U3 Topic 2: Central/Peripheral Nervous Systems

Central Nervous System (CNS)

- The central nervous system is “central” to the body in that:

        -  It consists of the brain and the spinal cord

        -  The spinal cord runs down the middle of the body

        -  It is from this centre that all the body’s activity is coordinated and integrated via communication with other areas

- The brain is the control centre for the body, allowing the body to respond to information both from within and outside of the body

- The spinal cord is the information route via which these messages are received and transmitted to other parts of the body.

Peripheral Nervous System (PNS)

-   The Peripheral Nervous System is made up of every neuron in the body outside of the CNS

-   The PNS receives information from the rest of the body and can send it to the CNS. The CNS can also send information to the PN

-   The PNS is subdivided into two divisions: the somatic nervous system and the autonomic nervous system

          Somatic Nervous System (SNS)

                      

        - The SNS is responsible for all voluntary (concious) movements and actions performed by an organism. These are formulated by communication with the CNS

        - The SNS controls voluntary movements by transmitting information about the body’s sensations to the brain and then coordinating the skeletal muscles to respond. Occurs through two different neurons:

o   Sensory Neurons (aka afferent neurons); are neurons that carry information up ascending tracts (sensory neural messages) about the body’s sensations to the brain so that it can coordinate a response.

o   Motor Neurons (aka efferent neurons); are neurons that carry information down descending tracts (motor neural messages) from the brain to the skeletal muscles giving instructions on how to move

HOT TIP: Use the acronym S.A.M.E to remember these neurons. S and A are together hence sensory neurons are afferent neurons. M and E are together meaning motor neurons are efferent neurons. 

        - In summary, the SNS operates by:

o   Sending sensory neural messages about the body and its environment to the CNS

o   Sending motor neural messages from the CNS to the skeletal muscles to initiate voluntary movement

        Autonomic Nervous System (ANS)

       - The ANS is responsible for initiating the responses of the body’s visceral muscles, organs and glands (MOG)

       - It also sends feedback to the brain about their activity

       - The MOG involved in the ANS are mostly self-regulating in that they don’t require conscious mental control to operate. However, we do have conscious control             over some of these actions. For example, we can regulate our breathing making it faster or slower

      - In the ANS there are two subdivisions/branches, that can have different levels of dominance at any given time

o   Sympathetic Nervous System (SNS)

    ☆   The SNS is responsible for activating the body’s visceral muscles and glands in order to prepare the body for dealing with high levels of activity such as exercise or escaping a threat

    ☆   The visceral muscles and glands need to be activated in a particular way to energize the body and be better able to deal with the threat

    ☆   The changes are called sympathetic responses. These responses occur during high levels of activity or under threat

    ☆   Releases Adrenaline

    ☆   Trigger’s fight-flight-freeze response

    ☆   Aids Survival (adaptive response - meaning that it increases chance of survival)

 

o   Parasympathetic Nervous System (PNS)                                                              

  

☆  The PNS is responsible for maintaining optimal levels of functioning of the visceral organs, muscles and glands and returning them to their balanced and ideal levels of functioning after the heightened arousal of a sympathetic response

☆  Parasympathetic responses occur during rest and inactivity

☆  If MOG keep functioning at sympathetic levels when there is no threat the body will go into depletion

☆  Homeostasis-equilibrium

Responding to Sensory Stimuli

-  Sensory Stimuli refers to anything that is registered by the body as a sensation

-  This sensation is first registered by sensory receptors which are nerve endings that detect such information

-  Generic answer scaffold (replace the red): 

o   The sensory receptors on the ___(body part)____ register the  ___(feeling)__. Sensory neural messages are initiated in the peripheral nervous system and are sent via the afferent tracts via the spinal cord to the brain where they are integrated by the brain. The brain coordinates a conscious motor response and initiates it by sending motor messages via efferent tracts to the peripheral nervous system via the spinal cord. The effector sites on the muscles/skeletal muscles of the ___(body part)___ receive the motor message and respond by ___(action)___.