chapter 11: fundamentals of the nervous system and nervous tissue

Nervous system

The body system that gathers sensory information, processes and interprets it, and produces responses.

Sensory input

The nervous system gathering information from sensory receptors.

Integration

The nervous system processing and interpreting sensory information to decide on an appropriate response.

Motor output

The nervous system sending signals to muscles and glands to produce a response.

Central nervous system (CNS)

The brain and spinal cord; the integrating and control center of the nervous system.

Peripheral nervous system (PNS)

All nervous system structures outside the brain and spinal cord.

Sensory (afferent) division

Carries impulses toward the CNS from sensory receptors.

Somatic sensory fibers

Carry sensory impulses from receptors in the skin, skeletal muscles, and joints.

Visceral sensory fibers

Carry sensory impulses from organs within the ventral body cavity.

Motor (efferent) division

Carries impulses from the CNS to effector organs such as muscles and glands.

Somatic nervous system

Consists of somatic motor nerve fibers that control skeletal muscles and allow conscious, voluntary movement.

Autonomic nervous system (ANS)

An involuntary system that regulates smooth muscle, cardiac muscle, and glands.

Neuroglia (glial cells)

Cells associated with neurons that provide protection and support.

CNS neuroglia

The four main types are astrocytes, microglia, ependymal cells, and oligodendrocytes.

Astrocytes

CNS glial cells that regulate the chemical environment around neurons and help with exchange between neurons and capillaries.

Microglial cells

CNS glial cells that monitor the health of neurons and perform defense functions.

Ependymal cells

CNS glial cells that line the central cavities of the brain and spinal cord and help circulate cerebrospinal fluid.

Oligodendrocytes

CNS glial cells that form myelin sheaths around neuron fibers.

PNS neuroglia

The two main types are satellite cells and Schwann cells.

Satellite cells

PNS glial cells that surround neuron cell bodies within ganglia; their function is largely unknown.

Schwann cells (neurolemmocytes)

PNS glial cells that surround nerve fibers and form myelin sheaths.

Neuron

A specialized cell that conducts messages throughout the body in the form of electrical impulses.

Neuron cell body (soma/perikaryon)

The major biosynthetic center of a neuron; contains mitochondria, protein-making organelles, cytoskeletal elements, and pigment inclusions.

Dendrites

The receptive regions of a neuron that receive signals from other neurons.

Axon

The conducting region of a neuron that carries nerve impulses away from the cell body.

Axon hillock

The region where the axon arises from the cell body.

Axon terminals

The secretory region at the end of an axon that releases neurotransmitters.

Neurotransmitter

A chemical released by axon terminals that can excite or inhibit another neuron or an effector cell.

Myelin sheath

A whitish, fatty, segmented covering around some axons that protects, insulates, and increases the speed of nerve impulse conduction.

Nodes of Ranvier

Gaps between segments of the myelin sheath along an axon.

Myelin in the PNS

Myelin is formed by Schwann cells wrapping around axons.

Myelin in the CNS

Myelin is formed by oligodendrocytes whose processes wrap around many axons.

Nucleus

A cluster of neuron cell bodies located in the CNS.

Ganglion

A cluster of neuron cell bodies located in the PNS.

Tract

A bundle of axons located in the CNS.

Nerve

A bundle of axons located in the PNS.

Multipolar neuron

The most common structural type of neuron; has three or more processes.

Bipolar neuron

A neuron with one axon and one dendrite; found in the retina and olfactory mucosa.

Unipolar neuron

A neuron with a single process extending from the cell body and associated with sensory receptors at the distal end.

Sensory (afferent) neuron

A neuron that carries impulses toward the CNS from sensory receptors.

Motor (efferent) neuron

A neuron that carries impulses from the CNS to effectors.

Interneuron (association neuron)

A neuron that carries impulses between sensory and motor neurons or participates in CNS integration pathways.

Structural classification of neurons

Classification based on the number and arrangement of processes extending from the cell body: multipolar, bipolar, or unipolar.

Functional classification of neurons

Classification based on what the neuron does: sensory, motor, or interneuron.

Synapse

A junction that transfers information between neurons or between a neuron and an effector cell.

Chemical synapse

The most common type of synapse; uses chemical neurotransmitters to transfer information.

Presynaptic neuron

The neuron sending the signal at a chemical synapse.

Postsynaptic neuron

The neuron receiving the signal at a chemical synapse.

Synaptic vesicles

Structures in axon terminals that store and release neurotransmitters.

Postsynaptic receptor region

The area of the postsynaptic membrane that contains receptors for neurotransmitters.

Electrical synapse

A synapse where neurons are electrically coupled through protein channels, allowing direct exchange of ions between cells.

Chemical neurotransmitter

A chemical messenger released from a presynaptic neuron that affects a postsynaptic neuron or effector.

Neurotransmitter chemical classes

Major classes include acetylcholine, biogenic amines, amino acid-derived neurotransmitters, peptides, purines, and gases/lipids.

Excitatory neurotransmitter effect

A neurotransmitter effect that promotes activity in the receiving cell.

Inhibitory neurotransmitter effect

A neurotransmitter effect that reduces activity in the receiving cell.

Direct neurotransmitter effect

A neurotransmitter effect produced directly through its receptor and associated ion channels.

Indirect neurotransmitter effect

A neurotransmitter effect produced through signaling pathways involving the receptor and intracellular mechanisms.

Neuromodulator

A substance that changes the strength of synaptic transmission.