nervous system

Nervous System

Receives information, processes information, and sends out signals to muscles and glands to elicit an appropriate response.

Nervous Tissue

Responsible for communication between cells of the body through a system of rapid electrical impulses.

Nuclei

Collections of cell bodies inside the central nervous system.

Tracts

Collection of nerve axons in the central nervous system.

Peripheral Nervous System

Includes all nerves not in the brain or spinal cord, connecting all parts of the body to the central nervous system.

Brainstem

Includes the midbrain, pons, and medulla.

Cranial Nerves

Project from the brainstem, generally innervate the face, head, and neck.

Spinal Nerves

Project from either side of the spinal cord, spread out to innervate the rest of the body.

Ganglia

Collections of cell bodies inside the peripheral nervous system.

Nerves

Collection of nerve axons in the peripheral nervous system.

Sensory (afferent) Division

Part of the peripheral nervous system that receives impulses from sensory organs.

Motor (efferent) Division

Relays signals from the central nervous system to muscles and glands; can be divided into somatic and autonomic.

Somatic Nervous System

Generally under conscious (voluntary) control.

Autonomic Nervous System

Not under conscious control; controls glands and smooth muscles of internal organs; can be divided into sympathetic and parasympathetic

Sympathetic Nervous System

Activates and prepares the body for vigorous muscular activity, stress, and emergencies.

Parasympathetic Nervous System

Operates during normal situations, permits digestion, and conserves energy.

Neurons

Nerve cells that conduct electrical impulses and relay information throughout the body.

properties of neurons

do not undergo mitosis, can survive an entire lifetime, and can only go a few minutes without oxygen

neuron information travel

sent and received in the same direction

Neuron Cell Body

Synthesizes all nerve cell products, consists of a large nucleus with surrounding cytoplasm containing the normal organelles

Dendrites

Receiving end of a neuron that conducts nerve impulses toward the cell body via numerous short extensions

Axon

Conducts nerve impulses away from the cell body to its axon terminals; can vary in length

Neurotransmitters

Chemicals stored in secretory vesicles at the end of the axon terminals, carrying nerve impulse transmissions between neurons; produced by the cell body

Synapse

A gap between two neurons for neurotransmitter crossing; fluid filled

Presynaptic Neuron

The signal-sending neuron before the synapse.

Postsynaptic Neuron

The neuron found after the synapse that receives the signal.

Multipolar Neurons

Neurons with three or more extensions; one axon with many dendrites. typically motor neurons.

Bipolar Neurons

Neurons with a central cell body and two extensions, found as receptor cells in the visual and olfactory systems

Unipolar Neurons

Neurons with one extension that branches into two; one central process running to the CNS and another peripheral process running to the sensory receptor.

Sensory Neurons (afferent)

Unipolar neurons carrying information from the peripheral to the central nervous system; most with impulses from the skin or internal organs to the CNS

Interneurons

Typically multipolar neurons found only in the central nervous system, transmitting impulses between different CNS; connects neurons

Motor Neurons (efferent)

Multipolar neurons sending messages from the central nervous system to the peripheral nervous system.

Nerve

Consists of hundreds of thousands of axons wrapped together in connective tissue.

Neuroglial Cells

Support cells important for neuron function.

Schwann Cells

Neuroglial cells in the PNS that are composed of a myelin sheath.

Myelin Sheath

A white fatty layer insulating the nerve fiber and increasing the speed of nerve impulses.

Nodes of Ranvier

Gaps between Schwann cell insulating sections.

Saltatory Conduction

Method for nerve impulse to jump to the next node.

Satellite Cells

Surround peripheral neuron cell bodies, regulating their environment.

Axonal Regeneration

Process where Schwann cells create a path for the axon to follow as it grows; very slow process

Ependymal Cells

Cells that circulate cerebrospinal fluid and facilitate fluid exchange between the brain, spinal cord, and cerebrospinal fluid.

Oligodendrocytes

Cells that act as insulation for central nervous system axons.

Astrocytes

Control the chemical environment of neurons by wrapping around the blood capillaries

Blood Brain Barrier

Physical barrier formed by astrocytes allowing selective substance passage into CNS.

Microglial Cells

Protect the CNS by scavenging dead cells and infectious microorganisms.

Nerve Impulse

An electrochemical charge moving along an axon created by ionic movement through an axon’s plasma membrane

Polarized

State of an axon at rest with different charges on either side of the membrane.

Resting Potential

When the axon is not conducting an impulse, equal to about -70mV.

Sodium Potassium Pump

Active transport mechanism pumping sodium out and potassium into the cell.

quantities pumped by sodium potassium pump

three sodium out, two potassium in

Action Potential

Stimulated axon's rapid polarity change that leads to nerve impulse conduction.

Resting Potential

Both sodium and potassium gates are closed.

Depolarization

The sodium gates open, and sodium rushes into the axon. Voltage travels to zero and then on up to +40 mV.

Repolarization

Sodium gates close and potassium gates open, allowing potassium to rush out of the axon; returns voltage negativity to the inside of the axon

Afterpolarization/hyperpolarization

Potassium gates close slowly and there is an undershoot of potential; voltage drops below -70mV before returning to resting state at -70mV

Self-Propagating

The ion channels are prompted to open whenever the membrane potential decreases (depolarizes) in an adjacent area, travels the axon like a wave

Acetylcholinesterase

Enzyme that breaks down the neurotransmitter acetylcholine.

Inhibition

Prevention of continuous stimulation.

Neurotransmitter Examples

Dopamine, epinephrine, norepinephrine, acetylcholine.

Neuromuscular Junctions

Synapses between motor neurons and muscles in the peripheral nervous system; contains acetylcholine

Reflexes

nearly instantaneous, automatic, and involuntary motor responses.

Reflex Arc

Neural pathway a nerve impulse travels.

Dorsal Root

Part where sensory info enters the spinal cord; contains axons of sensory neurons

Grey Matter

contains cell bodies of neurons, where neurons synapse with other neurons

White Matter

Contains axons of neurons, surrounding grey matter.

Dorsal Root Ganglion

Contains cell bodies of sensory nerves.

Posterior Horn

Where sensory neurons synapse on cells.

Anterior Horn

Location of motor neuron cell bodies.

Ventral Root

Where motor neurons exit the spinal nerve.

Spinal Reflexes

Occur faster than conscious decisions due to fewer involved neurons and not having to travel to the brain

Stretch Reflexes

Type of muscle reflex protecting muscles from overstretching; helps maintain upright posture

Muscle Spindles

Specialized muscle cells monitoring muscle stretch, triggers a reflex when overstretched

Patellar Reflex

Prevents quadriceps overstretching.

Flexor Withdrawal Reflex

Contracts the biceps and prevents contraction of the triceps to flex the elbow and remove it from heat