The Nervous System The Spinal Cord & Spinal Nerves Chapter 9

Parts of the nervous system are grouped according to structure or function Structural Divisions Central Nervous System (CNS): Brain Spinal Cord

Peripheral Nervous System (PNS): Cranial Nerves – carry impulses to and from the BRAIN Spinal Nerves – carry messages to and from the SPINAL CORD **Together, the CNS & PNS include all of the nervous tissue in the body

Functional Divisions Functionally, the nervous system is divided according to whether control is voluntary or involuntary A tissue or organ that carries out a command from the nervous system is called an EFFECTOR Effectors are our muscles and glands

The Somatic Nervous System Controlled voluntarily (by conscious will) and all the effectors are skeletal muscles

The Autonomic Nervous System Is an involuntary system and controls: Smooth muscle Cardiac Muscle Glands

Neuroglia Cells of the nervous system that serve to support & protect. Types with specialized functions include: Protection of nervous tissue Supporting nervous tissue & binding to other structures Aiding in the repair of cells Acting as phagocytes to remove pathogens Regulating fluids in between & around cells **Neuroglia continue to multiply throughout life (unlike typical nerve cells) **Disadvantage is the potential of tumor growth

Neurons Functional cells of the nervous system Highly specialized cells Main portion (cell body) contains typical nucleus & other organelles Distinguishing feature NOT found in any other cells: Long, threadlike fibers that extend out from the cell body & carry impulses across the cell called AXONS & DENDRITES

Types of Neurons Sensory Neurons – conduct impulses TO the spinal cord and brain Motor Neurons – carry impulses from the Central Nervous System to the muscles and glands

The Synapse Neurons do not work alone Impulses must be transferred between neurons to convey information The synapse becomes the “point of junction” or “gap” where impulses are transferred

Neurotransmitters Chemicals contained in the end of the axon They are released into the synapse to stimulate the next cell

The Reflex Arc A complete pathway through the nervous system Basic parts include: Receptor – detects a stimulus Sensory neuron – transmits the impulse TO the CNS CNS – impulses are coordinated & a response is organized Motor neuron – carries the impulse AWAY from the CNS Effector – a muscle or gland that carries out a response **The Patellar Reflex or “Knee-Jerk” Reflex

The Myelin Sheath An insulating layer that forms around nerves

Disorders Involving the Spinal Cord Multiple Sclerosis (MS) – Myelin sheath is damaged Fibers degenerate Although not fully understood, strong evidence indicates a person’s own immune system attacks the myelin sheath: Prior viral or bacterial infection Genetic make-up Environmental factors Different rate of progression Episodes of relapse or remission

Tumors Commonly found in tissue in or around the spinal cord Symptoms caused by pressure on the cord and spinal nerves Symptoms include: pain, numbness, weakness and loss of function Diagnosed through the use of MRI Treated by surgery and/or radiation (for malignant tumors)

Amyotrophic Lateral Sclerosis (ALS) Also known as “Lou Gherig’s Disease” Motor neurons are destroyed Progressive destruction that causes muscle atrophy and loss of motor control Eventually, the person is unable to swallow, talk or breathe Death follows soon after

Poliomyelitis (Polio) Viral disease of the nervous system Occurs commonly in children Gastrointestinal tract infection passes the virus into the bloodstream – eventually spreading to the CNS Virus multiplies in motor neurons within the spinal cord Leads to paralysis and death, if left untreated Vaccines have eliminated the disease in many countries – Jonas Salk (1954)

Spinal Cord Injuries Occur when vertebrae are broken or dislocated (car accidents, diving accidents, etc.) Because brain & spinal tissue cannot repair itself, severing of the spinal cord causes paralysis of all muscles supplied by nerves BELOW the level of the injury

Paraplegia Loss of sensation and movement in the lower portion of the body

Quadriplegia Loss of sensation and movement from the neck down