Nervous System Cells (online)

Anatomy and Physiology

• Made up of brain, spinal cord, and nerves
• Central nervous system: brain and spinal cord
  • Somatic nervous system
  • Autonomic nervous system
• peripheral nervous system: cranial nerves and spinal nerve
• Purpose is to communicate between different parts of body
  • Detects changes in internal and external environment, then initiates a response

Functional Classification of Neurons

Afferent (sensory): conduct impulses from sensory receptors to CNS

Interneuron: process information from afferent neuron, then sends out response

Efferent (motor): conducts outgoing impulses from the interneuron toward effectors (muscles/glands)

Terms

CNS: brain and spinal cord

PNS: nerves in outer regions, spinal and cranial nerves

Afferent nerves: sensory, collect from periphery to send to CNS

Efferent nerves: motor, send information from CNS to periphery

Somatic Nervous system: body and skeletal muscles, carries information to and from voluntary skeletal muscles

Autonomic nervous system: controls involuntary functions, sends out response to visceral (organs) effectors, eg. muscles, glands

Sympathetic nervous system:

• prepares body for threats, sends out appropriate response, eg. breathing rate increases

Parasympathetic nervous system:

• rest and repair system, keeping them in balance

Cells of Nervous system

Neurons

• Excitable cells that initiate impulses in nervous system
• Has dendrites, cell body, axon

Structure

Dendrites: receiving information from sensory receptors or other nerves, and then information sent to cell body

Nucleus: instructions to govern cell function

Mitochondria: atp for neuron

RER and ribosomes: protein synthesis of neurotransmitters

Cell body(perikaryon or soma): synthesizes material, protein and mitochondria, and material to maintain and regenerate nerve fibers

Axon: nerve fiber/process, takes information away from cell body, sometimes covered in myelin sheath, varies in size

Synaptic Knob: far end of neuron(distal), communicate with gland, muscle, or another nerve

Synapse: area where there is communication between synaptic knob and other effector

Nodes of renvier: in between myelin where axon is exposed, AP jumps from node to node to allow faster transmission

Axon Hillock: information gathers here and then gets sent along axon

Axon collateral: side branches of an axon

Cytoskeleton:

• Microtubules, mibrofilaments, neurofibrils(bundles of intermediate neurofilaments
• Structural support, allows for axon transport, can transport substances from cell body can travel along axon to specific areas

Axonal Transport

1. Mitochondria and vesicles with neurotransmittles can travel through the cell from the cell body, they do this buy travelling down microtubules
2. Motor molecules take the vesicles, and the materials are transported to end of axon, motor molecules use microtubules as a railway and walk it down the axon
3. Neurotransmitters are released into the synapse at the end of axon, some return back to terminate action
4. Reverse of this transport returns neurotransmitters and vesicle membrane back up where they are recycled or degraded

Functional Region of Neuron

Input zone: receives the input, includes dendrites and cell body

Summation zone: inputs are combined which generates impulse, includes axon hillock, many voltage gated sodium and potassium channels

Conduction zone: impulse conducts along axon away from cell body, includes axon

Output zone: neurotransmitters are released into a synapse to communicate, include telodendria and synaptic knobs of axon, has many voltage gated calcium channels

Glia Cells in CNS (Neuroglia)

• Support cells of nervous system
• Support neurons, promotes their efficiency
• Can retain capacity for cell division, but makes them susceptible to uncontrolled cell division, eg. cancer

Microglia

• Small, stationary, can become enlarged when brain tissues are inflamed
• Undergoes phagocytosis, engulfs and destroys microorganisms and cellular debris during inflammation

Ependymal Cells

• Thin sheets of epithelia cells, line fluid filled cavities in CNS
• Produce cerebroapinal fluid (CSF)
• Others cells have motile cilia to keep CSF moving

Oligodendrocytes

• Smaller than astrocytes, have fewer processes, specific to CNS
• Holds nerve fibers together and produce myelin sheaths (myelination)

Astrocytes

• Largest and most numerous of gliio, star shapes, have cell extensions that connect neurons and capillaries through brain tissue
• Transports snutrients from blood to neurons, helps restore ion gradients in extracellular fluid
• Intense neuron activity can lead to excess in electrolytes, and astrocytes help return to normal state
• Has feet that attache to basement membrane of brains blood vessels/capillaries to form transport barrier called blood brain barrier, barrier prevents certain substances from entering brain tissue

Glia Cells in PNS- Shwann cells

• Only in PNS
• Functional equivolent to oligodendrocytes
• Wrap around nereves, form sthick myelin sheath around peripheral nerve fiber, myelinated fiber
• In between where schwann cells have formed myelin there are gaps; nodes of envier
• Bundle of nerve fibers wrapped by a schwann cell, unmyelinated nerve fiber
• Satellite cells: schwann cells that cover cell bodies in ganglion in PNS
• Ganglion: collection of cell bodies of neurons in PNS
• Nuclei: collection of cell bodies of neurons in CNS

Myelinated axon appearance in PNS

Myelin: plasma membrane of shwann cells, made of white fatty substance (phospholipid), forms sheath around nerve axon

Myelin Sheath: the inner core made of many layers of myelin

Nodes of Ranvier: gaps in myelin sheath, faster conduction

Neurilemma: where the nucleus and cytoplasm of shwann cell is located at perimeter, essential for growth

Neurolemmocyte: another name for shwann cell

Neuronal sheath: both the myelin sheath and neurilemma surrounding nerve axon/fiber

Nerves and Tracts

CNS

• Bundles of nerve fibers/axons referred to as tracts
• Grey matter called nuclei
• White matter made of myelinated nerves, myelinated tracts are NOT held together by connective tissue layers
• Individual fibers can extend through a tract

PNS

• Bundles of nerve fibers/axons referred to as nerves
• Grey matter called ganglia
• Whit matter made of myelinated nerves, Myelinated nerves ARE held together by connective tissue layers
• We have nevers so that neurons can be packagedd together neurons that have common characteristics
• Individual fibers can exten through a nerve

Gray matter

• Made up of collections of cell bodies and unmyelinated fibers

Note

• Motor nerves: motor neurons,
• Sensory nerves: sensory neurons
• Mixed nerves: contain sensory and motor neurons

Connective tissue coverings of nerves in PNS

Endoneurium

• Each axon/nerve fiber wrapped by endoneurium,
• Fibrous connective tissue inner covering

Perineurium

• A group of axons/nerve fibers forming a fasicle that is held together by perineurium
• Connective tissue middle covering

Epineurium

• Grouping all of the fasicles together is an outer covering epineurium
• Has superficial and more deep layer, fibrous connective tissue

Repair of Nerve Fibers

• Mature neurons cannot go through cell division
• Damage to nervous tissue can be permanent
• Sometimes neurons can be prepared
  • Damage cannot be extensive
  • Cell body and neurilemma must be intact
  • Scarring has not occurred