Nervous System

• Acetylcholine (ACh) released in the CNS synapses, ANS synapses, and neuromuscular junctions. Excitatory or Inhibitory. Alzheimer disease (a type of senile dementia) is associated with a decrease in acetylcholine-secreting neurons. Mysathenia gravis (weakness of skeletal muscles) results from a reduction in acetylcholine receptors.
• Norepinephrine (NE) Selected CNS synapses and some ANS synapses. Excitatory. Cocaine and amphetamines increase the release and block the reuptake of norepinephrine, resulting in overstimulation of postsynaptic neurons.
• Serotonin CNS synapses, generally inhibitory. It is involved with mood, anxiety, and sleep induction. Levels of serotonin are elevated in schizophrenia (delusions, hallucinations, and withdrawal). Drugs that block serotonin transporters, such as Prozac, are used to treat depression and anxiety disorders.
• Dopamine, selected CNS synapses and some ANS synapses. Excitatory or inhibitory. Parkinsons disease (depression of voluntary motor control) results from destruction of dopamine-secreting neurons.
• Gamma-aminobutyric acid (GABA), CNS synapses, inhibitory. Drugs that increase GABA function have been used to treat epilepsy (excessive discharge of neurons).
• Glycine, CNS synapses. Inhibitory, receptors are inhibited by the poison strychnine. Strychnine increases the excitability of certain neurons by blocking their inhibition.
• Endorphins, descending pain pathways. Inhibitory, the opiates morphine and heroin bind to endorphin receptors on presynaptic neurons and reduce pain by blocking the release of a neurotransmitter.
• Sensory receptors are sensory nerve endings or specialized celcapable of responding to stimuli by developing action potential.
• Mechanoreceptos respond to mechanical stimuli, such as the bending or stretching of receptors
• Chemoreceptors respond to chemicals, allowing us to perceive smells
• Photoreceptors respond to light
• Thermoreceptors respond to temperature changes
• Nociceptors respond to stimuli that result in the sensation of pain
• Proprioception sense of movement and position of the body and limbs
• Free nerve endings are the simplest and most common type of sensory receptors
• Cold receptors and warm receptors are receptors for temperature
• Touch receptors

  A) Merkel disks

  B) Free nerve

  C) Meissner corpuscles

  D) Ruffine corpuscle

  E) Pacinian corpuscle

  F) Hair follicle receptor

  
• Touch receptors are structurally more complex than free nerve endings.
• The senses are the means by which the brain receives information about the environment and the body.
• Sensation is the process initiated by stimulating sensory receptors.
• Perception is the conscious awareness of those stimuli.
• The somatic senses provide sensory information about the body and the environment.
• The visceral senses provide information about various internal organs, primarily involving pain and pressure.
• Chemical messengers allow cells to communicate with each other to regulate body activities.
• Chemical substances called neurotransmitters act as these chemical signals and are stored in synaptic vesicles in the presynaptic terminal.
• Central nervous system consists of brain and spinal cord
• Peripheral nervous system (PNS) consists of all the nervous tissue outside the CNS
• Sensory division conducts action potentials from sensory receptors to the CNS
• Motor division conducts action potentials to effector organs, such as muscles and glands
• Somatic nervous system

  transmits action potentials from the CNS to skeletal muscles.
• Enteric nervous system a special nervous system found only in the digestive tract.
• Autonomic nervous system transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands
• Neurons

  • receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs.
• Glial cells

  • these cells do not conduct action potentials. It carries out different functions that enhance neuron function and maintain normal conditions within nervous tissue.
• A neuron (nerve cell) has a:

  • Cell body – which contains a single nucleus.
  • Dendrite – which is a cytoplasmic extension from the cell body, that usually receives information from other neurons and transmits the information to the cell body
  • Axon – which is a single long cell process that leaves the cell body at the axon hillock and conducts sensory signals to the CNS and motor signals away from the CNS
• Typical Neuron

  A) Dendrites

  B) cell body

  C) Axon

  D) Schwann cell

  E) Node of Ranvier

  
• Structural Types of Neurons

  • Multipolar neurons have many dendrites and a single axon.
  • Most of the neurons within the CNS and nearly all motor neurons are multipolar.
• Structural Types of Neurons

  • Bipolar neurons have two processes: one dendrite and one axon.
  • Bipolar neurons are located in some sensory organs, such as in the retina of the eye and in the nasal cavity.
• Structural Types of Neurons

  • Pseudo-unipolar neurons have a single process extending from the cell body, which divides into two processes as short distance from the cell body.
• Types of Neurons

  A) multipolar

  B) bipolar

  C) pseudo unipolar