Functions of the nervous system
Structure of the nervous system
Organisation of the nervous system
Control of cardiovascular system.
Functioning of endocrine system.
Maintenance of homeostasis.
Nervous system (NS) is a highly specialised, complex, interconnected network of neural tissue
It coordinates, interprets and controls the interactions among the various tissues of the body and as well as between the body and the surrounding environment.
Body is able to function as a single unit because the NS provides the necessary communication between the various systems, which enables them to work together in a coordinated manner.
Stressor — Autonomic NS — adrenal medulla — adrenaline — fight or flight.
The nervous system consists of:
b) Neurons – subdivided into:
iii)interneurons- association neurons.
c) Glial cells (neuroglia).
Detect changes both internally and externally.
Sensitive to a whole range of stimuli including:- temperature (thermoreceptors), touch/pressure, sound (mechanoreceptors), movement, stretch (proprioceptors), various chemicals and acidity (chemoreceptors).
Convert different types of stimuli into electrical nerve impulses.
Structure of sensory receptors
Dendrites of sensory neurons divided into:
a) free nerve enedings-bare dencdrites thermal, pain etc.
b) encapsulated nerve endings-dendrites enclosed in layer of connective tissue e.g. pressure.
Specialised cells that monitor changes in the internal or external environment and synapse with sensory neuron, e.g. vision, hearing and taste.
Conduct nerve impulses from one part of the body to another
Some are tiny and relay signals over short distances
Others form the longest cells in the body, e.g. from lumbar region of the spine to the foot allowing the movement of toes.
Components of a neuron: cell body
Cell body – contains nucleus, various organelles including mitochondria.
Acts to provide and control the growth and maintenance of the neuron.
Specialised organelles – rough endoplasmic reticulum called Nissl bodies, neurofibrils are microtubules that provide mechanism for intracellular transport and intermediate filaments support cell shape.
Components of a neuron: dendrites
Dendrites – usually conduct impulses towards the cell body.
Sensory neurons usually have a number of dendrites (1 input) that become a single process known as a Dendron (unipolar) which almost bypass the cell body to merge with the axon
Motor efferent neurons have many dendrites (multipolar), which are highly branched so that the neuron may receive messages from a large number of other neurons.
Components of a neuron: axon
Axon – a single specialised process.
Length varies between 1mm (within CNS) to 1m (spinal cord to toes)
May branch forming axon collaterals (side branches) axon terminals (fine processes) and then synaptic end bulbs (containing neurotransmitter).
Axonal buttons situated along the axon house vital organelles, including mitochondria.
Axon hillock keep a running total of incoming generator potential (electrical activity).
Axons may be myelinated or unmyelinated
Myelinated axons are surrounder by a Schwann cell like a swiss roll.
Schwann cells wrap themselves around axons many times as they grow
Eventually multiple layers of Schwann cell plasma membrane (i.e. phospholipid bilayer) surround the axon
Consists of up to 100 layers of Schwann cell membrane with Schwann cell cytoplasm and nucleus forming outer...