NERVOUS SYSTEMPNS
NEURONS 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.
THE TYPICAL NEURON
NS FUNCTIONS 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
CLASSIFICATION CONT..
3 major functional groups1) 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
12
34
5
6
NERVE IMPULSES –ACTION POTENTIALo The surface of a cell membrane is polarized (electrically
charged)o At rest, membrane potential is negative, membrane is polarized.
Na+++++++++++++
K+++++++++++
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 rate blood pressure Coughing vomiting Breathing sneezing
Patellar reflex: uses only 2 neurons, helps maintain upright posture
Withdrawal reflex: aids in limiting tissue damage caused by touching something harmful.