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.