5.5 Neural Control and Coordination

The Neuron

• Structure:
  • Cell Body (Soma): Contains the nucleus and Nissl's granules.
  • Dendrites: Receive signals and transmit them towards the cell body.
  • Axon: Transmits signals away from the cell body.
• Types: Unipolar, Bipolar, Multipolar, Pseudounipolar.

Nerve Impulse Generation

1. Resting Potential (Polarized): Outside of the membrane is positive (high Na⁺), inside is negative (high K⁺). Maintained by the Na⁺-K⁺ pump.
2. Action Potential (Depolarized): Stimulus causes Na⁺ channels to open, Na⁺ rushes in, and the membrane polarity reverses.
3. Repolarization: Na⁺ channels close, K⁺ channels open, K⁺ rushes out, and the resting potential is restored.

Nerve Impulse Conduction

• The action potential travels along the axon as a wave of depolarization.
• Saltatory Conduction: In myelinated axons, the impulse "jumps" from one Node of Ranvier to the next, which is much faster.

Synaptic Transmission

• Synapse: The junction between two neurons.
• Types:
  • Electrical Synapse: Direct flow of electrical current.
  • Chemical Synapse: Involves neurotransmitters.
• Mechanism (Chemical):
  1. Action potential arrives at the axon terminal.
  2. Neurotransmitters are released into the synaptic cleft.
  3. Neurotransmitters bind to receptors on the postsynaptic neuron, generating a new potential.

The Human Brain: Forebrain

• Cerebrum: Largest part, divided into two hemispheres connected by the corpus callosum. Responsible for thought, memory, and voluntary actions.
• Thalamus: Relay center for sensory and motor signals.
• Hypothalamus: Controls body temperature, hunger, thirst, and releases hormones.

The Human Brain: Midbrain & Hindbrain

• Midbrain: Connects the forebrain and hindbrain; controls reflex movements.
• Hindbrain:
  • Pons: Connects different brain regions.
  • Cerebellum: Controls balance and coordination.
  • Medulla Oblongata: Controls vital functions like breathing, heart rate, and blood pressure.

Spinal Cord

• A long, tubular structure extending from the medulla oblongata.
• Functions:
  • Conducts impulses to and from the brain.
  • Center for reflex actions.

Peripheral Nervous System (PNS)

• Somatic Nervous System: Controls voluntary movements of skeletal muscles.
• Autonomic Nervous System (ANS): Controls involuntary actions of smooth muscles and glands.
  • Sympathetic: "Fight or flight" response.
  • Parasympathetic: "Rest and digest" response.