Presentation on theme: "The Nervous System. 2 categories in nervous system. Central nervous system (CNS) – brain, spinal cord Peripheral nervous system (PNS) – nerves outside."— Presentation transcript:
Types of Neurons Structurally, 3 different types. 1 Multipolar – many dendrites – carry impulses to skeletal muscle. 2 Bipolar – single dendrite, single axon – special sensory areas (ears, eyes) 3 Unipolar – one nerve fiber (from skin to spinal cord)
Sodium-potassium pump – transports sodium out of cell, potassium inside. Causes concentration gradient – ions actively move across cell membrane through ion channels Every 3 Na + pumped out, 2 K + back in.
Outside of the membrane accumulates positive ions (potassium leaks out faster) Resting membrane potential – no impulses are transmitted
Potential on inside -70 mV. Change in membrane permeability to sodium – ions flow outward; inside becomes more positive – depolarization (+ 30 mV) Restored to normal – repolarization – potassium inward through ion channels, sodium channels close.
Depolarization followed by repolarization – impulse sent down axon. Nerve impulse – wave of ion reversals (changing charge of membrane)
Myelinated fibers- Conduct impulses faster than nonmyelinated fibers Node of Ranvier – gaps in axon of myelinated fibers Impulse jumps across myelin sheath from node to node – fastest conduction in body.
Types of Stimuli All-or-none – either impulse conducted or not. Threshold – minimum strength of stimulus needed for action potential. Subthreshold – no action potential. Series of subthreshold – summation (lead to action potential)
Central Nervous System 1 Spinal cord – from base of brain to 1 st, 2 nd lumbar vertebrae. Enters through foramen magnum of skull. Protected by vertebral column, fluid, and meninges (layers of membrane)
Direction of Impulses Ascending tract (up towards brain)– sensory information Descending tract (away from brain)– motor information Spinal cord also serves for reflexes – rapid response to emergency.
Cerebrum Cerebrum – higher brain – conscious thought, memory, learning. Divided into left and right cerebral hemispheres. Wrinkled structure (convolutions) – result from rapid growth during development.
Peripheral Nervous System Nerves, ganglia, sensory receptors. Communication between CNS and other areas of body. Nerve – composed of more than 1 type of tissue; responsible for transporting nerve impulses.