The peripheral nervous system

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Chapter 6

Neurons

A nerve cell
- The basic structural and functional unit of the nervous system

Schwann Cells

Cell that wraps around a nerve fibre forming the myelin sheath

Nodes of Ranvier

A gap in the myelin sheath of a nerve fibre

Neurilemma

A sheath surrounding a nerve fibre

Sensory neurons

A nerve cell that carries messages from receptors to the brain or spinal cord
- AKA receptor neuron

Motor neurons

A nerve cell that carries messages from the brain or spinal cord to eff ector organs (muscles and glands)
- AKA effector neuron

Interneurons

A nerve cell in the brain or spinal cord that carries messages between other nerve cells
- AKA association neurons or connector neurons

Multipolar neurons

A nerve cell with one axon and many dendrites
- The most common type of neuron

Bipolar neurons

a neuron with two processes—one axon and one dendrite—arising from opposite sides of the cell body - These neurons are sensory, such as the neurons found in the retina of the eye

Unipolar neurons

A neuron with a single process, an axon
- The cell body is to one side of the axon
- In humans such neurons are sensory and carry messages to the spinal cord

Nerve fibres

An axon with its associated coverings

Nerves

A bundle of nerve fibres

Synapse

The junction between the branches of adjacent neurons

Neuromuscular junction

The junction between branches of a motor nerve cell and a muscle fibre
- AKA: the motor end plate

PNS

The part of the nervous system that connects the central nervous system with the receptors, muscles and glands
- Peripheral Nervous System

Ganglion

A group of nerve cell bodies outside the
brain and spinal cord
- Ganglia

Cranial nerves

One of the twelve pairs of nerves that arise from the brain

Spinal nerves

One of the 31 pairs of nerves that arise from the spinal cord
- Joined to the spinal cord by dorsal and ventral roots

Ventral root

One of the two roots that link a spinal nerve to the spinal cord
- Located towards the front of the body
- Contains axons of motor neurons

Dorsal root

One of the two roots that link a spinal nerve to the spinal cord
- Located towards the back of the body and contains axons of sensory neurons

Dorsal root ganglion

A group of nerve cell bodies located in the dorsal root of a spinal nerve

Somatic sensory neurons

A nerve cell that carries messages from receptors in the skin, muscles, bones and joints into the brain and spinal cord

Visceral sensory neurons

A neuron that takes impulses from the internal organs to the central nervous system

Nerve impulse

The electrochemical change that travels along the membrane of a nerve cell
- The message carried by a nerve
- (See also action potential)

Electrochemical change

The change in electrical voltage brought about by changes in the concentration of ions inside and outside the cell membrane of the neuron

Saltatory conduction

The conduction of a nerve impulse along a myelinated nerve fibre
- The impulse seems to jump from one node of Ranvier to the next

Reflex

A rapid, automatic response to a change in the
external or internal environment
- Tries to restore homeostasis

Spinal reflex

A reflex carried out by the spinal cord, without involvement of the brain

Reflex arc

The basic pathway travelled by nerve impulses from receptor to effector

Spinal reflex arc

The basic pathway travelled by nerve impulses from receptor to effector in the case of a spinal reflex

Receptor

A structure that detects a stimulus

Effector

A muscle or gland that carries out a response to a stimulus

Acquired reflexes

A reaction that has been learned as a result of the occurrence of a stimulus

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