The Nervous System

The Nervous system coordinates actions and sensory information by transmitting signals to and from different parts of the body.

The Neuron

The Neuron
  • It is a specialised cell and functional unit of the nervous system
  • Approximately 100 billion neurons combine to form the nervous system
  • Major parts of the neuron Include: synaptic terminals, axon, cell body(soma) and dendrites
  • Neurons can communicate only one way

The soma of a neuron contains a nucleus and other organelles, including lysosomes, mitochondria, and a golgi complex. The axon is a cylindrical projection from the cell body that transmits nervous impulses to other neurons or effector sites (i.e.,muscles, organs, other neurons). The dendrites gather information from other structures and transmit it back into the neuron.

Neurons collectively innervate to form nerves, two divisions of the nerves include the central nervous system (which contain the brain and spinal cord) and peripheral nervous system (which contain nerves branching out of the central nervous system).

The Central Nervous System

  • Contains the brain and spinal Cord
  • Processes Information through interneurons
  • The CNS innervates to form PNS
  • Function of CNS: To process information received by it from the PNS and to Provide an Output to motor neurons

The Peripheral Nervous System

  • Receives and Sends Signals to and from the CNS from the ends of the body
  • There two types of nerves in the PNS, Sensory (Afferent) and Motor (Efferent) Neurons

Sensory (Afferent) Neurons:
send signals to the CNS from the ends of the body, They are commonly termed as “Receptors”, Major Receptors are:
Chemoreceptors detect the presence of chemical substances
Thermoreceptors detect changes in temperature
Mechanoreceptors detect changes in muscle length
Photoreceptors detect light during vision

There are two major mechanoreceptors, Golgi Tendon Organs (GTO) and Muscle Spindles.

  • Muscle Spindle: Located in the belly of the Muscle fibre, It is responsible for sensing the lengthening of a muscle
  • GTO: Located towards the ends of Muscles, GTO is responsible for sensing the tension present within the muscle

Motor (Efferent) Neurons: send signals from the CNS to the ends of the body

Motor Neurons are of Two types:
Somatic: Responsible for voluntary movements
Autonomic: Responsible for Involuntary Movements

Autonomic Neurons are of two types:

  • Sympathetic: activates what is often termed the fight or flight response.
  • Parasympathetic: regulates the body’s unconscious actions.