Quiz 33: Nervous Coordination: Nervous System and Sense Organs
• Neuron: A neuron is a nerve cell which has dendrites and an axon. • Axons: The axon is long fiber in a neuron which carries signals away from the cell. Axons are usually covered with a myelin sheath. • Dendrites: The processes seen in a neuron are called dendrites. They often look likes branches or spikes extending out from the cell body. It is primarily the surfaces of the dendrites that receive chemical messages from other neurons. Dendrites bring information to the cell body. • Myelin sheath: This insulating sheath is made up of the protein myelin which covers the axon of the neuron. It is responsible for accelerating the speed of the signal from the neuron to the target cell. • Afferent or sensory Neuron - These neurons are connected to receptors and convey the nerve signals from receptors to the central nervous system. • Efferent or motor Neuron - These neurons carry signals from the nervous system to the effectors. • Association neurons: These neurons connect the afferent and the efferent neurons. These are always present in the central nervous system.
Functions of glial cells in the peripheral nervous system: • Produces rings of myelin around vertebrate nerves • Surround neurons in sensory, sympathetic and parasympathetic ganglia • Homeostasis • Role in enteric system • Role in muscular digestive processes • Promotes the repair of damaged cells Functions of glial cells in the central nervous system: • Produce rings of myelin around vertebrate nerves • Nutrient and ion reservoirs for neurons • Providing a support during development of brain • Necessary for regenerative process after brain injury • Suppress repair of damaged neurons • Mediate neurotransmission • Create and secrete the cerebrospinal fluid • Physical support for neurons
The membrane is impermeable to ions during resting potential but become permeable during action potential. The ion pumps in the membrane maintain the resting potential of the membrane. The sodium-potassium exchange pump present in the membrane exchanges 3 ions for 2 ions to maintain the resting membrane potential. The intracellular ions can diffuse out of the nerve cell due to high concentration of ions. This makes the extracellular space relatively more positive than the intracellular space.