5.7.1 Architecture of Human Brain and Spinal Cord and Their Functions

The central nervous system consists of the brain and spinal cord, both of which are hollow. They are covered with three protective membranes called meninges. The brain is enclosed within the cranium, while the spinal cord is enclosed within the vertebral column. The brain is divided into three parts: forebrain, midbrain, and hindbrain. The spinal cord is a vital link between the brain and the body.

Definition

Central Nervous System (CNS): The central nervous system consists of the brain and spinal cord. Both are hollow. They are covered with three protective membranes called meninges.

Meninges: The brain and spinal cord are covered with three protective membranes called meninges (singular: meninx).

Cerebrospinal Fluid (CSF): Between the arachnoid and pia mater there is a fluid, the cerebrospinal fluid (CSF), which helps to cushion the brain from shock.

Main Idea

• CNS consists of the brain and spinal cord.
• Both are hollow.
• Covered with three protective membranes called meninges.
• Brain is enclosed within the cranium.
• Spinal cord is enclosed within the vertebral column.
• Brain is divided into three parts:
• Spinal cord is a vital link between the brain and the body.

Core Concept

• CNS = brain and spinal cord
• Meninges = three protective membranes
• Dura mater = next to the cranium
• Arachnoid mater = middle membrane
• Pia mater = next to the nervous tissue
• CSF = cerebrospinal fluid; cushions the brain
• Forebrain = cerebrum, thalamus, limbic system
• Midbrain = relay station
• Hindbrain = cerebellum, medulla oblongata, pons
• Spinal cord = link between brain and body

Detailed Explanation

Architecture of Human Brain

• Forebrain
• Midbrain
• Hindbrain

Forebrain

• Cerebrum
• Thalamus
• Limbic system

• The largest part of the human brain.
• Divided into two cerebral hemispheres.
• Interconnected by a band of axons called corpus callosum.
• Each hemisphere contains four surface lobes:
• Frontal lobe
• Parietal lobe
• Temporal lobe
• Occipital lobe
• Each lobe contains different functional areas e.g., auditory (hearing), visual area, etc.
• Each functional area consists of three sub-areas:
• Sensory area — receives impulses from different body parts.
• Association area — interprets or analyzes the incoming information.
• Motor area — controls responses of the body.
• Cerebrum also functions in the analysis and interpretation of memory, reasoning, judgement, thoughts and dreams.

• The surface of the cerebrum is called cerebral cortex.
• Cerebral cortex has many folds or convulsions forming ridges or gyri (singular, gyrus) which are separated by grooves.
• A shallow groove is called a sulcus (plural, sulci) and a deep groove is called a fissure.
• The two hemispheres are separated by longitudinal fissure.

• Below the cerebrum.
• Receives all sensory impulses (except sense of smell) and channels them to limbic system and to appropriate regions of the cortex for interpretation.

• A complex set of structures that lies on both sides of the thalamus, just under the cerebrum.
• Includes the hypothalamus, the amygdala, the hippocampus, and several other nearby areas.
• Hypothalamus — on the ventral side of the thalamus; maintains homeostasis; contains centres for regulating hunger, sleep, thirst, body temperature, water balance and blood pressure, menstrual cycle and sleep wake cycle; controls the pituitary gland; serves as link between the nervous and endocrine system.
• Amygdala — two almond-shaped masses of neurons on either side of the thalamus; control feeling and emotions of love, hate, anger, fear, rage and sexual arousal.
• Hippocampus — consists of two "horns" that curve back from the amygdala; important in converting things that are "in your mind" at the moment (in short-term memory) into things that you will remember for the long run (long-term memory).

Midbrain

• Reduced in humans.
• Acts as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum.
• Contains reticular formation, which is a relay centre connecting hindbrain with forebrain.

Hindbrain

• Cerebellum
• Medulla oblongata
• Pons

• Controls equilibrium i.e., body position and coordination of the actions of individual muscles to produce complex activities such as walking, running, riding bicycles, doing delicate work with hand.
• Also involved in learning memory storage for behaviour.

• Acts as a bridge between the cerebellum, medulla and cerebrum.
• Also controls rate and pattern of heartbeat and breathing.

Medulla: - Controls the automatic functions of the body, such as heartbeat, blood pressure, respiration, swallowing etc.

• Brain is hollow structure as it has cavities called ventricles.
• There are four ventricles in the brain.

Architecture of Spinal Cord

• The spinal cord is the most important structure between the body and the brain.
• The spinal cord extends from the medulla to the level of the lumbar vertebrae.
• It is a vital link between the brain and the body.
• A transverse section of the adult spinal cord shows:
• White matter in the periphery
• Grey matter inside
• A tiny central canal filled with CSF at its centre
• Grey matter is shaped like the letter "H" or a "butterfly".
• The grey matter consists of neuron cell bodies and nonmyelinated parts of the fibres.
• The white matter is made up of bundles of myelinated fibres.
• Several pairs of spinal nerves originate from ventral and dorsal horn of grey matter.
• Dorsal root of spinal nerves also contain ganglia present just beside the spinal cord.
• Arrangement of grey and white matter in brain is opposite to that of spinal cord.

