Transcript nerve cell
Warm Up: • What is regulation? • life process by which organisms and cells respond to our constantly changing internal and external environment Regulation Functions of Nervous Regulation • Respond to changes in environment • External and internal • Maintain homeostasis • Ability of cell to respond to environmental changes is called irritability Stimulus • Something that influences activity • Hot stove • Phone ringing Mechanisms of Nervous Regulation • Involves 3 basic structures • Receptors • Nerve cells • Effectors Receptors (Sense Organs) • Detects change in environment • Mouth, skin, nose, eyes, ears • Send messages known as impulses to nerve cells Nerve Cells • Carry impulses (messages) from receptor and eventually to effectors Effectors • Cause response • Either muscle or gland Sequence of events in regulation by nervous system • Stimulus activates a receptor • Triggers impulse along a nerve pathway • Causes a response by effector Brain • Bundle of nerve cells that coordinates and controls all activities of nervous system Neurons • Structural unit of nervous system is neuron or nerve cell • Specialized for rapid conduction of impulses Structure of Neurons • 3 basic parts • Dendrites • Cell body (cyton) • axon Dendrites • Short, highly branched fibers • Receive impulses • Transmit toward cell body Cell body (cyton, soma) • Contains nucleus and organelles Axon • Long, thin fiber that extends away from cell body • Carry impulses away from cell body and to other nerve cells or effectors • Surrounded by Schwann cells • On some cells, these form a fatty substance called myelin which forms a myelin sheath • Gaps in the myelin sheath are called Nodes of Ranvier Transmission of impulse is electrical Synapse • Axon usually has many branches at the end called terminal branches • Each makes contact with another cell • Synapse= place where 2 adjacent neurons meet • Axon ends in synaptic knob • Between 2 neurons is a gap called synaptic cleft • Transmission of impulse across cleft requires chemicals called neurotransmitters (neurohumors) Neuromuscular Junction • Points of contact between axons of motor neurons and muscles • Presence of neurotransmitters at synapse cause muscle cell to contract Types of Neurons • Sensory neurons • Carry impulses from receptors toward brain and spinal cord • Associative or interneurons • In brain and spinal cord • Motor neurons • Carry impulses from brain and spinal cord toward effectors Nerves • Bundles of nerve cells (neurons) • Sensory nerves • receptor SC and brain • Motor nerves • SC and brain effector • Mixed nerves • both sensory and motor nerve fibers Nerve cells • Cannot divide but may repair damaged axons or dendrites • Outside of brain and spinal cord, only if cell body is not damaged • A student accidentally places her hand on a tack and quickly pulls her hand away. The tack represents • • • • a stimulus an impulse a response an effector • What part of the neuron sends impulses to another nerve cell? 1 2 3 4