Nerves

• Body coordination


  The nervous system and the endocrine system are the two important systems responsible for body coordination

  
• Nervous system


  • Uses nerve cells to pass electrical impulses
  • Nerve cells act on their target cells by releasing neurotransmitters (chemicals)
  • Endocrine system releases hormones (chemicals) that are transported in the blood to their target cells
  • Target cells have specific cell surface receptors and changes in concentration of hormone stimulates them
• Divisions of the nervous system

  • Central nervous system (CNS) - consists of brain and spinal cord
  • Peripheral nervous system (PNS) - consists of nerves outside CNS, including cranial and spinal nerves

  
• Functions of the nervous system

  • Receives sensory input from sensory receptors in response to external and internal stimuli
  • CNS processes and integrates the input it receives from all over the body
  • CNS generates motor output
• Neurons


  Structural and functional units of the nervous system, basic unit of communication

  
• Neurons


  • Specialized to respond to chemical and physical stimuli, conduct electrochemical impulses and release chemical regulators
  • Enable perception of sensory stimuli, learning, memory & control of muscle and glands
• Supporting cells (glial cells)


  Aid the function of neurons, provide support and nourishment
• Parts of a neuron

  • Cell body (soma) - core of the neuron, contains nucleus and organelles
  • Axon - long process from cell body that carries nerve impulse away
  • Dendrites - short extensions from cell body that receive signals from other nerves at synapse

  
• Myelin sheath


  Fatty insulating sheath that covers axons, protects and electrically insulates the neuron, speeding up impulse transmission
• Nodes of Ranvier


  Periodic gaps in the axon where there is no myelin sheath, facilitate rapid conduction of nerve impulses

  
• Types of neurons


  • Sensory (afferent) neurons - carry messages from receptors to the CNS
  • Motor (efferent) neurons - transmit messages from the CNS to effectors (muscles and glands)
  • Interneurons (association neurons) - found entirely within CNS, pass signals from sensory to motor neuron and integrate these functions

  
• Nerve


  A group of neurons (bundle of neurons) with blood vessel and connective tissue in the PNS

  
• Types of nerves


  • Sensory (afferent) nerves - made up of only sensory neurons
  • Motor (efferent) nerves - made up of only motor neurons
  • Mixed nerves - contain both sensory and motor neurons
• Nerve tract


  Group of neurons in the CNS, often referred to as white matter due to the myelin sheath

  
• Synapse


  Gap between the end of one neuron and the beginning of another, where neurotransmitters are released

  
• Synaptic transmission


  1. Impulse in the presynaptic neuron signals the postsynaptic neuron via neurotransmitters

  2. Calcium diffuses into the synaptic knob, causing neurotransmitter release

  3. Neurotransmitters bind to receptors on the postsynaptic neuron

  
• Neurotransmitters


  The body's chemical messengers, used by the nervous system to transmit messages between neurons or from neurons to muscle
• Acetylcholine (ACh) is an abundant neurotransmitter in the human body, found in both the CNS and PNS
• Excitatory and inhibitory neurotransmitters

  Excitatory - promote the generation of action potential in the receiving neuron

  Inhibitory - prevent the generation of action potential in the receiving neuron
• Parts of the nervous system

  • Central nervous system (CNS) - brain and spinal cord

  Peripheral nervous system (PNS) - nerves that branch out from the brain and spinal cord

  
• Protection of the CNS

  • Enclosed by hard, bony structures (cranium and vertebral column)

  Protected by the meninges (dura mater, arachnoid mater, pia mater)

  Floats in cerebrospinal fluid (CSF) which cushions and supports the brain and spinal cord
• Cerebrospinal fluid (CSF)


  Thin fluid similar to plasma that surrounds the brain and spinal cord, provides cushioning and support, helps maintain constant pressure, and facilitates exchange of nutrients and waste
• Parts of the brain

  • Cerebrum - largest part, performs higher functions like speech, learning, reasoning, emotions, and fine motor control

  Hypothalamus - center for homeostatic control, regulates thirst, appetite, body temperature, and sex drive

  Thalamus - relay station for sensory information

  Midbrain - relay station for tracts passing between cerebrum and spinal cord or cerebellum

  Cerebellum - maintains body posture and balance, assists in learning new motor skills

  Brainstem (medulla oblongata, pons, midbrain) - connects the spinal cord to the rest of the brain, contains reflex centers

  
• Gray matter and white matter

  Gray matter - area consisting of unmyelinated nerve cell bodies

  White matter - area consisting of myelinated nerve cell axons

  
• New evidence suggests that the cerebellum is important in judging the passage of time
• Brain stem


  Consists of medulla oblongata, pons and midbrain & connects the spinal cord to the remainder of the brain

  
• Pons


  • Contains bundles of axons travelling between cerebellum & rest of CNS
  • Contains reflex centers for breathing and reflex centers for head movement in response to visual and auditory stimuli

  
• Medulla oblongata


  • Lies just superior to spinal cord
  • Contains reflex centers for regulating heartbeat, breathing rate and blood pressure
  • Contains reflex centers for: Vomiting, Coughing, Sneezing, Hiccupping, Swallowing
• Gray matter


  • Area that consists of unmyelinated nerve cells
  • Primarily made up of cell bodies
• White matter


  • Area that consists of myelinated nerve cells
  • Consists of bundled axons

  
• • In the brain white matter forms the inner layer & grey matter forms the outer layer
  • In the spinal cord white matter forms the outer layer & grey matter forms the inner layer

  
• Spinal cord


  • Tubular structure composed of nervous tissue that extends from brain stem to lower thoracic/upper lumbar region
  • Conus medullaris: tampered terminal(distal) end of the spinal cord
  • Encased and protected by the vertebrae making up the spine
  • Nerves that come out of the spinal cord are known as spinal nerves
  • Stretch to arms, legs, trunk and to rest of the body

  
• In the spinal cord the gray matter is located in the middle whereas the white matter is found on the outside

  
• At regular interval along the spinal cord there are entrance points for afferent nerves that bring information into CNS & exit points for efferent nerves carrying instructions from CNS

  
• Peripheral nervous system (PNS)


  Division of nervous system that contain all nerves that lie outside CNS

  
• Components of PNS


  • 31 pairs of spinal nerves
  • 12 pairs of cranial nerves

  
• Afferent division of PNS


  • Carry signals to the CNS
  • Includes all neurons that transmit sensory information from their receptors

  
• Efferent division of PNS


  Carry signals from the CNS to effectors (muscles & glands)
• Somatic nervous system


  • Part of PNS responsible for carrying out sensory & motor information to & from the CNS
  • Responsible for transmitting sensory information as well as for voluntary movement

  
• Autonomic nervous system (ANS)


  • Part of PNS that is responsible for regulating involuntary body functions such as blood flow, heartbeat, digestion and breathing
  • Allows these functions to take place without consciously thinking about what is happening