Summary Table of Brain Parts and Functions

Summary Table of Spinal Cord

Intermediate Level

Parts of the Brain

Meninges

Cerebrospinal Fluid (CSF)

Spinal Cord

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. CNS consists of the brain and spinal cord.
• 2. Both are hollow.
• 3. Covered with three protective membranes called meninges.
• 4. Brain is enclosed within the cranium.
• 5. Spinal cord is enclosed within the vertebral column.
• 6. Brain is divided into three parts: forebrain, midbrain, hindbrain.
• 7. Forebrain consists of cerebrum, thalamus, limbic system.
• 8. Cerebrum is the largest part of the brain.
• 9. Cerebrum has two hemispheres connected by corpus callosum.
• 10. Each hemisphere has four lobes.
• 11. Thalamus relays sensory impulses (except smell).
• 12. Limbic system includes hypothalamus, amygdala, hippocampus.
• 13. Hypothalamus maintains homeostasis.
• 14. Amygdala controls emotions.
• 15. Hippocampus is important for memory.
• 16. Midbrain is reduced in humans.
• 17. Hindbrain consists of cerebellum, medulla oblongata, pons.
• 18. Cerebellum controls equilibrium and coordination.
• 19. Pons controls heartbeat and breathing.
• 20. Medulla controls automatic functions.
• 21. Spinal cord extends from medulla to lumbar vertebrae.
• 22. White matter is in the periphery of the spinal cord.
• 23. Grey matter is inside the spinal cord.
• 24. Central canal is filled with CSF.
• 25. Spinal nerves originate from ventral and dorsal horn.

Remember

• - CNS = brain and spinal cord
• - Meninges = three protective membranes
• - Dura mater = next to the cranium
• - Arachnoid mater = middle membrane
• - Pia mater = next to the nervous tissue
• - CSF = cerebrospinal fluid; cushions the brain
• - Forebrain = cerebrum, thalamus, limbic system
• - Midbrain = relay station
• - Hindbrain = cerebellum, medulla oblongata, pons
• - Spinal cord = link between brain and body
• - White matter = periphery of spinal cord
• - Grey matter = inside of spinal cord
• - Central canal = filled with CSF

Common Mistakes

• 1. Confusing the parts of the brain — Forebrain, midbrain, hindbrain.
• 2. Mixing up the functions — Cerebrum: thinking; cerebellum: balance; medulla: automatic functions.
• 3. Forgetting the role of meninges — Protective membranes.
• 4. Mixing up the layers of meninges — Dura mater, arachnoid mater, pia mater.
• 5. Confusing the thalamus and hypothalamus — Thalamus: relay; hypothalamus: homeostasis.
• 6. Forgetting the role of the hippocampus — Memory.
• 7. Mixing up the arrangement of grey and white matter — Brain: grey outside, white inside; Spinal cord: white outside, grey inside.
• 8. Thinking the midbrain is large in humans — Midbrain is reduced in humans.
• 9. Forgetting the role of the pons — Controls heartbeat and breathing.
• 10. Confusing the central canal and ventricles — Ventricles in brain; central canal in spinal cord.

Quick Revision

The central nervous system consists of the brain and spinal cord, and both are hollow. The brain and spinal cord are covered with three protective membranes called meninges (singular: meninx). Brain is enclosed within the cranium while spinal cord is enclosed within vertebral column. The three meninges are dura mater (next to the cranium), arachnoid mater (middle membrane), and pia mater (next to the nervous tissue). Between the arachnoid and pia mater there is a fluid, the cerebrospinal fluid (CSF), which helps to cushion the brain from shock. The brain is divided into three parts: forebrain, midbrain, and hindbrain. Forebrain consists of cerebrum, thalamus and limbic system. Cerebrum is the largest part of the human brain. Cerebrum is divided into two cerebral hemispheres which are interconnected with each other by a band of axons, called corpus callosum. Each hemisphere contains four surface lobes: frontal, parietal, temporal and occipital lobe. Thalamus is below the cerebrum. It receives all sensory impulses (except sense of smell) and channels them to limbic system and to appropriate regions of the cortex for interpretation. The limbic system is a complex set of structures that lies on both sides of the thalamus, just under the cerebrum. It includes the hypothalamus, the amygdala, the hippocampus, and several other nearby areas. Midbrain is reduced in humans. It acts as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum. Hindbrain consists of cerebellum, medulla oblongata and pons. Cerebellum controls equilibrium i.e., body position and coordination of the actions of individual muscles to produce complex activities such as walking, running, riding bicycles, doing delicate work with hand. Pons acts as a bridge between the cerebellum, medulla and cerebrum. It also controls rate and pattern of heartbeat and breathing. Medulla controls the automatic functions of the body, such as heartbeat, blood pressure, respiration, swallowing etc. The spinal cord is the most important structure between the body and the brain. The spinal cord extends from the medulla to the level of the lumbar vertebrae. It is a vital link between the brain and the body. A transverse section of the adult spinal cord shows white matter in the periphery, grey matter inside and a tiny central canal filled with CSF at its centre. Grey matter is shaped like the letter "H" or a "butterfly". The grey matter consists of neuron cell bodies and nonmyelinated parts of the fibres. The white matter is made up of bundles of myelinated fibres. Several pairs of spinal nerves originate from ventral and dorsal horn of grey matter. Dorsal root of spinal nerves, also contain ganglia present just beside the spinal cord. Arrangement of grey and white matter in brain is opposite to that of spinal cord.

60-Second Revision

• CNS = brain and spinal cord
• Meninges = three protective membranes
• Dura mater = next to the cranium
• Arachnoid mater = middle membrane
• Pia mater = next to the nervous tissue
• CSF = cerebrospinal fluid; cushions the brain
• Forebrain = cerebrum, thalamus, limbic system
• Midbrain = relay station
• Hindbrain = cerebellum, medulla oblongata, pons
• Spinal cord = link between brain and body
• White matter = periphery of spinal cord
• Grey matter = inside of spinal cord
• Central canal = filled with CSF
• Warning: Arrangement of grey and white matter in brain is opposite to that of spinal cord

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• 5. Nervous System of Man

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• 5.7.2 CRANIAL AND SPINAL NERVES IN MAN

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