Central Nervous System (CNS) and protection

• CNS stands for Central Nervous System.
• PNS stands for Peripheral Nervous System.

Central Nervous System

• Contains the brain and spinal cord
• Includes the frontal lobe, occipital lobe, temporal lobe, parietal lobe and insula
• Certain neurotransmitters include dopamine, serotonin, acetylcholine, and adrenaline

Protection

• Bone: The cranium and vertebral canal are strong rigid structures that protect the brain.
• Meninges: Dura mater, arachnoid mater, and pia mater are connective tissue layers
• Cerebrospinal Fluid: Provides protection, support, and transport; it occupies spaces between the inner layers of meninges

Layers

• Dura mater is a thick layer of collagen fibers.
• Arachnoid is a thinner layer of collagen and elastin fibers.
• Pia mater is adjacent to nervous tissues and contains blood vessels and elastin fibers

Cerebrospinal Fluid

• Nutrient-rich cerebrospinal fluid is diffused from the layer of blood vessels in the subarachnoid space.
• Nutrients diffuse into the brain tissue and wastes diffuse out from the brain tissue to the CSF.
• The layers create a fluid filled space for the brain and spinal cord which acts as a shock absorption system
• Normal activity should not cause the brain to make contact with the cranium

Cerebrum

• Responsible for Thinking, Reasoning, Learning, Memory and Sense of Responsibility
• Largest part of the brain
• Impulses are carried to the cerebral cortex which allows it to initiate a response (voluntary muscle control).

Brain Composition

• The outer surface is thick grey matter cerebral cortex.
• Grey matter is part of the CNS and is made up of nerve cell bodies and unmyelinated fibers.
• White matter is part of the CNS and is made up of myelinated fibres.
• Basal ganglia: Nerve cell bodies that assist with skeletal muscle control
• Convoluted surface shallow downfolds sulci and deep downfolds fissures
• Longitudinal fissure separates the cerebrum into two different parts (corpus callosum)

Lobes of the Brain

• Frontal lobe: personality, emotions, thinking
• Parietal lobe: processes temperature, touch and taste
• Temporal lobe: processes memories, links them with senses
• Occipital lobe: vision
• Insula: recognition of senses and emotions

Functional Areas

• Sensory Areas: Interpret impulses from receptors
• Motor Areas: Control muscular movements
• Association Areas: Intellectual and emotional processes

Memory

• Memories are pathways of nerve cells, new links are made between neurons and existing links are modified.
• Myelin is a white matter composed of bundles of nerve fibers surrounded by a sheath of white fatty material
• It is found between the cerebral cortex and basal ganglia
• Within the CNS bundles of nerve fibers are called tracts, outside the CNS they are called nerves
• Areas of cortex connect, carry impulses between hemispheres, and connect cortex to brain or spinal cord

Corpus Callosum

• Facilitates Communication between the two hemispheres
• It is a wide band of nerve fibers which lies underneath the cerebrum at the base of the longitudinal fissure.
• Nerve fibers cross between the cerebral hemispheres to allow communication between the two sides

Cerebullum

• Controls Balance, Posture and Fine Coordination of Voluntary Muscles
• Under the rear part of the cerebrum (back of brain)
• Second largest part of the brain
• The surface is folded into a series of parallel ridges
• The outer folded part is grey matter and the inside is white matter which branch to all parts of the cerebullum

Sensory Information

• Inner ear controls posture and balance.
• Stretch receptors in skeletal muscles control information about the length of muscles
• All functions take place without you being aware (below conscious level)
• Impulses do not originate in the cerebellum, it modifies the motor commands to make movements more smooth and coordinated (via descending pathways)

Hypothalamus

• Responsible for Homeostasis
• Located in the middle of the brain
• Small but controls many bodily activities
• Maintains a constant internal environment homeostasis
• Autonomic nervous system regulates heart rate, blood pressure, secretion of gastric juices, movements of alimentary canal and diameter of pupil
• It also regulates body temperature
• Food and Water Intake
• Patterns of waking and sleeping
• Contraction of the urinary bladder
• Emotional responses like anger, fear, and aggression
• Hormone secretion coordinates parts of the endocrine system, which acts through the pituitary gland to regulate metabolism, growth, reproduction and stress

Medulla Oblongata

• Regulates Heart, Breathing and Blood Vessel Diameter
• Continuous with the spinal cord
• Many nerve fibers pass through the medulla
• It plays an important role in adjusting body functions
• Cardiac regulates rate and force of heart rate.
• Respiratory controls rate and depth of breathing.
• Vasomotor controls diameter of blood vessels.
• Other centres regulate swallowing, sneezing, coughing and vomiting
• All centres are influenced and controlled by different centres of the brain hypothalamus.

