The Nervous System

• Dendrites receive signals from other neurons, while the axon transmits signals to other neurons.
• In the nervous system, the body responds to changes in its environment through stimuli, receptors, and responses
• A stimulus is any information that the body receives and that causes a response
• Receptors are structures that detect changes (stimuli) and pass this information to other parts of the body
• The five senses used to detect external stimuli are:

  1. Sight – detection of light

  2. Hearing – detection of sound

  3. Smell – detection of chemicals in the air

  4. Taste – detection of chemicals in our mouths

  5. Touch – detection of pressure on our skin
• Specialized receptor cells found in sensory organs transmit information to the nervous system
• In the eyes, photoreceptor cells on the retina receive information about light (rod cells) and color (cone cells), sending it to the brain via the optic nerve
• Sound is detected through vibrations of air particles collected by the outer ear, leading to vibrations of the eardrum and ear bones, which are detected by the vestibule and cochlea
• Olfactory receptors in the nose detect chemicals in the air, sending information to the brain via the olfactory bulb
• Taste buds on the tongue detect chemicals in food/drink, sending information about tastes like sweet, salty, sour, bitter, and umami to the brain via nerves
• Touch is detected through nerve endings in the dermis of the skin, which can detect heat, cold, pressure, and pain, sending this information directly to the brain
• Functions of the nervous system:

  • Helps to detect changes and coordinates with other body systems to maintain homeostasis
  • Coordinates fast responses, including reflex responses
  • Works closely with the endocrine (hormone) system to detect changes in the external environment to maintain a constant internal environment
• The nervous system is composed of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS), both made up of nerve cells called neurons
• Central Nervous System (CNS):

  • Composed of the brain and spinal cord
  • Has a major role in controlling the activity of other organs
• Peripheral Nervous System (PNS):

  • Composed of the nerves that connect the CNS to the rest of the body (all the other nerves in the body)
  • Relays information to and from the CNS
• All neurons have three basic functions:

  • Receive signals (or information)
  • Integrate incoming signals (to determine whether or not the information should be passed along)
  • Communicate signals to target cells (other neurons or muscles or glands)
• Structure of a Neuron:

  • Cell body (soma): contains the nucleus, controls the cell's functions, and produces proteins for the cell
  • Dendrites: short, branching processes extending from the cell body, receive and process incoming information
  • Axon: longer process extending from the cell body, specialized to conduct action potentials
• Axon terminals:

  • Towards the end, the axon splits into many branches known as axon terminals or synaptic terminals
  • These axon terminals make connections to target cells by releasing neurotransmitters
• Myelin sheath:

  • Helps speed up the transmission of a nerve impulse down a long axon and protect the neurons
  • Myelinated neurons are typically found in the peripheral nerves (sensory and motor neurons), while non-myelinated neurons are found in the brain and spinal cord
  • Produced by Schwann Cells, act like insulation on an electrical wire, made of fat and protein
  • Nodes of Ranvier are gaps in the myelin sheath
• Myelin sheath:

  • Helps speed up the transmission of a nerve impulse down a long axon and protect the neurons
  • Myelinated neurons are typically found in the peripheral nerves (sensory and motor neurons), while non-myelinated neurons are found in the brain and spinal cord
  • Produced by Schwann Cells, act like insulation on an electrical wire, made of fat and protein
  • Nodes of Ranvier are gaps in the myelin sheath
• Functions of the nervous system:

  • Helps to detect changes and coordinates with other body systems to maintain homeostasis
  • Coordinates fast responses, including reflex responses
  • Works closely with the endocrine (hormone) system to detect changes in the external environment to maintain a constant internal environment
• The nervous system is composed of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS), both made up of nerve cells called neurons
• Central Nervous System (CNS):

  • Composed of the brain and spinal cord
  • Has a major role in controlling the activity of other organs
• Peripheral Nervous System (PNS):

  • Composed of the nerves that connect the CNS to the rest of the body (all the other nerves in the body)
  • Relays information to and from the CNS
• All neurons have three basic functions:

  • Receive signals (or information)
  • Integrate incoming signals (to determine whether or not the information should be passed along)
  • Communicate signals to target cells (other neurons or muscles or glands)
• Structure of a Neuron:

  • Cell body (soma): contains the nucleus, controls the cell's functions, and produces proteins for the cell
  • Dendrites: short, branching processes extending from the cell body, receive and process incoming information
  • Axon: longer process extending from the cell body, specialized to conduct action potentials
• Dendrites deliver information to the cell body, while the axon carries information away from the cell body
• Myelin sheath:

  • Helps speed up the transmission of a nerve impulse down a long axon and protects the neurons
  • Myelinated neurons are typically found in the peripheral nerves (sensory and motor neurons), while non-myelinated neurons are found in the brain and spinal cord
  • Produced by Schwann Cells, act like insulation on an electrical wire, made of fat and protein
  • Nodes of Ranvier are gaps in the myelin sheath
• Axon terminals, towards the end of the axon, make connections to target cells by releasing neurotransmitters
• In multiple sclerosis (MS), the body's immune system (T cells) attack the myelin sheath that protects the nerve fibers, resulting in slowed down action potentials and a slower response to stimuli
• Stimulus-Response Pathway:

  • Stimulus: a change in the environment
  • Reception: the change is detected by cells in sensory organs
  • Sensory neurons (afferent): send the message from sensory cells through the sensory neurons in the PNS
  • Interneurons (association): interpret the message from the stimulus in the CNS
  • Motor neurons (efferent): transport the message from the CNS to the effector
  • Effector: the muscle or gland that will physically respond to the stimulus
  • Response: movement or release of hormones in response to the stimulus
• Sensory Neurons:

  • Located in the PNS
  • Carry impulses from sense organs to spinal cord and brain (CNS)
  • Receive messages about changes in the external or internal environment and transmit the information to the interneuron in the CNS
• Sensory neurons detect a change in the external or internal environment and transmit the information to the interneuron in the CNS
• Interneurons, also known as relay neurons, are located only in the CNS and carry the signal from a sensory neuron to a motor neuron
• Interneurons connect sensory and motor neurons, process impulses in the brain and spinal cord
• Motor neurons, located in the PNS, carry impulses from the CNS to muscles and glands, causing them to respond
• Neurons carry information from outer parts of the body to the CNS (sensory neurons), within the CNS (interneurons), and from the CNS to the outer parts of the body (motor neurons)
• Neurons communicate using electrical impulses (action potentials) and chemical neurotransmission
• In neurotransmission, when the action potential reaches the axon terminal, it is converted into a chemical signal, with neurotransmitter molecules released into the synaptic gap
• The response caused by neurotransmitters depends on the type of post-synaptic tissue, whether another neuron or a muscle/gland