Nervous tissue

Central nervous system

Brain and spinal chord (+optic nerve)

Peripheral nervous system

All nervous tissue outside CNS

Sensory/afferent division

Information to the CNS

Motor/efferent system

Information from CNS to the organs (muscles and glands)

Nervous system helps to

• Maintain homeostasis

• Initiate voluntary movement

• Responsible for perception, memory, behaviour

Three major functions

• Sensory — external + internal stimulus transferred CNS

• Integrative — analysis + storing of info

• Motor — stimulus of effectors through PNS

Neurons

• Nerve cells that can be large

• Conscious + unconscious control

• Do not divide

• High metabolic rate — will quickly die without O2

• Has cell body where

  • short + branched dendrites convey nerve impulses

  • a longer single axon conducts nerve impulses to another neuron or tissue

Dendrite

Receiving/input part of neuron

Axon

Carries out the nerve impulse away from neuron

Output portion of neuron

Multipolar neurons

• Have 2 or more dendrites and a single axon

• Most common neurons in CNS

• All motor neurons (controlling skeletal muscle) are in this class

• Longest neuron type, from the spinal cord to the toes.

Bipolar neurons

• Two distinct processes

  • 1 dendritic process (can branch at tip but not at cell body)

  • 1 axon

• Has cell body between axon and dendrite

Unipolar neuron

• Dendrites and axon are continuous

• Cell body is off to one side

• whole thing to where dendrites converge called axons

• Most sensory nerves

• Very long, spine to toe

Anaxonic neurons

• Rare, function misunderstood

• cannot distinguish dendrites from axons

• Found in brain + special sense organs

Neurologlia

• Found in CNS and PNS

• makes up ~50% the volume of the CNS (“glue”)

• smaller than neurons but more numerous (5-50x)

• do NOT propagate action potentials, but can communicate

• can divide within the mature nervous system

Neuroglia functions

• Physical structure of nervous tissue

• Repairs framework of nervous tissue

• Undertake phagocytosis

• Supply nutrients to neurons

• Regulate interstitial fluid in neural tissue

Neuroglia in CNS

• Astrocytes

• Oligodendrocytes

• Microglia

• Ependymal cells

Neuroglia in PNS

• Schwann cells

• Satellite cells

Astrocytes

• Star shaped , largest, most numerous, syncytium network

• Support (have microfilament) and repair (scar)

• Communicate with neurons through gliotransmitters such as such as glutamate

• Maintain environment around neuron such as by regulating ions

• Maintain blood brain barrier through endothelium, wraps around vessels and influence permeability

Ogliodendrocytes

• Forms insulating multilayered myelin sheath (protein lipid layer) around CNS axons

• Can myelinated more than one axon, accelerates action potential

Microglia

• Phagocytes (resident macrophages) — protection

Ependymal cells

• Produces cerebral spinal fluid

• Lines CSF filled ventricles in the brain and the central canal in spinal cord

• Single layer of predominantly cuboidal cells have cilia (flow) and microvilli (sampling)

• Located in ventricles and other locations where CSF is found

• ACNS mechanical buffer, moves nutrients and waste

Shwann cells

• PNS version of ogliodendrocytes

• forms insulating myelin sheath around axons, or just support and surround several non myelinated axons

• Just one axon at a time for myelination, but many if for structure and support

Satellite cells

• Surround neuron cell bodies

• Support fluid and exchange, like astrocytes in CNS