The nervous system | CNS and PNS

The nervous system

The nervous system consists of two parts 

Central nervous system (CNS)  

Peripheral nervous system (PNS)

1: The central nervous system (CNS) 

It consist of brain and spinal cord

1. Brain is present within the cranial vault of skull.
2. Spinal cord is present within the vertebral canal, formed by the vertebrae.  The brain and spinal cord are connected at the foramen magnum. 

2. Peripheral nervous system (PNS)

It is present external to the CNS.  It consists of  

1. Sensory Receptors 2. Nerves 3. Ganglia 4: Plexus 

Components of peripheral nervous system 

Sensory receptors

They are the endings of nerve cells or separate, specialized cells that sense temperature, pain, touch, sound, light, pressure, odors, and other stimuli.  Sensory receptors are present in the skin, internal organs, joints, muscles and specialized sensory organs such as the eyes and ears.  Nerve 

It is a bundle of axons and their sheaths that connects the CNS to sensory receptors, glands, and muscles. Twelve pairs of cranial nerves arise from the brain, and 31 pairs of spinal nerves arise from the spinal cord.

Ganglion

It is a collection of neuron cell bodies present outside the CNS. 

Plexus 

It is an immense network of axons and, in some cases, also neuron cell bodies, present outside the CNS.

The PNS has two functional subdivisions:  

1. The sensory division  
2. The motor division  

1: The sensory division of PNS  

It senses stimuli and transmits information in the form of action potentials to the CNS.  Because CNS is primary site for processing information, starting responses, and integrating mental processes.

2: Motor division of PNS

It conducts action potentials from the CNS to glands and muscles. The motor division is further divided into two subdivisions:   

• Somatic nervous system, a voluntary division 
•  Autonomic nervous system (ANS), an involuntary division 

The somatic nervous system 

It controls conscious movements of our skeletal muscles. It is done through action potentials that arise in the CNS and are transmitted by the somatic nervous system to the skeletal muscles The cell bodies of somatic motor neurons are present within the CNS, and their axons extend through nerves to form connections with skeletal muscle cells. 

Autonomic nervous system

It controls unconscious activities. Contractions of smooth muscle, cardiac muscle, and secretion of particular glands. The ANS has of two sets of neurons that are arranged in a series between the CNS and the effector organs.  The ANS is divided into two types. 

 

1. Sympathetic division 

It regulates physical activity during fight or flight. 

       2. Parasympathetic division 

It controls resting functions, such as emptying of urinary bladder or digestion of food.