A&P - 12.1 Basic Structure and Function of the Nervous System

divisions of the nervous system

• central nervous system (CNS)

• peripheral nervous system (PNS)

central nervous system (CNS)

interprets sensory input and dictates motor responses based on past experiences, reflexes, and current conditions

• “seat of all mental activity”

main structures of central nervous system (CNS)

• brain

• spinal cord

brain

receives and processes sensory information, initiates responses, stores memories, generates thoughts and emotions

• the large organ of the central nervous system composed of white and gray matter, contained within the cranium and continuous with the spinal cord

spinal cord

conducts signals to and from the brain, controls reflex activities

• organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviors

peripheral nervous system (PNS)

cranial & spinal nerves are the communication lines between the CNS and the rest of the body

• functional divisions of the peripheral nervous system:

  • sensory division (somatic and visceral subdivisions)

  • motor division (somatic and visceral subdivisions)

    • somatic nervous system

    • autonomic nervous system

    • enteric nervous system

main structures of peripheral nervous system (PNS)

• cranial nerves

• spinal nerves

• specialized receptors

sensory (afferent) division

sensory organs to CNS

conducts impulses of the body into the CNS (carries signals from receptors to CNS)

• considered the “input” region

somatic sensory division

carries signals from receptors in the skin, muscles, bones, and joints - and then transmits the stimulus to the brain and spinal cord for interpretation

visceral sensory division

carries signals from the viscera (heart, lungs, stomach, and urinary bladder) - and then transmits the stimulus to the brain and spinal cord for interpretation

motor (efferent) division

CNS to muscles and glands

carries signals (motor neurons conduct impulses) from CNS to effectors (glands and muscles that carry out the body’s response) to produce a response to a stimulus

• considered the “output” region

• further subdivided functionally into:

  • somatic nervous system (SNS)

  • autonomic nervous system (ANS)

  • enteric nervous system (ENS)

somatic nervous system (SNS) - somatic motor division

controls voluntary movements

carries signals to skeletal muscles

• a voluntary system that conducts impulses from the CNS to skeletal muscles

• output produces muscular contraction as well as somatic reflexes (involuntary muscle contractions)

autonomic nervous system - visceral motor division 

controls involuntary responses

carries signals to glands, cardiac and smooth muscle

• involuntary because it conducts impulses from the CNS to cardiac muscles, smooth muscle, and glands

• its involuntary responses are visceral reflexes

• further subdivided functionally into:

  • parasympathetic nervous system

  • sympathetic nervous system

parasympathetic nervous system

“rest or digest”

conserves energy and maintains homeostasis

• tends to have calming effect

• slows heart rate and breathing

• stimulates digestive and urinary systems

sympathetic nervous system

“fight or flight”

mobilizes the body to respond to “emergency” situations or when the body has moved outside of homeostasis

• tends to arouse body for action

• accelerating heart beat and respiration, while inhibiting digestive and urinary systems

enteric nervous system (ENS)

frequently considered a part of the ANS but is specifically responsible for controlling the smooth muscle and glands of the digestive tract

• involved with digestive system (neural tissue associated with the digestive system)

• it is a large part of the PNS, and is not dependent on the CNS

functions of the nervous system

• sensory input

• integration

• motor output

• homeostasis

stimulus

an event in the external or internal environment that registers as activity in a sensory neuron

sensory input

sensation = use of sensory receptor to detect stimuli both inside and outside the body and then transmit those stimuli to the central nervous system

• receives information from the environment and translates it into the electrical signals of nervous tissue

integration

process and interpret sensory stimuli and then determine and/or trigger and appropriate motor response to those stimuli

• combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response

motor output

response = effects a response appropriate to the stimulus by sending an impulse from the central nervous system to the effector organs of the body such as the muscles and glands

• causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli

homeostasis

maintain homeostasis by acting as a regulatory or control center through sensory input, motor output, and integration functions