N ERVOUS S YSTEM PNS

N EURONS Nervous tissue contains masses of nerve cells called neurons. Specialized to react to physical and chemical changes. Transmit info in the form of electrochemical changes called nerve impulses. Bundles of axons make nerves. Also contains neuroglial cells that provide physical support, insulation, and nutrients for neurons.

T HE TYPICAL NEURON

NS F UNCTIONS SENSORY Neurons contain sensory receptors at their ends. Detect changes inside and outside the body Convert information into nerve impulses that travel through the PNS to the CNS INTEGRATIVE In the CNS, impulses are brought together creating sensations, adding memory, producing thoughts, etc. Making conscious and subconscious decisions MOTOR Impulses are carried from the CNS to effectors (muscles and glands). 2 categories Somatic Nervous System Consciously controlled; skeletal muscle Automatic Nervous system Involuntary; heart, smooth muscle, glands

CLASSIFICATION OF NEURONS Vary in structure, size, shape, and the number of connections they make with other neurons. 3 major structural groups (pg. 218) Bipolar : found in eyes, ears, nose Multipolar : found in brain and spinal cord Unipolar: lead to PNS and CNS, can form ganglia

C LASSIFICATION CONT.. 3 major functional groups 1) Sensory neurons Carry impulses from PNS to CNS Receptor cells found at end of dendrites or in skin or sensory organs Most are unipolar 2) Interneurons In brain and spinal cord Transmit impulses from one part of the brain or spinal cord to another multipolar 3) Motor neurons Carry impulses out of brain or spinal cord to effectors multipolar

NEUROGLIAL CELLS (PG. 215) Outnumber neurons in CNS Can divide (neurons do not normally divide) 4 TYPES 1) Microglial cells Support neurons and phagocytize bacterial cells and cellular debris 2) Oligodendrites Align along nerve fibers Provide insulating layers of myelin 3) Astrocytes Found b/w neurons and blood vessels Provide structural support Regulate nutrient and ion concentration within tissue Form scar tissue that fill spaces following an injury in the CNS “blood-brain barrier” Sheilds delicate tissue from chemical fluctuations Some drugs can get in some can’t

4.) Ependymal cells Forms an epithelia-like membrane that covers specialized brain parts Forms inner linings that enclose spaces within the brain and spinal cord * Schwann Cells : are neuroglial cells that form a myelin sheath around axons.

THE SYNAPSE The junction between two communicating neurons Synaptic cleft : the gap between Synaptic transmission : -process of the impulse crossing the cleft -one-way process carried out by neurotransmitters -n.t. can be excitatory or inhibitory - about 50 neurotransmittersin n.s -pg. 226 chart

NERVE IMPULSES NERVE IMPULSES – ACTION POTENTIAL o The surface of a cell membrane is polarized (electrically charged) o At rest, membrane potential is negative, membrane is polarized. Na K Na When the membrane reached its threshold stimulus, Na/K channels open, ions diffuse, and membrane is depolarized. K+K+Na+Na+ N+Na+ K+K+ Na/K channels open again, ions diffuse, and the membrane repolarizes. Na K++++++

A wave of action potentials is occurring throughout the membrane of a neuron. *This is an ALL-OR-NOTHING response*

SYNAPSE AFFECTORS/OTHER PROBLEMS Caffeine : stimulates the nervous system by lowering the threshold at the synapse so neurons are more easily excited. Antidepressants: keeps the neurotransmitter, serotonin, in the synapse longer. Epileptic seizures : caused when nerve impulses reach the synaptic knob to fast, exhausting the neurotransmitter.

Multiple sclerosis (MS): is a disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelinization and scarring. The body’s immune system attacks and damages the myelin. Axons can no longer effectively conduct signals. Symptoms include muscle weakness, spasms, difficulty in moving, coordination, balance, speech, or swallowing, visual problems, fatigue, and bladder and bowel difficulties.

NERVE PATHWAYS (PG. 229) Are routes nerve impulses follow as they travel through the nervous system. The simplest of these pathways includes only a few neurons called a reflex arc. Reflexes are automatic responses to stimuli that help maintain homeostasis. Heart rateblood pressure Coughing vomiting Breathingsneezing

Patellar reflex : uses only 2 neurons, helps maintain upright posture Withdrawal reflex : aids in limiting tissue damage caused by touching something harmful.