Building Blocks of the Nervous System

organisation

split into the central and peripheral nervous systems

neuron properties

• irritability

• conductivity

• receptors

• trains of impulses

irritability

capacity to act in a graded manner to physical or chemical stimuli

conductivity

ability to transmit excitation rapidly from one place to another

how are neurons excited

• receive stimulus

• flux of energy is transduced into electrical energy to make a nerve impulse

exteroceptors

receive stimuli from outside

interceptors & proprioceptors

receive stimuli from inside

trains of impulses

• signal to nerve centres

• additional patters of activity evoked

• result in sensations or motor responses

neuron structure

• cell body (soma)

• axon

• dendrites

cell body (soma)

• central nucleus

• usual organelles

• nissl bodies

• cytoskeleton

• no centrioles

nissl bodies

clusters of free ribosomes and RER

cell body cytoskeleton

• neurofibrils

• microtubules & neurofilaments

what does the cell body do

it is the processor

what does the axon do

the distributer; signal passes along the nerve from dendrites to axon terminals

axon contains

mitochondria and cytoskeletal proteins

axon

• long, thin cylindrical projection

• only one per neuron

• specialised to conduct action potential

neuroglia

support cells for neurons that are smaller but more numerous

what do neuroglia do

they do not propagate action potentials but determine flow signals through neuronal circuit

functions of neuroglia

• modulate synaptic and non synaptic transmission

• able to divide and multiply

• in disease will fill gaps left by neurons

neuroglial cells of the cns

• astrocytes

• microglia

• ependymal cells

• oligodendrocytes

neuroglial cells of the pns

• satellite cells

• schwann cells

what do astrocytes do

maintain chemical micro-environment and blood brain barrier

astrocyte functions

• forms brain injury scar tissue

• provides neurons with nutrients

• take up excess neurotransmitters

microglia

• protects cns by phagocytosis of pathogens

• clear away dead cell debris

ependymal cells

epithelial cells which line the ventricles of the brain and central canal of the spinal cord

what do ependymal cells do

• secrete some cerebrospinal fluids and aid in circulation using cilia

• monitor cerebrospinal fluid composition

ependymal cells properties

selectively permeable - allows exchange of fluid and substances across lining giving a barrier function

oligodendrocytes provide

• structural support and scaffolding to neurons

• forms myelin sheath for some cns cells

schwann cells

wraps a spiral around axons to be collectively known as myelin sheath

schwann cells importance

acts like insulation on wire - an intact sheath is critical to proper nerve impulses

satellite cells

flattened cells arranged around the cell bodies of neurons that regulate chemical environment and are involved in repair