Functional Organization of the Central Nervous System

Functional Organization of the Central Nervous System

Hierarchical orgnization CNS consists of the brain and the spinal cord The brain analyzes and interprets the information Response messages are passed from the brain through the spinal cord and to the rest of the body Spinal cord carries messages from the body to the brain

Functions of the nervous system Sensory Function sensory receptors gather information information is carried to the CNS Integrative function sensory information used to create sensations memory thoughts decisions Motor Function decisions are acted upon impulses are carried to effectors

General functions of the nervous system The three general functions of the nervous system Receiving stimuli sensory function Deciding about stimuli integrative function Reacting to stimuli motor function

The spinal cord Protected by a column of bones Produces some behaviors of its own (spinal reflexes) without the help of the brain These reflexes are automatic, requiring no conscious effort Sometimes they are influenced by thought and emotion - example: touching a hot iron

Spinal cord Extends from the medulla oblongata of the brain to the area around the first lumbar vertebra in the lower back Nerves from peripheral nervous system extend out from te spinal cord Protected by: Vertebral column Cerebrospinal fluid Meninges

Spinal cord Meninges are three layers of membranes that cover the brain and spinal cord Layers of meninges Dura mater outer tough fibrous membrane Arachnoid mater middle, weblike membrane containing CNF Pia mater iinnermost layer containing several blood vessels

The structure of multipolar neuron

Myelinated and unmyelinated axons Myelin sheathing is interrupted by bare patches of axon called nodes of Ranvier. Action potentials jump from node to node without depolarizing the region under the myelin sheath - called saltatory conduction. Myelin sheathing and saltatory conduction improves the speed of nerve impulse conduction.

Ion chanels in neurons Type of chanel Discription Location Leakage channels Gated chanels that ramdomly Found in all neuron cells open and close Ligand - gated channels Gated channels that open in Dendites and cell bodies of response to the binding of the motor neurons and interneurons ligand Mechanically gated channels Gated channels that open in response to mechanical stimuli (touch, pressure, vibration) Voltage gated channels Gated channels that opens in response to voltage stimulus ( change in voltage potential) Dendrites of some sensory neurons Axons of all type of neurons

Classification of neurons by shape Pseudounipolar: axon and dendrite look like one process e.g. sensory neurons Bipolar: one axon, one dendrite e.g. retina Multipolar: one axon, many dendrites e.g. motor neurons

Classification of neurons by function Sensory (or afferent): carry impulses from receptors (e.g. pain receptors in skin) to the CNS (brain or spinal cord) pseudounipolar or bipolar Association (or interneurons): carry impulses from sensory nerves to motor nerves located entirely within the CNS multipolar Motor (or efferent): carry impulses from CNS to effector (e.g. muscle to bring about movement or gland to bring about secretion of hormone) multipolar

Glial cells (supporting cells) We have: 100 billion neurons 10x more glial cells! Glial cells: Support neurons (physically and nutrients) Cover neurons with myelin Clean up debris

Types of neuroglial cells in te CNS Microglia Phagocytic cells Astrocytes Connect neurons to blood vessels Mop up the excess ions Induce synapse formation Oligodendrocytes Myelinating cells Ependyma (ependymal cells) Line central canal of spinal cord Line ventricles of brain

Sensory information to the spinal cord

Sensory information

Transmission of sensory information

Reflex arc Basic elements of reflex arc Receptor Sensory neuron Integration center Motor neuron Effector

Brain The brain is located within the cranial cavity of the skull and consists of: -Cerebrum -Diencephalon -Brainstem -Cerebellum

Functional areas of cerebrum

Cerebrum - Lateralization The largest, most conspicuous portion of the brain. 2 hemispheres connected by the corpus callosum lateralization. Has an outer cortex of gray matter surrounding an interior that is mostly white matter (except for a few small portions) In most people, the left hemisphere has a more control over language, math, and logic, while the right hemisphere is geared towards musical, artistic and other creative endeavors. Most individuals with left cerebral dominance are righthanded.

Cerebral cortex The cerebrum is covered by several thin layers of densely packed cells known as the cerebral cortex Allows for sensation, voluntary movement, selfawareness, communication, recognition, and other functions. On each cerebral hemisphere, deep fissures divide the cortex into 4 lobes frontal lobes parietal lobes occipital lobes temporal lobes

Cerebrum Frontal lobe: Emotional control Self awarness Motivation Judgment Problem solving Talking Movement

Temporal lobe: Memory Hearing Understanding language Processing information Parietal lobe: Sense of touch Awarness of spatial relationships Academic functions reading Occipital lobe Vision

Brain Cerebellum Balance Coordination Skilled motor activity Brain stem: Breathing Heart rate Arousal and cosciousness Sleep and wake cycles

Brain and functions Frontal lobe: Difficulty with motor activity Bladder control Social behaviour Personality Parietal lobe: Difficulty with reading, writting, math calculation, Distinguishing right from left Occipital lobe: Visual disturbances

Brain and functions Broca s area: Speech production- difficulty with expressing words Temporal lobe: Difficulty with memory Hearing Spoken language Wernicke s area Speech comprehension Difficulty with understanding spoken language

Diencephalon Forms the central core of the forebrain 3 paired structures: Thalamus Hypothalamus Epithalamus

Thalamus 80% of the diencephalon Sensory relay station - directs sensory messages to higher centers in the brain i.e. the sight of sunset is directed to a visual area The role of the thalamus is to filter information going to the cortex by preventing or enhancing the passage of specific information depending upon its significance to the individual

Hypothalamus Plays a central role in maintenance of homeostasis in the body: Autonomic regulatory center Influences HR, BP, respiration rate, GIT motility, pupillary diameter. Emotional response Involved in fear, pleasure Drive center: sex, hunger Regulation of body temperature

Hypothalamus Regulation of food intake Regulation of water balance and thirst Regulation of sleep/wake cycles Hormonal control Releases hormones that influence hormonal secretion from the anterior pituitary gland. Releases hormones: oxytocin and vasopressin

Epithalamus Above the thalamus Contains the pineal gland which releases melatonin involved in sleep/wake cycle involved in mood Contains a structure called the habenula involved in food and water intake

Brainstem the lower part of the brain, structurally continuous with the spinal cord, provides motor and sensory innervation to the face and neck via the cranial nerves regulation of cardiac and respiratory function maintenance of consciousness regulation of the sleep cycle

Cerebellum 2nd largest region of the brain. 10% of the brain by volume, but it contains 50% of its neurons Has 2 primary functions: Adjusting the postural muscles of the body Coordinates rapid, automatic adjustments, that maintain balance and equilibrium Programming movements controlled at the subconscious and conscious levels Compares motor commands with sensory info from muscles and joints, and performs any adjustments required to make the movement smooth