Chapter 7 - Nervous System

Neuron

A cell of the nervous system. Neurons typically consist of a cell body, which contains a nucleus and receives incoming nerve impulses, and an axon, which carries impulses away from the cell body. Also called nerve cell.

Neurotransmitter

A chemical that is released from a nerve cell which thereby transmits an impulse from a nerve cell to another nerve, muscle, organ, or other tissue. A neurotransmitter is a messenger of neurological information from one cell to another.

Nodes of Ranvier

A gap in the myelin sheath of a nerve, between adjacent schwann cells.

Myelin

A mixture of proteins and phospholipids forming a whitish insulating sheath around many nerve fibers, increasing the speed at which impulses are conducted.

Action potential

A momentary change in electrical potential on the surface of a neuron or muscle cell. Nerve impulses are action potentials. They either stimulate a change in polarity in another neuron or cause a muscle cell to contract.

Reflex arc

A neural pathway that controls a reflex. In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord.

Efferent neuron

A neuron conducting impulses outwards from the brain or spinal cord.

Interneuron

A neuron that transmits impulses between other neurons, especially as part of a reflex.

Nissl substance

A nissl body, also known as nissl substance, is a large granular body found in neurons. These granules are of rough endoplasmic reticulum (RER) with rosettes of free ribosomes, and are the site of protein synthesis.

Dendrite

A short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.

Schwann cells

Also called neurilemma cell, any of the cells in the peripheral nervous system that produce the myelin sheath around neuronal axons. Schwann cells are named after german physiologist Theodor Schwann, who discovered them in the 19th century.

Astrocytes

Also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. The proportion of astrocytes in the brain is not well defined.

Axon

An axon is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neuron's cell body. Axons are also known as nerve fibers. The function of the axon is to transmit information to different neurons, muscles, and glands.

Neuroglia

Another term for glia which is the connective tissue of the nervous system, consisting of several different types of cell associated with neurons.

Autonomic reflex

Any reflex involving the response of a visceral effector (cardiac muscle, smooth muscle, or gland). Such reflexes always involve two efferent neurons (preganglionic and postganglionic)

Involuntary nervous system

Autonomic nervous system: a part of the nervous system that regulates key involuntary functions of the body, including the activity of the heart muscle: the smooth muscles, including the muscles of the intestinal tract: and the glands.

Afferent neuron

Carrying sensory information toward a central organ or part, as a nerve that conducts impulses from the periphery of the body to the central nervous system.

Motor division

Composed of somatic motor nerve fibers that conduct impulses from the CNS to skeletal muscles. Autonomic nervous system consists of visceral motor nerve fibers that regulate activity of smooth muscles, cardiac muscles and glands.

Support cells

In the central nervous system, there are four types of supporting cells. 1. Oligodendrocytes. The axons of many neurons are insulated by a myelin sheath, which increases the rate at which an axon can conduct an action potential.

Depolarization

Loss of polarization, especially : loss of difference in charge between the inside and outside of the plama membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions the interior.

Microglia

Microglia are a type of neuroglia (glial cell) located throughout the brain and spinal cord. Micoglia accound for 10-15% of all cells found within the brain. As the resident macrophage cells, they act as the first and main form of active and immune defense in the central nervous system (CNS)

Proprioceptors

Proprioception is the medical term that describes the ability to sense the orientation of your body in your environment. Proprioception comes from sensory nerve endings that provide our brain with the information of the limb position.

Somatic reflex

Rapid involuntary response to a stimulus. Somatic reflexes involve the stimulation of skeletal muscles the somatic division of the nervous system.

Repolarization

Refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value.

Autonomic nervous system

The autonomic nervous system is a part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, and digestive glands. The autonomic nervous system has two main divisions: sympathetic.

Central nervous system

The central nervous system (CNS) is the part of the nervous system consisting of the brain and spinal cord.

Myelin Sheath

The insulating covering that surrounds an axon with multiple spiral layers of myelin, that is discontinuous at the nodes of Ranvier, and that increases the speed at which a nerve impulse can travel along an axon - called also medullary sheath.

Peripheral nervous system

The peripheral nervous system is the system outside the brain and spinal cord.

Sensory division

The sensory division is a part of peripheral nervous system, it runs from sensory organs to the CNS (brain and spinal cord). The sensory division collects information (touch,pain,pressure, vision, and taste etc.) from outside (somatic sensory) and inside (visceral sensory) of the body and carries them to the CNS.

Somatic nervous system

The somatic nervous system (SoNS or voluntary nervous system) is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The SoNS consists of afferent nerves or sensory nerves, and efferent nerves or motor nerves.

Synaptic cleft

The space between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter - called also synaptic gap.

Neurilemma

The thin sheath around a nerve axon (including myelin where this is present).

Oligodendrocytes

Their main functions are to provide support and insulation to axons in the central nervous system of some vertebrates, equivalent to the function performed by Schwann cells in the peripheral nervous system. They do this by creating the myelin sheath, which is 80% lipid and 20% protein.