Nervous System: Central Nervous System

Question 1

What is the Central Nervous System

Answer 1

• The CNS is made up of the brain, spinal cord and nerves
• It is responsible for controlling virtually all aspects of body functions
• It helps up move, think, remember and feel emotions
• Concepts:
• Brain: The most complex part of the CNS. It is responsible for processing information, directing activities and making decisions.
• Spinal Cord: A tube-like structure that connects the brain to the body. It carries messages between the brain and every other part of the body

Question 2

Grey and White Matter

Answer 2

• When parts of the nervous system are cut open different areas appear different colours
• Grey areas are called grey matter and consists of nerve cell bodies and unmyelinated fibres
• White areas are called white matter and consist of only myelinated fibres (axons)

Question 3

Protection of CNS

Answer 3

• The brain and spinal cord are very delicate and vital parts of the body and are heavily protected by:
• Bone
• Three membranes called meninges
• A fluid called cerebrospinal fluid (CSF)

Question 4

Protection of CNS: Bone

Answer 4

• Bone (Cranium protects the brain and the spinal cord runs through the vertebral canal) protects from physical injury/impact

Question 5

Protection of CNS: Meninges

Answer 5

• Three membranes called meninges cover the entire CNS
• Its role is to anchor and protect the brain and spinal cord, to help hold them into place
• The meninges also carry blood vessels that help supply the brain with blood
• Outer layer, called the dura mater, is tough and fibrous, sticks closely to the cranium/vertebral canal, it anchors the CNS to the bone
• The middle meningeal layer, arachnoid mater, is a loose mesh of fibres, that connect with the inner layer
• The inner layer, pia mater, is delicate, contains many blood vessels and sticks closely to the surface of the brain and spinal cord.

Question 6

Protection of CNS: Cerebral Spinal Fluid

Answer 6

• A fluid called cerebrospinal fluid (CSF) that acts as a shock absorber and supports the brain, giving it a medium in which to float.
• It occupies the space between the middle and inner meningeal layers (subarachnoid space), circulates through the four cavities in the brain(ventricles) and in the centre of the spinal cord
• It is a clear watery fluid containing cells, glucose, protein, urea and salts
• The CSF is formed from blood, circulates through the CNS, taking nutrients to the neurons and removing wastes eventually re-entering the capillaries.
• Function of the CSF:
• Act as a shock absorber, protect from the mechanical injury
• Deliver nutrients to the tissues of the central nervous system
• Remove wastes produced by the brain
• Regulation of the concentration of H+ and Co2, which regulates breathing
• Maintain fluid to bath cells of the brain (homeostatic balance)
• Transport chemical messengers around the CNS

Question 7

Cerebrum

Answer 7

• It consists of an outer surface of grey matter (2-4mm thick) called the cerebral cortex.
• The cerebral cortex is involved in such mental activities such as thinking, reasoning, learning, memory, intelligence, and sense of responsibility
• It is also concerned with perception of the senses and the initiation and control of voluntary muscle contraction
• Below that is white matter surrounding another section of grey matter called the basal ganglia.
• The cerebral cortex is folded, which greatly increases the surface area
• The folding produces rounded ridges called convolutions (or gyri)
• The shallow downfolds are called sulci and the deep downfolds are called fissures
• The longitudinal fissure (is the deepest) and separates the cerebrum into two halves called cerebral hemispheres
• Joining the two hemispheres at the base of the longitudinal fissure is an area of white matter consisting of a large bundle of transverse fibres, called the corpus callosum.
• The folds are relatively consistent from person to person, so certain fissures and sulci are used to further subdivide each hemisphere into four lobes:
• Frontal lobe
• Parietal lobe
• Occipital lobe
• Temporal lobe
• There is a fifth lobe called the insula, deep inside the cerebellum
• The white matter of the cerebrum is composed of bundles of fibres called tracts
• There are three types of tracts:
• Association fibres: tracts that connect various areas within the same hemisphere, which regulate and coordinate neural activity in the cortex
• Commissural fibres: tracts that carry impulse between the left and the right hemisphere (form the corpus callosum)
• Projection fibres: tracts that connect the cortex to other parts of the brain (other than the cerebrum) or to the spinal cord.
• There are three types of basic functional areas in the cerebral cortex:
• Sensory areas: which interpret impulses from receptors
• Motor areas: which control muscular movements
• Association areas: which are concerned with intellectual and emotional processes
• The basal ganglia (also known as cerebral nuclei) consist of groups of nerve cell bodies associated with control of skeletal muscles.
• They are important in regulating muscle tone and integrating complex muscle interactions in complicated, learned actions like walking.
• Nearly all the impulses from our sense organs are carried to the cerebral cortex, which has all the relevant information about the environment and can initiate responses accordingly.
• The impulse from the right side of the brain goes to the left side of the body. And impulses or information from the left side of the body goes to the right side of the brain.
• Memory
• One of the important functions of the cerebrum is memory
• The association areas of the cerebral cortex are involved in memory
• Incoming information may be held briefly in a sensory register while it is decided whether or not it should be retrievable
• If the information is to be held, it is passed on to the short-term memory, which can handle small amounts of information at a time
• To create long-term memories, new dendritic connections are established

Question 8

Cerebellum

Answer 8

• The cerebellum is the second largest part of the brain and lies under the rear part of the cerebrum
• It comprises of two hemispheres and has a surface that is folded into a series of parallel ridges
• The outer folded part of the cerebellum is grey matter
• The inside is white matter that branches to all parts of the cerebellum
• The cerebellum exercises controls over posture and balance and the fine coordination of voluntary muscle movement
• To carry out these functions the cerebellum has to receive sensory information from the inner ear (for posture and balance) and from stretch receptors in the skeletal muscles
• All the functions of the cerebellum take place below the conscious level
• Impulses do not originate in the cerebellum and so without it we could still move, but our movements would be spasmodic, jerky and uncontrolled.

Question 9

Hypothalamus

Answer 9

• The hypothalamus lies in the middle of the brain and cannot be seen from the outside
• Functions of the hypothalamus include the regulation of:
• The autonomic nervous system, including the regulation of heart rate, blood pressure, the secretion of digestive juices, movements of the alimentary canal, the diameter of the pupil of the eye and other functions
• Body temperature
• Food and water intake
• Patterns of walking and sleeping
• The contraction of the urinary bladder
• Emotional responses such as fear, anger, aggression, pleasure and contentment
• The secretion of hormones (oxytocin and antidiuretic hormone (ADH)) and coordination of parts of the endocrine system, including the pituitary gland

Question 10

Medulla Oblongata

Answer 10

• The medulla oblongata is a slightly expanded continuation of the spinal cord
• It is about 3cm long and extends from just above the point where the spinal cord enters the skull
• Many nerve fibres simply pass through the medulla going to or from the other parts of the brain, but the medulla does have an important role in automatically adjusting body functions
• The medulla oblongata contains the:
• Cardiac centre: which regulates the rate and force of the heartbeat
• Respiratory centres: which controls the rate and depth of breathing
• Vasomotor centre: which regulates the diameter of blood vessels.
• It also regulates the reflexes of swallowing, sneezing, coughing and vomiting
• All of the centres in the medulla oblongata re influenced and controller by higher centres in the brain, particularly the hypothalamus.

Question 11

Spinal Cord

Answer 11

• Ascending tracts are sensory axons that carry impulses upwards, towards the brain
• Descending tracts contain motor axons that conduct impulses downwards, away from the brain
• Thus, one of the functions of the spinal cord is to carry sensory impulses up to the brain and motor impulses down from the brain
• The second function of the spinal cord is to integrate certain reflexes (fast, automatic responses)