Nervous Basics Tissue Part 1

Nervous system functions

directs immediate responses to stimuli, coordinates or moderates activities of other organ systems, provides and interprets sensory information about external conditions

Central nervous system

consists of the brain and spinal cord

Peripheral nervous system (PNS)

the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body.

Nerve

a bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord

Cranial nerves

12 pairs of nerves that emerge from the brain- most of these connecting with areas in your head, such as eyes, ears, nose and face

Spinal nerves

31 pairs of nerves arising from the spinal cord that carry impulses to and from the spinal cord

Ganglia (ganglion)

small masses of nervous tissue, consisting primarily of neuron cell bodies, that are located outside the brain and spinal cord. They are closely associated with cranial and spinal nerves.

Enteric plexuses

extensive networks of neurons located in the walls of organs of the gastrointestinal tract

Sensory receptors

a structure of the nervous system that monitors changes in the external or internal environment. Ex-touch receptors in the skin, photoreceptors in the eyes, olfactory receptors in the nose.

Somatic nervous system (SNS)

the part of the peripheral nervous system that controls voluntary movement.

1-Sensory neurons that convey information from somatic receptors in the head, body wall, and limbs and from receptors for the special senses of vision, hearing, taste, and smell to the CNS.

2-motor neurons that conduct impulses from the CNS to skeletal muscles only.

Automatic nervous system (ANS)

a set of nerves that carries involuntary and automaticcommands that control blood vessels, body organs, and glands.

1-sensory neurons that convey information from autonomic sensory receptors, located primarily in visceral organs such as the stomach and lungs, to the CNS.

2-motor neurons that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands.

Sympathetic nervous system

the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations

Parasympathetic nervous system

the division of the autonomic nervous system that calms the body, conserving its energy

Enteric nervous system (ENS)

neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections

Sensory function of nervous system

The ability of the nervous system to sense changes in either the internal or external environment

Integrative function of nervous system

The ability of the nervous system to analyze and interpret sensory information to allow for proper decision making, which produces the appropriate response.

Motor function of nervous system

Effects a change to maintain homeostasis, brain tells effectors, causes muscles or glands to take action in order to help maintain homeostasis.

Neurons (nerve cells)

Electrically excitable cells that initiate, transmit, and receive nerve impulses.

Stimulus

any change in the environment that is strong enough to initiate an action potential.

Action potential (nerve impulse)

an electrical signal that propagates (travels) along the surface of the membrane of a neuron. It begins and travels due to the movement of ions (such as Na+ and K+) between interstitial fluid and the inside of a neuron through specific ion channels in its plasma membrane. Once begun, a nerve impulse travels rapidly and at a constant strength.

Cell body (soma)

the part of a neuron that contains the nucleus and other parts of the cell needed to sustain its life (cytoplasm, lysosomes, mitochondria, Golgi complex, free ribosomes, and prominent clusters of rough endoplasmic reticulum-nissl bodies)

Nissl bodies

RER in neurons -- synthesize enzymes (e.g., ChAT) and peptide neurotransmitters. Newly synthesized proteins are used to replace cellular components, as material for growth, and to regenerate damaged neurons in the PNS.

Lipofuscin granules

pigmented cytoplasmic inclusions (derived from lysosomes) that accumulate with aging, normal.

Nerve fiber

the axon of a neuron and the dendrites

Dendrites of neuron

little trees; the receiving or input portion of the neuron. The plasma membranes of dendrites (and cell bodies) contain numerous receptor sites for binding chemical messengers from other cells.

Usually short, tapering, and highly branched.

Axon

the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands

Contains mitochondria, microtubules, and neurofibrils (intermediate fibers) but NO PROTEIN SYNTHESIS

Axon hillock (trigger zone)

cone-shaped elevation of the cell body; initial segment of axon where the action potential is initiated

Trigger zone

Axon hillock and initial segment

Axoplasm

Cytoplasm of an axon

Axolemma

Plasma membrane of axon

Axon terminals (telodendria)

the many small terminal nerve branches that are found at the end of the axon

Synapse

the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron

Synaptic vesicles

Membrane-bounded compartments in which synthesized neurotransmitters are kept.

Neurotransmitters

A molecule released from a synaptic vesicle that excites or inhibits another neuron, muscle fiber, or gland cell. Many neurons contain two or even three types of neurotransmitters, each with different effects on the postsynaptic cell.

Slow axonal transport

conveys axoplasm in one direction only - from the cell body toward the axon terminals; moves materials 1-5 mm per day

Fast axonal transport

occurs at a rate of 20 to 400 mm/day and may be either anterograde or retrograde; uses proteins that function as motors to move materials along the surfaces of microtubules of the neuron's cytoskeleton.

Autograde

axonal transport that moves in a forward direction; moves organelles and synaptic vesicles from the cell body to the axon terminals.

Retrograde

moving backward; moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled.

Substances that enter the neuron at the axon terminals are also moved to the cell body by fast retrograde transport. These substances include trophic chemicals such as nerve growth factor and harmful agents such as tetanus toxin, and the viruses that cause rabies, herpes simplex, and polio.