GMED3008: Nervous tissue

Neurons

Functional units of a nervous tissue & where each responds to, transmits and communicates stimuli

Soma

The cell body of a neuron and contains major cytoplasmic organelles

3 types of neurons

Sensory neurons

Inter neurons

Motor neurons

Nissl bodies

Part of the soma which is formed by ribosomes and endoplasmic reticulum.

They synthesise proteins and neurotransmitters

Cytoskeleton

Part of a soma which contains neurofribils that provide support and microtubules that transport material throughout neuron

Dendrites

Short, cytoplasmic branches that radiate from soma and can receive input from axons of other neurons.

They can serve as receptors in sensory neurons

Hillock

Expanded area of the soma marking the origin of the axon, nerve impulses arise at the junction of the axon hillock

Axon

Carries information to other neurons, muscles, glands or lymphatic tissues

Myelin sheath

Formed by specific glial cells that wrap themselves around the axon. Spaces between these cells are known as the nodes of Ranvier

Terminal arborizations

Also known as telodondria and are branches of the axon.

The tips which form expansions as known as synaptic knobs that form synapses with other neurons, muscles or glands

These synapses contain synaptic vesicles filled with neurotransmitters that are release in response to an action potential.

Unipolar

Structural classification of a neuron:

Have dendrites and single axon as fused process

Cell bodies are located in ganglia

Their dendrites extend individually from cell body & function as sensory receptors

Stimulation of the dendrites can trigger unipolar neuron to fire action potential alongs its axon

Bipolar

Structural classification of a neuron :

Have one dendrite and one axon extending from their cell body

Make up part of special sensory organs; eye, inner ear and olfactory bulb

Multipolar

Structural classification of neurons:

Have multiple dendrites and single axon extending from their cell body

These make up majority of the CNS

Sensory neurons

Also referred to as afferent neurons

Convey sensory info from sensory receptors to the CNS

Mainly unipolar in structure

Exhibit sensory receptors on their dendrites or sit next to cells that exhibit sensory receptors

Activation of receptors initiate action potential in axon of sensory neurons

Motor neurons

Also known as efferent neurons

Relay impulses from the CNS to effector organs, muscles or glands

Usually multipolar in structure

Convey action potential away from CNS to generate motor response in periphery

Interneurons

Also known as association neurons

Found in the CNS and bridges the gap between sensory neuron and motor neurons

Usually multipolar in structure

Process sensory information in order to activate necessary motor neurons and trigger appropriate motor response

Neuroglia

Cellular components that hold the nervous tissue together and provides structural and functional support

Have the capacity to replenish damaged regions of mature nervous system through cell division

Astrocytes

Largest and most abundant of neuroglia in the CNS

Two types of- protoplasmic and fibrous

Form blood-brain barrier by wrapping around endothelial cells and secreting chemicals

They repair damages neural tissue

Oligodendrocytes

Smaller then astrocytes with few elongate cytoplasmic processes

Cytoplasmic processes of these wrap tightly around axons known as myelin sheath

Exert inhibitory influence on axonal regrowth

Microglial cells

Smallest of the neuroglia in the CNS Largest

Have a protective role within the CNS

Remove cellular debris, invade microorganisms and nervous tissue damaged by phagocytosis

Ependymal cells

Single row of cuboidal to columnar epithelial cells, lining the ventricles of the brain and central canal of the spinal cord

Secrete and monitor cerebrospinal fluid that resides in the cavities

Exhibit microvilli and cilia at apical surface which beat to help circulate CSF which nourish and cushion the brain and spinal cord

Schwann cells

Neuroglia within the PNS

Form the myelin cheat has around the axons in the PNS

Spirals around neural axon, forming multiple layer of plasma membrane

Role in regeneration of neurons by guiding and stimulating growth

Satellite cells

Neuroglia of the PNS

Flat cells surrounding neuronal cell bodies that reside within ganglia

Provide structural support and form barrier

Regulate exchange of substance bw neuronal cell bodies and surrounding interstitial fluid

Myelin

Layered covering of lipid and protein that surrounds axons of neurons

Insulates neurons and speed up neuronal propagation of impulses

Myelination

The process by which neurons are covered in myelin.

Oligodendrocytes in CNS

Schwann cells in PNS

Ganglion

Cluster of neuronal cell bodies in the PNS

Closely associated with the cranial and spinal nerves of the PNS

Nucleus

Cluster of neuronal cell bodies in the CNS

Nerve

Bundle of axons in the PNS

Tract

Bundle of axons in the CNS

Gray matter

Consists of unmyelinated axons, neuronal cell bodies, dendrites, axon terminals, supporting neuroglia and blood vessels

Presence of Nissl bodies gives it its gray appearance

White matter

Consists largely of myelinated axons and blood cells

Presence of myelin gives it white appearance

Nerve

Cord-like structure that transfers sensory information to the CNS, motor info from the CNS or mixed or does both

Nerve fiber

Neuronal axon embedded in endoneurium

Nerve fascicle

Formed by groups of nerve fibers and held together by perineurium

Contains nerve fibres

Packed with endoneurium

Wrapped in perineurium

Endoneurium

Type of fibrous connective tissue that fills spaces between nerve fibers

Perineurium

Tough membrane that encloses each fascicle

Nerve

Cord-like structure that transfer electric signals to and from CNS

Contains nerve fascicles

Wrapped in and paced with epineurium