The nervous system is the body’s control centre and communications network – it is the main controlling, regulatory and communicating system within the body. It is responsible for all mental activity, including thought, learning and memory.
The nervous system works in conjunction with the endocrine system to regulate and maintain homeostasis by picking up information about the external and internal environment through its receptors.
The 3 Functions of the Human Nervous System
- SENSORY – senses changes within the body as well as within the outside environment
- INTEGRATIVE – is able to interpret and understand changes
- MOTOR – provides a responsive action to its interpretation of sensed changes through muscular contractions or glandular secretions
The 2 Principal Divisions Emerging From The Nervous System
The Central Nervous System
- Consists of the brain and the spinal cord
- Controls the entire nervous system
- Responsible for thoughts, emotions and memories
- Integrates and correlates all kinds of incoming sensory information thanks to receptors that relay the information
- Triggers nerve impulses to stimulate muscle contractions and gland secretions
The Peripheral Nervous System
- Made up of various nerve processes which connect the brain and spinal cord through receptors, muscles and glands
- Divides into the Afferent System (nerve cells ‘afferent neurones’ that convey information from peripheral receptors to the CNS) and the Efferent System (nerve cells ‘efferent neurones’ that convey information from the CNS to muscles and glands)
- The Efferent System subdivides into the Somatic Nervous System (voluntary effect by efferent neurones conducting impulses from the CNS to the skeletal muscle tissue) and the Autonomic Nervous System (involuntary effect by efferent neurones conveying impulses from the CNS to smooth muscle tissue, cardiac muscle tissue and glands)
Nervous Tissue Histology
Nervous tissue consists of 2 types of cells:
NEURONS:
- Contain well developed excitability and conductivity properties that have the ability to respond to adequate stimulus by initiating an action potential that reaches to the cell’s other end, relaying the action potential to another
- Responsible for the receiving and transmitting of nerve impulses such as sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions
- Is made up of 3 parts, namely the CELL BODY, which contains a nucleus surrounded by cytoplasm with all organelles and nissl bodies; DENDRITES, responsible for receiving or input; and the AXON, which propagates nerve impulses towards another neuron, muscle fibre or gland cell
Neuron Types
BIPOLAR NEURON (a.k.a. Interneuron)
- One main dendrite
- One axon
- Commonly found in the retina of the eye, the inner ear and the brain’s olfactory area
UNIPOLAR NEURON (a.k.a. Sensory Neuron)
- Begins in the embryo as bipolar neurons
- Dendrites extend into the periphery from the axon
- Axon branch extending into the CNS ends in synaptic end bulbs
MULTIPOLAR NEURON (a.k.a. Motor Neuron)
- Several dendrites
- One axon
- Commonly found in the brain and the spinal cord
NEUROGLIA:
- Smaller in size than neurons
- Constitute half the CNS volume
- Do not generate or propagate action potentials
- Have the ability to multiply and divide within the mature nervous system
- Support, nourish and protect neurons
- Maintain homeostasis in the interstitial fluid that surrounds the neurons
Nervous System Cell Types
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