Neurophysiology- Terminology

Terms commonly used in Neurophysiology Neuron / Nerve fiber Afferent & Efferent Antidromic Vis a vis Orthodromic Centre, Nucleus, Ganglia Dorsal root ganglion Sensory neuron, Interneuron, Motor neuron Modulation

Neuron Functional unit of Nervous System Exists in many forms

Various forms of Neurons

A Typical Motor Neuron

‘In the CNS neurons are myelinated’ ‘Schwann cells provide myelin for peripheral neurons’ ( The term Neuron is used to refer to the nerve fiber or axon--)

Myelination of Axon in the peripheral & Central NS

Afferent & Efferent Afferents: Nerve fibers that carry impulses from periphery to center / CNS Efferents : Nerve fibers that carry impulses from center to periphery / --

Afferents & Efferents / Orthodromic & Antidromic

Center, Nucleus, Ganglia Collection of neurons in: the brain stem- Center - e.g Respiratory center CNS that give rise to main nerve tracts Nuclei e.g Trigeminal Nucleus periphery Ganglia e.g sympathetic ganglia

Nuclei ---

Dorsal root ganglion Located in the intervertebral foramina seen as nodules on the dorsal roots are the cell bodies of sensory nerve fibers.

Dorsal root ganglia

Note: The neurons in the dorsal root ganglion are pseudo unipolar type i e they have an axon with two branches. The cell body in the dorsal root ganglion only supports the nerve fiber. There are no synapses in the dorsal root ganglion.

Sensory neuron, Interneuron, Motor neuron The cell bodies of the sensory neurons are located in DRG. Their axon extends in both directions: a peripheral axon to receptors & a central axon passing into the spinal cord. The latter axon usually terminates at an interneuron.

Gray matter - an area of unmyelinated neurons where cell bodies and synapses occur. In the spinal cord the synapses between sensory and motor and interneurons occurs in the gray matter. The cell bodies of the interneurons and motor neurons also are found in the gray matter. White matter - an area of myelinated fiber tracts. Myelination in the CNS differs from that in nerves.

Nerve - a group of fibers (axons) outside the CNS. The spinal nerves contain the fibers of the sensory and motor neurons. Tract - a group of fibers inside the CNS. The spinal tracts carry information up or down the spinal cord, to or from the brain. Tracts within the brain carry information from one place to another within the brain. Tracts are always part of white matter.

Terms- Fasciculus, Funiculus, Lemniscus Fasciculus (Bundle of N fibers) Fasciculus Gracile & Fasciculus Cuneate

Fasciculus & Funiculus A small number of nerve fibers enclosed in perineurium makes a Fasciculus A number of fasciculi enclosed together in a membrane form Funiculus Fig.

Funiculus

Lemniscus A bundle of Sensory nerve fibers within brain stem which terminate in specific relay nuclei in the midbrain

Lemniscus

Neuromodulation

Learning Outcomes State the differences between the terms neuron and nerve fiber Explain the terms Central Nervous System and Peripheral Nervous System Explain the following terms: afferent neuron; interneuron; efferent neuron; nucleus; ganglia; fasciculus; funiculus; lemniscus; gray matter; white matter

Learning Outcomes ( Cont. ) Differentiate the terms nucleus & ganglion Identify from the name of a tract whether an ascending or a descending pathway. Classify neural ganglia Explain the term 1st order neuron, 2nd order neuron etc. in context to neurons in a sensory pathway

Thank You