Nervous system
Nervous system
CNS PNS
Peripheral Nervous System
S keletal(S omatic)
S ympathetic P arasympathetic
Autonomic
P eripheral Nervous S ystem
Peripheral nervous system• Sensory
(Afferent) : conveys information to the CNS from the sensory receptors (specific neurons or groups of neurons)
• Motor (efferent) division: conveys information away from the CNS
A. Somatic (voluntary) nervous system: neurons go to skeletal muscle
B. Autonomic (involuntary): neurons go to smooth,cardiac muscle and all glands.
Autonomic nervous system
Parasympathetic• “ Rest and digest ” system• Calms body to conserve and
maintain energy• Lowers heartbeat,
breathing rate, blood pressure
Sympathetic• “ Fight or flight” response• Release adrenaline and
noradrenaline • Increases heart rate and
blood pressure• Increases blood flow to
skeletal muscles• Inhibits digestive functions
Nervous tissue cells
• Neurons: respond to stimuli and conduct impulses
• Supporting cells (or neuroglia) : support, nourish, repair and protect neurons.
Neuron
• Cell body: central part of neuron which contains nucleus, and the sorrounding cytoplasm, exclusive of cell processes.
• Responsible for nutrition, growth, and repair of neuron
Nucleus
• It contains DNA and the nucleus also contains nucleolus which in turn is made of RNA.
• Nissle bodies: rough endoplasmic reticulum
• Dendrites : Conduct incoming messages toward cell body
• Axon: conducts nerve impulses away from cell body.
• Axon hillock : portion of cell body from where axon originates.
Neuron classification
• By structure : 1. Multi-polar neuron2. Bipolar neuron3. Pseudounipolar neuron
• By function:1. Sensory (afferent)
neurons2. Motor (efferent)
neurons3. Association
(Interneurons) neurons
• Multi-polar neuron: one axon and many dendrites
• Multipolar neurons constitute the majority of neurons in the brain and include motor neurones
• Bipolar neuron: two processes: one axon and one dendrite
• Bipolar cells are specialized sensory neurons for the transmission of special senses.
• As such, they are part of the sensory pathways for smell, sight, taste, hearing and vestibular functions.
• Pseudounipolar neuron: single process comes off to the cell body and divides into two branches
• The cell bodies are located in the dorsal root ganglion.
Neuron classification
• Sensory (afferent) neurons : bring information to the CNS
• Motor (efferent) neurons : take information from CNS to the other parts of the body
• Association (Interneurons) neurons : allows for communication between neurons within CNS
Supporting cells
• Microglia : ingests damaged neurons and foreign substances. Microglia are a type of glial cells that are the resident macrophages
• Astrocytes
• Oligodendrocytes : Myelinate axons in CNS. Speeds up conduction
• Ependymal cells : lines central canal and ventricles – help circulate CSF
The following are present in CNS
Astrocytes
• Astrocytes: regulates transfer of nutrients from blod to the brain;helps form a part of blood brain barrier.
• Astrocytes (also known collectively as astroglia) are characteristic star-shaped glial cells in the brain and spinal cord
Supporting cells in CNS
Supporting cells• Satellite cells :
sorround neuron cell bodies in spinal ganglia.
{Ganglion : group of neuron cell bodies located outside CNS}.
They supply nutrients to the surrounding neurons , protects, cushioning of cells.
• Schwann Cells : myelinate axons in PNS
Myelination of Axon• Myelination = process
of wrapping an axon with myelin,which speeds up conduction
• One schwann cells wrap around a portion of an axon successively
• Cytoplasm and nucleus of schwann cells gets squeezed to the periphery
Myelination of Axon• Inner successive layers of
myelin sheath are the cell membrane of the schaawn cells
• Schwann cells don’t contact each other. They are seperated by nodes of ranvier.
• This allows for the electric impulses to skip along the axon,called saltatory conduction
• Myelination in CNS is the same as PNS but one oligodendrocyte myelinates portions of many axons.