Bio 30 CNS PNS

• The central nervous system (CNS) consists of the brain and spinal cord.
• Neurons:

  • Sensory Neurons: Transmit sensory information from sensory receptors to the central nervous system (CNS).
  • Motor Neurons: Transmit signals from the CNS to muscles or glands, controlling their activity.
  • Interneurons: Found within the CNS, they facilitate communication between sensory and motor neurons.
• Components of a Myelinated Neuron:

  • Dendrites: Receive signals from other neurons or sensory receptors.
  • Axon: Conducts electrical impulses away from the cell body.
  • Myelin Sheath: Insulating layer around the axon, speeds up signal transmission.
  • Neurilemma: Outermost layer of Schwann cells, aids in regeneration of damaged axons.
  • Schwann Cells: Produce myelin in the peripheral nervous system (PNS).
  • Axon Terminal: Site where neurotransmitters are released to communicate with other neurons or muscles.
• Myelinated vs. Unmyelinated Neurons:

  • Myelinated: Neurons with myelin sheaths, forming white matter. Signal propagation is faster.
  • Unmyelinated: Neurons without myelin sheaths, forming gray matter. Signal propagation is slower.
• Reflex Arcs:

  Steps:

  1. Receptor detects a stimulus.

  2. Sensory neuron transmits signal to the spinal cord.

  3. Interneuron in the spinal cord relays signal to motor neuron.

  4. Motor neuron carries signal to effector (muscle or gland).

  5. Effector responds to the stimulus without input from the brain.
• Action Potential:

  Transmission of Electrical Impulse:

  • Polarization, Depolarization, Repolarization, Refractory Period.

  Sodium and Potassium Ions:

  • Sodium influx during depolarization, potassium efflux during repolarization.

  Membrane Potential Graph:

  • Resting potential (-70 mV), Depolarization (rise to around +30 mV), Repolarization (fall back to -70 mV), Refractory period (brief period below -70 mV).

  Synaptic Transmission:

  Events:

  • Release of neurotransmitters from presynaptic neuron.
  • Diffusion of neurotransmitters across synaptic cleft.
  • Binding of neurotransmitters to receptors on postsynaptic neuron.

  Role of Neurotransmitters:

  • Facilitate or inhibit signal transmission.

  Excitatory vs. Inhibitory Neurotransmitters:

  • Excitatory: Promote signal transmission.
  • Inhibitory: Prevent signal transmission.

  How Excitatory & Inhibitory Neurotransmitters Work:

  • Excitatory neurotransmitters depolarize the postsynaptic membrane, making it more likely to generate an action potential.
• • Inhibitory neurotransmitters hyperpolarize the postsynaptic membrane, making it less likely to generate an action potential.
• Central Nervous System:

  • Spinal Cord: Transmits signals between the brain and the rest of the body, also responsible for reflexes.
  • Meninges and Cerebrospinal Fluid: Meninges are protective membranes around the brain and spinal cord, while cerebrospinal fluid cushions and protects the CNS.
  • Hemispheres of the Brain: Left hemisphere is typically associated with language and analytical functions, while the right hemisphere is associated with creativity and spatial abilities.
• Principal Structures of the Brain:

  • Cerebrum: Higher brain functions such as thinking and voluntary actions.
  • Cerebellum: Coordinates voluntary movements and balance.
  • Corpus Callosum: Connects the two hemispheres, facilitating communication between them.
  • Thalamus: Relay center for sensory information.
  • Hypothalamus: Regulates homeostasis and basic survival functions.
  • Pituitary Gland: Master gland, regulates other endocrine glands.
  • Amygdala: Involved in processing emotions, particularly fear.
  • Pons: Relays signals between cerebrum and cerebellum.
  • Hippocampus: Involved in memory formation.
  • Medulla Oblongata: Controls autonomic functions like breathing and heart rate.

  Four Lobes of the Cerebrum:

  • Frontal: Motor control, reasoning, planning, problem-solving.
  • Parietal: Sensation, perception, integration of sensory information.
  • Temporal: Auditory processing, memory, language.
  • Occipital: Visual processing.

  Broca’s and Wernicke’s Areas:
• • Broca’s Area: Responsible for speech production. Damage can lead to expressive aphasia.
  • Wernicke’s Area: Responsible for language comprehension. Damage can lead to receptive aphasia.
• Peripheral Nervous System:

  • Somatic Division: Controls voluntary movements and senses.
  • Autonomic Division: Regulates involuntary bodily functions.

  Sympathetic vs. Parasympathetic Response:

  • Sympathetic: "Fight or flight" response, prepares body for action.
  • Parasympathetic: "Rest and digest" response, conserves energy and promotes relaxation.