Man and his environment - National University Tissue .pdf · Copyright © 2004 Pearson Education,...

Dr. Elriah M. Makie 0122858517

Man and his environment

Nervous Tissue

BSc.M.Sc .MBBS

Introduction The nervous system is divided into two main parts:

The central nervous system (CNS) comprising the brain and spinal cord.

The peripheral nervous system (PNS) comprising the nerves which run between the CNS and other tissues, together with nerve 'relay stations' termed ganglia

Introduction The nervous system is designed to deliver rapid and

precise communication between different parts of the body by the action of specialised nerve cells called neurones.

These highly specialised cells are interconnected and function togather and process information and then generate appropriate response signals.

Introduction Functionally, the nervous system is divided into the

somatic nervous system which is involved in voluntary functions and the autonomic nervous system which exerts control over many involuntary functions.

Histologically, the entire nervous system merely consists of variations in the arrangement of neurones and their supporting tissues.

Histology of neural tissue

Two types of neural cells in the nervous system:

Neurons - For processing, transfer, and storage of

information

Neuroglia – For support, regulation & protection of

neurons

Neuroglia (glial cells)

CNS neuroglia:

• astrocytes

• oligodendrocytes

• microglia

• ependymal cells

PNS neuroglia:

• Schwann cells (neurolemmocytes)

• satellite cells

Classification of neurons

Structural classification based on number of processes:

Multipolar neuron

• multiple dendrites & single

• most common type

Bipolar neuron

• two processes coming off cell

body – one dendrite & one axon

• only found in eye, ear & nose

Unipolar (pseudounipolar)

neuron

• single process coming off

cell body, giving rise to

dendrites (at one end) &

axon (making up rest of

process)

Classification of neuronsFunctional classification based on type of information & direction of

information transmission:

• Sensory (afferent) neurons –

• transmit sensory information from receptors of PNS towards the

• most sensory neurons are unipolar, a few are bipolar

• Motor (efferent) neurons –

• transmit motor information from the CNS to effectors

(muscles/glands/adipose tissue) in the periphery of the body

• all are multipolar

• Association (interneurons) –

• transmit information between neurons within the CNS; analyze

inputs, coordinate outputs

Anatomical organization of neurons

Neurons of the nervous system tend to group together into organized

bundles

The axons of neurons are bundled together to form nerves in the

PNS & tracts/pathways in the CNS. Most axons are myelinated so

these structures will be part of “white matter”

The cell bodies of neurons are clustered together into ganglia in the

PNS & nuclei/centers in the CNS. These are unmyelinated

structures and will be part of “gray matter”

Anatomical structure of Nerves

Myelin Sheath is formed by 2 types of Glia The myelin sheath is the wrapping seen

around the axons of some neurons.

Oligodendrocytes – form myelin sheaths on axons in the CNS

Schwann cells – form myelin sheaths on axons in the PNS

• Gaps between myelin sheath cells are the Nodes of Ranvier.

Thanks

Man and his environment - National University Tissue .pdf · Copyright © 2004 Pearson Education,...

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