, memory, emotions, and voluntary actions. The brain is protected by the skull, meninges, CSF, and the blood-brain barrier.

35. Development of the Brain the brain does not appear all at once — it develops gradually as the embryo grows. the brain and spinal cord begin to form very early in pregnancy, just about three weeks after fertilization. Both structures develop from a special layer of cells in the embryo called the ectoderm. From this layer, a hollow tube known as the neural tube forms — this tube becomes the central nervous system .

36. Formation of the Neural Tube Around day 19 of embryonic life, cells of the ectoderm thicken to form a structure called the neural plate. The edges of this plate fold upward and meet to form the neural tube. The upper (anterior) part of the tube develops into the brain, while the lower (posterior) part becomes the spinal cord. The hollow space inside the neural tube later develops into the ventricles of the brain and the central canal of the spinal cord, which will be filled with cerebrospinal fluid Summary : The brain starts as a flat sheet of cells → rolls into a tube → the front end enlarges to form the brain → the rest forms the spinal cord..

37. Primary Brain Vesicles By about the 4th week of development, the front part of the neural tube (the brain region) swells into three main sections, called primary brain vesicles: Prosencephalon – the forebrain Mesencephalon – the midbrain Rhombencephalon – the hindbrain These are the primitive divisions that will later grow into the major parts of the adult brain.

38. Secondary Brain Vesicles By about the 5th week, each of the primary vesicles develops further into five secondary vesicles. These form the different regions of the adult brain. Transformation of Brain Vesicles (Simplified) Forebrain (Prosencephalon) divides into: Telencephalon → forms the Cerebrum (the largest part of the brain). Diencephalon → forms the Thalamus, Hypothalamus, and Epithalamus. Midbrain (Mesencephalon) does not divide — it remains the Midbrain, which is part of the Brainstem. Hindbrain (Rhombencephalon) divides into: Metencephalon → forms the Pons and Cerebellum. Myelencephalon → forms the Medulla Oblongata.

39. summary the Telencephalon grows rapidly to become the Cerebrum, which is responsible for intelligence, thought, memory, and voluntary movement. The Diencephalon forms the Thalamus, Hypothalamus, and Epithalamus, which control sensory processing and internal body functions. The Mesencephalon develops into the Midbrain, which coordinates eye movement and auditory reflexes. The Metencephalon forms the Pons (which helps control breathing) and the Cerebellum (which controls balance and coordination). The Myelencephalon forms the Medulla Oblongata, which controls heartbeat, blood pressure, and breathing.