Spinal Cord

• Acts as a Pathway for Communication
• Extends from the foramen magnum (opening at base of skull) to the second lumbar vertebra (waist level).
• Enclosed in the vertebral canal, inside the ring of bone are three meningeal layers.
• The outer meningeal layer is a space containing fat, connective tissue and blood vessels.
• Consists of grey matter (surrounded by white matter) and white matter on the surface
• Grey matter is roughly H shape (cross bar is a small space (central canal))
• Central canal runs the length of the spinal cord and contains cerebrospinal fluid
• White matter arranged in bundles called ascending and descending tracts.
• Sensory axons carry impulses towards the brain via the Ascending Tract.
• Motor axons conduct impulses away from the brain via the Descending Tract
• Integrates certain fast, automatic responses from reflexes

Area of the Brain and Main Roles

• Cerebral cortex: Thinking
• Frontal lobe: Personality, emotions
• Parietal lobe: Sensory
• Temporal lobe: Memory
• Occipital lobe: Vision
• Inner areas of the cortex, including the insular and limbic areas: Senses and emotions
• Cerebellum: Balance, posture
• Corpus Callosum: Communication between the two hemispheres
• Thalamus: Relay messages back and forth to sensory senses
• Hypothalamus: Homeostasis, hunger, thirst, heart beat, sleep and wake cycles
• Pituitary gland: Makes and secretes hormones
• Pineal gland: Secretes melatonin
• Pons varolii: Transmit signals between forebrain and cerebellum
• Medulla oblongata: Body functions heart rate and breathing, vasoconstriction and vasodilation
• Braca's Area and Wernicke's Area: Speech production

Peripheral Nervous System

• Connects the central nervous system with receptors, muscles and nerves.
• Includes Cranial nerves and Spinal nerves
• Efferent/Motor nerves and Afferent/Sensory nerves

Cranial Nerves

• There are 12 pairs of nerves arising from the brain
• Most are mixed nerves: different fibers carry impulses to and from the brain.
• Sensory fibers carry impulses into the CNS
• Motor fibers carry impulses away from CNS

Spinal Nerves

• One of the 31 pairs of nerves arising from the brain, joined to spinal cord by dorsal and ventral roots.
• Dorsal root contains axons for sensory neurons
• Dorsal root ganglion: cell bodies in a small swelling on the dorsal root
• Ventral root contains axons for motor neurons

Afferent Division

• Carries impulses into the CNS by sensory neurons
• Receptors in skin, muscles and joints receive signals
• Somatic sensory neurons: impulses from the skin and muscles
• Visceral sensory neurons: impulses from the internal organs

Efferent Division

• Carries impulses away from the CNS
• Somatic division carries impulses from the CNS to the skeletal muscles.
• Autonomic division carries impulses from the CNS to the heart muscle, involuntary muscles and glands.
• The autonomic division contains sympathetic and parasympathetic divisions

Autonomic Nervous System

• Controls the body's internal environment and mechanisms to keep them constant
• Operates without conscious control, regulated by groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex
• Controls heart rate, blood pressure, body temperature, digestion, release of energy, pupil diameter, air flow to the lungs, defecation and urination
• Nerve fibres of ANS make up part of spinal nerves and some of the cranial nerves
• Carries impulses to heart as well as other muscles of internal organs and glands

Nerves

• Impulse travels along to CNS neurons to an organ controlled by the ANS
• The first neuron is myelinated and has a cell body in the CNS
• The second neuron is unmyelinated and has a cell body in the ganglion (group of nerve cell bodies outside the CNS)
• Impulses travel from the CNS to the effector

Autonomic nerves

• Messages from autonomic nerves to muscles and glands under their control are carried by a neurotransmitter at the nerve endings

Parasympathetic

• Maintains body during quiet conditions
• Nerve endings release acetylcholine

Sympathetic

• Prepares body for strenuous physical conditions
• Nerve endings release noradrenaline

Fight or Flight response

• We are not aware of the activities of the CNS
• Threatening situations upset the balance of sympathetic and parasympathetic stimulation which lead to sympathetic stimulation becoming dominant
• Fear, anger and stress provoke the fight or flight response or alarm reaction

Additional Notes

• Increased activity and skeletal muscles produce more movement and level or alertness
• Increased need for greater supply of oxygen and glucose = increased blood flow to relevant structures = activation of sympathetic division
• Airways in the lungs dilate and rate and depth of breathing increase
• Secretion from sweat glands increases
• Blood vessels dilate in organs involved in strenuous activity
• Heart rate increases and strength of contraction whereas parasympathetic stimulation decreases the rate and strength of contraction
• Dilation of the iris and contraction of the pupil
• Decreased secretion of saliva and increased secretion of salvia